The Environment in Galicia: A Book of Images: Galician Environment Through Images 3031331133, 9783031331138

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Avelino Núñez-Delgado Esperanza Álvarez-Rodríguez David Fernández-Calviño   Editors

The Environment in Galicia: A Book of Images Galician Environment Through Images

The Environment in Galicia: A Book of Images

Avelino Núñez-Delgado · Esperanza Álvarez-Rodríguez · David Fernández-Calviño Editors

The Environment in Galicia: A Book of Images Galician Environment Through Images

Editors Avelino Núñez-Delgado Engineering Polytechnic School University of Santiago de Compostela Lugo, Spain

Esperanza Álvarez-Rodríguez Department of Soil Science and Agricultural Chemistry University of Santiago de Compostela Lugo, Spain

David Fernández-Calviño Soil Science and Agricultural Chemistry Area, Faculty of Sciences Universidade de Vigo Ourense, Spain

ISBN 978-3-031-33113-8 ISBN 978-3-031-33114-5 (eBook) https://doi.org/10.1007/978-3-031-33114-5 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

The scientific editors are really glad to have the opportunity of working on this volume, which is seen as the first one of a new Book Series to be entitled The Environment in Galicia: A Book of Images. It was a real pleasure receiving the chapters elaborated by all the top researchers that have submitted their high-quality contributions to the book. This volume could be considered the first one of its kind, a book of images illustrating different scientific views of the environment in Galicia, where all the authors work, covering a variety of scientific domains but all of them having in common their marked interest (and/or passion) for the environment, and specifically for the environment of their country (Fig. 1). The scientific editors of the book would like to thank all the authors, reviewers and the staff of Springer Nature involved in it. We really wish that the book will be appreciated and enjoyed by its readers.

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Fig. 1 Images—at different scales—including Galicia, in the Iberian Peninsula, specifically on the NW of Spain, in Europe. Source of the maps Freeworldmaps.net

Preface

Lugo, Spain Ourense, Spain Lugo, Spain

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The Scientific Editors of the Book Esperanza Álvarez-Rodríguez David Fernández-Calviño Avelino Núñez-Delgado

Contents

The Atmosphere Atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Juan A. Añel

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Pyrocumulus: A New Cloud in Galician Skies . . . . . . . . . . . . . . . . . . . . . . . . Juan Taboada, Pablo Hermo, and Manuel Martínez

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Geology Introduction to the Geology of Galicia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Juan Ramón Vidal Romaní Al-Rich Speleothems in Granite Caves: A Poorly Known Geologic Material and Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jorge Sanjurjo-Sánchez, Carlos Arce Chamorro, Juan Ramón Vidal Romaní, Victor Barrientos, and Joeri Kaal Caves: Underground Landscapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marcos Vaqueiro Rodríguez The Courel Mountains UNESCO Global Geopark: An Amazing Geological History Extended Along 600 Million Years . . . . . . . . . . . . . . . . . Irene Pérez-Cáceres, Daniel Ballesteros, Pablo Caldevilla, Jose Bienvenido Diez, Xose Carlos Barros, Ramón Vila, José Ramón Martínez Catalán, Fidel Martín-González, Juan Carlos Gutiérrez-Marco, Manuel García-Ávila, Mercedes Fuertes-Fuente, Susana Timón Sánchez, Miguel Llorente, and Martín Alemparte Endogenous/Exogenous Forms of Granite Geomorphology in Galicia . . . Juan Ramón Vidal-Romani

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Soils Soils of Galicia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 Eduardo García-Rodeja, Juan Carlos Nóvoa-Muñoz, and Xabier Pontevedra-Pombal Landscape Modeling and Environmental Implications for Vineyard Cultivation in NW of Spain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Manuel Arias Estévez Peatlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 Noemí Silva-Sánchez, Lourdes López-Merino, Olalla López-Costas, Álvaro Moreno Martín, Tim Mighall, and Antonio Martínez Cortizas Coastal Soils and Their Associated Habitats in Galicia . . . . . . . . . . . . . . . . 179 Xosé L. Otero, María del Carmen de la Cerda Marín, and Augusto Pérez-Alberti Soil Biodiversity in Galician Peatlands: A Unique Home for Specialised Invertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Maria J. I. Briones and I. Ferradás Grasslands on Acid Soils: Use of Different Amendments in the Context of Galicia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 M. J. Fernández-Sanjurjo, A. Barreiro, and E. Álvarez-Rodríguez Forest Soils from Galicia: Aluminium Fractionation and Speciation . . . . 235 E. Álvarez-Rodríguez, A. Barreiro, C. Eimil, and M. J. Fernández-Sanjurjo Andosols and Podzols at Galicia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Eduardo García-Rodeja, Xabier Pontevedra-Pombal, and Juan Carlos Nóvoa-Muñoz Water Fresh Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293 Francisco Díaz-Fierros Viqueira Research on Cyanobacterial Blooms and Cyanotoxin Production in Galician Inland Waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 Fernando Cobo Gradín, Sandra Barca Bravo, Rufino Vieira Lanero, and M. Carmen Cobo Llovo Perspectives on Irrigation in Galicia (NW Spain) . . . . . . . . . . . . . . . . . . . . . 323 T. S. Cuesta, J. J. Cancela, X. X. Neira, and J. Dafonte Geomorphology and Landscapes Geomorphology and Landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 Augusto Pérez Alberti

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‘The Cultural Landscape of Galicia: A History of the Inappropriable’ A Scientific Story of Galicia’s Landscapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391 Federico López-Silvestre The Geological Landscape. 1. Geoforms in the Inland Galicia . . . . . . . . . . 419 Rogelio Pérez Moreira and María Teresa Barral Silva The Geological Landscape. 2. Geoforms in the Coastal Galicia . . . . . . . . . 445 Rogelio Pérez Moreira and María Teresa Barral Silva Vegetation Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469 Manuel Antonio Rodríguez-Guitián Agriculture Land in Galicia. Pastures and Crops to Feed Humans but Above All Cattle in the Country of One Million of Cows . . . . . . . . . . . 501 David Fernández Calviño Environmental Problems and Alternatives to Solve These Issues Introduction to the Part “Environmental Problems and Alternatives to Solve These Issues” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521 Avelino Núñez-Delgado, David Fernández-Calviño, and Esperanza Álvarez-Rodríguez A Storyboard of Wildfires in Galicia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 551 Adrián Regos and Montserrat Díaz-Raviña Soil Erodibility: Influencing Factors and Their Importance in Post-fire Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597 E. Benito, M. E. Varela, M. Rodríguez-Alleres, R. García-Corona, and J. L. Santiago Soil Erosion in NW Spain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 615 Francisco Díaz-Fierros Viqueira Some Environmental Effects of Slate Exploitation and Palliative Treatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625 Avelino Núñez-Delgado

The Atmosphere

Atmosphere Juan A. Añel

The atmosphere seems to be something similar all around our planet, the air and clouds that move and surround land. Its behavior, specifically the variability in its lower part, the troposphere, determines the weather. Moving upper we find the stratosphere and upper layers. The role and impact of the stratosphere on tropospheric weather has gotten increasing attention and acknowledgement over the last decades. Also, over the last few years, winter phenomena such as the behaviour of the stratospheric polar vortex or the jet stream have got increasing attention, and are being studied for their implications for the climate, mainly in the northern hemisphere, affecting extratropical regions. In such regions of our planet, in the Northern hemisphere, it is located the one that we describe here, Galicia. Over time, climate and weather depend on the characteristics of a particular area, being location a primordial issue, as position in the planet and orography define tropical climates, extratropical ones, or microclimates. The atmosphere not only influence on weather and climate, but it is also the fluid transporting dust and many types of chemicals. Its relevance has grown in the last decades from the point of view of air quality, something that in a so heavily human-intervened planet is of utmost importance, with severe health implications. The atmosphere is vital among Galicians; if because of something Galicia is renowned for, it is because of its weather. The part of the Iberian Peninsula where rain and the Atlantic Ocean shape a good part of its climate. Weather reigns, and the atmosphere shapes this magnificent part of the Earth in a very different way to most of the West Mediterranean, identified in the collective imagination as sunny and drought. It is popular how locals look at the sky, feel the wind, and forecast the weather themselves, which is so essential for many socioeconomic activities. The atmosphere is, in this way, reflected in popular proverbs.

J. A. Añel (B) EPhyslab, CIM-UVigo, Universidade de Vigo, Campus As Lagoas, 32004 Ourense, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_1

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However, before going more in-depth about it, let us begin by giving some context, a general perspective, on how Galicia is located on the planet to understand better how the atmosphere behaves around it. Galicia occupies a region of 2 degrees of latitude and 2.5 degrees in longitude, located between 41.82ºN and 43.78ºN and between 6.7ºW and 9.3ºW; that is, Galicia is located in the extratropics of the Earth’s northern hemisphere, on its west side surrounded by the Atlantic Ocean and in the north by the Cantabrian Sea. In this way, the seesaw of cyclones and anticyclones, jointly with the, already mentioned, extratropical jet stream and the Azores High, rule its weather many times throughout the year. Being on the east side of the Atlantic Ocean, Galicia gets milder weather than its American counterpart, the region going from Boston to Nova Scotia. In this way, the climates in Galicia, through their Köppen classifications, embrace the Oceanic one in several subcategories, which are more typical of the coastal zones; meanwhile, the inner part of Galicia is closer to a Continental climate, mainly when it comes to temperatures. Formally, part of Galicia can also be considered to feature a Mediterranean climate, warm, with drought summers. Climate change is modifying the spatial equilibrium between these types over the last decades. The atmosphere in Galicia has been studied throughout history. They exist good accounts of the meteorological observatories that go back to 1849 (Díaz-FierrosViqueira 2008). These observatories were not set up only because of an aim to study the weather. Sometimes concerns about health and the study of the air were behind it. For example, astronomy, and astronomical observatories, as in many parts of the world, were more popular. However, some good meteorological studies were performed, and being weather so important for Galicia, its study got traction. Since the end of the nineteenth century, there has been a good knowledge about how cyclones and anticyclones rule Galician weather, society and lives. Fishing has been a traditional economic activity, and Galician fishermen master the seas, to a massive toll in the form of deaths fighting the weather, sometimes dangerous on the Galician coast to the point that in the northwest, around the end of the world, FinisTerrae as Romans named it, we call it A Costa da Morte (“Coast of Death”). In this way, Father Baltasar Merino, former ex-president of the International Academy of Botanical Geography, from its meteorological observatory in A Guarda (Añel et al. 2017), which is in South Galicia in the Miño river border with Portugal, wrote a treaty in 1893 about cyclones in the coast of Galicia (Merino 1893). To write this book, it was necessary to have access to information provided by telegrams with meteorological data from other observatories worldwide, to draw the synoptic charts that allowed weather forecasts. Father Merino realized the role of atmospheric pressure in weather, and in this way, is regarded by saving uncountable lives, though, in a time without meteorological radars, online instantaneous weather reports, radio communications, or the ability to disentangle the mysteries of the atmosphere beyond what your sees and experience dictated. He distributed aneroid barometers between fishermen on the coast and instructed them to come back to port when the pressure dropped fast as an indicator of a coming cyclone and challenging weather. In a region where sometimes the weather changes quickly, this was very important.

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Over the last years, Galicia has seen how the atmosphere threatens it with a new phenomenon that being under study, it seems to have high odds of being linked to global anthropogenic climate change. This recent phenomenon is excursions of hurricanes, sometimes born on the other side of the Atlantic, simply remainders of hurricanes that have lost strength and can not be longer considered as such, which can move and reach the European coasts because of a warmer ocean that now opens this highway for them, which before did not exist because of the cold oceanic temperatures. Father Merino would have suffered because of this. Galicia is a region of contrast when it refers to the weather. For example, there are striking seasonal differences. The atmosphere can be wild, with strong winds, rain and storms in winter; meanwhile, in summer, it can result in lovely days on the coast, or causing sometimes prolonged heatwaves, especially hard in inner Galicia. Indeed, hot summer nights have become an issue of concern over the last few years, boosted by climate change. This is something that many people in Galicia are not used to, mainly in the coastal regions where traditionally, the temperatures overnight used to be milder. The differences in the climate of Galicia between the coast and the more inland zones can be striking. For example, around the Ribeira Sacra canyon, shaped by the Miño and Sil rivers, and also in the city of Ourense, sometimes summers can be scorching, with thermal sensation temperatures above 50 ºC. Orography has a central role in this. On the other hand, along those canyons, a strong phenomenon of thermal inversion usually happens in the lower part of the atmosphere. As a result, on many days, temperatures are higher in the surrounding mountains; meanwhile, fog is common in the valleys of the canyon. In fact, existing sizeable artificial water reservoirs along those canyons make fog episodes happen during autumn and winter, sometimes daily, for all morning or even the day (Fig. 1). Also, the landscape and the vegetation in Galicia are shaped by those differences between the coast and interior. Sometimes, it snows in Galicia; it is not usual, but it happens. Orography does not help snowfall as the highest point in Galicia, Pena Trevinca, features a peak altitude of 2124 m. It is in this region that it is the only sky resort in Manzaneda. Days with snowfall are around fifteen per year (Martí et al. 2019), and usually, snow does not last for too long; as temperatures increase and rain appears, they melt the snow that has fallen in previous days. For recreational use, snow canyons are used sometimes in this sky resort, but they need a range of temperatures that are often not maintained. Also, rising minimum temperatures because of climate change make the number of days per year with conditions for snow decrease. The region mentioned is Terras de Trives and, jointly with the part of Os Ancares, which is northward, and also in oriental Galicia, is where most of the snow falls, and they feature its particular microclimate. Overall, the behaviour of the atmosphere can also be described by means of teleconnection patterns and weather types. The North Atlantic Oscillation (Gimeno et al. 2004), as the name clearly points out, is a regional teleconnection pattern very relevant for Galicia (García et al. 2005); in an easy way, over winter, depending on its sign (positive or negative), it shows if the weather is rainy or cold. However, it is

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Fig. 1 Fog over the Castrelo reservoir. Author: X. Dosi Veiga

a simplification of a more complex reality, as it is well known that a teleconnection index that provides a hemispheric picture, the Northern Annular Mode, better explains the weather over Galicia when combined with weather types. Similarly happens with the Eastern Atlantic teleconnection pattern (Lorenzo et al. 2008). The basis of weather typing is that many days, which can be clustered into a few types, respond to similar atmospheric patterns, usually catalogued using sea level pressure. The number of different weather types, in which the state of the atmosphere can be classified, changes depending on the atmospheric variable and other choices. For example, for Galicia, applied to the precipitation, some authors have divided them into a range between ten and fourteen (Lorenzo et al. 2008; Eiras-Barca et al. 2018). But the atmospheric phenomenon par excellence that defines Galicia is rain. Most of its main capital cities feature more than 130 days of rain per year, and in this way, the color for most of Galicia is green. It can be said that it is green everywhere. Santiago de Compostela, in northwestern Galicia, is regarded as a place with very rainy weather, the second rainiest in Spain and challenging others in Europe. It rains a lot; some say that nowadays less than used because of climate change, but there needs to be a data series long enough to confirm it, despite in western Galicia, some trends begin to be clear. To the surprise of many, it rains more than in London, though London is more humid and has fewer sun hours throughout the year. So, in this way, the wisdom of former architects and the population has made Galician cities feature arcades in their downtown, usually in old towns. In the southeastern, the Ourense province, with its capital city of the same name, is famous for being the land of umbrella makers. This fame that has Ourense contrasts with the fact that it retains the ability to register some of the records in the highest temperatures in the Iberian Peninsula throughout the year, as mentioned before—maybe doing a double use of the

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Fig. 2 Noctilucent clouds seen from Guntimil (Muiños) (circa 6 am local time, 24 June 2021). Author: María José Araujo

arcades above mentioned as protection for sun during the summer days. Rain comes from clouds, and a few types of the ones in the cloud atlas of the World Meteorological Organization can be seen in Galicia. Some are quite strange and surprising, as for example the noctilucent clouds (although these are not related to rainfall). Noctilucent clouds are located in the Earth’s mesosphere, and they are unusual in latitudes below 50°, although its probability to be observed more equatorward is increasing because of the increase of water vapor in the mesosphere, probably due to the anthropogenic emissions of methane (Lübken et al. 2018) (Fig. 2). In fact, part of Galicia is pretty cloudy, with around 65% of cloudy days. The distribution of cloud coverage is dominated by latitude, being the south the part with the lower one with only about 35% of cloudy days. However, although clouds could be less usual in this part, meteorological phenomena linked to clouds have happened in the south of Galicia. We refer here to downbursts. To those unfamiliar, a downburst happens when clouds suddenly “break” and let all the water fall suddenly and violently, usually generating a dangerous downwind force (see Fig. 3). Rainfall, the blood of Galicia, runs trough their 499 rivers (though Galicia is usually nicknamed “the land of the one thousand rivers”) (Otero Pedrayo, 1977), with two main ones staying above all of them, the Miño and Sil. Those have through millennia carved canyons mainly in the south of Lugo and through Ourense. One could say that with merit, maybe not so impressive in size as the famous Colorado Canyon, but those in Galicia are profound, narrow and carved in granite. In this way, this zone has unique conditions for hydropower exploitation. There was a huge development of dams and reservoirs along the 1960 and 1970s, and the exploitation of these rivers made through a cascading system of dams, of very variable sizes, from small ones to some that once were the largest in the continent. To give some additional numbers, more than one hundred dams are built along the 340 km of the

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Fig. 3 Downburst over the city of Ourense (17 July 2021). Author: Nieves Lorenzo

Miño river since it is born in Lugo, through Ourense and to its death in the Atlantic Ocean. One issue is that it rains very differently along all the rivers because of the different kind of climates that happen. Those dams were primarily built to take advantage of the huge fertility that the atmosphere brings to Galicia in the form of energy, something that has been especially important along the last sixty years. Rainfall used to be the primary energy resource, in the form of hydropower. The cloudy weather transforms in rainfall, sowing Galician rivers, which water was traditionally what powered the many watermills used for grinding grain. The atmosphere sometimes shapes Galicia in the form of extreme precipitation episodes, nowadays boosted by climate change. They come in the form of daring droughts, that feel like leaving without blood to Galicia, and sometimes as extreme rainfall, which however it is easier to cope with, as climate change consistently makes that the average level of the reservoirs is lower than when they were built. The other way how atmosphere feeds Galicia with energy is through wind power because Galicia is windy. Over the last few decades, wind farms have begun to appear all around, becoming Galicia, at some points, a leading world player in the power production of this kind. Surprisingly, compared to other regions in Iberia, it is not so common to think about the use of windmills in Galicia; at least, they are not acknowledged so much use throughout history. Despite it, some have existed and been documented, with, for example, some relevant that go back to the XVII century (Bas López 1991). The potential for wind power generation in Galicia is in such a way, and improvements in wind exploitation make so many regions suitable for it, that, indeed, over the years, the ability to exploit so much in so many places has hit back in the form of need to protect the gorgeous Galician landscape from visual impact and noise

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Fig. 4 Saharan dust over the sky of Ourense (15 March 2022). Author: Susana Bayo-Besteiro

pollution. Civil protests are becoming common, someway a mix of environmental protection and the local expression of nimbyism. Also, despite the fact that wind power is so crucial for the energy mix of Galicia and the whole Iberian Peninsula, less attention than would be desirable has been paid to its research (Bayo-Besteiro et al. 2021). But winds are not always good in Galicia, infamous at its coast for being the companion of tempests, which provokes waves and sinks ships, causing enormous environmental disasters sometimes. Those winds also transport Saharan dust or ozone, which can disturb many activities and stir health alerts because of respiratory problems. In fact, when episodes of Saharan dust intrusions happen (Fig. 4), it is because Galicia features a particular wind pattern that reaches the region without affecting the remainder of the Iberian Peninsula (Cachorro et al. 2008; Mandija et al. 2018). Also, several wind patterns can be deemed responsible for explaining high ozone pollution episodes (Saavedra et al. 2012), originating in central Spain, Portugal, or even northern France or the British islands. Anomalous high easterlies are responsible for large wildfires in the coastal provinces of Galicia, too (Vieira et al. 2020), which is relevant because Galicia is one of the most prone regions to wildfires in the Mediterranean basin (Pinto et al. 2018). After rain, snow or winds, Galicia can be sunny too. Sun delimits two different parts of Galicia someway too, and just around the latitudinal middle of Galicia can be drawn an imaginary line that delimits the mean annual 2000 h of sun. North of it, the number of hours decreases, almost fitting to latitudinal bands below 1700 h; meanwhile, the southern part of Galicia accounts for more than 2250 h per year (Martí et al. 2019). As Galicia is regarded as cloudy and rainy, taking advantage of the sun to generate solar power has not been among the more popular ways used to feed energy. However, after advances in solar generation technologies over the last decades, and comparisons to the possibilities and exploitation in other countries with fewer sun hours, and having reached a point where renewable power is so necessary, solar energy has begun to make its path in Galicia.

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It is fair to acknowledge that Galicia has also had, in the last decades, a shameful relationship with its atmosphere, one of pollution. So much as Galicia stands nowadays as a leading producer of renewable energy in Europe, for years, it was home to polluting carbon thermal plants, one of them among the most polluting in the European continent, and closed not so much time ago. This pollution was emitted to the atmosphere and later to the rainfall (Vázquez et al. 2003). Fortunately, the opposite for the Galician atmosphere is also true. On the other hand, it has some places with the best night sky that is currently exploited for astronomical tourism and observation. This is the case of the region of Pena Trevinca (Bará 2016), which has clear and unpolluted skies for 60% of the nights of the year and is a certified Starlight reserve. Like in many other places around the world, the behavior of the atmosphere also impacts many different facets of the Galician life, from fisheries (deCastro et al. 2008) to agriculture, pollen distribution, health or tourism. To summarize, Galicia is a place on the Earth where the atmosphere and the weather do not go unnoticed, to the point that the works of all the prominent Galician writers have plenty of references. For example, Rosalía de Castro raged against the hot and drought weather, saying to love the Galician winter. Still, at the same time, she said that Santiago de Compostela was atrociously cold. Someway, the importance of weather is reflected in the fact that the long-time weather presenter of the state Galician television channel is so popular that he was awarded the Castelao Medal, the highest Galician honor. Hopefully, we will be able to preserve the Earth from anthropogenic climate change, and in this way, the pleasant atmosphere of Galicia and all the elements that confer it a so characteristic climate and weather. Acknowledgements I would like to thank suggestions and comments by Susana Bayo Besteiro and X. Dosi Veiga.

References Añel JA, Sáenz G, Ramírez-González IA, Polychroniadou E, Vidal-Mina R, Gimeno L, de la Torre L (2017) Obtaining meteorological data from historical newspapers: La Integridad. Weather 72:366–371. https://doi.org/10.1002/wea.2841 Bará S (2016) Anthropogenic disruption of the night sky darkness in urban and rural areas. R Soc Open Sci 3:160541. https://doi.org/10.1098/rsos.160541 Bayo-Besteiro S, García-Rodríguez M, Labandeira X, Añel JA (2021) Seasonal and subseasonal wind power characterization and forecasting for the Iberian Peninsula and the Canary Islands: A systematic review. Int J Climatol 42(5):2601–2613. https://doi.org/10.1002/joc.7359 Cachorro VE, Toledano C, Prats N, Sorribas M, Mogo S, Berjón A, Torres B, Rodrigo R, de la Rosa J, De Frutos AM (2008) The strongest desert dust intrusion mixed with smoke over the Iberian Peninsula registered with Sun photometry. J Geophys Res 113:D14S04. https://doi.org/ 10.1029/2007JD009582 DeCastro M, Gómez-Gesteira M, Lorenzo MN, Alvarez I, Crespo AJC (2008) Influence of atmospheric modes on coastal upwelling along the western coast of the Iberian Peninsula, 1985–2005. Clim. Res. 36:169–179. https://doi.org/10.3354/cr00742

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Díaz-Fierros Viqueira F (2008) Historia da meteoroloxía e climatoloxía de Galicia (ed) Consello da Cultura Galega, p 212. ISBN: 978–84–96530–72–0 Eiras-Barca J, Lorenzo N, Taboada J, Robles A, Míguez-Macho G (2018) On the relationship between atmospheric rivers, weather types and floods in Galicia (NW Spain). Nat Hazards Earth Syst Sci 18:1633–1645. https://doi.org/10.5194/nhess-18-1633-2018 García NO, Gimeno L, de la Torre L, Nieto R, Añel JA (2005) North Atlantic Oscillation (NAO) and precipitation in Galicia (Spain). Atmósfera 18(1):25–32 Gimeno L, García-Herrera R, Trigo RM, de la Torre L (2004) La Oscilación del Atlántico Norte y su Influencia Sobre la Península Ibérica y Canarias, p 231. AICA, ISBN: 84–95780–15–1 López BB (1991) Muiños de Marés e de Vento (ed) Fundación Barrié, p 440. ISBN 9788497521680 Lorenzo MN, Taboada JJ, Gimeno L (2008) Links between circulation weather types and teleconnection patterns and their influence on precipitation patterns in Galicia (NW Spain). Int J Climatol 28:1493–1505. https://doi.org/10.1002/joc.1646 Lübken F-J, Berger U, Baumgarten G (2018) On the anthropogenic impact on long-term evolution of noctilucent clouds. Geophys Res Lett 45:6681–6689. https://doi.org/10.1029/2018GL077719 Mandija F, Chavez-Perez VM, Nieto R, Sicard M, Danylevsky V, Añel JA, Gimeno L (2018) The climatology of dust events over the European continent using data of the BSC-DREAM8b model. Atmos Res 209:144–162. https://doi.org/10.1016/j.atmosres.2018.03.006 Martí A, Taboada J, Royé D, Fonseca X (2019) Os tempos e o clima de Galicia, Xerais (ed), p 208, ISBN:978–84–9121–506–6 Merino B (1893) Estudio sobre las borrascas en la costa occidental de Galicia, (ed) Tipografía Gallega (Tuy), p 108 Pedrayo RO (1977) Os ríos galegos, Castrelos (ed), p 108. ISBN:8470410482 Pinto MM, DaCamara CC, Trigo IF, Trigo RM, Turkman KF (2018) Fire danger rating over Mediterranean Europe based on fire radiative power derived from Meteosat. Nat Hazards Earth Syst Sci 18:515–529. https://doi.org/10.5194/nhess-18-515-2018 Saavedra S, Rodríguez A, Taboada JJ, Souto JA, Casares JJ (2012) Synoptic patterns and air mass transport during ozone episodes in Northwestern Iberia. Sci Total Environ 441:97–110. https:// doi.org/10.1016/j.scitotenv.2012.09.014 Vázquez A, Costoya M, Peña RM, García S, Herrero C (2003) A rainwater quality monitoring network: a preliminary study of the composition of rainwater in Galicia (NW Spain). Chemosphere 51(5):375–386. https://doi.org/10.1016/S0045-6535(02)00805-6 Vieira I, Russo AM, Trigo R (2020) Identifying local-scale weather forcing conditions favorable to generating Iberia’s largest fires. Forests 11(5):547. https://doi.org/10.3390/f11050547

Pyrocumulus: A New Cloud in Galician Skies Juan Taboada, Pablo Hermo, and Manuel Martínez

Abstract Climate change together with the depopulation of rural areas are causing forest fires in Galicia to become increasingly intense. If the meteorological circumstances are adequate, with vertical instability, these large fires produce a specific type of cloud, called pyrocumulus or pyrocumulonimbus. The aim of our story is to relate climate change of anthropogenic origin to the increasingly frequent appearance of this type of cloud over Galician skies. For this goal, we will use photographs taken during the fire season of the summer of 2022. A season marked in Galicia by drought and heat waves, which led to the appearance of high intensity forest fires.

1 Scientific Story on Pyrocumulus Clouds are part of the landscape of the skies anywhere on our planet, but in each area, they take on different shapes and configurations depending on atmospheric conditions. Galicia is a region in the NW of the Iberian Peninsula, located in the middle latitudes and therefore in the western belt. Therefore, it is subject to the passage of low pressure travelling through the North Atlantic with frontal systems that affect the region mainly between September and March, when solar radiation is less in the northern hemisphere and cold air masses from polar origin approach our latitudes. This makes nimbostratus very common in our community, as well as cumulus of different topology, appearing after the passage of the fronts. In the months between April and September, the visit of these low-pressure systems becomes more and more infrequent and cumulonimbus clouds associated with local instabilities predominate. These instabilities take place when the sun heats the surface and the air in contact with it gains temperature and therefore tends to rise. J. Taboada (B) MeteoGalicia(DXCASCC)—Consellería Medio Ambiente, Xunta de Galicia, Santiago, Spain e-mail: [email protected] P. Hermo · M. Martínez Servicio de Prevención Contra Incendios Forestais (SPIF), Consellería Do Medio Rural, Xunta de Galicia, Santiago, Spain © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_2

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As it rises, it cools until it can no longer contain the humidity, beginning the condensation process. This process can continue in height, giving rise to clouds with a great vertical evolution. They are clouds of great beauty, but also dangerous. Within these clouds, vertical movements are so strong that can even compromise the lift of aircraft. For this reason, the position of these clouds is marked on air navigation charts in order to avoid them along the route. Moreover, these clouds are the ones that cause electrical storms, hail and in the worst cases even the presence of tornadoes. The photos that accompany this story contain this type of cloud, but its formation is not as the one explained in the previous paragraph. In this case, the heat emitted by forest fires produced the vertical movement of the air (convection). Technical name of these kind of clouds are flammagenitus, according to the World Meteorological Organization classification of clouds (OMM 407), but in the scientific literature, they are frequently named as pyrocumulus or pyrocumulonimbus. The first one (Fig. 1) was taken in a wildfire near Verín in the southeastern area of Galicia. This forest fire started at noon on Wednesday, August 3 during a heatwave and with a vertical atmospheric structure that facilitate the appearance of these clouds. The story we want to tell, related with the environment of Galicia and based on these clouds, is a story about how human influence can even change the appearance of our skies. These flammagenitus clouds do not necessarily have to be human-caused since they have their origin, as we have said above, in forest fires. However, the

Fig. 1 Pyrocumulus in a forest fire near Verín on August 3, 2022

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ones we can observe in this story are in different ways related to humans. Thus, for example, the Verín fire (Fig. 1) was not a wildfire provoked by nature itself but was human-caused by an inhabitant of the area. Forest fires have always been part of nature in Galicia. But rural depopulation, with the consequent abandonment of the forest, and climate change, with the consequent increase in temperature, but also in the frequency and intensity of phenomena such as droughts or heat waves (Abatzoglou et al. 2019; Di Virgilio et al. 2019), have brought forest fires to a level that was hardly accessible in previous decades (Jones et al. 2022). We have entered a phase in which the preconditions of the fuel and the meteorological parameters (high temperature, low humidity) make the existence of sixthgeneration fires more and more likely. These fires are usually beyond the extinguishing capacity (Jolly et al. 2015) and are very prone to formation of this type of cloud that will therefore become part of our celestial landscape in the coming years, mainly in the summer. The next photo (Fig. 2) was taken in another wildfire in summer 2022, in the southeastern area of Galicia, near Laza in Camba on August 10. This year 2022 has been a good example of the type of weather conditions that give rise to the appearance of these clouds. On the one hand, the region had been Fig. 2 Pyrocumulus in a forest fire near Laza on August 10, 2022

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experiencing a significant drought since the previous winter, particularly since the months of January and February, which were very dry. This means that the components of the fire risk index associated with soil moisture acquire very high values. Therefore, if the fire occurs, we knew that their power will be high. Moreover, during the months of June, July and August we suffer consecutive anticyclone situations and the arrival of warm air masses from North Africa, causing several consecutive heat waves that also increased the fire weather index (FWI). Taking into account the preconditions of drought and the successive heat waves, the FWI remained at extreme values for much of the summer. Wildfires were caused in some cases by human actions, as was the case of Verín (Fig. 1), but in other cases nature itself provoke the ignition. The high surface temperatures caused atmospheric instability, measured by indices such as CAPE (Convective Available Potential Energy) or the K index, to be very high. This high instability led to the formation on the afternoon of 14 July of a mesoscale convective system, which in a few hours left more than 6000 lightning strikes. In some places these strikes came with little or no precipitation, in the form of a dry storm. Dry storms of 14th July led to several fires. Two of them, one in Valdeorras, in the southeastern part of Galicia, and another one in Courel, a mountain area located at the east of Galicia, turned out to be the largest fires in the history of our region. In image 3, we can see a pyrocumulus produced in the forest fire of Courel on July 17th (Fig. 3).

2 Conclusion The change in land use together with the climatic drift of recent decades provoke that in Galicia, in addition to the varied range of clouds that we can normally see in our skies, others are being added such as the flammagenitus clouds, also called pyrocumulus or pyrocumulonimbus. These clouds arise from the coupling of the fire with the atmosphere which modifies the fire itself. To be produced we need deep flaming and atmospheric instability. Those circumstances appear to be more frequent in Galicia and give account of how human influence even changes the landscape that we can observe when looking at the sky every day from the earth’s surface.

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Fig. 3 Pyrocumulus in a forest fire on Courel area on July 17, 2022

References Abatzoglou JT, Williams AP, Barbero R (2019) Global emergence of anthropogenic climate change in fire weather Indices. Geophys Res Lett 46(1):326–336. https://doi.org/10.1029/2018GL 080959 Di Virgilio G, Evans JP, Blake SA, Armstrong M, Dowdy AJ, Sharples J, McRae R (2019) Climate change increases the potential for extreme wildfires. Geophys Res Lett 46:8517–8526 Jolly WM, Cochrane MA, Freeborn PH, Holden ZA, Brown TJ, Williamson GJ, Bowman DMJS (2015) Climate-induced variations in global wildfire danger from 1979 to 2013. Nat Commun 6. https://doi.org/10.1038/ncomms8537 Jones MW, Abatzoglou JT, Veraverbeke S, Andela N, Lasslop G, Forkel M et al (2022) Global and regional trends and drivers of fire under climate change. Rev Geophys 60:e2020RG000726. https://doi.org/10.1029/2020RG000726 OMM-Nº 407 Atlas Internacional de Nubes Manual de observación de nubes y otros meteoros. https://cloudatlas.wmo.int/es/home.html

Geology

Introduction to the Geology of Galicia Juan Ramón Vidal Romaní

Abstract The geology of Galicia has very specific characteristics. It is made up of very old elements, from the end of the Precambrian, which have been intensely deformed and agglomerated in bands that correspond to the collision zone between several lithospheric plates. These rocks between 750 and 305 million years ago formed an agglomerated isotropic base in the megacontinent of Pangea that during the Mesozoic was subjected to continuous erosion. In the Cenozoic, as a result of the rupture of Pangea, the Iberian Plate was differentiated, creating the current coastline that defines the base level for the Galician rivers guided by tectonic movements due to the interaction between the Iberian Plate and the bordering plates to the North and South. From the end of the Cenozoic to the present, what has most influenced the surface of Galicia have been the eustatic changes in the sea level due to the Quaternary glaciations. Keywords Galician geology · Intraplate cliffs · Galician Rias · Climbing dunes · Shingle beachs · Galician glaciers · Alpine tectonic

1 Introduction to the Geology of Galicia The geology of Galicia has very specific characteristics. It is made up of very old elements, from the end of the Precambrian, which have been intensely deformed and agglomerated in bands that correspond to the collision zone between several lithospheric plates. These rocks between 750 and 305 million years ago formed an agglomerated isotropic base in the megacontinent of Pangea that during the Mesozoic was subjected to continuous erosion. In the Cenozoic, as a result of the rupture of Pangea, the Iberian Plate was differentiated, creating the current coastline that defines the base level for the Galician rivers guided by tectonic movements due to the interaction between the Iberian Plate and the bordering plates to the North and South. From the end of the Cenozoic to the present, what has most influenced the J. R. V. Romaní (B) Instituto Universitario de Geología, Universidad de Coruña, A Coruña, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_3

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surface of Galicia have been the eustatic changes in the sea level due to the Quaternary glaciations.

2 The Formation of Galicia, 0th Phase. The Oldest Pieces of the Geological Puzzle of Galicia: The Zircons of Cabo Ortegal When rocks weather, they are destroyed creating sediments but not all the minerals that form them disappear. Some, the so-called resistates, are preserved practically intact by being incorporated into the new sediments and the inherited mineral can continue to grow in the new rock. It is a process that has been repeated on Earth for millions of years. In any coastal or fluvial sandbank in Galicia we can see resistates, minerals from the destruction of older rocks. The most common are quartz, cassiterite, magnetite, ilmenite, rutile, zircon, monazite, etc. One of them is of special interest in our history, zircon (Zr SiO4), a nesosilicate common in some igneous rocks such as syenites, diorites and granites. In 2014 (Valley et al. 2014) the oldest zircon crystal (4.4 billion years old) on Earth was dated in Jack Hills (Western Australia). This proves that at that very early stage of our planet there were already solid rocks. The rocks of Galicia contain similar information, although not as old. When studied (Sánchez Martínez 2009), the Cabo Ortegal ophiolites, a type of volcanic rock formed 750 million years ago, were found to contain 1.16 billion-year-old zircon crystals from a previous magmatic rock that was destroyed by weathering. 750 million years ago, the zircon crystals were incorporated into the ophiolite that was transformed, millions of years later, into the Purrido amphibolite. Paleomagnetic data indicate that the Purrido amphibolite was part of a mega continent, Rodinia, located far away from where Galicia is now (which did not even exist then). It can be said that these zircon crystals are the oldest minerals found so far in rocks from Galicia, although the rock where they were formed has disappeared.

3 The Formation of Galicia, 1st Phase. Galician Rocks However, most of the rocks that now make up Galicia are more modern. They are arranged according to an arched lineation that has received different names since it was first defined by Lotze in 1945. Among others: Asturian Arch or Knee, Iberian Armorican Arch, Variscic Belt (Martínez Catalán et al. 2009) and the most recent, Ibero Armorican Oroclinal, (Brandon Weil et al. 2013). And it is not limited to Galicia but extends to the rest of the Iberian Peninsula and neighboring areas of Europe. The sedimentary and volcanic rocks accreted in the Ibero-Armorican Orocline were formed for the most part under the water of two Tornquist and Rheic oceans located between Gondwana (South America, Africa, Arabia, India and Antarctica)

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and Laurussia (Laurentia, Avalonia and Baltica) that They constituted the World of that time. They were compressed during the collision between the two continents between 380 and 370 million years before now, being intensely folded, deformed and metamorphosed. Since they were formed far from their current location, they are non-native rocks.

3.1 The Senso Lato Granitic Rocks During the subduction collision stage between Gondwana and Laurrussia another type of rock was generated: the “senso lato” granitic rocks. Like the granites s.l. they formed where they are now are native rocks. The subduction between Gondwana and Laurrusia generated many magmatic bodies that rose until they reached the earth’s surface (Pastor Galán 2013). Subsequent erosion, mainly during the Mesozoic, (Grobe et al. 2014) washed away both the materials accreted between Gondwana and Laurentia and the volcanic edifices developed on the surface of what would later become Iberia. For this reason we now only see the roots of consolidated intrusive magmatic bodies 20 km deep inside the lithosphere. Granitic rocks, senso lato, are the dominant rocks in the Peninsular Hesperian Massif, especially in Galicia, and appear intercalated between the different bands of the Ibero-Armorican Oroclinal. Its relationship with the host rock has very specific characteristics. Essentially they adapt to the sinuous structure of the Orocline; in some cases they form elongated bodies parallel to the great lines of the Orocline: they are the concordant granite bodies, the earliest to intrude. In others they present a circular contour that cuts the structures of the Orocline (and for this reason they are called discordant bodies) and are the ones that intruded later. Granites are the last types of rocks, with significant volume, to be incorporated into the terrestrial lithosphere in Galicia and their injection ended approximately 305 million years ago (Gutiérrez et al. 2011), putting an end to the main rock-forming process in Galicia. Almost only the rocks have been preserved from this first stage of geological construction in Galicia. However, there are two types of shapes in the current landscape that help us understand what happened during the collision-subduction process between Gondwana and Laurrussia. The first type of form is the remnants, still recognizable, of the folding produced during the collision that originated Pangea (Fig. 1). We can see them in Galicia, from north to south in different parts of the provinces of Lugo and Ourense, although without a doubt the most famous outcrop is the so-called O Courel or Campodola-Leixazós. The second type of forms is represented by late granitic bodies (discordant) whose intrusive morphology we now see as domes or “moas”. The best preserved example is the granitic massif of O Pindo and its morphology corresponds to a magmatic body consolidated in the interior of the Earth, about 20 km deep 305 million years ago (Gutiérrez et al. 2011). Now it can be seen on the surface as it was unearthed by the prolonged erosion that affected Galicia throughout the Mesozoic (Grobe et al. 2014).

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Fig. 1 Synthesis of the geology of Galicia

4 The Formation of Galicia, 2nd Phase. The Breakup of Pangea. The Definition of the Contour of Galicia The main rock-forming stage in Galicia ends with the Paleozoic. During the next stage, the Mesozoic, the dominant geological processes in Galicia were almost exclusively erosive. I do not mean to say that Galicia, as part of a megacontinent, did not go through the same ups and downs as the rest of Pangea, including the presence of the dinosaurs. But erosion has made disappear, with few exceptions, the sedimentation corresponding to this stage. At the beginning of the Mesozoic about 200 million years ago during the Triassic, Pangea begins to break up, beginning the individualization of the Iberian Peninsula with the development of its most characteristic feature: the coastline of Galicia, both to the north and to the west. This characteristic right angle between the Bay of Biscay and the Atlantic is due to the activity of a triple point (union of 3 mid-ocean ridges). The separation of Iberia will be produced by the opening of two rift valleys that will define the coast of Galicia. During the Triassic these two depressions had endorheic characteristics as indicated by the type of sedimentation accumulated in them (evaporites, gypsum and halides). Remains of this sedimentation are still preserved on the horst of the Banco de Galicia then joined to Iberia and now located 200 km from the coast of Galicia and at a depth of 600 m. And they are also visible in the center of the Iberian Peninsula (Fernández Lozano 2014). However, the first marine sediments deposited in the marine perimeter of the Iberian Peninsula (then it would be an island), correspond to the Cretaceous (Cenomanian)

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about 100 million years ago. It is at this time that the sea reaches the Galician coast for the first time. During this stage the dominant feature of the Galician coast was that of a cliff coast as a result of the breakup of Pangea.

4.1 The Intraplate Cliffs of Galicia. Cape Ortegal and Further South On other coasts of the world even today remains of the cliffs formed during the breakup of Pangea are recognized. The best examples can be found in Serra do Mar (Brazil), The Great Escarpment in South Africa, La Grande Falaise in Madagascar, The Western Ghats in the Deccan Peninsula, The Great Escarpment in Eastern Australia. All of these cliffs are now located far away from the sea and the plate edge where they formed and are therefore called intraplate cliffs. And they are not of marine origin but tectonic. To the previous list we must add the intraplate cliffs of Galicia (with the singularity that here they are bathed by the sea). They are, without a doubt, the best preserved in the entire Iberian Peninsula. They can be seen on the northern Cantabrian edge, but more especially on the western Atlantic edge (Cabo Ortegal, Monte Pindo, Barbanza, Monte Xiabre, Serra do Galiñeiro, etc.). Initially these cliffs were compact shapes that could be followed along the coast of Galicia. But the dismantling of the coast of Iberia began very soon. It first took place along the coastline due to the action of large listric faults, although this part of the coast normally goes unnoticed as it is now below sea level (Moullade and Boillot 1988). Later, it continues to happen right now, the coastline was modified by minor gravitational landslides. Undoubtedly the most spectacular examples can be seen in the Serra da Capelada where the cliff collapses, 200 million years later, in the form of large translational landslides (Os Aguillóns-Punta Candieira section). Sometimes the degradation of the cliff is caused by rotational landslides (Santo André de Teixido valley, Cedeira) or further south (Cabo Cociñadoiro landslide in Buño), as the rock in these areas is much more weathered.

4.2 Fluvial Erosion and Galician-Portuguese Rivers However, most of the Galician-Portuguese Atlantic coast was degraded by the erosion of the Atlantic rivers on their way to the sea. According to this, the Galician coast (Otmann 1967), is not of marine origin (secondary coast), but of continental origin, having been formed by diastrophic processes (large faults and landslides) and by fluvial erosion. Its current appearance, as marine as it seems, is very recent since it was reached in the last 15,000 years during the marine transgression that began at the end of the last glacial phase when the melting of glacial ice flooded the relief

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adjacent to the coast. Although it may not seem like it, the stretches of coast of marine origin in Galicia stricto senso are very scarce (essentially beaches and sandy bars). As I said during almost the entire Mesozoic, (Grobe et al. 2014) inland Galicia was also exposed to continuous erosion, we assume that it was of fluvial origin. Obviously, although erosion acted in coastal areas by marine action, it was also effective (Pannekoek 1966) along its riverbeds. This is what the longitudinal profiles of the current Atlantic rivers tell us, which preserve discontinuities in their longitudinal profile indicating how far the ascending erosive wave that began on the coast reached. Most of these discontinuities are found in the interior of Galicia, hidden under the waters of the reservoirs, and only in the case of the Xallas river does it sometimes manifest itself in all its splendor in the cadoiro (waterfall) of the Aguadero de Lezarus. It is therefore not very risky to assume that Galicia would be criss-crossed by a fluvial network that flowed into the sea, either to the North (Cantabrian coast) or, mainly, to the west (Atlantic coast) (Pais et al. 2012). The arrival of the rivers from Galicia and the North of Portugal to the sea is a process that culminated on different dates. In some cases 100 million years ago for the great Atlantic rivers: Tambre (Muros), Ulla (Arousa), Lérez (Pontevedra), Verdugo-Oitavén (Vigo), Miño/MinhoSil (Caminha-Camposancos), Lima/Limia (Viana do Castelo), Cávado (Esposende), Ave (Vila do Conde) and Duero/Douro (Porto), and perhaps for some of the great Cantabrian rivers: Eo (Ribadeo), Masma (Foz) and Navia (Navia). The other rivers must have reached the sea later (between 24 and 5 million years) at least in their current course, since the subsequent formation of the Cantabrian Chain interfered with the development of the river network.

5 The Formation of Galicia, 3rd Phase. Alpine Tectonics in Galicia and the Current Relief of Galicia During the Mesozoic, the Atlantic coast was subject to a distensive regime, as it corresponded to a passive plate edge moving away from the continents located on the other side of the Atlantic Ocean. However, the situation changed in Galicia during the Cenozoic, especially during the Paleogene or Tertiary inferior (between 65 and 35 million years before now), (Ribeiro 2002) due to the convergence between the Eurasian Plate and the Iberian Plate, which turns the coast of Galicia into a compressive edge (Gallastegui Suárez 2000).

5.1 The Elevation of the Rasa Cantábrica. The Rasa in the Rest of the Galician Coast As a result of this compression or collision, the Cantabrian Mountain Range will be formed and associated with it, the Rasa Cantabrica will rise, an etche or chemical

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corrosion surface now fossilized by slope fans and by the fluvial terraces of the Cantabrian rivers (Flor 1983; Mary 1983), Navia, Eo, Masma, which in response to the Paleogene uplift fit into their valleys,. This explains why, despite their limited hydrographic basin and their low erosive capacity, they have been able to excavate the reliefs of the Cantabrian Mountains, although without laterally widening their valleys (Flor 1983; Mary 1983). For a long time it was considered that both the Rasa and the Cantabrian Mountains were limited to the north coast of Iberia, however the latest interpretations allow both the Cantabrian Mountains and the Rasa to be extended to the rest of the Galician coast. However, the plain of western Galicia is not as well preserved as on the north coast because the much more important and active Atlantic rivers have almost completely dismantled it.

5.2 The Ourense Corridor and Its Influence on the Cenozoic Evolution of the Galician River Network Until recently, it was considered that the Cantabrian Mountains ended in the active Becerreá-Sárria-Triacastela seismic triangle. However, the new interpretations allow the Cordillera Cantábrica to be extended further south, following a system of faults in direction, active from the Oligocene until, practically, the end of the Cenozoic. These faults determined the generation of a large subsidence, a graben or strike-sleep-fault tectonic trench, called Ourense Corridor (from Vicente and Vegas 2009). The most important Galician tertiary basins were developed on this great depression: Vilalba, Sarria, Monforte de Lemos, Xinzo de Limia, Maceda, where sometimes up to 200 m of lacustrine sediments accumulate (which implies that there was a appreciable sheet of water). Part of the drainage of the fluvial network that went towards the future estuaries was diverted towards the Ourense Corridor and channeled towards the sea through a narrow channel, the neoMiño, until its confluence in Los Peares with the Sil river. For this reason we know that the Miño River could only form and establish itself in its current layout when the filling of the Galician Tertiary basins was completed, at the end of the Tertiary (Pliocene). And yet the Sil river “tributary of the Miño” already existed during the Tertiary (Heredia et al. 2015) and even reached the sea as evidenced by the quartzite gravel terraces of the final course of the Miño that can only come from the headwaters of the Sil in the Bierzo. For this reason, the most surprising conclusion is that the most important Galician river in terms of volume and drainage basin, the Miño River, is the youngest of all the Galician rivers and has a maximum age of 5 million years (at least up to Os Peares where confluent with Sil). The other Galician rivers, even though they are less important in terms of length, flow or surface area of their current drainage basin, (with the exception of the Sil river) are, however, older than the Miño. And we must also conclude that the most notable flat surface of Galicia, the Terra Chá, is much more modern than previously thought, since it is also defined when the filling of the inner tertiary basins of Galicia ends, which occurs at the end from the Upper Tertiary (Pliocene).

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5.3 The Formation of the Galician Estuaries (Rías). The Galician-Portuguese Dry Estuaries (Rías) The collapse of the Ourense Corridor had dramatic effects on the evolution of the Galician-Portuguese estuaries, especially the central ones, due to the capture by the neo Miño of the headwaters of the rivers that flowed into the future lower Galician estuaries. The main Galician Atlantic rivers, Tambre (Muros), Ulla (Arousa), Lérez (Pontevedra), Verdugo and Oitavén (Vigo), were deprived of the water they had received until then and were unable to continue eroding their valleys with the same intensity as before. Then. This explains why all the Rías Bajas have dimensions that are too large for the entity of the rivers that now drain into them. An attempt has been made to resolve this apparent inconsistency by assigning a set of ad hoc faults for each estuary and proposing an individualized subsidence for each of them. This hypothesis is not supported by any consistent geological evidence (as previously stated, the Cantabrian plains associated with the Galician uplift during the Tertiary have their equivalent also on the Atlantic coast of Galicia). And furthermore, a system of faults associated with each estuary does not resolve the anomaly that the Miño River, the most benefited by capturing a large part of the waters that previously went to the estuaries, would not have been able to develop an estuary in its final section. For some time it was argued that the final stretch of both the Miño and the other Portuguese rivers, the Limia/Lima, the Ave, the Cávado and the Duero, would have been silted up by their own fluvial deposits (Lautensach 1941, 1945). The latest studies for the lower course of the Miño river (Viveen et al. 2012, 2013a and b) have shown that this idea is not true, since the supposed filling postulated by Lautensach does not exist. To explain the non-existence of estuaries from the Miño (Minho) to the Douro (Douro), one must resort to the tectonics that acted in northwestern Iberia during the Paleogene (lower Tertiary) (de Vicente and Vegas 2009). In Galicia, the Ourense Corridor is interrupted when it reaches the height of Celanova, where it connects with the last section of the Cantabrian Mountain Range in Galicia, which divides into two branches: one parallel to the limit between Galicia and Portugal, between the Budiño- Tui and the sea, and another further south, from Lindoso in the Serra do Gerês to Viana do Castelo. Although the heights reached in this last section are lower than those of the rest of the Cantabrian Chain (here they do not exceed 700 m in altitude), the elevation of the Cantabrian Mountains in this final part affected the riverbeds of the Miño/Minho rivers, Lima/Limia, Cávado, Ave, Duero/ Douro, raising their valleys, (which were already excavated), from the end of the Tertiary to the present, not allowing their flooding during the last rise in sea level that began 15,000 years ago. This is the reason for the formation of the so-called “Rías Secas” in the Iberian NW.

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5.4 The Galician Coast: Sinking and Rising One of the consequences of this new interpretation of the evolution of the Galician relief is that, contrary to what was thought until now, the Galician coast is an uplifting coast, as deduced (Viveen et al. 2012, 2013a and b) from the study of the terraces of the Miño in its final section between As Neves and the sea, and which is synthesized in the magnificent stepped sequence of terraces of the O Rosal valley located at the mouth of the Miño. And the traces of uplift are not limited to the mouth of the Miño river but are recognized along the entire Galician-Portuguese coast to the north and south of the Miño (Minho), in the form of sea levels located at different heights above the sea level on the Atlantic coast of Iberia.

5.5 The Collateral Effects of the Tertiary Tectonics in Galicia As we have seen so far, the role of tertiary or alpine tectonics is crucial in defining the relief of Galicia: it creates the Cantabrian Chain and its westernmost termination, the Ourense Corridor, and also causes the lifting of the blocks defined by the tertiary fractures, diverting part of the flow of the Galician rivers that it channels towards what will later become the Miño, transforming it into the youngest river and also the mightiest of all the Galician rivers (even discounting the contributions of the Sil). Another consequence of the uplift of Galicia during the Tertiary is that it allows some of its reliefs to be located above 1000 m in height, a fact of relevant importance in the next stage of the geological evolution of Galicia: the Pleistocene or the age of ice ages.

6 The formation of Galicia, 4th Phase. The Pleistocene or the Ice Age in Galicia: Its Influence on the Galician Coast and Its Interior Mountains. Ice Cap Glaciers (Xurés, Manzaneda, Pena Trevinca) and Mountain Glaciers (Ancares and Courel) Indeed, the lifting of the relief during the Tertiary had additional effects that are felt during the Pleistocene (last 2.58 million years). In this stage of the Earth’s geological history there was an alternation of 20 glacial phases with 20 interglacial phases extended to the entire Earth and that in Galicia have a very peculiar development. Despite the fact that the Iberian Peninsula is very far from the front of the maximum advance of the ice in the Northern Hemisphere, Tertiary tectonics produced selective elevations of the relief of the entire Cantabrian Mountains, from the Pyrenees to Galicia. The reliefs located at elevations of 1000 m, or higher, become areas of

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accumulation of snow first, which then evolves into glacial ice. Although the Pleistocene glacialism of Galicia is not quantitatively relevant, it is very important from a qualitative point of view. However, outside the areas covered by ice (Courel, Cabeza de Manzaneda, Ancares, Xurés/Gêrez, Peneda and Cabreira), which barely occupy a total area of 260 km2, there are hardly any glacial or glacigenic deposits. And even in undeniably glaciated areas, glacially abraded rocky surfaces predominate over sediment-covered ones. This justifies that until the advent of stable cosmogenic isotope dating (Vidal Romaní et al. 1999; Fernández Mosquera et al. 2000), it was not possible to date the Pleistocene glacial phases that acted in Galicia. Of the Pleistocene glaciation in the Iberian northwest, only remains of the last 3 phases have been preserved, due to the fact that each glaciation erased, with more or less effectiveness, the traces of the preceding glaciation. For this reason, the preserved sedimentary record barely represents the last 500,000 years (Vidal Romaní et al. 1999; Brum et al. 2000). Other areas of Galicia and the north of Portugal with a smaller area, well located at the same levels or a little lower, such as Avión, Serra de Larouco, Baltar, Pindo-Ruña, Xistral, Barbanza, Galiñeiro, were only affected by processes periglacial but never glacial.

6.1 The Emptying of the Estuaries (Rías). The Galician-Portuguese Dry Estuaries (Rías) However, the main effect of the cooling of the world climate during the last 2.58 million years in Galicia was not in the action of the glacial processes in the mountains, but in what occurred on the coastline. During the Quaternary, the sea level goes from about 50 m above the current level during the interglacial stages to about -200 m below the current level during the glacial stages. The iteration in the oscillation of the base level occurs up to 40 times during the Pleistocene and its greatest effect is in the reactivation of the fluvial erosive processes in the areas closest to the coast. Despite being superimposed on the slow tectonic uplift of Galicia that began in the Tertiary, the Pleistocene eustatic changes on the Galician coast produce a total emptying of the sediments accumulated in the estuaries and their current deepening (Fig. 2). These sea level changes occur in geologically short time intervals (approximately every 100,000 years). During interglacials, as is the case now, the sea penetrated deep into the interior of the continent, flooding the final stretch of the rivers and forming estuaries. During the glacial periods, with a lower sea level, up to −200 m below the current one, the sea moves away up to 40 km from its current position, increasing the erosive energy of the rivers. The effectiveness of these processes of emptying the sediments accumulated in the Galician estuaries is proven by the modernity of the deposits that are preserved in them, which does not exceed 30 or 40,000 years before now. However, in the dry Rías (corresponding to the Miño and Lima rivers), and where erosion has not been so intense, the age of fluvial sediments can be at least 700,000 years old (Viveen et al., 2012, 2013a, b).

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Fig. 2 Pebble beaches corresponding to the previous interglacial in Costa da Morte (Coruña, Spain)

6.2 Aeolian Episodes During the Pleistocene in Galicia River erosion during the glacial and interglacial phases on the Galician coast was, obviously, only active in the strict area of the estuaries (rías). But in the interfluves between estuaries, other sedimentary processes have left records of a certain age (up to 300 ka, Trindade et al. 2013) throughout the Galician coast. This is the case of the eolian sand mantles, which covered the entire coast with climbing dunes and which can still be recognized today. The formation of this type of dunes is contemporaneous with the glacial stages on a global scale, with a sea level below the current one. There are many outcrops of Pleistocene dunes on the Galician coast, although they often go unnoticed as soils have developed on the oldest and even on the current ones. The Pleistocene dunes would begin to form during the glacial stages on the seashore, sometimes up to 40 km away from the current coast. Then, at the end of each glaciation and as the sea recovered its current level, they would move towards the coast, driven by the wind until they were held against the firmer rocky reliefs. They must have covered a large part of the coastal reliefs in a very similar way to what is happening now in Cabo de Home, Cíes, A Lanzada, O Grove, Playa de Trece (Xaviña), or Monte Branco (Ponteceso, Anllóns), Doniños, Frouxeira, etc.., and hence its name rampant dunes or climbing dunes (Fig. 3). Although we now see them at the edge of the coast, they have traveled a great distance from their original location at the edge of the sea, sometimes up to 40 km away. They moved driven by the wind until the rise of the sea covered their feeding area with sand. At present these dunes, unable

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Fig. 3 Fossil forest on the coast of Ponzos, Coruña) developed on the shingle beach of the previous interglacial. In the background the dunes that correspond to the rise of the Holocene sea

to receive more contributions, are destroyed by the wind that transforms them into tabular accumulations of sand that the vegetation quickly colonizes.

6.3 The Coastal Lagoons of the Galician Coast In other cases, the dunes, on their way to the continent during the postglacial period, intercepted small inlets (Frouxeira, Doniños, Barrañán, Baldaio, Traba, Caldebarcos, Carnota, Louro, Xuno, Carregal, etc.), giving rise to the formation of coastal lagoons. However, as is the case with the coastal dunes of Galicia, the current rise in sea level is leading these coastal lagoons (a fundamental part of the Natura Network) towards irreversible destruction. This changing climatic panorama described for the Galician coast during the Holocene undoubtedly involved catastrophic environmental changes for both fauna and flora that were not limited to the end of the Quaternary but were repeated up to 40 times during the last 2.58 million of years. And yet it has not received the least attention from researchers, at least so far.

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6.4 The Pleistocene Coastal Forests of the Galician-Portuguese Atlantic Coast A good example of the environmental crises that affected the Galician coast during the Quaternary are the fossil forests. Periodically discovered by marine erosion along the entire coast of northern Portugal and Galicia, they seem to have been buried under the sand of the beach, that is, buried by the sea. The reality is that they were buried by the traveling dunes displaced towards the mainland at the end of each glacial phase as the sea level rose. Its excellent degree of conservation, the existence of plants in a living position and the conservation of the original forest floor confirms its burial by the dunes. Now marine erosion brings them to the surface, briefly, before their final destruction (Fig. 3). The age of these forests, around 7,000 years before now, indicates that they are remains of the vegetation that colonized the Galician coast at the end of the last glacial period. Taking into account the position of the sea level at the time of the beginning of the last postglacial marine transgression, we can say that the retreat of the coastline has taken place at an average speed of 4 m per year. If we compare the advance of the sea during the Holocene on the Galician coast with what is happening now on the northern coast of Portugal, it must have been a catastrophic event for coastal ecosystems. Once again, despite its undoubted paleoecological interest, this stage in the history of Galicia and the changes associated with it have hardly aroused the interest of scientists, except in isolated cases. Acknowledgements I would like to thank my colleagues for their support of this work, mainly Professor Aurora Grandal d’Anglade during all the years of my active life at the University of Coruña.

References Brandon Weil A, Gutiérrez-Alonso G, Johnston ST, Pastor-Galan D (2013) Kinematic constraints on buckling a lithospheric-scale orocline along the northern margin of Gondwana: a geologic synthesis. Tectonophysics 582:25–49. https://doi.org/10.1016/j.tecto.2012.10.006 Brum de Ferreira A, Vidal Romaní JR, Zezere JL, Rodrigues ML (2000) A Glaciação plistocénica da Serra do Gerês. Finisterra XXXV(69):39–68 e Vicente G, Vegas R (2009) Large-scale distributed deformation controlled topography along the western Africa-Eurasia limit: tectonic constraints. Tectonophysics 474:124–143 Fernández MD, Vidal MK, Romaní JR, Weigel D (2000) Late Pleistocene deglaciation chronology in the NW of the Iberian Peninsula using cosmic-ray produced 21 Ne in quartz. Nuclear Instruments Methods Phys Res B 172:1–6 Fernández Lozano J (2014). Cainozoic deformation of Iberia: a model for intraplate mountain building and basin development based on analogue modelling. Serie NOVA TERRA, vol 46, p 161, Coruña Flor G (1983) Las rasas asturianas: ensayo de correlación y emplazamiento. Trabajos De Geología 13:65–81 Gallastegui Suárez J (2000) Estructura cortical de la cordillera y margen continental cantábricos: perfiles ESCI-N. Trabajos de Geología, vol 22. Universidad de Oviedo, Oviedo, p 221

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Grobe RW, Álvarez-Marrón J, Glasmacher UA, Stuart FM (2014) Mesozoic exhumation history and palaeolandscape of the Iberian Massif in eastern Galicia from apatite fission-track and (U+Th)/ He data. Int J Earth Sci 103:539–561 Gutiérrez-Alonso G, Fernández-Suárez J, Jeffries TE, Johnston ST, Pastor-Galán D, Murphy JB, Piedad Franco PM, Gonzalo JC (2011) Diachronous post-orogenic magmatism within a developing orocline in Iberia, European Variscides. Tectonics, 30:TC5008. https://doi.org/10.1029/ 2010TC002845 Heredia N, Fernandez LP, Martin-Gonzalez F, Bahamonde JR (2015) Depositional style and tectonostratigraphic evolution of El Bierzo Tertiary sub-basin (Pyrenean orogen, NW Spain). Geologica Acta 13(1):1–23. ISSN 1695-6133 Lautensach G (1941) Interglaciale Terrasenbildung in Nord Portugal, und ihre Bezrehungen zu den allgemenen. Petermanns Geografische Mitteilungen Fasc 9:297–311 Lautensach H (1945) Formação dos terraços interglaciarios do Norte de Portugal e as suas relações com os problemas da epoca glaciaria. Soc Geol de Portugal 1–39 Martínez Catalán JR, Arenas R, Abati J, Sánchez Martínez S, Díaz García F, Fernández Suárez J, González Cuadra P, Castiñeiras P, Gómez Barreiro J, Díez Montes A, González Clavijo E, Rubio Pascual FJ, Andonaegui P, Jeffries TE, Alcock JE, Díez Fernández R, López Carmona A (2009) A rootless suture and the loss of the roots of a mountain chain: the Variscan belt of NW Iberia. Comptes Rendues Geosci Tectonic 341(2009):114–126 Mary G (1983) Evolución del margen costero de la Cordillera Cantábrica en Asturias desde el Mioceno. Trabajos De Geología 13:3–35 Moullade M, Boillot G (1988) Subsidence and deepening of the Galicia Margin: the paleoenvironmental control (1988). Proc ODP Sci Results 103:733–740 Ottman F (1967) Introducción a la geología marina y litoral. Manuales EUDEBA. Buenos Aires Pais J, Cunha PP, Pereira D, Legoinha P, Dias R, Moura D, Brum da Silveira A, Kullberg JC, González-Delgado JA (2012) The Paleogene and Neogene of Western Iberia. A Cenozoic Record in the European Atlantic Domain. Springer briefs of Earth Sciences, Springer, 158 Pannekoek AJ (1966) The Ria problem. Tijdschr Kon Ned Aardr Gen 83:289–297 Pastor Galán D (2013) Evolución geodinámica del Oroclinal Ibero Armoricano. Geología estructural, modelización análoga y geocronología. Serie Nova Terra, 43:183 Ribeiro A (2002) Soft plates and impact tectonics. Springer, 324 Sánchez Martínez S. (2009). Geoquímica y geocronología de las ofiolitas de Galicia. Serie Nova Terra 37, 351 pp. Trindade MJ, Prudencio MI, Sanjurjo SJ, Vidal-Romaní JR, Ferrez T, Fernández MD, Dias MI (2013) Post-depositional processes of elemental enrichment inside dark nodular masses of an ancient aeolian dune from A Coruña Northwestern Spain. Geol Acta 2:231–244 Valley JW, Cavosie AJ, Ushikubo T, Reinhard DA, Lawrence DF, Larson DJ, Clifton PH, Kelly TF, Wilde SA, Moser DE, Spicuzza MJ (2014) Hadean age for a post-magma-ocean zircon confirmed by atom-probe tomography. Nat Geosci. https://doi.org/10.1038/NGEO2075 Vidal Romaní JR, Fernández Mosquera D, Marti K, de Ferreira AB (1999) Nuevos datos sobre la cronología glaciar pleistocena en el NW de la Península Ibérica. Cadernos do Laboratorio Xeolóxico de Laxe 24:7–30 Viveen W, Braucher R, Bourlès D, Schoorl JM, Veldkamp A, Van Balen RT, Wallinga J, FernándezMosquera D, Vidal-Romaní JR, Sanjurjo-Sanchez J (2012) A 0.65 Ma chronology and incision rate assessment of the NW Iberian Miño River terraces based on 10Be and luminescence dating. Global Planet Change 94–95:82–100 Viveen W, Schoorl J, Veldkamp A, Van Balen R, Desprat S, Vidal-Romaní JR (2013a) Reconstructing the interacting effects of base level, climate and tectonic uplift in the Lower Miño River terrace record: a gradient modelling evaluation. Geomorphology 186:96–118 Viveen W, Schoorl J, Veldkamp A, Van Balen R, Vidal-Romaní JR (2013) Fluvial terrace map of the northwest Iberian lower Miño River. J Maps. 9(4):513–522

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Yepes Temiño J, Vidal Romaní JR (2004a) Morphological analysis of the river network in the basin of the Miño and Sil (Ourense) rivers. Contribuciones Recientes Sobre Geomorfología 1:127–134 Yepes Temiño J, Vidal Romaní JR (2004b) History of granitic morphogenesis. Cadernos do Laboratorio Xeolóxico de Laxe 29:331–360

Al-Rich Speleothems in Granite Caves: A Poorly Known Geologic Material and Environment Jorge Sanjurjo-Sánchez, Carlos Arce Chamorro, Juan Ramón Vidal Romaní, Victor Barrientos, and Joeri Kaal

Abstract Caves are frequent in some granite massifs, that are very common in the NW of the Iberian Peninsula. Water trickling through joints and discontinuities of granitic massifs is the cause of the formation of speleothems that have been related to the biological activity of several organisms. They can be usually found in the water output of fissures, showing a variable morphology. Thus, they are referred such as biominerals. The most frequent and abundant speleothems are those made of Si-rich (commonly opal-A) and authigenic Al-rich organic bearing deposits. In the last years the formation process of opal-A speleothems has been studied in detail and better understood. However, Al-rich analogues have been scarcely studied and their formation process is poorly understood. A recent study has proposed a formation mechanism and it shows that they are very interesting as environmental archives, as occurs with speleothems in limestone caves. Keywords Speleothems · Pseudokarst · Al-rich deposits · Granite caves · Biological weathering

1 Introduction Caves are relatively frequent in granite massifs. When compared with limestone caves, in granite caves are smaller, with maximum dimensions around 1000 m. They are referred to as pseudokarst caves. They are common in Galicia (NW of Spain) and Northern Portugal. This is one of the areas of the World with a high number of granite caves, being some of them among the largest (Chabert and Courbon, 1997; Vidal Romaní et al. 2007, 2014). Water flowing through the rock discontinuities causes a slow both chemical and physical weathering process related to biological J. Sanjurjo-Sánchez (B) · C. A. Chamorro · J. R. V. Romaní · V. Barrientos Instituto Universitario de Geología “Isidro Parga Pondal”, Universidade da Coruña, ESCI, Campus de Elviña, 15071 A Coruña, Spain e-mail: [email protected] J. Kaal Pyrolyscience, Plaza Ciudad de Viena 6, 28040 Madrid, Spain © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_4

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Fig. 1 Granite caves with occurrences of flowstones of Al-rich compounds of a granite cave of NW Spain (picture by Juan Ramón Vidal Romaní). They are usually formed in caves, from water seepage through fissures of the ceiling and walls of granite caves. The variable colours observed in the picture are common (Fig. 1)

activity. The stone components are firstly eroded and later deposited in rock fissures, cave surfaces or the water output of fissures (Vidal Romaní et al. 2003, 2010). Such processes result in the formation of deposits that are considered as speleothems. They show a very variable morphology depending water trickling rock fissure systems and deposition mode. Their formation processes are comparable to those found in karstic systems but smaller in size and volume (Hill and Forti 1995; Vidal Romaní et al. 2010, 2015).

2 Granite Caves and Speleothems: A Poorly Known Environment Speleothems formed in granite caves are considered as a suitable environment for the development of microorganisms such as bacteria, fungi, algae and diatoms, and microfauna that has been identified living on them, such as polychetes or mites, at least in a part of their vital cycle (Aubrecht et al. 2008; Vidal Romaní et al. 2010, 2015). Some of such organisms and microorganisms have been identified. Due to the quick process of deposition of the speleothems (Sanjurjo-Sánchez and VidalRomaní 2011) it is necessary a high rate of weathering of poorly soluble minerals such as quartz or feldspars. Thus, it has been argued that biological activities of such organisms have a key role in the formation of such speleothems (Vidal Romaní et al. 2010, 2015; González-Pimentel et al. 2018; Sauro et al. 2018).

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Fig. 2 Detailed picture of the surface texture of Al-rich flowstones. This kind of surface texture is usual in this type of speleothems. Water flows running from above to below in the picture (picture by Juan Ramón Vidal Romaní)

There are products that come from the metabolic activity of these organisms that can be incorporated to the water flowing, that increase its weathering capability, affecting to the rock minerals. Thus, it is considered that their biological activity is directly involved the formation of the speleothem (Vidal Romaní et al. 2010, 2015; González-Pimentel et al. 2018; Sauro et al. 2018). The microorganisms promote the weathering of the rock, contributing to the production of new minerals (such as opal-A). Thus, they are referred as biominerals. It is also considered that the organic activity of the microorganisms acts as sedimentation trap of the resulting materials. The most frequent and abundant speleothems are composed of either Sirich (usually opal-A) or authigenic Al-rich mineraloids (Webb and Finlayson 1984; Hill and Forti 1995; Vidal Romaní et al. 2015). Both the geochemical composition of opal-A speleothems and their formation process have been studied in detail, being fairly well understood (Vidal Romaní et al. 2010, 2015). However, there is a poor knowledge on the process that result in the formation Al-rich speleothems (Fig. 2), despite some studies published in the last years has provided new light on their composition and formation processes (Filippi et al. 2020). Some of such studies has been carried out in caves and speleothems of this region (Sanjurjo-Sánchez et al. 2021).

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3 Al-Rich Speleothems: Geological Value Such Al-rich speleothems are of particular interest for several reasons. Contrary to Si-rich speleothems they can reach large sizes, being reported speleothems with thickness ranging from centimeters to a meter, and surface extension of some meters. As some studies show they are formed by accretion of layers. Thus, they could be used as proxies (Fairchild and Baker 2012), to get environmental and climatic data. A recent study carried out by Sanjurjo-Sánchez et al. (2021) shows that they are related predominantly to materials that are transported by water that infiltrates from the soil layers formed above the cave ceiling. Although they are probably transformed by the activity of organisms living within the speleothem as it has been observed from the study of the organic matter fraction. Slow water flowing through the cave fissures transports dissolved ions (from granite minerals), a variable amount of detrital siliciclastic grains and organic matter coming from the soil layers located above the cave. Thus, the speleothems are formed by accretion of layers, which are preserved under stable temperature and humidity conditions. Thus, the process of accretion is controlled by changes in rainfall and soil moisture, being the layers potentially environmental of environmental changes that occurred in the past. Among organic matter compounds plant derived components have also been identified, being a possible source of information of vegetation in the past. This is of special value because the study of climate and environmental changes is performed on calcite speleothems, found in caves of limestones. Thus, in areas with different lithology than limestone similar environmental information can be obtained from the study of speleothems. The only ages obtained in such kind of speleothems are based on radiocarbon dating, and they provided ages ranging from 1200 to 3000 years BP (Vidal Romaní et al. 2015; Sanjurjo-Sánchez et al. 2021). This means that they could provide information of recent climate and environmental changes, but still more speleothems must be studied in detail to know the age range that it can be studied. The dated speleothems were not very thick (less than 0.5 m), so thicker speleothems could provide older ages) (Fig. 3).

4 Final Remarks As this paper shows, the study of speleothems found in pseudokarst caves, namely granite caves but not excluding other types of rocks are of special interest because of the role of organisms on the weathering of minerals and their role in the formation of some speleothems, but also on the possible use of such speleothems as environmental archives, as occurs with speleothems in limestone caves. In this sense, Al-rich speleothems are frequent in granite caves and specially interesting because of their quick deposition, thickness and their geochemical content (ions, detrital minerals

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Fig. 3 Picture of a broken Al-rich flowstone in a granite cave. The broken surfaces provides a view of the cross-section of the speleothem with accretion of layers due to water flowing through the surface of the deposit. In the left-down corner the surface texture of the speleothem can be observed

and organic matter), that can provide information of environmental changes in the past. Acknowledgements The research for this paper has been supported by a grant of the Programme “Consolidación y estructuración de unidades de investigación competitivas: Grupos de potencial de crecimiento” (ED431B 2021/17) of Consellería de Cultura, Educación e Universidade, Xunta de Galicia.

References Aubrecht R, Brewer-Carias C, Smida B, Audy M, Kovacik L (2008) Anatomy of biologically mediated opal speleothems in the World’s largest sandstone cave: Cueva Charles Brewer. Chimantá Plateau Venezuela Sedimentary Geology 203:181–195 Chabert C, Courbon J (1997) In: Pre de Mme Carle (ed) Atlas des cavités non calcaires du monde. Paris, p 109 Fairchild IJ, Baker A (2012) Speleothem science: From process to past environments. Wiley, Chichester, p 416 Filippi M, Bruthans J, Skála R, Mészárosová N (2020) Speleothems of the granite Gobholo Cave in Eswatini. J Afr Earth Sc 172:103986 González-Pimentel JL, Miller AZ, Jurado V, Laiz L, Pereira MFC, Saiz-Jimenez C (2018) Yellow coloured mats form lava tubes of La Palma (Canary Islands. Spain) are dominated by metabolically active Actinobacteria. Sci Rep 8:1944–1955 Hill CA, Forti P (1995) The classification of cave minerals and speleothems. Int J Speleol 24:77–82

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Sanjurjo-Sánchez J, Vidal-Romaní JR (2011) Luminescence dating of pseudokarst speleothems: A first approach. Spectrosc Lett 44:543–548. https://doi.org/10.1080/00387010.2011.610422 Sanjurjo-Sánchez J, Arce Chamorro C, Vidal Romaní JR, Vaqueiro-Rodríguez M, Barrientos V, Kaal J (2021) On the genesis of aluminum-rich speleothems in a granite cave of NW Spain. Int J Speleol 50 25–40. https://doi.org/10.5038/1827-806X.50.1.2358 Sauro F, Cappelletti M, Ghezzi D, Columbu A, Hong P-Y, Zowawi HM, Crabone C, Piccini L, Vergara F, Zannoni D, De Waele J (2018) Microbial diversity and biosignatures of amorphous silica deposits in orthoquartzite caves. Sci Rep 8(1):17569–17569. https://doi.org/10.1038/s41 598-018-35532-y Vidal Romaní JR, Vaqueiro M (2007) Types of granite cavitites and associated speleothems: Genesis and evolution. Nature Conservation 63:41–46 Vidal Romaní JR, González López L, Vaqueiro M, Sanjurjo-Sánchez J (2015) Bioweathering related to groundwater circulation in cavities of magmatic rock massifs. Environ Earth Sci 73:2997– 3010 Vidal Romaní JR, Sanjurjo J, Vaquerio M, Fernández Mosquera D (2010) Speleothem development and biological activity in granite cavities. Geomorphologie: Relief Process Environ 4:337–346 Vidal Romaní JR, Vaqueiro M, Sanjurjo J, (2014) Granite landforms in Galicia. In: Gutierrez M, Gutierrez M (Eds) Landscapes and landforms of Spain. Springer, Dordrecht, pp 63–39. https:// doi.org/10.1007/978-94-017-8628-7_4 Webb JA, Finlayson BL (1984) Allophane and opal speleothems from granite caves in south-east Queensland. Aust J Earth Sci 31:341–349

Caves: Underground Landscapes Marcos Vaqueiro Rodríguez

Abstract In Galicia there are caves in different types of rocks. Although they are typical morphologies in limestone and dolomites that are soluble rocks, they also appear in rocks with low solubility such as quartzite and some types of sandstone, and even in non-soluble rocks such as granites, gneisses, schists and slates. Associated with the several types of caves, there is an underground landscape that is very different from what we can see on the Earth’s surface, and which is decorated with specific morphologies that are the result of the interaction of physical, chemical, and biochemical processes. These processes do not act in the same way on one or another type of rock. And although in caves developed in rocks of different nature we can find very recognizable shapes with similar morphologies, these are not always the result of the same process. This diversity of forms and processes make caves one of the great resources to show morphodiversity and geodiversity. Keywords Caves · Speleothem · Biospeleothem · Erosional forms · Solutional forms

1 Caves A cave is any underground natural space accessible (due to its size) to the human being (Chavert and Courbon 1997). This definition does not establish any lithological limitation (due to the type of rock or substrate where it is located) or genetic (due to the process that gives rise to its existence). And these are two important nuances because although the cave concept is traditionally related to the dissolution of carbonate rocks, the reality is that they are forms that are present all over the world (Boston 2004; Chavert and Courbon 1997; Palmer 2012) and that they exist in practically everything M. V. Rodríguez (B) University Institute of Geology (University of A Coruña) Pseudokarst Commission at the International Union of Speleology, A Coruña, Spain e-mail: [email protected] Atlas of Caves and Canyons at the Galician Federation of Speleology, Galicia, Spain © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_5

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type of rocks (Chavert and Courbon 1997; Urban and Oteska-Budzyn 1998; Halliday 2007; Palmer 2012). The largest caves are located in soluble rocks (carbonates, gypsum, halides and quartzites). But there are also caves developed in insoluble rocks (granites, slates and schists, gneiss, …) more modest in size but no less interesting. See Fig. 1. Under the term karst s.s. we encompass the forms of surface or subterranean landscape created by the dissolution of carbonate rocks. When the rocks are not carbonated but are soluble, such as gypsum, halides, quartzite and certain sandstones, and give rise to karst-like landscapes, many authors use the term parakarst (Gilli, 2015: 4). And under the term pseudokarst are included all morphologies similar to

Fig. 1 Different types of rock give rise to caves with different morphologies. But this does not mean that both spaces cannot be considered as caves. To the left. Buraca das Choias—La Cripta System (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain), a cavity formed in the limestone of the Vegadeo series. It is an incised keyhole passage in where a great abundance of calcite dripstone, flowstone and composite flowstone-dripstone speleothems can be seen. To the right, vadose passage in the roofed canyon of O Tronceda (municipality of Mondoñedo, province of Lugo, Galicia, Spain), a pseudokarst cave developed in two-mica granite. The passage shows a great abundance of pigotite (AOS, aluminium-bearing organic compounds (Sanjurjo-Sánchez et al. 2021)) composite flowstone-dripstone speleothems above the flood level

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those of karst but produced mainly by a different process of dissolution (Field, 2002; Halliday 2007).

2 Karst, Parakarst and Pseudokarst in Galicia Galicia is a geologically complex area, the result of the collision with subduction of Gondwana with the Laurrussian continent 370–380 million years ago. The collision of these plates produced, on the one hand, the compression, metamorphism and folding of the sediments accumulated at the bottom of the Tornquist and Rheico oceans, while subduction gave rise to the formation of three generations of magmatic bodies (Den Tex 1978). This gave rise to an uneven lithological distribution with a predominance of plutonic rocks in the western part of Galicia and metasedimentary rocks (limestone, dolomite, slate and quartzite) in its eastern part. Limestone and dolomite barely account for 4% of the surface and yet it is, unsurprisingly, the type of rock where a greater number of cavities have been located (see Table 1), and also where the resulting caves are generally larger (see Table 2). Table 1 Number of cavities inventoried in Galicia grouped by type of cave and rock

Type of caves

Rock type

Number of caves

Shore caves

Quartzite

69

Plutonic

46

Slates, schists and other types of rock

87

Karst caves

Limestone and dolomites

Parakarst caves

Quarzite and Quarzt

24

Pseudokarst caves

Plutonic

82

Quartzite

3

Slates, schists and other types of rock

290

13

In general, we only compute cavities with more than 5 m of total development. The caves located on the coast are not included within the three main groups of caves (karst, parakarst and pseudokarst caves) since many are ancient cavities that are currently being invaded and modified by the sea, but whose origin would not have to be due exclusively to sea wave erosion. Source Atlas of Caves and Canyons of the Galician Federation of Speleology (http://espeleoloxia.org/atlas), 09/2022

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Table 2 The ten largest caves in Galicia Province

Municipality

Cave

Cave Length (m)

Type of rock

Lugo

Mondoñedo

Rei Cintolo Cave

7696

Limestone

Lugo

Folgoso do Courel

Sima Teixeira

3051

Limestone

Lugo

Folgoso do Courel

Buraca das Choias—La Cripta System

1892

Limestone

Pontevedra

Tui

A Trapa System

1618

Granite

Lugo

Folgoso do Courel

A Arcoia Cave

1186

Limestone

Ourense

Rubiá

K1—Cubelas system

1184

Limestone

Ourense

Avión

Albarellos system

951

Granite

Pontevedra

Vigo

O Folón system

935

Granite

Lugo

O Incio

Bermún Cave

900

Limestone

Ourense

Rubiá

Párama P-1 Cave

810

Limestone

Source Atlas of Caves and Canyons of the Galician Federation of Speleology (http://espeleoloxia. org/atlas), 09/2022

3 Types of Caves Most of the rocks in which we can find caves are poorly permeable materials. Therefore, the formation of caves does not start arbitrarily and the development of their passages will generally be associated with areas of weakness in the substrate (fractures and bedding planes) where permeability is higher (Veni 2004; Palmer 2012). Occurs in Nature, in certain places of the Earth’s crust, that part of the water coming from rain and rivers infiltrates into the interior of the Earth through these discontinuities and holes through which water can circulate. This subterranean circulation of water is capable of dissolving in some cases, or washing and eroding in others the rock walls, which can also be made up of different lithologies, generating in turn certain “forms” excavated in the rock, which are perfectly recognizable by their geometric characteristics and that define a specific landscape both on the surface (exokarst or superficial forms) and inside the outcrops (endokarst or underground forms). In the case of karst, the prevalence of more or less sub-horizontal discontinuities will give rise to more or less horizontal passages and galleries, whose cross-sectional profile or section will again be determined by the structure (fractures and bedding planes) and by the water circulation regime (vadose, phreatic), while the prevalence of more or less subvertical discontinuities will give rise to vertical caves (simas, chasms) or vertical passages (pits or wells). See Fig. 2. In plutonic rocks, however, the circulation of water is not a determining factor for the development of the cave. We can find three fundamental types of caves (Vidal Romaní et al. 2006) (see Fig. 3):

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Fig. 2 Above, chamber defined at the intersection of a subvertical diaclase with the bedding plane of limestone, in Traslacosta Sima (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain). Below to the left, passage resulting from the coalescence of several parallel rounded (phreatic) tubes, Rei Cintolo cave (municipality of Mondoñedo, province of Lugo, Galicia, Spain). Below to the rigth, wide passage guided by a subvertical diaclase in A Tara da Triega Cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain)

1. The tafone (plural tafoni): They are very common forms in granites although not exclusive to this lithology (Vidal Romaní 1984, 1989; Vidal Romaní et al. 1998). Tafoni are microforms that vary from a few centimeters in width and height to several meters. The largest give rise to small caves, located inside a

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Fig. 3 Types of caves we can find in plutonic rocks: Above, tafone-type cave. 3D photogrammetry of the vault of Coto da Moura Cave (municipality of Gondomar, province of Pontevedra, Galicia, Spain). Below to the left, fissure cave, Manueleche Shore Cave (Ons Island, province of Pontevedra, Galicia, Spain). Below to the right, cave of blocks (roofed canyon), Albarellos cave System (municipality of Avión, province of Ourense, Galicia, Spain)

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block of rock. They are related to the phase of elastic deformation during granite intrusion (Vidal Romaní 2008). 2. Structural caves that are cavities located in fissures, joints, fractures and faults, formed in the rock from the mobilization of parts of it. It can be caused simply by the action of gravity, although it is presumed that some large caves are the result of seismic and/or tectonic events. 3. And the caves formed by accumulations of blocks, in the slopes and in the bottoms of valleys or depressions. These accumulations give rise to granite caves with larger dimensions (extension, development and volume). Their vertical development is conditioned by the thickness of the accumulation of blocks and by the orography of the relief that they fossilize. In the valley bottoms they form cave systems called block streams or river of blocks. The most spectacular configuration occurs when the river of blocks fossilizes a channeled rock course, giving rise to what we call roofed canyon. It should be noted that structural caves can occur in all types of rock. In Galicia, many fissure caves appear due to sliding parallel to the slope. It occurs in limestone (municipalities of Baralla and Mondoñedo, province of Lugo), in schist and slate (municipalities of Abadín, A Fonsagrada, and Folgoso do Courel, province of Lugo, Galicia, Spain) and in granites (all provinces). Cavities associated with shear bands appear in granites (municipalities of Moaña, Gondomar, Baiona, A Lama), in quartzite (municipalities of Riós and Castrelo do Val, province of Ourense, Galicia Region, Spain) and quartz (municipality of Boqueixón, province of A Coruña, Galicia Region, Spain). Caves formed by accumulations of blocks occur in any type of rock. For this to happen it is necessary that the spacing among the different discontinuities be large enough to allow the formation of blocks of sufficient size. Until now in Galicia this type of cave has been located in plutonic rocks and quartzites.

4 Morphogenesis: Forms and Processes All caves are the result of the interaction of various processes. Some act on the substrate, “destroying” it to generate the void or hole that defines the cave, while others intervene in a more constructive way, filling and decorating those underground voids. Obviously, the latter cannot occur if the former have not previously occurred. We have already indicated that the different processes that contribute to the formation of these underground voids generally begin at the weakest points of the substrate, acting on discontinuities and inhomogeneities such as faults, joints, bedding planes, foliations, different schistosities, mineral veins and even the changes of facie present in the rock. This gives the different types of caves, regardless of the type of rock where they are located, a marked structural character which is mainly reflected in the pattern followed by the network of passages, that is the geometry of the cavity (see Fig. 4), as well as in the geometry of the passage itself.

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Fig. 4 The caves evolve following the intersection of the different families of discontinuities, with preferential development in the most significant ones. This feature is common to any type of cave, and can be seen from the trace of the topographic axes of its passages: Above, Rei Cintolo cave (municipality of Mondoñedo, province of Lugo, Galicia, Spain). It is a multilevel maze karst cave in which the directions of the passages are generally coincident with those of the faults associated with the Alpine orogeny. Below, A Trapa granite cave system (municipality of Tui, province of Pontevedra, Galicia, Spain). It is a block stream defined by a big rock slide (more than 119,453 m3 of rock) in favor of the sheet structure, and induced by the movement of a reverse fault. In the figures, the color of the segments depends on their elevation (red highest elevation, violet lowest elevation)

Processes can be of physical nature, such as mechanical breakage (see Fig. 5) or erosion that remove particles from substrate fragments; or of chemical nature, such as dissolution and corrosion (see Fig. 6); and others, much less visible, of biological (biochemical) nature, where the action of certain microorganisms (see Fig. 7) contribute to dissolving “insoluble” minerals such as quartz and certain silicates present in many non-karst cavities (Vidal Romaní et al. 2014). The action of these different processes involves the removal of parts of the rock at different scales, while producing certain visible forms that are integrated into the underground landscape (see Figs. 6 and 8): Examples of this are potholes and resulting from evorsion in bedrock when high-energy turbulent flows are present. There are also many natural processes that fill in and decorate the empty spaces that encloses a cave. They are called depositional processes: Some are physical in nature and give rise to clastic (gravitational), fluvial and lacustrine deposits; others

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Fig. 5 The partial collapse of a vault is nothing more than the breakage with mobilization of part of the rock that forms the cavity. For this mobilization to take place, there must be a previous void towards which the material can move: To the left, sliding in favor of the sheet structure, in Albarellos granite Cave System (municipality of Avión, province of Ourense, Galicia, Spain). To the right, large collapse produced in Pena Paleira Cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain), where the filling of blocks and fragments has a thickness of 14 m and extends over more than 100 m of gallery

are chemical in nature and give rise to many speleothems (neominerals); and others are biochemical in nature, and give rise to the appearance of biospeleothems (biominerals). Note that a speleothem is nothing more than the deposit of a secondary mineral (or substance) (Moore 1952). The term refers to the mode of occurrence of that mineral (or substance) deposit, that is, to the visible form in which the mineral (or substance) is presented (Hill and Forti 1997). Again, the definition does not establish restrictions on the composition, environment or process that gives rise to these microforms. The different processes can affect the entire cave or only a part of the underground volume. They can concur in the same space, or act in completely different zones and environments within the same cavity. They can also act simultaneously (although not at the same points) or follow one another over time, acting in the same areas and on previously built morphologies. Also there are processes that are incompatible with each other: They do not occur simultaneously, or if they occur, the most energetic predominates, which is generally also the most destructive (see Fig. 9). Thus, the underground landscape that we can contemplate at a given moment is the result of the combined action of all these processes, in such way that the visual ensemble integrates the morphologies derived from the predominant processes at present, together with the remains of the previous ones, built by those processes that prevailed at a given moment in the history of the cave.

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Fig. 6 Field of scallops, erosional-corrosional form related with turbulent flows in karst systems. Above, Cova Grande de Santalla Cave (municipality of Samos, province of Lugo, Galicia, Spain). Below, 3D photogrammetry of a passage in the cave of Praducelos (municipality of Pol, province of Lugo, Galicia, Spain) in which we can see scallops of metric size (low-speed flow) on which scallops of centimeter size (high-speed flow) have been sculpted

5 Depositional Forms Many of the shapes that make up the underground landscape are related to how water has moved in the past or how is moving today. High-energy flows give rise to sculpted forms in the rock (see Fig. 8). The appearance of terraces, or sand and clay banks, represent sedimentation processes, graded as the water currents lose speed and energy. In relatively static waters, with few disturbances, as occurs in lakes, rhythmites deposits are produced (see Fig. 10).

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Fig. 7 Quartz crystal partially transformed into an opal-A (or biogenic opal) speleothem. The process is due to the action of certain microorganisms that attack the quartz causing its transformation into a silica gel (Vidal-Romaní et al. 2014). A Cunchosa granite Cave System (municipality of Cangas do Morrazo, province of Pontevedra, Galicia, Spain)

And when the velocities are much slower, accretion phenomena (chemical or biochemical) can occur, giving rise to speleothems: Some caused by dripping (called dripstone speleothems) (see Fig. 11), others by flows or slow runoff (called flowstone speleothems) (see Fig. 12), others by a combination of dripping-runoff (called composite dripstone-flowstone speleothems) (see Fig. 13), others by pressure circulation in fissures (seeping water speleothems) (see Fig. 14). But they also occur in quasi-static waters inside small reservoirs (called pool speleothems) (see Fig. 15). There are also biospeleothems associated with the points where the substrate is moistened by capillarity or where the condensation of the water vapor present in the air of the caves occurs (see Fig. 16) (Vaqueiro-Rodríguez 2017). And the last scenario, possibly the one that involves almost zero movement of water, is the grow of pool spars in aqueous undisturbed environment (see Fig. 17).

6 Final Remarks It is a fact that caves exist in all types of rock. And also that underground landscapes are the reflection of a wide variety of processes that have taken place over time, leaving their traces in the cavity. And this is one of the great values that caves treasure: They are windows to the past, a reflection of the evolution of the climate and the territory where they are located. Understanding which processes prevailed and when they occurred allows us to reconstruct part of the history of the Earth.

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◄Fig. 8 Sculpted forms: Above to the left, potholes 11.5 m tall in Albarellos granite Cave System (municipality of Avión, province of Ourense, Galicia, Spain). Above to the right, pseudo-scallops in A Trapa granite Cave System (municipality of Tui, province of Pontevedra, Galicia, Spain). You can compare this shape with its convergent in the karst (Fig. 6). Below to the left, furrows in shist-limestone, in A Ceza cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain). Below to the right, photogrammetry of several hierarchical compound potholes sculpted on fossiliferous dolomite in A Forcadiña Cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain)

Fig. 9 Mechanical evorsion that gives rise to a pothole requires turbulent and supercritical flows, while the formation of a speleothem on the same rock surface requires very slow water flows. If both forms appear on the same surface, they could not have been produced at the same instant of time: To the left, potholes fossilized about 4000 years ago by a pigotite flowstone. This speleothem is related to microflows. Potholes are currently being exhumed due to the reactivation of the underground course (again turbulent flow). To the right, groove produced by erosion (rapid flows) on a flowstone of pigotitta (related to microflows). Its erosion allows us to observe the accretion structure of the deposit. Both images are from A Trapa granite Cave System (municipality of Tui, province of Pontevedra, Galicia, Spain)

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Fig. 10 Marine fossil deposit located in granite Shore Cave of Manueleche (Ons Island, province of Pontevedra, Galicia, Spain). The roof level of this deposits is located approximately + 15 m above sea level

Of all the types of caves that exist in Galicia, those formed in plutonic rocks were until a few years ago practically unknown and little valued. And yet, as we have seen throughout this scientific history, they constitute complex environments of high scenic and scientific value, the result of the concurrence and succession of physical, chemical and biochemical processes inside these spaces. See Fig. 18. Finally, it should be noted that most of the forms that decorate the caves, regardless of lithology, are related to how the water has moved or moves underground. Turbulent flows produce sculpted shapes and medium and slow flows produce different types of detrital (physical deposition), chemical (speleothems) and biochemical (biospeleothem) deposits. The latter two give rise to scenic spaces of great beauty. But true beauty and real value are inside: • Many speleothems, mainly carbonates, allow us through isotopes of oxygen and uranium/thorium to reconstruct the evolution of the past climate. They are therefore a source of paleoclimatic data. As an example, from several stalagmites of Galician caves Railsback et al. (2011, 2016) have reconstructed the sequence of glacial and interglacial episodes that occurred in Galicia in the last 550,000 years. • Biospeleothems preserve fossilized in each of the layers formed by accretion, a part of the trophic chain that gave rise to the deposit. The fossil DNA of bacteria, algae, fungi, amoebas and arthropods (springtails, mites, isopods, tisanuros and arachnids) is thus preserved (Vidal-Romaní et al. 2010a, 2010b, 2013). All this ancient life gives us a reflection of the environment in each of the growth phases of the biodeposit. They are therefore a source of paleoenvironmental data. As an example, Vidal Romaní et al. (2014) carry out the genetic study on these types

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Fig. 11 Dripstone speleothems: Above, calcite stalactites (roof) and stalagmites (floor) in A Forcadiña cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain). Below to the left, like-soda straw of pigotite in A Trapa granite Cave system (municipality of Tui, province of Pontevedra, Galicia, Spain). Below to the right, soda straws and draperies composed possibly of goethite in Coliño Shore Cave (Illa Ons Island, province of Pontevedra, Galicia, Spain)

of sediments which have allowed identifying the presence of a great variety of specific bacteria and comparing it with the usual one in genetic studies carried out on karstic or lava tube caves. Also Sanjurjo-Sánchez et al. (2011) carry out dating of siliceous speleothems containing fossilized ancient pollens in their different accretion layers.

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Fig. 12 Microgours are a subtype of flowstone speleothems: Above to the left, furled pigotite rimstone dams and microgours in the granite cave system of O Folón (municipality of Vigo, province of Pontevedra, Galicia, Spain). Above to the right, furled and stepped calcite microgours in the karstic cave of Castro de Parada (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain). Above to the left, biogenical opal flowstone in the parakarst area of Portozón (municipality of Castrelo do Val, province of Ourense, Galicia, Spain). And above to the right, goethite-limonite microgours in Mina Consuelo (municipality of A Pontenova, province of Lugo, Galicia, Spain)

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Fig. 13 Composite flowstone-dripstone speleothems: Above to the left, pigotite column and draperies, in A Trapa granite cave system (municipality of Tui, province of Pontevedra, Galicia, Spain). Above to the right, pigotite furled draperies, in O Tronceda cave system (municipality of Mondoñedo, province of Lugo, Galicia, Spain). Below, calcite composite dripstone-flowstone speleothems, in A Arcoia cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain)

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Fig. 14 Seeping water speleothems: Above to the left, calcite anthodites, in Cova do Rei Cintolo cave (municipality of Mondoñedo, province of Lugo, Galicia, Spain). Above to the rigth, calcite cave flower, in A Ceza Cave (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain). Below, grass-shaped opal-A biospeleothem, O Forno cave (municipality of Valença do Minho, North Region, Portugal)

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Fig. 15 Selfstone speleothems are a type of pool speleothem. It is an indicator of a present or past cave pool level because always grows at the air–water interface: Above to the left, calcite forming ledges around a submerged element. In the center a detail of the rimstone dam crystallization. Buraca das Choias—La Cripta cave system (municipality of Folgoso do Courel, province of Lugo, Galicia, Spain). Above to the right and below, pigotite selfstones in Manueleche Shore Cave (Ons Island, province of Pontevedra, Spain). Pigotite is not a mineral and does not form crystals. Its growth is also radial but showing dendrites throughout its perimeter. It is believed to be induced by the filamentous microorganisms associated with the biodeposit

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Fig. 16 Opal-A deposits can grow where the substrate is moistened by capillarity or by condensation: Above, opal-A microstromatolites in the quartzite cave Val de Cubelas I (municipality of Paradela, province of Lugo, Galicia, Spain). Below to the left, opal-A microstromatolites in A Trapa granite cave system (municipality of Tui, Pontevedra province, Galicia, Spain). Below to the right, detail (a few millimeters wide) of a similar biomineral under study, in paleo-shore cave of Furna da Laghoa (municipality of Baiona, Pontevedra province, Galicia, Spain)

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Fig. 17 Pool spars grow in undisturbed aqueous barely saturated environment. This occurs only in soluble rocks. Pool spars can cover all the surfaces of the pool including those of other pre-existing forms. Above and in the center, A Buraca das Choias—La Cripta cave system (municipality of Folgoso do Courel, Lugo province, Galicia, Spain). Below, two different deposits in Cova do Rei Cintolo cave (municipality of Mondoñedo, Lugo province, Galicia, Spain)

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Fig. 18 Caves in plutonic rocks are complex systems whose underground landscape is related to various environments and processes. Thus, on a section of one of these caves, we synthesize the different environments (violet labels), processes/agents (yellow labels), forms (green labels) and minerals/substances (blue labels) that we can find inside (Vaqueiro-Rodríguez 2017)

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Acknowledgements To my wife Begoña and children Marcos and Esteban who liveily participate in the many explorations and expeditions that have allowed me to study the Galician caves. Also to my master and friend, the emeritus Ph.D. Juan Ramón Vidal-Romaní. And finally to my friends and cavers Rei and Rosa, who have generously dedicated their time to exploring and topography caves with me for over 20 years.

References Boston PJ (2004) Extraterrestrial caves. In: Gunn J (ed) Encyclopedia of Cave and Karst science. Fitzroy-Dearborn Publishers Ltd, London, pp 355–358 Chavert C, Courbon P (1997) Atlas des Cavités Non Calcaires du Monde. Union Internationale de Spéléologie au pré de Madame Carle, p 110. ISBN: 2–912402–02–06. Den-Tex, E. 1978. El Zócalo policíclico y su importancia en la evolución de la Cadena Varisca en Galicia Occidental. En Geologia de la parte Norte del Macizo Ibérico Edición Homenaje a Isidro Parga Pondal. Cuadernos de Estudios Cerámicos de Sargadelos 27, pags.141–157. Ediciones l Castro, Sada Coruña ISBN 84–85134–89–3. Field MS (2002) A Lexicon of Cave and Karst terminology with special to environmental Karst hydrology. EPA/600/R-02/003, EPA, Washington, DC Gilli E (2015) Kartology. Karst, caves and springs. Elements of fundamental and applied karstology. CRC Press, p 244 Halliday WR (2007) Pseudokarst in the 21st century. J Cave Karst Stud 69(1):103–113 Hill C, Forti P (1997) Cave minerals of the World. Second edn. National Speleological Society, p 463 Moore GW (1952) Speleothems—a new cave term. Natl Speleol Soc News 10(6):2 Palmer AN (2012) Geología de cuevas. Published by Cave Books. International Union of Speleology, p 502. ISBN-13:978-0-939748-66-2 Railsback LB, Liang F, Vidal-Romaní JR, Grandal-D’Anglade A, Vaqueiro-Rodríguez M, SantosFidalgo L, Fernández-Mosquera D, Cheng H, Edward L (2011) Petrographic and isotopic evidence for holocene long-term climate change and shorter-term environmental shifts from a stalagmite from the serra do courel of northwestern spain, and implications for climatic history across europe and the mediterranean. Palaeogeogr Palaeoclimatol Palaeoecol 305(2011):172– 184. https://doi.org/10.1016/j.palaeo.2011.02.030 Railsback LB, Liang F, Vidal-Romaní JR, Garrett KB, Sellers RC, Vaqueiro-Rodríguez M, Grandald’Anglade A, Cheng H, Edwards RL (2016) Radiometric, isotopic, and petrographic evidence of changing interglacials over the past 550,000 years from six stalagmites from the Serra do Courel in the Cordillera Cantábrica of northwestern Spain. Palaeogeogr Palaeoclimatol Palaeoecol 466(2017):137–152. https://doi.org/10.1016/j.palaeo.2016.11.020 Sanjurjo-Sánchez J, Arce-Chamorro C, Vidal-Romaní JR, Vaqueiro-Rodríguez M, Barrientos V, Kaal J (2021) On the genesis of aluminum-rich speleothems in a granite cave of NW Spain. Int J Speleol 50(1):25–40. Tampa, FL (USA) ISSN 0392–6672. https://doi.org/10.5038/182780650.1.2358 Sanjurjo-Sánchez J, Vidal-Romaní JR (2011) Luminescence dating of pseudokarst speleothems: a first approach. Spectrosc Lett 44(7–8):543–548. https://doi.org/10.1080/00387010.2011. 610422 Urban J, Oteska-Budzyn J (1998) Geodiversity of pseudokasrt caves as the reason for their scientific importance and motive of protection. Geologica Balcanica 28:3-4, Soifa, Decem, 163–166 Vaqueiro Rodríguez M (2017) Cavidades Naturales En Rocas Magmáticas—Las Cuevas En Rocas Plutónicas. Tesis Doctoral, programa de Ciencia y Tecnología Ambiental da Universidade de A Coruña. https://doi.org/10.13140/RG.2.2.30080.33289 (http://hdl.handle.net/2183/19154)

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Veni G (2004) Passages, in Encyclopedia of Caves by Culver DC, White WE, Academic Press, p 680 Vidal Romaní JR, Sanjurjo Sánchez J, Vaqueiro Rodríguez M, Fernández Mosquera D (2010a) Speleothem development and biological activity in granite caves. Géomorphologie: Relief Processus, Environnement 4:337–346 Vidal Romaní JR, Sanjurjo Sánchez J, Vaqueiro Rodríguez M, Fernández Mosquera D (2010b) Speleothems of granite caves. Comunicações Geológicas, INETI, t.97:71–80 Vidal Romaní JR, Sanjurjo Sánchez J, Vaqueiro Rodríguez M, González López L, López Galindo MJ (2013) Speleothems in cavities developed in magamtic rocks. In: Proceedings of international speleological congress, Brno Vidal Romaní JR, González López L, Vaqueiro Rodríguez M, Sanjurjo Sánchez J (2014) Bioweathering related to underground water circulation in cavities of magmatic rock massifs. Environ Earth Sci 73(6)

The Courel Mountains UNESCO Global Geopark: An Amazing Geological History Extended Along 600 Million Years Irene Pérez-Cáceres, Daniel Ballesteros, Pablo Caldevilla, Jose Bienvenido Diez, Xose Carlos Barros, Ramón Vila, José Ramón Martínez Catalán, Fidel Martín-González, Juan Carlos Gutiérrez-Marco, Manuel García-Ávila, Mercedes Fuertes-Fuente, Susana Timón Sánchez, Miguel Llorente, and Martín Alemparte

Abstract The Courel Mountains UNESCO Global Geopark (2019) stands out in SW of Europe because of its geoheritage, its biodiversity and its cultural heritage, all of it considered of international interest. These aspects shape the local development economic and cultural improvement and development. The geoheritage is the result of three geological cycles since the Proterozoic, involving the Cadomian-AvalonianPan-African orogeny, the opening of the Rheic Ocean and the Variscan orogeny, and I. Pérez-Cáceres (B) · D. Ballesteros · P. Caldevilla · J. B. Diez · X. C. Barros · R. Vila · J. R. Martínez Catalán · J. C. Gutiérrez-Marco · M. García-Ávila · M. Fuertes-Fuente · S. T. Sánchez · M. Llorente · M. Alemparte Courel Mountains UGGp, Rúa do Courel 21, 27320 Quiroga, Spain e-mail: [email protected] D. Ballesteros e-mail: [email protected] P. Caldevilla e-mail: [email protected] J. B. Diez e-mail: [email protected] X. C. Barros e-mail: [email protected] R. Vila e-mail: [email protected] J. R. Martínez Catalán e-mail: [email protected] J. C. Gutiérrez-Marco e-mail: [email protected] M. García-Ávila e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_6

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finally the Permian-Mesozoic continental expansion and the Alpine orogeny. The geological history of Courel Mountains is one of singular rocks, huge recumbent folds, valuable metallic mineralization, and invertebrate fossils preserved within metamorphic rocks. This long history is recorded in an exceptional Variscan basement that we can ravel thanks to the exhumation during the Alpine uplifting, when the present-day Courel Mountains were built. M. Fuertes-Fuente e-mail: [email protected] S. T. Sánchez e-mail: [email protected] M. Llorente e-mail: [email protected] M. Alemparte e-mail: [email protected] I. Pérez-Cáceres · J. R. Martínez Catalán Departamento de Geología, Universidad de Salamanca, Facultad de Ciencias, Plaza de la Merced s/n, 37008 Salamanca, Spain D. Ballesteros Departamento de Geodinámica, Universidad de Granada, Facultad de Ciencias, Campus Fuentenueva s/n, 18071 Granada, Spain P. Caldevilla · M. García-Ávila Escuela Superior y Técnica de Ingenieros de Minas, Universidad de León, Campus de Vegazana s/ n, 24071 León, Spain J. B. Diez Departamento de Geociencias Marinas y Ordenación del Territorio, and Asociación Paleontolóxica Galega, Universidade de Vigo, Campus Universitario Lagoas Marcosende, 36310 Vigo, Spain R. Vila Museo Xeolóxico de Quiroga, Rúa do Courel 21, 27320 Quiroga, Spain F. Martín-González Área de Geología-ESCET, Universidad Rey Juan Carlos, c/Tulipán s/n, 28933 Móstoles, Spain e-mail: [email protected] J. C. Gutiérrez-Marco Facultad de Ciencias Geológicas, Instituto de Geociencias (CSIC-UCM) and Área de Paleontología GEODESPAL, c/José Antonio Nováis 12, 2ª, 28040 Madrid, Spain M. Fuertes-Fuente Departamento de Geología, Universidad de Oviedo, c/ Jesús Arias de Velasco s/n, 33003 Oviedo, Spain S. T. Sánchez Unidad de Salamanca, Instituto Geológico y Minero de España (CSIC), Plaza de La Constitución 1, 3°, 37001 Salamanca, Spain M. Llorente Instituto Geológico y Minero de España (CSIC), c/Ríos Rosas 23, 28003 Madrid, Spain

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Keywords Alpine exhumation · Geoheritage · Stratigraphic succession · Palaeozoic fossils · Recumbent folding · UNESCO Global Geopark

1 Introduction Five thousand inhabitants and thousands of visitors enjoy the Courel Mountains UNESCO Global Geopark (UGGp) since 2019, admiring its geological history hidden after 600 million years of evolution in the present SW of Europe (Fig. 1). The tale started somewhere around the South Pole and continues today with the uplift of the present-day mountains at their current position in the Northern Hemisphere. During this time, the basement gradually acquired its outstanding features associated with three geological cycles (Cadomian-Avalonian-Pan-African, Variscan and Alpine) from the late Neoproterozoic to the Present (Fig. 2); although the geological record is scarce between the Permian and the Paleogene. This geological history resulted in a current geoheritage of international relevance. A Global Geosite (comprising five places) and other 66 geosites (Fig. 1c) form the basis of the local development of Courel Mountains since its declaration as UGGp in the region of Galicia (NW Spain) in 2019 (Ballesteros et al. 2022). The story described here can be visited by touring Courel Mountains (578 km2 in extension) through the network of 22 geological viewpoints, the Geological Museum of Quiroga and other visitor centres. The Cadomian-Avalonian-Pan-African and Variscan cycles (Fig. 2) formed the geological bedrock, mainly of Palaeozoic age (Sect. 2 of this work). The outcrops yielded invertebrate fossils unique for the region of Galicia (Sect. 3), shows impressive and huge recumbent folds forming during the Variscan orogeny (Sect. 4) and remarkable metallic ore deposits exploited since the Iron Age (Sect. 5). The geological story of Courel Mountains ends with the uplifting of the current mountains during the Cenozoic (Sect. 6) as a result of the Alpine orogeny (Fig. 2). Afterwards, a new fluvial network was organized as its present form, with water flow the S, where the Sil river runs, while other geomorphological processes and soil development finished shaping the relief (see Pérez Alberti 2018) but that is another story. A rain shadow constrained by the Alpine relief caused the convergence of the Atlantic and Mediterranean bioregions in the UGGp, creating an enormous variety of habitats, many of them influenced by the altitude, between 230 and 1641 m, and the presence of basic or acidic bedrocks (see Ballesteros et al. 2022). The humid north part of the UGGp features native deciduous forests (Fig. 3); handed chestnut woodlots (Guitián et al. 2012) and other habitats for relevant species, such as orchids (Manzaneda et al. 2005) brown bears and syrphids (Ricarte et al. 2014), amongst many others. For all these reasons, northern Courel Mountains have been included M. Alemparte Grupo de Desarrollo Rural Ribeira Sacra-Courel, Rúa Doctor López Lallana 6, 1°D, 27340 Bóveda, Spain

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Fig. 1 a Location of the Courel Mountains UNESCO Global Geopark (UGGp) in the SW of Europe and within the Iberian Massif (the largest outcrop of the Variscan bedrock of the Iberian Peninsula). Variscan area according to Martínez Catalán et al. (2021) and references therein. b The UGGp overlaps the Ribeira Sacra e Serras do Oribio e Courel Biosphere Reserve (2021) and the Ancares-Courel Site of Community Importance—Natura 2000 Network (2004). C Map of the UGGp showing Global Geosites and other geosites, as well as visitor centres. The digital elevation model is from Instituto Geográfico Nacional

Fig. 2 Geological history of Courel Mountains UGGp involving Cadomian-Avalonian-PanAfrican, Variscan and Alpine geological cycles. The main tectonic and magmatic events and fossil record are depicted

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Fig. 3 Deciduous native forest of A Rogueira comprises 40% of the terrestrial vascular plants of Galicia region due to, among others, a high vertical range of ca. 900 m and the development of acidic and basic soils on Palaeozoic detrital and carbonate bedrock. A nature interpretation centre is located at the entrance of this woodland that received the Forest Stewardship Council’s verification for ecosystem services in 2022

into the Ancares-Courel Site of Community Importance (European Nature 2000 Network) in 2004, and the entire UGGp is part of the Ribeira Sacra e Serras do Oribio e Courel Biosphere Reserve since 2021 (Fig. 1b). The southern part allows the cultivation of olive three and vineyards for a consolidated and suitable wine and olive oil industry.

2 Rock Milestone The Courel Mountains UGGp belongs to the Iberian Massif, the large Neoproterozoic to Palaeozoic outcrop of the Variscan basement occupying the west half of the Iberian Península (Fig. 1a). The Variscan and roughly coeval orogenic events caused the accretion of continental masses creating Pangea supercontinent and the Variscides (Variscan mountain range of central and western Europe) between 400 and 300 million years ago (Matte 1991). In addition, the oldest rocks of the Iberian Massif also recorded an older orogeny named either Cadomian, Avalonian or Pan-African Orogeny (Murphy and Nance 1989). All these tectonic processes gave rise to the exposed bedrock of Courel Mountains, whose understanding was made possible

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thank to pioneer geologists in the mid-twentieth century (Hernández Sampelayo 1915, 1935; Carlé 1945; Drot and Matte 1967; Matte 1963, 1968; Riemer 1963, 1966; Teixeira 1969). The geological map exhibits 14 geological units categorised as formations (Fm.) ranging from the Neoproterozoic to lower Carboniferous (Fig. 4). Dark-grey slate and light quartzite dominate the basement together with grey metalimestone in the N and brownish gneiss in the SW of the UGGp. The geological story of our UGGp started with the Neoproterozoic slate and schist (Vilalba Fm.; Fig. 4a) formed after detrital sediments on the margin of northern Gondwana, then in the Southern Hemisphere (Fig. 5), and that was involved in the Cadomian-Avalonian-Pan-African orogeny (Fernández-Suárez et al. 2014; RubioOrdóñez et al. 2015). Afterwards, the Gondwana margin experienced rifting with the

Fig. 4 a Simplified geological map of the Courel Mountains UGGp after Villar Alonso et al. (2018) and references therein. The stratigraphic section is mainly based on Matte (1963, 1968), Riemer (1963, 1966), Dozy (1983) and Pérez-Estaún et al. (1990). b Geological cross-section along Courel Mountains after Martínez-Catalán et al. (1992, 2004) showing the three huge recumbent folds. The position of the cross-section is depicted in A

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opening of the Rheic Ocean during the Cambrian and Ordovician (Fernández-Suárez et al. 1999, 2000a). The Variscan cycle began at this moment, when Neoproterozoic sediments were overlain by a Cambrian and Lower Ordovician variety of detrital, carbonate and volcanic sediments. The rifting caused also a voluminous and scattered magmatism along the Iberian Massif (e.g., Rubio-Ordóñez et al. 2015) represented by the Ollo de Sapo Fm. in SW of Courel Mountains (Fig. 4). This geological unit corresponds mainly to a porphyroid gneiss according to its petrography and mineralogy (Fig. 6). In Courel Mountains, it resulted from low-grade metamorphism of volcanic, subvolcanic and other rocks deposited during the late Cambrian and Lower Ordovician (Fernández-Suárez et al. 1999, 2000b). The Cambrian rifting evolved to a stable passive margin until the early Devonian (Fig. 5a–c) and an Ordovician to Devonian sequence deposited. A major unconformity is found at the Ordovician–Silurian boundary (Fig. 4a) (Dozy 1983). Ordovician Armorican Quartzite (Fig. 7), slaty Luarca Fm. (Fig. 8) and a bed of slaty pebbly mudstones of glaciomarine origin (Fig. 9) stand out in the stratigraphic sequence of the UGGp. The Middle and Upper Ordovician is partially eroded beneath the Ordovician–Silurian regional unconformity in the UGGp (Figs. 2 and 4a), which underlies ampelitic black slates with singular minerals such as pre-tectonic graphite and pyrite and metamorphic chloritoid (Dozy 1983). The black colour of this slate contrasts with the yellow stains associated with the leachate and oxidation of sulphates.

Fig. 5 Palaeogeographic reconstruction depicting the position of continents and the evolution of the Rheic Ocean during the Variscan cycle (after Gómez Barreiro et al. 2007; Weil et al. 2013)

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Fig. 6 The singular porphyric gneiss of Ollo de Sapo Fm. that crops out at Cubela hiking route geosite (SW of Courel Mountains). Major crystals correspond to K-feldspars while grey-bluish minerals are Ti-enriched quartz. This colour and shape relate to the name of the rock, Ollo de Sapo, meaning “toad’s eye” in Galician regional language

In Devonian times, while continents were approaching each other to form the Pangea (Fig. 5), carbonate deposition took place in the wide continental shelf of northern Gondwana, forming the Seceda Fm. cropping out in the NW of the UGGp. Shortly after in geological terms, the Variscan orogeny started due to continental collision, producing folding and faulting or the stratigraphic sequence during the Carboniferous. Simultaneously, a mountain range was uplifted and began to be eroded, producing the synorogenic turbidites of San Clodio Fm. cropping out in the southern UGGp. They consist of conglomerate (Fig. 10), greywacke, shale, and lydite that were weakly metamorphized shortly after (Martínez Catalán et al. 2004). The Variscan orogeny generated also a voluminous magmatism producing different kinds of granitoids during the late Carboniferous and early Permian (Fernández-Suárez et al. 2000a), as the two-mica granite cropping out at the SE of the UGGp.

3 The Palaeozoic Fossils, Witnesses of the Geological History The record of Palaeozoic invertebrates evidences the amazing geological story of Courel Mountains, since they habited the Gondwanan continental shelf facing the Rheic Ocean (Gutiérrez-Marco et al. 2009). However, the Variscan deformation

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Fig. 7 Armorican Quartzite is of international relevance as it is recognized in the NW and central parts of Iberian Peninsula and in Britany (NW of France; Fig. 1a). Locally, Armorican Quartzite constitutes the main rocky areas and natural scarps of the landscape (see Pérez Alberti 2018), showing the folded beds that reveal the major geological structure of the central and southern parts of Courel Mountains (Fig. 4)

and metamorphism destroyed most fossil remains, so that its occurrence within metamorphic rocks is another singularity of the UGGp (Ballesteros et al. 2021). Sixteen Palaeozoic fossil sites of regional relevance were inventoried by GarcíaÁvila et al. (2022) including crinoids, trilobites, gastropods (Fig. 11), graptolites, archaeocyathids, tentaculites and others. The Cambrian explosion was recorded in Courel Mountains by the preservation of archaeocyathids and encrusting microbial communities structures (Russo and Bechstädt 1994), and trilobites within Cambrian meta-limestone and slate. In addition, characteristic trilobites of Iberian Massif inhabited the muddy shelf environments related to the well-known Ordovician slate used for roofing (Hammann 1983). The first fossils derived from vertebrates in the UGGp are conodonts, the teeth of chordates living in the Rheic Ocean, and found in Ordovician and Silurian meta-limestone interbedded with slate sequences. The deep seas associated with Silurian black shale (later transformed into slate in the UGGp) influenced the occurrence of swimming and free-floating organisms in the palaeontological record of Courel Mountains, hosting an association between monograptids (Gutiérrez-Marco et al. 2001) and orthoceratids (Rábano et al. 1993), including also the presence of uncommon record of Spanish Pridoli (uppermost Silurian) graptolites (Piçarra et al. 1998). Other fossil groups like the crinoids, brachiopods and other fossils saw the closure of the Rheic

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Fig. 8 Slate of Luarca Fm., widely quarried for house roofing in many European countries. This geological unit is related to the Iberian Roofing Slate, nominated to Global Stone Province Resource by the Heritage Stones Subcommission of International Union of Geological Sciences (Cardenes et al. 2015)

Fig. 9 Slaty pebbly mudstone of Bendollo quarry geosite. The slate represents a glacio-marine muddy diamictite with dispersed dropstones related with the end-Ordovician glaciation (GutiérrezMarco et al. 2001). Calcareous clasts were carried by icebergs and then deposited on the sea floor after ice melting

Ocean during the Devonian, including also tentaculites (Fig. 12) discovered in the UGGp for the first time in the Galicia region (Barros Lorenzo et al. 2022).

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Fig. 10 Meta-conglomerate of San Clodio Fm. (early Carboniferous) at the San Clodio’s Iron Bridge geosite showing rounded clasts of quartz, quartzite, slate and meta-lydite resulted from the erosion of the Variscan mountain range

Fig. 11 Silurian cephalopod belonging to the subclass Nautiloidea discovered in the N of the Courel Mountains UGGp Fig. 12 The discovery of these Devonian tentaculitids by Barros Lorenzo et al. (2022) allowed definition of a new geosite in southern Courel Mountains UGGp. Rounded features correspond to transversal section of calcitic, ribbed and cone-shaped shells

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4 The Variscan Orogeny Exhibition Variscan orogeny gave rise to characteristic folds and associated cleavages, as well as thrust faults that are ascribed to three successive compressional deformational phases (named D1, D2 and D3) and a late-Variscan faulting event (Martínez Catalán et al. 1992, 2004). The main structures are seen as lineaments visible from the space and recorded in satellite images (Martín-González et al. 2007). Only D1 and D3 phases are identified in the Courel Mountains UGGp. Firstly, compressional stresses related to plate convergence produced D1 recumbent folds with a W-E attitude and northern vergence (Martínez Catalán et al. 1992). The largest of these folds are the Courel syncline and the Piornal anticline (Fig. 4), yet recognized by Riemer (1963) and Matte (1963, 1968). Both structures span most of Courel Mountains and are clearly visible in five sections in the central part of the UGGp (stars in Fig. 4a), notable for their singularity and scientific interest. Among them, the section of Campodola-Leixazós (Fig. 13) is a unique exhibition of a huge recumbent fold that was mathematically modelled to detail the folding mechanism (Fernández et al. 2007; Bastida et al. 2010, 2014). For these reasons, the first geological viewpoint of Galicia region was built here in 2004 and the section was declared Natural Monument by the Regional Government of Galicia in 2012. Phase D2 produced thrust sheets in the Galicia region, one of the largest being the Mondoñedo thrust sheet (Bastida et al. 1986), of which Courel Mountains form part. However, the sole thrust fault of this allochthonous unit does not crop out in the UGGp, but occurs several kilometres depth. Finally, phase D3 is evidenced by vertical folds, which are smaller than the recumbent folds, causing a distinctive superposed folding in the southern part of the UGGp, such as the Castro Dares anticline geosite. Other noteworthy structures are NNESSW high-angle faults created during the late Variscan orogeny and cutting across the previous Variscan structures. These structures were reactivated during the Alpine orogeny (Sect. 6). An extraordinary example of these faults is Santa Eufemia fault geosite located in the centre of Courel Mountains (Fig. 4a).

Fig. 13 Courel recumbent fold at the Campodola-Leixazós section, declared Global Geosite (2011) and Natural Monument (2012). This syncline is characterised by the folded layers of Armorican Quartzite (Sect. 2)

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5 Metallic Mineralization, Valuable Minerals The Variscan orogeny favoured magmatic-hydrothermal processes forming metallic mineralizations; nevertheless, former concentrations also occurred from Cambrian to Silurian (Fig. 2). Besides, some mineral deposits can be related with or affected by magmatic-hydrothermal processes associated with the intrusion of diabase-gabbro dykes during the Jurassic or Cretaceous (Fig. 4a), probably associated to the rifting that ended with the opening of North Atlantic Ocean and break up of Pangea supercontinent (Vergés et al. 2019). Human development of Courel Mountains cannot be explained without the gold, lead, antimony and iron mining. Native gold precipitated in quartz veins within minor Variscan folds (Cepedal et al. 2018; González-Menéndez et al. 2021) and was also accumulated in alluvial deposits due to the weathering of the bedrock during the Cenozoic (see Sect. 6). Both types of gold deposits were widely exploited by the Roman Empire during the first and second centuries CE (Fig. 14) (e.g., FernándezLozano et al. 2019). Pb–Zn minerals as galena and sphalerite formed stratabound deposits or are disseminated within Cambrian meta-limestone (Tornos et al. 1995) while antimony (Fig. 15) was deposited within the Upper Ordovician meta-limestone interbedded into slate of low permeability in the Courel recumbent fold (Gumiel and Arribas 1987). The Variscan mountain range was eroded during the Permian and probably later periods, and therefore no Mesozoic rocks were preserved in Courel Mountains. At a certain time, iron deposition took place in Upper Ordovician metalimestone, leading to relevant Fe mineralization. These deposits allowed a lucrative iron industry to operate in Courel Mountains during sixteenth–nineteenth centuries.

6 Relief Building, Mountain Growing The Alpine orogeny uplifted mountain ranges the Iberian Peninsula and northern Africa to the Himalayas in Asia. In northern Spain, Courel Mountains were built at the western end of Cantabrian Mountains-Pyrenees during the Oligocene and Miocene (Grobe et al., 2010; De Vicente et al., 2011; Martín-González et al., 2012). Alpine NE–SW thrusts with NNW vergence are the main responsible for the Courel Mountains uplift (Fig. 16; Martín-González 2009; Martín-González and Heredia 2011a). The thrusts exhibit an arcuate geometry, and dip 22–70° to the SE (Martín-González and Heredia 2011b). As a consequence, a new fluvial network was developed trending south, to the Sil river, whose watershed covers 798 km2 in extent. The upper watercourses are highlighted by the occurrence of over 20 noticeable waterfalls more than 20 m high. The Alpine orogeny exhumed the Palaeozoic basement and the Variscan structures formed at 10–15 km depth (Sect. 4) were exposed at the surface (Fig. 17). This process, along with the development of N-S fluvial valleys made it possible to investigate on sedimentation, life and evolution of the past Rheic Ocean, the course

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Fig. 14 A Toca roman gold mine (first–second centuries CE) in northern Courel Mountains UGGp. The Roman Empire re-structured the territory for exploiting gold (Alonso et al. 2010) as can be seen in the Roman gold mining visitor centre located in San Clodio (Fig. 1b) Fig. 15 Antimony sample from Villarbacú mines exploited at the core of the Courel recumbent fold (centre of Courel Mountains UGGp) during the twentieth century (Museo Geominero collection; ref. 2788)

of the Variscan orogeny, the formation of metallic minerals and, especially, to watch noticeable sections of an enormous recumbent fold. Courel Mountains began to be eroded, producing sediments which filled the newly formed Quiroga pop-down tectonic basin (Fig. 18) in the southern UGGp (e.g.,

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Fig. 16 Alpine thrusts and other faults associated with present-day earthquake activity that uplifted Courel Mountains. Santa Eufemia late-variscan fault (reported in Sect. 4) worked as a reverse structure named Folgado thrust by Martín-González (2009). Earthquakes (1986 to Present) and the digital elevation model are from Instituto Geográfico Nacional

Martín-González 2009). The basin shows similar tectonic patterns than other nearby basins (De Vicente and Vegas 2009). Quiroga basin is part of the Sil river valley (Fig. 18), which formed a 600 m-depth canyon (Fig. 19). After the Alpine uplifting, Courel Mountains continued their evolution linked to geomorphological and soil processes (see Pérez Alberti 2018 for further data). The vegetation grown after the Last Glacial Maximum (Santos et al. 2000; Muñoz Sobrino et al. 2001) and the human colonization and development took place since the Palaeolithic (e.g., de Lombera-Hermida 2011; Tejerizo-García and Canosa-Betés 2018).

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Fig. 17 Palaeozoic rocks forming the summit of Courel Mountains because of the Alpine uplifting (picture courtesy of M. Yera). Beds are inclined toward the Courel syncline

Fig. 18 Quiroga Cenozoic pop-down tectonic basin constrained by Alpine faults and filled with Oligocene to Pleistocene alluvial fans generated due to the uplift of Courel Mountains

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Fig. 19 Sil River canyon at A Cubela geosite evidencing the great fluvial incision on continental palaeosurfaces (Yepes Temiño and Vidal Romaní 2003) derived from the Alpine uplifting

7 Final Remarks Courel Mountains are the result of three geological cycles along 600 million years. While the first cycle is poorly represented in the UGGp, the second cycle formed sedimentary, igneous and metamorphic rocks, minerals of commercial interest, provided the preservation of organisms such as fossils, and created a spectacular edifice of folds and faults that once exhumed at the surface during the last geological cycle, yielded the scenic views that are a the significant characteristic of the UGGp. Rocks, minerals, fossils, folds, faults and mountains reinforce the international geoheritage of the UGGp and are the basis for the landscape today, as well as the noticeable local biodiversity and human development. All these issues are the engine of the rural development run by the UGGp to enable the well-being of its inhabitants, the enjoyment of tourists and the preservation of nature and cultural heritage. Acknowledgements This work forms part of the scientific programme of the Courel Mountains UGGp.

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References Alonso F, Currás BX, Romero D (2010) Perceived landscapes: roman gold mines in the Iberian Northwest. In: Leveque L, Ruiz Árbol M, Pop L (eds) Patrimoine, images, mémoire des paysages européens. L’Harmattan. 396 pp, pp 189–201. ISBN 978-2-296-10887-5 Ballesteros D, García-Ávila M, Diez JB, Vila R, Barros XC, Gutiérrez-Marco JC, Caldevilla P, Alemparte M (2021) Management of the Palaeozoic Palaeontological Heritage associated with metamorphic bedrocks: Courel Mountains UNESCO Global Geopark (Spain). Geoconservation Res 4:66–69. https://doi.org/10.30486/gcr.2020.1912243.1039 Ballesteros D, Caldevilla P, Vila R, Barros XC, Rodríguez-Rodríguez L, García-Ávila M, Sahuquillo E, Llorente M, Diez JB, Fuertes-Fuente M, Timón-Sánchez SM, de Lombera-Hermida A, Álvarez I, Pérez-Cáceres I, Acebo M, Orche Amaré P, García JH, Martín-González F, Alemparte M (2022) A GIS-supported multidisciplinary database for the management of UNESCO Global Geoparks: the Courel Mountains Geopark (Spain). Geoheritage 14:41. https://doi.org/10.1007/ s12371-022-00654-3 Barros Lorenzo XC, Gutiérrez-Marco JC, Cózar P, Vinn O, Ballesteros D, Vila R, Alemparte M (2022) Nuevos fósiles del Pragiense (Devónico Inferior) del Geoparque Mundial de la UNESCO Montañas do Courel (Lugo, NO de España) y sus implicaciones geológicas. Geogaceta 71:15–18 Bastida F, Martínez Catalán JR, Pulgar JA (1986) Structural, metamorphic and magmatic history of the Mondoñedo nappe (Hercynian belt, NW Spain). J Struct Geol 8:415–430. https://doi.org/ 10.1016/0191-8141(86)90060-X Bastida F, Aller J, Pulgar JA, Toimil NC, Fernández FJ, Bobillo-Ares NC, Menéndez CO (2010) Folding in orogens: a case study in the northern Iberian Variscan belt. Geol J 45:597–622. https:/ /doi.org/10.1002/gj.1199 Bastida F, Aller J, Fernández FJ, Lisle RJ, Bobillo-Ares NC, Menéndez O (2014) Recumbent folds: key structural elements in orogenic belts. Earth Sci Rev 135:162–183. https://doi.org/10.1016/ j.earscirev.2014.05.002 Cardenes V, Cnudde V, Cnudde JP (2015) Iberian roofing slate as a global heritage stone province resource. Episodes J Int Geosci 38(2):97–105. https://doi.org/10.18814/epiiugs/2015/v38i2/005 Carlé W (1945) Ergebnisse geologischer Untersuchungen im Grundgebirge von Galicien (Nordwest-Spanien). Geotekto-Nische Forschungen 6:13–36 Cepedal A, Fuertes-Fuente M, Martín-Izard A, Arias D, Aragón, A., 2018. The Portas deposits (Lugo, NW of Spain): an orogenic gold deposit related to Paleozoic ironstones. p. A72. In: Proceedings of the 15th Quadrennial International Association on the Genesis of Ore Deposits Symposium. SEGEMAR, Buenos Aires. De Lombera Hermida A (2011) Caves and people. Archaeological research at the eastern margins of NW Iberia. In: De Lombera Hermida A, Fábregas Valcarce R (eds) To the west of Spanish Cantabria: the Palaeolithic settlement of Galicia, BAR, 2283, pp 111–122 De Vicente G, Vegas R (2009) Large-scale distributed deformation controlled topography along the western Africa-Eurasia limit: tectonic constraints. Tectonophysics 474:124–143. https://doi. org/10.1016/j.tecto.2008.11.026 De Vicente G, Cloetingh S, Van Wees JD, Cunha PP (2011) Tectonic classification of Cenozoic Iberian foreland basins. Tectonophysics 502:38–61. https://doi.org/10.1016/j.tecto.2011.02.007 Dozy JJ (1983) The geology of the region to the Southeast of Lugo (N.W. Spain). Leidse Geol Meded 52:513–524 Drot J, Matte P (1967) Sobre la presencia de capas del Devoniano en el límite de Galicia y León (N. W. de España). Notas y Comunicaciones De Instituto Geológico y Minero De España 93:87–92 Fernández FJ, Aller J, Bastida F (2007) Kinematics of a kilometric recumbent fold: the Courel syncline (Iberian massif, NW Spain). J Struct Geol 29:1650–1664. https://doi.org/10.1016/j. jsg.2007.05.009 Fernández-Lozano J, Palao-Vicente JJ, Blanco-Sánchez JA, Gutiérrez-Alonso G, Remondo J, Bonachea J, Morellón M, González-Díez A (2019) Gold-bearing Plio-Quaternary deposits: insights from airborne LiDAR technology into the landscape evolution during the early Roman

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Endogenous/Exogenous Forms of Granite Geomorphology in Galicia Juan Ramón Vidal-Romani

Abstract Ever since geology has existed, attempts have been made to understand the Earth by looking at the granite rocks on its surface. There are two ways to tackle this task. Some look at the rocks and interpret how they were formed. Others look at the forms and from them interpret how and when they were formed. Although they are different ways to achieve the same end, the truth is that they have sometimes given rise to very different interpretations and also in some cases they have led to misinterpretation. Galicia, in the north-west of the Iberian Peninsula, constitutes one of the most genuine representations of the geology of Hercynian granite in the whole of Europe. In this area, very intense erosion took place during the Mesozoic and Cainozoic ages, which has resulted in levelling of its sediments down to the granite massifs which explains the abundance of granites on the surface. Keywords Granite geomorphology · Mega-forms · Minor forms · Tafone · Gnamma · Inselberg

1 Introduction In the general climatic context of Galicia, we can observe a wide variety in the geomorphic sub-environment where Galician granite outcrops are to be found: marine or continental, fluvial, aeolian, periglacial and glacial, (the latter being fossil, evidently). Thus, while the northern regions have extremely heavy rainfall, the southernmost zones may on the other hand register rainfall levels which border on those of the semi-arid areas. In the same way, the mild temperatures of the coastal areas can be contrasted with those inland, which have frost and ice during the winter nights and even show a certain periglacial-type activity. In such conditions, then, it is logical that a great diversity of granite forms should correspond to the lithological, structural, geomorphological sub-environment variety, since all researchers in this field admit, as being influential in the generation of granite J. R. Vidal-Romani (B) Instituto Universitario de Geología, Universidade de Coruña, Coruña, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_7

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forms, one or more of the above-mentioned factors. The reality don’t corresponds in our case, with the theoretical expectations and show that granitic geomorphology does not depend on climate but on the structure (discontinuities) of the rock. And the structure of granitic bodies depends exclusively on the conditions in which the intrusion of the rocky body occurred. We have followed the guidelines of similar studies carried out in other geographic locations. In particular we base ourselves on the inventory realized by Twidale (1982), which we consider the most systematic and most thorough of all those, with occasional modifications. Thus, we have classified the granite forms to be found in Galicia in two major groups, i.e., Megaforms, or larger forms, and Microforms or minor forms, our criteria being solely their dimensions, and following the classification produced by Godard (1977). Megaforms are those whose minimum dimensions are around 100 m, although it is usual that they should measure around a kilometer. Thus we are dealing with features which allow a macroscopic definition of a relief. In spite of this dimensional criterium it should not be taken in its strictest sense. Microforms are those morphological types whose maximum dimensions are no greater than ten meters. In general, however, we are dealing with forms having dimensions of one meter or even less. As a rule, Microforms appear associated with Megaforms, providing them with a greater degree of detail (e.g. the case of an inselberg, or that of a dome, without the associated weather pits. It is not normal for Microforms to appear alone, but rather associated with one another or with the megaforms to give clearly differentiated features in the landscape.

2 Forms Found in Galicia. Mega and Minor The most important megaforms, with reference to the surface-area which they occupy are the granite-plains (Twidale 1982). These are chiefly characterized by their monotony or regularity which allow us to speak of a topographic isotropy for this form. In Galicia the small size of the granite outcrops, considered on regional scale, explains the rarity of these forms. Nevertheless, we can point out fine examples of plains of chemical corrosion in some patches of the best-preserved parts of the morphological unity «Fundamental surface» (Nonn 1966) of Galicia the innermost areas of Galicia where the embedding of the Galician rivers has not been very severe. It is the area that essentially coincides with the section of the Miño river located between its source and Os Peares where it meets the Sil river. As examples we may indicate Monte Xalo (Meirama, A Coruña) or to the north of the town of Ourense (Cea Region). In other cases (North of Lugo area comprising Baamonde-Begonte-CarralOuteiro de Rei), an accumulation of Pliocene alluvial gravels has been deposited on top of the flattened granite substratum. Examples of epigenic plain or denudation plain carried out over granite areas due to the limited area of the granite outcrops

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only appear as small patches coinciding with glacial and periglacial areas: Serra de Queixa, Serra do Xurés, Serra de Larouco (Ourense). In the same way we include in this section of granite macroforms the small benches of etching developed on granite rocks (Burela, Lugo, Balarés (Ponteceso) (Photo 1), or A Guardia-Baiona flattening, (Pontevedra). As far as the Stepped or Multicyclic Surfaces are concerned, the very tectonic instability of the area of Galicia from the end the Palaeogene down to the present day, makes it possible select areas such as Serra de Barbanza (A Coruña), where forms of this type have been observed (Nonn 1966), there is a form of steeps due to obviously tectonic effects. Other good examples of this type of megaforms in inland Galicia are the Alto do Rodicio-Castrocaldelas (Ourense) (Yepes 2002). Convex forms are generally given the name «Inselbergs» and are defined in the literature as mountainous elevations, ridges or ranges which just out brusquely from flat areas surrounding them, like islands in the sea. They can be of four main types (Thomas 1987). Let us look briefly at the characteristics of these convex macroforms in their appearance in Galicia. Bornhardt or Rock Dome These are the largest sized differentiated megaforms. Their main feature is that they are bounded by denuded rock surfaces, with adventitious deposits at their base. The

Photo 1 Etche surface of non-marine origin, on the beach of Balarés, Ponteceso, Coruña, Spain

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Photo 2 Granitic dome of Maríz (Guitiriz, Coruña, Spain), showing a characteristic sheet structure that has been exposed on the surface by quarry work

cases in Galicia never present flared or overhanging walls, sometimes the characteristic counter-slope in the pediment surrounding them. The surface rounded by curved declasses, sheet structure, is represented in the cases in Galicia (Photo 2). Most cases cited (Nonn 1966; Pannekoeck 1967; Vidal-Romaní 1979; De Uña Alvarez 1986), are characterized by an intense dissection during the Cainozoic age. Thus they can be said to be young forms. In Galicia they are given the name of «Moa» (molar) because of their rounded and sticking out morphology. As the best developed instance we may indicate the «O Pindo» complex, defined by Nonn (1966) as a complex inselberg. The most outstanding cases are to be found in coastal areas (Photo 3) (e.g. Monte Louro, Coruña). Also, in inland zones subjects to glacial and periglacial modelling activity, instances of these forms are often to be seen though smaller in size (Serra de Larouco, Serra do Xurés in Ourense province). Castle-Kopje These are convex relief determined by systems of orthogonal discontinuities which give rise to castle shaped reliefs. In Galicia toponyms referring to this fact are common and are called “castelos” (Coruña) or “cotos” (Pontevedra). (Penedos de Pasarela y Traba (Coruña) (Vidal-Romaní et al. 2022) (Photo 4) are good examples. They can reach a size of some tens of meters.

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Photo 3 Monte Louro inselberg from the middle of Ría de Muros. Observe the characteristic counter-slope in the pediment surrounding the mountain

Nubbins Although sorne writers consider that this form coincides with the initial stages of development of the rock domes (Twidale 1982), we may define it as a common form in Galicia. Nubbins or rock domes are often found in their initial to late stages of exhumation in the O Cuadramon (Lugo) and Penafiel (Ézaro, A Coruña) (Photo 5) and in the Serra do Xurés (Ourense). The “cons” of Ria of Arousa can be considered also as nubbins. Tor Although the use of this term in geomorphological literature is very confusing, we use it here to describe convex forms with long-wise vertical development, which can appear either isolated or in groups of Tors, or also associated with other megaforms. They are common in geomorphic situations with high rates of erosive degradation, coastal (Cabo Vilan) and O Pindo, (Photo 6) both in Coruña province) or continental areas subjected to glacial and periglacial modelling (Serra do Xurés, Larouco, etc. in Ourense province) or Penas das Rodas en Outeiro de Rei (Coruña). This is the smallest unit within Macroforms, defined as a consequence of the stripping processes of the granite rock massifs. The size of the rocks varies widely, although being always determined by the structure of the rock massif. The may reach

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Photo 4 The convex relief is determined by systems of orthogonal discontinuities which give rise to castle shaped reliefs. (Traba Massif, Camariñas, Coruña, Spain)

Photo 5 Rock domes found in their late stages of exhumation in Penafiel (Ézaro, A Coruña)

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Photo 6 Tor form in Penas das Rodas en Outeiro de Rei (Coruña)

sizes of anything from 10 or so meters down to half a meter in diameter, the latter being more usual. This could be called an extreme or transition form tending towards the minor or microforms, so that its inclusion within the macroform group is purely conventional. Micro or Minor Forms It is, however, in another dimensional order, where granite geomorphology reaches a greater variability or degree of detail. Actually, whenever we consider on a smaller scale (one meter or so), the granite landscapes, factors come into play which on a macroscopic level could go unnoticed. Besides the structure of the rock and of the lithology, considered on a macroscopic level, mineralogy (for example) also intervenes (both at grain level and at compositional banded zones, accumulates, xenoliths, etc.). In the same way the structure at a micro scale, presents a greater diversity and degree of detail. Also, the processes of alteration or the external geodynamic have a greater morphological variability on the level of smaller dimensions. It is clear that it is on this scale of work where, for example, a polishing of glacial origin can be differentiated from a mirror fault or an aeolian or fluvial polishing, which would allow us to define completely different geomorphic environments and which on a macroscopic scale would be hard to differentiate.

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Thus, on this other scale it is Microforms which will be of greatest profit for use. Microforms are defined as those whose maximum dimensions are around a meter, though it is normal for them to be less than a meter. In general, as has already been noted, they are associated with Macroforms being considered by some authors as part of the evolution of some types of Macroforms (this, for instance, is the case of the association of pedestal, plinth or tafone forms, with the base overhanged of the Bornhardts (Twidale 1982). The Microforms are, due to their dimensional size, pointed, even more so when compared with the Macroforms, so that they appear to be the outcome, rather than of a process at a regional scale (e.g., exfoliation due to unloading of a rock massif), of a particular process, one within a smaller spatial context, within a set of processes which defines the large-scale morphology of rocky massifs. The Microforms can in some cases be clearly related to the structure of the rock (foliation, discontinuities, layering, magmatic differentiation, etc.) (Photo 7a and b). In other cases, the relationship not so evident and the various genetic interpretations (e.g. about the origin of gnammas and tafoni) being the cause of endless discussion. Microforms Without Any Evident Relationship to Structure We shall group together within this category all the Microforms in whose genesis the rock structure appears not to be decisive (we are referring to the system of discontinuities of the rock in each case), or rather, where not all authors admit the relationship of form to structure. In general, the genesis and development of these microforms is considered to be directly linked to exogenous geodynamic processes (chemical edaphogenesis, physical weathering, etc.). They are divided into linear forms, i.e., when the form develops preferentially in one of the directions in space, and planar forms, i.e. when they develop preferentially in two directions in space. Linear Forms (Runnels and Gutters) The prototype for antonomasia is made up of channel shaped features able to con centrate the superficial waters which flows over rock surfaces (Photo 8). In the English language, the terminology is much richer than in Spanish, in which it is hard to find terms equivalent to those in English.

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Photo 7 a Granite sheared in a horizontal plane during the intrusion of the rock. Castro de Baroña, Porto do Son, A Coruña). b Granite sheared in a horizontal plane during the intrusion of the rock. Monte Louro, Muros, A Coruña)

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Photo 8 Rills produced by the dissolution of granite in a block located on the seashore in Boiro (Coruña, Spain). The dissolution does not occur at the present time since the surface is covered by lichens but during the previous glacial when the rock was covered by a dune with bioclasts

They develop on surfaces with all kinds of inclinations from sub-horizontal to steeply inclined. They receive different nomenclature, runnels and gutters (Photo 9) when they develop on a horizontal or very slightly sloped topography. On the other hand, the grooves and flutings correspond to similar features developing on inclined surfaces. In Galicia, this type of microform is particularly well-developed along the coast although it is a fossil feature corresponding to the previous glacial period. Also in the interior of the continent they can be observed in areas where the granites are, or were, covered by Paleozoic limestone. Once the intrusion of the granites occurred and due to erosion, the infiltration of the runoff circulating through the limestones reached the granitic rock, producing its dissolution (alkaline waters circulating over granite). The process is observed throughout the coast where, during the glacial phases of the Pleistocene, the rocky reliefs were covered by thick mantles of calcareous dunes. In them, the infiltration of rainwater through the accumulations of bioclasts alkalinized the waters, allowing the granites to dissolve on the surface when they reached the rock. They are equally fossil traits. It is almost always related to small blocks, and linked to the draining of the gnammas. In others they are simply drainage channels or at least function as such. As examples we can quote those of Monte Castelo (Viveiro and Costa de Papel, Foz in Lugo province), Cabo Veo (Camelle, Roncudo and Balarés in A Coruña province) and Porriño (Pontevedra province).

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Photo 9 Rocky outcrop of Tal beach (Muros, Coruña) with a surface affected by polygonal cracking

Planar forms (Polygonal Cracking) In granites, the development of polygonal cracking is synchronous with the intrusion of the rock and coeval with the generation of the sheet structure. All these deformations, although they are a continuum of deformation, have received various names such as: polygonal cracking, boudinage, disjunction in onion layers, or shortening with the formation of folds, affecting the rock during the development of non-intrusive movement planes (sheet structure). When they are exposed by erosion, what can be observed are the large blocks with spheroidal or onion-leaf disjunction. For many years they were erroneously interpreted as forms of alteration when in fact they are s.t.c., a deformed structure that is sometimes used by surface weathering to progress more quickly. The appearance it presents is that of a polygonal network of fractures that affect a plane (discontinuity) of the rock, as occurs in Tal, Ría de Muros Coruña, Galicia).

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Until now, polygonal cracking in granitic rocks had only been mentioned by a few authors (Twidale 1982; Twidale and Vidal Romani 1994; Vidal Romaní and Twidale 1998; Twidale and Vidal Romani 2005), although it was not initially understood as a deformational structure. Some authors (see Twidale 1982) justify them as weathering, interpreting the fracture pattern as due to a process similar to that of desiccation cracks in clayey sediments soaked in water (shrinkage cracks); in this case it would be the same effect but it would develop with the altered rock (¿). They have also been interpreted as due to periglacialism acting in the outermost part of a granite rock outcrop (see Twidale 1982). It is only from 1994 (see Twidale and Vidal Romani 1994, 2005; Vidal-Romaní 1991, 2008) when polygonal cracking began to be identified, and also sheet structure, with the deformation structures produced in granite massifs during the intrusion of the rock. According to this, first the surfaces would be generated that would immediately be affected by the shearing and consequently the polygonal cracking would be formed on them (Vidal-Romaní 2008; Vidal-Romaní et al. 2014). The main difficulty in admitting this mechanism, in the case of plutonic magmatic rocks, is that they initially lack, (which does not occur with sedimentary and metamorphic rocks), lithological discontinuities (strata), or areas of weakness (planes) bedding), and that, when the massif is deformed, guide the development of the shear. Punctual Forms In this case we shall distinguish between Concave and Convex forms. Concave Pointed Forms This is one of the most conspicuous types of minor forms in the whole of granite geomorphology, and may be said to be present in any Galician granite landscape. This type of form, known in other geographical areas under different names (gnamma, vasque, pit, etc.) is called “pía”, in Galicia. Here, too like in other areas (Twidale 1972), they have been interpreted as forms of anthropic origin, because of their relationship, in some cases, with prehistoric or archaeological remains. It is clear that, these forms, undoubtedly of a natural origin may have been used by man for different ends; which would explain the confusion (Vidal-Romaní et al. 2018). Besides this hypothesis, others have been suggested to explain the origin of the gnammas, which we can group together in two classes. On the one hand there are the monophase hypothesis, which speak of a subaerial or epigenic origin for these minor forms. According to these it is only water which, resting on a rock surface (with or without the presence beforehand of a hollow), develops, by physical or chemical alteration, or both, the gnamma. The variants in this class of monophase hypotheses are in the different origins postulated for the formation of the initial concavity (mineral saltation, weathering of basic xenoliths, etc.), in the mechanisms proposed to explain the weathering of the rock (either chemical or physical) and in the processes of evacuation of the detrital resulting from the alteration (wind, water) from the interior of the concavity (Twidale 1982; Vidal-Romaní 1979, 1983; Twidale and Corbin 1963).

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The class of hypotheses called polyphase, (Vidal-Romaní 1984a, b, 1989; Twidale 1986, 1989) has in common an origin for the gnamma in several well-differentiated stages. For some writers (Twidale1982; Centeno 1989), the gnamma are formed beneath an edaphic profile, as the consequence of an irregular advance of the front of weathering which brings about initial irregularities (concavities and convexities in it). Once the covering of regolith disappears due to erosion, and the existing concavities in the substratum begin to act as receptors and retainers, receiving and holding the waters, for instance, those of rain (a «sine qua non» condition for the gnamma to evolve), the process will be governed by what has been described in any one of the monophase hypotheses. Another of the polyphase hypothesis (Vidal-Romaní 1983, 1989; Vidal-Romani et al. 2019), postulates a genetic process for the gnamma more complex, the intrusive phase of the granite, which is made in the solid state and which is when the system of discontinuities is formed though the same hypotheses may be valid to explain the formation of other types of natural cavities in granite (e.g., tafone) as well as the different varieties of gnamma (pit, pan, cylindrical hollows, armchair-shaped hollows, rock doughnuts, etc.). According to this hypothesis (Vidal-Romaní 1983, 1989; Vidal-Romaní et al. 2019) the formation of the gnamma is due to process of concentration of charges in particular points of a rock granite massif during the process of formation of discontinuities in the massif. There are two possibilities considered here of concentration of charges, which take place in natural processes: by edaphic alteration and by tectonic deformation. By means of at least these two processes, and according to the Elastic Model of Cavities Formation (Vidal-Romaní 1983, 1989), both gnamma-type and tafone-type can be generated. Tafone («Cachola», Cavernous Weathering) Although in the geomorphological literature the «tafone» tend to be described as minor forms (microforms) independent of the «gnammas», we consider them, as been seen in the previous section, to be both spatially and genetically associated forms (as has already been indicated before, the same type of process which is described in the M. E. F. C., will also be used to explain the creation, birth of genesis of the “tafone” (Cachola) in Galice. In Galicia it is a not only abundant but also very well developed morphological feature, regardless of what any author (Nonn 1966) might say to the contrary.

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They are forms present in all the granite outcrops of Galicia, in an unusually abundant quantity; normally associated with the zones of most active geodynamic evolution: coastal benchs or the main system of drainage, but also present in other zones of Galicia. There exists a great deal of literature which has tried to explain the origin of the «tafone», since they were described by Hans Reusch in 1883, and given the name «tafone» or «tafoni» (window in the Corsican dialect). Just like the «gnammas», they were interpreted as forms of subaerial development, with a previous, probably subedaphic stage (Vidal-Romaní1979, 1983, 1989; Twidale 1986, 1989). In the case of the «tafone», most authors adding them a totally subaerial origin. Only a few authors (Vidal-Romaní 1983, 1989; Twidale 1982, 1989), accept the possibility of a stage previous to the subaerial one in the development of the tafonetype form. Some identify it as subedaphic and also, as in the case of the «gnammas», related to unequal advances of the alteration front on acting, above all, at the base of Inselberg-type reliefs (bornhardt or rocky domes/cupolas) (Twidale 1974, 1982, 1989). Our idea, as in the case of the «gnammas», is that what is demonstrated, are deformative features produced by loads concentrated at points in the massif. As has been mentioned before, the «tafone» in the lower part of a block is a reflexion of the gnamma in the underlying block. The Tectonic Process We refer to the concentration of loads produced during the phases of tectonic deformation to which the granite massifs, like other types of rock, are subject. In fact, it is quite normal to observe, to a greater or lesser extent, a diaclasement of the bodies of granite. Whilst in some cases the tectonic deformation follows regional guidelines which allow us to elucidate the behavior, on a large scale, of tectonic processes, in others, this deformation is restricted to more localized areas (e.g. movements caused by faulty planes, zones of fragile shearing, etc.) (Photo 10). In all these cases the traces or marks of concentration of loads are clear (expressed, for example, by grooves and breaks), (Vidal-Romaní 2008; Vidal-Romaní et al. 2019), and can be noted in fault planes, brittle punching, etc. (Courrioux et al. 1984; Vidal-Romaní and Gracia 1988) In the case of a tectonic deformation, it is not that difficult to explain how the loads, which are concentrated at one point, can attain values which vastly exceed the resistance to simple compression of the rock (1.500 kg/cm2 ), even in those cases where the latter is not altered in any way (Photo 11).

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Photo 10 Group of gnammas in Punta Nariga (Malpica, Coruña). The most remarkable thing is that the areas covered by water when it rains are the only ones where there is no lichen cover. Also the square contour of the concave since it is normally circular

Photo 11 Tafone at the top associated with its counterpart at the bottom that has become a gnamma with the ability to retain rainwater. The honey comb is only visible at the top of the shape. (Ezaro, Dumbria, Spain)

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3 Final Remarks In what precedes we have tried to show the main small-scale and large-scale granitic forms that form in granitic rocks and that are related to the structure/texture of the rock developed during the period of rock intrusion. The fact that in Galicia the same types of forms are developed in the same types of exogenous environments existing in Galicia and on any of the types of granite that exist here indicates their relationship rather with the endogenous stage. And this conclusion is reinforced by the fact of finding the same type of forms in any other part of the world (Twidale and Vidal-Romani 1995). Acknowledgements During these years of studying granite forms, I have had with me two exceptional people. Dr. Ramón Vidal de Artaza who helped me develop the Elastic Model of Cavity Formation and Dr. C. R. Twidale with whom I discussed for years, without reaching a complete agreement, about the origin of the granitic forms. Without them I would never have been able to develop my current genetic model that solves all the obstacles that existed to understand the morphology not only of granitic rocks but also of many other rocks (limestone, sandstone, quartzite, etc.). Sincerely thank you very much.

References Centeno JD (1989) Evolución cuaternaria del relieve en la vertiente sur del Sistema Central Español. Las formas residuales como indicadores morfológicos. Cuadernos do Laboratorio Xeoloxico de Laxe, n.º 13 de Uña Alvarez E (1986) El Macizo de A Coruña. Análisis estructural y morfología de un afloramiento granítico. Tesis Doctoral. Universidad de Santiago, 1058 págs. (No publicado) Godard A (1977) Pays et paysages du granite. Presses Uníversitaires de France. Vendóme, 232 pp; Klaer W (1956) Verwiterungsformen im granit auf Korsika. U. E. B. Hermann Haack Geographysch-kartographische Anstalt Gotha, 146 pp Nonn H (1966) Les régions cotiéres de la Galice (Espagne). Etude Géomorpbologique. Publications de la Faculé de Lettres de l’Université de Strasbourg. These. Doctorale. 591 pp. 2 tom Pannekoeck AJ (1967) The geomorphology of the surroundings of the Ria de Arosa (Galicia, NW, Spain). Leidse Geolologische Mededelingen 37:7–32 Reusch HH (1883) Note sur la géologie de la Corse. Paris Société Geologique Bulletin 11:53–67 Thomas MF (1987) The study of inselbergs. Zeitsfricht für Geomorphologie Supplement. Band 31, 1–41, Berlin Twidale CR (1986) Granite landforms evolution: features and implications. Geol Rundsch 7513:769–779 Twidale CR, Corbin EM (1963) Gnammas. Revue De Geomorphologie Dynamique 14:1–20 Twidale CR (1982) Granite landforms. Elsevier Publishing Company, Amsterdam, 372 pp Twidale CR (1989) La iniciación subsuperficial de las formas graníticas y sus implicaciones en las teorías generales de evolución del paisaje. Cuadernos do Laboratorio Xeoloxico de Laxe n.º 13 Vidal-Romaní JR (1984a) Microformas graníticas tipo tafone y gnamma. Un micromodelado sin relación con el clima o la estacionalidad. Cuad Lab Xeol Laxe 7:273–277 Vidal-Romaní JR (1989) Granite geomorphology of Galicia, NW Spain. Cadernos Do Laboratorio Xeolóxico De Laxe 13:41–47

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Vidal-Romaní JR, Gracia FJ (1988) Formación de cavidades en granito bajo condiciones no epígénícas. Cuad Lab Xeol Laxe 12:47–58 Vidal-Romaní JR, Grajal M, Vilaplana JM, Rodriguez R, Macias F, Fernandez S, Hernandez Pacheco A (1979) Procesos actuales. Micromodelado en el granito de Monte Louro, Galicia, España (Proyecto Louro). Actas IV Reunión del Grupo Español de Trabajo de Cuaternario. Banyoles, pp 256–266 Vidal-Romaní JR, Vilaplana JM, Martí Bono C, Serrat D (1983) Rasgos de micromodelado periglaciar actual sobre zonas graníticas de los Pirineos Españoles (Panticosa, Huesca y Cavallers. Lleida). Acta Geolologica Hispánica t. 18(n1):55–65 Vidal-Romaní JR, Sanjurjo J, Gandald’Anglade A, Vaqueiro M, Costas R (2018) Archeology and geology with a special mention to the relationship between rocky substrate and rock art (petroglyphs). Férvedes 9:51–57. ISSN 1134-6787 Vidal-Romaní JR, Song Z, Liu H, Sun Y, Li H (2019) Orogenic movements during the Paleozoic and the development of granitoid forms in the northwest of the Iberian Peninsula (Spain). J Earth Sci 31(3):611–620. https://doi.org/10.1007/s12583-019-1268-z Vidal-Romaní JR (1983) El Cuaternario de la provincia de A Coruña. Geomorfología granítica. Modelos elásticos de formación de cavidades. Publicaciones de la Universidad Complutense de Madrid (l985), 600 págs., 2 tomos Vidal-Romaní JR (1984b) Micromodelado de rocas graníticas. Un nuevo modelo genético. Actas. 1º Congreso Español de Geología. Segovia, pp 585–594 Yepes J (2002) Geomorfología de un sector comprendido entre las provincias de Lugo y Ourense (Galicia, Macizo Hespérico). Serie Nova Terra, 21, 272 pp, Edicions do Castro, Coruña

Soils

Soils of Galicia Eduardo García-Rodeja, Juan Carlos Nóvoa-Muñoz, and Xabier Pontevedra-Pombal

Abstract After a short summary of the general background knowledge on soil studies in Galicia, an analysis is made of the main soil types present in Galicia (NW Iberian Peninsula), their most outstanding properties and the processes that give rise to them. Within an apparent homogeneity, with a predominance of poorly developed soils such as Umbrisols, Leptosols, Regosols and Cambisols, the existence of a wide variety of soil types is revealed. As a general rule, the formation of these soils is strongly conditioned by the nature of the parent material. Keywords Parent material · Organic matter · Acid soils · Al (Fe)-humus complexes · Pedodiversity · NW Iberian Peninsula

1 Background Perhaps the first study on the soils existing in Galicia can be attributed to Huguet del Villar (1935), who compiled the work carried out for his publication ‘Mapa Edafológico de la Península Luso-Ibérica’ (Huguet del Villar 1938). In this study, the author highlighted the dominance of acid and desaturated soils, of a ‘xeropeaty’ character and an AC profile on granitic and other crystalline rocks and areas with ‘humid sialitic’ and ‘xerosialitic’ soils with B horizons. Later, in the framework of the elaboration of the soil map of the Spanish humid zone, Guitián Ojea (1967) presented a synthesis of the main soil types and the genetic relationships of the soils of Northern Spain. In this publication, he pointed out that the normal evolution (using the classification of Kubiena 1953) begins with the formation of ‘protoranker’, followed by different types of ‘rankers’ which evolve E. García-Rodeja (B) · X. Pontevedra-Pombal Departamento de Edafoloxía e Química Agrícola, Facultade de Bioloxía, Universidade de Santiago de Compostela, Santiago de Compostela, Spain e-mail: [email protected] J. C. Nóvoa-Muñoz Departamento de Bioloxía Vexetal e Ciencias do Solo, Facultade de Ciencias, Universidade de Vigo, Vigo, Spain © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_8

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into ‘brown ranker’ and ‘brown earth’. The podzolizing tendencies, associated with colder and wetter climates in mountain areas, or due to the acidic nature of the parent material or to the influence of the podzolizing effect of heathland vegetation, give rise to ‘dystrophic ranker’ and ‘podzolized brown earth’ soils and, on sandstones, quartzites and their weathering products, ‘podzols’. The same study also indicated the existence of ‘lehm’ soils on clayey sediments and basic and ultrabasic rocks; of ‘protorendzinas’, ‘rendzinas’ and ‘calcareous brown earths’ on limestone rocks, ‘anmoor’ and ‘gley’ soils and ‘peatlands’ under hydromorphic conditions, ‘alluvial’ soils and soils modified by human activity. The results of these studies were published as monographies in the ‘Estudios Agrobiológicos’ and in the ‘Mapas Provinciales de Suelos’ of the four Galician provinces. This series of studies, generically called the ‘Soils of the Spanish Humid Zone’, continued between the 1970s and 1990s, with a large production of academic works that contributed to increase the knowledge of Galician soils, their properties, and the influence of soil-forming factors. After Guitián Ojea’s studies, it should be mentioned the book about the soils of the province of A Coruña (Macías and Calvo 1992a), as well as the book chapter on soils in the ‘Atlas de Galicia’ (Macías and Calvo 2001). Both studies included a soil cartography at a scale of 1:200,000 and 1:500,000 respectively, using the Revised Legend of the Soil Map of the World (FAO-UNESCO-ISRIC 1990) and the World Reference Base (FAO 1998) as classification system. More recently, Carballas et al. (2016) presented a review on the soils of the temperate-humid zone of Spain, while the book ‘Atlas digital de propiedades de suelos de Galicia’ (Rodríguez Lado et al. 2016) is a fine complement to previous studies due to the inclusion of additional cartographic information on climate and soil properties.

2 The Soils of Galicia The formation of soils in Galicia was the result of a complex interrelation between the different soil-forming factors. Thus, the humid climate that affects most of the Galicia territory favours the processes of leaching and acidification, while a complex and diverse topography facilitated both erosive and accumulation processes that explain the surface rejuvenation processes often found in Galician soils. The parent material, initially identified as a key factor in the diversity of the types and properties of soils in Galicia (Guitián Ojea and Carballas 1969), together with weathering processes and trends, will ultimately determine soil properties as was evidenced in later studies (Macías et al. 1982; Macías and Calvo 1992b). In order to provide a quick overview of the properties, processes and types of soils in Galicia, they were grouped into soils developed from granitic rocks (widespread in Galicia, including all types of granitoids and orthogneisses), from basic and metabasic rocks (including gabbros, metagrabbros, amphibolites and granulites), ultrabasic rocks (peridotites with various degrees of deformation and serpentinization), soils formed from different metamorphic materials such as slates, phyllites, quartz-rich schists and biotitic schists (such

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as those present in the Complex of Ordes), sandstones, quartzites, carbonate rocks and sediments. Time is also an important factor in the formation and development of soils and thus, on geomorphologically stable surfaces or in areas with ancient sediments, paleosols are preserved, intensely weathered or whose characteristics result for a long period of evolution. After the observation of the ‘Soil Atlas of Europe’ (ESBN 2005), it reveals that Umbrisols (Humic Cambisols and Umbric Regosols from the Revised Legend of the Soil Map of the World, FAO-UNESCO-ISRIC 1990) cover most of Galicia, accompanied by small areas with Leptosols, Podzols and Histosols. Following the World Reference Base (IUSS Working Group WRB 2015) Umbrisols, together with Leptosols, are the most frequent soil types in Galicia and they can be developed from almost any type of parent material. Umbrisols are soils with an AC, ABwC

Fig. 1 Leptosols (a, c granite; b limestone; d quartzite)

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Fig. 2 Umbrisols on granite (Ah C profile)

Fig. 3 Umbrisols with cambic Bw horizon (a granite coluvial deposit on granite saprolite; b gneiss coluvial deposit on weathered gneiss)

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Fig. 4 a Regosol (granite); b Cambisol (slates); c Cambisol (schist); d gleyic Cambisol (sediments)

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Fig. 5 Atlantic Rankers (cumulic Umbrisols) on granitic rocks

Fig. 6 Phaeozems (a limestones; b serpentinites)

or even an AR profile, moderately acid, with Ah umbric horizons, organic matter rich and a cation exchange complex dominated by Al. When the thickness of the A horizon is not sufficient to classify it as umbric, these soils would be classified as Regosols (AC profile), Cambisols (ABwC profile) or Leptosols (AR profile). However, the predominance of umbric surface horizons and Umbrisols hides a much greater diversity of soil types in Galicia. Thus, in addition to the abovementioned, soils from other GSRs of the WRB are present in Galicia. Depending on soil position

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Fig. 7 a Podzol (sandstone sediments); b Andosol (amphibolite)

in the landscape it can be found hydromorphic soils, whereas depending on the parent material it can appear many other SRG of the WRB, from Arenosols to Acrisols, as well as anthropogenic soils. Examples of different soil types in Galicia are presented in Figs. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 13.

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Fig. 8 a Gleysol (sediments); b Gleysol (slates)

Fig. 9 Fluvisols

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Fig. 10 Ombric Histosols (Blanket bogs)

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Fig. 11 Polycyclic soils with buried A horizons (a paragneiss deposit over a paleosoil on granodiorites), b complex deposit with slates; polycyclic Umbrisol with a well-defined ‘stone line’ (paragneiss)

Soils of Galicia

Fig. 12 Polycyclic soils with fragic horizon

Fig. 13 Anthropogenic soils built on terraced fields (socalcos)

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3 Soils of Galicia and Parent Material 3.1 Soils Developed from Granitic Rocks The relative stability of the components of granitic rocks, and the frequency and intensity of the erosion processes on a contrasting topography, with steep to moderate slopes, contribute to a weak soil development in these areas. Therefore, the soils derived from granitic rocks are mostly young soils, often developed on colluvial deposits (colluvic material) where evidence of polycyclic phenomena occur regularly. On the other hand, it is common that these materials show an intense sandblasting that led to a very permeable saprolite (xabre) that favours the development of B horizons. The degree of weathering of granitic rocks is low to medium, being present among the dominant minerals in the clay fraction micas at different stage of degradation, integrated mica-vermiculite. Al interlayered vermiculites are more frequent and abundant in the upper horizons than in the C horizons, where kaolinite and/or halloysite and gibbsite predominate (Macías et al. 1982; Calvo and Macías 1983). Among the properties of soils derived from granitic rocks can be cited a high organic matter content in the A horizons, with a crumby structure, strong acidity, a low degree of saturation and a cation exchange complex dominated by Al, which led to call these soils as ‘aluminic soils’ (Macías et al. 1982). Regarding their physical properties, a low bulk density (especially in surface horizons), high porosity and a clear dominance of coarse textures (loamy-sand or sandy-loam) can be mentioned. The soils derived from granitic rocks generally have Ah-umbric and Bw-cambic horizons, whose characterisation become complex due to colluviation processes (Silva and Guitián Ojea 1984). The most frequent soil types are Leptosols and Umbrisols. When the A horizons are thin, the soils are included in Cambisols (without umbric and with cambic horizons) or, less frequently, Regosols (on granite saprolites). A particular case of Umbrisols are the ‘Atlantic Rankers’ (Guitián Ojea and Carballas 1968; Kaal et al. 2008), soils developed in areas of slope breaks or at bottom slope where the accumulation of eroded materials is favoured, resulting in a very thick A horizon that frequently presents stone lines indicative of periods of greater instability of the surfaces. These characteristics give them a noteworthy value in the study of environmental changes at a local scale (Kaal et al. 2013). Soils developed on, or formed from, granitic materials do not easily exhibit hydromorphic features due to their coarse texture. However, hydromorphic soils, Gleysols, Histosols and gleyic variants of other GSRs can be found in topographic positions with a near-surface water table or in slope areas where runoff flows regularly. Fluvisols are found on riverbanks, receiving materials from alluvial origin but also a significant contribution of colluvial materials, particularly when they are in narrow valleys. A last group of soils derived from granitic materials are the Podzols and soils with podzolic characteristics, although their presence is limited to sites in very humid mountains (Guitián Ojea and Carballas 1968). These soils are usually characterised by the absence of a defined E horizon, although they have Bs horizons (Silva and Guitián Ojea 1984),

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being also frequent the occurrence of layers cemented by iron, organic matter, and aluminium (placic horizons, ortsteins) generated by lateral eluviation. Rather than true Podzols in the modern classification systems, these soils should be considered as soils with cambic horizons, whose properties are close to those of the spodic horizons.

3.2 Soils Developed from Slates, Phyllites and Quartz-Rich Schists Soils formed from slates, phyllites and mica-schists also show a low degree of development, shallow depth and a predominance of inherited minerals. The most important neoformed materials are 1:1 phyllosilicates and gibbsite, although in a smaller proportion than in soils from granitoids (Macías et al. 1982). The properties of these soils are similar to those developed on granitic materials, reason why they are also included in the ‘aluminic soils’, although they generally have finer textures (tending to silty loam in slates) and greater acidity, particularly in soils developed from slates and phyllites containing sulphides. Consequently, they are soils with A horizons, often umbric, and a predominance of cambic B horizons. The most widespread soils on these materials are Leptosols, Umbrisols, Cambisols and Regosols. Hydromorphic soils, more common in the case of slates, can occur in flat areas, in the bottom of river valleys and in gentle slopes. In these areas Histosols, Gleysols and Umbrisols or Cambisols with hydromorphic features can appear, being less acidic, richer in organic matter in the superficial horizons, with a lesser desaturation of the cation exchange complex and a finer texture than soils derived for the same parent materials in upland areas.

3.3 Soils Developed from Sandstones and Quartzites The composition of these materials, in which quartz predominates, is very poor in weatherable minerals, low base cations, Fe and Al contents, and a high permeability, together with the high rainfall in many areas of Galicia, provide all the favourable conditions for the occurrence and development of the podsolization. These conditions allow the formation of a typical Podzols in Atlantic climates (Guitián Ojea 1967) and, in fact, most of the Podzols or podzolic soils in Galicia are developed from these lithological materials. The properties of Podzols have been studied, among others, by Guitián Ojea and Carballas (1968), Macías (1980) and Macías et al. (1988). In addition to Podzols, soils with a cambic horizon can appear in this type of materials being characterised as Umbrisols or Cambisols, together with Leptosols and, in favourable topographic positions, hydromorphic soils (Gleysols and Histosols).

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3.4 Soils Developed on Schists Rich in Weatherable Minerals This type of lithology results in a smooth landscape with large flat areas and gentle slopes. I these areas can be found soils developed on fresh (or scarcely weathered) schists to saprolites and paleosols with an intense weathering degree. The different types of soils found on these schists have been studied, among others, by Macías et al. (1981a, b) and Silva and Macías (1983). An incipient alteration on fresh schist outcrops generates soils with brown or yellowish-brown colours, loamy or coarser texture and a mineralogy characterised by a certain loss of plagioclases and the presence of 1:1 phyllosilicates, non-crystalline Al compounds and gibbsite. On geomorphologically more stable surfaces, the high intensity of weathering results in red to yellowish red saprolites, silty or with a finer texture, acid reaction and a mineralogy dominated by kaolinite, Fe oxyhydroxides and 2:1 inherited minerals. Saprolites affected by alternating hydromorphic processes show mottling, finer textures, and a mineralogy close to that of well-drained environments, although differing in the abundance of Fe and Mn nodules and concretions. In reducing environments, mica-type minerals and some smectite-type minerals are abundant, with smaller amounts of phyllosilicates 1:1. On fresh or slightly altered schists, the soils are weakly developed having an AR, AC or ABwC profile with surface horizons, often umbric, and subsurface cambic horizons (Leptosols, Umbrisols, Cambisols). Occasionally, andic properties are found in Ah horizons rich in organic matter (Silva et al. 1984). More evolved soils are deeper, with intense colourations, hydromorphic features and the B horizons often results from an ancient pedogenesis, being also common polycyclic and polygenetic soils. These B horizons show properties at the boundary between cambic and ferralic horizons, sometimes with more clay than the adjacent horizons but with poorly defined illuviation features (Silva et al. 1984). In these soils, the A horizons are dark brown to dark reddish-brown in colour and have a crumby structure, while the B and C horizons are redder in colour and have subangular or prismatic structure. On these surfaces the most frequent soils are Umbrisols and Cambisols, with welldeveloped and intensely weathered cambic horizons. Exceptionally, soils with B horizons that comply with the argic (Acrisols, when the A horizon is shallow) or ferralic (Ferralsols) horizons have been identified. Hydromorphic soils appear when the topography favours waterlogging, although in the B horizons of highly evolved soils there may be relict evidence of hydromorphism.

3.5 Soils Developed from Basic and Metabasic Rocks The basic and metabasic rocks, mainly gabbros and amphibolites, give rise to a smoothed landscape where the profiles show deep weathering and remains of ancient pedogenesis. In hillside areas, polycyclic soils are frequent appearing as colluvial

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deposits or soils with stone lines overlying paleosols. Under the typical environmental conditions of Galicia, the weathering processes and incipient pedogenesis in gabbros (Macías et al. 1978a, b; Puga et al. 1978) and amphibolites (García Paz et al. 1986; García-Rodeja et al. 1986) in well-drained environments, lead to the formation of gibbsite, halloysite and Fe oxyhydroxides. However, in the presence of organic matter, gibbsite may not be present and interlaminar chlorite-vermiculites are formed. The intense weathering of this lithology lead to a predominance of kaolinite (with higher crystallinity) and high percentages of Fe oxyhydroxides, while gibbsite is scarce or absent. From a geochemical point of view, in the weathering of these materials, there is a geochemical fermonosiallitic evolution, characterised by a strong mobilisation of bases and, to a lesser extent, silica, and accompanied by an accumulation of iron and aluminium, all this showing a clear tendency towards the so-called ‘residual system’ (Chestworth 1973). In confined areas where hydromorphic environments are frequent, the weathering is characterised by an intense clay formation and a slow mineralogical evolution. According to (Macías et al. 1978a, b; Silva et al. 1988), the pedogenetic characteristics of the soils derived from gabbros and amphibolites can be summarized in: – Well-drained soils of the current cycle formed from fresh or scarcely weathered rock (or from colluvial deposits): these are scarcely developed soils with Ah horizons, generally umbric and, sometimes, an incipient cambic B. Their properties include low bulk density, high porosity and high water retention capacity, fine crumby structure, thixotropy, loamy to silty loam textures, high organic matter content, acidic pH and low base saturation. – Soils with relict pedogenesis in well-drained environments: soils with B and C horizons with diffuse boundaries, reddish or yellowish colouring, loamy to silty loam texture, massive structure when wet and tending to polyhedral-prismatic blocks when dry. They are acid horizons, poor in organic matter, with a low cation exchange capacity and a base saturation lesser than 50%. Above these paleosols, it is common to find a current cycle of pedogenesis evidenced by the presence of a stone line or a colluvial deposit, with an Ah horizon (generally umbric) and a cambic horizon when the development of the current soil cycle is greater. – Soils developed under hydromorphic conditions, with ‘gleyic properties’, are characterised by greenish or bluish colours in Cr horizons, and by white and brownish or yellowish mottling in Bl horizons with alternating oxidation–reduction conditions. In terms of soil classification, the Ah horizons of the present cycle usually present ‘andic properties’ (Macías et al. 1978b; Silva et al. 1988), whereas the B horizons of the paleosols are cambic horizons with properties close to those of the ferralic horizons, and occasionally to the argic horizon. In summary, young soils with low to medium degrees of weathering, as well as intensely weathered soils as result of a long evolution time, are found on basic and metabasic rocks. In the first case, when organic matter is present, umbric horizons

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predominate often showing ‘andic properties’ and often underlying by a subsurface cambic horizon. Under these conditions, the dominant soils are non-allophanic Andosols (García-Rodeja et al. 1987) where the andic character is associated with the abundance of Al (Fe)-humus complexes. Otherwise, Umbrisols, Cambisols and Leptosols occur in the topographic positions most favourable to erosion. When weathering is intense, soils with cambic horizons and highly weathered saprolites are found. The hydromorphic soils are Gleysols, and small areas of Histosols. In the granulites of the Cape Ortegal Complex, the soils have similar properties to those formed on gabbros and amphibolites, being included in the GSR Leptosol, Andosol, Umbrisol and Cambisol, with Gleysols also being common. In the same area, in the eclogite outcrops, an intense weathering is not found due to their great compactness even despite their mineralogical composition, showing in general a great resistance to weathering. The soils have an AR or AC profile (Leptosols, Umbrisols), and soils with a cambic horizon (Umbrisols, Cambisols) can develop only in flat areas or in places where tectonic processes have favoured greater alteration.

3.6 Soils Developed from Ultrabasic Rocks The weathering in soils and saprolites of ultrabasic rocks takes place in a hypermagnesic environment, with pH values close to the neutrality and a high silica activity in soil solution, conditions in which magnesian chlorites and 1:1 trioctahedral phyllosilicates are very stable. The weathering of serpentine materials is usually low and slow due to the Fe oxidation that creates a patina on the surface of the mineral, slowing down the progress of further weathering (López López et al. 1984). This explains the high content of extractable iron and the strong colours of these soils despite their scarce evolution. Macías and Calvo (1992b) characterise the process as a hydrolysis close to neutrality with incipient ferrugination (sometimes fermonosiallitization) in well-drained areas, and bisiallitization in poorly drained systems. Soils derived from ultrabasic rocks have a higher pH and a lower organic matter content than other soils in Galicia, a cation exchange complex highly saturated in base cations being Mg the dominant one. These soils have a low chemical fertility due to deficiencies in some macronutrients (N, P, K), imbalances in the Ca/Mg ratio and a high heavy metal content (especially Ni and Cr). However, the physical fertility showed by these soils is quite appropriate thanks to their balanced texture, welldeveloped structure, and good water retention capacity (Guitián Ojea and López López 1980). Following this, on ultrabasic rocks of Galicia, the surface horizons are umbric or mollic while the subsurface ones are cambic. Accordingly, the most frequent soils are Leptosols, Umbrisols, Phaeozems, Cambisols and Gleysols.

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3.7 Soils Developed from Carbonate Rocks Carbonate rocks such as limestone, and to a lesser extent dolomites, occupy a small area in Galicia, appearing in its easternmost part forming bands of variable thickness mixture with schist, slate, sandstone, and quartzite. These materials generate landscapes with steep slopes where the erosion and transport of materials hinder the development of the soils. The most outstanding characteristics of soils from carbonate rocks are a circumneutral pH, a higher saturation of the cation exchange complex (with Ca and Mg as dominant cations), a colluvial character related to the topography of the area where limestone is mixed with other materials (shales, schists, quartzites), and a certain level of decarbonation (Taboada Castro and Silva Hermo 1999). As consequence, the soils can show different profiles such as AR, AC, ABwR, ABtBwR or ABtR (Taboada Castro and Silva Hermo 1997). On steep slopes, and in the upper parts of the slopes, the soils present a thin and dark Ah horizon (sometimes mollic), with silt loam textures and pH around neutral. Soils with an AR profile are characterised as Leptosols, usually rendzic, and those with an AC profile as Regosols (calcareous), exceptionally, soils with a calcic horizon can be found. In flat or gently slope areas, soils are usually developed on colluvial deposits with Bw and/or Bt horizons where clay illuviation is observed. These soils are classified as Cambisols (in the absence of mollic or umbric horizons) and as Phaeozem when they have a mollic horizon and base saturation in B horizon is high. If they present an argic horizon and the A horizon is shallow, they are included in the GSR Luvisol or Alisol if decarbonation is intense (Taboada Castro and Silva Hermo 1997). Only in cases of very intense decarbonation soils with an argic horizon be characterized as Acrisols.

3.8 Soils Developed from Sedimentary Materials In Galicia there are several types of sedimentary materials from which different types of soils are developed, such as Tertiary clayey sediments from tectonic depressions, alluvial sediments from river basins and alluvial-marine sediments located around river mouths, coastal lagoons, as well as coastal sandy sediments. In the Tertiary tectonic depressions, the soils have a different evolution and mineralogical composition depending on their position in the depression and the degree of hydromorphism affecting them. The most evolved soils develop on the edges of these basins, characterised by the presence of argic horizons and, in some cases, with fragic horizons (Guitián Ojea and Macías 1976). Soils with fragipan, generally polycyclic, show several phases of illuviation and a mineralogy dominated by kaolinite, hematite and/or goethite (Macías et al. 1976). The soils have Ah horizons, sometimes umbric, with cambic and/or argic horizons as the most common subsurface diagnostic horizons. These are Cambisols or Umbrisols, with cambic

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horizon, Acrisols or Alisols with argic and without horizons, and soils with ‘stagnic properties’, due to waterproofing caused by clay illuviation and/or clayey substrate. In areas with recent continental sediments, the soils develop an organic matter rich A horizon (umbric) and sometimes with Bw horizons, which can be cambic. In any case, soils are diverse depending on the nature of sediment and the topographical position: Arenosols (eutric, dystric, calcareous) in coastal sandy sediments; Fluvisols, together with Regosols, Umbrisols or Cambisols in alluvial sediments. In the sediments of estuaries and coastal lagoons Fluvisols (eutrophic, dystric, calcareous, thionic) are developed. Depending on the vegetation they support and the degree of influence of the tides, soils can be sapropels (only uncovered at low tide) and marsh (not covered by the tide and supporting halophilic vegetation). This type of soils is characterised by high organic matter contents in the uppermost soil layers, pH values ranging from slightly acidic to neutral and a wide range of variation in Eh levels (Otero and Macías 2003).

4 Organic Soils In Galicia, peatlands and peaty soils systems have a homogeneous distribution and a considerable, but very fragmented, relative extension. They are mostly minerotrophic peatlands covering depressions associated with river courses, hollows resulted from intense weathering in granitic areas and glacial structures, and on all types of lithology, but there are also ombrotrophic peatlands in mountain areas with high rainfall (Pontevedra-Pombal et al. 1996). The latter peatlands are located at the southwestern limit of their European range (Pontevedra-Pombal et al. 2006), which makes them particularly important in scientific terms. They serve to analyse the effects of climate change (Castro et al. 2020), their role as carbon sinks as well as their great utility as records of environmental change (Pontevedra-Pombal et al. 2018) and human activity (Martínez-Cortizas et al. 1999). The soils developed in these ecosystems are various types of Histosols including: ombric, rheic, generally dystric, but occasionally eutrophic, ferric, hemic, sapric, and often drainic. The rheic Histosols of Galicia began to form during the Middle Holocene (8200–4200 years BP), while the ombric Histosols begin their development in the Early Holocene (10,000–8200 years BP) (Pontevedra-Pombal et al. 2017). While the physico-chemical properties of ombric Histosols are relatively homogeneous between peatlands, there is a large variability in the properties of rheic Histosols associated with the litho-hydrological nature of the catchment. Acidic to very acidic Histosols (pH 2.5–5.0) are the most abundant, but mesoeutrophic rheic Histosols (pH 5.5–7.3) also develop in association with basic and ultrabasic lithologies. The effective cation exchange capacity is low to moderate and, mostly, the cation abundance sequence in ombric Histosols is Mg+2 > Ca+2 and Al+3 > Na+ -K+ » Fe+2 and Mn+2 , while that of rheic Histosols is Al+3 > Ca+2 > Mg+2 > Na+ > K+ » Fe+2 and Mn+2 (Pontevedra-Pombal et al. 2001).

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5 Anthropogenic Soils Human activity has modified soil properties substantially through agricultural, livestock and forestry activities. In addition, these properties have also been altered due to land use changes associated with the expansion of urban and industrial areas. In this regard, Yaalon and Yaron (1966) considered that human-induced changes in soil formation processes should be recognised as an independent soil formation factor. More recently, Dror et al. (2022) maintains that, since the Anthropocene, humans are the main driving force modulating the action of traditional soil-forming factors. Undoubtedly, the most obvious effects of agricultural and forestry activity on soils are the mixing of horizons by tillage. As a result, soils show a tendency towards a diminution in organic matter content, loss of biological diversity, and several modifications in their properties resulting from different soil management activities (liming, fertilisation, slurry addition, etc.). Although many of the cultivated soils do not meet the diagnostic criteria for anthropogenic horizons, many of them have anthric properties due to the practice of liming, for which the qualifiers aric, by deep ploughing, and escalic, in the cultivated terraces widely distributed throughout Galicia and defining the landscape in some places, can be applied in several GSRs. Despite this, only occasionally some of these soils could be characterised as Anthrosols. Other soils with a strong human influence are Technosols, whose main characteristic is that they contain a significant quantity of artefacts. They are soils with very diverse properties that occupy small areas, generally urban soils (urbic) or mine soils (spolic), soils from places where urban wastes were deposited (garbic) or with transported materials (transportic). In the case of mining areas, Technosols tend to consist mostly of tailings, with strongly acidic soils being common where materials with sulphides are present. Low organic matter content is also frequent, although it can be higher if there are traces of carbonaceous materials, low cation exchange capacity and a high concentration of heavy metals in bioavailable forms (Monterroso et al. 1993). Nevertheless, soils from mining areas have shown remarkable improvements in their physicochemical properties because of environmental restoration processes (Monterroso et al. 1999; Rivas-Pérez et al. 2016).

6 Final Remarks Within a general trend towards acidification, the main processes of soil formation in Galicia located in well-drained systems are aluminosiallitization and monosiallitization. (Table 1). Aluminosiallitization takes place in surface horizons in the presence of organic matter and gives rise to horizons with high Al saturation of the cation exchange complex, abundance of Al (Fe)-humus complexes and non-crystalline forms of Al. In horizons B, C and saprolites, monosiallitization is moderate, under hydrolysis to acidolysis conditions. These soils, which can be grouped under the term ‘aluminic soils’ (Macías et al. 1982; García-Rodeja and Macías 1984), include

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Leptosols, Umbrisols, Cambisols and Regosols. When the parent material is rich in weatherable materials and the surface horizons are rich in organic matter, pedogenesis is oriented towards andosolization, resulting in abundant Al, (Fe)-humus complexes, non-crystalline aluminosilicates and ferrihydrite. Podzolization, mostly restricted to materials rich in quartz and poor in weatherable minerals, can also appear in granitic areas in cold humid mountain areas. On the other hand, the rejuvenation processes widely spread in Galicia lead to the predominance of weakly developed soils where gibbsite and phyllosilicates 1:1 are formed from the initial stages of pedogenesis (allitization followed by moderate monosiallitization in the B and C horizons and saprolites). On older geomorphological surfaces with a lithology rich in weatherable minerals, saprolites and intensely weathered soils dominated by kaolinite and goethite are preserved, generated through a process of fermonosiallitization which, in some cases, approaches ferrallitization. In ultramafic rocks and well-drained environments, weathering is incipient and consistent with the fermonosiallitic type while, under hydromorphic conditions, the medium richer in basic cations favours the formation of smectites through a process of bisiallitization (Macías and Calvo 1992b). The abovementioned processes result in a wide diversity of soils whose properties and typological characterisation are related to the nature of the parent material (Table 2). The most frequent types are weakly developed soils (Leptosols, Umbrisols, Cambisols and Regosols) due to rocks outcropping by erosive processes during the Quaternary and to the soil rejuvenation caused by colluviation processes on the slopes. On rocks rich in weatherable minerals (basic and metabasic rocks), in addition to the previous mentioned soil types, Andosols are also common. On stable geomorphological surfaces, relict alterations are preserved and soils with highly altered B horizons (only occasionally Ferralsols), and sometimes with clay illuviation (Acrisols), can be found. The formation of Podzols is restricted to materials very poor in alterable minerals, while other SRGs such as Phaeozems are found on ultrabasic and calcareous rocks, whereas Luvisols also occur in carbonate rocks. On sedimentary materials there are very weakly developed soils (Arenosols, Fluvisols) up to Acrisols and Alisols, sometimes with a fragic horizon, in old Tertiary and Quaternary sediments. In topographically depressed areas, whatever the parent material or in clayey sediments, appear soils with hydromorphism such as Gleysols and Histosols. Finally, human activity has led to the formation of Anthrosols and Technosols, the latter particularly linked to agricultural and mining activities and urban development.

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Table 1 Weathering mechanisms and processes in the soils of Galicia (adapted from Macías et al. 1982; García-Rodeja and Macías 1984; Macías and Calvo 1992a, b) Weathering degree

Horizon

Weathering mechanism

Weathering process

Colloidal system

Acidolysis/moderate acid complexolysis

Aluminosiallitization

OMC, PM, M, Md

Acidolysis/hydrolysis

Monosiallitization (Allitization)

OMC, PM, M, Md, K, Gb

Granitic rocks (PM: Q, F, M) Low/medium A B, C

Slates, phyllites and quartz-rich schists (PM: Q, M) Low

A

Acidolysis

Aluminosiallitization

OMC, PM, M, Md, H

B, C

Hydrolysis

Monosiallitzation

PM, M, Md, H

Sandstones and quartzites (PM: Q) Low

A, E

Strong acid complexolysis

Podzolization

OMC, PM, Md, OMC

Bh Bs, C

Moderate acidolysis Hydrolysis

Aluminosiallitization (Monosiallitization)

OMC Md, H, Gb

Biotite rich schists (PM: M, F, Q, Cl) Low

A

Acidolysis

Aluminosiallitization (Andosolization)

OMC, PM, M, Md, K, (Am)

Medium

A

Acidolysis / Hydrolysis

Monosiallitization (Aluminosiallitización)

OMC, PM, K, Q, H, Fe

B, C

Hydrolysis

Monosiallitization

K, Q, H, Fe, PM

B, C

Hydrolysis

Monosiallitization

K, Q, H, Fe

High

Basic and metabasic rocks (PM: P, A, Px, Cl, M) Low

A

Acidolysis

Aluminosiallitisation, Andosolization

OMC, PM, Am; K, Gb, H, Md

Medium

A

Acidolysis / Hydrolysis

Andosolization

PM, Am; K, Gb, H

B, C

Hydrolysis

Allitization, Fermonosiallitization

K, H, Fe, Gb

B, C

Hydrolysis

Fermonosiallitization

K, H, Fe

Fermonosiallitization Ferbiasillitization

PM, Cl, Cl-V

High

Ultrabasic rocks (PM: S, Cl, O, Px) Low/medium B, C Bg, Cg, Cr

Hydrolysis (Hypermagnesic system)

S, Sp, Fe

A amphiboles; Am materials with low degree of order; Cl Chlorites; Cl-V interstratified chloritevermiculite/smectite; F Feldspars; Fe iron oxides; Gb Gibbsite; H halloysite, kaolinite (low crystallinity); K kaolinite; M micas; Md degraded micas (micas, hydroxy interlayered vermiculites; interstratified mica-vermiculite); O olivine; OMC organo-metallic complexes; P plagioclases; PM primary minerals; Px pyroxenes; Q quartz; S smectites; Sp serpentine group minerals

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Table 2 Main Soil Reference Groups (SRG) and some common qualifiers according to the parent material in soils of Galicia SRG

Principal (secondary) qualifiers

Parent material

Leptosols

Lithic, nudilithic, skeletic, Umbric, Dystric, (Humic) Rendzic Mollic

All materials (but some sediments) Limestones Ultrabasic rocks

Umbrisols

Leptic, Cambic, Skeletic, Haplic, (Colluvic, Pachic, Hyperhumic) All materials (but some Mollic sediments) (Protoandic) Ultrabasic rocks Basic and metabasic rocks

Regosols

Leptic, Colluvic, Skeletic, Dystric Calcaric

All materials Limestones

Cambisols

Leptic, Dystric, Humic Andic, Sideralic, Chromic Eutric, Chromic

All materials Basic and metabasic rocks Ultrabasic rocks, Limestones

Andosols

Aluandic, Umbric, Dystric, (Colluvic, Fulvic, Hyperhumic)

Basic and metabasic rocks (occasionally in biotite-rich schists)

Podzols

Albic, Entic, Umbric, (Placic) Entic, Umbric, (Placic)

Quartzite and quartz-rich sediments Granitoids (continued)

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Table 2 (continued) SRG

Principal (secondary) qualifiers

Parent material

Acrisols

Fragic, Haplic

Old sedimentary deposits

Alisols

Chromic, Haplic

Limestones, old sedimentary deposits

Ferralsols

Humic, Chromic, Rhodic

Basic and metabasic rocks, biotite-rich schists

Phaeozem

Cambic, Haplic, (Colluvic, Chromic) Rendzic, Calcaric, Luvic

Ultrabasic rocks, Limestones Limestones

Luvisols

Haplic, Chromic, Endocalcaric

Limestones

Fluvisols

Dystric Subacuatic, Tidalic, Calcaric, Eutric (Humic, Sulfidic)

Fluvial sediments Fluvial-marine sediments

Arenosols

Dystric, Eutric, (Aeolic, Ochric)

Dunes and coastal sandy deposits

Gleysolsa

Histic, Umbric, Dystric, (Colluvic) Mollic

All materials Ultrabasic rocks

Histosols

Fibric, Hemic, Sapric, Ombric, Rheic, Dystric, (Hyperorganic)

Organic deposits

Anthrosolsb Plaggic, Hortic, Terric, (Escalic, Aric)

Cultivated soils (all materials)

Technosols

Mostly urban and mine soils

Urbic, Garbis, Spolic, Transportic

a In favourable topographical positions. Gleyic qualifier: Applicable to other SRGs under these conditions. b (escalic/aric/anthric) in other SRG

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References Calvo R, Macías F (1983) Transformaciones en la organización durante la alteración y edafogénesis de rocas graníticas de Galicia. An Edaf Agrobiol 40:1559–1572 Carballas T, Rodríguez-Rastrero M, Artieda O, Gumuzzio J, Díaz-Raviña M, Martín A (2016) Soils of the temperate humid zone. In: Gallardo JF (ed) The soils of Spain. World soils book series. Springer, Berlin, Germany, pp 49–144 Castro D, Souto M, Fraga I, García-Rodeja E, Pérez-Díaz S, López Sáez JA, Pontevedra-Pombal X (2020) High-resolution patterns of paleoenvironmental changes during the Little Ice Age and the Medieval Climate Anomaly in the north-western Iberian Peninsula. Geosci Front 11:1461–1475 Chesworth W (1973) The residual system of chemical weathering: a model for the chemical breakdown of silicate rocks at the surface of the Earth. J Soil Sci 28:490–497 Dror I, Yaron B, Berkowitz B (2022) The human impact on all soil-forming factors during the Anthropocene. ACS Environ 2:11–19 ESBN (European Soil Bureau Network European Commission) (2005) Soil Atlas of Europe. Office for Official Publications of the European Communities, L-2995 Luxembourg. 128 pp FAO (1998) World reference base for soil resources. World Soils Report No. 84, 88 pp. Rome FAO-UNESCO-ISRIC (1990) Soil map of the world: revised legend. World Soil Resources Report 60, 88 pp. FAO, Rome García Paz C, Silva BM, García-Rodeja E, Macías F (1986) Meteorización de las anfibolitas del macizo ‘Santiago-Ponte Ulla.’ An Edaf Agrobiol 45:1271–1298 García-Rodeja G, Silva BM, García Paz C, Macías F (1986) Propiedades de los suelos desarrollados sobre las anfibolitas de “Santiago-Ponte Ulla.” An Edaf Agrobiol 45:1271–1298 García-Rodeja E, Macías F (1984) Caracterizacion de suelos ácidos (Podsoles-Andosoles-Suelos alumínicos) de Galicia: relación con los procesos edafogeoquímicos. Actas 1er Congreso Nacional de la Ciencia del Suelo, vol II, pp 589–602 García-Rodeja E, Silva BM, Macías F (1987) Andosols developed from non-volcanic materials in Galicia (NW of Spain). J Soil Sci 38:573–591 Guitián Ojea F, López López I (1980) Suelos de la zona húmeda española X: suelos sobre serpentinas. I. Morfología y características generales. An Edaf Agrobiol 39:403–415 Guitián Ojea F (1967) Suelos de la zona húmeda española. I. Tipos principales y sus relaciones genéticas. An. Edaf. Agrobiol. 26:1369–1378 Guitián Ojea F, Carballas T (1968) Suelos de la zona húmeda Española. III. Ránker Atlántico. An Edaf Agrobiol 27:57–73 Guitián Ojea F, Carballas T (1969) Suelos de la zona húmeda española. V. Factores de formación: Material geológico. An Edaf Agrobiol 28:191–204 Guitián Ojea F, Macías F (1976) Suelos de la zona húmeda española. VIII. Suelos con fragipán 1. Morfología y datos generales. An Edaf Agrobiol 35:47–69 Huguet del Villar E (1935) Los tipos de suelo de Galicia. Las Ciencias, Año II(4):970–1000 Huguet del Villar E (1938) Soils of the Lusitano-Iberian Peninsula (Spain & Portugal). Thomas Murby & Co., London IUSS Working Group WRB (2015) World Reference Base for Soil Resources 2014, update 2015 International soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports No. 106. FAO, Rome Kaal J, Criado-Boado F, Costa-Casais M, López-Sáez JA, López-Merino L, Mighall T, Carrión Y, Silva Sánchez N, Martínez Cortizas A (2013) Prehistoric land use at an archaeological hot spot (the rock art park of Campo Lameiro, NW Spain) inferred from charcoal, synanthropic pollen and non-pollen palynomorph proxies. J Archaeol Sci 40:1518–1527 Kaal J, Costa-Casais M, Ferro-Vázquez C, Pontevedra-Pombal X, Martínez-Cortizas A (2008) Soil formation of “Atlantic Rankers” from NW Spain—a high resolution aluminium and iron fractionation study. Pedosphere 18:441–453 Kubiena WL (1953) The soils of Europe. Thomas Murby and Co., London

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López López I, Macías F, García Paz C, Guitián Ojea F (1984) Suelos de la zona húmeda española X: suelos sobre serpentinas. 3. Mineralogía. An. Edaf. Agrobiol. 43:1055–1075 Macias F (1980) Características micromorfológicas de podsoles y suelos podsólicos de la zona húmeda española. An. Edaf. Agrobiol. 39:879–898 Macías F, Calvo R (1992a) Suelos de la provincia de La Coruña. Ed. Diputación Provincial de A Coruña. A Coruña. 85 pp Macías F, Calvo R (1992b) Caractérisation pédogéochimique des sols de la Galice (NW Espagne) en relation avec la diersification lithologique. Mise en évidence d’un milieu de transition entre les domains tempérés et subtropicaux humides. CR Acad Sci Paris 315:1803–1810 Macías F, Calvo R (2001) Atlas de Galicia. Los Suelos. Tomo I, 173–217. In: Precedo, Sancho (eds) Atlas de Galicia. Tomo I. Sociedade para o Desenvolvemento Comarcal de Galicia, 50 pp Macías F, Calvo RM, García-Paz C, García-Rodeja E, Silva B (1982) El material original: su formación e influencia en las propiedades de los suelos de Galicia. An Edaf Agrobiol 41:1747– 1768 Macías F, García Paz C, Silva BM, García-Rodeja E, Taboada Rodríguez T (1988) Micromorfología y génesis de podsoles y suelos podsólicos. An Edaf Agrobiol 47:431–464 Macías F, Puga Pereira M, Guitián Ojea F (1978a) Suelos de la zona húmeda española. IX. Estudio de una catena sobre gabros. An Edaf Agrobiol 37:117–138 Macías F, Puga Pereira M, Guitián Ojea F (1978b) Caracteres ándicos de suelos sobre gabros de Galicia (NW de España). An Edaf Agrobiol 37:187–203 Macías F, Villar MC, Guitián Ojea F (1976) Suelos de la zona húmeda española. VIII. Suelos con fragipán 2. Mineralogía. An Edaf Agrobiol 35:111–125 Macías F, García Paz C, Giménez M, Villar M (1981a) El factor material de partida de los suelos de las Mariñas. 2. Alteración de los esquistos en medios bien drenados. Acta Científica Compostelana 17:265–291 Macías F, García Paz C, Giménez M, Villar M (1981b) El factor material de partida de los suelos de las Mariñas. 2. Alteración de los esquistos en medios confinados y con humedad alternante. Acta Científica Compostelana 17:247–263 Martínez-Cortizas A, Pontevedra-Pombal X, García-Rodeja E, Nóvoa-Muñoz JC, Shotyk W (1999) Mercury in a Spanish peat bog: archive of climate change and atmospheric metal deposition. Science 284:939–942 Monterroso C, Álvarez E, Fernández-Marcos ML, Macías F (1999) Geochemistry of aluminium and iron in mine soils from As Pontes, Galicia (N.W. Spain). Water Air Soil Pollut 110:81–102 Monterroso C, Álvarez E, Macías F (1993) Caracterización de los suelos de la escombrera de la mina Puentes (La Coruña) en proceso de restauración ambiental. Cuad Lab Xeol Laxe 18:307–316 Otero XL, Macías F (2003) Spatial variation in pyritization of trace metals in salt-marsh soils. Biogeochemistry 62:59–86 Pontevedra Pombal X, Nóvoa Muñoz JC, García-Rodeja E, Martínez Cortizas A (2001) Composición y propiedades de las turberas de Galicia. In: Martínez-Cortizas A, García-Rodeja E (eds) Turberas de Montaña de Galicia. Colección Técnica – Medio Ambiente, Xunta de Galicia, Santiago de Compostela, pp 129–139 Pontevedra-Pombal X, Castro D, Carballeira R, Souto M, López-Sáez JA, Pérez-Díaz S, Fraga MI, Valcárcel M, García-Rodeja E (2017) Iberian acid peatlands: types, origin and general trends of development. Mires and Peat 19:1–19 Pontevedra-Pombal X, Castro D, Souto M, Fraga I, Blake WH, Blaauw M, López-Sáez JA, PérezDíaz S, Valcárcel M, García-Rodeja E (2018) 10,000 years of climate control over carbon accumulation in an Iberian bog (southwestern Europe). Geosci Front 10:1521–1533 Pontevedra-Pombal X, García-Rodeja E, Martínez Cortizas A (1996) Caracterización edafogeomorfológica de las turberas de las Serras Orientais de Galicia. In: Pérez Alberti A, Martini IP, Chesworth W, Martínez Cortizas A (eds) Dinámica y Evolución de Medios Cuaternarios. Xunta de Galicia, Santiago de Compostela, pp 243–258. ISBN 978-8445316276

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Pontevedra Pombal X, Nóvoa-Muñoz JC, García-Rodeja E, Martínez Cortizas A (2006) Mountain mires from Galicia (NW Spain). In: Martini IP, Martínez Cortizas A, Chesworth W (eds) Peatlands: Evolution and Records of Environmental and Climate Changes. Developments in Earth Surface Processes 9:85–109, Chapter 4, Elsevier, 2006 Puga M, Macías F, Guitián Ojea F (1978) Pedological and geomorphological cycles in a catena of Galicia (NW Spain). CATENA 5:375–387 Rivas-Pérez IM, Fernández-Sanjurjo MJ, Núñez-Delgado A, Monterroso C, Macías F, ÁlvarezRodríguez E (2016) Evolution of chemical characteristics in an afforested coal mine dump over 20-year period. Land Degrad Develop 27:1640–1649 Rodríguez Lado L, Tapia L, Pérez Rodríguez M, Taboada Rodríguez T, Martínez-Cortizas A, Macías F (2016) Atlas digital de propiedades de suelos de Galicia. USC, Santiago de Compostela, España, 112 pp Silva BM, Macías F (1983) Transformaciones en la organización durante la alteración y edafogénesis de rocas esquistosas en Galicia. An Edaf Agrobiol 42:1867–1883 Silva BM, García-Rodeja E, Macías F (1984) Caracterización y génesis de los suelos sobre esquistos de Las Mariñas (La Coruña). An Edafol Agrobiol 43:523–546 Silva BM, García-Rodeja E, García Paz C, Macías F (1988) Génesis y clasificación de los suelos desarrollados sobre las anfibolitas de ‘Santiago-Ponte Ulla.’ An Edafol Agrobiol 47:867–885 Silva BM, Guitián Ojea F (1984) Horizontes B sobre materiales graníticos en Galicia. An Edafol Agrobiol 43:111–132 Taboada Castro MT, Silva Hermo BM (1997) Evolution of soils developed over limestone in a humid temperate region (Galicia, NW Spain). Agrochimica 41:85–96 Taboada Castro MT, Silva Hermo BM (1999) Factores de formación y propiedades de los suelos formados sobre calizas en Galicia. Cuadernos Lab. Xeolóxico De Laxe 24:121–139 Yaalon DH, Yaron B (1966) Framework for man-made soil changes-an outline of metapedogenesis. Soil Sci 102:272–277

Landscape Modeling and Environmental Implications for Vineyard Cultivation in NW of Spain Manuel Arias Estévez

Abstract The cultivation of the vine in Galicia (NW of Spain) has the particularity that it is carried out fundamentally in the valleys and slopes of rivers. This results in a high incidence of cryptogamic diseases. For this reason, copper-based fungicides have been applied to prevent or cure these diseases. This continuous application over the years caused Cu to accumulate in these soils, mainly in the superficial layers. On the other hand, due to the high slopes where this crop is planted, erosion phenomena are important and as a consequence the surrounding waters come into contact with sediments with high concentrations of Cu (more than the soils from which they come). This can negatively affect aquatic organisms that are subjected to high concentrations of Cu. Finally, soil microorganisms can also be negatively affected and even other crops that are later planted in the vineyard, due to changes in land use, which can negatively affect the production and quality of agricultural products. Keywords Vineyard soils · Soil contamination · Copper · Vineyard cultivation

1 Introduction Vine cultivation is spread over the 5 continents and occupies 6.97 million Ha of agricultural land (FAOSTAT 2018). Over the years, global vineyard cultivated land remains constant; however, in some continents such as Europe the trend is to decrease while in other continents such as Asia it is to increase. This crop in Europe occupies 3.23 million Ha (46% of the total) highlighting 3 countries with the largest cultivated area: Spain, France and Italy. Spain is the first country in the world in area cultivated per vineyard (13% of the total) which is distributed in more than 55 denominations of origin and 42 geographical indications, although the trend is to decrease in recent years (FAOSTAT 2018). M. A. Estévez (B) Department of Vegetal Biology and Soil Science, University of Vigo. Faculty of Science, As Lagoas S/N, 32004 Ourense, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_9

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In Galicia (NW of Spain) around 24.8 thousand Ha are cultivated, which represents 2.6% of the cultivated area in Spain. It is the fourth crop in importance in terms of the area occupied. Approximately 25 thousand cultivated hectares are covered by one of the 5 denominations of origin (“Monterrei”, “Rías Baixas”, “Ribeira Sacra”, “Ribeiro” and “Valdeorras”) or the 4 protected geographical indications (“Betanzos”, “Barbanza and Iria”, “Valle del Miño-Ourense” and “Ribeiras do Morrazo”). There are also some domestic farms that do not have any official protection. The five denominations of origin are fundamentally extended by the provinces of Ourense and Pontevedra and which we briefly describe below.

2 Monterrei Denomination of Origin This area is located to the south of the province of Ourense and is drained by the Támega river that rises on the edges of the basin in the San Mamede Mountain range and flows into the Duero river. The surface dedicated to the vineyard is about 3,000 Ha and only about 650 Ha are covered by the denomination of origin. The climate has Mediterranean characteristics with a continental trend with hot, dry summers and cold winters. The average annual temperature is 12.8 ºC and the average annual rainfall is 683 mm. The geological materials from which soils are formed consist of granites, schists, and sediments. The surface soils (0–20 cm) are acidic with an average pH value of 4.9 and with a highly variable organic carbon content, ranging between 3 and 55 g kg−1 and the textures are loam or sandy loam (Fernández-Calviño et al. 2009). Two sub-areas are distinguished in this denomination: “Val de Monterrei” Subarea and “Ladeira de Monterrei” Sub-area. Figure 1 shows cultivation areas that, in general, occupy the Támega river valley (Fig. 1a, b) but also occupy areas with a certain slope (Fig. 1c) and there are even areas where said slope is corrected to through the construction of terraces (Fig. 1d) and abandoned vineyard areas (Fig. 1e–f).

3 Rías Baixas Denomination of Origin This denomination covers towns in the western part of the province of Pontevedra as well as in the southwestern part of the province of A Coruña. Some 3500 ha of vineyards are cultivated in this denomination. In this case, the climate is predominantly Atlantic with wet winters, although there are quite a few differences depending on the different sub-zones such as: “Condado do Tea”, “O Rosal”, “Ribeira do Ulla”, “Soutomaior” and “Val do Salnes”. The most relevant geological materials are granites, sediments and fluvial terraces, although in some areas schists also appear.

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Fig. 1 Images of different vineyard growing areas of the Monterrei Denomination of Origin. a and b Vineyards in the Támega river valley; c Vineyards in slope areas; d terraces with vineyard cultivation; e and f Abandoned vineyards

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The soils generally have a higher pH than other denominations of origin, varying between 5.3 and 7.9 with an average of 6.6 (Fernández-Calviño et al. 2009). These higher pHs are attributed to the addition of mussel shells and other molluscs that notably increase the pH of these soils. On the other hand, the organic carbon content ranges between 22 and 66 g kg−1 and the textures are generally loamy-sandy (Fernández-Calviño et al. 2009). In general, the cultivation of the vine in this denomination of origin occupies the valleys and takes place in the form of a talk vineyard, unlike other denominations of origin. But other cultivation modalities similar to the other appellations of origin also appear (Figs. 1 and 2).

4 Ribeira Sacra Denomination of Origin The denomination of origin “Ribeira Sacra” is located at the confluence of the Miño and Sil rivers and encompasses municipalities in both the province of Lugo and the province of Ourense. The area occupied by vineyards is about 2500 ha, of which approximately half are registered with the Denomination’s Regulatory Council. In this denomination there are 5 subzones: “Amandi” Subzone, “Chantada” Subzone, “Quiroga-Bibei” Subzone, “Ribeiras do Miño” Subzone and “Ribeiras do Sil” Subzone. The climate is characterized by high temperatures in summer and mild in winter with an average annual temperature of 13.9 ºC in the Miño valley and 13.2 in the Sil valley. Precipitation is an annual average of 800 mm, although it is quite variable depending on the sub-areas in question, with the Miño sub-area being the rainiest with an annual average of 900 mm. The geology is highly variable, with metamorphic rocks such as schists, slates and gneiss (“Ollo de Sapo” Formation) being very common, but granitic rocks also appear in some areas. Geomorphologically, it is an area of high slopes where the vineyards occupy the slopes of the Sil and Miño rivers. This led to crops being carried out on terraces with a total or almost total correction of the slope and where the vines that remain today are fully integrated into the landscape. The soils are acidic with pHs between 4.3 and 6.3 and with a mean value of 5.0. Organic carbon contents range between 15 and 86 g kg−1 and soil textures are generally loamy-sandy (Fernández-Calviño et al. 2009). The cultivation of the vine in this denomination of origin is not very mechanized and requires significant human effort and, for this reason, it is called heroic viticulture. In general, the cultivated areas are on south-facing slopes, while the north-facing areas are currently mostly abandoned (Fig. 3).

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Fig. 2 Images of different vineyard growing areas of the Rías Baixas Designation of Origin. a and b Salnés Subzone; c and d Condado subzone; e and f Rosal subzone

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Fig. 3 Images of different vineyard growing areas of the Ribeira Sacra Designation of Origin. a and c general views; b, d e and f vineyards seen up close

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5 Ribeiro Denomination of Origin This Denomination of Origin is located in the western part of the province of Ourense at the confluence of the “Avia”, “Arnoia” and “Miño” rivers. In this denomination, some 3000 ha are dedicated to the cultivation of vines, occupying both river valleys and mountain slopes up to a height of about 450 m, in the latter case the slopes are often corrected by means of terraces parallel to the level curves. Climatically, it is a transition zone between an oceanic climate typical of coastal areas and a Mediterranean climate more typical of the inland areas of Galicia. The climate, in general, is characterized by being humid with an annual rainfall of 950 mm and an average annual temperature of between 14 and 16 ºC. Usually there is a strong summer drought. The geology is characterized by granitic rocks (granites and granodiorites) although metamorphic rocks also appear, especially schists and sedimentary materials, especially on the terraces of the rivers. The soils are generally acid, with values between 4.1 and 6.9 with an average of 4.9; Some values close to neutrality appear, which is attributed to the application of chicken manure to these soils. The carbon content ranges between 11 and 77 g kg−1 with an average value of 21 mg kg−1 and the predominant textures are loamy-sandy, although soils with loamy-clay-sandy and loamy textures also appear (FernándezCalviño et al. 2009). Figure 4 shows different vineyards in full production (Fig. 1a–c), abandoned vineyards (Fig. 1d) and vineyards installed on terraces (Fig. 1e).

6 Valdeorras Denomination of Origin The municipalities that belong to this appellation of origin are located in the eastern part of the province of Ourense, occupying the valleys and slopes of the Sil, Xares and Bibei rivers. Some 1350 ha are cultivated, occupying the slopes of the mountains up to approximately 400 m in altitude. Today the south-facing valleys and slopes are cultivated and the north-facing slopes are abandoned. The dominant climate is continental with Atlantic influence with an average rainfall of 850–1000 mm per year and an average annual temperature of about 11 °C. Metamorphic rocks are the predominant material based on slates and schists, although the presence of granites and sediments and fluvial terraces is also noteworthy. In the easternmost part of the denomination of origin there is also a strip of limestone material.

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Fig. 4 Images of different vineyard growing areas of the Ribeiro Denomination of Origin. a b and c active vineyards in valley areas; d abandoned vineyard; e vineyards on the edge of the Castrelo de Miño reservoir; f terrace vineyard built with granite stone

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The soils are acidic with a pH that varies between 4.4 and 6.5 with an average value of 5.6; the organic carbon content varies between 5 and 34 g kg-1 while the textures vary from sandy loam to clay loam depending on whether the soils are from the valley, with finer textures, or if they are from the mountainside, with textures sandier (Fernández-Calviño et al. 2018). Figure 5 shows some images of the cultivation of the vine in the Valdeorras denomination of origin, which is fundamentally cultivated in the valleys of the rivers, especially the Sil and, as previously mentioned, on the slopes facing south.

7 Some Environmental Effects Due to Vineyards The cultivation of vineyards in the NW of Spain is fundamentally extended to the south, both in the Atlantic zone and in the continental zone. This crop clearly marks the landscape of these areas, on some occasions, as in the case of the “A Ribeira Sacra” denomination of origin, becoming a strong tourist attraction in addition to its importance in wine production. On the other hand, due to the fact that the cultivation is carried out fundamentally on the slopes of rivers, where the relative humidity is very high and the incidence of cryptogamic diseases is also very high. Because of this, significant amounts of cupric-based antifungal agents are applied (Fig. 6). In fact, total Cu has been measured in the 5 appellations of origin (FernándezCalviño et al., 2018), obtaining results in most cases higher than the phytotoxicity limit established at 100 mg kg−1 (Kabata-Pendias and Pendias 2011). The results of total Cu in the different appellations of origin are presented in Table 1. Given that many of the vineyards are located on soils with high slopes (Fig. 7), during significant precipitation events, strong erosion occurs that produces sediments that end up in riverbeds. Normally these sediments have a higher concentration of Cu than the soils from which they come (Fernández-Calviño et al., 2008a). When these sediments come into contact with water, they can increase Cu concentration in this liquid media, which occurs mainly during rainy periods (Fernández-Calviño et al., 2008b). This can negatively affect living organisms in rivers. Another aspect to take into account is the change in land use from vineyard to another crop (Fig. 8). The abandonment of the vineyard causes the Cu present in the soil to pass into more recalcitrant forms (less bioavailable and in principle its potential toxicity is reduced (Fernández-Calviño et al., 2008b). This is very important when it comes to obtaining safe food. In soils with significant amounts of Cu, as is the case with vineyard soils.

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Fig. 5 Images of different vineyard cultivation areas of the Valdeorras Denomination of Origin. a General view of vine cultivation in the valley and on the mountainside; b and c Vineyards cultivated in the valley; d and e vineyards cultivated on slopes; f semi-abandoned vineyard without traditional agricultural work

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Fig. 6 Vineyard treated with cupric-base antifungal products

Table 1 Total Cu levels in the 5 denominations of origin studied “Monterrei”

“Rías Baixas”

“Ribeira Sacra”

“Ribeiro”

“Valdeorras”

Mean

100

139

260

248

174

Maximum

272

560

511

666

387

Minimum

25

33

122

47

55

Taken from Fernández-Calviño et al. (2018)

Also remarkable is the fact that the accumulation of Cu in vineyard soils causes negative effects on soil microorganisms such as: the decrease in the activity of the phosphatase enzyme, changes in the structure of the bacterial communities in the soil and an increase in the tolerance of the bacterial communities to copper (Fernández-Calviño et al., 2011; Fernández-Calviño and Bååth 2016). However, the effects are very different depending on the type of soil, which gives complexity to the establishment of Cu concentration limits with respect to its effect on microorganisms.

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Fig. 7 Vineyard in an area with marked slopes

Fig. 8 Abandoned vineyard with no current use

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References FAOSTAT (2018). https//www.fao.org/faostat/es/#data Fernández-Calviño D, Pateiro- Moure M, López-Periago E, Arias-Estévez M, Nóvoa-Muñoz JC (2008a) Copper distribution and acid-base mobilization in vineyard soils and sediments from Galicia (NW Spain). Eur J Soil Sci 59:315–326 Fernández-Calviño D, Rodríguez-Suárez JA, López-Periago E, Arias-Estévez M, Simal-Gándara J (2008b) Copper content of soils and river sediments in a winegrowing area, and its distribution among soil or sediment components. Geoderma 145:91–97 Fernández-Calviño D, Nóvoa-Muñoz JC, Díaz-Raviña M, Arias-Estévez M (2009) Copper accumulation and fractionation in vineyard soils from temperate humid zone (NW Iberian Peninsula). Geoderma 153:119–129 Fernández-Calviño D, Arias-Estévez M, Díaz-Raviña M, Bååth E (2011) Bacterial pollution induced community tolerance (PICT) to Cu and interactions with pH in long-term polluted vineyard soils. Soil Biol Biochem 43:2324–2331 Fernández-Calviño, Bååth E (2016) Interaction between pH and Cu toxicity on fungal and bacterial performance in solis. Soil Biol Biochem 96:20–29 Fernández-Calviño D, Nóvoa-Muñoz JC, Arias-Estévez M (2018) El cobre en suelos de viñedo del noroeste de la Peninsula Ibérica. Universidade de Vigo. Servicio de Publicaciones. ISBN: 978-84-8158-778-4 Kabata-Pendias A (2011) Trace elements in soils and plants, 4th edn. ISBN: 978-1-4200-9368-1. CRC Press

Peatlands Noemí Silva-Sánchez, Lourdes López-Merino, Olalla López-Costas, Álvaro Moreno Martín, Tim Mighall, and Antonio Martínez Cortizas

Abstract Galicia, an oceanic region located in the NW of the Iberian Peninsula, hosts a large diversity of peatlands. Here we briefly describe them, based on the body of research conducted since the mid 1940s, that was largely boosted since the 1990s. Galician peatlands are both present key landscapes, libraries of past landscapes and priority protected landscapes, i.e., windows to our past, present and future. Regarding typology, blanket bogs, raised bogs, and several types of fens can be recognized. They are mostly acidic and are mainly located in mountain areas. Grasses, sedges and reeds are the dominant components of the vegetation, while mosses are a much less relevant group compared to northern European mires. Peat formation started at the Early Holocene in many places, but there are also peatlands that started to form in the Mid and Late Holocene. As the peat deposit grows and increases in depth/age, peatlands store information in the form of biotic (pollen, spores, diatoms, organic compounds, etc.) and abiotic (minerals, spheroidal particles, etc.) indicators. Thus, they provide long-term (i.e., centuries to millennia) records of environmental changes—including human activities. Research developed in peatlands from Galicia enabled to reconstruct vegetation changes, atmospheric pollution (metals and organic N. Silva-Sánchez Consejo Superior de Investigaciones Científicas (INCIPIT-CSIC), Instituto de Ciencias del Patrimonio, 15705 Santiago de Compostela, Spain L. López-Merino · Á. Moreno Martín ENVIROVEG (Grupo UCM 910164), Unidad de Botánica, Facultad de Farmacia, Universidad Complutense de Madrid, 28040 Madrid, Spain O. López-Costas EcoPast (GI-1553), CRETUS, Area of Archaeology, Departamento de Historia, Facultade de Xeografía e Historia, Universidade de Santiago de Compostela, 15702 Santiago de Compostela, Spain T. Mighall Department of Geography and Environment, School of Geosciences, University of Aberdeen, Aberdeen, UK A. Martínez Cortizas (B) CRETUS, EcoPast (GI-1553), Departamento de Edafoloxía e Química Agrícola, Facultade de Bioloxía, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_10

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pollutants), climate changes (rainfall, temperature, and storminess) and dust deposition, as well as peatlands’ ecological evolution along the Holocene. The relevance of the ecosystem services provided by peatlands (hydric regulation, carbon-storage, biodiversity reservoir) together with the pervasive increase in the pressures and threats they are facing, prompted their inclusion as priority protection habitats in the Habitats Directive. Natura2000 Network is the legal European framework under which large efforts are been made to stablish the ecological bases for conservation, improve mapping, and implement new protection and restoration measures. Keywords Peatlands · Galicia · NW Iberia · Palaeoenvironment · Environmental change · Peatlands conservation · Natura2000

1 Introduction Global environmental change is a pressing issue in socio-political agendas. The conservation of carbon-storage ecosystems, such as peatlands, has been proposed as a key mechanism to buffer carbon dioxide emissions, as recognized in 2015 by the United Nations Framework Convention on Climate Change (UNFCCC) in the Paris Agreement. Peatlands mitigate the effects of climate change by acting as carbon sinks (Yu 2012), locking away carbon dioxide for centuries to millennia. However, they are rapidly being destroyed or degraded, leading to losses of ecosystem services with major environmental and economic consequences (Turetsky et al. 2015). In this sense, recognizing the value of research of (and on) peatlands is key to understanding the present, and ecologically very important, landscapes they form (Image 1). Peatlands are much more than present landscapes, as they are effective archives of environmental change, including both climate changes and human activities. As such, they are witnesses of past environments (Martini et al. 2006 and references therein) and, therefore, libraries of the past, the present and the, yet undetermined, future. In this sense, peatlands are time machines and, therefore, to formulate efficient conservation policies of these carbon sinks requires a deeper understanding of how ecosystem’s structure, function and services have changed over time. Peatlands also represent an ideal combination of both natural and cultural heritage, owing to their extant biodiversity and functions and their value in reconstructing the past. Galicia is the home to several types of peatlands at their European southernmost geographical limit due to this region’s unique climate and biogeography (Martínez Cortizas and García-Rodeja Gayoso 2001 and references therein). Furthermore, Galicia benefits from the interest of several national and international research groups that are focusing their investigations on understanding these peatlands. Therefore, a sound corpus of fundamental and technical knowledge is available and provides invaluable information for researchers interested in ecology, climate, soils, palaeoenvironment, botany, archaeology, geography, etc., as well as for environmental authorities for their effective management.

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Image 1 Tremoal do Pedrido mire, a raised bog in the Xistral Mountains. The mire is in the mist, due to the very humid climate of these mountains, one of the factors maintaining the characteristic peat cover of the area—but it is also a poetic representation of the value and fragility of peatland ecosystems. Photo credit Olalla López-Costas

In this chapter we first introduce the concept of peatland, a singular wetland system that has unique features, as well as the importance in the environments of Galicia. Second, we focus on the role of peatlands as environmental archives and how the palaeoenvironmental reconstruction is performed, providing a review of the work done on Galician peatlands and the variety of environmental proxies that have been analysed on them throughout the years. And, finally, we characterise Galician peatland habitats within the Natura2000 Network, their conservation and management is a very important task under the present scenario of Global Change.

1.1 Galician Peatland Landscapes at Present Peatlands are continental areas covered with peat of varying thickness. Galicia, in the Northwestern corner of Spain, is an Atlantic region of western Europe in which peatlands are found, and probably represents the southernmost limit of the distribution of some types (e.g., blanket mires). Galician peatlands were usually neglected in publications concerned with world peatlands distribution (Image 2), despite the abundant research done on them since the late 1990s (see Martínez Cortizas and García-Rodeja 2001; Pontevedra-Pombal 2002; Pontevedra-Pombal et al. 2006; and other references along this chapter). This has been recently, and partially, resolved as they have been recognised and included in the most recent peatland inventories (Tanneberger et al. 2017). Defining a peatland implies defining peat (Image 3). The latter is not as simple as it may seem, since several classifications in which different organic matter contents (or ash content) exist. The main characteristics of peat are: (i) it is an organic material largely composed of plant remains accumulated in situ, (ii) with varying degree of decomposition (from easily recognisable plant remains—fibric peat—to an amorphous, plastic, material—sapric peat—or any degree in between—hemic), (iii) brownish to black in colour, (iv) having more than 50% organic matter content (see Pontevedra Pombal et al. 2008).

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Image 2 (Left) World map showing peatland area per country (modified from Parish et al. 2008). (Right) Map of Galicia highlighting in red those areas with a larger concentration of peatland habitats (modified from Pontevedra-Pombal and Martínez Cortizas 2004)

Image 3 Sections of a peat core taken at the Terral mire in the Xistral Mountains. The upper picture shows different layers of the typical brownish fen peat at the top of the section, while the bottom of the section and the lower picture show a more detritus peat. Photo credit Álvaro Moreno Martín

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In some areas of Galicia where peat cover is extensive, as in the Xistral Mountains within the Septentrional Ranges, a continuous transition between peat and organicrich mineral soils occurs, which sometimes creates problems in determining the aerial extent of the peatlands. This is also governed by the thickness of the peat for an area to be considered as a peatland. In the context of the Natura2000 Network of priority protected habitats of Spain, a comprehensive framework accounting for this situation has been put in place in order to resolve these issues, which is discussed in the third section of this chapter. Almost all peatlands of Galicia are mires, that is to say, they actively accumulate peat at present (see Martínez Cortizas et al. 2008). However, examples of buried peat layers and relic peats also appear, particularly in coastal settings, which are not mires. Mires were formed by two main paths: terrestrialization and paludification. Terrestrialization occurs through the infilling, first with sediments and later with peat, of a water body (e.g., shallow lake, lagoon, etc.), and these mires are usually called fens. Paludification refers to peat accreting directly on flat, slopes or slightly convex surfaces, and the mires are usually called bogs. These two modes of formation constrain the hydrology of mires and largely determine their nutrient status: all mires formed by paludification are oligotrophic (i.e., poor in nutrients) as they are exclusively fed by rainfall and atmospheric deposition (ombrotrophic peatlands), while those formed by terrestrialization are fed not only by rainfall, but also by runoff waters and sub-superficial waters (minerotrophic peatlands), and are oligomesoeutrophic and, exceptionally, eutrophic (when receiving waters draining from calcareous materials, as for example Braña de Lamelas mire in Ancares Mountains; Pontevedra Pombal et al. 2006). Although not very abundant in Galicia, there are also raised bogs, mires that started their formation as fens and then evolved into bogs because the rapid peat accretion isolated the upper peat section (comprising metres of peat thickness) from the runoff and seepage waters and, thus, become highly oligotrophic. The mires Tremoal do Pedrido (Martínez Cortizas et al. 2020; Image 1) and Chao de Veiga Mol (Pontevedra-Pombal et al. 2019), in the Xistral Mountains, are good examples of raised bogs. Almost all main types of peatlands are present in Galicia. Regarding their topographic setting, most mires in Galicia appear as somewhat isolated entities, i.e., confined by a small catchment, as mesotopes of a few hectares to hundreds of hectares—essentially fens but also raised bogs. However, in the mountains located in the north (Septentrional Range) there are macrotope-scale formations of blanket bogs that extend from mountain tops to slopes, and flat surfaces, in a continuum of peat of varying thickness (Image 4). In this area, a wealth of fens also appear, some of which are connected through hydrological pathways in what has been called a fen mire complex (Image 5). These play an important role in rain-water storage and delivery to the network of streams of the area. Also, while most bogs have flat surfaces, i.e., lawns, and peat cuts, i.e., hags (in blanket bogs), fens are richer in microtopography units, with well-expressed low and high ridges, mounds, hummocks, hollows, and even permanent pools (Image 6). Raised bogs also tend to show spatial differentiation between the dome (of ombrotrophic peat) and the fen lag (of minerotrophic peat).

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Image 4 Macrotope-scale formations of blanket bogs at the Xistral Mountains. Photo credit Olalla López-Costas

Image 5 Fen mire complex, minerotrophic mires connected through hydrological pathways at the Xistral Mountains. Photo credit Olalla López-Costas

One of the most characteristic aspects of mires is their vegetation. Peat-forming vegetation is particularly adapted to partial or prolonged waterlogging, strong acidity, and the nutrient-poor conditions that prevail in these ecosystems. Vascular plants, like grasses (Poaceae), sedges (Cyperaceae) and reeds (Juncaceae), are the dominant components of the vegetation (Image 7). They tend also to show clear preferences regarding the mire hydrology, more species being present in drier than in wetter areas. In comparison with mires from boreal regions, mosses are a much less relevant group in Galician mires, with 10 species identified; as well as 41 species of other bryophytes and 3 species of lichens (Fraga Vila et al. 2001). Mosses, other bryophytes and lichens do not seem to show preferences regarding bog surface wetness or type of mire (bog or fen).

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Image 6 Example of the microtopographic richness in peatlands: (left) in a fen, Terral mire, (right) in a raised bog, Tremoal do Pedrido, at the Xistral Mountains. Photo credit: Álvaro Moreno Martín (left), Olalla López-Costas (right)

Image 7 Accounting for peatland flora means performing vegetation surveys. The three pictures show the research team surveying peatland vegetation in three different peatlands at the Xistral Mountains. While bogs (e.g., left picture) showed lower number of species, fens (e.g., right pictures) showed higher diversity owing to their more diverse microtopography. Photo credit Álvaro Moreno Martín (left), Olalla López-Costas (right)

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It is also interesting to note here that extant vegetation is just a snapshot of the dynamic mire vegetation. In some ways, vegetation is the texture of the landscape of Galician peatlands. These ecosystems can range from an intense green colour in spring to a mottled orange-red in autumn, owing to species of Juncaceae. It is worth sightseeing peatlands at different times of the year to observe this rainbow of colours. Plant composition also changes over short time scales but also at longer, from centuries to millennia, time scales. The investigation of the palaeoecological records hosted by the peat tells the hidden stories of the peatland landscapes as well as those of the surrounding areas—see Sect. 2. As it may be evident from what is described above, peatlands in Galicia are mainly located in mountain areas at elevations above 700 m a.s.l. that have relatively low mean annual temperatures (T < 10 °C) and high mean annual precipitation (P > 1600 mm) with low to moderate seasonality (Martínez Cortizas and Pérez Alberti 1999; Martínez Cortizas and García-Rodeja Gayoso 2001). Due to the oceanic nature of the region and the constant flux of humidity (rainfall and fogs) associated with the westerlies, some peatlands also occur at lower elevation in mountains near the coast. In contrast, in the inland, eastern mountains (150–200 km from the coast) peatlands tend to be located at a higher altitude (>1000 m a.s.l.) and associated with terrain depressions where the water table is at the surface, at least in autumn and winter (Image 2). We should bear in mind that the present climate may contribute to the preservation and growth of mires, but it is not responsible for their formation. Galician mires formed thousands of years ago. The available radiocarbon ages indicate that the oldest mires started to accumulate peat in the Early Holocene, some 10,000 years ago (e.g., Tremoal do Pedrido mire, Martínez Cortizas et al. 2020; Chao de Veiga Mol mire, Pontevedra-Pombal et al. 2019) and accreted peat at a rate of 1 cm every 20–25 years. This is comparable with what has been described for Iberian peatlands in general (Pontevedra-Pombal et al. 2017). Other mires started their formation in the Middle and Late Holocene. Thus, climate changes were involved in peat initiation at different times during the Holocene. To this we must add the role played by humans, at least since the Late Holocene. Many human activities (such as fires, deforestation, drainage, etc.) have contributed to the demise of the area covered by mires, while some past activities have also resulted in an expansion or change in the biogeochemical conditions of some mires. Ironically, in some cases the changes ended in a type of peatland ecosystem that is of priority protection in the Natura2000 Network (see the example of La Molina mire, an Asturian peatland in López-Merino et al. 2011). Unravelling these types of human-induced changes is also the aim of palaeoecological research in mires, and the obtained information on how peatland ecosystems respond to anthropogenic perturbations provides invaluable data that could be incorporated to habitat management. Mires are threatened ecosystems all over the world and Galicia is no exception. Despite what we already have indicated about human activities in the past, whether detrimental or favourable, no evidence of the direct use of peat in prehistory or historical times exists in Galicia, and recent exploitation has been quite limited (in Montes de Buio). Past atmospheric pollution has been recorded in several peatlands

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Image 8 The “greening” due to expansion of pasture areas facilitated by the roads and trails built for wind farms. Source Google Earth

of the area (see Sect. 2), but it seems not to have damaged the ecosystem functioning of the mires. Drainage of mires for forestry and mire-to-pasture conversion with superficial fires are by far the most serious threats to Galician peatlands, together with the more recent construction of wind farms (see Sect. 3.2). While the production of wind energy is a “green” objective in itself, the opening of new roads and trails has given access to areas that were somewhat remote, affecting the mires—as with their transformation to pasture (Image 8).

2 Palaeoenvironments Reconstructed Using Peat Records Palaeoenvironmental research utilizes environmental archives to analyze a series of indicators in order to build long-term records of environmental change. An environmental archive is a system that stores and preserves the evidence of past environmental change and that, according to the International Atomic Energy Agency: (i) has high temporal resolution, (ii) is sensitive to environmental changes, (iii) records continuous environmental time-series, (iv) has a global distribution, and (v) could be chronologically dated. Therefore, such information provides insights to infer environmental conditions that occurred centuries, thousands or, even, millions of years ago. Some examples of paradigmatic archives are ice cores, tree rings, corals, sediments, etc. Peatlands meet the criteria to be considered excellent archives of environmental change as well. They usually cover continuous Holocene time spans that can be easily radiocarbon dated owing to the large, in-situ accumulated, organic matter

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content that forms the peat itself. In addition, the accumulation of peat under different environmental conditions affects its physicochemical properties as well as the stored biological remains, providing insights into past environmental variability. Finally, although most peatlands are located in the Northern Hemisphere, they can also be found in the Southern Hemisphere (Image 2). Therefore, peat archives (Godwin 1981) are books that store information in the form of environmental records of the changes occurred over time (Image 9). This environmental information can be read using different languages or, the socalled palaeoenvironmental proxies. Proxies are indicators of past environmental changes that inform about varied environmental properties. Some examples of proxies analyzed in peat archives are fossil organisms or peat properties. These two examples epitomize how proxies are traditionally divided in two main categories, i.e., biotic and abiotic. Biotic proxies, which are very well preserved in the anaerobic waterlogged conditions of peat, and mainly have a botanical (such as pollen, fern and algal spores, and plant macrofossils) and zoological origin (invertebrates, testate amoebae), can be studied to reconstruct biological time-series. Both micro- and macro-remains are considered together, providing a way to reconstruct from regional landscape to local peatland biodiversity and, hence, their changes over time. Abiotic proxies are the physicochemical properties of the peat, including the study of inorganic and organic chemical properties as well as physical features such as loss-on-ignition, density, colour, pH, etc.

2.1 Galician Peatlands as Archives of Environmental Change As Galicia hosts an extraordinary amount of peatlands owing to its climate and topography, palaeoenvironmental research has been prolific. As most of the peatlands in Galicia are mountain mires (Image 2), as aforementioned, most of the palaeoenvironmental studies performed are on mires located in mountain areas, such as the Xistral Mountains of the Septentrional Ranges (e.g., Ramil-Rego 1992; Martínez Cortizas et al. 1997a, b, 1999, 2002, 2005, 2007, 2012, 2020; Mighall et al. 2006; Pontevedra-Pombal et al. 2012a, b, 2019; Stefanini et al. 2017), the Ancares Mountains (e.g., Muñoz-Sobrino et al. 1997), the Queixa Mountains (e.g., Santos Fidalgo 1992; Maldonado Ruiz 1995; Santos et al. 2000a, b) and the Bocelo Range (Taboada Castro et al. 1993; Aira Rodríguez et al. 1994; Silva-Sánchez et al. 2014; Martínez Cortizas et al. 2021). However, and although very infrequent, coastal peat settings have also been analyzed (Santos Fidalgo et al. 1993), usually with peat layers in between sedimentary facies (Bao et al. 2007). Pollen is the most studied biotic proxy so far as well as one of the earliest indicators to be analyzed in samples from Galician peatlands (e.g., Bellot and Vieitez 1945; Menéndez Amor and Florschütz 1971; Menéndez Amor 1969, 1971; Jato 1974; Törnqvist et al. 1989; Aira Rodríguez et al. 1992, 1994; Ramil-Rego 1992; Santos Fidalgo 1992; Ramil-Rego and Aira Rodríguez 1993a, b, c, d, 1994, 1996; RamilRego et al. 1993, 1994, 1998; Díaz Losada et al. 1994; Ramil-Rego and Taboada 1994;

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Image 9 Coring of peatlands at the Xistral Mountains for palaeoenvironmental research. (Left) Coring of Terral fen with a Russian peat corer in 2022. (Right) Coring of the Tremoal do Pedrido bog with a Waardenar peat corer in 2017. Photo credit Noemí Silva-Sánchez (left), Olalla López-Costas (right)

Maldonado Ruiz 1995; Muñoz-Sobrino et al. 1997, 2005; González and Saa 2000; Santos et al. 2000a, b). Holocene pollen records inform us about postglacial vegetation development in Galicia: the spread of deciduous forests comprising deciduous oaks, hazel, birch, alder, etc. In addition, they reconstruct periods of forest retreat with the expansion of shrubs and herbs, that in some cases have been related to climate change events and in other cases with anthropogenic disturbance. In the last few decades, non-pollen palynomorphs (NPP, Image 10) and charcoal analyses have also been included in the study of micro-remains in the peatlands of Galicia (Mighall et al. 2006; Silva-Sánchez et al. 2014; Stefanini et al. 2017). Charcoal analysis informs of past fire activity, while NPP include spores of ferns, fungi, algae, together with other botanical or faunal remains appearing in palynological samples, and provide invaluable information to reconstruct patterns of local change and, thus, those processes directly affecting peatland systems (Image 11). On the other hand, pollen records reconstruct, most likely, landscape-scale changes. Other biological proxies include plant macrofossil remains that, although less frequently studied in Galician peatlands, also offer botanical information for the reconstruction of local vegetation changes (Ramil Rego et al. 2001; Rubiales et al. 2012; Castro et al. 2015, 2020; Souto et al.

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2016, 2017, 2019; Stefanini et al. 2017). Phytoliths, microscopic silica structures found in some plant tissues, have been studied preliminary in some samples in a Xistral mire (Fernández et al. 2010). Most recently, other organic proxies are being evaluated, such as diatoms (Bao et al. 2007), microbiological functional diversity (Pérez-Rodríguez and Martínez Cortizas 2014) and testate amoebas (Carballeira and Pontevedra-Pombal 2021). Microbial functional diversity has only been preliminarily analyzed in the first 100 cm of a Xistral mire. Testate amoebas have been studied in many European peatlands as indicators of their ecological status, whereas in Iberia these kinds of studies are lacking. The only cited one assessed the ecological status of 37 western Iberian peatlands but in superficial peats only. The study of physical properties has also been conducted on the peatlands of Galicia in combination with some palynological works or being exclusively analyzed in several peat cores (Taboada Castro et al. 1993). These physical properties range from peat description, loss-on-ignition, pH, density, to color following standardized classifications. More recently, CIELAB colorimetry is providing quantitative information to perform color classification that, compared with organic matter properties, has the potential to study the organic matter properties of the peat (Sanmartín

Image 10 Microphotographs of some of the hydro-hygrophytes (pollen types of local mire communities) and NPP that could be found in Galician Holocene peat records. a Cyperaceae pollen, b Typha angustifolia type pollen, c Myriophyllum verticillatum pollen, d Potamogetonaceae pollen, e Pteridium aquilinum spore, f Invertebrate remains of Acari (Oribatei), g HdV-52 (animal hairs of unknown origin), h Invertebrate remains of Alona rustica (postabdomina of Cladocera), i Algal colonies of Pediastrum (Chlorophyceae), j Invertebrate Gyratrix hermaphroditus oocytes (Neorhabdocoela), k Basidiospores of Entorrhiza (Basidiomycota), l Ascospores of Sordaria-type (Ascomycota), m Ascospores of Byssothecium circinans (Ascomycota), n HdV-18 (ascospores of unknown origin), o cf. Persiciospora sp. (HdV-124). Photo credit Lourdes López-Merino

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Image 11 Coprophilous fungi living on dung found in a peatland at the Xistral Mountains. The spores of these species, considered a NPP (see the example of Sordaria-type in Image 10), appear in the palaeoecological records and provide information about the presence of herbivores in the peatland. Photo credit Olalla López-Costas

et al. 2015). However, although pollen analysis was the pioneering palaeoenvironmental technique in the study of Galician peatlands, geochemical analyses, that usually are combined with the study of physical properties, have taken over and are now the most abundant. The elemental composition of peat provides information on organic matter (e.g., elements such as C, H, N, S) as well as lithogenic elements and heavy metals, allowing the reconstruction of the dynamics of the organic matter, fluxes of mineral input including dust deposition and atmospheric metal pollution, respectively. Researchers from the Universidade de Santiago de Compostela initiated these analyses in the 1990s (Martínez Cortizas et al. 1997a, b, 1999), studying ombrotrophic peats from the Xistral Mountains, opening a very productive research program focusing upon palaeoclimate and atmospheric palaeopollution reconstruction in Galicia, that has identified patterns and processes of environmental change driven by both climate change and human interference (Rauch et al. 2010; Pontevedra-Pombal et al. 2012a, 2019; Martínez Cortizas et al. 2020). These studies have also been enriched by Pb isotope analyses, that help to elucidate the origin of the atmospheric metal pollution for the last five millennia (Martínez Cortizas et al. 2002, 2012; Kylander et al. 2005), and by radionuclide dating to accurately date the most recent peat layers (Olid et al. 2008). Organic geochemistry (PontevedraPombal et al. 2001; Buurman et al. 2006; Kaal et al. 2007) and molecular chemistry of vegetation markers have helped to reconstruct hydrological changes and species composition of peat (Schellekens et al. 2011), whilst the reconstruction of polycyclic

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aromatic hydrocarbons (Pontevedra-Pombal et al. 2012b) revealed their atmospheric deposition occurred prior to the Industrial Revolution due to earlier human activities. Finally, the study of the molecular composition of peat using spectroscopy is opening new avenues of research not only to study peat decomposition, but also to investigate peat mineral content (Martínez Cortizas et al. 2021).

2.2 Multi-proxy Records and the Use of Galician Peatlands’ Records in Local, Regional and Global Reconstructions While it is fascinating the palaeoenvironmental histories that have been unraveled using biotic and abiotic proxies alone when studying Galician peatlands, the ideal situation is when both kinds of approaches can be combined to deliver more comprehensive histories of change and no circular reasoning is involved when interpreting, for example, the response of biological proxies to palaeoenvironmental perturbation reconstructed with the same proxies. The combination of palynological and geochemical approaches has delivered in depth long-term biotic and abiotic proxy records on both minerotrophic (Silva-Sánchez et al. 2014) and ombrotrophic (Martínez Cortizas et al. 2005, 2007) mires that have enabled reconstructing patterns of environmental change and the processes behind them. At Cruz de Bocelo mire, a fen located at the Bocelo Range, a combination of high-resolution physical (density, loss-on-ignition), geochemical (elemental composition), and palynological (pollen and NPP) records (Silva-Sánchez et al. 2014) allowed the researchers to link forest cover with soil erosion and changes in the hydrology of the mire for the last three millennia, disentangling whether the detected changes were related to climate change and/or human activities. Similarly at Pena da Cadela mire, a blanket bog located at the Xistral Mountains, the combination of high-resolution pollen and lithogenic elements (Martínez Cortizas et al. 2005) examined the processes behind the variation in the fluxes of lithogenic elements supplied to the bog by atmospheric deposition. This variation was linked to changes in the forest cover that were, in turn, driven by human activity. In the same bog, Martínez Cortizas et al. (2007) combined NPP with the records of δ15 N, C/N, Se, Br, I, Hg and Ti, and they were able to show the relationship between wetter and drier climate phases and peat decomposition which affected the concentration of some pollutants in the peatland. As an additional example of the potential of the combination of proxies, we show the records of four different proxies from three different mires studied at the Xistral Mountains and compare the information they provide for the last 3000 years. Pollen curves—main tree and shrub types—and the microcharcoal record of the Pena da Cadela blanket bog (PDC, Mighall et al. 2006) are compared with the lead isotopic relationship Pb206 /Pb207 of the Penido Vello blanket bog (PVO, Kylander et al. 2005) and the preliminary macrocharcoal record of the Tremoal do Pedrido raised bog (TPD, unpublished results) (Image 12). This combination detects three main phases of fire activity at both regional level in PDC by microcharcoal and local level at

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TPD by macrocharcoal. The first phase of fire activity seems to be related to Roman mining and or metallurgical activities, as a change in the lead isotope signal in PVO indicates atmospheric metal pollution. Woodlands were also affected, with a decline in oak and hazel pollen as recorded in PDC, although once pollution finished, the woodland regenerated. The second phase of fire activity, during the Early Middle Ages is also coeval to a rise in atmospheric metal pollution, and the woodland was also affected. Interestingly, woodland did not regenerate after this anthropogenic pressure, and shrubs expanded, meaning a tipping point in the regional landscape of the Xistral Mountains, hence a threshold was crossed. Finally, metal pollution has increased since the last millennia, with the coeval expansion of the shrubland, except during the third phase of fire activity in which the shrubland was affected. This is most likely because the fire was not to obtain fuel from the woods, but to open the landscape for pasture. The multi-proxy approach has also been applied to other Iberian peatlands (in the Central Pyrenees, Aragón: González-Sampériz et al. 2006; in Asturias: LópezMerino et al. 2010, 2011, 2014; in the Gata Range in western Iberia: Silva-Sánchez et al. 2016; in the Basque Country: Pérez-Díaz et al. 2016), confirming the findings of the usefulness of multi-proxy studies. The good temporal resolution and the quality of Galician peatlands (e.g., Martínez Cortizas et al. 2000; Pontevedra-Pombal et al. 2006) make them important archives when compiling regional or global trends. In this sense, proxy records from them have been used in both environmental and archaeological review papers. For example, and related to archaeological perspectives, Fábregas Valcarce et al. (2003) reviewed NW Spain environmental proxy records covering the Chalcolithic in order to understand social dynamics, and Martínez Cortizas et al. (2009) those covering from the Holocene onset to the V century BC to highlight the coupling of environmental change and human activities. In addition, Silva-Sánchez (2015) reviewed northern Iberia palaeo-records in order to understand the impact that mining and metallurgical activities had on forests from the V to the XI centuries AD, while López-Costas (2021) included palaeoenvironmental reconstructions performed on Galician peatlands as a suitable way to approach every-day life during Prisciliam times (IV to VI centuries AD). Several reviews of palynological records, including those from Galician peats, have also evaluated the reliability of the data, vegetation dynamics, peatland genesis and dynamics (Ramil-Rego et al. 1996, 1998, 2000, 2001, 2018; Muñoz Sobrino et al. 2007), and have assessed Holocene climatic events in N and NW Iberia (Muñoz Sobrino et al. 2005; Ramil-Rego et al. 2009). They have also been used in Iberian reviews on Holocene vegetation history (Carrión et al. 2010). Finally, geochemical proxy records have been included in more regional reviews in order to understand one of the coldest stages of the Holocene—the Little Ice Age—in Iberia (Oliva et al. 2018), or in global reviews on the reconstruction of atmospheric metal pollution (Bindler 2006; Biester et al. 2007) or the response of peatlands’ carbon sink to climate change (Gallego-Sala et al. 2018).

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Image 12 Example of a comparison of proxies from several bogs at the Xistral Mountains for the last three millennia (see text for explanation). a Microcharcoal concentration record from PDC (Mighall et al. 2006). b Pollen records of selected trees (deciduous Quercus and Corylus) in green and selected shrubs (Erica and Calluna) in gold from Pena da Cadela blanket bog (Mighall et al. 2006). c Record of 206 Pb/207 Pb from PVO (Kylander et al. 2005). d Macrocharcoal concentration record from TPD (Álvaro Moreno Martín, preliminary unpublished results). For all proxies, dots indicate the data, and the curves represent three-sample moving averages for smoothing purposes

3 Peatlands as Priority Protection Habitats 3.1 Why Do Peatlands Matter? Peatlands fulfil important ecological functions: (1) Peatlands are featured biodiversity reservoirs, at species, ecosystems and genetic levels. Peatlands are often considered as relatively species-poor ecosystems but with large biodiversity importance owing to the particular habitats they provide for some peatland typical species and the genetic pools of other nonrestricted peatland species (Images13 and 14). Fens are the mires hosting a larger plant species richness, with continental fens richer than oceanic fens. Bogs are

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usually less rich, but the drier areas of the bogs have a higher species richness than the wetter areas. Vegetation surveys in Galician mires have recorded up to 182 species (133 vascular plants, 46 bryophytes—11 of the Sphagnum genus—and 3 lichens). However, just 40 species could be considered as the main constituents of the vegetation cover (Fraga Vila et al. 2001). From the total of inventoried species, 26 are protected species, 11 are present in inland fens, 17 are present in the oceanic fens, and 9 in the blanket bogs (Martínez Cortizas et al. 2009). Regarding ecosystem diversity, the variety of Galician peatland habitats is noteworthy. Here, there is the southern limit of blanket bog distribution, which is represented by the Xistral Mountains macrotope, with a good representation of other types of bogs and fens as well (see Sect. 1). From the genetic point of view, Galician peatlands, as it tends to occur in other Atlantic locations, are isolated, providing exceptional conditions to retain characteristic genetic pools. (2) Peatlands are involved in the regulation of several environmental processes at local, regional, and global scales. Peatlands are considered among the best carbon sinks of the world, which makes them a key factor in the regulation of global climate. It is estimated that although they only occupy 3% of the global land area (Yu et al. 2010), peatlands contain about 25% of global soil carbon—twice as much as the world’s forests (Joosten and Couwenberg 2008). A global review by Gallego-Sala et al. (2018) highlighted that Galician peatlands are among the ones with a higher sink capacity at a global scale, with a mean annual carbon accumulation rate of 90 g C m−2 yr−1 during the last millennium. Another study estimates that the peatlands of Xistral Mountains alone store 8.6 × 106 Tn of carbon (Gómez-Orellana et al. 2014). At a local and regional level, due to their capacity of water storage, peatlands influence local climate affecting both temperature and humidity conditions, throughout the evapotranspiration process. Besides climate, peatlands are also important in the regulation of hydrological processes and water quality at a basin scale. They provide a water reservoir mitigating both floods and drought and they retain multiple pollutants, particularly those with a net negative charge, as due to its organic nature, peat is mostly positive charged. (3) Peatlands have a high historical and cultural value. Peatlands are among the few ecosystems that record their own environmental history at both local, regional and even hemispherical levels. Progressively, as the peat accumulation grows thicker, peatlands build a record of past environmental changes, including those linked to human activity. Therefore, they are invaluable from both environmental and cultural heritage perspectives.

3.2 Peatland Pressures and Threats Commercial peat extraction and drainage for forestry or agriculture have caused the destruction of many peatlands in Europe. Quantifying the extent of this process is difficult due to a lack of data. However, there is a general agreement that for a long time, many types of wetlands, including peatlands, have been seen as unpleasant

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Image 13 Galician peatlands are important biodiversity reservoirs. Some of the species they host are typical of peatlands whereas others also occur in other habitats. a Sphagnum sp., b Eriophorum angustifolium, c Parnassia palustris, d Calluna vulgaris, e Erica mackaiana, f Drosera rotundifolia, g Myrica gale, h Carex panicea, i Succisa pratensis. Photo credit Olalla López-Costas (a, b, d, e, i), Noemí Silva-Sánchez (c, f, g), Álvaro Moreno Martín (h)

spaces that should be desiccated in order to make them suitable for land use. Even nowadays, despite the rise in the awareness about peatlands’ ecosystem services, they continue suffering from many of the traditional pressures and threats together with new challenges. Traditionally, the most important pressure for Galician peatlands was drainage for forestry and agriculture. In Galicia, no traditional use of peat as fuel is documented, as timber was preferred for fuel. Peat extraction is, therefore, a recent process of minor importance with only one commercial mine with limited action at Montes do Buio in the Xistral Mountains (Image 15). Nowadays, the occupation of peatland habitat with infrastructures such as roads, wind farms, etc., as well as intensive grazing, land use change by fertilisation or fires,

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Image 14 Galician peatlands are important biodiversity reservoirs of fauna as well. a Arandus diadematus male, b Pelophylax perezi, c Trypocopris sp., d Arandus diadematus female, e Rana iberica, f Aeshna isoceles. Photo credit Noemí Silva Sánchez (a, d, e, f), Olalla López Costas (b), Álvaro Moreno Martín (c)

are becoming increasing threats (Image 16). In the case of the Galician peatlands, the spread of wind farms, and the associated roads to their maintenance, has made peatlands more accessible in areas that were kept intact because of their remoteness, meaning that they are now being transformed to pasturelands and afforestation plantations (Image 17). Even in the Xistral Mountains, regardless of the concomitant LIC status of the area, the ongoing rapid development of wind energy in the late 1990s led to the construction of 23 wind farms (25% of the Galician wind plan). Here, the impacts of wind farms have been directly related with the reduction of the Carici durieui Eriophoretum angustifolii endemic community (i.e., the most representative plant association of the Xistral Mountains blanket bogs) and its substitution by wet heaths or humid grasslands, in addition to the appearance of new communities (wet meadows) (Fraga-Vila et al. 2008). The emergence of global climate change contributes to the value of the role of peatlands as global carbon reservoirs. However, it also creates a new challenging scenario for peatlands. The carbon sink potential of peatlands depends on the balance of carbon uptake by plants and microbial decomposition. The rates of both these processes will increase with warming. A recent study by Gallego-Sala et al. (2018) concluded that present-day global sink capacity of peatlands will increase slightly until around AD 2100 but decline thereafter. Minerotrophic peatlands (fens), besides being affected by the abovementioned direct actions on the peatland itself, are also particularly sensitive to the indirect effects of transformations at a catchment level, such as hydrological modifications, soil erosion, soil and water pollution, soil fertilization as well as changes in soil

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Image 15 Evolution of peat extraction process at O Buio (Xistral Mountains). Top: Orthophoto from the American Flight (1956–57). Middle: orthophoto from the SIGPAC (Geographic Information System for Agricultural Parcels) flight (1997–2003). Latest orthophotos of the Spanish National Plan for Aerial Orthophotography

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Image 16 Many Galician peatlands are in the process of being transformed into pastures and afforested lands. a Mosaic land with pastures and shrubland occurring over peat soils (Xistral Mountains). b Afforestations with Eucalyptus globulus and wind farms in the margins of a fen (Bocelo Range). c Drained fen still preserving some of its microtopographical features although with an evident vegetation change in favour of grassland (Barbanza Range). d Wild horses drinking in a pond (Xistral Mountains). The ponds in peatland areas have traditionally offered a drinking supply for grazing animals. Low pressure grazing, contrary to intensive grazing, is not considered a risk for peatlands. Photo credit Noemí Silva-Sánchez (a, b, c), Olalla López-Costas (d)

use (Silva-Sánchez et al. 2014). In Galicia, one of the most common degradation forms of fens is Eucalyptus (and sometimes Pine) afforestation on the margins of the peatlands which, through the increased water demand of the plantation, leads to peatland drainage. Fens are particularly sensitive because they often occur in small patches within other habitat types, complicating their inventory and, hence, their protection. Moreover, the fact that the whole catchment has to be considered makes them particularly vulnerable.

3.3 Legislation on Peatlands: Natura2000 Network and International Conventions Globally, the importance of peatlands and the need for their conservation, restoration and sustainable use is increasingly recognized (Image 18). Adopted in 1992, the Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and wild fauna and flora established the EU wide Natura2000 ecological network of protected areas. The Interpretation Manual of European Union Habitats—EUR28 defines a total of 12 habitats of community interest within the groups 71: Sphagnum acid bogs, 72: Calcareous fens and 73: Boreal mires. Sphagnum acid

170 Image 17 Evolution of the road construction, wind farm creation, pasture spread and afforestation process in a sector of the Xistral Mountains. a Orthophoto from the American flight (1956–57). b Interministerial flight photograms (1973–1986). c Quinquennial flight photogram (1998–2003). d Orthophoto from the SIGPAC (Geographic Information System for Agricultural Parcels) flight (1997–2003). e Latest orthophotos of the Spanish National Plan for Aerial Orthophotography

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bogs are well represented in Galicia, whereas the appearance of Calcareous fens is limited to exceptional cases. Another relevant mire habitat would be the type 91D0: Bog woodland, whose presence in Galicia has only been recently identified (Martínez Cortizas and Silva-Sánchez 2019). The mire habitat types defined by the EUR28 have been subjected to some degree of criticism due to the lack of consistent criteria in the habitat definitions, which undermine the coherence of the typology. This is particularly notorious within the group 72 where a mixture of habitats related with marshlands, tufa formations and peatlands are considered all together (see Martínez Cortizas et al. 2019). Despite this, Directive 92/43/EEC has greatly contributed to promoting the awareness of member countries about habitat conservation and monitoring. All the member states have the compromise of reporting every six years the land occupied by their priority habitats, their conservation status and the future perspectives. This led to a big effort at the national level to standardize the variables and procedures through which these aspects will be determined. The projects ‘Preliminary ecological bases for the conservation of habitat types of community interest in Spain’ (VV.AA. 2009) and ‘Methodologies for the monitoring of the conservation status of Spanish habitats’ of the Spanish Ministerio de Medio Ambiente, y Medio Rural y Marino and Ministerio para la Transición Ecológica y el Reto Demográfico are good examples of these efforts. Among the main products of the working group on peatlands and parapeaty habitats, is a specific typology for mire and other para-peaty habitats (Martínez Cortizas et al. 2009; Martínez Cortizas and Silva-Sánchez 2019), the definition of a methodology to determine the total land occupied by mires and para-peaty habitats (Pontevedra-Pombal et al. 2019a; b), the selection and description of variables to be used to determine the conservation status of the parameter “structure and function” (Silva-Sánchez et al. 2019a, 2019b), the “future perspectives” for mires and para-peaty habitats (Silva-Sánchez and Martínez Cortizas 2019; Silva Sánchez et al. 2019b, c), as well as the scientific and technical criteria to determine a set of monitoring locations across the country (Pontevedra-Pombal 2019; Pontevedra-Pombal and García-Rodeja 2019).

Image 18 Raising awareness on peatland value is essential to engage the community. Informative panel at Cruz do Bocelo fen (Bocelo Range). Photo credit Anibal Mejuto Fernández

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After the pioneering role of the Council Directive in peatland habitat protection, the Convention on Wetlands (Ramsar Convention) has explicitly addressed peatlands since 1996, and the Convention on Biological Diversity (CBD) endorsed the first ‘Global Assessment on Peatlands, Biodiversity and Climate Change’ in 2007 (Parish et al. 2008). The United Nations Framework Convention on Climate Change (UNFCCC) unnoticed peatlands for many years in the land use sector. This disregard started to change in 2006, and in 2010 peatland rewetting was accepted as an accountable activity under the Kyoto Protocol (Joosten 2011). Additionally, the United Nations Food and Agriculture Organization (Joosten et al. 2012; Biancalani and Avagyan 2014), the Intergovernmental Panel on Climate Change (IPCC 2013) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) (Sirin et al. 2018) have paid greater, and much deserved, attention to peatlands. The most recent recognition of peatlands value was performed by the United Nations Environment Assembly (UNEA) resolution on ‘Conservation and Sustainable Management of Peatlands’, adopted by all UN member states in 2019. The resolution acknowledged the contribution of peatlands to the implementation of the 2030 Agenda for Sustainable Development (UNEP 2019). Currently, the United Nations Decade on Ecosystem Restoration 2021–2030 provides a key framework opportunity for global action on peatland restoration. Hopefully, this increasing international awareness about the importance of mires will favor the conditions necessary for the fair protection and restoration of Galician peatland habitats, today and in the future. Acknowledgements LLM, AMC and TM are supported by the Plan Estatal de Proyectos I+D+I Retos Investigación 2020 (Ref.: PID2020-115580RB-I00, PALAEOFUN project) funded by the Spanish Ministry of Science and Innovation. AMC and OLC are supported by Grupos de Referencia Competitiva (ED431C 2021/32) funded by the Xunta de Galicia and Plan Nacional de Investigación (Ref: PID2019-111683RJ-I00AEI/https://doi.org/10.13039/501100011033). LLM and AMM are supported by the Programa de Atracción de Talento, modalidad 1 (Ref.: 2019-T1/AMB-12782, ECOSINK project) funded by the Comunidad de Madrid. NSS is supported by a Juan de la CiervaFormación fellowship (FJC2018-036266-I) and OLC by a Ramón y Cajal fellowship (RYC2020030531-I), both funded by the Spanish Ministry of Science and Innovation.

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Martínez Cortizas A, Pérez Alberti A (Coords) (1999) Atlas Climático de Galicia. Xunta de Galicia, Santiago de Compostela, 207 pp Martínez Cortizas A, Pontevedra Pombal, Nóvoa Muñoz JC, García-Rodeja Gayoso E (1997a) Four thousand years of atmospheric Pb, Cd and Zn deposition recorded by the ombrotrophic peat bog of Penido Vello (Northwestern Spain). Water Air Soil Pollut 100:387–403 Martínez Cortizas A, Pontevedra Pombal, Nóvoa Muñoz JC, García-Rodeja Gayoso E (1997b) Paleocontaminación: evidencias de contaminación atmosférica en Galicia durante los últimos 4000 años. Gallaecia 16:7–22 Mart´ınez Cortizas A, Pontevedra Pombal, Garc´ıa-Rodeja E, Nóvoa Muñoz JC, Shotyk W (1999) Mercury in a Spanish peat bog: archive of climate change and atmospheric metal deposition. Science 284:939–942 Martínez Cortizas A, Pontevedra-Pombal, Nóvoa-Muñoz JC (2008) Mire. In: Chesworth W (ed) Encyclopedia of soil science. Springer, Dordrecht, The Netherlands, pp 482–485 Martínez Cortizas A, Pontevedra Pombal, Nóvoa Muñoz JC, Rodríguez Fernández R, López Sáez JA (2009) Turberas ácidas de esfagnos. In: Bases ecológicas preliminares para la conservación de los tipos de hábitat de interés comunitario en España. Ministerio de Medio Ambiente, y Medio Rural y Marino, Madrid, 64 pp Martínez-Cortizas A, Costa-Casais M, López-Sáez JA (2009) Environmental change in NW Iberia between 7000 and 500 cal BC. Quatern Int 200:77–89 Martini IP, Martínez Cortizas A, Chesworth W (eds) (2006) Peatlands. Evolution and records of environmental and climate changes. Elsevier, 587 pp Menéndez Amor J, Florschütz F (1971) Contribución al conocimiento de la hostoria de la vegetación en España durante el Cuaternario. Estud Geol 17:83–99 Menéndez Amor J (1969) Análisis esporo-polínico de tres perfiles situados en la cuenca hidrográfica del río Deo (La Coruña). Bolet´ın de la Real Sociedad Española de Historia Natural (Sección Geología) 67:161–167 Menéndez Amor J (1971) Estudio esporo-polínico de dos turberas en la Sierra de Queija (Orense). Bolet´ın de la Real Sociedad Española de Historia Natural (Sección Geología) 69:85–92 Mighall TM, Martínez Cortizas A, Biester H, Turner SE (2006) Proxy climate and vegetation changes during the last five millennia in NW Iberia: pollen and non-pollen palynomorph data from two ombrotrophic peat bogs in the North Western Iberian Peninsula. Rev Palaeobot Palynol 141:203–223 Muñoz-Sobrino C, Ramil-Rego P, Rodríguez Guitián M (1997) Upland vegetation in the north-west Iberian peninsula after the last glaciation: forest history and deforestation dynamics. Veg Hist Archaeobotany 6:215–233 Muñoz-Sobrino C, Ramil-Rego P, Gómez-Orellana L, Díaz Varela RA (2005) Palynological data on major Holocene climatic events in NW Iberia. Boreas 34:381–400 Muñoz-Sobrino C, Ramil-Rego P, Gómez-Orellana L (2007) Late Würm and early Holocene in the mountains of northwest Iberia: biostratigraphy, chronology and tree colonization. Veg Hist Archaeobotany 16:223–240 Olid C, García-Orellana J, Martínez Cortizas A, Masqué P, Peiteado E, Sanchez-Cabeza JA (2008) Role of surface vegetation in 210Pb-dating of peat cores. Environ Sci Technol 42:8858–8864 Oliva M, Ruiz-Fernández J, Barriendos M, Benito G, Cuadrat JM, Domínguez-Castro F, García-Ruiz JM, Giralt S, Gómez-Ortiz A, Hernández A, López-Costas O, López-Moreno JI, López-Sáez JA, Martínez-Cortizas A, Moreno A, Prohom M, Saz MA, Serrano E, Tejedor E, Trigo R, ValeroGarcés B, Vicente-Serrano SM (2018) The Little Ice Age in Iberian mountains. Earth Sci Rev 177:175–208 Parish F, Sirin A, Charman D, Joosten H, Minayeva T, Silvius M, Stringer L (eds) (2008) Assessment on peatlands, biodiversity and climate change. Global Environment Centre and Wetlands International, Kuala Lumpur, Malaysia; Wageningen, The Netherlands, 206 pp Pérez-Rodríguez M, Martínez Cortizas A (2014) Preliminary characterization of microbial functional diversity using sole-C-source utilization profiles in Tremoal do Pedrido mire (Galicia, NW Spain). Spanish Journal of Soil Science 4:158–178 Pérez-Díaz S, López-Sáez JA, Pontevedra-Pombal, Souto-Souto M, Galop D (2016) 8000 years of vegetation history in the northern Iberian Peninsula inferred from the palaeoenvironmental study of the Zalama ombrotrophic bog (Basque-Cantabrian Mountains, Spain). Boreas 45:658–672

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Ramil-Rego P, Aira Rodríguez MJ (1996) Estudio palinológico de la turbera de Schwejk (Lugo). Stvdia Botanica 12:1259–1269 Ramil-Rego P, Taboada Castro T, Aira Rodríguez MJ (1993) Estudio palinológico y factores de formación del Tremoal da Gañidoira (Lugo, España). In: Fumanal MP, Bernabeu J (eds) Estudios sobre Cuaternario, Medios Sedimentarios, Cambios Ambientales y Hábitat Humano. Universidad de Valencia-A.E.Q.A, Valencia, pp 191–197 Ramil-Rego P, Aira Rodríguez MJ, Taboada Castro T (1994) Análisis polínico y sedimentológico de dos turberas en las Sierras Septentrionales de Galicia (Noroeste de España). Rev Paléobiol 12:9–28 Ramil-Rego P, Muñoz-Sobrino C, Rodríguez-Guitián M, Gómez-Orellana L (1998) Differences in the vegetation of the North Iberian Peninsula during the last 16,000 years. Plant Ecol 138:41–62 Ramil-Rego P, Rodríguez Guitián MA, Muñoz-Sobrino C, Gómez-Orellana L (2000) Some considerations about the postglacial history and recent distribution of Fagus sylvatica in the NW Iberian Peninsula. Folia Geobot 35:241–271 Ramil-Rego P, Muñoz-Sobrino C, Gómez-Orellana L (2001) Historia ecológica de Galicia: modificaciones del paisaje a lo largo del Cenozoico. SEMATA, Ciencias Sociais e Humanidades 13:67–103 Ramil-Rego P, Gómez-Orellana L, Nóvoa Fernández B, Muñoz-Sobrino C, García-Gil S (2009) Cambio climático y dinámica del paisaje en Galicia. Recursos Rurais 5:21–47 Ramil-Rego P, Gómez-Orellana L, Muñoz-Sobrino C, Rodríguez-Guitián M (1996) Valoración de las secuencias polínicas del Norte de la Península Ibérica para el Último ciclo glaciar-interglaciar. In: Ramil-Rego P, Fernández Rodríguez C (eds) Paleoecología y Arqueometría del Norte de la Península Ibérica. Férvedes 3:20–123 Ramil-Rego P, Gómez-Orellana L, Ferreiro da Costa J, Muñoz Sobrino C, Rodríguez Guitián MA (2018) Génesis y dinámica de las turberas de la región biogeográfica Atlántica de la Península Ibérica. In: Fernández-García JM, Pérez FJ (eds) Identificación, valoración y restauración de turberas: contribuciones recientes: LIFE+ Ordunte Sostenible. Bizkaia, pp 207–224 Ramil-Rego P (1992) La vegetación cuaternaria de las Sierras Septentrionales de Lugo a través del análisis polínico. PhD thesis, Universidade de Santiago de Compostela, 356 pp Rauch S, Peucker-Ehrenbrink B, Kylander ME, Weiss DJ, Martínez Cortizas A, Heslop D, Olid C, Mighall TM, Hemond HF (2010) Anthropogenic forcings on the surficial osmium cycle. Environ Sci Technol 44:881–887 Rubiales JM, Ezquerra J, Muñoz Sobrino C, Génova MM, Gil L, Ramil-Rego P, Gómez Manzaneque F (2012) Holocene distribution of woody taxa at the westernmost limit of the Circumboreal/ Mediterranean boundary: evidence from wood remains. Quatern Sci Rev 33:74–86 Sanmartin P, Silva-Sánchez N, Martínez-Cortizas A, Priero B (2015) Usual and unusual CIELAB color parameters for the study of peat organic matter properties: tremoal do Pedrido bog (NW Spain). J Phys: Conf Ser 605:012014 Santos L, Vidal Romaní JR, Jalut G (2000a) History of vegetation during the Holocene in the Courel and Quiza Sierras, Galicia, northwest Iberian Peninsula. J Quat Sci 15:621–632 Santos L, Vidal Romaní JA, Jalut G (2000b) History of vegetation during the Holocene in the Courel and Quixa Sierras, Galicia, northwest Iberian Peninsula. J Quat Sci 15:621–632 Santos Fidalgo L (1992) Estudio polínico de una turbera reciente en la Serra de Queixa (Ourense, Galicia, España). Cuadernos Del Laboratorio Geolóxico De Laxe 17:137–143 Santos Fidalgo L, Bao Casal R, Jalut G (1993) Estudio micropaleontológico de una turbera litoral holocena en la Rúa de Ares (A Coruña, España). Cuadernos Del Laboratorio Geolóxico De Laxe 18:175–188 Schellekens J, Buurman P, Fraga I, Martínez Cortizas A (2011) Holocene vegetation and hydrologic changes inferred from molecular vegetation markers in peat, Penido Vello (Galicia, Spain). Palaeogeogr Palaeoclimatol Palaeoecol 299:56–69 Silva-Sánchez N (2015) Mining and metallurgical activities in N Iberia and their link to forest evolution using environmental archives (centuries AD V to XI). Estudos Do Quaternário/quaternary Studies 12:15–26 Silva-Sánchez N, Martínez Cortizas A, López-Merino L (2014) Linking forest cover, soil erosion and mire hydrology to late-Holocene human activity and climate in NW Spain. The Holocene 24:714–725

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Coastal Soils and Their Associated Habitats in Galicia Xosé L. Otero, María del Carmen de la Cerda Marín, and Augusto Pérez-Alberti

Abstract Galicia is one of the Spanish autonomous communities with the longest coastline, one of the most complex in the Iberian Peninsula. Dune, marsh, and cliff environments are interspersed along coastal areas, on which soils with highly contrasting features and properties develop. In dune environments, soils show poor edaphic development, with the addition of organic matter and substrate decalcification as the main processes. The most representative soil types are Calcaric Arenosols, corresponding to white and grey dune areas, and Calcaric Gleyic Arenosols, associated with inter-dune depressions, where small seasonal lagoons form. The main characteristics and diagnostic features in saltmarsh soils are gleyic properties, sulfidic materials, and concentration of salts derived from marine influence. The most representative soils are Reductigley Tidalic Gleysol (Hyposulfidic), characteristic of salt marsh plains and corresponding to habitat Nat2000 1330, Atlantic salt meadows; Histic Tidalic Gleysol (Hipersulfidic, Toxic), a soil type characteristic of back saltmarshes, where the Scirpus maritimus community is located, are organic soils with a strongly reduced horizon already at their surface (Eh < 100 mV), high pyrite and H2 S contents, but low salinity; Reductigley Tidalic Gleysol (Hypersulficic), associated with the presence of Spartina maritima, are strongly reduced soils with high pyrite concentrations, and Reductigley Subaquatic Gleysol (Hyposulficidc), which corresponds to submarine Zostera nolti and Zostera marina meadows, are anoxic at their surface and show high contents of sulfidic materials. Cliff soils are characterized by being shallow, slightly acidic, with high organic matter content, low electrical conductivity, and the cation exchange complex saturated by basic cations. According to these variables, soils are classified as Lithic Leptosol (Arenic), Mollic Leptosol (Arenic) and Mollic Umbrisol (Arenic, Colluvic). The main habitat associated with these soils is Nat2000 1230 Vegetated sea cliffs of the Atlantic and Baltic Coasts, which in Galicia is still poorly characterized. X. L. Otero (B) · M. del Carmen de la Cerda Marín · A. Pérez-Alberti Departamento de Edafoloxía e Química Agrícola, School of Biology, CRETUS, Universidade de Santiago de Compostela, Santiago, Spain e-mail: [email protected] X. L. Otero Estación Científica Do Courel, REBUSC, Rede de Estacións Bioloxicas da Universidade de Santiago de Compostela, Seoane, Folgoso de O Courel, Lugo, Spain © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_11

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Keywords Sea cliffs · Saltmarshes · Coastal dunes · Soil processes

1 Introduction The length of the Galician coastline is 2,100 km (POL Galicia 2010). Considering a band 1000 m wide, 68.29% of the coastline is less than 50 m tall and only 3.15% exceeds 300 m (Pérez Alberti 2022). The topographic and lithological contrasts generated by a wide diversity of alternating rock types (granitic, mafic, ultramafic, metamorphic, and sedimentary) lead to a great variety of environments. Morphologically, it is worth highlighting the rias, seawater inlets that penetrate the continent, delimited by narrow and straight land segments, showing an intense relationship between the inlet and protrusion networks and their lithology and fracture patterns. The seaboard is located within a mesotidal environment, with an average tidal range of 2.5 m and a maximum tidal range around 4 m. As for wave regime, Galicia is located in a transition area between swell-affected and storm wave-affected areas. Ground swell waves come predominantly from the NW and, less frequently, from the W and SW. Taller waves (> 3 m) are more frequent during the winter and generally come from the NW and W due to the low-pressure zones moving from these areas. The design of coastal shapes is closely related to the geotectonic evolution of Galicia and can be studied from different perspectives: from megashapes, which determine the general features of the coast, to microshapes, which introduce differentiating aspects at a detailed scale. The interrelations among factors present in coasts, along with a wide range of processes that have occurred throughout time, explains the diversity of existing environments, which allow for a first categorization of the Galician coastline into rocky, sedimentary, and marine areas, as well as for a more detailed categorization into cliffs, platforms, and boulder beaches; sand beaches and dunes; intertidal flats, and saltmarshes. Among them, from the edaphic standpoint, it is worth highlighting cliffs, dunes, and saltmarshes. Coastal dunes occupy an area of 2138 ha (POL Galicia 2010). Galician dune systems show different geoforms: embryo or incipient dunes, sand tails, tongueshaped dunes, foredunes, pyramid dunes, parabolic dunes, barchanoid and climbing dunes, tabular sand sheets and, as an unique case, the Corrubedo transverse dune (Pérez Alberti and Vázquez Paz 2011). Among all these, only those stabilized by plants (creating grey or fossil dunes) have allowed generating soils. These constitute the final stage in dune evolution, with a smooth topography and virtually covered by different plant community strata. Saltmarshes cover 2071 ha (POL Galicia 2010), mainly located in the inner sections of rias, in low-energy areas that allow for the accumulation of fine-grained sediments. These environments are highly influenced by tides, their substrate shows a silt granulometry, and their redox conditions are mainly suboxic or anoxic; all of these characteristics define the essential features of soils developing on them.

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Cliffs occupy an area of 4179 ha (POL Galicia 2010). According to their design, they can be categorized as cliffs with back plains, flat-topped cliffs, steeply sloped cliffs, gently sloped cliffs, overhanging cliffs, and convex cliffs. Considering the nature of the substrate, the following can be differentiated: cliffs formed on metamorphic rocks, on rocks, and on slope deposits, both eolian deposits formed during the last Eemian interglacial period (Pérez Alberti et al. 2018) and those accumulated in cold environmental conditions (Costa Casais et al. 2008). Adding to this, the slopes and their degree of instability have determined the development of a soil mantle, particularly on slope cliffs, concave cliffs, and those formed on recent deposits.

2 Dune Soils Dune soils show poor edaphic development, the main processes being addition of organic matter on the surface and progressive substrate decalcification. Both processes become more evident as we move from the coastline (beach) inwards (grey dunes). According to the IUSS Working Group WRB classification (2015), the most characteristic soil groups are Calcaric Arenosol, corresponding to the most representative unit for white and grey dunes, while Calcaric Gleyic Arenosol can occur in inter-dune depressions, where small seasonal lagoons develop, showing gleyic properties as their most relevant edaphic feature as a result from prolonged flooding leading to the development of suboxic or anoxic conditions. Arenosols are soils with a loamy sand texture class or coarser; therefore, these soils have a low cation exchange capacity (CEC) (white dunes: 5.3 ± 0.9 cmol(+) kg−1 ; grey dunes: 10.4 ± 3.7 cmol(+) kg−1 ), largely dependent on organic matter content, and Ca and Mg are predominant. Interestingly, despite their proximity to the sea, these soils show low salinities (generally between 100 and 300 µS cm−1 ) due to high rainfall and high substrate permeability in the Galician coasts, which allow for salt lixiviation (Table 1). On the other hand, Galician dune systems host a certain degree of plant diversity, whose distribution along bands running approximately parallel to the coast determine several habitats of European interest as defined by Annex I of the Habitats Directive 92/43/EEC (1992) (Fig. 1). The distribution of plant communities is closely related to several variables such as degree of substrate stability, nutrient availability, and water availability, which change as soil-generating processes advance (Pigott et al. 2000). At the front of the dune system are embryonic shifting dunes (habitat Nat2000 2110) and shifting dunes along the shoreline with Ammophila arenaria (white dunes, habitat Nat2000 2120), where sand deposition is still active. Embryo dunes host a small number of plant species, such as Elymus farctus or Euphorbia paralias, while white dunes show a higher plant diversity, Ammophila arenaria and Othanthus maritimus being the most representative species. Ammophila arenaria crowns the ridge of still mobile primary and secondary dunes. In these conditions, the substrate is composed of sandy sediment with poor soil development beyond a certain level

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Table 1 Average content (maximum and minimum contents in parentheses) of calcium carbonate, organic C, pH, and electric conductivity in horizon A of soils in the different dune systems in Galicia Habitat Embryonic shifting dunes (Nat2000 2110)

White dunes (Nat2000 2120)

Grey dunes (Nat2000 2130*)

Humid dune slacks (Nat2000 2190)

Ría de ortigueira

26.4* (36–20)

28.8* (34–25)

25.2* (30–16)

18 (23–11)

Xuño beach

n.d

n.d

25.6 (17–29)

3.9 (2.2–4.3)

Corrubedo natural park

n.d

n.d

37 (20–47)

15.6 (28–10)

Cíes islands national park

n.d

n.d

5.5 (8.8–2.9)

4.41 (5–6)

CaCO3 (%)

Total organic C (%) Ría de ortigueira

75%), followed by silt (15%) and clay (10%) (Table 3). A relevant aspect is the high organic C content, which often exceeds 10% (Table 3), due to the high plant coverage (particularly of Gramineae species), which is promoted by the input of guano in seabird colonies. It is worth highlighting the organic matter contribution by Armeria pubigera, which sometimes forms extensive prairies and, following their collapse by still unclear reasons, generate an organic substrate that significantly promotes water and nutrient retention and on which different plant communities grow; these communities are still poorly characterized from the phytosociological standpoint (De La Peña-Lastra 2019; Otero 2016; Otero et al. 2016). As for the composition of the cation exchange complex, Ca (70.7–24.2 cmol(+) kg−1 ) and Mg (11.5–5.3 cmol(+) kg−1 ) are the dominant cations, followed by Na (6.2–3.9 cmol(+) kg−1 ) and K (1.1–0.7 cmol(+) kg−1 ); conversely, Al is found at very low concentrations (Table 3). As main diagnostic criteria, it is worth mentioning the presence of a mollic A horizon, sandy texture, and shallow depths ranging from less than 10 to 40 cm. According to these variables, soils are classified as Lithic Leptosol (Arenic) when they are less than 10 cm thick, Mollic Leptosol (Arenic) when depth ranges between 10 and 25 cm, and Mollic Umbrisol (Arenic, Colluvic) when depth is greater than 25 cm. The main habitat associated with these soils is Nat2000 1230 Vegetated sea cliffs of the Atlantic and Baltic Coasts, which in Galicia is still poorly characterized. (De La Peña-Lastra 2019). Another aspect worth highlighting is the impact of seabird colonies on these environments. In recent years, different studies have been performed on yellowlegged gull colonies in the Atlantic Islands of Galicia National Park, revealing that,

1030 ± 755

513 ± 201

5.7 ± 0.6

5.0 ± 0.3

861 ± 294

216 ± 97

dS

cm−1

Elec. cond

Xubenco cliffs

6.0 ± 0.9

6.0 ± 0.8

pH

Centulo cliffs

Ons island

Porta cliffs

Cíes islands

Cape Home cliffs

Cape home

Site

Cation exchange capacity

13.6 ± 1.5

14.5 ± 2.7

12.9 ± 4.3

11.1 ± 1.8

%

Org C kg−1

51.8 ± 35

51.5 ± 21

70.7 ± 33

24.2 ± 8.5

cmol(+)

Ca

10.1 ± 6.3

5.3 ± 0.6

11.5 ± 3.7

6.80 ± 2.50

Mg

Table 3 Soil composition and physicochemical features in Galician cliffs (Otero et al. 2016)

6.2 ± 2.9

4.0 ± 0.3

3.9 ± 0.9

4.40 ± 1.2

Na

1.1 ± 0.8

0.7 ± 0.2

1.0 ± 0.34

0.94 ± 0.2

K

0.06 ± 0.05

< LD

< LD

< LD

Al

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in addition to the impact on plant communities (De La Peña-Lastra 2019; Guitián and Guitián 1990), soils in seabird colonies are clearly enriched in nutrients and trace elements, but do not meet the conditions for the Supplementary qualifier Ornithic according to the IUSS Working Group WRB classification (2015). This is due to these environments being subjected to intense washing, thus preventing the accumulation of guano as observed in other coastal areas in arid climates (De La Peña-Lastra 2019; Otero 1998; Otero and Fernández-Sanjurjo 1999, Otero et al. 2015; Otero et al. 2018).

5 Final Remarks The available knowledge on coastal habitats and their soils in Galicia is still limited. Such poor knowledge often leads to incorrect assignation of the habitats listed in Annex I of Directive 92/43/EEC (1992) (Gómez-Pazo et al. 2020). On the other hand, coastal environments as a group constitute the most sensitive ecosystems to global change, particularly to increasing sea levels and land use changes. Currently, dunes, saltmarshes, coastal lagoons, and cliffs have already experienced substantial changes that affect their stability and dynamics (Fraga et al. 2019). Increases in sea level promote their erosion and prolong flooding time, which in turn leads to reduction of Fe/Mn oxyhydroxides and mobilization of elements adsorbed on them, among which P and potentially toxic metals are worth highlighting. Future studies should be aimed at understanding the resilience of these environments to increasing sea levels and their potential role as a source of eutrophicating and toxic elements into coastal waters.

References Casais MC, Blanco R, Cortizas AM, Pérez-Alberti A (2008) Los episodios Heinrich en la costa de Galicia (NW de la Península Ibérica). Un análisis a través de los sedimentos continentales. Territoris 7:39–53 Clark RB (1997) Arbuscular mycorrhizal adaptation, spore germination, root colonization, and host plant growth and mineral acquisition at low pH. Plant Soil, 192:15–22 De La Peña Lastra (2019) Influencia de las aves marinas sobre nutrientes y elementos traza en medios costeros: efectos a escala local y global. PhD theis, Universidade de Santiago de Compostela, Santiago de Compostela, Spain Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora Fraga P, Gómez A, Pérez-Alberti A, Montero P, Otero XL (2019) Trends in the evolution of coastal lagoons and lakes in Galicia (NW Iberian Peninsula). J Mar Sci Eng 7:272. https://doi.org/10. 3390/jmse7080272 Gómez-Pazo A, Pérez-Alberti A, Fraga-Santiago P, Souto-Souto M, Otero XL (2020) Contribution of GIS and geochemical proxies to improving habitat identification and delimitation for the Natura 2000 network: the case of Coastal lagoons in Galicia (NW Iberian Peninsula). Appl Sci 10:9068. http://dx.doi.org/10.3390/app10249068

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Guitián J, Guitián P (1990) A paisaxe vexetal das Illas Cíes. Xunta de Galicia. Santiago de Compostela Howarth RH (1984) The ecological significance of sulfur in the energy dynamics of salt marsh and coastal marine sediments. Biogeochemistry 1:5–27 IUSS Working Group WRB (2015) World reference base for soil resources 2014, update 2015: international soil classification system for naming soils and creating legends for soil maps. World Soil Resources Reports No. 106. FAO, Rome Long SD, Mason CF (1983) Sallmarsh ecology. Blackie, London Mitsch WJ, Gosselink JG (1993) Wetlands. Van Nostrand Reinhold, NewYork Otero XL (1998) Effects of nesting yellow-legged gulls (Larus cachinnans Pallas) on the heavy metals content of soils in Cíes Islands (Galicia-NW Spain). Mar Pollut Bull 36:267–272. https:/ /doi.org/10.1016/S0025-326X(98)80010-6 Otero XL, Fernandez-Sanjurjo M (1999) Seasonal variation in inorganic nitrogen content of soils from breeding sites of yellow-legged gulls (larus cachinnans) in the Cíes islands natural park (NW Iberian peninsula). Fresen Environ Bull 8:685–692 Otero XL (2000) Biogeoquímica de metales pesados en ambientes sedimentarios marinos. PhD thesis, Universidade de Santiago de Compostela, Santiago de Compostela, Spain Otero XL, Macías F (2001) Caracterización y clasificación de suelos de las marismas de la ría de Ortigueira en relación con su posición fisiográfica y vegetación (Galicia–NW de la península ibérica). Edafología 8:37–61 Otero XL, Macías F (2002) Fraccionamiento de Fe en fluvisoles de las marismas de la ria de Ortigueira (Galicia). Edafología 9:257–272 Otero XL, Ferreira TO, Huerta-Díaz MA, Partiti CSM, Souza V Jr (2009) Geochemistry of iron and manganese in soils and sediments of a mangrove system, Island of Pai Matos (Cananeia—SP, Brazil). Geoderma 148(3–4):318–335 Otero XL, Guevara P, Sánchez I, López M, Queiroz H, Ferreira A, Ferreira TO, Nóbrega G, Carballo R (2023) Pyrites in a salt marsh-ria system: Quantification, morphology, and mobilization. Mar Geol 455. https://doi.org/10.1016/J.MARGEO.2022.106954 Otero XL, Tejada O, Martín-Pastor M, De la Peña S, Ferreira TO, Pérez-Alberti A (2015) Phosphorus in seagull colonies and the effect on the habitats. The case of yellow-legged gulls (Larus michahellis) in the Atlantic Islands National Park (Galicia-NW Spain). Sci Total Environ 532:383–397. https://doi.org/10.1016/j.scitotenv.2015.06.013 Otero XL (2016) Efecto de las colonias de gaviota patiamarilla sobre la pérdida de la biodiversidad vegetal en el Parque Nacional Marítimo Terrestre de las Islas Atlánticas de Galicia. Informe inédito Fundacion BBVA Otero XL, De la Peña Lastra S, Pérez-Alberti A, Macías F (2016) Variabilidad espacio-temporal de formas de nitrógeno y fósforo en suelos de las colonias de gaviota patiamarilla (Larus michaellis, Naumann 1840) en el Parque Nacional Marítimo-Terrestre de las Islas Atlánticas de Galicia. En: Proyectos de investigación en parques nacionales: 2011–2014. Organismo Autónomo de Parques Nacionales, Ministerio de Medio Ambiente, pp 123–140 Otero XL, De La Peña-Lastra S, Pérez-Alberti A, Ferreira TO, Huerta-Diaz MA (2018) Seabird colonies as important global drivers in the nitrogen and phosphorus cycles. Nat Commun 9(1). https://doi.org/10.1038/S41467-017-02446-8 Pérez Alberti A, Vázquez Paz MC (2011) Caracterización y dinámica de sistemas dunares costeros de Galicia. In: Las dunas en España. Sociedad Española de Geomorfología. Sociedad Española de Geomorfología, pp 161–185 Pérez-Alberti A, Cunha PP, Otero XL (2018) La terraza costera de Sanxenxo: un registro sedimentario del MIS 5 a MIS 2, en la Ría de Pontevedra (NO de la Península Ibérica). En: Proceedings of the IX Symposium on the Iberian Atlantic Margin, Coimbra Pérez Alberti A (2022) Propuesta metodológica para la caracterización y tipificación de las costas españolas. Aplicación a las costas de Galicia. Cuad Invest Geográfica 48(2):269–291

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Pigott CD et al (2000) Maritime communities and vegetation of open habitats. En: Rodwell JS (ed) British plant communities, vol 5, for the U.K. joint nature conservation committee. Cambridge University Press POL (Plan de Ordenación do Litoral de Galicia), Galicia (2010). Retrieved from http://webpol. xunta.gal/web/index.php/introduccion/gl Rozema J, Laan P, Broekman R, Ernst WHO, Appelo CAJ (1985) On the lime transition and decalcification in the coastal dunes of the province of North Holland and the island of Schiermonnikoog. Acta Bot Neerl 34(4):393-411 Sánchez JM, Izco J, Medrano M (1996) Relationships between vegetation zonation and altitude in a saltmarsh system in northwest Spain. J Veg Sci 7:695–702 Sánchez JM, Otero XL, Izco J (1998a) Relationships between vegetation and environmental characteristics in a salt-marsh on the coast of Northwest Spain. Plant Ecol 136:1–8 Sánchez JM, Otero XL, Izco J (1998b) Relationships between vegetation and environmental characteristics in a saltmarsh system on the coast of Northwest Spain. Plant Ecol 136:1–8 Tait RV (1987) Elementos de Oceanografia. In: Acnbia SAZ (ed) Turner FT, Patrick WH (1968) Chemical changes in waterlogged soils as a result of oxygen depletion. In: 9th Congr Soil Science, vol IV. Adelaine, Australia, pp 53–65

Soil Biodiversity in Galician Peatlands: A Unique Home for Specialised Invertebrates Maria J. I. Briones and I. Ferradás

Abstract The environmental conditions that allow the persistence of peatland ecosystems (waterlogged, acidic and nutrient poor) makes them unsuitable habitats for many soil plant and animal species. However, a wide range of specialised soil invertebrates find these peaty soils to be the perfect home to feed, grow and reproduce, converting these ecosystems into unique environments in terms of composition and structure of their soil communities. Among them, enchytreids (Oligochaetes) are usually dominant in terms of biomass, whereas microarthropods (e.g., mites, collembolans, small insects), despite their numerical abundance, represent 3% of the total biomass. Since these ecosystems are extremely vulnerable to climatic and anthropogenic changes (e.g., conversion to agricultural land), more comprehensive protection measures should be implemented to ensure the preservation of its soil biodiversity. Keywords Enchytraeids · Collembolans · Mesofauna · Mites · Microarthropods · Bogs

1 Peatlands Are Relic Ecosystems Peatlands cover 3% of planet’s surface (Xu et al. 2018) but hold nearly 30% of all carbon locked in the soil (Gorham 1991). Although they are present in most regions of the globe, in the northern hemisphere they are located at high latitudes (Limpens et al. 2008). In Spain, they are mainly concentrated in those wetter areas of the inland mountains and in the northern fringes, where they are more exposed to more frequent precipitations and cooler conditions. Therefore, they can be considered relict ecosystems, whose conservation should be prioritised as a vestige of what they probably were Iberian peatlands before land transformations changed our landscapes. Galicia is the Spanish region with the largest presence and variety of peat bogs, with a total of 10,000 ha of upland peat bogs, of which approximately 80% is M. J. I. Briones (B) · I. Ferradás Departamento de Ecoloxía e Bioloxía Animal, Universidade de Vigo, Vigo 36310, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_12

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Image 1 Peat deposit at Serra do Xistral

concentrated in the Northern Sierras (Martinez-Cortizas et al. 2000) and where the ombrotrophic blanket peatlands, one of the scarcest habitats in the world, reach their most south-western limit in Europe (Bain et al. 2011). Among them, those located in the ZEC Serra do Xistral (ES1120015) within the Reserve of the Terras do Miño Biosphere constitute the most occidental location of these ecosystems in the Iberian Peninsula, with their peat deposits reaching up to 4 m in depth (Ramil-Rego et al. 2017; Image 1).

2 Peatlands Comprise Complex Habitat Mosaics The altitudinal gradients present in Serra do Xistral favour the existence of a different altitudinal zonation based on temperature (colline < 400–650 m; montane 650 – > 890 m) and precipitation shifts (humid < 380 m; hyperhumid 380–800 m; ultrahyperhumid > 800 m). This coupled with the different degree of slope exposure to prevailing moist oceanic winds (depending on whether they face north or south) and the Föhn effect (resulting in adiabatic cooling of moist air as it encounters high grounds) causes increased precipitation and more frequent fogs (Ramil-Rego et al. 2017). All these climatic variations have been associated with an altitudinal zonation of the peat bog plant communities (Izco-Sevillano and Ramil-Rego 2001) with high ecological value. Indeed, many of these habitats are considered to be of priority interest according to the Council Directive 92/43/EEC (Image 2): (i) blanket bogs (Nat-2000 7130; * if active bogs) in the cuminal zones (> 800 m) dominated by Eriophorum angustifolium (cotton-grass), Juncus squarrosus (heath rush) and Molinia caerulea (purple moor-grass); (ii) active raised bogs (Nat-2000 7110*) between 700–800 m represented by mats of Sphagnum spp. (moss) and (iii) transition mires (Nat-2000 7140) developing in wet valley bottoms (< 600 m) and associated with Atlantic wet heaths of Erica mackayana and Calluna vulgaris (Nat-2000 4020*). The area also includes extensive representations of other plant communities, such as

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depressions on peat substrates of the Rhynchosporion (Nat-2000 7150) and Nardus herbaceous formations (Nat-2000 6230*), among others. Some of these habitats and plant communities are better represented in the Galician region than in other areas of the world.

Image 2 Examples of peatland habitats. a: Atlantic wet heath of Erica mackayana and Calluna vulgaris (Nat-2000 4020*); b: active blanket bog of Eriophorum angustifolium (Nat-2000 7130*); c: active blanket bog of Molinia caerulea (Nat-2000 7130*); d: transition mire with Sphagnum spp. (Nat-2000 7140)

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3 Peatlands Are Home to a Wide Variety of Soil Organisms The soil communities are typically dominated by annelids and a wide variety of small arthropods (arachnids, mites, springtails, myriapods and various orders of insects) (Carrera and Briones 2013a, b). Despite their tiny size (body width < 2 mm and thus belonging to “mesofauna” according to the body size classification established by Swift et al. 1979), they play a crucial role in the breakdown of organic residues, returning nutrients to the soil. Phylum Annelida: Class Oligochaeta: Family Enchytraeidae Enchytreids (Image 3) are a family of aquatic and terrestrial oligochaetes, with a body length ranging between 1 and 30 mm. They are especially abundant in acid soils with high organic matter content such as moorlands, where they can reach densities of up to 300,000 individuals m−2 (Briones et al. 2007) and dominate the soil fauna communities in terms of biomass (67–99%; Cragg 1961). However, in Galician peatlands their populations are less numerous, in the range of 10–77,000 individuals m−2 (Carrera and Briones 2013a; Juan-Ovejero et al. 2019). One particular species, Marionina filiformis was collected for the first time in Ferreira de Valadouro (Lugo) and represents the most southern European record of this species (Schmelz et al. 2008). Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Order Araneae Like all arachnids, spiders have two body regions: cephalotorax that bears two pairs of cephalic appendages (one pair of chelicerae and one pair of pedipalps) and four pairs of thoracic appendages (walking legs) and abodomen without appendages (Image 4). In peat soils they are not very abundant, reaching between 20–170 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Order Opiliones Typically ranging from 1 to 10 mm in length (Image 5), their most distinctive feature is their extremely long legs compared to its globose body (the cephalothorax is

Image 3 Microphotographs (stereomicroscope) of an enchytraeid. a: full specimen; b: lateral view of the anterior region

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Image 4 Microphotographs (stereomicroscope) of a spider. a: dorsal view showing the two body regions (the ocelli or simple eyes are located on the anterior end of the cephalothorax); b: ventral view showing the chelicerae shaped as articulated fangs

fused to the abdomen). They are also commonly known as “harvestmen” and unlike spiders they do not have silk glands and therefore do not build webs. Their densities in Galician peatlands are very low, less than 35 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019), although this is probably an underestimate because they live on the surface and move very rapidly and hence, not easily captured (Glime 2013). Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Order Pseudoscorpionida Pseudoscorpions are also known as “false scorpions” because their abdomen is shorter and lacks the extended region or post-abdomen bearing the sting. They are small arachnids (< 5 mm) with eight walking legs and the typical cephalic appendages present in Chelicerata, i.e. two short chelicerae and two large pedipalps, but both ending in chelae (pincers), which strongly resemble those found in true scorpions (Image 6). The abundance of these predators recorded in Galician peatlands is low,

Image 5 Microphotographs (stereomicroscope) of an opilion. a: dorsal view showing its joined body regions and two ocelli; b: ventral view showing its long legs

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ranging between 2 and 38 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Subclass Acari: Order Mesostigmata This order includes free-living predatory mites that live in soil and litter. They are variable in size (200–2500 µm) and shape, from the elongated members of the family Parasitidae to the round “turtle” shape of those belonging to the family Uropodidade (Image 7). Their abundances in Galician peatlands are also extremely variable, ranging from just a few specimens to 5,300 individuals m−2 depending on the habitat (Carrera and Briones 2013b; Juan-Ovejero et al. 2019).

Image 6 Microphotographs (stereomicroscope) of a pseudoscorpion. a: dorsal view showing the cephalic appendages; b: ventral view showing the four pairs of walking legs

Image 7 Microphotographs (stereomicroscope) of Mesostigmata mites. a: dorsal view of an individual of the family Parasitidae; b: ventral view of an individual of the family Uropodidae

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Image 8 Microphotographs (stereomicroscope) of a Prostigmata mite. a: dorsal view showing the soft “velvety” appearance; b: lateral view showing the cephalic and thoracic appendages

Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Subclass Acari: Order Trombidiformes: Suborder Prostigmata Highly heterogeneous group of mites, in terms of size (100 µm–16 mm), biology and ecology (Carrera and Briones 2013b), but they can be best described by its lack of sclerotisation (Image 8) and the anterior position of the respiratory openings or “stigmata” (thus the name of the suborder). Many species are plant parasites (at least in one stage of its life cycle) and considered pests. In the Sierra do Xistral up to 14 prostigmatid families have been identified (Carrera and Briones 2013b), with abundances varying greatly, from < 3 to 30,000 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Subclass Acari: Order Trombidiformes: Suborder Astigmata Soft and pale mites with slow movements and without “stigmata” (thus the name of the suborder). They are typically small in size, ranging from 0.15 to 2 mm in length, and exhibit a variable number of feeding strategies including associations with bird and insect nests. This is because many species have a deutonymph stage adapted for phoresy (i.e., attaching to another mobile animal for transport). Their presence in Galician peatlands has been confirmed but in low numbers (< 1300 individuals m−2 ; Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Subclass Acari: Order Sarcoptiformes: Suborder Endeostigmata Another group of soft-bodied mites with low pigmentation and small size (ranging between 100 and 400 µm), and sometimes hypertrichous (i.e., high number of setae). Their abundances in peatland soils are low, usually less than 100 individuals m−2 , but in some Galician peat bogs they can exceed 3,500 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019).

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Phylum Arthropoda: Subphylum Chelicerata: Class Arachnida: Subclass Acari: Order Sarcoptiformes: Suborder Oribatida Highly sclerotized mites that could also bear sclerotized shields for extra-protection, reasons why they have commonly known as “armoured mites” and “beetle mites”. Members of the family Phthiracaridae can fully retract their legs and encapsulate by folding the anterior shell-like plate over the legs (ptychoid defense mechanism) and so they are known as “box mites” (Image 9a). Due to the hardening of the cuticle they are darker in colour, varying from yellowish to various shades of brown (Image 9). Its size may vary from 150 µm to 1.5 mm, although the majority range between 300 and 700 µm. They are well represented in peatlands (Barreto and Lindo 2018), and in Galician bogs they can reach high abundances (> 75,000 individuals m−2 ; Carrera and Briones 2013b; Juan-Ovejero et al. 2019) distributed among 22 different families (Carrera and Briones 2013b). Phylum Arthropoda: Subphylum Miriapoda: Class Chilopoda Also commonly known as “centipedes”, although their total number of legs ranges from 15 and 181 (Image 10a). They can be described as having a slightly flattened body measuring a few cm in length, although some species can reach 15 cm (Shelley 2002), but their most distinctive characteristic is the highly modified first pair of

Image 9 Microphotographs (stereomicroscope) of Oribatid mites. a: lateral view of an individual of the family Phthiracaridae; b: dorsal view of an individual of the family Camisidae; c: ventral view of an individual of the family Damaeidae

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Image 10 Microphotographs (stereomicroscope) of Myriapoda. a: lateral view of an individual of the class Chilopoda; b: lateral view of an individual of the class Symphyla

thoracic legs called “forciples” used for capturing preys by injecting venom with their claws. These predators have been recorded in Sierra do Xistral in low numbers, less than 150 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Miriapoda: Class Symphyla These small myriapods (2 to 15 mm in length) are usually whitish in colour, have 15 body segments and 11 to 12 pairs of walking legs. The most striking characteristic is their “moniliform antennae” because their round segments resemble a string of beads (Image 10b). Generally, in peat soils, their population numbers are low, although in those habitats dominated by shrubs and grasses they can reach up to 3,000 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Hexapoda: Class Entognatha: Order Collembola: Suborder Entomobryomorpha This suborder contains the largest collembolans (up to 17 mm), which usually occupy the upper soil horizons (epiedaphic) and can be easily identified by their long antennae and legs as well as well-developed furcula (Image 11a, b) that can propel them when threatened. In peat soils, they can reach high densities, on average 2,000–9,000 individuals m−2 but can exceed 30,000 individuals m−2 in certain habitats (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Hexapoda: Class Entognatha: Order Collembola: Suborder Poduromorpha These soil invertebrates have a rounded body shape and short stubby legs (Image 11c). Unlike the previous suborder their first thoracic segment is well developed and their furcula is short and flat. They are euedaphic, that is, true inhabitants of the soil and slow-moving (Orgiazzi et al. 2016) and small in size (generally 0.5 to 2 mm). In peat bogs they can reach 8,000 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019).

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Image 11 Microphotographs (stereomicroscope) of Collembola. a: lateral view of an individual of the suborder Entomobryomorpha; b: detailed view of its furcula; c: lateral view of an individual of the suborder Poduromorpha; d: lateral view of an individual of the suborder Symphypleona

Phylum Arthropoda: Subphylum Hexapoda: Class Entognatha: Order Collembola: Suborder Symphypleona Very round collembolans, almost spherical, and lacking distinct segmentation, with long antennae and short legs (Image 11d). Their minute size (generally < 4 mm in length) makes them inconspicuous. Like Entomobryomorpha they are also epiedaphic collembolans, living in the upper soil layers and good jumpers thanks to their well-developed furcula. Their populations in Galician peatlands are less numerous than those of the previous two suborders, on average 1,000–2,000 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Hexapoda: Class Ectognatha: Order Thysanoptera These are small insects (rarely exceed 5 mm) with an elongated body shape (Image 12a) and their wings, when present, are narrow and fringed (thus the name of the order, derived from the Greek “thysanos” meaning fringe and “ptera” meaning wings). They have rasping-sucking mouthparts, which are asymmetrically arranged, involving only one mandible (the right mandible is atrophied and the left mandible forms a stylet) and the maxillae bearing stylets. The three stylets together form the feeding apparatus that allows them to suck plant fluids. Previous studies indicate that its presence in Serra do Xistral is scarce, rarely exceeding 200 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019).

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Image 12 Microphotographs (stereomicroscope) of two insect orders. a: ventral view of an individual of the order Thysanoptera; b and c: lateral views of two nymphs of the order Hemiptera

Phylum Arthropoda: Subphylum Hexapoda: Class Ectognatha: Order Hemiptera The immature stages of these insects are commonly found in soils and their main identification feature is their sucking buccal apparatus, resembling a “beak” in which the modified mandibles and maxillae form a “stylet”. The nymphs typically look like small, wingless adults although they may differ in colour and markings (Image 12b, c). Their presence in peat soils is very low, ranging from 40 to 200 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Hexapoda: Class Ectognatha: Order Coleoptera Both adults and larval stages are common habitants of the litter layer and upper soil horizons (Orgiazzi et al. 2016). Their main features are their hardened first pair of wings or “elytra” that protects the second pair of functional wings (Image 13a, b), if present, and their well-developed jaws that use to capture a wide array of small invertebrates (although there are species that are phytophagous (feed on plants), fungivorous (feed on fungi) and feeding on seeds). The larvae can be easily identified by their well sclerotized head, ocelli and well-developed mandibles (Image 13c). Their populations in Galician peatlands can range from 90 to 700 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019).

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Image 13 Microphotographs (stereomicroscope) of Coleoptera. a: lateral view of a an individual of the family Chrysomelidae; b: lateral view of an individual of the family Staphilinidae; c: lateral view of two Coleoptera larvae

Phylum Arthropoda: Subphylum Hexapoda: Class Ectognatha: Order Diptera The adults only have a pair of functional wings (thus the name of the order), whereas the hindwings are modified as gyroscopic organs of equilibrium known as “halteres” or “balancers” (Image 14). Many species spend all their immature developmental stages in the soil, and together with the Coleoptera they are the insects best represented in most soils. In Gañlician peatlands, they can reach up to 9,000 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019). Phylum Arthropoda: Subphylum Hexapoda: Class Ectognatha: Order Lepidoptera Only the larval stage lives in the soil, which can be identified by the presence of four pairs of “false legs” located in the abdomen in addition to the three pairs of thoracic legs (Image 15). Unlike the adults, they have well-developed mandibles that they use for chewing green plants and thereby, are often considered pests. Their abundances in peat soils are low, typically < 8 individuals m−2 (Carrera and Briones 2013b; Juan-Ovejero et al. 2019), although it might be an underestimation due to limitations of sampling methods. Phylum Arthropoda: Subphylum Hexapoda: Class Ectognatha: Order Hymenoptera Their main features of this insect order are the four membranous wings and a narrow waist that connects the abdomen to the thorax. In soils, this group is mainly represented by ants (family Formicidae; Image 16), eusocial insects that live in large complex colonies with a division of labour, such as workers, soldiers, and queens.

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Image 14 Microphotographs (stereomicroscope) of Diptera. a: frontal view of an adult specimen; b: lateral view of an adult specimen showing the club-shaped halteres

Image 15 Microphotographs (stereomicroscope) of Lepidoptera larvae. a: ventrolateral view; b: ventral view showing the “true” and “false” legs

They are the dominant soil invertebrates in tropical climates, but can also be found in temperate soils, including peatlands, although in low abundances. Their populations in Sierra do Xistral range from 10 to 180 individuals m−2 (Juan-Ovejero et al. 2019).

Image 16 Microphotographs (stereomicroscope) of Hymenoptera (Formicidae). a: dorsal view of a worker ant showing the narrow waist; b: ventral view showing the well-developed jaws

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4 Final Remarks The environmental conditions (temperature and water regimes) that ensure peatlands persistence play a critical role in shaping their above- and belowground communities. In the case of soil invertebrates, their communities are dominated by smallsized organisms exhibiting different feeding (ranging from herbivores to omnivores) and locomotion strategies to explore their surroundings. However, because they are mostly aerobic and feed on plant derived inputs, they tend to be concentrated in the uppermost layers of the peat and hence, more exposed to climate and water extremes. It is their tolerance to drought and water saturation which determines their population numbers and vertical distribution (Juan-Ovejero et al. 2019), their impact on C mineralisation and mobilisation (Briones et al. 2014) and ultimately, peatland ecosystem stability. Acknowledgements This work was jointly funded under two projects: CICYT research grant (Ref. REN2002-03224/GLO) and MINECO research grant (Ref. CGL2014-54861-R).

References Bain C, Bonn A, Stoneman R, Chapman S, Coupar A, Evans M, Gearey B, Howat M, Joosten H, Keenleyside C, Labadz J, Lindsay R, Littlewood N, Lunt P, Miller CJ, Moxey A, Orr H, Reed M, Smith P, Swales V, Thompson DBA, Thompson PS, Van de Noort R, Wilson JD, Worrall F (2011) IUCN UK commission of inquiry on peatlands. IUCN UK Peatland Programme, Edinburgh Barreto C, Lindo Z (2018) Drivers of decomposition and the detrital invertebrate community differ across a hummock-hollow microtopology in boreal peatlands. Écoscience 25:39–48. https://doi. org/10.1080/11956860.2017.1412282 Briones MJI, Ineson P, Heinemeyer A (2007) Predicting potential impacts of climate change on the geographical distribution of enchytraeids: a meta-analysis approach. Glob Change Biol 13:2252–2269. https://doi.org/10.1111/j.1365-2486.2007.01434.x Briones MJI, McNamara NP, Poskitt J, Crow SE, Ostle N (2014) Interactive biotic and abiotic regulators of soil carbon cycling: evidence from controlled climate experiments on peatland and boreal soils. Glob Change Biol 20:2971–2982. https://doi.org/10.1111/gcb.12585 Carrera N, Briones MJI (2013a) Oligochaeta communities from Galician upland peatlands. In: Riosmena-Rodríguez R (ed) Invertebrates: classification, evolution and biodiversity. Nova Science Publishers Inc., New York, USA, pp 67–89 Carrera N, Briones MJI (2013b) Arthropod community structure and diversity from Galician upland peatlands. In: Riosmena-Rodríguez R (ed) Invertebrates: classification, evolution and biodiversity. Nova Science Publishers Inc., New York, USA, pp 1–65 Cragg JB (1961) Some aspects of the ecology of moorland animals. J Ecol 49:477–506 Glime JM (2013) Chapter 8: Arthropods: harvestmen and pseudoscorpions. In: Glime JM (ed) Bryophyte ecology, vol 2. Bryological interaction. Ebook sponsored by Michigan Technological University and the International Association of Bryologists Gorham E (1991) Northern peatlands: role in the carbon cycle and probable responses to climatic warming. Ecol Appl 1:182–195 Izco J, Ramil-Rego P (2001) Análisis y valoración de la Sierra de O Xistral: un modelo de aplicación de la Directiva Hábitat en Galicia. Consellería de Medio Ambiente. Xunta de Galicia, Santiago de Compostela, p 162

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Juan-Ovejero R, Benito E, Barreal ME, Rodeiro J, Briones MJI (2019) Tolerance to fluctuating water regimes drives changes in mesofauna community structure and vertical stratification in peatlands. Pedobiologia 76:150571. https://doi.org/10.1016/j.pedobi.2019.150571 Limpens J, Berendse F, Blodau C, Canadell JG, Freeman C, Holden J, Roulet NT, Rydin H, Schaepman-Strub G (2008) Peatlands and the carbon cycle: from local processes to global implications–a synthesis. Biogeosciences 5:1475–1491. https://doi.org/10.5194/bg-51475-2008 Martínez-Cortizas A, Pontevedra-Pombal X, Nóvoa-Muñoz JC, García-Rodeja E (2000) Turberas de montaña del noroeste de la Península Ibérica. Edafologia 7:1–29 Orgiazzi A, Bardgett RD, Barrios E, Behan-Pelletier V, Briones MJI, Chotte J-L, De Deyn GB, Eggleton P, Fierer N, Fraser T, Hedlund K, Jeffery S, Johnson NC, Jones A, Kandeler E, Kaneko N, Lavelle P, Lemanceau P, Miko L, Montanarella L, Moreira FMS, Ramirez KS, Scheu S, Singh BK, Six J, van der Putten WH, Wall DH (2016) Global Soil Biodiversity Atlas. Publications Office of the European Union, Luxembourg, European Commission Ramil-Rego P, Gómez Orellana L, Guitián MAR, Castro HL, Real C, da Costa JF, Sobrino CM (2017) Tipología y sistemas de classficación. In: Ramil-Rego P, Guitián MAR (eds) Hábitats de Turbera en la Red Natura 2000. Diagnosis y Criterios para su Conservación y Gestión en la Región Biogeográfica Atlántica. Horreum-Ibader, Lugo, pp 29–148 Schmelz E, Collado R, Briones MJI (2008) Notes on Marionina filiformis Nielsen & Christensen, 1959 (Enchytraeidae, Oligochaeta, Annelida). Verh Naturwissenschaftlichen Vereins Hamburg (neue Folge) 44:23–35 Shelley RM (2002) A synopsis of the North American centipedes of the order Scolopendromorpha (Chilopoda). In: Memoir 5. Virginia Museum of Natural History, Martinsville. Retrieved from http://refhub.elsevier.com/B978-0-12-415955-6.00005-0/rf0735 Swift MJ, Heal OW, Anderson JM (1979) Decomposition in terrestrial ecosystems. Blackwell Science, Oxford Xu J, Morris PJ, Liu J, Holden J (2018) PEATMAP: Refining estimates of global peatland distribution based on a meta-analysis. Catena 160(2018):134–140. https://doi.org/10.1016/j.catena. 2017.09.010

Grasslands on Acid Soils: Use of Different Amendments in the Context of Galicia M. J. Fernández-Sanjurjo, A. Barreiro, and E. Álvarez-Rodríguez

Abstract The large importance of the bovine sector in Galicia, which situate it among the top 10 dairy regions in Europe, would explain the high agricultural area that is occupied by grasslands (70% of the usable agricultural area). These grasslands are, in most cases, placed on unproductive and acid soils, whereby the addition of amendments and fertilizers is essential. Since last mid-century numerous research studies about the impact of liming and fertilization practices on different Galician soils have been performed. In this chapter, the main results from three different studies related with amendment addition in grassland soils are presented chronologically, including pictures that help to recognize the edaphic and landscape context where these grasslands develop. The first study investigated the residual effect of CaCO3 addition, at different doses (0.75, 1.5, 3.0, 6.0 and 12 Mg ha−1 ), on different parameters of grassland soils developed on three lithological materials (granite, slate and gabbro). Starting from 3.0 Mg ha−1 of limestone, a residual effect was observed even 6 or 7 years after the amendment application, with tenfold higher Ca and a decrease in Al saturation up to 50% in the plots with the highest doses, compared with the control ones. In the second study the possibility to replace, as regular liming product, the commercial limestone with mussel shell, a very abundant residue in the region, was investigated. Tests were performed using mussel shell (grinded or calcined) with different particle size. The mussel shell applied doses (3.0 Mg ha−1 ) was enough to increase Ca and to decrease Al saturation, from 60% in the control soils to less than 20% in the non-rhizosphere soil and to less than 5% in the rhizosphere. These results, together with plant production ones, were similar to those obtained with commercial limestone. The third study, performed in 2009/2010, analysed the fertilizing and liming capacity of several mixtures prepared with residues from the canning and forestry industries. The results from plots where these mixtures were added, plots with just NPK fertilization, plots with NPK and mussel shell addition (NPK + MS) and control plots, were compared both in the rhizosphere and nonrhizosphere area. The NPK + MS treatment was the one that caused the better soil M. J. Fernández-Sanjurjo (B) · A. Barreiro · E. Álvarez-Rodríguez Department of Soil Science and Agricultural Chemistry, Engineering Polytechnic School, University of Santiago de Compostela, Lugo 27002, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_13

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chemical conditions, but the mixtures also significantly improved the acidic conditions of these soils compared with the control and NPK treatments. The production of the species sowed in the plots with mixtures and with NPK + MS was similar and significantly higher than in the plots with NPK and the control ones. The rhizosphere area presented better conditions for plant growth than the non- rhizosphere soil in all the plots, proving the importance of the study of this root contact area in these grassland soils. Keywords Grassland · Acid soils · Limestone · Residues · Mussel shell · Rhizosphere soil

1 Introduction The lithology of Galicia (NW Spain) is very differentiated, even though the predominant rocks are granites (45%) and schist and slates (45%), appearing as well basic and ultrabasic rocks (5%), carbonated rocks and sedimentary material of different percentage valuation (Macías et al. 1982; Macías and Calvo 2001). This lithological variability entails a wide-ranging chemical composition and mineral stability and is one of the main factors explaining the existence of a great soil diversity in this region. The noticeable influence of the bedrock in the distribution and properties of the soils was already suggested in the 60’s of the last century (Guitián and Carballas 1969). Since then, these soils have been well studied (Calvo and Díaz-Fierros 1981; Calvo et al. 1983; García Rodeja et al. 1987; Macías et al. 1982; Macías and Chesworth 1992 among others). Despite the high lithological variability, most of the soils in Galicia are acid due to the humid climate, a hilly topography, and a wide hydrographic net, which involves the existence of open and subtractive alteration systems. This situation causes the loss of bases and a relative enrichment in elements from the residual system, reinforced by the siliceous rock prevalence. These soils are also rich in organic matter, with high values of changeable Al and in forms potentially toxic in solution, with a low cation exchange capacity (CEC) and presenting colloids with variable charge. These characteristics limit the production and explain the high number of studies that have been realized with the objective of knowing the amendment and fertilization type and the more suitable doses which are needed in the different soils and crops, as well as their residual impact (Mombiela and Mateo, 1984; Fernández-Sanjurjo et al. 1995a, b; Álvarez et al., 2010; Fernández-Sanjurjo et al. 2011; Illera-Vives et al. 2017; among others). In connection with fertilization, there are a great number of studies using organic fertilizers (slurry and manure), chemical fertilizers, mixtures of both, as well as different industrial residues and by-products. Regarding the acidity correction, different liming products have been studied, the most efficient dose and size and the duration of the amender effect in different soils. In this chapter, we present three research studies related to the amendment addition on grassland soils in Galicia, where is showed the progress of these studies over

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time. Firstly, the main results from a study about the residual impact of the addition of different doses of limestone to grasslands located on different lithological material is show. The second study analyse the possibility of replacing limestone as a regular liming product with mussel shell, a very abundant residue in the region. Finally, in the third study the possible replacement of the traditional amendments and fertilizers (NPK) with different mixtures elaborated with several industrial residues was analysed.

2 Grasslands in Galicia Galicia represents 5.8% of the Spanish territory area but produces 14% of the beef produced in Spain and 40% of the milk, positioning in the last 30 years in the top 10 dairy regions in the UE (https://www.campogalego.es/-2022). This explains that fodder crops, especially grasslands, constitute an essential part of the agricultural systems in this region. From a total of 2.957.674 ha that comprise the Galician territory, currently grassland occupy 470.458 ha (Statistics-Xunta de Galicia 2022), standing out for around 75% of the usable agricultural area (Anuario 2020– Fundación de Estudios Rurales). The concept of grassland will be used generically in this chapter, but numerous terms exist that define different types of grasslands and varies depending on the area (meadow, prairie, pasture, fodder areas…) (Peeters et al. 2014). The temporal grassland integrated in fodder areas would be a polyphyletic grassland, sown and compound overall by grasses and leguminous plants, used for mowing or grazing and associated with a rotation with other crops (corn, wheat, oat…) (Ferrer et al. 2011). This grassland type is the most common in the numerous cattle farms existing in Galicia, usually in rotation with corn (Fig. 1). When farms are dedicated to beef production, the grasslands are more used for grazing, meanwhile in the dairy production farms, grasslands are more used for mowing and ensilage (Fernández-Lorenzo et al. 2009). For this reason, in the Galician landscape the areas dedicated to grasslands and corn production abound, together with forest and/or shrubland areas, creating the typical mosaic landscape (Fig. 2). In some areas, this kind of landscape is being removed, due mainly to two reasons: (1) the strong Galician forestry sector, which produces 57% of the timber of Spain (Xunta de Galicia 2022), creates wide areas mainly dedicated to pines and eucalyptus plantations (Fig. 2). (2) Additionally, in certain areas, the shrubland area is increasing due to agricultural activity abandonment, even though in these areas the regional government is encouraging the recovery of grassland area in the last years (Grassland Plan: https://www.xunta.gal/hemeroteca/-/nova/134248/). The goal is that these areas will work both as firewalls to prevent the advance of the numerous wildfires that happens in this region, and as fodder provider specially for extensive cattle raising. From the edaphic point of view is interesting to highlight the great soil variety of the soils where these grasslands settle in. This diversity is justified, among other

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(a)

(b)

(c)

(d)

Fig. 1 Images of different types of grassland in Galicia): a Natural grassland; b Semi-natural grassland; c Wet grassland for mowing (meadow); d Temporal grassland with corn rotation (fodder areas)

factors, by the lithological variability in Galicia already pointed out (Macías and Calvo 2001). In the Fig. 3 two grassland profiles on granite are showed. The first presents a shallow A horizon on fresh rock. The second profile is developed on more stable surfaces, showing the usual organic-rich A horizon; the abundance of resistant minerals and the region climate, favour the formation of wide saprolites with light

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Fig. 2 Typical mosaic landscape, very frequent in Galicia (above). Grasslands and recent forest plantations (below)

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colours. These are acid and aluminous soils, with a sandy and sandy-loam texture and a frequent summer water deficit. Figure 4 corresponds to grasslands developed on slates. These soils are shallow, especially in the areas with the highest slope where the colluvial processes act (see the stone line in the first profile) that, together with the usual geological dip difficult the edaphic stability because they favour slide and erosion. Despite the low alterability of this rock, in the areas with lower slope a bigger profile development is possible (Fig. 4, third profile). Similar to granite, these soils are very acid but, in this case, frequently present loam texture, which implies a hydromorphic risk. Figure 5 corresponds to grasslands on basic rocks (gabbro). The high alterability of these rocks under the climate of this region originates deep soils, with reddish

Fig. 3 Soil profiles on granite (up) and panoramic view of grasslands on this lithology (bottom)

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Fig. 4 Different soil profiles on slates (up) and panoramic view of grasslands on this lithology (bottom)

brown colour (due to the abundance of ferromagnesian minerals), with low degree of order and high variable charge clays (andic properties). This implies low phosphorous availability due to the high fixation. These soils are relatively less acid and richer in Ca and Mg. Both their clayey texture and profile depth favour water retention. Regarding schists, their properties are intermediate between the ones from acid rocks and basic rocks. Soils on schists more acid (muscovite schists) have characteristics closer to the soils developed on granitic rocks (Fig. 6a, 6b). Schists with more basic nature (biotitic schists) (Fig. 6c, 6d) create soils less acid, deeper and more reddish, with less deficit of Ca and Mg (comparing with soils on acid rocks) and K (comparing with soils on basic rocks), and with loam textures. Generally, these soils have good aptitudes for crop establishment and important cattle farms settle on them (Fig. 6e). Everything previously exposed, together with the importance of grass crops in Galicia, justifies the scientific interest and the numerous studies realized since years ago about these acid and Al saturated soils. In the following sections, the main

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Fig. 5 Grassland soil profiles developed on gabbro

results of three studies arranged chronologically, are explained, where the different approaches over time is noted.

3 Residual Effect of the Addition of Different Limestone Amendment Doses in the Establishment of Permanent Grasslands The liming practise in Galicia, which is long serving, started in the coastal area by adding directly to the soil bivalve shell remains that are abundant there. In the inland areas it was less common since this material was not available. Afterwards, the arrival of the limestone did not generalize this practise, due to the high cost of the limestone amendments, aggravated because of the high doses that were recommended to increase the pH up to neutrality (10 or 12 Mg ha−1 of calcium carbonate) (Guitián and Muñoz 1962). However, later studies proved that the most important feature of the liming practises is the decrease in the Al toxicity. With this new criterion, the recommendations regarding the amount of limestone to add decrease (2–4 Mg ha−1 ), obtaining also better correlations with production by avoiding over liming (Mombiela and Mateo 1984; Farina and Channon 1991; Moody et al. 1998). This caused that the liming practice expanded all over Galicia and, in parallel, an increase in the studies related with the topic (Condron et al. 1993; Fernández-Sanjurjo et al. 1995a; Castro et al. 1998; Álvarez et al. 2010). The work presented below is situated in this context. The study analysed the transformation of soils dedicated to forest and shrub into permanent grasslands. It was intended to study the residual effect of adding limestone and chemical fertilizers in the different chemical and mineralogical properties of soils developed on different geological material (Fernández-Sanjurjo 1994; Fernández-Sanjurjo et al. 1995a, b a,

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(e)

Fig. 6 Grassland soil profiles developed on micaceous schists (a and b), on biotitic schists (c and d) and panoramic view of grasslands on this last lithology (e)

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b; Fernández-Sanjurjo et al. 1996). In this chapter only the results from the liming experiment will be exposed. The establishment of the experimental plots was performed by Mabegondo Center of Agricultural Research–CIAM (A Coruña province), in three areas of Galicia with different geology (granite, slate, gabbro) in 1981/1982. The main characteristics of the natural soils are showed in Table 1. The liming experiment consisted of 6 plots (5 × 8 m), with five different doses of CaCO3 (0.75, 1.5, 3, 6 and 12 Mg ha−1 ) and one control plot (without limestone) for each type of soil. Limestone was added to the soil just at sowing time, meanwhile all the plots, including the control one, received a basal NPK fertilization annually. Sowing was realized with a mixture of English ryegrass (Lolium perenne), hybrid ryegrass (Lolium hybrid), white clover (Trifolium repens) and red clover (Trifolium pratenses). The experiments with the soils on granite and slate started in 1981 and the samples were sampled in 1988, two years after the last NPK fertilization and seven years after the lime addition. The experiment with the soil on gabbro started in 1982 and the samples were sampled also in 1988 (one year after the last fertilization and 6 years after the last liming). The results confirmed the acidity of the natural soils on granite and slate (Table 1), with low Ca concentration and high values for Al in the exchange complex (with Al saturation higher than 80%). These chemical conditions improve, in some cases, with the NPK fertilization and specially with the liming added 6/7 years before the sampling (Fig. 7). All the limed soils showed higher pH compared with the control plots (NPK) reaching, both on granite and on gabbro, values close to 6.0 in the plots with 12 Mg ha−1 . The liming maintained its influence on the exchangeable Al (Fig. 7), one of the main problems of the acid soils, observing a clear decrease of this high values compared with the plots with NPK (and natural soils) developed on granite and slate. Similar behaviour was observed for the Al in solution. The effect was almost always clearer as from the addition of 3 Mg ha−1 of lime (Fig. 7). Regarding other parameters (not shown), the effects were also evident as from 3 Mg ha−1 of added lime, increasing the exchangeable Ca and decreasing the Al saturation up to less than 30% in the soils on granite and slate. In the soil on granite, the limed plots showed more available P (data no show), possibly due to the increment Table 1 Some chemical characteristics and the classification (WRB 2014) of the three natural soils Soils

WRB-Clasif (2014)

pH

Ca exch cmolc

Al exch

eCEC

kg−1

Al sat %

Granite

Cambic umbrisol

4.0

0.44

5.08

6.07

84

Slate

Distric gleysol

4.3

0.38

3.22

4.16

87

Gabbro

Cambic (andic) umbrisol

5.4

4.80

0.95

6.91

14

Exch Ca, exch Al: exchangeable Ca and Al; eCEC: effective cation exchange capacity; Al sat: Al saturation in the exchange complex

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Fig. 7 pH in water, in KCl and in the soil solution (SS pH), as well as exchangeable Al (cmolc kg−1 ) and Al in solution (mg L−1 ) in the control plots (NPK or dashed line) and in the limed plots (1 = 0.75; 2 = 1.5; 3 = 3.0; 4 = 6.0; 5 = 12 Mg ha−1 of limestone added)

in the negative charges of the colloids with variable charge of these soils. Soils on slate and gabbro maintained low concentrations of P (data no show), probably due to the fixation to the abundant non-crystalline Fe and Al compounds that presented these soils. These results indicated a clear residual effect of the liming of forest soils for the establishment of these grasslands elapsed 6 or 7 years after the addition and already detected as from 3 Mg ha−1 of lime added.

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4 Mussel Shell as Soil Liming: A Possible Alternative to the Commercial Limestone Most of the amendments added to acid soils use CaCO3 coming from calcareous rocks, which extraction process cause a strong environmental impact. Since there are many waste products with a certain liming power, the possibility of using them instead of limestone was considered. It would be an alternative environmentally friendly, safe and economical. In Galicia, between 66,000 and 94,000 t of waste mussel shells are generated yearly by the mussel industry (Barros et al. 2009). Storage of this waste generates serious environmental problems. Some dedicated businesses transform mussel shell waste, by subjecting it to different treatments, into marketable products of different particle sizes (Fig. 8). The objective of this study was to investigate the effects of the addition of mussel shells, with different treatments and commercially available, in acid grassland soils. The effects on the chemical properties of the acid soil (mainly pH and Ca and Al contents), production of pasture species and the quality of the pasture were determined and compared with those produced by the addition of a commercial lime to the rhizosphere and non-rhizosphere soil (Álvarez et al. 2012a, b). The study was realized in a soil developed on granite, classified as Haplic Umbrisol (WRB 2014). The experimental plot was divided into sub-plots where the following treatments were applied: commercial lime (CL); ground dried mussel shells, 0– 2 mm (MDF); ground dried mussel shells, 2–4 mm (MDC); calcined-mussel shells < 63 µm (MHF); and calcined-mussel shells, 0–2 mm (MHC). Control plots that were not limed were also established. The sown species were: Dactylis glomerata var. Amba, Trifolium repens var. Hvia, and Lolium perenne var. Tove. The experiment was established in March 2007 and soil and plant sampling was realized in June 2008. In this chapter, some of the main analysed parameters (pH, exchangeable Ca and Al, Al saturation and grass production) will be presented.

Fig. 8 Mussel shell subjected to different treatments (calcined or not calcined) and with different particle sizes

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Figure 9 represents different parameters of the solid phase, both from rhizosphere and non-rhizosphere soil. The efficiency of the treated mussel shell, especially the one calcined and with lower size (MHF), was similar to the commercial limestone in relation to the increment in pH and exchangeable Ca and the decrease in exchangeable Al and Al saturation. These effects were much more obvious in the rhizosphere area (Fig. 9). The treatment doses of 3 Mg ha−1 applied was enough to reduce the Al saturation up to values lower than 20% in the non-rhizosphere soil and up to 5% in the rhizosphere. Regarding grass yield, the production of the native species was similar in all the plots (Fig. 10), while the sown species were more abundant in the treated plots

Fig. 9 pH in water, exchangeable Ca, exchangeable Al, and Al saturation in the control plot and the plots amended with limestone (CL) and with mussel shell ground dried 0–2 mm (MDF) and 2–4 mm (MDC), calcined-mussel shells < 63 µm (MHF) and calcined 0–2 mm (MHC). Different letters indicate significant differences at p < 0.05 among treatments, according to Tukey’s test

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Native species

5 4

a

Sown Species a

a

a a

Mg ha-1

a 3

b

b 2 1

ab

a

ab

ab

0 Control

CL

MDF

MDC

MHF

MHC

Fig. 10 Production of native and sown species in the control and amended plots with limestone (CL) and with mussel shell ground dried 0–2 mm (MDF) and 2–4 mm (MDC), calcined-mussel shells < 63 µm (MHF) and calcined 0–2 mm (MHC). Different letters indicate significant differences at p < 0.05 among treatments, according to Tukey’s test

compared with the control ones (significative differences with CL and MHF); this agrees with the better chemical conditions that the treated plots presented, especially in the rhizosphere area. Again, the plots with MHF treatment stand out with a higher production of these species, overcoming even the plot with commercial lime (CL), even though the difference was not significative. Based on these results, and the rest found in the works cited above, we can conclude that the mussel shell, especially the calcined one and with smaller particle size, can replace commercial lime in the amendment of acid soils.

5 Use of Various Mixtures of Industrial Residues as Liming Products and Fertilizers in Grassland Soils This new study is a continuation of the research line described in the previous section. The topic is the possible utilization of industrial residues as substitutes for, not only traditional liming products, but also for the inorganic fertilizers usually applied to grasslands. In this case, several mixtures with different residues from the forestry and canning industries were tested. These activities are very important in Galicia since produces 57% of the cut wood from all the Spanish state (Xunta de Galicia 2022) and worldwide is the third mussel producer. The large amount of waste shell

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produced is treated by the mussel shell processing industry, washing, grounding and/ or performing calcinations of the raw shell to obtain valued materials. During these treatments, the mussel shell industry generates some problematic wastes, such as shell calcination ash and sewage sludge, that are difficult to recycle due to various problematic characteristics, namely high electrical conductivity and pH values. However, putting together adequate mixtures of those wastes with wood ash from the timber industry, or with a certain proportion of valued mussel shell, could give final materials with overall improved characteristics, which could be recycled in acid soils. The objective of this study was to analyse how the addition, at the grass sowing time, of several of the previously mentioned residue mixtures impacted in the soil chemical properties and grass production. The study started in May 2009 in an acid soil developed on slate (Haplic Umbrisol, WRB 2014). After doing several mixtures with the different residues, three of them that presented the better organoleptic, physical and chemical properties were selected. The percentage composition (w/w, dry weight) of each mixture was: mixture M78 = 47% sewage sludge, 48% shell ash, and 5% wood ash; mixture M58 = 47% sewage sludge, 40% shell ash, and 13% mussel shell, and mixture M32 = 45% sewage sludge, 51% shell ash, and 4% mussel shell. The experimental plot was divided into sub-plots of 25 m2 each one (Fig. 11). For comparison purposes, plots with only inorganic fertilization (NPK), with inorganic fertilization supplemented and mussel shell (NPK + MS) and control plots (no treatment) were also included. The doses added at the sowing time were: 6 Mg ha−1 of each mixture, 0.5 Mg ha−1 of conventional inorganic fertilizer (NPK) and 0.5 Mg ha−1 of NPK + 6 Mg ha−1 of mussel shell. Totally, 24 plots were defined, including 4 replicates of each treatment. After the spreading the treatments, the plots were sown with the pasture species Lolium multiflorum Lam. and Trifolium pratense L. The field study was maintained for two years (2009 and 2010). The pasture was harvested twice a year, in the summer and fall, sampling soil and plant samples each time to be analysed. In this chapter some of the results from the samplings realized in July 2009 and 2010 are presented (pH, exchangeable Ca and Al, Al saturation, Al

Fig. 11 Detail of the experiment establishment and the different grass development depending on the plot treatment

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form in solution and grassland production). Additionally, an intermediate sampling was realized in October 2009, in which the rhizosphere soil (RS) was separated from the non-rhizosphere soil (NRS) (Seco et al. 2014). The obtained results indicated that, in the first sampling, even though the pH values were always low, the plots amended with residues or with NPK + MS presented the higher values, significantly different from the values obtained from the control plots and the plots where only NPK was used for fertilization (Table 2). The higher soil pH values found in the mixture-treated and NPK + MS-treated plots would be related to the alkaline pH of MS and the mixtures. The results of Ca showed a similar trend that the pH values (Table 2), with the highest concentration in the amended plots, standing out the plots with NPK + MS treatment (39.3 cmolc kg−1 ), significantly higher than the concentration obtained in the control and NPK plots (< 0.6 cmolc kg−1 ). Regarding the eCEC, the results showed an identical trend to Ca, meanwhile the Al (and its percentage on the exchange complex) behaved inversely (Table 2). Thereby, the amendments reduced the Al saturation from more than 70% up to levels lower than 20%. In the second sampling, the trends were similar, even though the values of exchangeable Ca and eCEC clearly decreased, inducing an increment in the Al saturation in the amended plots in comparison with the first sampling (Table 2). The impact of the amendments on the Al fractionation and speciation in the soil solution were also studied (Seco et al. 2014). Table 3 shows the Al species solely. All these Al species decreased in the amended plots, disappearing the most toxic specie Table 2 Chemical parameters determined in the solid phase of the soil and the production of sown species (PPS), for each sampling date, corresponding to the control and treated plots. Treatments: NPK, NPK + MS (NPK + mussel shell) and the mixtures (M78, M58, M32). Different letters indicate statistically significant differences among treatments, referred to each sampling date (p < 0.05) Control

NPK

NPK + MS

M78

M58

M32

July–09 July–10

4.26ab

4.15a

5.18e

4.92de

4.61 cd

4.86a

4.73a

5.42b

5.22ab

5.18ab

4.56bc 5.02ab

Exch Ca

July–09 July–10

0.45a 0.77a

0.54a 0.57a

39.43c 5.60b

19.32b 5.06b

15.14b 3.81ab

13.04b 4.24b

Exch Al

July–09 July–10

7.58c 6.34b

7.49c 6.49b

0.66a 2.04a

2.01ab 3.09a

3.78b 3.32a

3.93b 3.92a

eCEC

July–09 July–10

10.72a 8.10a

9.95a 7.93a

43.04b 8.76a

24.15a 9.35a

21.94a 8.11a

19.97a 9.17a

Al sat

July–09 July–10

71.45c 77.75b

75.12c 82.13b

1.73a 23.02a

8.49ab 35.16a

20.37b 41.57a

20.31b 43.44a

PPS

July–09 July–10

0.00a 0.00a

1.04b 0.00a

1.84c 5.25c

0.99b 3.72b

0.82b 4.43c

0.80b 3.98b

pH

Exch Ca, Exch Al: exchangeable Ca and Al (cmolc kg−1 ); eCEC: Effective cation exchange capacity (cmolc kg−1 ); Al sat: Al saturation in the exchange complex (%); PPS: sown-species plant production (Mg ha−1 )

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(Al3+ ), and this trend was sustained in the second sampling. These effects, caused by both the treatment NPK + MS and the mixtures, are the expected effects of the traditional liming practices (Álvarez et al. 2010; Drábek et al. 2007). Regarding the production of the sown species (Table 2), in the first sampling there were not big differences between the differently treated plots. On the other hand, in the second sampling stands out the disappearance of the sown species in the NPK plot but their clear increase in the amended plots, especially the ones with the NPK + MS and M58 treatments. The production of these last plots was similar to the production obtained in other plots were the liming product used was commercial limestone (Álvarez et al. 2009). Regarding the October 2009 sampling, where the rhizosphere (RS) and nonrhizosphere (NRS) soil was differentiated (Fig. 12), no very marked differences were observed between the various plots when the NRS was considered. However, in the soil in contact with the roots (RS), the values of most of the parameters analysed were significantly different in the plots NPK + MS and in the plots where residues were added, compared with the control and NPK plots. This could imply that the grass roots were situated in the areas with the best chemical conditions (less acid, with more Ca and less Al). The fact of not considering the RS in the fertility studies might cause an underestimation of the soil nutritive state and provoke an unnecessary addition of fertilizers and amendments. This would also explain the discrepancies obtained sometimes between the values of plant production and the soil properties. Table 3 Speciation of the Al monomers in solution (labile Al) in the plots corresponding to the control (C) and treated plots. Treatments: NPK, NPK + MS (NPK + mussel shell) and the mixtures (M78, M58, M32) (LoD: Limit of Detection) Al+3

Al–F

Al–OH

Al–SO4

C

2.2

1.8

8.5

0.4

NPK

4.8

2.4

6.1

0.5

NPK + MS

< LoD

< LoD

1.4

< LoD

M78

< LoD

< LoD

6.0

< LoD

M58

< LoD

0.5

3.1

< LoD

M32

< LoD

0.5

2.5

0.2

C

2.4

2.6

7.1

< LoD

NPK

4.2

2.9

4.8

< LoD

NPK + MS

< LoD

0.5

1.9

< LoD

M78

< LoD

0.6

1.8

< LoD

M58

< LoD

0.6

1.8

< LoD

M32

< LoD

2.0

4.0

< LoD

July–09

July–10

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Fig. 12 Exchangeable Al, pH, effective cation exchange capacity (eCEC) and exchangeable Ca corresponding to the control and treated plots. Treatments: NPK, NPK + MS (NPK + mussel shell) and the mixtures (M78, M58, M32). NRS: non rhizospheric soil; RS: rhizospheric soil. Different letters indicate statistically significant differences among treatments, (p < 0.05)

6 Final Remarks The importance of the bovine sector in Galicia entails that a wide area of the region´s surface is dedicated to grasslands. In the acid soils, characteristic of this region, numerous studies have been realized since the middle of the last century related to fertilization and liming of grassland soils, three of them being presented in this chapter. The first study, realized in the mid 80’s, proved the residual effect of the limestone addition at sowing time in soils developed on different lithology during the transformation to grasslands. The effects of the limestone maintained during 6 or 7 years since its addition, being the intensity of this effect dependent on the soil type and added doses. The results showed that it would be enough the addition of 3 Mg ha−1 limestone at sowing time in order to keep the better conditions for the grass growth, compared with the natural and control soils. The second study, which was performed in the years 2007/2008, reflected the concern for the valuation of some residues that are abundant in this region, such as the mussel shell. Therefore, the possibility of using this residue as a liming for grassland soils, in replacement of commercial limestone was investigated. The obtained results showed that the effects of mussel shell on the soil chemical properties and grass production, were very similar to the ones caused by limestone. Base in this, the

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products derived from mussel shells could substitute the commercial lime in the amending of acid soils, therefore increasing the value of the shells and limiting the environmental problems derived by their disposal. The huge quantity of mussel shell produced is treated by several industries before being commercialized; and in this process other residues are generated (ash and sludge). The third study, realized in 2009/2010, investigated the possibility of using this difficult-to-manage residues as well. In the study, these residues were mixed with other residues produced by the forestry industry (ash) and were applied to grasslands at sowing time to test their liming and fertilizing power. The different mixtures caused effects in the soil chemical properties and grass production similar to the ones caused by liming and conventional fertilization. The studied mixtures could complement or even substitute the more conventional treatments based on limestone and NPK. The two last studies highlighted the improvement in the chemical conditions obtained in the rhizosphere area compared with the non-rhizosphere area, which indicates the importance of the study of the rhizosphere soil in order to know the real soil productive capacity. Acknowledgements The authors thank all the researchers who have collaborated in carrying out the studies presented in this article. Thanks are also due to Cristina and Juan Fraga for their help in part of the photographic report.

References Álvarez E, Viadé A, Fernández-Marcos ML (2009) Effect of liming with different sized limestone on the forms aluminium in a Galician soil (NW Spain). Geoderma 152:1–8 Álvarez E, Viadé A, Fernández-Marcos ML, Hernández-Nistal J (2010) Limestone particle size and liming scheduling influence soil properties and pasture production. Soil Sci 175:601–613 Álvarez E, Fernández-Sanjurjo MJ, Núñez A, Seco N, Corti G (2012a) Aluminium fractionation and speciation in bulk and rhizosphere of a grass soil amended with mussel shells or lime. Geoderma 173:322–329 Álvarez E, Fernández-Sanjurjo MJ, Seco N, Núñez A (2012b) Use of mussel shells as a soil amendment: effects on bulk and rhizosphere soil and pasture production. Pedosphere 22:152–164 Barros MC, Magán A, Valiño S, Bello PM, Casares JJ, Blanco JM (2009) Identification of best available techniques in the seafood industry: a case study. J Clean Prod 17:391–399 Calvo R, Díaz-Fierros F (1981) Consideraciones acerca de la acidificación de los suelos de la zona húmeda española a través de la vegetación. Anales Edafología Agrobiología 40:411–425 Calvo RM, García-Rodeja E, Macias F (1983) Mineralogical variability in weathering microsystems of a granitic outcrop of Galicia (Spain). CATENA 10:225–236 Castro J, Novoa R, Blazquez R (1998) Liming with slurry enriched with calcium carbonate used like bedding material in a dairy cow’s stall. In: Waste management strategies, pp 385–388 Condron LM, Tiessen H, Trasar-Cepeda C, Moir JO, Stewart JWB (1993) Effects of liming on organic matter decomposition and phosphorus extractability in an acid humic ranker soil from northwest Spain. Biol Fertil Soils 15:279–284 de Galicia X (2022) Inventario Forestal Continuo de Galicia (IFCG). Consellería de Medio Rural. Retrieved from https://mediorural.xunta.gal/es/temas/forestal/inventario-forestal-continuo Drábek O, Bor˚uvka L, Pavl˚u L, Nikodem A, Pírková I, Vacek O (2007) Grass cover on forest clear-cut areas ameliorates some soil chemical properties. J Inorg Biochem 10:1224–1233

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Farina MPW, Channon P (1991) A field comparison of lime requirement indices for maize. Plant Soil 134:127–135 Fernández-Sanjurjo MJ (1994) Modificaciones inducidas por las técnicas de transformación y cultivo de pratenses en suelos de Galicia. PhD thesis, Universidad de Santiago de Compostela, Spain Fernández-Sanjurjo MJ, Álvarez E, García-Rodeja E (1995a) Efecto del encalado sobre ciertas propiedades de la solución del suelo, la fracción coloidal y la disponibilidad de fósforo. Rev Soc Esp Cienc Suelo 1:119–127 Fernández-Sanjurjo MJ, Álvarez E, García E (1995b) Efecto de un abonado NPK sobre las propiedades químicas y mineralógicas de tres suelos de Galicia (NO. de España). Agrochimica XXXIX:43–52 Fernández-Sanjurjo MJ, Álvarez E, García-Rodeja E (1996) Efecto residual de un abonado potásico en ciertos parámetros del suelo: comparación con parcelas control y suelo natural. Agrochimica XL:216–227 Fernández-Lorenzo B, Flores G, Valladares J, González-Arráez A, Pereira S (2009) Caracterización do sistema de producción das explotacións de vacún de leite de Galicia. Afriga 82:12–20 Fernández-Sanjurjo MJ, Álvarez-Rodríguez E, Corti G (2011) Effect of the addition of cattle slurry plus different types of livestock litter to an acid soil and on the production of grass and corn crops. Waste Manage Res 29:268–276 Ferrer C, Miguel AS, Olea L (2011) Nomenclátor básico de pastos en España. Pastos 31(1):7–44 Fundación de Estudios Rurales (2020) Agricultura Familiar en España. Informe Socioeconómico, pp.202–230. Unión de Pequeños Agricultores y Ganaderos, Anuario. Retrieved from https:// www.upa.es/upa/_depot/_adjuntos/135dc2edd8540621594721410.pdf García-Rodeja E, Silva BM, Macías F (1987) Andosols developed from non-volcanic materials in Galicia, NW Spain. J Soil Sci 38:573–591 Guitián F, Muñoz M (1962) Efectos del encalado en los suelos ácidos. Anales Edafología Agrobiología 19:261–270 Guitián-Ojea F, Carballas T (1969) Soils of the Spanish humid zone. V. Factors of soil formation: geological material. Anales Edafologia Agrobiologia, pp 191–204 Illera-Vives M, Labandeira SS, Iglesias Loureiro L, López-Mosquera ME (2017) Agronomic assessment of a compost consisting of seaweed and fish waste as an organic fertilizer for organic potato crops. J Appl Phycol 29:1663–1671 Macías F, Calvo RM, García C, García-Rodeja E, Silva B (1982) El material original: su formación e influencia en las propiedades de los suelos de Galicia. Anales Edafología Agrobiología 41:1747– 1768 Macías F, Chesworth W (1992) Weathering in humid regions, with emphasis on igneous rocks and their metamorphic equivalents. In: Developments in Earth Surface Processes, vol 2. Elsevier, pp 283–306 Macías F, Calvo R (2001) Atlas de Galicia: Los suelos. Consellería da Presidencia. Xunta de Galicia, p 50 Moody PW, Dickson T, Aitken RL (1998) Field amelioration of acidic soils in south-east Queensland. III. Relationships of maize yield response to lime and unamended soil properties. Aust J Agric Res 49:649–656 Mombiela FA, Mateo ME (1984) Lime needs for pastures in shrubland soils, 1: Relationships with exchangeable Al in soils derived from granite and slate of Galicia [Spain]. In: Anales del Instituto Nacional de Investigaciones Agrarias, Serie Agricola (Spain), vol 25, pp 129–143

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Peeters A, Beaufoy G, Canals RM, De Vliegher A, Huyghe C, Isselstein J, Jones J, Kessler W, Kirilovsky D, Van Den Pol-Van Dasselaar A (2014) Grassland term definitions and classifications adapted to the diversity of European grassland-based systems. In: Grassland science in Europe, vol 19–25th EGF General meeting on EGF at 50: the future of European grasslands, pp 743–750 Seco N, Fernández-Sanjurjo MJ, Núñez-Delgado A, Álvarez E (2014) Spreading of mixtures including wastes from the mussel shell treatment industry on an acid soil: effects on the dissolved aluminium species and on pasture production. J Clean Prod 70:154–163 WRB (2014) World reference base for soil resources. World Soil Resources Report No. 106. FAO, Rome

Forest Soils from Galicia: Aluminium Fractionation and Speciation E. Álvarez-Rodríguez, A. Barreiro, C. Eimil, and M. J. Fernández-Sanjurjo

Abstract In this chapter different issues related with forest soils from Galicia are addressed presenting a collection of images. Firstly, several chemical properties (especially Al fractionation and speciation) from soil profiles developed on different parent material (granite, slate and limestone) and underneath the different forest vegetation predominant in this region (pine, oak and eucalyptus), are discussed. Secondly, the work is focus in the most abundant specie in Galicia, Pinus pinaster, tackling several aspects related with the nutrition and the site index of this specie in soils developed on different geological materials (quartzite, slate, granite, gneiss, migmatite, micaceous schist, biotitic schist and quaternary sediments). The results showed that all the studied forest soils were acid (pH 4.5–5.3) and had the exchange complex Al saturated (55–70%). Despite these general properties a clear influence of the parent material and the vegetation cover of these soils was observed; the more acid pH and the highest concentration of the more toxic Al species in soil solution (Al3+ + Al–OH) corresponded to soils developed on limestone (more evolved) and under pine. The study of the soils under Pinus pinaster founded a good adaptation of this specie to soils developed on biotitic schists, granitic rocks, gneiss and migmatites, where this specie has the largest growths and, generally, higher levels of foliar nutrients, particularly K. The foliar K, together with soil depth and medium annual temperature, explained most of the site index variance, both considering all the rocks (52%) or just the granitic rocks (53%). Regarding the Al forms in the solid fraction of the soils, the highest concentration of non-crystalline Al (Alo) and organic Al (Alp) were obtained on biotitic schist, tending to form organic-aluminic complexes highly stables (Alp–Alcu). In soils developed on slate and micaceous schists predominated the more labile forms of Al (Alla and AlNH4 ), which are more susceptible to be transfer to the soil liquid fraction and be absorbed by plants; actually, the concentration of Al species considered most toxic (Al3+ and Al–OH) was higher in soils developed on these materials, according to their lower site index. All the Al toxicity indices applied (obtained from soil solid fraction, soil solution, leaves, roots) showed a higher risk in the plots developed on slate and micaceous schists, and E. Álvarez-Rodríguez (B) · A. Barreiro · C. Eimil · M. J. Fernández-Sanjurjo Department of Soil Science and Agricultural Chemistry, Engineering Polytechnic School, University Santiago de Compostela, 27002 Lugo, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_14

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the lack of problems caused by this element in the plots developed on biotitic schists. The toxicity indices obtained from the soil solution (labile Al and Al3+ + Al–OH) indicated that there is no risk of Al toxicity in the plots on granite, which matches with the high productivity and biomass obtained in this plots; however, applying the rest of indices (obtained from soil solid fraction, leaves or roots) would indicate toxicity by this element, so in this case it´s utilization would not be appropriate. Keywords Geological materials · Pine · Oak · Eucalyptus · Al fractionation · Site index

1 Introduction Galicia occupies a surface of three million hectares, with more than 2 million that are under forest use, of which 70% is forest wooded area (considering forest area when at least 10% is covered by trees) and 30% is forest with dispersed trees (IV IFN 2011). Conifers occupy 30.65% of forest wooded area in this region, being Pinus pinaster the predominant specie (15.35%); eucalyptus represent 20.32%; other broadleaves species occupy 29.32%, prevailing Quercus robur in pure stands (8.81%) or mixed with other autochthonous broadleaves species (8.59%); finally mixed stands suppose 17.73% and low-density woods 1.98% (IV IFN 2011) (Fig. 1). The area dedicated to wood production in Galicia represents 4% of the dedicated area for wood production in Spain and produces 57% of the total timber of the country (Xunta de Galicia 2022). These forest stands settle on soils developed on a wide variety of geological materials, even though 90% of the surface is occupied by granitic rocks (45%) and rocks with low degree of metamorphism (slates and schists) (45%). There are also rocks with basic (gabbro, amphibolite, granulite) and ultrabasic (dunites, serpentinized rocks) composition (5%), besides sediments with different age, texture and composition (Macías 1992; Macías and Calvo 2001). Predominant rocks are composed of aluminium silicates with K, Na or Ca while the presence of ferromagnesian silicates is limited. There are also rocks with just one mineral in their composition, such as quartzites and sandstones (quartz) or carbonate rocks (calcite) (Macías 1992). The wide diversity of geological materials also leads to a wide soil variety where the forest stands develop. Thereby, following the FAO (WRB 2014) classification, on very acid rocks (sandstones and quartzites), due to their resistance to alteration due to being are composed almost exclusively of quartz, skeletal soils such as Leptosol are formed (Fig. 2); while under special conditions of cold temperatures and low slope Podsol soils (with one eluvial leaching horizon and another illuvial horizon with accumulation of organic matter, and Fe and Al sesquioxide) are formed. Upon acid rocks (granites, slates, phyllites, and quartz and muscovite rich schists) there are shallow soils, such as Leptosols, mainly in the highest topographic positions and the hillsides; while in the areas with low slope, in the valley, Umbrisols can be developed, which are soils with an A horizon rich in organic matter and the exchange complex Al saturated, with or without a B cambic horizon (alteration horizon, Bw)

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Fig. 1 a: Forest landscape in Galicia; b, c, d: soil under pine, oak, and eucalyptus

and sometimes with very deep saprolites (Fig. 2). On slates and phyllites, in stable areas, waterlogging problems are possible due to the soil silty texture, being possible the development of Gleysols (with waterlogging in the superficial 50 cm). Regarding basic rocks (gabbro, amphibolite, biotitic schist), in the first evolution phases, in addition to Leptosols and Umbrisols, is possible the formation of Andosols (with low crystallinity minerals that have variable charges and present strong phosphorous retention at acid pH). These rocks are easily altered, due to their ferromagnesian composition, and over time form deep soils, such as Umbrisols (with a well-developed B cambic horizon), and soils with a B horizon of clay accumulation (B argic), for example Acrisols. In stable positions, due to high clay content, Gleysols can be developed and even Histosols (in environments with the water table on the surface most of the year). Upon ultrabasic rocks (serpentinites) soils such as Phaeozem, with a A mollic horizon and a B cambic base saturated horizon, may exist (Fig. 2). Soils on serpentinites are characterized by an elevated content of Mg and imbalance in Ca/Mg and

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Fig. 2 a: Leptosol on slate; b; Umbrisol on muscovitic schist; c: Umbrisol on granite; d: Lixisol on amphibolite; e: Phaeozem on serpentinite; f: Umbrisol with gleyic properties on sediments

d

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K/Mg ratios, that together with the presence of specific heavy metals (Ni, Cu) can caused fertility problems. Finally, upon sedimentary materials soils present very different properties due to the distinct origin of the sedimented materials, forming Fluvisols (associated to river courses), Arenosols (with coarse texture and therefore low water retention capacity), Gleysols and Histosols (Calvo de Anta 1992; Macías and Calvo 2001). All these different types of soils existing in Galicia have evolved under humid climate, whereby they have similar characteristics (with some exceptions such as Phaeozem soils on serpentinites): soils are acid, rich in organic matter, with variable charge colloids, with low cation exchange capacity, nutrient poor and with the exchange complex Al saturated, which can transfer to the soil solution and cause toxicity problems. However, these general characteristics can be of different magnitude depending on, besides the rock type, topographic position and time of evolution, other factors such as the type of vegetation that cover the soil and human intervention. Forest vegetation and soils have evolved together during a large period (Osman 2013). Some crop soils have also been reforested many years ago, and due to the tree vegetation influence they are considered forest soils (Osman 2013). Forest soils have some properties that differ from agricultural soils, due to the management which the latter are subjected; generally, forest soils are porous, aggregated, with abundant organic matter (Fig. 3) and a high biotic activity. The tree species established during long periods can affect the soil properties (Angst et al. 2019; Álvarez et al. 1992, 2002, 2005; Calvo and Díaz-Fierros 1981; Chandra et al. 2016; Cremer and Prietzel 2017; Eimil et al. 2014; Hou et al. 2021; Messenger 1980; Osman 2013, among others). In this chapter images from different forest soils (pine, oak and eucalyptus vegetation) and on different parent material (granite, slate and limestone), in Galicia, are presented and several chemical properties, especially Al forms and species under Pinus radiata, Quercus robur and Eucalyptus globulus, are discussed. In the second part of the chapter, the study is focused on the predominant forest specie in Galicia, Pinus pinaster, tackling aspects related to nutrition, Al toxicity risk and site index of this specie, in soils developed on different geological material (quartzite, slate, granite, gneiss, migmatite, micaceous schist, biotitic schist and quaternary sediments).

2 Forest Soils Under Oak, Pine and Eucalyptus, Developed on Granitic Rocks, Slate and Limestone As previously commented, the soil formation processes in Galicia take place on a wide variety of rocks, which are altered and form soils in open and strongly subtractive environments (Macías et al. 1982; Macías and Calvo 2001). Therefore, the lithology is a decisive factor in the soils of this region, since conspicuously influences soil properties, even in the ones from the surface horizons (Macías et al. 1982).

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Fig. 3 a Forest soils from Galicia with an A horizon rich in organic matter, on different geological material and type of vegetation. a, b, c: forest soils on granite, biotitic schists and gabbro; d: forest soil on granite with pine. e, f: forest soils on granite with eucalyptus and with oak

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Over time, a lot of studies have tried to determine the possible effects that different forest species could induce on the soil (Álvarez et al. 1992, 2002, 2005; Angst et al. 2019; Burgess-Conforti et al. 2019; Calvo and Díaz-Fierros 1981; Chandra et al. 2016; Cremer and Prietzel 2017; Hou et al. 2021; Messenger 1980; Osman 2013,among others), being this a controversial topic. Several studies associate process of soil acidification and degradation with conifers (Cremer and Prietzel 2017; Matzner and Ulrich 1983; Messenger 1980 among others), while other studies point out that the vegetation has a very secondary role in the soil formation, subordinate to climate and parent rock material (Macías et al. 1982). Due to the high pluviosity and the presence of open environments, as previously indicated, Galician soils are acid, even the ones developed on basic rocks, and have the exchange complex Al saturated, being this element one the main responsible of the low fertility of these soils. Our team researched the impact of three forest species (Pinus radiata, Quercus robur and Eucalyptus globulus) on the chemical properties of soils developed on three geological materials (granitic rocks, slate and limestone) (Fig. 4), analysing the Al fractionation and speciation (Fig. 5) and applying the toxicity indices for this element proposed by Cronan and Grigal (1995). To realize this, besides the solid phase, the liquid phase of these soils was studied because is more sensitive to short-term changes and can reflect better than the solid phase the impact of the tree species (Álvarez et al. 1992, 2002, 2005). Our studies indicate a high acidity and exchangeable Al concentration in pine forest soils developed on limestone. Other authors had already found an elevated acidity under conifers, which they attributed to the differences in humus quality, leaf litter decomposition, rock weathering and nutrient absorption (Cremer and Prietzel 2017; Messenger 1980). It can be surprising the fact that more acidic conditions were detected on limestone than on granites and slate, however, it should be pointed out that the studied soils on limestone are very deep and highly evolved (Fig. 4) and are strongly decarbonated and debasified (Álvarez et al. 2002, 2005), which justify also the low values of total non-crystalline Al (Alo), total organic Al (Alp) and organoaluminium complexes with low- medium- stability (Alcu) obtained on this material. In accordance with the higher acidity obtained in the soils developed on limestone and with pine vegetation, is in these soils where the highest concentrations of total Al in the soil solution are obtained, as well as the as well as the higher concentration of the most labile forms of Al (AlL )and the most toxic species (Al3+ and Al–OH). Indeed, applying the Al toxicity indices which was proposed by Cronan and Grigal (1995), that considers different critical levels for the indices obtained from the soil solution (Al3+ + Al–OH and ratio Ca/Al), from the roots (Ca/Al) and from the leaves (Ca/Al), it was obtained that there was risk of toxicity for this element only in soil samples under pine and on limestone (according to some indices), particularly in spring time (Table 1) (Álvarez et al. 2005).

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Fig. 4 a, b, c: pine, oak and eucalyptus on granite; d, e, f: pine, oak and eucalyptus on slate; g, h, i: pine, oak and eucalyptus on limestone

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Fig. 5 Diagram of Al fractionation in the soil solid and liquid phases

3 Rock’s Influence in the Nutrition, Al Toxicity and Growing of Pinus Pinaster Pinus pinaster is one of the most important tree species in Spain, both in terms of occupied surface (1.68 Mha as pure and mixed species stands) and wood production (more than 3.1 Mm3 cutted down in 2010) (Eimil et al. 2014) (Fig. 6). In Galicia, is the most abundant forest specie, takin up 0.53 Mha as pure and mixed stands (Eimil et al. 2014) (Fig. 7). Due to the importance of this specie, a study was realized in order to analyse the influence of different geological materials (quaternary sediments, micaceous schists, phyllites, slates, quartzites, sandstones, gneiss, migmatites and granites) (Fig. 8) in the soil and pine needle nutrients concentration, as well as the

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Table 1 Intervals of Al3+ + Al–OH concentration in the soil solution (mmol L−1 ), Ca/AlL molar ratio in the soil solution (AlL : labile Al), and Ca/Al in leaves and roots of different tree species for soils developed from various parent materials (Eucal = Eucalyptus) Granodiorite Oak

Slate

Limestone

Pine

Eucal

Oak

Pine

Eucal

Oak

Pine

Eucal

Soil solution a Al3+

+ Al–OH

Autumn

< 17

< 17

< 17

< 17

< 17

< 17

< 17

~ 17

< 17

Spring

< 17

< 17

< 17

< 17

< 17

< 17

< 17

> 17

~ 17

Winter

< 17

< 17

~ 17

< 17

~ 17

< 17

< 17

~ 17

< 17

Autumn

> 10.5

> 10.5

> 10.5

> 10.5

> 10.5

> 10.5

> 10.5

~ 10.5

> 10.5

Spring

> 10.5

~ 10.5

> 10.5

~ 10.5

> 10.5

> 10.5

> 10.5

~ 10.5

1–10.5

Winter

> 10.5

~ 10.5

~ 10.5

> 10.5

> 10.5

> 10.5

> 10.5

~ 10.5

~ 10.5

< 6.2

< 1.8

< 6.2

> 12.5

< 6.2

> 12.5

> 12.5

< 1.8

< 12.5

> 0.48

> 0.48

< 0.48

< 0.48

> 0.48

> 0.48

> 0.48

> 0.48

> 0.48

b Ca/Al

c Leaves

Ca/Al d Roots

Ca/Al

Soil solution Al3+ + Al–OH: 17 mmol L−1 critical level proposed by Truman et al. (1986), for labile Al for sensitive species as Pinus radiata b Soil solution Ca/Al: 0.5 < Ca/Al < 1: risk of Al toxicity between 75 and 50%, Cronan and Grigal L 1995); Ca/AlL > 10.5: risk of Al toxicity, Truman et al. (1986) c Leaves, Ca/Al: 6.2 < Ca/Al < 12.5: risk of Al toxicity between 75 and 50%, Cronan and Grigal (1995); Ca/Al: < 1.8: risk of Al toxicity, Truman et al. (1986) d Roots, Ca/Al in roots: 0.1 < Ca/Al < 0.2: risk of Al toxicity between 75 and 50%, Cronan and Grigal (1995); Ca/Al = 0.48 critical level proposed by Truman et al. (1986) a

plot site index (SI, related with the trees height and diameter) (Fig. 9: pine needle sampling). The more severe nutrient deficiencies together with the lower growths and site index values of Pinus pinaster were observed in soils developed from quaternary sediments, micaceous schists, phyllites, slates, quartzites and sandstones; while the more favourable conditions corresponded to soils developed from biotitic schists, gneiss, migmatites and granites (Fig. 10). Two regression models were developed to predict the site index. The complete model, which includes all the geological materials, foliar Ca and K, soil depth and average annual temperature explained 52% of the site index variation. The other model, which includes only granitic rocks and the previous parameters, except foliar Ca, explained 53% of the site index variation (Eimil et al. 2014). In another study it was studied the rock´s influence, in this case with just four types of rock (slates, granites, biotitic schists and micaceous schists) (Fig. 11), in the Al species of soils under Pinus pinaster and the relation of the toxicity indices by this element with the growing of this specie (Eimil et al. 2015, 2016).

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Fig. 6 Plantation of Pinus pinaster (a) and obtained wood for the transformation industry (b, c, d)

The results showed that for all the mentioned materials, all the studied soils were acid, organic matter rich, with alic characteristics (percentage of exchangeable Al > 60%) and with low levels of Ca and Mg. Despite these general properties, the geological material had significant effect in most of the analysed parameters. Regarding the Al fractionation, on biotitic schists it was obtained the highest contents of non-crystalline Al (Alo), organic Al (Alp) and organoaluminium complex with high stability (Alp-Alcu), and the lowest values of labile organoaluminium complex (Alla), exchangeable Al (AlNH4 ), which is the most susceptible form to go over to the soil solution, total Al in soil solution and the most toxic Al species (Al3+ and Al–OH) (Fig. 12). Therefore, on this material, the organic matter acts by eliminating the Al from the soil solution and from the exchange positions to create organoaluminium complex that are highly stable in the solid phase. The opposite situation happens in the soils that are more acid, developed on slates and micaceous schists, which presented the higher concentrations of the most labile Al forms in the solid phase (Alla, AlNH4 ), as well as the most toxic Al species in the soil solution. The site index, total biomass, needle biomass and the foliar area index were higher in the plots developed on biotitic schist and granite. This result is more consistent with the Al toxicity indices estimated from the soil solution parameters (Al3+ + Al–OH) than the estimated from the roots and needles, since these ones estimated Al toxicity in soils on granite, despite their elevated productivity.

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Fig. 7 a: pure pine stand; b: mixed pine stand

4 Final Remarks The studies realized by our research team bring out the influence of the geologic parent material and the forest species in the chemical properties of the soils from Galicia, in order that the more acid soils and the higher Al toxicity risk appear in soils developed on limestone (strongly evolved, debasified and decarbonated) and under pine. The studies perfomed in forest soils under Pinus pinaster also indicated the importance of the parent material in the chemistry of the Al and in the site index, obtaining

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Fig. 8 Soil profiles on: biotitic schists (a), micaceous schists (b), granites (c), quartzite colluvium (d), slates (e) and quaternary sediments (f)

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Fig. 9 Pine needle sampling

20 18

a

a

16

a

a

14 b

SI (m)

12

b

b

b

QUAR

MSCH

SEDM

10 8 6 4 2 0

BSCH

GNEI

MIGM

GRAN

SLAT

Fig. 10 Site index (SI) of Pinus pinaster plots developed on biotitic schists (BSCH), gneiss (GNEI), migmatite (MIGM), granite (GRAN), slate (SLAT), quartzite (QUAR), micaceous schists (MSCH) and sediments (SEDM)

Forest Soils from Galicia: Aluminium Fractionation and Speciation

Fig. 11 Plots with pine on slate (a), granite (b), biotitic schist (c) and micaceous schist (d)

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a

16

b

14

a

Al-F

ab

Al-OH

12 μmol L-1

Al 3+

Al-SO4

10 8 a

b

6 4 2 0

a

b

b

a Slate

a B

t

Mica schist

Granite

Fig. 12 Al fractions in the solid phase (a) and labile Al species in liquid phase (b) of soils with Pinus pinaster on different geological materials

the highest growth of this specie on biotitic schists, whose soils had the highest content of organic-aluminic complex with a strong stability in the soil phase, and the lowest content of the more labile and more toxic species of Al. Soils developed on granite presented a high site index too, according with the lack of Al toxicity estimated by the indices obtained from the soil solution, but not so with the indices obtained from the roots and needles. The smallest production was obtained on slate and micaceous schist, coinciding with larger amounts of the more labile Al forms and with the higher toxicity risk by this element.

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Acknowledgements The authors are grateful to all the researchers that have worked in this topic and are part of the published papers related with the topic.

References Álvarez E, Martínez A, Calvo R (1992) Geochemical aspects of aluminium in forest soils in Galicia (N.W. Spain). Biogeochemistry 16:167–180 Álvarez E, Monterroso C, Fernández Marcos ML (2002) Aluminium fractionation in Galician (NW Spain) forest soils as related to vegetation and parent material. For Ecol Manage 166:193–206 Álvarez E, Fernández-Marcos ML, Monterroso C, Fernández-Sanjurjo MJ (2005) Application of aluminium toxicity indices to soils under various forest species. For Ecol Manage 211:227–239 Angst G, Mueller KE, Eissenstat DM, Trumbore S, Freeman KH, Hobbie SE, Chorover J, Oleksyn J, Reich PB, Mueller CW (2019) Soil organic carbon stability in forests: distinct effects of tree species identity and traits. Glob Change Biol 25:1529–1546 Burgess-Conforti JR, Moore PA, Owens PR, Miller DM, Ashworth AJ, Hays PD, Evans-White MA, Anderson KR (2019) Are soils beneath coniferous tree stands more acidic than soils beneath deciduous tree stands? Environ Sci Pollut Res 26:14920–14929 Calvo R, Díaz-Fierros F (1981) Consideraciones acerca de la acidificación de los suelos de la zona húmeda española a través de la vegetación. Anales Edafología Agrobiología 40:411–425 Calvo R (1992) El suelo medio de vida. In: Guía de la Naturaleza Galicia, vol 17. Faro de Vigo, Vigo, pp 321–340 Chandra LR, Gupta S, Pande V (2016) Impact of forest vegetation on soil characteristics: a correlation between soil biological and physico-chemical properties. Biotech 6:188–200. https://doi. org/10.1007/s13205-016-0510-y Cremer M, Prietzel J (2017) Soil acidity and exchangeable base cation stocks under pure and mixed stands of European beech, Douglas fir and Norway spruce. Plant Soil 415:393–405. https://doi. org/10.1007/s11104-017-3177-1 Cronan CS, Grigal DF (1995) Use of calcium/aluminum ratios as indicators of stress in forest ecosystems. J Environ Qual 24:209–226 de Galicia X (2022) Inventario forestal continuo de Galicia (IFCG). Consellería de Medio Rural. Retrieved from https://mediorural.xunta.gal/es/temas/forestal/inventario-forestal-continuo Eimil-Fraga C, Rodríguez-Soalleiro R, Sánchez-Rodríguez F, Pérez-Cruzado C, Álvarez-Rodríguez E (2014) Significance of bedrock as a site factor determining nutritional status and growth of maritime pine. For Ecol Manage 331:19–24 Eimil-Fraga C, Álvarez-Rodríguez E, Rodríguez-Soalleiro R, Fernández-Sanjurjo MJ (2015) Influence of parent material on the aluminium fractions in acidic soils under Pinus pinaster in Galicia (NW Spain). Geoderma 255–256:50–57 Eimil-Fraga C, Fernández-Sanjurjo MJ, Rodríguez-Soalleiro R, Álvarez-Rodríguez E (2016) Aluminium toxicity risk for pinus pinaster in acid soils (Galicia, NW Spain). Land Degrad Dev 27:1731–1739 IV IFN (2011) Cuarto inventario forestal nacional. Ministerio para la transición Ecológica y el Reto Demográfico. Retrieved from https://www.miteco.gob.es/es/biodiversidad/temas/ inventariosnacionales/inventario-forestal-nacional/cuarto_inventario.aspx Hou L, Zhang Y, Li Z, Shao G, Song L, Sun O (2021) Comparison of soil properties, understory vegetation species diversities and soil microbial diversities between Chinese fir plantation and close-to-natural forest. Forests 12:632–649 Macías F, Calvo R, García C, García-Rodeja E, Silva B (1982) El material original; su formación e influencia en las propiedades de los suelos de Galicia. Anales Edafología Agrobiología 41:1747– 1768

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Macías F (1992) Génesis y evolución de los suelos de Galicia. In: Guía de la naturaleza de galicia, vol 16. Faro de Vigo, Vigo, pp 298–320 Macías F, Calvo R (2001) Atlas de Galicia: los suelos. Consellería da Presidencia, Xunta de Galicia, p 50 Matzner RE, Ulrich B (1983) The turnover of protons by mineralization and ion uptake in a beech (Fagus silvatica) and a Norway spruce ecosystem. In: Ulrich B, Pankracth J (eds) Effects of accumulation of pollutants in forest ecosystems. Reidel, Holland, pp 93–104 Messenger AS (1980) Spruce plantations effects on soil moisture and chemical element distribution. For Ecol Manage 3:113–125 Osman KT (2013) Forest soils. In: Soils. Springer, Dordrecht. https://doi.org/10.1007/978-94-0075663-2_14 Truman RA, Humphreys FR, Ryan PJ (1986) Effect of varying solution ratios of Al to Ca and Mg on the uptake of phosphorus by pinus radiata. Plant Soil 96:109–123 WRB (2014) World reference base for soil resources. International soil classification system for naming soils and creating legends for soil maps. Roma

Andosols and Podzols at Galicia Eduardo García-Rodeja, Xabier Pontevedra-Pombal, and Juan Carlos Nóvoa-Muñoz

Abstract A review is made of the knowledge of properties, genesis, and classification of andic and podzolic soils of Galicia. The parent material is the main factor that determines the formation of this type of soils. Andic soils develop particularly from basic and metabasic rocks, although similar characteristics can be found in soils from other materials. In contrast, Podzols are formed from quartz rich materials, from coastal to mountain areas, while in mountain areas, colder and more humid, podzolic soils develop from granitic rocks and other materials, developing a spodic horizon or evidence of podzolization (brown podzolic soils, cryptopodzolic soils). The formation of these soils, characterised by properties due to the abundance and reactivity of Al and Fe humus complexes, is conditioned by the nature of parent material and the role of organic matter in the weathering stabilisation of metastable phases and translocation processes. The fact that the aforementioned components are also present in the umbric horizons, that characterizes many Galician soils, leads to the conclusion that parent material, through its weatherable mineral content and modulated by environmental conditions, and organic matter are the main responsible for the pedogenetic tendencies that lead to the formation of Andosols, Podzols and Umbrisols at Galicia. Keywords Andic soils · Podzolic soil · Parent material · Organic matter · Weathering · Pedogenesis · Classification

E. García-Rodeja (B) · X. Pontevedra-Pombal Departamento de Edafoloxía e Química Agrícola, Facultade de Bioloxía, Universidade de Santiago de Compostela, Santiago de Compostela, Spain e-mail: [email protected] J. C. Nóvoa-Muñoz Departamento de Bioloxía Vexetal e Ciencias do Solo, Facultade de Ciencias, Universidade de Vigo, Ourense, Spain © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_15

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1 Introduction Andosols: the central concept Andosols (World Reference Base, IUSS WRB Working Group 2015) or Andisols (Soil Taxonomy, Soil Survey Staff 1999) refers to young soils, generally with a dark surface horizon, developed from volcanic materials, whose properties are a consequence of a colloidal fraction dominated by shortrange order materials and/or Al (Fe)-humus complexes. The dominant process in their formation, which takes place under near all climatic conditions, is a weathering of primary aluminosilicates leading to the formation of allophane, imogolite, and ferrihydrite, and/or accumulation of organic matter complexed with aluminium and, to a lesser extent, iron. This combination of metastable components can persist for a long time if environmental conditions are favourable (humid climates with little seasonal contrast). These soils are found in volcanic regions all over the world, covering an area between 110 (WRB 2015) and 124 (ST 1999) million hectares. The criteria for the classification of Andosols (or Andisols) have changed over time. From their inclusion in modern classification systems, diagnostic criteria based on the existence of an exchange complex dominated by amorphous material (FAOUNESCO 1974; ST 1975), changed to the different definitions of ‘andic horizon’ (FAO-ISRIC-ISSS 1998), ‘andic properties’ (FAO-UNESCO 1990; WRB 2015) and ‘vitric properties’ (WRB 2015) or ‘andic soil properties’ (ST 1999). Currently WRB (2015) defines ‘andic properties’, a consequence of the presence of short-range-order minerals and/or organo-metallic complexes, as a function of the presence of a minimum amount of acid oxalate extractable non-crystalline Fe and Al components (Alox + 1/2Feox ≥ 2%), a low bulk density (≤0.9 kg dm−3 ), and high phosphate retention (≥85%); ‘vitric properties’ are defined using the same criteria, with less demanding parameter values, reflecting a lower degree of weathering and thus a lower content of short range-order minerals, but require the presence of volcanic glass in the soil. A NaF pH value ≥ 9.5 (Fieldes and Perrot 1966) is used as a test for the presence of allophane and/or organo-aluminium complexes in carbonate-free soils, but this test response also occurs in many Ah horizons, in particular in umbric, spodic (especially Bs horizons) and some cambic horizons, due to the presence of reactive forms of Al (Al-humus complexes, Al interlayered vermiculites and poorly crystalline forms of Al) (García-Rodeja et al. 1985). To differentiate between soils dominated by non-crystalline aluminosilicates (allophane, imogolite) and soils dominated by Al-humus complexes, the WRB distinguishes between silandic and aluandic properties. Silandic properties are characterised by an acid oxalate (Siox ) extractable silica content ≥ 0.6%, interpreted as Si forming part of these aluminosilicates and, as additional characteristics, a ratio between pyrophosphate extracted Al (Alpy , indicative of Al in complexes with humus) and acid oxalate extracted Al (Alox , Al bound to organic matter and in non- or poorly ordered forms, including allophane and imogolite), < 0.5, and, generally, a pH H2 O ≥ 4.5. On the other hand, Aluandic properties occur if Siox < 0.6%, Alpy /Alox ≥ 0.5 and pH H2 O < 4.5. Soil Taxonomy (1999) defines andic soil properties with the same criteria as the WRB andic properties, which are less demanding on the

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amount of Alox + 1/2Feox as the volcanic glass content increases, in a similar way to the definition of vitric properties. When these properties occur at a minimum soil thickness, the soil is classified in the Reference Soil Group Andosol (WRB) or in the Order Andisol (ST). The fact that many of these soils have surface horizons rich in organic matter has led to the definition of the diagnostic melanic and fulvic horizons in WRB and melanic epipedon in ST. Melanic horizons are horizons at or near the surface, organic matter rich, thick, and dark, in which humic acids predominate over fulvic acids (melanic index < 1.7). The WRB fulvic horizon differs from the melanic horizon by having a less dark colour and a melanic index ≥ 1.7. In the most recent version of the WRB (IUSS Working Group WRB 2022), these horizons were excluded. Among many other options, WRB uses the principal qualifiers aluandic and silandic to differentiate Andosols dominated by organometallic complexes from those dominated by non-crystalline aluminosilicates, as well as the supplementary qualifiers fulvic and melanic depending on the presence of one of these horizons. Although ST 1999 does not define the fulvic horizon, it uses the prefixes melan- and fulv-, at the Great Group level, to differentiate Andisols with a melanic horizon from those with horizons with similar characteristics but less dark and with a melanic index ≥ 1.7. Although Andosols are considered characteristic of volcanic materials, weathering of primary minerals in non-volcanic parent materials, in humid, cool to temperate climates, can lead to the formation of soils with components like those characterising Andosols, in particular the accumulation of stable organo-mineral complexes. Some of these non-volcanic soils can also be classified as Andosols. The formation of non-volcanic Andosols, generally aluandic Andosols associated with humid mountain areas, has been reported in England (Loveland and Bullock 1976), Spain (Iñiguez and Barragán 1974; García-Rodeja et al. 1987; Macías et al. 1978a; Silva et al. 1988), France (Aran et al 1998), Austria (Delvaux et al 2004a, b), Germany (Kleber and Jahn 2007), Nepal (Baumler and Zech 1994), India (Caner et al. 2000), Butan (Bäumler et al. 2005), among others. Podzols: the term podzol, which is used in many classification systems, refers to soils formed under heathland (Erica sp, Calluna sp) or forest vegetation by weathering of siliceous rock resulting in soils with a texture predominantly coarse. When they develop in clay-rich materials, their formation is preceded by clay illuviation or weathering processes that reduces their clay content to a critical level (ST 1999). The most typical morphology of podzols is characterised by an Ah horizon rich in organic matter (sometimes with an overlying O horizon) below which there is a bleached, ash grey in colour, eluvial horizon (E), with a residual accumulation of low weatherable minerals, especially quartz, and a tendency to have coarse textures. Below this eluvial part, generally with a net transition, appears a B horizon characterised by the accumulation of organic matter, Al and Fe which, in the best developed podzols, separates into a sub-horizon of black to dark brown colour, with accumulation of organic matter, Al and Fe (Bh) followed by another, with less organic matter and generally dark reddish-brown or redder colours, in which poorly crystalline phases

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of Fe and Al accumulate (Bs). Below them, a C horizon scarcely affected by the accumulation processes of organic matter and sesquioxides or, sometimes, an illuvial clay accumulation horizon (Bt), which may result from a process prior to podzolization. There are many variations on this general model depending on climate, parent material, drainage, and time of evolution. Podzols cover an area of about 485 million ha (WRB), mainly in regions with cold and humid climates, although they also occur in areas with temperate-humid climates and in the humid tropics, in this case mainly on quartz-rich residual materials. In morphogenetic classification systems, podzols are included in the Reference Soil Group Podzol (WRB 2015) or the Order Spodosol (ST 1999). In both cases they are defined based on the existence of an illuvial horizon, the spodic horizon, in which illuvial organic matter with Al and usually also Fe accumulates. Diagnostic characteristics of the spodic horizon in the WRB and of the spodic materials, which define this horizon in ST, are very similar and include a pH in water < 5.9, an organic C content ≥ 0.5% or an optical density of the oxalate extract ≥ 0. 25 at least in part of the horizon, in addition to several colour criteria (very dark to red with high chroma). When spodic horizons are not overlaid by a bleached E horizon meeting the definition of albic material (WRB) or an albic horizon (ST), they must meet some additional criteria (cementation, presence of cracked coatings on the sand grains, a minimum amount of oxalate extractable Al and Fe, at least twice as much as in the horizons above it, the presence of Fe lamellae and a minimum thickness). The albic horizon and the albic material are defined by colour criteria (light Munsell colours, with high values and low chroma). In the 2022 version of the WRB, the definition of albic horizon is recovered, and albic material is replaced by claric material. Their definitions are very similar to those of the previous version, and the difference between claric material and albic horizon is that the latter must be the consequence of a process of pedogenesis. The cemented horizons referred to in the definition of the spodic horizon are the placic horizon and the ortstein of ST (1999), which in the case of podzols are horizons cemented by spodic materials (Fe and/or Mn, Al, and organic matter), only differing in thickness (ortstein ≥ 25 mm, placic < 25 mm) and in the degree of cementation, less in the ortstein. In WRB, materials equivalent to these horizons are defined in the qualifiers ortsteinic and placic. In summary, a Podzol (Spodosol) is characterised by the presence of a spodic horizon, with illuvial accumulation of amorphous compounds of organic matter, Al and Fe characterised by dark to reddish colours, a high pH-dependent charge, a relatively large surface area and high water retention, above which there is generally a grey to light grey (colour similar to that of uncoated quartz grains) albic horizon. The presence of thin cemented layers or coatings on mineral grains and rounded aggregates of organic matter may also characterise a spodic horizon. On the surface they may have a O horizon and an Ah horizon, sometimes umbric. In the absence of an albic horizon above the spodic horizon there is a dark eluvial horizon with many uncoated sand grains. Regarding the genesis of podzols, the adsorption/precipitation theory (McKeague et al. 1978; Mokma and Buurman 1982; Petersen 1976; among others), is the most

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widely accepted. It consists in the dissolution of primary minerals by relatively high molecular weight soluble organic compounds (fulvic acids) in the topsoil ( fulvate theory), which migrate to the B horizons in the form of organometallic complexes with Al and Fe where they are immobilised, mainly by the increase of the C/ metal ratio during illuviation and by adsorption on components of the B horizon (Buurman 1985). The accumulation of organic matter in the B horizons of welldrained podzols can also derive from root degradation, as roots tend to grow in the more favourable conditions of these horizons (Buurman and Jongmans 2002, 2005). The increase in the thickness of the E horizons of podzols is attributed to the redissolution of organometallic complexes and their reprecipitation at greater depth. The clear evidence of complexation of Fe and Al with organic acids, together with their proven ability to promote mineral dissolution, implies that their role is of great importance in the formation of E horizons of podzols and, consequently, the transport of Fe and Al as organic complexes is the predominant accepted mechanism of eluviation. Another model to explain the podzolization process, the biodegradation theory (Lundström 1993; Lundström et al 2000), confers a fundamental role to low molecular weight organic acids in the weathering processes in the eluvial horizons, and explains their accumulation in the B horizons by microbial decomposition of these readily biodegradable compounds. This process is followed by the release of Fe and Al that would precipitate in the B horizon as low-order Al-Si–OH (allophane or imogolite) and Fe-OH (ferrihydrite) solid phases, that could subsequently act as surfaces capable of adsorbing high molecular weight organic compounds. The frequent occurrence of low-order aluminosilicates in some illuvial horizons of podzols and the fact that these components cannot form from organic complexes (Childs et al. 1983; Gustafsson et al. 1995; McKeague and Kodama 1981; Ugolini and Dahlgren 1986among others), supports the theory of proto-imogolite migration (Anderson et al. 1982; Farmer et al. 1980; Farmer 1982, 1987a, b, among others). In this model, the mobilisation of Al and Si from the surface horizons occurs in the form of soluble sols (positively charged Al-Si–OH complexes with an Al/Si ratio around 2, proto-imogolite, of which Fe may also be a part) that precipitate in the B horizon. Iron and Al would be dissolved by readily biodegradable organic acids and their immobilisation in the B horizon would occur by precipitation on organic matter in the upper part of the B horizon. The dissolution process continues acting on the materials deposited in the B horizon, where imogolite-type materials would be more soluble than Fe. In this way, the upper part of the B horizon (Bh) is enriched in Fe and the Bs in proto-imogolite which is afterwards transformed into allophane. Regardless of the process (see Sauer et al. 2007 for a review), the illuvial horizons of podzols are characterised by the accumulation of metals complexed with organic matter, low-order aluminosilicates and Fe and Al oxides with a predominance of noncrystalline forms due to the inhibitory effect of organic matter. The wide diversity of environments in which podzols develop suggests that the processes may not be the same in all cases, with the specific combination of factors in each locality determining which processes are possible and to what degree they take place (Buurman and Jongmans 2005; Ferro et al. 2020; Lundstrom et al. 2000).

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Andosol and Podzols: Andosols and Podzols are morphologically very different soils, but they have in common the fact that their defining properties (andic materials, spodic horizon) are a consequence of the presence of the same type of components: metal-humus complexes, non-crystalline forms of Fe and Al and short rangeorder aluminosilicates. These components give them similar properties such as the predominance of variable charge, abundance of Al (and Fe) bound to organic matter (extractable with pyrophosphate) and of Al and Fe in non-crystalline components (extractable with oxalate), high reactivity to NaF, and high anion binding capacity. Thus, many spodic horizons may exhibit properties close to andic properties (Alexander et al. 1993), although their bulk density is generally higher. The convergence between andosolization in non-volcanic materials and podzolization has been reported in places with moderate or cooler temperatures and high humidity, high input of organic material and good drainage (Bäumler 1994; Bäumler et al. 2002; Ugolini and Dahlgren 1991). The dominant process in most soils with andic materials is weathering and transformation of 2:1 minerals. Translocation within the soils and accumulation of the translocated compounds are minimal in Andosols, while it is important in Podzols. When the illuviation of aluminium, iron and organic matter is not important enough to form a spodic horizon, the process of translocation of Al(Fe)-humus complexes is called cryptopodzolization (Bruckert et al. 1975; Blaser et al. 1997; Duchauphour and Souchier 1968, among others). The presence of a horizon with albic material, indicative of the illuviation process, allows the separation of Podzols and Andosols, as in the later translocation processes do not occur or are very limited. In the absence of an albic horizon, the mineralogy of the clay fraction of the spodic horizons usually contains appreciable amounts of Al interlayered vermiculites and humus and sesquioxide coatings on sand and silt grains, which help to distinguish between both types of soils.

2 Andosols in Galicia Andosols on non-volcanic materials in Galicia develop mainly from rocks where alterable minerals are dominant, especially basic and metabasic rocks (García-Rodeja 1985; García-Rodeja et al. 1987, 2004a, b; Macías et al. 1978a). In the development of the properties that allow their characterisation as Andosols, the nature of parent material and the accumulation of organic matter are the key factors. Mineral weathering, under well-drained conditions, releases significant amounts of Al which forms complexes with the organic matter slowing down the formation of crystalline minerals and leading to the stabilisation, and subsequent accumulation, of organic matter. In these soils, the andic properties (ST 1999; WRB 2015) occur exclusively in surface Ah (umbric) horizons, rich in organic matter, and which must have a minimum thickness to be included in the RSG Andosol or in the Order Andisol. On the other hand, in Galicia there are soils developed from other lithology such as granitic rocks and biotitic schists, which have andic properties in similar conditions to those mentioned above. In this case, andic properties are present in the whole of

Andosols and Podzols at Galicia

259

the umbric horizon or in its subsurface part, but the soils are not usually characterised as Andosols due to the insufficient thickness of the horizons with these properties. Soils Developed From Gabbro and Metabasic Rocks Studies on the weathering processes, properties and classification of soils developed from gabbro (García Paz and Macías 1983; Macías et al. 1978a, 1978b) and amphibolite (García Paz et al. 1986; García-Rodeja et al. 1986; Silva et al. 1988) in Galicia show similarities in both morphology and properties. In areas where erosion expose the geological substratum, soils have Ah horizons of variable thickness overlaying the rock. In colluvial deposits, where fresh or slightly weathered rock fragments have been deposited, the soils have Ah horizons of variable thickness followed by transitional, AB or BA horizons and sometimes Bw, cambic horizons. In these highly morphodynamic environments, it is common to find polycyclic soils with a stoneline below which the remains of ancient pedogenesis are preserved with B horizons formed in situ that gradually change to an intensely weathered saprolite. Examples of soils developed from these materials are presented in Images. 1, 2 and 3. Table 1 (gabbro) and Table 2 (amphibolite and granulite) include data of selected properties of soils developed from these materials. The Ah horizons of soils with profile AR and those appearing in the surface cycle of polycyclic soils are characterised by high organic matter content, high porosity and low bulk density which diminish as soil organic matter increases, an acid pH (pHH2 O≈5.5) and a high water retention capacity. Their dominant textures are sandy

Image 1 Aluandic Andosols on gabbro colluvial deposit (Monte Castelo, A Coruña) (left) and on amphibolite (Aríns, A Coruña) (up)

260

E. García-Rodeja et al.

Image 2 Aluandic Andosols (amphibolite, left), and Umbrisol with andic properties in Ah horizon (gabbro, right) developed from highly weathered saprolites. Both soils are polycyclic with a surface cycle developed from colluvium and an old cycle with Bw horizons developed from the saprolite (in the soil on gabbro part of an A horizon is preserved)

Andosols and Podzols at Galicia

261

Image 3 Aluandic Andosols on amphibolite at Serra da Capelada (A Coruña) (left) and Santiago de Compostela (right). Both are polycyclic soils, with a surface cycle developed on coluvial deposits with fresh rock fragments over 2Bw horizons developed from a weathered saprolite

loam to sandy clay loam, whereas most frequent colours are dark reddish brown when wet (hue 5YR, value and chroma 3 or less) and dark brown to dark reddish brown (hues 5YR or 7.5YR, values 4 and chromas 4 or less) when dry. These soil horizons have a weak to moderate crumb structure, are friable to very friable, slightly adherent, and not or slightly plastic. In most cases they smear easily and become hydrophobic when dried. The BA and Bw horizons have sandy loam or silty loam textures and weak to moderate subangular blocky structure, with abundant rock fragments (gravels to stones) poorly weathered, although those more altered are covered with Fe oxyhydroxides. As the organic matter content decreases, smeariness tends to disappear, plasticity increases, and the low bulk density increases. The main characteristic of the B horizons of the old cycle of polycyclic soils is their high degree of weathering, having a massive appearance when wet, intensely coloured in reddish or yellowish tones (with 5YR or 7.5YR hues) and fracture surfaces with black accumulations of sesquioxides are frequently observed in the saprolite. The dominant textures are silty loam with not very abundant clay, but the formation of sand- and silt-sized pseudoparticles has been reported. In terms of soil mineralogy, the most remarkable characteristic of the clay in humus-rich horizons is its low crystallinity which difficult its identification by XRD. Together with well-preserved primary minerals, chlorites, vermiculites and Al-interlayered phyllosilicates are the dominant crystalline minerals, and variable

15–35

35–55

55–90

AB

2Bw

> 105

2BC

Ah2

> 80

2Bw

0–15

50–80

AB

Ah1

20–50

> 140

2BC

0–20

> 60

2Bw

Ah2

40–60

Bw

Ah1

0–40

20–40

Ah2

Ah

0–20

Ah1

5.5

5.4

5.3

5.3

5.1

5.3

5.3

4.9

4.9

5.0

5.0

4.8

4.9

5.8

5.6

pHH2 O

1.16

9.28

11.0

13.9

0.2

0.8

4.5

7.8

10.7

0.2

0.3

1.0

12.3

8.9

9.0

%OC

1.16

0.82

0.70

0.60

1.12

1.13

0.75

0.71

0.67

1.12

1.13

0.85

0.68

0.62

0.63

BD

46

98

98

96

39

59

86

97

96

43

47

60

94

97

97

P ret %

9.6

11.1

11.2

10.9

8.6

9.6

11.3

11.5

11.5

9.2

9.5

10.2

11.5

11.4

10.8

pH NaF

0.60

3.00

2.65

2.10

0.55

0.70

2.70

3.15

2.50

0.30

0.40

0.70

2.05

2.60

2.50

Alox

0.01

2.10

1.85

1.55

0.05

0.05

1.82

1.80

1.50

0.05

0.05

0.60

1.60

2.20

1.90

Alpy

0.23

0.78

0.91

0.74

0.28

0.31

0.62

0.65

0.78

0.10

0.05

0.44

0.53

0.72

0.76

Feox

0.20

0.72

0.87

0.73

0.09

0.50

0.57

0.71

0.73

0.06

0.14

0.28

0.54

0.64

0.62

Fepy

3.81

4.61

4.89

4.33

5.49

3.64

3.54

3.70

4.40

3.06

2.63

3.57

1.88

4.69

4.89

Fedc

0.02

0.40

0.32

0.20

0.01

0.01

0.32

0.54

0.38

0.01

0.01

0.05

0.15

0.28

0.25

Siox

0.72

3.39

3.11

2.47

0.69

0.86

3.01

3.48

2.89

0.35

0.43

0.92

2.32

2.96

2.88

Alox + 1/2Feox

0.02

0.70

0.74

0.74

0.09

0.07

0.67

0.57

0.60

0.17

0.13

0.86

0.78

0.85

0.76

Alpy / Alox

0.06

0.17

0.19

0.17

0.05

0.09

0.18

0.18

0.18

0.03

0.02

0.12

0.28

0.15

0.16

Feox / Fecd

0.1

2.8

2.3

1.4

0.1

0.1

2.3

3.8

2.7

0.1

0.1

0.4

1.1

2.0

1.8

Allo %

0.0

0.1

0.1

0.0

0.3

0.0

0.09

0.0

0.1

0.1

0.0

0.3

0.0

0.1

0.2

Fh %

ox , Feox , Siox : Al, Fe and Si extracted with acid ammonium oxalate; Alpy , Fepy : Al and Fe extracted with Na-pyrophosphate; Fedc : Fe extracted with citrate-dithionite; Allo: Allophane; Fh: ferrihydrite. Allophane and Ferrihydrite estimated following Childs (1985) and Parffit and Childs (1988) respectively. Source García-Rodeja et al. 1987; Macías et al. 1978b

OC: organic carbon; BD: bulk density (kg dm−3 ); P ret: Phosphate retention (Blakemore et al. 1987); pHNaF: pH in NaF 1 M measured after 2 min.; Al

Gb5

Gb4

Gb3

Gb2

Depth cm

Table 1 Selected data from Andosols and andic soils developed from gabbros in Galicia (Monte Castelo, A Coruña)

262 E. García-Rodeja et al.

Ah1

> 105

2Bw

Gn2

75–105

2Ah

0–25

0–45

50–75

Ah

25–50

Ah3

70–140

2Bw

Ah2

40–70

Bw

0–25

20–40

BA

Ah1

0–20

38–75

2Bw

Ah

15–38

Gn1

Am5

Am4

0–15

AB

40–80

2Bw

Ah

20–40

Ah2

Am3

0–20

Ah1

Am2

0–20

Ah

Am1

Depth cm

5.0

4.7

5.3

4.9

4.8

4.8

4.9

5.6

5.6

5.3

5.3

5.2

5.3

5.3

5.2

5.1

5.5

5.2

pHH2 O

7.06

11.1

1.8

6.3

6.5

9.1

8.9

0.2

0.2

1.10

11.4

0.5

4.5

10.9

0.4

7.9

8.8

13.1

%OC

0.86

0.81

0.95

0.82

0.81

0.74

0.73

1.02

0.94

0.85

0.71

1.13

0.79

0.67

1.03

0.74

0.70

0.62

BD

91

87

66

96

95

93

91

58

56

71

97

53

91

97

29

96

96

91

P ret %

11.1

11.7

9.2

11.1

10.7

11.0

10.6

9.0

9.1

9.8

11.3

9.3

11.2

11.4

8.2

11.0

11.0

11.6

pH NaF

1.20

1.46

0.61

2.12

1.88

1.69

1.55

0.17

0.27

0.54

2.35

0.38

1.41

2.55

0.10

2.59

2.38

1.76

Alox

1.20

0.92

0.71

1.33

1.37

1.55

1.46

0.10

0.20

0.55

1.66

0.22

0.68

0.68

0.20

1.44

1.04

1.60

Alpy

3.06

2.00

0.51

0.95

0.77

0.71

0.68

0.16

0.23

0.65

1.00

0.19

0.68

0.61

0.08

0.73

0.75

0.66

Feox

1.15

0.52

0.68

0.79

0.67

0.75

0.68

0.10

0.35

0.81

0.80

0.27

0.34

0.16

0.14

0.30

0.21

0.61

Fepy

5.79

3.80

8.37

6.71

6.77

6.31

6.01

7.47

6.82

5.52

5.20

11.15

7.15

4.75

9.50

5.35

6.27

3.60

Fedc

nd

0.11

0.20

1.00

0.86

0.47

0.47

0.01

0.02

0.05

0.25

0.02

0.30

0.55

0.10

0.45

0.40

0.10

Siox

2.73

2.46

0.86

2.59

2.26

2.04

1.89

0.25

0.39

0.87

2.85

0.48

1.75

2.86

0.14

2.96

2.76

2.09

Alox + 1/2Feox

1.00

0.63

–

0.63

0.73

0.92

0.94

0.59

0.74

1.02

0.71

0.58

0.48

0.27

2.00

0.56

0.44

0.91

Alpy / Alox

0.53

0.53

0.06

0.14

0.11

0.11

0.11

0.02

0.03

0.12

0.19

0.02

0.10

0.13

0.01

0.14

0.12

0.18

Feox / Fecd

nd

0.8

–

7.1

6.1

3.4

3.3

–

0.1

0.4

1.8

–

2.1

3.9

–

3.2

2.8

0.7

3.3

2.5

–

0.3

0.2

0.0

0.0

–

0.0

0.0

0.4

–

0.6

0.8

–

0.7

0.9

0.1

Fh %

(continued)

Allo %

Table 2 Selected data from Andosols and andic soils developed from amphibolite (Am) in Galicia (Santiago de Compostela, A Coruña) and granulite (Gn) in Serra da Capelada (A Coruña)

Andosols and Podzols at Galicia 263

25–55

5.4

pHH2 O

4.62

%OC

dm−3 );

0.90

BD 82

P ret % 11.1

pH NaF 1.01

Alox 1.07

Alpy 1.88

Feox 0.53

Fepy 6.50

Fedc nd

Siox 1.95

Alox + 1/2Feox 1.06

Alpy / Alox 0.29

Feox / Fecd nd

Allo % 2.3

Fh %

OC: organic carbon; BD: bulk density (kg P ret: Phosphate retention (Blakemore et al. 1987); pHNaF: pH in NaF 1 M measured after 2 min.; Alox , Feox , Siox : Al, Fe and Si extracted with acid ammonium oxalate; Alpy , Fepy : Al and Fe extracted with Na-pyrophosphate (%); Fedc : Fe extracted with citratedithionite (%); Allo: Allophane; Fh: ferrihydrite. Allophane and Ferrihydrite estimated following Childs (1985) and Parffit and Childs (1988) respectively. Source García-Rodeja et al. (1986) and unpublished data for granulite

Ah2

Depth cm

Table 2 (continued)

264 E. García-Rodeja et al.

Andosols and Podzols at Galicia

265

amounts of halloysite, 2:1 gibbsite, and Fe oxyhydroxides. In these horizons the influence of organic matter, which generates more acidic conditions, leads to the formation of highly reactive secondary products (Al-humus complexes, iron oxyhydroxides and small quantities of allophane). When organic matter is absent, the initial stages of weathering are characterised by a mixture of primary minerals, degradation products of micas, gibbsite, halloysite and Fe oxyhydroxides (García Paz et al. 1986; Macías et al. 1980). In the more advanced weathering stages, horizons 2Bw, 2C and saprolites of the older cycle are characterised by a low proportion of weatherable minerals and a predominance of Fe oxyhydroxides (mainly goethite), gibbsite and kaolinite (García-Rodeja et al. 1986; Macias et al. 1978a). In soils from gabbro and metabasic rocks, variable charge predominates, and the cation exchange complex is characterized by a low exchange capacity (which increases with organic matter content) and low exchangeable base cations content, particularly in Ah horizons of polycyclic soils. Exchangeable Al (KCl extractable Al) is low in the Ah horizons of well-drained soils, but it increases in the deeper horizons up to reach a strongly aluminized cation exchange complex. In these soils, a nonbuffered CuCI2 solution is much more effective than KCl extracting Al indicating a predominance of non-exchangeable organically bond Al compounds. As was abovementioned, one of the main characteristics of Andosols is the occurrence of metal (Al, Fe)-humus complexes as well as inorganic compounds of Al and Fe with different degree of crystallinity. The pools of each of these Al and Fe compounds, as well as Si, can be operatively quantified applying extractable solutions such as Na-pyrophosphate (py), acid ammonium oxalate-oxalic (ox) and Na-dithionite-citrate (dc), and interpreted as follows (García-Rodeja et al. 2004a, b, 2007): Alox : reactive Al, mostly in humus complexes and allophane; Alpy : Al in humus complexes; Alox –Alpy : Al in allophane; Siox : Si in allophane; Fedc : Total free Fe pool; Feox : Fe in ferrihydrite and Fe-humus complexes; Fedc –Feox : crystalline Fe oxyhydroxides; Fepy : Fe in Fe-humus complexes, and Feox –Fepy : Fe in ferrihydrite. The Ah horizons of soils from gabbro and amphibolite have relatively high quantities of Alox and Alpy , but with small differences among them in most samples, and low levels of Siox . The highest values of Alox and Alpy appear in Ah and, sometimes, in AB horizons of polycyclic soils, being lower in Ah horizons of AR soils and even lower in BA and Bw horizons, where Siox is hardly extracted. The amounts of allophane, estimated from Siox (Parfit and Childs 1988), are usually low but its presence cannot be ignored in several surface horizons of these soils. The small amount of Feox , as compared to Fedc , indicates the predominance of crystalline iron oxides and the scarcity of non-crystalline Fe compounds. The low Feox /Fedc ratios indicate a high crystallinity of Fe oxides in the B horizons, particularly in those from the older soil cycle. The Na-dithionite-citrate extractable Al (Aldc ) in B horizons accounted to the presence of Al substituting in the Fe oxides that are dissolved by the extracting solution, but which remains undissolved by oxalate due to its crystallinity. Closely related to the reactivity of the Al compounds in soils from gabbro and metabasic rocks, pHNaF values are > 11 in humus-rich horizons, but under 9.4 in most horizons of the old cycle. A strong reaction with NaF of umbric and many cambic horizons of well-drained soil is common in Galician soils formed from other

266

E. García-Rodeja et al.

materials and indicates the abundance of active Al (Garcia-Rodeja et al. 1985). The abundance of reactive Al and iron oxyhydroxides explains the high capacity of these soils to retain sulphate (Camps and Macías 2000; Merino and García-Rodeja 1992). Phosphate retention is also very high in Ah and AB horizons (> 85% and even 90%, following the method of Blakemore et al. (1987)), diminishing in BA and Bw horizons, and even lower in 2Bw buried horizons. Regarding classification, the Ah horizons are umbric when they reach enough thickness, in many cases have andic properties, dark colour and a melanic index higher than 1.7. Therefore, they can often be characterised as fulvic horizons. The Bw horizons of the surface cycle are cambic whereas the B horizons of the old cycle, formed in situ from intensely weathered saprolites, show properties that lie on the boundary between the cambic, argic and ferralic horizons. The problematic classification of these B horizons is typical for soils with a mineralogy dominated by low activity clays being, in most cases, characterised as strongly evolved cambic B horizons (García Paz et al. 1986, García-Rodeja et al. 1986; Macías et al 1978b). Therefore, many soils developed from gabbro and amphibolite having thick Ah horizons can be classified as Andosols according the WRB 2015. The soils developed on gabbro (Table 1) are umbric aluandic Andosols, likewise soils Am2, Am5, Gn1 and Gn2 developed from metabasic rocks (Table 2). Other soils have an umbric horizons with andic properties, but they cannot be classified as Andosols because of the insufficient thickness of the Ah horizon (< 30 cm). In this case, they would be an umbric Leptosol (proto-Andic) (Am1), a cambic Umbrisol (proto-Andic) (Am3) and a proto-andic Cambisol (Am4). Thus, the classification of soils on gabbro and amphibolite depends mainly on the properties of the horizons of the surface cycle, the Ah horizons. They are superficial horizons, rich in organic matter, whose properties are mainly related to the abundance of Al-humus complexes accompanied by halloysite and small amounts of allophane. Therefore, the classification as Andosols of soils formed from this type of materials is not only a consequence of fulfilling the conditions required by the classification systems, but also because many of their properties are close to those of typical Andosols, in particular to those of nonallophanic or aluandic Andosols, whose properties are due to the abundance of reactive Al(Fe)-humus complexes. This similarity between soils in Tables 1 and 2 with those non-allophanic or aluandic Andosols, can be easily evidenced by a comparison with Andosols developed from basalts in France (Cantal, Massif Central) (Table 3), which have very similar properties in the Ah horizons (Chesworth et al. 1983; García-Rodeja and Silva 1994). The andic properties are mainly (basalt) or exclusively (gabbro, amphibolite) associated with Ah horizons, Alox + 1/2 Feox is higher in basalt than in gabbro and amphibolite soils, phosphate retention reaches similar values (> 90%) and low bulk densities (< 0.90 kg dm−3 ) are associated with high organic matter contents. Other properties related to the andic character of these horizons, such as pH in NaF or water retention, are of the same order. The main differences lie in the Bw horizons of basalts, as they have a bulk density somewhat higher than required to meet the criteria defining the andic properties and a lower crystallinity of the Fe oxides in the Bw and C horizons. In the case of gabbro and amphibolite soils, none of the conditions

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are met. As far as classification is concerned, soils from basalt also show umbric horizons with andic properties (aluandic in Ah horizons, silandic in Bw horizons). The non-allophanic character of Ah horizons from basalts is not as widespread as in gabbro and amphibolite soils, whereas in Bw horizons the allophanic character is evident, with higher allophane contents. Regarding to the processes involved in the formation of these soils, in organic matter rich Ah horizons, the fast weathering of primary minerals under the influence of organic acids and CO2 (moderate acid complexolysis to acid hydrolysis) slows down mineral neoformation. The process, defined as andosolization, that affects parent materials rich in weatherable minerals depend on the weathering kinetics, the existence of adequate conditions for the stabilization of intermediate, metastable, products, and absence of vertical redistribution. In this geochemical scenario, organic matter plays a double role as it can accelerate the weathering and contribute, together to the humidity, to the stabilization of the disordered phases (García-Rodeja and Macías 1984; Macías et al. 1982; Macías and Calvo 1992). In B horizons and saprolites where organic matter is almost absent, the weathering trend changes to a fermonosiallitization under conditions of acid hydrolysis. The trend is the same in B horizons of the surface and the old cycle, but the intensity of the process is much higher in the later. This led to the formation of intensely altered B horizons, with a composition approaching the residual system (Chesworth 1973) and characteristics close to the ferralic horizon, but characterized as cambic horizons which, in some cases, meet the ferralic properties defined by FAO 1990, but not the ferralic qualifier of WRB 2015. Other Soils with ‘Andic Properties’ As was aforementioned, in Galicia there are soils developed on other materials such as granitic rocks, biotitic schists and gneisses, having Ah umbric horizons that meet or are close to meeting the criteria defining andic properties. Compared to soils formed from basic and metabasic rocks, the weathering under conditions of moderate acid complexolysis to acid hydrolysis is slower. This leads to the destruction of weatherable primary minerals, degradation of micas and formation of Al (Fe)-OM complexes, aluminization of 2:1 minerals, with formation of halloysite and very infrequently, allophane (Romero et al. 1985, 1990; Silva et al. 1984). The dominant process is an aluminosialitization and the soils (aluminic soils) are characterised by high variable charge due mainly to organic components, moderate to high reactivity and high Al saturation (García-Rodeja and Macías 1984; Macías et al. 1982; Macías and Calvo 1992). Usually, these soils are not classified as Andosols due to the insufficient thickness of the horizons with andic properties, but the qualifiers andic or protoandic can be applied to them. Table 4 shows some examples of soils with andic properties in the umbric horizon or in some of its sub-horizons (Sc5, Sc6, Gr1, Gr2), and the protoandic qualifier could be applied to them (Sc1, Sc5, Sc6 and Gr2). Among these soils, only the soil Gr1 can be characterised as Andosol, due to the thickness of the Ah2 horizon, while the others are Umbrisols.

0–20

20–40

Ah2

60–100

Bw

Ah1

30–60

BA

75–90

BC

10–30

50–75

Bw

Ah2

30–50

AB

0–10

10–30

Ah2

Ah1

0–10

Ah1

5.1

4.6

4.8

4.7

4.7

4.8

4.9

4.9

4.7

4.8

4.8

pHH2 O

8.4

15.9

0.7

3.9

7.4

9.8

0.7

1.8

6.2

10.0

12.1

% OC

0.76

0.68

0.91

0.81

0.76

0.73

1.16

1.01

0.78

0.75

0.75

BD

97

93

91

97

96

93

92

95

97

95

93

P ret %

11.4

10.9

11.3

11.5

11.7

11.2

10.7

11.4

11.7

11.6

11.1

pH NaF

3.50

2.90

2.60

3.55

3.00

2.65

2.70

2.90

3.00

2.70

2.40

Alox

1.52

1.22

0.38

1.03

1.75

1.31

0.34

0.59

1.72

1.90

1.60

Alpy

2.00

1.54

0.56

1.56

1.70

1.40

0.72

1.03

1.60

1.64

1.54

Feox

1.65

1.35

0.20

1.10

1.25

0.85

0.10

0.35

0.85

0.85

0.75

Fepy

7.12

5.75

4.50

6.75

7.12

4.75

3.92

4.37

6.25

5.87

5.20

Fedc

0.30

0.15

0.65

0.80

0.70

0.45

0.80

0.80

0.70

0.50

0.36

Siox

4.50

3.67

2.88

4.33

3.85

3.35

3.06

3.42

3.80

3.52

3.17

Alox + 1/2Feox

0.43

0.42

0.15

0.29

0.58

0.49

0.13

0.20

0.57

0.70

0.67

Alpy/ Alox

0.28

0.27

0.12

0.23

0.24

0.29

0.18

0.24

0.26

0.28

0.30

Feox/ Fedc

2.1

1.1

4.6

5.7

5.0

3.2

5.7

5.7

5.0

3.6

2.6

Allo %

0.6

0.3

0.6

0.78

0.8

0.9

1.1

1.2

1.3

1.3

1.3

Fh %

OC: organic carbon; BD: bulk density (kg dm−3 ); P ret: Phosphate retention (Blakemore et al. 1987); pHNaF: pH in NaF 1 M measured after 2 min.; Alox , Feox , Siox : Al, Fe and Si extracted with acid ammonium oxalate; Alpy , Fepy : Al and Fe extracted with Na-pyrophosphate; Fedc : Fe extracted with citrate-dithionite; Allo: Allophane; Fh: ferrihydrite. Allophane and Ferrihydrite estimated following Childs (1985) and Parffit and Childs (1988) respectively. Source García-Rodeja and Silva (1994)

Bs3

Bs2

Bs1

Depth cm

Table 3 Selected data from Andosols developed from basalts in France (Cantal, Massif Central, France)

268 E. García-Rodeja et al.

0–20

20–40

Ah2

30–100

Ah2

Ah1

0–30

22–40

Ah1

10–22

Bw

45–70

Bw2

Ah2

21–45

Bw1

0–10

10–21

Ah1

0–10

Ah2

15–25

Ah2

Ah1

0–15

Ah1

4.1

4.2

4.7

4.8

4.90

4.8

4.9

4.9

4.9

5.0

5.1

4.7

4.8

pHH2 O

11.5

8.4

15.7

10.2

1.6

8.8

8.8

0.6

1.1

8.4

9.4

4.5

6.4

% OC

0.68

0.83

0.83

1.00

1.08

0.81

0.82

1.21

1.11

0.83

0.79

0.90

0.85

BD

95

35

94

60

59

85

84

50

51

82

85

81

76

P ret %

11.7

8.7

11.9

10.0

10.4

11.7

11.5

9.3

9.5

10.6

11.4

10.80

10.90

pH NaF

2.74

0.91

1.95

0.60

0.52

1.90

1.85

0.16

0.20

1.70

1.85

1.11

1.15

Alox

2.26

0.78

1.37

0.54

0.56

1.40

1.45

0.02

0.05

0.92

1.00

1.10

1.12

Alpy

1.65

0.79

2.01

1.12

0.32

0.58

0.57

0.06

0.11

0.62

0.68

1.78

1.32

Feox

1.60

0.77

1.82

0.89

0.47

0.84

0.53

0.04

0.09

0.43

0.38

0.36

0.59

Fepy

1.87

1.28

2.16

2.19

2.11

2.03

2.97

2.23

2.30

2.66

2.39

2.90

2.32

Fedc

nd

nd

0.19

0.10

nd

nd

nd

nd

nd

0.29

0.25

0.31

0.28

Siox

3.49

1.30

2.96

1.16

0.68

2.19

2.14

0.19

0.26

2.01

2.19

2.00

1.81

Alox + 1/2Feox

0.82

0.86

0.70

0.90

1.08

0.74

0.78

0.13

0.25

0.54

0.54

0.99

0.97

Alpy / Alox

0.80

0.60

0.93

0.51

0.15

0.29

0.19

0.03

0.05

0.23

0.28

0.61

0.57

Feox / Fecd

nd

nd

1.4

0.7

nd

nd

nd

nd

nd

2.1

1.8

2.2

2.0

Allo %

0.1

0.0

0.3

0.4

0.0

0.0

0.1

0.0

0.0

0.3

0.5

2.4

1.2

Fh %

ox , Feox , Siox : Al, Fe and Si extracted with acid ammonium oxalate; Alpy , Fepy : Al and Fe extracted with Na-pyrophosphate; Fedc : Fe extracted with citrate-dithionite; Allo: Allophane; Fh: ferrihydrite. Allophane and Ferrihydrite estimated following Childs (1985) and Parffit and Childs (1988) respectively

OC: organic carbon; BD: bulk density (kg dm−3 ); P ret: Phosphate retention (Blakemore et al. 1987); pHNaF: pH in NaF 1 M measured after 2 min.; Al

Gr2

Gr1

Sc6

Sc5

Sc1

Depth cm

Table 4 Selected data from ‘andic soils’ developed from schists (Sc) and granites (Gr)

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3 Podzols in Galicia In Galicia, podzols develop mainly from materials poor in weatherable minerals (sandstones, quartzites, quartz-rich deposits from the alteration of these rocks or from large quartz dykes), but also in humid and cold mountain areas from other types of parent materials, especially granitic rocks. The difference between them is a general presence of E horizons (albic horizons) and a separation of the spodic horizon into Bh and Bs sub-horizons in the former (quartz rich rocks), whereas the E horizon is absent in those formed from other materials which usually only present a Bs horizon, whose characterisation as spodic is close to the limit of the properties it must fulfil. From a taxonomic point of view, many podzolic soils developed from quartz materials are characterised as Podzols, but when these soils are developed from other materials their classification as Podzols has changed with the modifications in the definition of the spodic horizon in the FAO-WRB and Soil Taxonomy classification systems. Podzols and podzolic soils, have been extensively studied from the initial works on their morphology and properties (Aguilar et al. 1980; Alias and Pujalte 1968; Guitián and Carballas 1968), mineralogy (Macías et al. 1987), their macro- and micromorphological characteristics (Macías 1980; Macías et al. 1988), the geochemical conditions that favour their development and the pedogenetic processes (Chesworth et al. 1982; Chesworth and Macías 1985; Ferro et al. 2014, 2020; García-Rodeja and Macías. 1984; Macías et al. 1987; Moares et al. 1996, among others). Podzols and Podzolic Soils on Quartzites and Quartz-Rich Sediments The best developed Podzols are formed from quartz-rich sedimentary deposits in well-drained environments, showing a typical sequence of horizons: O, Ah (sometimes umbric), E (meeting albic material/albic horizon) and well differentiated Bh and Bs spodic horizons (Images. 4, 5a, 6). In some cases, the E horizon is absent or poorly differentiated (soils with AE horizon, with abundant uncoated quartz sands) (Image 5b). Below the A or AE horizon, a Bs horizon develops with accumulation of non-crystalline forms of Fe and Al as well as organic matter. Furthermore, in some of podzols derived from quartzrich material, a clay accumulation horizon (Bt) is found with features of illuvial origin under the spodic horizon. The presence of that clay accumulation is interpreted as consequence of illuviation processes prior to podzolization, although in some cases it seems that clay illuviation is still active (Macías et al. 1988). Sometimes these soils present thin layers cemented by Fe, Al and organic matter (placic horizon, placic qualifier), which can appear below the E horizon (Images. 7, 8) or in the spodic horizon. These layers can sometimes generate hydromorphic conditions favouring, in some areas, the formation of histic horizons and later of blanket bogs. Table 5 includes selected data on the properties of soils developed from quartz-rich materials. The O horizons have variable thickness, but they are generally thin, with abundant undecomposed or very weakly decomposed plant remains below which develop Ah horizons. The Ah horizons have also a variable thickness, with colours between

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Image 4 Two albic Podzols at Monte Acibro (Lugo) developed from quartzite sediments

black and very dark grey, sandy textures, organic carbon contents in the range 3–5%, acid to strongly acid pH (pHH2 O between 4 and 5), low ECEC and high Al saturation of the exchange complex. The coarse components in these Ah horizons consist mainly of sand-sized quartz grains and fragments of quartzite, whereas its organic matter organic can be distinguished between (a) biogenic, the transformation of plant remains with the production of polymorphic organic matter, and (b) physicochemical, in which precipitates of organo-aluminium complexes (monomorphic organic matter) are produced, mixed with the fine mineral fraction covering the mineral grains (Macías et al. 1988). The E horizons, with thickness ranging from 10 to 25 cm, have a grey colour, sandy textures (sandy loam, loamy sand), pH less acidic than the overlying mineral horizons (range 4.5–5.5) and very low organic carbon content. The scarce organic matter is heterogeneously distributed as thin and discontinuous punctuations or coatings on the grains. Locally, excrements and plant-remains in different

272

E. García-Rodeja et al.

Image 5 Variability in podzol development: an albic Podzol (a) and a entic Podzol (b), developed from quartz rich sediments from Pico Sacro dyke. The distance between pits is about 4 m

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273

Image 6 Morphological diversity in albic Podzols developed from quartz rich sediments in different environments. a Negradas (Lugo), 30 m a.s.l., 1 km to the sea, b Courel (Lugo), 600 m a.s.l., 110 km to the sea

stages of transformation can be observed in the E horizons, similar to those existing in the A horizons (Macías 1980; Macías et al. 1988). In the eluvial horizons, resistant species predominate (quartz, muscovite and as accessories tourmaline, zircon, etc.). The clay fraction is constituted by different proportions of quartz, micaceous minerals (partially degraded to mica-vermiculite intergrades) and, especially in the Ah horizons, mica-smectite (García-Rodeja et al. 1998; Macías et al. 1987) and kaolinite-type minerals, which together usually account for more than 80% of the crystalline fraction. The spodic horizons are usually divided into two sub-horizons, a Bh of highly variable thickness (from 2 cm to more than 15 cm), dark colour (black to very dark brown), organic C contents (3–5%) sometimes exceeding that of the Ah horizons and often abundant clay fraction (sandy clay loam textures are common). Below this horizon, a brownish (strong brown to yellowish brown) with lower clay content Bs horizon develops, which gradually passes into the underlying horizons. Sometimes the spodic horizons are heterogeneous and presents parts with characteristics of Bh (sometimes in the form of lamellae, Image 7) interspersed with others with

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Image 7 Entic Podzol with a placic horizon and a Bh lamellae in the spodic horizon (Serra do Xistral, Lugo)

characteristics of Bs. The pH values are generally more acidic in Bh than in Bs and tend to increase towards the lower part of the spodic horizon, where values above pH 5 are reached. The ECEC is very low, slightly higher in the Bh than in Bs horizons, closely related to their higher content in organic matter and clay. In any case, the cation exchange complex is dominated by Al. In the spodic horizons, Al(Fe)humus complexes dominate, the 2:1 minerals are partially aluminised and beside them, halloysite, kaolinite, gibbsite, forms of Al and Fe oxides of low crystallinity (ferrihydrite) and, occasionally, aluminosilicates of low order rank are identified. These components would explain why many properties of these soils are close to those used to define the andic properties. The organic matter in the Bh sub-horizons is both monomorphic (coatings) and polymorphic (pellets or aggregates) indicating that, in addition to organic matter illuviation, root growth may contribute to the accumulation of organic matter in this horizon when the environment is favourable for their development. The Bs horizons are characterised by the presence of Fe and/or clay oxyhydroxide coatings on the coarse grains, whereas the fine organic matter is

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275

Image 8 An ortstein (up) and a placic horizon (down) in quartzite deposits (Montouto, Serra do Xistral, Lugo)

monomorphic and is present forming thin coatings, sometimes superimposed on the previous ones (Macías 1980; Macías et al. 1988). The mobilisation of Fe and Al, and their accumulation in the spodic horizons, is evident in all cases but quite variable in amounts and intensity. The maximum of Fe (Fepy , Feox and Fedc ) is usually present in the Bh sub-horizon, while Al shows a greater variation although Alpy is usually higher in Bh than in Bs. Organically complexed Al (Alpy ) predominates over non-crystalline inorganic forms, suggesting

P. Sacro

Acibro

Rasa

13–57

57–70

70–80

Bhs

Bs

> 80

2Bt

E

42–80

Bs

0–13

30–42

Ah

10–30

> 70

2Bt

Bhs

37–70

Bs

E

30–37

Bhs

0–10

12–30

E

A

0–12

A

5YR4/4

7.5YR2/1

7.5YR5/1

7.5YR2/1

10YR4/4

7.5YR3/4

7.5YR2/1

10YR4/1

10YR3/1

10YR5/4

7.5YR3/4

7.5YR3/2

10YR5/1

10YR3/1

7.5YR6/4

7.5YR3/1

7.5YR6/1

7.5YR3/1

10YR5/6

10YR4/4

10YR3/2

10YR5/1

10YR4/1

10YR6/4

7.5YR5/5

10YR3/4

10YR6/1

10YR4/1

5.0

4.8

5.4

4.7

5.6

5.6

5.0

5.9

5.0

4.9

5.1

4.7

5.7

4.8

1.06

12.27

0.72

1.94

1.24

2.11

5.36

0.69

1.89

1.00

1.89

7.92

0.18

1.00

1.72

14.90

1.81

2.48

1.52

2.48

6.80

0.83

2.59

2.06

3.08

9.15

0.56

2.45

2.24

2.33

0.23

2.57

0.99

1.34

4.38

0.86

3.26

0.93

1.92

4.84

0.36

4.48

1.79 sl

2.25 scl

0.21 af

1.52 sl

0.47 sl

0.79 sl

2.54 scl

0.02 s

0.31 ls

0.29 scl

1.22 scl

3.99 scl

0.21 sl

1.10

1.42

0.10

0.16

0.28

0.60

0.59

0.01

0.06

0.85

1.78

1.25

0.13

0.31

Text Alox

1.48 sl

Depth cm Colour wet Colour dry pHH2 O AlKCl ECEC OC % Cpy

0.98

0.77

0.01

0.08

0.22

0.56

0.56

0.02

0.07

0.47

1.24

0.75

0.03

0.14

Alpy

1.87

3.85

0.07

0.18

0.59

1.14

1.87

0.07

0.14

0.96

2.05

3.43

0.14

0.46

Fedc

1.04

2.59

0.03

0.08

0.24

0.61

1.59

0.01

0.05

0.4

0.89

3.03

0.06

0.18

Feox

0.84

2.46

0.01

0.05

0.21

0.6

1.28

0.01

0.01

0.26

0.55

1.73

0.04

0.17

1.62

2.72

0.11

0.20

0.40

0.90

1.39

0.02

0.09

1.05

2.23

2.77

0.16

0.40

(continued)

11.6

7.6

7.1

6.6

10.8

11.5

9.2

7.6

7.2

11.6

11.8

10.5

7.7

8.6

Fepy Alox + 1/ pH NaF 2Feox

Table 5 Selected data from Podzols (albic Podzols, except Cadramón—Entic Podzol) developed from quartzite sediments (Rasa, Acibro, Cadramón—Lugo) and deposits from quartz dikes (P. Sacro, Bares—A Coruña)

276 E. García-Rodeja et al.

10YR4/4

> 120

70–90

Bs2

7.5YR3/4

7.5YR4/6

7.5YR2/2

10YR2/1

10YR6/4

7.5YR5/6

10YR3/2

10YR7/3

10YR5/8

10YR3/2

10YR6/1

10YR4/1

7.5YR7/4

4.5

4.5

4.2

4.8

4.5

4.1

4.3

3.7

5.2

0.97

1.55

2.73

1.63

2.94

8.43

1.49

2.69

0.54

2.17

2.03

5.65

1.92

3.43

9.19

2.39

4.06

1.91

1.69

2.48

4.77

1.91

2.69

5.19

1.02

3.97

1.99

0.54 sl

0.77 sl

1.09 sl

1.27 sil

2.08 sil

4.06 scl

0.39 sl

1.39 sl

1.75 sl

0.99

0.49

0.12

1.39

0.87

1.02

0.01

0.11

0.91

Text Alox

0.71

0.52

0.21

0.68

0.85

0.75

0.04

0.14

0.88

Alpy

1.68

2.28

1.06

1.30

2.63

4.31

0.22

0.33

0.77

Fedc

0.83

1.86

0.69

0.83

2.09

4.04

0.09

0.20

0.33

Feox

0.82

1.36

0.68

0.43

1.96

2.96

0.07

0.17

0.20

1.41

1.42

0.47

1.81

1.91

3.04

0.06

0.21

1.08

11.3

10.2

7.5

11.6

10.8

9.0

8.0

7.8

11.2

Fepy Alox + 1/ pH NaF 2Feox

AlKCl: Al KCl extractable (cmolc kg−1 ); ECEC: effective cation exchange capacity (cmolc kg−1 ); OC: organic carbon; Alox , Feox , Siox : Al, Fe and Si extracted with acid ammonium oxalate; Cpy , Alpy , Fepy : Al and Fe extracted with Na-pyrophosphate (%); Fecd : Fe extracted with citrate-dithionite (%); pHNaF: pH in NaF 1 M measured after 2 min.; Text: soil texture (s: sand; ls: loamy sand; sl: sandy loam; scl: sandy clay loam; sil: silt loam)

25–70

Bs1

0–25

70–120

Bs

C

10YR3/3

60–70

Bh

10YR3/1

15–60

E

7.5YR3/0

7.5YR4/3

0–15

A

Bs/C 80–90

Cadramón AE

Bares

Depth cm Colour wet Colour dry pHH2 O AlKCl ECEC OC % Cpy

Table 5 (continued)

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a mobilisation of Al bound to organic matter. The reactivity to NaF (after 2 min of reaction) is negative in the eluvial horizons but it increases towards deepest horizons. The response is moderately (pHNaF > 9.4) to strongly (pHNaF > 11) positive in the spodic horizons, reaching maximum values in the Bs sub-horizons, but it can be very weak in the more organic-rich Bh horizons (García-Rodeja et al. 1984, 1985). Podzols and Podzolic Soils on Granitic Rocks and Other Materials From materials richer in weatherable minerals (granites, granodiorites, among others), the soils present a superficial Ah horizon (often umbric) rich in organic matter and with evidence of leaching in form of abundant uncoated sands, which are sometimes characterised as AE horizons. In less developed podzolic soils, monomorphic organic matter is identified in the Ah horizons, generally with a predominance of polymorphic forms in the upper part and coatings in the lower part of the horizon (Macías 1980; Macías et al. 1988). Below this surface horizon (Ah or AE), B horizons with ochre colours and enriched in non-crystalline Fe and Al components develop. These B horizons are characterised as cambic or spodic but having properties close to the latter, and E horizons are no present. These soils represent a transition between Umbrisols or Cambisols (acid brown soils) and Podzols. Examples of soils developed from these materials are presented in the Images. 9 and 10, whereas Table 6 includes selected data on their properties. In soils developed from granitic rocks and other materials, the formation of Bms horizons (ortsteins, Image 8) and thin cemented pans of Fe (placic horizon) is frequent (Image 9). These are mineral horizons of variable thickness (generally thin), frequently associated with coarse-textured soils and subject to intense lateral drainage. They are located at different levels within the profile, being discontinuous and irregular, cemented by Fe- and Al-rich compounds with low amounts of organic matter. They are black, reddish-brown, or dark red in colour, changing from brownish tones on the surface to more reddish colours in the interior. These changes have been attributed to a transformation of Fe-humus complexes and ferrihydrite to dehydrated and more crystalline oxides. In these lithologies, granitic rocks and paragneiss, soils characterised as Umbrisols or Cambisols are found. In them, the accumulation of reactive forms of Fe and Al and cracking of coatings on mineral grains are observed in the lower part of the Ah horizon, which would indicate a limited mobilisation of these components that could suggest an incipient podzolization process (cryptopodzolization) (Image 10) (Moares et. al. 1996). Genesis and Classification of Podzols of Galicia In soils formed from rocks with very low alterable mineral content, pedogenesis is controlled by organic acids. The more acidic environment in the superficial horizons and the activity of organic matter lead to an intense alteration of primary minerals under conditions of strong acid-complexolysis (García-Rodeja and Macías 1984; Macías et al. 1987; Macías and Calvo 1992). As consequence it is observed an intense degradation of micas and little neoformation, with the translocation to subsurface horizons of organometallic complexes with a low C/metal ratio (cheluviation), in a

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Image 9 Podzolic soils on granodiorite and a detail of an ortstein (Montes da Toxiza, Lugo)

process of podzolization. In the illuvial horizons (spodic horizons), the geochemical conditions are less acidic (acid hydrolysis) (García-Rodeja and Macías 1984; Macías and Calvo 1992) and the organometallic complexes, with a low C/metal ratio (8– 15 in podzols of Galicia, Fernández Marcos et al. 1980), precipitate (chiluviation). As result, components similar to those that characterise aluminic (or andic) soils developed on other materials are formed, including a predominance of Al(Fe)-humus complexes and non-crystalline forms of Al and Fe (ferrihydrite).

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Image 10 Cryptopodzolic soils on paragneiss (left) and granite (right) (Serras Setentrionais, Lugo)

In podzolization sensu stricto, the translocation of organic matter, Fe and Al in well-drained podzols takes place mostly in the form of organo-metal complexes, which precipitate in the illuvial horizon due to the surpass of the metal load of the complex. However, some hypotheses on podzolization consider that this would take place, in a first stage, through the mobilisation of soluble compounds of imogolitelike structure (proto-imogolite). This compound (proto-imogolite) migrates through the E horizon towards the Bs horizons where they transform into imogolite. In a second stage, fulvic acids from the upper horizons migrate through the profile until they are adsorbed by the previously illuviated imogolite. In Galicia, imogolite has been identified in Bs horizons of podzolic soils on granite (García-Rodeja and Macías 1986a, b). However, the role of imogolite in the podzolization process is considered unlikely, as acidic conditions and the abundance of reactive organic matter would prevent the formation of this component in the eluvial horizons (Chesworth and Macías 1985; Macías et al. 1987, 1988). However, imogolite could be formed either by in situ alteration or by combination of silicon with the aluminium released from the organic ligand in Bs horizons. This is more likely in soils derived from granitic rocks, where a greater abundance of weatherable primary minerals and Al, accompanied by higher pH values, makes its formation possible (García-Rodeja and Macías 1984; Macías et al. 1988). In terms of classification, the characterisation of a soil as a Podzol (WRB) or Spodosol (ST) depends on the presence of a spodic horizon at a certain depth. Over

10–60

(At Bhs)

Bhs

Ortstein

> 80

C

0–10

40–80

Bhs

AE

0–40

25–53

Bhs

AE

0–25

A

7.5YR4/4

7.5YR4/4

10YR4/3

10YR6/6

10YR5/3

10YR3/1

7.5YR4/4

7.5YR3/0

Colour dry

5.0

5.2

4.4

4.4

4.2

4.2

4.4

3.8

pHH2 O

4.44

0.97

3.47

1.09

1.96

4.94

0.44

1.33

AlKCl

5.43

2.27

3.72

1.66

2.70

8.68

1.72

2.94

3.11

3.23

4.54

0.94

2.01

6.69

3.39

5.69

OC %

2.38

2.67

1.61

0.26

1.59

1.87

2.72

3.99

Cpy

ls

sl

sl

sl

sl

sl

scl

scl

Text

1.41

2.15

0.35

0.63

1.55

0.36

0.60

0.45

Alox

kg−1 ); OC: organic carbon; Al

ECEC

kg−1 ); ECEC: effective cation exchange capacity (cmol

2.5YR2/2

5YR2/4

10YR3/2

10Y8/3

5YR3/2

10YR2/1

5YR3/3

5YR2.5/1

Colour wet

1.13

1.20

0.33

0.35

0.97

0.39

1.30

0.40

Alpy

0.98

0.73

0.30

0.12

0.30

0.42

3.25

2.68

Fedc

0.98

0.63

0.25

0.08

0.23

0.38

2.82

2.00

Feox

0.70

0.57

0.22

0.05

0.23

0.39

2.20

1.40

Fepy

1.90

2.47

0.48

0.67

1.67

0.55

1.70

1.45

Alox + 1/ 2Feox

11.0

11.1

8.8

10.7

11.5

8.4

9.4

7.8

pH NaF

AlKCl: Al KCl extractable (cmolc c ox , Feox , Siox : Al, Fe and Si extracted with acid ammonium oxalate; Cpy , Alpy , Fepy : Al and Fe extracted with Na-pyrophosphate (%); Fedc : Fe extracted with citrate-dithionite (%); pHNaF: pH in NaF 1 M measured after 2 min.; Text: soil texture (s: sand; ls: loamy sand; sl: sandy loam; scl: sandy clay loam; sil: silt loam). Source Unpublished data (Toxiza) and García-Rodeja and Macías (1986a) (Piornedo)

Piornedo

Toxiza 2

Toxiza 1

Depth cm

Table 6 Selected data from Podzols (entic Podzols) developed from granitic rocks at Montes da Toxiza and Serra de Ancares (Lugo)

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time, the properties that determine the characterisation of a horizon as spodic have changed from criteria based on the amount of reactive forms of Fe and Al bound to organic matter in relation to the clay content, or a so-called index of accumulation of amorphous material. Additional criteria were certain textural and morphological requirements, such as the occurrence of cracked coatings on sand grains, the existence of horizons cemented by organic matter with Al and/or Fe (e.g., in FAO 1990), or criteria the colour of the horizon becomes a fundamental property for its characterisation as spodic. More recently, other criteria based on the presence of cemented layers, cracked coatings and/or a certain accumulation of oxalate extractable Fe and Al were taken into account (e.g., WRB 2015). These continuous changes have led to soils that were classified as Podzols in the past cannot be included in this GSR nowadays, mostly due to fail in the colour-based criteria. In the most recent versions of the WRB (WRB 2015, WRB 2022) soils of quartzrich materials having an E horizon with albic horizon are classified as albic Podzols, whereas in their absence are entic Podzols. In podzolic soils developed from non quartz-rich materials, when the B horizon meets the requirements for spodic they are classified as entic Podzols, otherwise these soils will be classified as Umbrisols or Cambisols. Podzols and the Environment Organic Matter in Podzols Soils have been given a prominent role in climate change mitigation strategies (Glaser et al. 2002). In this context, soil genetic processes are key to carbon accumulation and stabilisation. One of the most potentially effective processes is that of podzolization. In Galicia, podzols have been found with organic matter accumulated in Bh horizons for periods of more than 1000 years (Macías et al. 2004). However, this long-term accumulation is conditioned by the nature, in terms of lability, reactivity or recalcitrance, of the soil organic matter. Previous studies (unpublished) on several podzols in Galicia, using chemical fractionation techniques of SOM, show several relevant patterns. The main fraction of SOM, more than 60%, is oxidisable organic carbon (with K2 Cr2 O7 ), while the more stable or recalcitrant fraction (Simpson et al. 2007), composed of humic acids, fulvic acids and, essentially, humin, never exceeds 20%. Of the oxidisable organic carbon fraction, the humified carbon varies depending on the type of horizon from values of less than 15% in the O and A horizons, to values above 40% in the Bh–Bs horizons. In all cases, the carbon of the most labile, water-soluble fractions does not exceed 3%. Assuming these results of organic matter fractionation as representative for Podzols of Galicia, these particular soil type have a substantial pool of reactive carbon which, depending on the evolution of environmental conditions, will tend to stabilise and accumulate in the soils or to be mobilised. Podzolization seems to be an effective mechanism promoting the accumulation of organic carbon in the spodic horizons in two ways. Firstly, podsolization can remove a large amount of organic carbon from soil surface through an intense biorecycling of organic matter.

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Secondly, the high positive correlation found between Na-pyrophosphate and ammonium oxalate-oxalic acid extractable Al and Fe (Alpy , Fepy , Alox , Feox ) and humified organic carbon, indicate that in these soils occur favourable conditions to promote the formation of organometallic compounds characterized by its high chemical stability and hardly decomposable. Is There Anything Else Mobilizing During Podzolization? During podsolization, other compounds may be mobilized throughout the soil profile such as heavy metals and metalloids, which are of particular concern due to their potential toxicological effects in the environment. In three podzols of Galicia, Chesworth et al. (1998) reported that total contents of Cr, Co, Pb, Zn and As showed similar vertical patterns of Al and Fe, suggesting that podsolization influenced in their distribution with soil depth. In addition to vertical patterns, heavy metal and trace elements also distributed differently among different aggregate size fractions. Thus, Piñeiro et al. (2002) observed that silt plus clay fraction of two podzolic soils from Serra do Xistral were considerable enriched in Zn, Pb, Cu, Ni and As compared to the fine earth fraction, finding peaks of Zn and Pb in the spodic horizons which were mobilized due to podzolization. In addition, it has been determined in several podzols in Galicia (Ferro et al. 2017), that the vertical distribution patterns of certain heavy metals (such as Zn and Pb) and their enrichment in the spodic horizons can be attributed to mobilization and immobilization mechanisms associated with the pedogenetic processes of podzolization and the involvement of certain soil components. The results showed that E and Bs horizons had the lowest and highest total Pb values, respectively. Regarding Pb isotopes, the ratio 206 Pb/207 Pb increased from surface to deeper horizons suggesting that some Pb reaching subsurface horizons should derived from atmospheric deposition. The vertical pattern of total Pb agreed with that expected due to podsolization, being secondary inorganic Al and Fe compounds and soluble organometallic (Al, Fe)-complexes responsible for Pb redistribution. More recently, several studies were focused on the geochemical behaviour of Hg (a highly toxic global pollutant) in podzols and podzolic soils from Galicia. Studying two podzols of Monte Acibro, Gómez-Armesto et al. (2020a, 2021) evidenced that total Hg (THg) peaked in A and B spodic horizons, and they obtained a model that predicted satisfactory the vertical pattern of Hg using soil parameters related to the podsolization such as total organic C, well-humified organic C (i.e., pyrophosphate extractable C) and Al-humus complexes. In a subsequent study, performed in a wider population of podzols and podzolic soils from Galicia, the occurrence of the THg peaks in A or in illuvial horizons (Bh-Bhs) depended on the intensity of the eluviation/ illuviation process (Gómez-Armesto et al. 2021). Moreover, podsolization was found to promote Hg mobilization from A and E horizons towards illuvial horizons (Bh and Bhs), a biogeochemical process where Al-humus and Fe-humus complexes played a key role. Additionally, this Hg behaviour during podzolization is also conditioned by soil texture (Gómez-Armesto et al. 2018, 2020b). Fine silt and clay size aggregates show a noticeable Hg enrichment, ranging from 2.5 and 10.8 times more Hg than the

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bulk soil (< 2 mm), and these fractions were those with the greatest Hg enrichment accounting for up to 65% of the total Hg present in the assessed Bs and Bhs horizons. In these horizons, metal (Al, Fe)-humus complexes, total organic C and Al and Fe oxyhydroxides were significantly correlated to THg indicating that, a great reactivity and high specific surface area provided by these compounds favoured Hg retention in illuvial horizons of podzols. In environmental terms, Hg removal from A horizons due podsolization contributes to lessen its accumulation in the uppermost soil layers and minimize the risks of toxicity for soil biota (plants, microorganisms, small invertebrates), and its incorporation to the food web would be constrained. Moreover, less Hg will be available in the soil surface to be mobilized by runoff. The potential danger derived from Hg transport downwards into soil as result of the podzolization, which could finally affect to groundwater quality, may be strongly restricted due to the illuvial horizons may behave as a geochemical barrier retaining Hg. It is also noticeable that Hg retained in illuvial horizons of podzols is more protected against land use changes or global warming, which are recognized as powerful disrupting factors of the biogeochemical cycle of Hg in terrestrial ecosystems.

4 Concluding Remarks: Andosols, Podzols and Umbrisols, the Same Processes? Umbric horizons in the soils of Galicia are characterised by the accumulation of organic matter, strong acidity, desaturation in bases of the exchange complex and abundance of Al(Fe)-humus complexes. These properties and components are similar to those of non-allophanic Andosols. The fact that many humic horizons have andic properties is mainly related to the nature of the parent material, particularly the abundance of weatherable minerals. When the parent material is less rich in these minerals (mainly granites and schists), under favourable weathering conditions, the umbric horizons do not often exhibit andic properties but they often have a high reactivity to NaF (indicative of significant Al activity), a fact which sometimes also occurs in cambic horizons. Under environmental conditions favourable to a slower weathering (cooler climate and humidity), the mobility of organic matter over short distances is facilitated without horizon differentiation (cryptopodzolization). This process of cryptopodzolization seems to occur in thick Ah horizons where the amount of reactive Al (acid oxalate extractable) increases towards the lower part of the soil, where the formation of horizons with similar characteristics to spodic horizons may take place although without the development of E horizons (as occurs in granites, schists and gneises). When the parent material is very poor in weatherable minerals (as in sandstones, quartzites, and quartz-rich sediments), organic matter is more mobile and it can transport Fe and Al in the soil profile accumulating them in subsurface spodic horizons, resulting in the formation of a Podzol which often show a well-developed albic E horizon.

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Image 11 Right: aluandic Andosol (amphibolite, Aríns). Middle: cambic Umbrisol (granite, Monte Pedroso). Left: albic Podzol (quartz rich sediments, Pico Sacro) in the surroundings of Santiago de Compostela

In this sequence, the parent material factor through its weatherable mineral content, modulated by environmental conditions favourable to weathering, plays a primordial role. Organic matter plays a triple function: it accelerates weathering processes, stabilises non-crystalline components through its association with Al and Fe (surface horizons of aluminic soils and andic soils and B horizons of podzolic soils) and contributes to their mobilisation over short distances (cryptopodzolization, in aluminic soils) or over long distances (podzolization). Thus, at the local scale, under homogeneous climatic conditions and wide diversity of parent materials (e.g., Santiago de Compostela), in hillside topographic positions and with heathland vegetation, soils characterised as Andosols (in amphibolite), Umbrisols (in granite, schist and gneiss) can be found (Image 11). In these cases, Ah horizons that meet or are close to meet andic properties, and Podzols with albic material, in quartz-rich sediments from a large quartz dyke, can appear in the territory. In fact, it could be affirmed that, in Galicia, the formation of Andosols, Umbrisols or Podzols is a consequence of the same process, an acidcomplexolysis. As result, an intense leaching of bases favour the formation of complex Al(Fe) humus, from lower to higher mobility in the soil profile depending on the speed of weathering and the contribution of Fe and Al by the parent material (content and alterability of the minerals of the parent material). This coincides with Delvaux et al. (2004a), for whom the occurrence of nonvolcanic Andosols, mostly non-allophanic (aluandic) Andosols in Europe is linked to crystalline materials and their distribution fits quite well with that of Umbrisols which, when they develop in ‘cool and humid regions, mostly mountainous and with little or no soil moisture deficit’, are also associated with Podzols. Acknowledgements To all those who contributed to the knowledge of the soils of Galicia, especially to Prof. Francisco Guitián Ojea and his disciples.

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García-Rodeja E, Macías F (1986b) Materiales de bajo grado de orden (imogolita y geles alumínicos) en alteraciones y suelos podsólicos derivados de rocas graníticas de Galicia. Cuad Lab Xeolóxico Laxe 10:191–208 García-Rodeja E, Hermo BMS, Paz CG, Macías F (1986) Propiedades de los suelos desarrollados sobre las anfibolitas de “Santiago-Ponte Ulla”. An Edaf Agrobiol 45:1271–1298 García-Rodeja E, Hermo BMS, Macías F (1987) Andosols developed from non-volcanic materials in Galicia, NW Spain. J Soil Sci 38:573–591 García-Rodeja E, Silva Hermo BM (1994) Comparison between andosols developed from gabbros in Galice (NW Spain) and basalts in Massif Central (France). In: 15th International congress on soil science, Mexico García-Rodeja E, Monterroso C, Martínez Cortizas A (1998) Podzols from coastal areas in northwestern Spain. In: Proceedings of the 16 world congress of soil science, Montpellier (France). ISSS-AISS-IBC-SICS-AFES. En CD-ROM (CIRAD) García-Rodeja E, Muñoz JCN, Pombal XP, Cortizas AM, Buurman P (2004a) Aluminium fractionation of European volcanic soils by selective dissolution techniques. CATENA 56:155–183 García-Rodeja E, Taboada Rodríguez T, Martínez Cortizas A, Silva Hermo BM, García Paz C (2004b) Soils with andic properties developed from non-volcanic materials, genesis and implications in soil classification. In: Óskarsson H, Arnalds O (eds) Volcanic soil resources in Europe, COST 622 final meeting. RALA Report, vol 214. Agricultural Research Institute, Reikjavík, Iceland, pp 74–75 García-Rodeja E, Nóvoa Muñoz JC, Pontevedra Pombal X, Martínez Cortizas CM, Buurman P (2007) Aluminium and iron fractionation of European volcanic soils by selective dissolution techniques. In: Arnalds O, Bartoli F, Buurman P, Oskarsson H, Stoops G, García-Rodeja E (eds) Soils of volcanic regions of Europe. Springer, Berlin Hiedelberg, pp 325–351 Glaser B, Lehmann J, Zech W (2002) Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal. Biol Fertil Soils 35:219–230 Gustafsson JP, Battacharya P, Bain DC, Fraser AR, McHardy WJ (1995) Podzolisation mechanisms and the synthesis of imogolite in northern Scandinavia. Geoderma 66:167–184 Hermo BMS, García-Rodeja E, Macías F (1984) Caracterización y génesis de los suelos sobre esquistos de Las Mariñas (La Coruña). An Edaf Agrobiol 43:523–546 Hermo BMS, García-Rodeja E, Paz CG, Macías F (1988) Génesis y clasificación de los suelos desarrollados sobre las anfibolitas de “Santiago-Ponte Ulla”. An Edaf Agrobiol 47:867–885 Iñiguez J, Barragán E (1974) Andosuelos desarrollados sobre filitas en Ulzama (Navarra). An Edafol Agrobiol 33:1055–1068 IUSS Working Group WRB (2015) World reference base for soil resources 2014, update 2015. World Soil Resources Reports No. 106. FAO, Rome IUSS Working Group WRB (2022) World reference base for soil resources, 4th edn. International Union of Soil Sciences (IUSS), Vienna, Austria Kleber M, Jahn R (2007) Andosols and soils with andic properties in the German soil taxonomy. J Plant Nutr Soil Sci 170:317–328 Loveland PJ, Bullock P (1976) Chemical and mineralogical properties of brown podzolic soils in comparison with soils of other groups. J Soil Sci 27:523–540 Lundström OS (1993) The role of organic acids in soil solution chemistry in a podzolized soil. J Soil Sci 44:121–133 Lundström OS, van Breemen N, Bain D (2000) The podzolization process: a review. Geoderma 94:91–107 Macías F, Puga M, Ojea FG (1978a) Caracteres ándicos en suelos sobre gabros de Galicia. An Edaf Agrobiol 37:187–203 Macías F, Puga M, Ojea FG (1978b) Suelos de la zona húmeda española. IX. Estudio de una catena sobre gabros. An Edaf Agrobiol 37:117–138 Macías F (1980) Características micromorfológicas de Podsoles y Suelos podsólicos de la zona húmeda española. An Edafol Agrobiol 39:879–898

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Macías F, Paz CG, Giménez M, Villar MC (1980) El factor material de partida en los suelos de Las Mariñas. Alteración de rocas metabásicas. Cuad Lab Xeolóxico Laxe 1:205–223 Macías F, Calvo de Anta RM, García-Paz C, García-Rodeja E, Silva Hermo B (1982) El material original: su formación e influencia en las propiedades de los suelos de Galicia. An Edaf Agrobiol 41:1747–1768 Macías F, Fernández Marcos ML, Chesworth W (1987) Tansformacións mineralogiques dans les podzols et sols podzoliques de la Galice (NW Espagne). In: Righi D, Chauvel A (eds) Podzols and podzolization. INRA, Paris, pp 163–177 Macías F, Paz CG, Hermo BMS, García-Rodeja E, Rodríguez TT (1988) Micromorfología y génesis de podsoles y suelos podsólicos. An Edaf Agrobiol 47:431–464 Macías F, Calvo de Anta R (1992) Caractérisation pédogéochimique des sols de la Galice (NW Espagne) en relation avec la diversification lithologique. Mise en évidence d’un milieu de transition entre les domaines tempérés et subtropicaux humides. C R Acad Sci Paris 315(Série II):1803–1810 Macías F, de Anta RC, Lado LR, Verde R, Perez XP, Arbestain MC (2004) El sumidero de carbono de los suelos de Galicia. Edafología 11:341–376 Marcos MLF, Macías F, Ojea FG (1980) Estudio comparativo de dos métodos de obtención de la solución del suelo: aplicación al estudio de la solución de suelos podsólicos de Galicia. An Edafol Agrobiol 39:1587–1607 McKeague JA, Ross GJ, Gamble DS (1978) Properties, criteria of classification and genesis of podzolic soils in Canada. In: Mahaney WC (ed) Quaternary soils. Geo Abstracts, Norwich, pp 27–60 McKeague JA, Kodama H (1981) Imogolite in cemented horizons of some British Columbia soils. Geoderma 25:189–197 Merino A, García-Rodeja E (1992) Capacidad de adsorción de sulfato en suelos de Galicia. Actas III Congreso Nacional de la Ciencia del Suelo. Pamplona (españa) 1992:139–144 Moares C, Taboada Rodríguez T, García-Rodeja E, Martínez Cortizas A (1996) Tendencias a la podsolización durante el cuaternario reciente en áreas de montaña. In: Alberti AP, Martínez Cortizas AM Avances en la Investigación Paleoambiental en las Áreas de Montaña Lucenses. Cap. VII. Diputación Provincial de Lugo Mokma DL, Buurman P (1982) Podzols and podzolization in temperate regions. ISM Monograph, vol 1. International Soil Museum, Wageningen, The Netherlands, p 126 Ojea FG, Carballas T (1968) Suelos de la zona húmeda española, IV. Podsoles. An Edafol Agrobiol 27:747–781 Parfitt RL, Childs CW (1988) Estimation of forms of Fe and AI: a review and analysis of contrasting soils using dissolution and Mössbauer methods. Aust J Soil Res 26:121–144 Paz CG, Macías F (1983) Evolución geoquímica de las rocas gabroicas en Galicia durante su meteorización. Cuad Lab Xeolóxico Laxe 5:255–280 Paz CG, Hermo BMS, García-Rodeja E, Macías F (1986) Meteorización de las anfibolitas del macizo “Santiago-Ponte Ulla”. An Edaf Agrobiol 45:1163–1188 Petersen L (1976) Podzols and podzolization. PhD thesis, Royal Veterinary and Agricultural University, Copenhagen Rebolo RP, Varela EP, Cortizas AM (2002) Distribución de elementos metálicos (Cr, Mn, Ni, Cu, Zn, Pb, Th) y Arsénico en dos suelos policíclicos podsólicos. Edafología 9:85–102 Romero R, Paz CG, Macías F (1985) Determinación de familias mineralógicas en suelos sobre rocas graníticas de la provincia de La Coruña. Cuad Lab Xeolóxico Laxe 10:171–190 Romero R, Taboada Rodríguez TM, García Paz C (1990) Cristalinidad de filosilicatos en productos de alteración y edafogénesis en rocas graníticas de a Coruña. Cuad Lab Xeolóxico Laxe 15:297– 316 Sauer D, Sponagel H, Sommer M, Giani L, Jahn R, Stahr K (2007) Podzol: soil of the year 2007. A review on its genesis, occurrence, and functions. J Plant Nutr Soil Sci 170:581–597

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Simpson AJ, Song G, Smith E, Lam B, Novotny EH, Hayes MH (2007) Unraveling the structural components of soil humin by use of solution-state nuclear magnetic resonance spectroscopy. Environ Sci Technol 41:876–883 Soil Survey Staff (1975) Soil taxonomy. Agriculture handbook, vol 436. SCS, USDA Soil Survey Staff (1999) Soil taxonomy, 2nd edn. Agriculture Handbook, vol 436. SCS, USDA Ugolini FC, Dahlgren RA (1986) A new theory on podzolización and synthesis of imogolite/ allophane. Trans XIII Congr AlSS, Hamburg 3:1306–1307 Ugolini FC, Dahlgren RA (1991) Weathering environments and occurrence of imogolite/allophane in selected andosols and spodosols. Soil Sci Soc Am J 55:1166–1171 Vázquez CF, Muñoz JCN, Casais MC, Klaminder J, Cortizas AM (2014) Metal and organic matter immobilization in temperate podzols: a high-resolution study. Geoderma 217–218:225–234 Vázquez CF, Muñoz JCN, Klaminder J, Armesto AG, Cortizas AM (2020) Comparing podzolization under different bioclimatic conditions. Geoderma 377:114581

Water

Fresh Waters Francisco Díaz-Fierros Viqueira

Blessed is the Lord because he allowed me to be born, to grow, to become an adult and now grow old in this great kingdom called Galicia; in this great kingdom of the ‘Finisterre’, that extends from the mountains to the sea, where they shine with the wind; to this land of ten thousand rivers … (Álvaro Cunqueiro 1981)

1 Introduction This fragment of a speech delivered by the great Galician writer Álvaro Cunqueiro (1911–1981) the year he died, contains one of the expressions most frequently used to define the character and landscape of Galicia: “the country of the ten thousand rivers”, and with which he also intends to express the significance that water has in the life and destiny of this people. Not only does a large proportion of Galician agriculture depend on it, but also does its industry, commerce, and energy, as it usually happens in all European Finisterres, where the Atlantic fronts bring heavy rain exceeding 1000 mm annually. But Galicia is also located within the Mediterranean climate area and, therefore, the summer season is dry-sometimes very dry-, and on this duality also lies one of the characteristics of its climate, the fact of standing at the crossroads, a turning point where heavy rains in autumn and winter can overlap severe shortages of water in summer. The high annual rainfall variability also introduces uncertainty, and this determines climatic situations where inhabitants must live periods in which heavy rain cause floods and destructive runoff and, at the same time shortages of water can jeopardise crops and water supplies and, above all, they promote conditions in which the increasingly frequent forest fires devastate forests. F. Díaz-Fierros Viqueira (B) Emeritus Professor, Santiago de Compostela University, Galicia, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_16

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2 Water Balance The average rainfall in Galicia is estimated at 1400 mm (Díaz-Fierros 2003) which does not prevent that, as a consequence of its special topography, there are maximum rainfall records that exceed 2500 mm in altitudes closer to the coast, whereas do not reach 900 mm in inland valleys that are sheltered from the humid winds (Gómez Viñas et al. 1996). Its typically Mediterranean monthly rainfall pattern shows a maximum record between December and January, exceeding 100 mm, and a minimum record in July and August, with values generally lower than 50 mm (Gómez Viñas et al. 1996). Such water contribution is returned to the atmosphere as evapotranspiration with values of 615 mm that, in general, involve less annual variability than rainfall. Since this water is mainly mobilized by the vegetation, it is called “green water” (Rinjersma et al. 2003) to distinguish it from the water that flows on the surface or inside the Earth, known as “blue water”, that feeds the underground water resources and the surface and subsurface flows, with values of 785 mm. As the water regime in Galicia is typically exoreic, all the blue water is returned in the end to the sea in different periods of time.

3 Green Water Out of the 2,957,413 ha of the Galician surface, only 3% would correspond to urbanized areas, public roads, rocks, quarries and mines, as well as sheets of water and marshes; the rest, that is, the vast majority, would be evapo-transpiring from plant areas that produce green water. Taking into account the forest cover offered by the last forest inventory of Spain (IFN4) for Galicia (Dirección General del Medio Natural y Política Forestal 2011) as well as other land use data (Díaz et al. 2007) and based on evapotranspiration (ET) values determined or calculated for the different types of vegetation dominant in Galicia (Soto and Díaz-Fierros 1996) it was possible to determine the fractionation of the 615 mm of green water among the main types of coverage: Woodland………………323 mm Brushwood………………76 mm Meadows and forage…...191 mm Crops…………………….25 mm It can be inferred from this that more than half of the green water returned to the atmosphere in Galicia can be assigned to forest cover, and out of this, 76% would correspond to the surfaces occupied by the Pinus and Eucalyptus species. Slightly more than 50% of the evapo-transpired water values are concentrated between June and September, a period in which there is the highest demand for water from plant surfaces and when it would be necessary to cover the rainfall deficits in order to maintain potential evapotranspiration values. If these deficits were not compensated with irrigation or soil water reserves, the real evapotranspiration

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values would decrease between 5 and 35% of their potential values, which could be considerably higher in soils less than 50 cm thick, that is, a surface of about 760,000 ha in Galicia (Díaz-Fierros and Gil Sotres 1982), whereas in valley soils or peneplains in Ordes schist areas, which are 150–200 cm thick, and with deep rooting plants such as maize, the rainfall deficit would be very low, and transpiration would be almost identical to the potential one.

4 Blue Water (Surface and Subsurface Flows) A small part of the rainfall affecting the territory (0.6%) falls directly on the 17,000 hectares of water bodies and the rest does falls on the land or on vegetal canopy, where part of it is infiltrated, and the rest origins surface flows. These surface flows can be caused by Hortonian processes when the intensity of the rainfall is stronger than the water infiltration capacity of the soil, which could be less common in Galicia since soils are especially permeable in this region. Only those soils submitted to compaction due to the use of tractor on too humid soils, or in areas particularly affected by forest fires, where hydrophobia can take place (Varela et al. 2005), this Hortonian flow would be relevant. In addition, it could also occur briefly in other exceptionally rainy areas. A more important process that generates surface runoff would be the “available source area” (saturation overland flow), which occurs during periods of abundant and persistent rainfall that saturate the soil with water and, in the end, this water overflows on the surface. These two processes are deemed not to reach 10% of the rainfall and when they reach the riverbeds they would partially feed the so-called “quick flow” of rivers. Water reaching vegetal canopy undergoes a direct evaporation process known as interception, which, although it is slightly different from one cover to the other and even in the same year, it is estimated that, on average, in Galicia could account for 40% of the total ET, that is, 246 mm. Water drained from this canopy or that reaching the land directly during periods in which it is without vegetation, infiltrates in it and begins a complex process of distribution inside. First, infiltrating water will be used to fill up the deposit volume, known as “available water”, that is taken by the vegetal covers and returned to the atmosphere by means of a transpiration process, reaching 369 mm. This quantity added to that corresponding to the interception of the canopy would give rise to 615 mm of the evapo-transpired water. The remaining water would origin subsurface and underground flows. The former, which can account for up to 70–80% of the difference between precipitation and ET, has two transmission routes inside the soil: the first one is the delayed or “matrix flow”, which is essentially slow and is produced by the porous space of the soil matrix, and the “fissural flow” that takes advantage of the cracks and fissures to flow much faster, and that would be included in surface flows and the precipitation that falls directly on basins in order to complete the “quick flow”. This portion of the

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whole river flow, although it is quite different from one basin to the other, in Galicia could be on average over 40% of annual flows (Álvarez Enjo et al. 2002).

5 Blue Water (Underground Flow) The portion of water that infiltrates in the soil and is not retained as available water or is transmitted by means of subsurface flows (fissural and retarded flows) will produce the filling up of underground aquifers. We have estimated this portion to be 157 mm, a very similar value to that of 168 mm estimated by Estrela (1999) for the basins Norte I and Galicia-Costa. These deposits are distributed quite irregularly throughout the Galician territory. Therefore, three categories can be distinguished: (a) In the first one, there are some well delimited in A Limia and O Baixo Miño and they have average water flows reaching values of 10–100 L s−1 . (b) In the second one, alluviums from great rivers, having a small length, reaching values of 6–30 L s−1 . And finally (c), the third one, with sandy materials included in tertiary deposits, reaching values of 0.3–3 L s−1 , such as in A Terra Cha. In addition, there are also scattered cracks and fissures through which the delayed subsurface flow runs and which, together with the outlets of the aquifers, serve to feed the basal flow of the Galician “ten thousand rivers” which, according to Fetter’s classification, can be considered as clearly “winning” channels (Álvarez Enjo et al. 2002). A very small portion of 7 mm pours directly into the sea.

6 Water Resources and Basins The 56% of the rainfall water that is not returned to the atmosphere as ET and feeds the surface and underground flows amounts to 23,294 hm3 year−1 . These water resources are called “total renewable resources” since they can be renewed every year. In any case, only a small portion of that volume can be used due to the different water demands of the Galician population. In general, “available” resources are considered those corresponding to basal flow of rivers, which, on average, amounts to 36% of the total annual flow in Galician waters, that is, 12,685 hm3 year−1 including reservoirs (Díaz-Fierros 2017). If they were excluded, a possibility that cannot be ignored because most of them are used as a resource for energy production, the available water would be 8,386 hm3 year−1 . With these values, the main demands for water in Galicia would be met, with data shown below (Díaz-Fierros 2017): Agricultural, industrial and domestic demands = (983 + 146 + 299) = 1428 hm3. year-1 Environmental reserves (ecological flow) = 2322 hm3 year-1 Total demands = 3750 hm3 year−1myp This could mean that the demands for water could be widely met with the available renewable water resources, either with or without reservoirs.

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Table 1 Water balance of the large fluvial systems of Galicia River system

Surface (km2 )

Rainfall (mm)

ETP (mm)

Real ET (mm)

Runoff (mm)

Flow (hm3 year−1 )

Cantabrian

3366

1405

653

604

801

2696

Artabrian

3500

1463

675

638

825

2887

Atlantic

7528

1615

750

674

941

7084

1284

709

563

721

8830

1190

725

465

721

1739

Miño-Sil Southern Total

12,247 2412 29,053

23,236

Source of data White Paper on water, 2000, As concas fluviais de Galicia, 1993, As augas de Galicia, 1996

The fluvial system of Galicia, with the current distribution, exists as such since the late Tertiary. The presence of the Miño-Sil basin, the central radial axis of Galician rivers, was already identified as relevant in the climatic difference found on both sides of the Galician mountain range. On the other hand, the Atlantic rivers, that is, Xallas, Tambre, Ulla, Umia and Verdugo, would flow through the “rift valley” along the region, from the North to the South, and very close to the Western coast without apparent alteration of their beds. Consequently, it can be accepted that more than 20 million years ago, the main lines of the Galician hydrographic network (MiñoSil, Atlantic rivers and probably also the Cantabrian ones) already had the main traces shown at present. Subsequent events could cause small variations in their beds mainly due to changes in erosion and sedimentation processes, that originated the different terrace systems, so that the final configuration of the basins was finished during the last relevant morphogenetic episode in Galicia: the Würmian glaciation (Díaz-Fierros et al. 1993). The large units into which the Galician hydrographic system can be divided are: (1) The Miño-Sil basin, well defined by the Xistral, Cordal Gallego, Queixa and San Mamede reliefs. (2) The Atlantic rivers, with a very well-defined W-SW orientation and limited by the reliefs of the mountain range. (3) The Cantabrian rivers, whose sources are situated in O Xistral and Ancares mountains. (4) Those belonging to the Artabro Arch, which flow into the North Atlantic coast. (5) The Southern fluvial system, in which the riverbeds of the Limia and Duero rivers, flow along the “dry line”. The water balance values of these large units are summarized in Table 1.

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Fig. 1 Galician water balance. Values for precipitation, evaporation, and transpiration, are in mm

Fresh Waters

Fig. 2 Miño river. Photo Pérez Moreira, R.

Fig. 3 Sil river. Photo Pérez Moreira, R.

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References Álvarez Enjo M, Rial Rivas E, Díaz-Fierros F (2002) As augas subterráneas en Galicia. In: Xeoloxía (Coord. Díaz-Fierros). Proxecto Galicia XXXVI:499–521. Editorial “Hércules”. A Coruña Díaz J, Aller D, Martin A, Barcia B, Pereira S (2007) Dos perspectivas sobre cartografía de coberturas y usos del suelo en Galicia. Rev Gal Economía 16(1):1–23 Díaz-Fierros F, Gil Sotres F (1982) Capacidad Productiva de los suelos de Galicia: mapa 1:200.000. Universidad de Santiago de Compostela. Santiago de Compostela Díaz-Fierros F, Nuñez Delgado A, López Periago E (1993) As concas fluviais de Galicia. Universidad de Santiago de Compostela, 295 pp. Santiago de Compostela Díaz-Fierros F (2003) Hidroloxía. Gran Enciclopedia Galega. Silverio Cañada 23:58–70. El Progreso-Diario de Pontevedra. Lugo Díaz-Fierros F (2017) Auga para todos. Universidad de Santiago de Compostela, 181 pp. Santiago de Compostela Dirección General del Medio Natural y Política Forestal (2011) Cuarto Inventario Forestal Nacional, Galicia, 49 pp. Madrid Estrela T (1999) Evaluación de los recursos subterráneos. In: Jornadas sobre las Aguas Subterráneas en el Libro Blanco del Agua. AIH-GE. Madrid Gómez Viñas P, Sanchez González R, Sanchez Cela R (1996) As precipitacións. In: As augas de Galicia, pp 41–105. (Coord. Díaz-Fierros, F.) Consello da Cultura Galega. 611 pp.Santiago de Compostela Rinjersma J, Batjes N, Dent D (2003) Green water: definitions and data for assessment. ISRIC. World Soil Information, 84 pp. Wageningen Soto González B, Díaz-Fierros F Balance Hídrico. In: As augas de Galicia, pp 108–147. (Coord. Díaz-Fierros, F.) Consello da Cultura Galega. 611 pp. Santiago de Compostela Varela M, Benito E, de Blas E (2005) Impact of wildfires on surface water repellency in soils of northwest Spain. Hydrol Processes 19(18):3649–3657

Research on Cyanobacterial Blooms and Cyanotoxin Production in Galician Inland Waters Fernando Cobo Gradín, Sandra Barca Bravo, Rufino Vieira Lanero, and M. Carmen Cobo Llovo

Abstract Cyanobacterial blooms are a global environmental concern, with sometimes serious implications for human and animal health. Consequently, they represent a major problem in the management of water and aquatic ecosystems and therefore, the design of good control and monitoring programs, as well as the development of applied research on methods of mitigating blooms is imperative. To this end, advancing in the understanding of these phenomena is also essential. This scientific story describes the studies carried out by our research group in response to the environmental urgency caused by the proliferation of blooms in inland waters of Galicia (Spain), as a consequence of the increasing eutrophication of the reservoirs in this territory. Keywords Cyanobacteria · Water-reservoir · Monitoring · Eutrophication · Blooms

1 Introduction Cyanobacterial blooms can modify the chemical conditions of the water with the consequent impact on the survival of other aquatic organisms (Almodóvar et al. 2004; Cobo et al. 2012; Cobo 2015). Additionally, they are generally associated with the presence of cyanotoxins (Brittain et al. 2000; Hitzfeld et al. 2000; Freitas de Magalhães et al. 2001; Park et al. 2001; Humpage 2008), as numerous cyanobacterial species can produce toxins (Bláha et al. 2009; Paerl and Otten 2013; Svirˇcev et al. 2019), including some of the most potent toxins known (Humpage 2008), and it is estimated that 50% (25–75%) of cyanobacterial blooms are toxic. Morover, generally about 75% of the cyanobacteria that appear in a bloom can produce one F. C. Gradín (B) · S. B. Bravo · R. V. Lanero Laboratory of Hydrobiology, Department of Zoology, Genetics and Physical Anthropology, University of Santiago de Compostela, 15782 Santiago de Compostela, A Coruña, Spain e-mail: [email protected] M. C. C. Llovo Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_17

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or more types of toxins. Thus, CyanoHABs (cyanobacterial harmful algal blooms) constitute a serious environmental problem, with implications in human and animal health (Jone 1994; Chorus and Bartram 1999; Sivonen and Jones 1999; Cobo 2015; Niamien-Ebrottie et al. 2015; Chorus and Welker 2021). Numerous known cases of lethal poisoning of animals and even of human populations occurred worldwide (Huisman et al. 2018; Svirˇcev et al. 2019), but is important to consider that the damage produced by toxins varies depending on the affected organism. In non-lethal doses, these toxins have been attributed a tumor-promoting action, and epidemiological studies suggest an incidence affecting the especially the liver, but also other organs, such as kidney, heart, gills, skin, marrow, and blood. In addition to the health implications, cyanobacterial blooms have an economic impact with increasing costs of drinking-water treatments and the decrease of recreational water values (Cobo 2015; Svirˇcev et al. 2019; Kapsalis and Kalavrouziotis 2021). Therefore, they must be considered in the management of water and aquatic ecosystems. The frequency and intensity of blooms have recently risen worldwide. This increase has been attributed to anthropogenic changes, primarily the over-enrichment with nutrients and river regulation (Carvalho et al. 2013; Xia et al. 2016). The possible effects of climate change on water eutrophication, and consequently the raised risk of potentially toxic cyanobacterial blooms, have also been noted (Paerl and Huisman 2008; Xia et al. 2016). Because of this increase and its health and management implications, blooms have drawn the attention of environment agencies, water authorities, and human and animal health organizations with the consequent development of monitoring programs and the publication of numerous technical reports, e.g., (Confederación Hidrográfica del Ebro 1996; Jaurlaritza 2002; Confederación Hidrográfica del Duero 2006; Infraeco & Confederación Hidrográfica del Ebro 2006a, b, UTE Red Biológica Ebro and Confederación Hidrográfica del Ebro 2007; Junta de Andalucía 2014; Confederación Hidrográfica del Júcar 2016; Confederación Hidrográfica del Tajo 2017; Xunta de Galicia 2017). Additionally, the Water Framework Directive (WFD) (Directive 000/60/EC [1]59) specifies that the ecological status based on phytoplankton should be defined by measuring the biomass, composition, and blooms, especially cyanobacterial blooms. Consequently, new methodological approaches to monitor, control, or eliminate cyanobacteria from the environment are being developed (Forján-Lozano et al. 2008; Lago 2015). In Spain, most lentic systems are reservoirs, with different degrees of eutrophication, which favors the proliferation of cyanobacteria and thus of CyanoHABs. Despite this situation and the growing interest, the available official information is scattered, and cyanobacterial bloom episodes have gone unnoticed frequently in Spanish waters. According to our recent revision (Vieira et al. 2022) among the 19 Spanish river basin districts, Galicia-Costa is the one with the most cyanobacterial records (66.67%) and with the highest number of reservoirs in which blooms have been recorded (37%).

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2 Control and Monitoring Programs In temperate regions, cyanobacterial blooms usually occur during the summer, when temperature and light intensity are high and nutrient renewal and water column conditions stable (Sivonen 1996; Dasí et al. 1998; Sanchis et al. 2002; Cook et al. 2004). Some environmental factors can determine an increased abundance of potentially toxic cyanobacteria during a bloom: high phosphorus and nitrogen concentration, low N:P ratio, high residence time and low water renovation rate, low turbulence, high light intensity, high temperature, the increase of dissolved organic matter, iron, and trace metals, and low planktophages rates (Paerl and Otten 2013). In the Iberian Peninsula, even though a slightly higher percentage of cyanobacterial records were made in calcareous areas (53.17% against 46.83% in siliceous areas), blooms have been mainly recorded in siliceous areas (Vieira et al. 2022). The increase of bloom records during the last decade may be due to an improvement in the monitoring effort. Nevertheless, the effect of anthropogenic actions and climate change cannot be ruled out. Therefore, an increased monitoring effort as well as standardization of sampling and analysis are desirable to mitigate the potential adverse effects of blooms, especially the toxic or potentially toxic ones. In Galicia, the recorded episodes of massive proliferation of cyanobacteria occurred more frequently in the reservoirs of the Miño-Sil basin (Cobo 2008; Cobo et al. 2012). The first recorded episode took place in the Castrelo de Miño reservoir in 1990 (Table 1), with the dominant species being Microcystis aeruginosa (Kützing) Kützing, 1846. Nevertheless, as it was mentioned before, it is known that blooms have sometimes gone unnoticed, so the number of these previous episodes in Galician reservoirs could be more frequent and earlier. Seven reservoirs which have regularly presented blooms belong to the of Miño-Sil basin (Cachamuíña, Castadón, Faramontaos, Os Peares, Prada, Salas and Vilasouto) (Lago et al. 2016a). The studies of our research group carried out in these reservoirs included the identification and quantification of the cyanobacteria species present in the blooms, and the determination of the concentration values of the microcystinLR (MC-LR), both the sestonic and the dissolved fraction, by means of an enzyme immunoassay. In all these reservoirs, within the identified species ten morphospecies of potentially toxic cyanobacteria were found (Figs. 1 and 2). In addition to the Miño-Sil basin, other basins have been monitored and studied by our research group in the last years. Non all the recorded blooms were toxic, for example, in the Limia river basin non-toxic blooms were recorded in two reservoirs (As Conchas and Lindoso). Despite being located next to each other, the species dominance in the blooms were different being M. aeruginosa the dominant one in As Conchas reservoir and Aph. flos-aquae in Lindoso. A particularly remarkable episode is the bloom of M. aeruginosa in A Baxe reservoir (Umia river), detected for the first time in 2006 (Cobo 2008; Cobo et al. 2012). The fire at the Brenntag chemical company on September 1, 2006 (Fig. 3) brought the Umia river to the attention of the media, technicians, and scientists, as never before in Galicia. On September 5th, a commission of experts met in Caldas de

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Table 1 Characterization of the 29 Galician reservoirs with cyanobacteria records Reservoir

RBD

River

Height (m)

Capacity (Hm3 )

CC

WU

Geo

YCD

As Forcadas

G-C

Forcadas

–

10.7

1967

Ws-Rec

J

2006–2017

Rio Cobo

G-C

Cobo

31

5.68

1979

Ind

J

2012–2017

Xunco

G-C

Xunco

–

0.72

1791

Ws

P

2013–2017

Ribeira, La

G-C

Eume

54

32.8

1961

Hyd

J

2012–2017

Rosadoiro

G-C

Seijedo

16

1.87

1970

Ws

J

2012–2016

Beche

G-C

Roufrío

–

0.24

2000

Rec

U

2012–2017

Cecebre

G-C

Mero

23

21.69

1976

Ws

U

2008–2017

San Cosmade

G-C

Vilasenín

18

1.4

1979

Ind

U

2000–2017

Vilagudín

G-C

Veduino

33

18.3

1981

Ind

U

2000

Barrié de la Maza

G-C

Tambre

48

31.5

1958

Hyd

J

2008

Ponteolveira

G-C

Xallas

26

0.7

1966

Hyd

J

2012–2017

Santa Uxía

G-C

Xallas

80

13.6

1988

Hyd

J

2012–2017

Con

G-C

Con

16

0.28

1961

Ws

J

2012–2017

A Baxe

G-C

Umia

38

6.15

2000

Ws

J

2006–2017

Pontillón Castro

G-C

Rons

23

1.4

1943

Ws

J

2012–2017

Eiras

G-C

Oitaven

51

22.17

1977

Ws

J

2012–2017

Zamanes

G-C

Zamanes

29

1.9

1961

Ws

T

2012–2017

A Baiña

G-C

Baíña

45

0.48

1985

Ws

J

2012–2017

Belesar

M-S

Miño

129

654.1

1963

Hyd

R

2001–2017

Vilasouto

M-S

Mao

59

20.52

1969

Ws-Irr

I

2011–2017

Peares, Los

M-S

Miño

94

182

1955

Hyd

R

2009–2017

Castrelo/ Miño

M-S

Miño

30

60

1969

Hyd

J

1990–2016

Castadón

M-S

Lonia

24

0.2

1929

Ws

J

1998–2017

Cachamuíña

M-S

Lonia

19.65

2

1954

Ws

J

1994–2017

Prada

M-S

Xares

85

121.07

1958

Hyd

J

2008–2017

Lindoso

M-S

Limia

110

350

1968

Hyd

J

2013–2016

Conchas, Las

M-S

Limia

48

78.33

1949

Hyd

J

2000–2017

Salas

M-S

Salas

50

86.87

1971

Hyd

J

2015–2017 (continued)

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Table 1 (continued) Reservoir

RBD

River

Height (m)

Capacity (Hm3 )

CC

WU

Geo

YCD

Presa de Gudín

M-S

Faramontaos

–

0.1

1994

Ws-Irr

J

2012–2017

RBD, River Basin District; CC, Construction completion year; WU, Water uses; Geo, Geology; YCD, Years with Cyanobacterial data. RBD: (G-C: Galicia-Costa; M-S: Minho-Sil) WU: (Hyd: Hydroelectric; Ind: Industrial: Irr: Irrigation; Rec: Recreational; Ws: Water supply). Geo: (I: Gneiss, schist, marble and vulcanite; J: Granitoid; P: Quartzite, slate, sandstone, limestone and vulcanite; R: Sandstone, slate and limestone; T: Schist, grey wake, paragneiss and basic vulcanite; U: Slate, schist and paragneiss). Data from Vieira-Lanero et al. (2022)

Reis and issued a report that included the initial situation and an action and monitoring plan. The first water analyses, conducted on water collected at different points of the river the day of the spill, indicated a high conductivity (around 1700 S/cm at the discharge point), strong reduction (COD: 5730), strongly acid pH (2.2), 660 mg/L of SO24 = 217 mg/L of NO− 3 , 45 mg/L of total hardness, and important contents of Styrene (8540 g/L, in the zone of maximum affection), m + p-Xylene (1720.0 g/L), Toluene (1640.0 g/L), Ethylbenzene (720.0 g/L), 1,2, 4-Trimethylbenzene (600 g/L), and other BTX’s, in addition to Chloroform (65 g/L), Tetrachloroethene (38.1 g/L), as well as relatively significant amounts of Al and Fe salts and the water was strongly stained blue and with a large amount of foam (Cobo et al. 2006). Simultaneously, although without any causal relationship, during the collection of samples upstream of the spill, it was observed that the water from A Baxe reservoir had the typical appearance of cyanobacterial bloom and that it was producing a high mortality of fish downstream. Samples collected in the reservoir were analyzed and that confirmed the situation of eutrophication of the water and the phytoplankton bloom, for which the species Microcystis aeruginosa was responsible (Fig. 4). Since then, cyanobacteria blooms have been repeated in the reservoir of A Baxe each summer, compromising the water supply for human consumption in the area. This can be used as an example of how monitoring efforts and awareness on the existence of blooms are essential to avoid risk situations derived from CyanoHabs. Monitoring of potentially toxic cyanobacterial blooms is usually included in broader water quality monitoring programs, but risk assessment protocols designed by WHO, and widely applied in various countries, establish alert levels based on simple indicators such as cell identification and count, biovolume, chlorophyll a concentration or phosphorus levels. However, there are so many sources of uncertainty and variability that their occasional determination can limit the reliability of monitoring systems. In this regard, remote sensing monitoring can provide an adequate estimate of the surveillance parameters. The basis of this strategy is based on the differences in the spectral signal of the objects on the surface to be studied, the spatial and spectral resolution of the sensors used, the characteristics of the acquisition platform and the interferences and interactions with the environment. For this reason, in this scientific story, the study carried out using unmanned aerial vehicles

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Fig. 1 Bloom at Cachamuíña and Castadon reservoirs (Miño-Sil basin) in 2013. In this reservoirs as in Vilasouto, Os Peares and Faramontaos reservoirs, MC-LR was recorded. The species that emerged were: Microcystis aeruginosa, Anabaena circinalis, Woronichinia naegeliana and Anabaena flosaquae

(UAVs) in the remote monitoring of cyanobacterial blooms has a special relevance. Through this project, the suitability of UAVs to successfully address studies based on remote sensing was proven, overcoming the disadvantages caused by adverse weather conditions and the rapid changes that characterize cyanobacterial blooms. The Castadón reservoir (Lonia river, Miño-Sil basin) was selected for the preliminary studies of this project. In this reservoir, blooms of potentially toxic cyanobacteria species have been recorded since 1998: Anabaena crassa (Lemmermann) Komarkova-Legnova and Cronberg, 1992 and Microcystis aeruginosa (Kutzing)

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Fig. 2 Images of the bloom in the Vilasouto reservoir (Miño-Sil basin) in 2013. All the identified species are potentially toxic: Anabaena planctonica, Gomphosphaeria sp., Planktothrix agardhii and Planktothrix rubescens, being the last one the dominant species during the first part of the year. In addition, the concentrations of sestonic and dissolved MC-LR in this reservoir frequently exceeded the limit value proposed by the WHO (1 µg/l). To date, the most intense bloom recorded in this reservoir was in 2013, with a maximum abundance of 257,550 cells/ml in February and 1,448,000 cells/ml in April, and that lasted until July

Kutzing, 1846, the latter being the dominant species during blooms. The images captured by the drone, using a multispectral camera, were processed using specific software to create reflectance maps and by applying semi-analytical algorithms, maps of the chlorophyll-a index and the phycocyanin index were generated. For the first one, a strong correlation was obtained with selected parameters measured directly

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Fig. 3 Images of the Umia river after the spill caused by the fired in the Brenntag factory, September 2006. The water analyses, conducted on water collected at different points of the river the day of the spill, indicated a high contamination and the water was strongly stained blue and with a large amount of foam

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Fig. 4 Bloom in A Baxe reservoir (Umia river) in 2006, documented during the sampling efforts to evaluate the consequences of the fire in the Brenntag factory

from the water samples (chlorophyll, phytoplankton abundance in cels./ml, Secchi disk depth, turbidity, and suspended solids) (Fig. 5). Continuing with this framework, our research group is currently participating in the Artificial Intelligence-powered forecast for Harmful Algal Blooms (AIHABs) project (2021). Aquatic Pollutants.

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Fig. 5 a Castadón reservoir (Lonia river, Miño-Sil basin) The images captured by the drone, using a multispectral camera, were processed using specific software to create reflectance maps and by applying semi-analytical algorithms, maps of the chlorophyll-a index and the phycocyanin index were generated. b Visible-RGB. c Near infrared (790 nm BP40). d Chlorophyll_index (high concentration) R705 nm − R665 nm /R705 nm + R665 nm . e Phycocyanin_Index R705 nm – R620 nm / R705 nm + R620 nm

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3 Experiences in Mitigation and Bioremediation The need to resolve the problems associated with cyanobacteria has led to the use of multiple techniques to reduce their uncontrolled development and improve water quality. Among the most common ones found in the literature are those focused on the factors that regulate the primary production and therefore, the reduction of the external phosphorus loading. This is sought through the control of inputs in the basin (agriculture, sanitation, industry, etc.), but also by acting directly on the water body (Paerl and Otten 2013). In addition, there have also been attempts to limit incident light (Visser et al. 1996; Huisman et al. 2004; Verspagen et al. 2006; Mitrovic et al. 2011), physical elimination of cyanobacterial biomass (Robb et al. 2003; Henderson et al. 2008; Van Oosterhoutand and Lürling 2011), application of ultrasound (McComas and Stuckert 2011), etc. Chemical control experiments have also been carried out using a variety of compounds with very different effects, ranging from the application of algaecides or herbicides to oxidants and other substances such as Cu, K2 MnO4 , H2 O2 , etc. (Lam et al. 1995). Many agents for biological control have also been tested with varying success (e.g., viruses, bacteria, protozoa, fungi, aquatic plants, fish) (Safferman and Morris 1964; Newman and Barrett 1993; Imamura et al. 2000, 2001; Nakamura et al. 2003; Choi et al. 2005; Tucker and Pollard 2005; Shi et al. 2006; Yoshida et al. 2006; Gumbo et al. 2008) and plant materials in aerobic decomposition have been widely used (Gross et al. 1996; Nakai et al. 2000, 2005; Kolmakov 2006). These chemical treatments, which involve an expensive methodology requiring specific training for their application, do not necessarily have immediate environmentally harmful effects but their main risk is their accumulation in high concentrations in sediments. In general, all these techniques have not proved to be very effective, being either very expensive or with questionable environmental consequences. Therefore, the search for a cyanobacteria removal system that is economical and environmentally friendly continues to be a major concern. In this context, several field studies have been carried out on the use of barley (Hordeum vulgare) to control cyanobacteria (Everall and Lees 1997; Martin and Ridge 1999; Butler et al. 2001; Hartz 2004). The basis of this methodology is the microbial activity that arises when barley straw decomposes. This treatment has been commonly used with success in the British Islands, in inland ecosystems of various types, such as lakes of different sizes, drinking water reservoirs, canals and flowing waters. This contrasts with the results found in the USA where it has been observed that there is a risk of overdosing so that an excess of material can reinforce the trophic state of the reservoir by supplementary nutrient supply (Ó hUallacháin and Fenton 2010). With these experiments as background, our research group developed a project in As Forcadas reservoir (Forcadas river, Valdoviño A Coruña). In this reservoir, which supplies water to a large population, blooms of Microcystis aeruginosa are frequent since 2006 (Fig. 6) accompanied by other species such as: Anabaena sp.,

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Gomphosphaeria sp., A. planctonica, Microcystis sp. and W. naegeliana (Cobo et al. 2012; Lago 2015). For our study, in addition to barley we used bark and chips of Eucalyptus globulus, and autoclaved barley, the latest to test whether, as Newman and Barrett (1993) stated, the inhibitory effect of barley disappears if it is autoclaved beforehand. The main objective of the study was to evaluate the effects of different doses of the selected products on cyanobacteria and the interactions occurring within the plankton communities (Cobo et al. 2011). Limnocorrals with different treatments and doses were placed at the reservoir; (Fig. 7) and periodical samplings of water and records of the environmental conditions (data loggers) were carried out during 2009 to 2011. A decrease in chlorophyll and microcystin-LR concentration was observed in the treated limnocorrals in relation to the control, which means a reduction of photosynthetic organisms and, among them, especially of toxin-producing cyanobacteria. Likewise, in the treated limnocorrals, the dominance of chromophytes, especially diatoms, increased, while cyanobacteria decreased, which could indicate a change in the trophic relationships in the water column. Coinciding with the observations of McComas (2005) and McComas and Stuckert (2007, 2008), phenolic compounds were also not detected. As a result of this work, in 2013 a patent was registered: “Method for bioremediation of cyanobacterial blooms by using waste from the eucalyptus (Eucalyptus spp.) timber industry in fresh waters” (Spanish Patent and Trademark Office, no.: 2413129, 18/10/2013). Eucalyptus chips or bark function as a delayed source of carbon added to the system that is used for microbial growth limited by this element. Thus, with the availability of carbon assured, there is an increase in the microbial communities and as consequence significant amounts of phosphorus are diverted by the microbial loop, so that, the eucalyptus, when decomposing, indirectly causes a decrease in the phosphorus available to the cyanobacteria, making it, therefore, a limiting factor, without the need for inhibition by the release of chemical compounds. Due to its slow decomposition speed, eucalyptus is an ideal material to avoid the problem of the possible eutrophication of the water mass due to an excess in the dosage and allows spacing the maintenance doses in specific cases. The success of the method depends on several factors that have to be controlled: the treatment must be applied in advance of the proliferation of cyanobacteria, the dosage and adequate aeration of the chips or bark and the appropriate placement in the water body. This methodology has been applied since then in the reservoir of A Baxe (Caldas de Reis) (Fig. 8).

4 New Research Approaches Galicia, together with the North of Portugal, forms the first European region in quantity of thermal waters and is the main spa destination in Spain. However, although the medical literature is beginning to proliferate, little is known about the relationship between water-related environmental problems and their impact on balneotherapy. In this context, it is known that balneotherapy can cause adverse reactions to the usual

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Fig. 6 Bloom in As Forcadas reservoir in 2009. For our study, in addition to barley we used bark and chips of Eucalyptus globulus, and autoclaved barley, the latest to test whether the inhibitory effect of barley disappears if it is autoclaved beforehand. The main objective of the study was to evaluate the effects of different doses of the selected products on cyanobacteria and the interactions occurring within the plankton communities

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Fig. 7 Field work at As Forcadas reservoir. Limnocorrals with different treatments and doses were placed at the reservoir and periodical samplings of water and records of the environmental conditions (data loggers) were carried out during 2009 to 2011

doses of application of treatments, that consists of a non-specific clinical picture, the so-called “thermal crisis” or “balneointoxication”. Despite its clinical similarity (gastric discomfort, hepatic congestive outbreaks, cutaneous reactions, etc.) with that observed in acute cyanotoxin poisonings, thermal crisis has never been associated with the abundant growth of potentially toxic cyanobacteria in the mineral water sources. Furthermore, microbial biofilms communities in mineral waters and hot springs have a particular composition with species belonging to different groups such as epsilonproteobacteria and gammaproteobacteria or different siderobacteria and other chymoautrophic organisms, in addition to certain bacillaryophytes, chlorophytes and especially cyanobacteria. In view of this our research group developed a programme of sampling of the biofilm in the thermal waters throughout Galicia (Fig. 9), to verify the hypothetical role of cyanotoxins in this clinical picture. Samples from mostly sulphurous water sources, with thermal characteristics ranging from cold to hyperthermal waters were analysed. ELISA (both in solution and in cellular matrix samples), LC-ESI-HRMS (in cellular matrix samples), and analysis of potential toxicity by means of a standardized bioassay were carried out. The toxic effect observed in the toxicity bioassays in one third of the sources may be related to the existence of microcystins and nodularins and even with other cyanobacterial peptides detected. In

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Fig. 8 Treatment with barley straw on cyanobacterial blooms in A Baxe reservoir (Caldas de Reis)

addition, several responses observed in the toxicity analyses reflect a pattern, probably linked to a type of hormetic response (hormesis is an adaptive response to low levels of stress, characterized by a biphasic dose–response curve) (Cobo et al. 2022a, b). Final remarks Since 2012, the research team has been part of the Iberian Cyanotoxin Network. From these studies were derived the works published by the research team, among which Cobo 2015, Lago et al. 2015a, 2016a, Vieira et al. 2022, stand out. In addition, the group has communicated the results of its research at various international conferences and symposia: Cobo et al. (2007, 2016a, b, 2017, 2022a, b), Cobo (2013), Lago et al. (2013, 2015b, c, 2016b; 2017), Barca et al. (2019), Flores et al. (2022). A student obtained her Ph.D. degree being Dr. Fernando Cobo and Dr. Rufino Vieira her advisors. The dissertation title is “Cyanobacteria bloom inhibition treatments under controlled conditions using limnocorrals” (Lago 2015). Among the developed research projects, the following stand out: – Work of sampling and water analysis during the Bloom of Microcystis aeruginosa in the reservoir of Caldas de Reis and calculation of the biological damage of the 8 km of the Umia river affected by the discharge of the company Brenntag (2006).

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Fig. 9 Examples of water sources, with thermal characteristics ranging from cold to hyperthermal. The toxic effect observed in the toxicity bioassays in one third of the sources may be related to the existence of microcystins and nodularins and even with other cyanobacterial peptides detected. In addition, several responses observed in the toxicity analyses reflect a pattern, probably linked to a type of hormetic response (hormesis is an adaptive response to low levels of stress, characterized by a biphasic dose–response curve)

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Dirección Xeral de Conservación da Natureza, Consellería de Medio Ambiente, Xunta de Galicia. Assessment of cyanobacteria blooms in As Forcadas reservoir and remediation proposal (2009). Augas de Galicia, Xunta de Galicia. Experimental validation of the treatment with barley straw on cyanobacterial blooms in As Forcadas reservoir (Valdoviño) (2010). Augas de Galicia, Xunta de Galicia. Analysis of cyanobacterial taxa and toxins (2013–2014). Miño-Sil Hydrographic Confederation. Eutrophication control analysis in reservoirs of the Miño-Sil basin (2014–2018). Miño-Sil Hydrographic Confederation. Study of the incidence of cyanobacteria in the water purification process in the specific case of Caldas DWTP (2020). Municipality of Caldas de Reis. Artificial Intelligence-powered forecast for Harmful Algal Blooms (AIHABs) (2021). Aquatic Pollutants.

References Almodóvar A, Nicola GG, Nuevo M (2004) Effects of a bloom of Planktothrix rubescens on the fish community of a Spanish reservoir. Limnetica 23:167–178 Barca S, Vieira-Lanero R, Cobo F (2019) Crisis termal, microcistinas y toxicidad potencial en surgencias termales e hipotermales de Galicia (NW España). In: 2º Congreso Iberoamericano/ 6º Congreso Ibérico de Cianotoxinas. Murcia, España Bláha L, Babica P, Maršálek B (2009) Toxins produced in cyanobacterial water blooms-toxicity and risks. Interdiscip Toxicol 2:36. https://doi.org/10.2478/v10102-009-0006-2 Brittain S, Mohamed Z, Wang J, Lehmann V, Carmichael W, Rinehart K (2000) Isolation and characterization of microcystins from a River Nile strain of Oscillatoria tenuis Agardh ex Gomont. Toxicon 38:1759–1771. https://doi.org/10.1016/S0041-0101(00)00105-7 Butler B, Terlizzi D, Ferrier D (2001) Barley straw: a potencial method of algae control in ponds. In: Water quality workbook series. Maryland Cooperative Extension. University of Maryland Collage Park. 4pp Carvalho L, Poikane S, Solheim AL, Phillips G, Borics G, Catalan J, De Hoyos C, Drakare S, Dudley BJ, Jarvinen M et al (2013) Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes. Hydrobiologia 704:127–140. https://doi.org/10.1007/s10750012-1344-1 Chorus I, Bartram J (1999) Toxic Cyanobateria in water: A guide to their public health consequences, monitoring and management. World Health Organization, London, UK, p 416 Chorus I, Welker M (2021) Toxic Cyanobacteria in water: A guide to their public health consequences, monitoring and management. Taylor & Francis, Abingdon, UK, p 858 Cobo F (2008) Floracións de Cianobacterias tóxicas en augas continentais. CERNA 54:24–28 Cobo F (2013) Métodos de control de las floraciones de Cianobacterias. In: III Congreso Ibérico de Cianotoxinas/V Reunión de la Red ibérica de Cianotoxinas. Blanes (Girona, España) Cobo F (2015) Métodos de control de las floraciones de cianobacterias en aguas continentales. Limnetica 34:247–268 Cobo F, Barca S, Lago L (2016a) Normativa ambiental internacional para la regulación de las floraciones algales. In: Seminario Internacional de Taxonomía y Ecología de las Floraciones Algales en Aguas Continentales. Libro de revisiones. Aletheya Eirl. Aerequipa, Perú, 77–89 p

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Perspectives on Irrigation in Galicia (NW Spain) T. S. Cuesta, J. J. Cancela, X. X. Neira, and J. Dafonte

Abstract Agriculture in Galicia has been linked to the development of basic products for animal feed, as well as to a subsistence economy of the population, covering the basic demands for food, without pursuing economic profitability or maximizing income. Until a few years ago, the climatic reality in Galicia has presented water requirements that were covered by the usual precipitation patterns, reducing the importance of irrigation in this territory. Although, the trend towards a change in precipitation patterns, together with the increase in temperatures, makes it necessary to address the incorporation of irrigation in Galician agriculture. Crops such as vineyards and horticultural production stand out, among others, where irrigation is already incorporated into their production systems. This chapter includes the contextualization of irrigation systems, focusing on a presentation in chronological order, from the past to the present, of the large irrigation infrastructures in Galicia. Finishing with an exposition of the future perspectives of the same, regarding the management of irrigation in private plots, and its relevance to make agriculture sustainable in Galicia. Keywords Large irrigation areas · Digitization · Schedule irrigation · Water management

1 Introduction The northwest of Spain is a territory characterized by a great economic dependence on the agricultural sector. This economic activity is strongly conditioned by high rainfall and the existence of numerous surface water streams of low flow that favour rainfed agriculture (Cuesta et al. 2005). Despite this availability of water resources in agriculture, the need for irrigation is justified by the interaction of several factors T. S. Cuesta (B) · J. J. Cancela · X. X. Neira · J. Dafonte Research Group PROEPLA “Projects and Planification”, Department of Agroforestry Engineering, Higher Polytechnic School of Engineering, Campus Terra, University of Santiago de Compostela, Lugo, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_18

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of different natures (Neira et al. 2005). We find a physical environment characterized by a peculiar topography, a relative abundance of water resources, a great dispersion of the rural population and a significant fragmentation of ownership (Crecente et al. 2002). In important rural areas of Galicia, despite having significant rainfall, there is a need to resort to irrigation given the low average depth of agricultural soil (Cancela et al. 2006a), the low capacity for water retention in the soil (Martínez et al. 2011) and the irregular rainfall that affects a practically generalized summer shortage (MirásAvalos et al. 2009), and according to the predictions of the Intergovernmental Panel on Climate Change (IPCC) in the context of current anthropic climate change, this irregularity will increase (Kong et al. 2022). As it appears in law 147/1963 of the Civil Law of Galicia, irrigation waters have a reduced and abnormal flow that prevents the creation of communities of irrigators (CCRRs). Despite this restriction, in 2003, there were a total of 397 CCRRs in Galicia, distributed throughout the territory (Image 1), based on the records available from the water agencies, Confederación Hidrográfica del Norte and Aguas de Galicia (Cancela 2004). According to Pérez García (2003), the importance of irrigation is clear in the modern history of Galicia. In the coastal regions, irrigated areas have a remarkable distribution in land growing cereals, judging by the high percentages of Salnés or Ulla. In some areas in the west of the province of Ourense, they also represent important areas, while in the Galician interior, the presence of irrigation has been associated with the development of permanent pastures. According to Bouhier (1979), in the Cadastre of Ensenada of the year 1752, reference was made to the irrigated domains in Galicia; among the most noteworthy data, it can be highlighted that almost all of the current province of Pontevedra and the southwest region of the province of Ourense were covered by irrigated areas. These provinces had more than 2% of their utilised agricultural area dedicated to irrigation. In the traditional form of irrigation, namely surface water irrigation, water resources are obtained from small dams in water streams, pools, springs, or horizontal pits such as traditional “water mines” (Image 2). According to Neira et al. (1994), the amount of land dedicated to irrigation is highly variable in Galicia. In the province of Pontevedra, irrigation represents around 25% of the cultivated area; on the contrary, in the province of Lugo, it barely represents 1.9%. Most irrigation is carried out on natural meadows (80,000 ha), with irrigated arable land (not grassland) reaching 55,000 ha in area. In the studies carried out within the preparation of the final document of the National Irrigation Plan (PNR2000), the irrigable area in Galicia was estimated at 134,027 ha, compared to the 85,490 actually irrigated, and map number 20 in PNR-2000 shows the distribution of irrigated areas in Spain. In Image 3, an example of sprinkler and surface irrigation in the “Terra Chá” irrigation area in the province of Lugo is shown. The orographic characteristics of Galicia, according to the data derived from the 200 m digital terrain model (DTM) of the National Geographic Institute (IGN), has an average elevation above sea level of 503 m and an average slope of 12.6%. This

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orography can be seen in the digital elevation model combined with the shadow map (Image 4), which provides us with an idea of the complicated orography for irrigation. The area of Galicia is 29,575 km2 , of which the area classified as agricultural is approximately 9000 km2 according to data from the CORINE Land Cover (2018). It should also be noted that of the entire agricultural area, only 2070 km2 has a slope of less than 5% and 5263 km2 has a slope between 5 and 10%. These topographic characteristics greatly limit the existence of large irrigable areas in Galicia. In terms of climatology, the region is located in an oceanic climate, with an average rainfall of 1180 mm and a reference evapotranspiration of 712 mm (Naranjo and Muñuzurri 2006). To demonstrate the existence of a water deficit in Galicia during the summer season (May–August), estimates of precipitation and reference evapotranspiration were performed using the method of Penman–Monteith. These data came from the stations belonging to the network of Meteogalicia (Conselleria de Medio Ambiente, Territorio e Vivenda), and the climatological data corresponded to the period of 2006 to 2020 inclusively. For the special interpolation, the techniques of ordinary kriging and residual kriging were used; in the latter case, X, Y and elevation

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Image 2 Traditional water mine in Galicia

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Image 4 a DTM 200 and b difference between the values of precipitation and ETo for the months of May–August for the period 2006–2021

were used as secondary variables. A more extensive description of the methodology used in the special interpolation is found in Rangel-Parra et al. (2023). As a result, a map of the difference between precipitation map and reference evapotranspiration (ETo) for these months was obtained, as shown in Image 4b, in which the height of the water deficit ranges from 50 to 300 mm, being higher in the southeast area, corresponding to areas with lower summer rainfall and higher ETo values. This justifies the need for irrigation in Galicia. There is also a water deficit along the western coast.

2 Irrigation in Galicia Cancela et al. (2004) pointed out that, for some time now, in countries belonging to the temperate-humid area of Europe, supplemental irrigation has been accepted as a necessity to improve the competitiveness of their crops. This irrigation, called a complement because of its subsidiary nature in the set of factors that affect plant production, became a widespread practice as agriculture was modernized in Galicia. Water is one of the fundamental factors that can limit the future of a livestock alternative based on the production of forage, as in fact it has been until now in the framework of traditional agricultural practices (Álvarez et al. 2014). This situation explains why Galicia has been described as a “land of small irrigated areas”. These small irrigated areas, mostly the result of private initiatives, have a combined surface area close to 16,500 ha, according to the Ministry of Agriculture, Food and Environment (MAPA 2021). In addition, it is worth noting the existence of almost 12,000 ha of irrigated natural meadows and meadows, along with more than 1500 ha of vineyards (Image 5).

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Image 5 a Use of groundwater for irrigation in A Limia, b irrigation head in Quiroga in vineyards and c irrigation wheel in maize field in Terra Chá

2.1 Large Irrigation Areas in Galicia The history of irrigation in Galicia is marked by the abundance of river streams that cross the entire territory, which together with the population dispersion and the high fragmentation of the territory have led Galicia to be covered by small farms (Casal 1984). The study of the different dynamics that exist in Galician irrigation have been analysed by Bouhier (1979), who stressed that climatic conditions make irrigation necessary in these areas. From the year 1950 onwards, due to the push developed in the rest of the peninsula, the Ministry of Public Works undertook the transformation of some Galician areas into large irrigable areas. The areas that were decreed to be transformed into irrigated areas were the Ulla Valley, in the province of A Coruña, Sarria, Terra Chá, the Lemos Valley and the Lourenzá Valley in Lugo and the Antela Lagoon in the province of Ourense (Cancela et al. 2006b) (Table 1 and Image 6). Among all the planned areas, only four were able to carry out infrastructure works and only three are irrigated by taking advantage of the existence of the distribution network (Antela Lagoon, Valle de Lemos and Terra Chá). Only three of the six planned irrigation areas are currently irrigated: Lemos Valley, Antela Lagoon and Terra Chá. There are irrigation communities in the last two of these. At present, the area of the Lemos Valley is in the process of the creation of a community of irrigators, of which its statutes have recently been approved.

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Table 1 Irrigable areas planned in Galicia Denomination

Province

Date declaration of national interest

Date of approval of the general transformation plan

Total irrigation area planned (ha)

Antela Lagoon Ourense

27/12/1956 30/12/1958

06/07/1972

4.000

Lemos Valley

Lugo

01/12/1966

16/08/1969

5.500

Terra Chá

Lugo

18/08/1972

Sarria

Lugo

13/08/1971

20/07/1076

3.304

Lorenzana Valley

Lugo

13/08/1971

20/07/1976

3.304

Ulla Valley

A Coruña –

–

1.150

2.869

Image 6 Irrigable area in Galicia, with those that were developed in grey

The action carried out in the Antela Lagoon, after its desiccation, consisted of the transformation of 2500 ha of the lagoon itself and 1500 ha of the surrounding perimeter. The current irrigation system allows the irrigation of 600 ha under pressure based on the water stored in the sanitation channels of the lagoon (MAPA 1993).

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Undertaken in the early years of the twenty-first century, the modernization of irrigation consisted of two actions, directed by the Ministries of Agriculture and the Xunta de Galicia, covering a total of more than 2600 ha. The great difference of this irrigation area with respect to the other irrigation areas in Lugo is the origin of the water; in this area, it is obtained from the extraction of groundwater and the use of ponds to store water (Image 7), while in the other two areas, it comes from surface water resources. The irrigable area of the Lemos Valley is delimited by three main channels and a ditch that comprise the valley of the Mao River and the Cabe River. The initial area to be irrigated was initially 5500 ha. At present, the irrigation that we can observe in the area is a form of gravity irrigation of low cost and low efficiency, practiced in an area much lower than that projected (Image 8).

Image 7 Water storage pond in the ‘A Limia’ region. Irrigation modernization actions

Image 8 Example of the misuse of water in the Lemos Valley irrigation area, with low efficiency

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The lack of facilities as well as the lack of interest on the part of social agents are the main causes of this case of irrigation misuse in the area (Cuesta 2001). Several studies are currently being carried in this area by our research group to modernize the irrigation system and improve water use efficiency in irrigation. Finally, the Terra Chá area is divided into three sectors, with about 1900 ha of irrigation, with 50% of the irrigable area being irrigated by sprinklers (Image 9). One of the irrigation sectors (Sector II) undertook the modernization process in 2008, implementing a modern irrigation network on demand, covering a total of 777 ha (SEIASA del Norte). In addition to the areas of action mentioned in Table 1, in the 1960s, technical studies were carried out that reflect the need to transform land from other regions into irrigated land (Table 2). The distribution of irrigated farmland, as defined by the 1999 Agricultural Census Project, suggests that Galicia possesses less than 1% of the area of irrigated farmland in Spain, although the data presented above show that this value is clearly higher.

Image 9 Elevated irrigation channel in Arneiro, Terra Chá

Table 2 Possible irrigable areas in Galicia Denomination

Main municipality affected

Province

Area (ha)

Xubia

Ferrol

A Coruña

300

Xallas

Cee

A Coruña

250

Umia Valley

Cambados

Pontevedra

4.100

Minho

Tui

Pontevedra

985

O Rosal

O Rosal

Pontevedra

107

Vega de San Clodio

Quiroga

Lugo

105

Arnoia-Tiaira-Maceda

Allariz

Ourense

1.745

Verín Valley

Verin

Ourense

6.300

Source Consejo Económico Sindical Intersindical del Noroeste (1964)

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The following sections delve into the irrigable areas of the province of Lugo, as characteristic examples of large irrigable areas in Galicia.

2.1.1

Terra Chá Irrigation District

The irrigation districts of Terra Chá are in Northeast Galicia, Spain. The average rainfall is 1027 mm, irregularly distributed by year. The area consists of seven irrigator communities, where the dominant crops are silage maize and grass pasture, which account for about 20% and 80% of the total irrigated area, respectively. Previous socio-economic studies in this region were performed by López (1979), Cardesín (1987) and, more recently, by Maseda et al. (2004), referring to the dairy farms in the region. Irrigation and water management practices were studied by FernándezLavandera and Pizarro (1980) and Neira (1994), while soils were characterised by Castelao (1989). Although the use of surface irrigation prevails in Galicia, sprinkler irrigation with lateral movement and a stationary distribution system is used in the study area, where water is pumped from the river Miño and its main tributaries. More information about the socio-economic situation of agriculture in Terra Chá can be found in Marín et al. (2010). The area belongs to a livestock tradition, especially dairy cattle, and hence the existing crops are meadows and forage corn, having the second lowest weight in terms of area, although in recent years, the cultivation of corn has been increasing, at around 20% of the current producing area (Gómez et al. 2003), which today may reach 40% of the total irrigable area. The poor state of the water collection and distribution network before the modernization of irrigation in 2008 can be seen in Images 10, 11 and 12. In 2008, the modernization works of the irrigation of the Community of Irrigators Río Miño-Pequeno-Franqueira were completed, which represented a relevant technological advancement, providing a pressurized network and all of the most advanced remote-control systems of the moment (Image 13.). The general irrigation network was built in cast iron and polyethylene, with a hydrant pressure of 65 m.c.a, such that it allows irrigation with an irrigation cannon. This energy aspect has meant an increase in the energy bill that the community members have to pay, in addition to the consequent wear of the mechanical elements of the installation (pumps, valves, etc.).

2.1.2

Lemos Valley Irrigation District

The Lemos Valley irrigation district, in the NW of Spain, is located to the south of the province of Lugo, in the Autonomous Community of Galicia. The establishment of this district in 1966 provided for the irrigation development of about 5300 ha by using natural flows from the river Cabe and regulated water flows from the river Mao. The design criteria used in 1996 were based on the limited capacity of the distribution network and on the lack of internal water storage (Neira et al. 2005).

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(a)

(b)

(c)

Image 10 a Irrigation infrastructures in Terra Chá: uptake water river section in Loentía, b Loentia pumping uptake and c spillway sector II

The main distribution network consists of three main channels, with a total length of 78.5 km and flows ranging from 5.5 m3 /s at the inlet to 0.2 m3 /s at the outlet, directly before discharging into the river Cabe. A network of channels with different capacities and states of maintenance and with an approximate total length of 147 km branch off from these channels (Images 14 and 15). The area is characterized by a temperate Mediterranean climate, with an average annual temperature in the period of 2000–2021 of 13.7 °C, which varies between the maximum average monthly temperature of 20.6 °C (July and August) and the minimum average monthly temperature of 3.6 °C (January). The actual annual rainfall recorded in this period was 387.2 mm. We can highlight the erratic nature of summer rainfall (from June 22 to September 23) in the study area: in the period of 2000/2021, we observe an average value of 95.8 mm, with a minimum of 11.5 mm, a maximum of 274.5 mm and a standard deviation that reaches a value of 51.3.

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Image 11 Water distribution channels, Terra Chá

Image 12 Obsolete water pumping equipment, River Lea

The traditional cropping pattern of the area consists of an annual rotation of artificial pastures and silage maize. This rotational scheme is characteristic of cattleoriented agriculture in the region (Cuesta et al. 2004). Rotations of forage crops lead to the use of pastures and silage maize or to the combined rotation of both crops. Other patterns tested in previous studies are less suitable. The main farm irrigation system is free draining borders, a type of surface irrigation. Irrigation is only applied to a small percentage of the surface of those fields bordering canals, due to the incomplete state of the distribution network within

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(b)

(c)

Image 13 Terra Chá irrigation modernization project. a PE pipe installation trench, b basic project data, and c supervisory control and data acquisition (SCADA)

the irrigation perimeter. Therefore, water must be conveyed to many fields through furrows, leading to excessive water delivery, estimated at 12,500 m3 /ha (Cuesta et al. 2007). The water source used for both maize (31.7% of the area) and artificial pastures (68.3% of the area) is the distribution channels. A high temporal variability was observed in flow measurements, conducted in different channels during the irrigation evaluations. The irrigation water supply largely depends on the capacity of the canal from which water is delivered and on the state of preservation of secondary and tertiary channels (Image 16). Irrigation time and irrigation frequency data also show high variability. Results vary not only among different irrigation users, but also among different irrigation areas within the same field. During the studied season, the average irrigation times declared by farmers were significantly different depending on the type of irrigated crop; 7 h per field in the case of maize, and 5 h per field in the case of pasture. The

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Image 14 Irrigation channels in the Lemos Valley

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Image 15 Infrastructures for passage of topographic obstacles in Lemos Valley: a siphon and b aqueduct

application efficiency values obtained are low or very low, reaching a mean value of 35.2%; however, the distribution uniformity (DU) values are acceptable. The structure of land tenure limits the improvement and modernisation of this irrigation area. Land consolidation does not provide a solution to fragmented land ownership, because the consolidated plots would still be too small. The discharge and volume applied to fields and channels must be controlled by installing flowmeters. A significant improvement of the organisation of the irrigable perimeter requires irrigation on demand and the control of the water demanded by each user. In addition to these actions, farmers must be given advice, and information about irrigation techniques must be diffused among them. This information was not provided when this area was established as an irrigation district.

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Image 16 Secondary water distribution channel

3 Private Irrigation: Irrigation Management An alternative model of irrigation is the irrigation of small areas in Galicia, widely used for particulate uses and in small areas or linked to crops with a high added value such as vineyards or cut flowers. An example of this type of management is the irrigation plot in Berlai-Guntín (Lugo), where the pit left by a clay mining operation (Image 17) was used to collect autumn and winter runoff water, performing supplementary irrigation in forage maize using a pivot. A second example, related to the irrigation of a vineyard, includes the installation of surface drip irrigation, while there are facilities with subsurface drip irrigation, that have been operating for more than 15 years, showing the relevance of providing the water needs required by the plant at critical moments of the cycle, as well as providing nutrients (fertigation) through irrigation water (Image 18).

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(b)

(a)

(c) Image 17 Irrigation area in Berlai-Guntín-Lugo. a aerial photograph of July 1983, b flight SIGPAC 2001 and c Flight PNOA 2020

Image 18 Surface drip irrigation in Condado do Tea vineyards (protected designation of origin Rías Baixas-Pontevedra)

3.1 Irrigation Modelling and Programming The changes in the dynamics of rainfall distribution, especially during the spring and summer months, has generated an incipient interest in water management in Galician irrigation, both in large and small areas. The programming of irrigation based on

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climate information, available throughout Galicia, facilitates irrigation management in a sustainable way. It is important to mention the existence of the SIAR (Advisory service to irrigators) network (http://www.siar.es/), regulated by the Ministry of Agriculture and Fisheries, Food and Environment through the General Subdirectorate of Irrigation and Rural Infrastructure, from which the farmer can perform estimates of the water demand of their crop. The database available in the SIAR allows consultations of water needs from 2006 to the present to be performed. It is worth mentioning the low number of stations in Galicia—four in total, located in the provinces of A Coruña and Lugo. The stations of Boimorto (Bo), Monforte de Lemos (ML) and Castro de Rei (CR) were considered to extract information for the main crops: grasslands, maize, vineyard and potato. Image 19 shows trends in net water requirements over the past 17 years. There are other platforms such as Climate Data Store in Copernicus (https://cds. climate.copernicus.eu/), which allow us to access aggregated historical climate data, with which we can make comparisons with different scenarios in the short, medium and long term. As an example, the variation of the average temperature in the summer months (June, July and August) in the centre of the province of Lugo is depicted (Image 20). The trend towards an increase in average temperature in the period of 1985–2020 can be observed, as well as the forecast of a continued rise in temperature in the short term. This aspect again highlights the importance of establishing tools that allow the management of irrigation in real time, as well as the importance of it in temperate regions, such as Galicia.

(a)

(b)

(c)

(d)

Image 19 Evolution of crop water requirements from 2006 to 2022, for a grassland, b maize, c vineyard and d potato. Data from SIAR Boimorto (Bo), Monforte de Lemos (ML) and Castro de Rei (CR)

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Image 20 Evolution of average temperature (top), and projected average temperature (bottom), using ERA5 Land and RCP4.5 scenario in Lugo province (Copernicus)

As explained by Pereira et al. (2021a), in an update to the method of estimating water needs established by FAO (Allen et al. 1998), for a correct assessment of irrigation needs, corrections of cropping coefficients (Kc) to local conditions are necessary. So, the water needs of the meadow in Galicia should be lower than those reported from the SIAR, considering a Kc = 0.8, with something similar happening in the remaining crops. References to modelling water needs, adapted to the growing conditions and climate in Galicia, are limited. Adapted (calibrated) crop coefficients have been obtained for crops such as maize (Cancela et al. 2006a, 2013), potato (Cancela et al. 2007), meadows (Cancela et al. 2006a), vineyards (Fandiño et al. 2012a, b; Fandiño et al. 2013; Cancela et al. 2015a; Fandiño 2021) and hops (Fandiño et al. 2015), so there is a broad field of work to address, even more so if we take into account the fact that the option of introducing new crops is available, derived from the current climatic conditions. The works of Pereira et al. (2021b, c) and Rallo et al. (2021) collected reference values for vegetable and field crops and trees and vine fruit crops, respectively, facilitating the adequacy of crop coefficients for the correct determination of water needs in Galicia. In Image 21, the net irrigation needs for maize and grassland in Galicia are presented (Cancela et al. 2006a). It is worth mentioning the importance of considering the fraction of soil cover and the height of the crop to obtain the water requirements without increasing or reducing them, assuming a total coverage of the crop, when this does not occur, or vice versa (Pereira et al. 2020). These authors also presented an example of using satellite image data, whose application, together with the basic information of the crop, allows us to recalculate in real time the water needs throughout the irrigation campaign, improving the use of water.

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(b)

Image 21 a Empirical probability distribution of non-exceedance of the net irrigation requirements for silage maize (squares) and grass pasture (triangle) and b variation of available soil water (grey line) for irrigated silage maize

3.2 Digitization of Irrigation: Images and Sensors Precision agriculture pursues the appropriate use of resources (inputs) to maximize agricultural production, involving the implementation of different processes, such as the opening and closing of irrigation sectors, as well as the application of artificial intelligence to help in decision-making processes by the farmer (Cancela et al. 2015b). Today, the availability of open satellite images (COPERNICUS) is a reality, as well as low-cost and solid sensors (Fandiño et al. 2012b), allowing efficient irrigation management and its implementation in small plots (Rodríguez-Fernández et al. 2021). In addition, unmanned platforms such as UAVs have the capacity to fly over crops at strategic moments throughout the crop cycle, obtaining high-resolution images, below 10 cm pixels, with which we can obtain vegetation indices (NDVI, PCD, SAVI, …) or physical parameters of the crop, feeding the decision support systems based on artificial intelligence processes (Rodríguez-Fernández et al. 2020). In relation to irrigation management, thermal cameras have provided a breakthrough in the detection of areas with greater water stress, using indices such as the Crop Water Stress Index (CWSI) (Cancela et al. 2021), either from satellite images or from images obtained by a UAV (Image 22). Finally, it is worth noting the relevance of knowledge of the physical properties of the soil, where the zoning of the plot, based on the apparent electrical conductivity of the soil (Image 23b), is very useful (Mirás-Avalos et al. 2020). In recent decades, considerable efforts have been devoted to process automation in agriculture. Regarding irrigation systems, the effort to address this demand has experienced several difficulties, including the lack of communication networks and the large distances to electricity supply points. With the recent implementation of LPWAN wireless communication networks (SIGFOX, LoRaWAN, and NBIoT), and the expanding market of electronic controllers based on free software and low-cost hardware (i.e., Arduino, Raspberry, ESP, etc.) with low energy requirements, new perspectives have appeared for the automation of agricultural irrigation networks (Fernández-Ahumada et al. 2019). In the figure below, you can see an example of an ESP32-based low-cost system with two air temperature and relative humidity sensors with a radiation shield, two capacitive soil moisture sensors, a watermark sensor

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(b)

(a)

(c)

Image 22 a NDVI in veraison for cv ‘Albarino’ grapevines under different irrigation treatments, b dynamics of soil moisture content in a hop field, and c evolution of SAVI index in a hop field in Galicia

for measuring water potential in the soil, and two soil temperature measurement sensors, powered by solar energy and with data transmission via the Lora protocol, to a gateway that sends the data via email and, in turn, registers them on a microSD card (Image 23c).

4 Challenges for the Future of Irrigation in Galicia In the current global climate context, and in Galicia, where the increase in average temperatures in the summer period and the irregularity of rainfall is a reality, improving the efficiency of existing irrigation systems and introducing new irrigation systems is of vital importance in pursuing sustainable agriculture in rural Galicia. This aspect, linked to the changes in the CAP (common agricultural policy) (2023–2027), opens the door to decoupled payments from production with the introduction of different eco-regimes that make production more sustainable, although in these, it is necessary to apply deficit irrigation strategies to maintain productive and qualitative levels that make Galician agriculture and livestock competitive. It opens up the opportunity to expand the range of crops to be cultivated by improving the climatic conditions for their effective development, although again, they require the contribution of water through irrigation in a sustained way over time. In addition, the existence of information technology tools such as sensors, satellites, drones, and platforms providing access to open climate data will allow the adequate management of irrigation systems, and therefore water, as a scarce resource, facilitating decision making considering parameters of the soil–plant–atmosphere complex and the productive objectives of the farmer, incorporating artificial intelligence into the final tools. In this sense, the modelling of the water needs of crops not studied so far, in the climatic conditions of Galicia, requires the support of public

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(b)

(c)

Image 23 a Soil water content sensors in a Galician vineyard, b soil electrical conductivity equipment in the field, c connections scheme of several soil and climate sensors with a low-cost microcontroller ESP32

institutions that finance them and will allow for the completion of the database of cultural coefficients for the implementation in the medium term of a System of Help and Information to the Galician Irrigator, as occurs in other Spanish communities. The existing meteorological network in Galicia (MeteoGalicia), together with the agrometeorological stations of private companies, would be a good starting point with which to advance with the purpose of providing farmers with a Galician SIAR, making their farms more competitive and sustainable, maintaining the population in the rural environment.

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For all the above, the future scenario is encouraging because there are technical and human resources with which we can achieve efficient water management in Galicia, thus anticipating critical situations in the medium term, where the responses will not be effective. It is necessary to solve the current energy problems, where large irrigation systems have obstacles to their use, as their operation depends on the cost of the energy. This will involve developing water storage systems that allow the pressurization of networks using gravitational energy, as well as using photovoltaic and wind energy as a sustainable resource that allows for the feeding of pressurization/ pumping units, reducing energy costs, in the face of the energy transition and the implementation of a circular economy in the Galician territory.

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in Terra Chá soils and its influence on the genesis and productive capacity.] Doctoral Thesis, Universidad de Santiago de Compostela, Santiago de Compostela, Spain Consejo Económico Sindical Intersindical del Noroeste (1964) El sector agrario y las bases de su expansión. Ordenación y Expansión de los regadíos CORINE Land Cover 2018 (Spain) [Internet] (2019) [cited 2023 Jan 4]. Available from: http://data. europa.eu/88u/dataset/spaignclc2018 Crecente R, Álvarez C, Fra U (2002) Economic, social and environmental impact of land consolidation in Galicia. Land Use Policy 19(2):135–147 Cuesta TS, Cancela JJ, Dafonte J, Valcarcel M, Neira XX (2005) Social aspects influencing water management in the Lemos Valley Irrigation District, Spain. Irrig Drainage 54(2):125–133 Cuesta TS, Neira XX, Cancela JJ (2004) Gestión del agua en la zona regable del Valle de Lemos (Lugo). Riegos y Drenajes XXI 136:64–71‘ Cuesta TS, Neira XX, Álvarez CJ, Cancela JJ (2007) Caracterización del regadío en la zona regable del Valle de Lemos (Lugo, España). Recurso Rurais 1(3):23–30 Cuesta TS (2001) Gestión y uso del agua en la zona regable del Valle de Lemos, Lugo. Tesis Doctoral. Universidad de Santiago de Compostela (EPS). Lugo Fandiño M, Cancela JJ, Rey BJ, Martínez EM, Rosa RG, Pereira LS (2012a) Using the dualKc approach to model evapotranspiration of Albariño vineyards (Northwest Spain) with consideration of active ground cover. Agric Water Manage 112:75–87 Fandiño M, Martínez EM, Rey BJ, Cancela JJ (2013) Effect of irrigation systems on the Albariño variety: simple cultivation coefficients and water stress. Spanish J Rural Dev 4:43–54 Fandiño M, Olmedo JL, Martínez EM, Valladares J, Paredes P, Rey BJ, Mota M, Cancela JJ, Pereira LS (2015) Assessing and modelling water use and the partition of evapotranspiration of irrigated hop (Humulus lupulus), and relations of transpiration with hops yield and alpha-acids. Ind Crop Prod 77:204–217 Fandiño M, Martinez EM, King BJ, Cancels JJ (2012b) Plant water status in vineyards combining sensors in soil and plant. In: International conference of agricultural engineering—CIGR— AgEng 2012b. Valencia, Spain Fandiño M (2021) Necesidades de Agua e Influencia de los Sistemas de Riego en Vitis vinifera cv. Albariño. Ph.D. Thesis, Universidad de Santiago de Compostela, Santiago, Spain Fernandez-Ahumada LM, Ramírez-Faz J, Torres-Romero M, López-Luque R (2019) Proposal for the design of monitoring and operating irrigation networks based on IoT, cloud computing and free hardware technologies. Sensors 19:2318. https://doi.org/10.3390/s19102318 Fernández-Lavandera O, Pizarro A (1980) El suelo, el desagüe, el riego y la economía. II. Terra Chá. [Soil, outlet, irrigation and economy. II. Terra Chá.] Instituto Nacional de Reforma y Desarrollo Agrario, Ministerio de Agricultura, Madrid, Spain Gómez A, Cancela JJ, Neira XX, Cuesta TS (2003) Desarrollo rural entorno al regadío en la comarca de Terra Chá (Lugo). In: V Coloquio Hispano-Portugués de Estudos Rurais, Bragança, Portugal Kong X, Wang X, Chen H, Wang A, Wan D, Xu L, Miao Y, Huang J, Liu Y, Xie R, Chen Y, Lang X (2022) Mapping precipitation changes. In: Atlas of global change risk of population and economic systems. Springer, Singapore, pp 41–65 López JM (1979) Estructura y morfología agraria en la Terra Chá. USC. Santiago de Compostela MAPA (1993) Modernización de Regadíos—Galicia. A Coruña MAPA (2021) Encuesta sobre Superficies y Rendimientos Cultivos (ESYRCE). Ministerio de Agricultura, Alimentación y Medio Ambiente, Madrid Marín A, Neira XX, Cuesta TS (2010) Satisfaction of human needs as a tool for the evaluation of sustainability through indicators. Int J Environ Rural Dev 2:7–11 Martínez E, Cancela JJ, Cuesta TS, Neira XX (2011) Review. Use of psychrometers in field measurements of plant material: accuracy and handling difficulties. Spanish J Agric Res 9(1):313–328 Maseda F, Díaz F, Álvarez C (2004) Family dairy farms in Galicia (N.W. Spain): classification by some family and farm factors relevant to quality of life. Biosyst Eng 87(4):509–521

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Mirás-Avalos JM, Mestas-Valero RM, Sande-Fouz P, Paz-González A (2009) Consistency analysis of pluviometric information in Galicia (NW Spain). Atmos Res 94(4):629–640 Mirás-Avalos JM, Fandiño M, Rey BJ, Dafonte J, Cancela JJ (2020) Zoning of a newly planted vineyard: spatial variability of physico-chemical soil properties. Soil Syst 4(4):62 Naranjo L, Muñuzuri VP (eds) (2006) A variabilidade natural do clima en Galicia. Caixa Galicia Foundation—Xunta de Galicia, p 290 National Irrigation Plan (2022) Royal decree 329/2002, of 5 April, by which approves the National Plan of Irrigation. https://www.boe.es/eli/es/rd/2002/04/05/329 Neira XX, Álvarez CJ, Cuesta TS, Cancela JJ (2005) Evaluation of water use in traditional irrigation: an application to the Lemos valley irrigation district, northwest of Spain. Agric Water Manag 75(2):137–151 Neira XX (1994) Desenrolo de técnicas de manexo de auga axeitadas a un uso racional de irrigatedos. [Development of technologies for water management adapted to the rational use of irrigation.] Doctoral Thesis, University of Santiago de Compostela, Lugo, Spain Neira Seijo XX, Paz Gonzále A, Álvarez López CJ, Velo Sabín RL (1994) Sistemas de regadío en Galicia. Agricultura: Revista agropecuaria y ganadera, 742:392–393 Pereira LS, Paredes P, Hunsaker DJ, López-Urrea R, Jovanovic N (2021a) Updates and advances to the Fao56 crop water requirements method. Agric Water Manag 248:106697 Pereira LS, Paredes P, López-Urrea R, Hunsaker DJ, Mota M, Shad ZM (2021b) Standard single and basal crop coefficients for vegetable crops, an update of FAO56 crop water requirements approach. Agric Water Manag 243:106196 Pereira LS, Paredes P, Melton F, Johnson L, Wang T, López-Urrea R, Cancela JJ, Allen R (2020) Prediction of crop coefficients from fraction of ground cover and height. Background and validation using ground and remote sensing data. Agric Water Manage 240:106197 Pereira LS, Paredes P, Hunsaker DJ, López-Urrea R, Shad ZM (2021c) Standard single and basal crop coefficients for field crops. Updates and advances to the FAO56 crop water requirements method. Agric Water Manage 243:106466 Pérez García J (2003) Irriguer ou non: La guerre de l’eau en Galice (1600–1850). Histoire Soc Rurales 20:37–52. https://doi.org/10.3917/hsr.020.0037 Rallo G, Paço TA, Paredes P, Puig-Sirera À, Massai R, Provenzano G, Pereira LS (2021) Updated single and dual crop coefficients for tree and vine fruit crops. Agric Water Manag 250:106645 Rangel-Parra R, Neira X, Dafonte J (2023) Estimation of water budget and management using simulation models: case of the Cabe river basin. Tecnología y Ciencias Del Agua. https://doi. org/10.24850/j-tyca-14-4-1(Inpress) Rodríguez-Fernández M, Fandiño P, Fandiño M, Cancel JJ, Gonzalez XP (2020) Evaluation of spectral vegetation index obtained through satellite and UAVs Images for vineyard management. In: XVI European society for agronomy congress (ESA), Seville, Spain Rodriguez-Fernandez M, Fandiño M, Gonzalez XP, Cancel JJ (2021) Estimation water status of the vineyard by calculating multispectral index from satellite images. In: European geosciences union. General Assembly 2021(EGU2021), Vienna, Austria

Geomorphology and Landscapes

Geomorphology and Landscape Augusto Pérez Alberti

Abstract Nowadays, a traditional image of Galicia still survives showing the country as a uniform territory, but in fact there is a very different reality that materializes in a wide set of spaces with numerous contrasting landscapes. Keywords Geomorphology · Landscape · Galicia · Northwestern Iberian Peninsula

1 Introduction Nowadays, a traditional image of Galicia still survives showing the country as a uniform territory, but in fact there is a very different reality that materializes in a wide set of spaces with numerous contrasting landscapes. This is due to several factors: (a) firstly, the existence of an extensive coastal strip and a wide continental territory; (b) secondly, the existence of altitudinal contrasts, linked from the coast to the interior; (c) thirdly, different climatic and biogeographic environments that can be found both on the coast and inland; (d) and, fourthly, a long geomorphological and anthropic evolution affecting to this geographic area. The contrast between the coast and the interior is, without a doubt, a first element that explains the diversity of Galicia’s landscapes. The length of its coasts -more than 2000 km- and its sinuous profile, with numerous inlets and outlets, due to the chaining of estuaries, bays, inlets, and capes, favored the genesis of contrasting spaces, with linked rocky coasts, beaches, lagoons, estuaries and rías and dune systems. In addition, from the coast inland, a clear staggering of terrain levels is observed (Fig. 1a). On the same seashore stands a set of mountains, which reach 500/600 m of altitude. This is the case of A Capelada and Montes da Candieira, between the Ortigueira and Cedeira estuaries; O Barbanza, between those of Muros/Noia and Arousa; the A. P. Alberti (B) Department Edafoloxía e Química Agrícola (Soil Science and Agricultural Chemistry), Faculty of Biology, University Santiago de Compostela, Campus Vida, Santiago de Compostela, Santiago, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_19

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Montes do Castrove, between those of Arousa and Pontevedra, or the Montes da Groba and O Galiñeiro, situated in the south of the Vigo estuary. The above commented staggering becomes more relevant towards the interior. If a west–east cut is made, it is seen that the terrain rises to 1100 m in the western sierras, descends to 400/500 m in the interior of Lugo and Ourense, and reaches 2000 m again in the eastern sierras, in the limits with Asturias and Castilla y León. Also to add the existence of a wide and diverse fluvial network that is intensely embedded, with a large number of narrow and deep valleys that give rise to hills with a diversity of slopes (Fig. 1b). If lithological diversity is also added to this, it is easier to understand the reasons for the visible differences in the landscapes. From west to east, igneous and metamorphic rocks and, to a lesser extent, sedimentary rocks, are situated in a linking chain. On the Atlantic façade, granites and granodiorites are dominant. In the central regions, mafic and ultramafic rocks are present (as peridotites, eclogites, or gabbro). In the north, schists. In the center and in the south, again granites. In the eastern regions, there are slate, quartzite, limestone and dolomite bands, with small granitic intrusions. This diversity of lithology, topography and endogenous or exogenous processes, that took place in Galicia over millions of years, has given rise to the presence of landscapes marked by geological factors and that are visible in different places in the Iberian northwest.

2 Lithological Control Affecting the Landscape The rocky landscapes, which could be called “lithoscapes” (Pérez Alberti et al. 2014), are among the most spectacular that can be admired. Among them, the modeling on granitic rocks, basic rocks or limestone, stands out, but also what takes place on other rocks such as peridotites (Fig. 2a) or quartzites (Fig. 2b) is remarkable. In some places the spectacularism of the landscape is reinforced by the existence of tectonic elements such as folds (Fig. 2c). In the genesis of the former, tectonics and the processes of alteration and subsequent erosion have played a fundamental role. The combination of fractures with different directions and curvatures favored the delimitation of geo-forms and was the result of the long geotectonic evolution of Galicia, where two fundamental events intervened: (a) the Variscan (or Hercynian) orogeneses, and (b) the Alpine orogenies, developed due to convergence processes of tectonic plates and subsequent intra-plate movements (De Vicente and Vegas 2009). In the case of granitic rocks, their mineral composition, their texture, and the density of joints and fractures have undoubtedly influenced the rate of weathering. Being composed of intertwined crystals of quartz, feldspar and mica, when they are fresh, they have low porosity and permeability, but, when fractured, they are more permeable because the water penetrates the rock along the discontinuities that occur at different scales, from the microcracks inside the minerals to those that may reach much more larger dimensions. Fractured rocks are more susceptible to weathering

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Fig. 1 a Map of the relief of Galicia; b Map of slopes

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Fig. 2 a Landscape on peridotites. A Capelada (A Coruña). b Rocky outcrop on quartzites (Campodola, Courel Mountains, Quiroga, Lugo). c Anticline on quartzites. Summit at Serra de Ancares (Lugo-León)

than those in which fractures are absent, widely separated, or tightly closed. There is no doubt that there is a clear structural control in the evolution of granitic landscapes (Migo´n 2004; Pérez Alberti and Blanco-Chao 2005). Thus, granites rocks present in the middle latitudes in which Galicia is located, resist well to the action of water currents or sea waves. However, this resistance to mechanical action is altered by the discontinuities that generate lines of weakness and that become the paths along which weathering progresses. Its effectiveness increases as a function of higher temperatures and rainfall, since chemical reactions are accelerated, especially hydrolysis causing the alteration of micas, feldspars and quartz, which leads to the

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washing of silica and basic cations, giving rise to clayey minerals and a concentration of metallic residues in the form of hydroxides. It should be noted that climatic conditions in Galicia have not remained stable throughout geological history, which conditioned the evolution of granite forms, given that rock alteration processes are not the same under the current temperate climatic conditions compared to those that dominated in the past. It should bear in mind that, during the Cenozoic period, the Galician territory remained under tropical climatic conditions, characterized by high environmental humidity and high temperatures (Macías-García et al. 2007). Since the degree of weathering advances parallel to the topography, although there are variations in depth derived from the degree and design of the fracturing of the rock, once the alteration layer is destroyed a set or chain of linked shapes appears along the hillslopes. In the upper segments, where the dismantling has been greater, ridged forms stand out, with pointed protrusions. Below, some columns may appear, made up of blocks stacked vertically. And, in the lower segment, rounded boulders dominate. In some places, the culminating sectors are crowned with dome shapes, which appear surrounded by a large procession of forms of varied geometry. Granite landscapes are built by the combination of various shapes, from convex (in the case of domes, ridges and rocky castles, castle kopjie, columns, tors, whale backs or bowling pins of very varied design), to concave shapes, such as alveoli, as a kind of circular depressions. When expanding the scale, linear shapes appear, such as grooves, rounded, such as “pilancones” or “pías”, gnammas or others related to the structure of the rock in the form of pseudo-stratification. In Galicia, domes receive the popular name of “moas”. They are limited by clear walls, with hardly any compartmentalization, which result in the appearance of large slabs that follow the curved jointing of the discharge, which is the dominant one. Good examples appear in the O Pindo massif (Carnota, A Coruña) (Fig. 3a) or in the Faro de Budiño (literal lighthouse, but it is a rocky landform) (Porriño, Pontevedra) (Fig. 3b). The rocky ridges design sawtooth alignments, formed by the intersection of two receding slopes. Good examples appear in O Pindo (Fig. 3c), Pena Corneira (Carballeda de Avia, Leiro and Avión, Ourense). The so-called “castelos” are sharp shapes, determined by orthogonal joint systems. They are very abundant around Ourense and Allariz, in San Pedro de Rochas, in Esgos, as well as in Requiás, on the border with Portugal (Fig. 3d), in Mount Pindo, in Traba, in the mouth of the Ferrol ría, in the Arousa ría or in the Manzaneda massif. The tors, in the form of rectangular towers or staggered bowling pins, are also located in many places, as those of the Manzaneda Massif, San Pedro de Rocas, Monte Pindo (Fig. 4a), Penedos de Pasarela e Traba (Fig. 4b), Caldas de Reis, Ponteareas, Pena Corneira, Monte Lobeira or Budiño. The landscapes in which granite boulders dominate are very abundant. They present different sizes, and may reach 10–15 m in diameter. They stand out in Serra de Queixa, in the Manzaneda sector (Fig. 5a), in certain points of the Sil river valley, in the Penedos de Pasarela e Traba, in Mount Pindo, in Pena Corneira, in the Massif da Toxiza, in Serra do Xistral (Lugo), in Terra Cha (Lugo), Ponteareas (Pontevedra),

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Fig. 3 a A Moa (O Pindo, Carnota, A Coruña). b Faro de Budiño (Porriño, Pontevedra). c Granite ridge in O Pindo (Carnota, A Coruña). d Granite pitons (Requiás. Muiños, Ourense)

Estaca de Bares (A Coruña), in terra de Melide (Fig. 5b), and in Caldas de Reis (Pontevedra). Due to the combination of shapes of different sizes and geometry, those that stand out from all the indicated places are the Penedos de Pasarela (Vimianzo and Laxe, A Coruña) (Pérez-Alberti 2022). A place where anthropomorphic, zoomorphic, and multiform shapes are combined, resulting a geographic point of incalculable value (Fig. 5c). Limestone rocks, with little surface development in Galicia, also build unique landscapes marked by dissolution processes favored by the action of slightly acid water. Water becomes more acidic when enriched in carbon dioxide and reacts with

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Fig. 4 a Tor in O Pindo (Carnota, A Coruña). b Tor in Penedos de Pasarela e Laxe (Laxe-Vimianzo, A Coruña)

carbonate to form bicarbonate, which is soluble. In this way, the surface and ground waters, taking advantage of the extensive network of fractures through which they can enter, have been dissolving the rocks, forming galleries and caves in depth, or “lapiaces” or “dolinas”. In Serra da Enciña da Lastra, in the Oulego sector (Fig. 6a), and especially in the Courel Mountains, there are numerous caves (endokarstic forms) as well as superficial forms (exokarstic forms) such as “lapiaces” (Fig. 6b) or sinkholes (Fig. 6c). The best examples of forms modeled on limestone are found in Monte Cido, around the Taro Branco (Fig. 6d) or in the Val das Mouras (Courel Mountains), in the vicinity of Baralla, or in the place of Os Grobos (Becerreá-As Nogais, Lugo) (Fig. 7a) or Baralla (Lugo) (Fig. 7b). In this place there is a mixture of small sinkholes and corridors

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Fig. 5 a Granite bolus. Rabal (Chandrexa de Queixa, Ourense). b Granite bolus. Melide (A Coruña). c Granite forms in the Penedos de Pasarela e Laxe (Laxe-Vimienazo, A Coruña)

formed by the collapse of the old system of caves and galleries. Nearby, at Millares, a recent collapse (November 2010) created a deep sinkhole (Fig. 7c).

3 Geomorphological Processes and Landscapes The environmental changes that took place throughout the geological history of Galicia were many and diverse, which motivated different dynamics. These were associated with alluvial or fluvial, glacial, or periglacial processes, that gave rise to forms of erosion or accumulation, building differentiated landscapes in a territory that has an extensive coastal strip in which the variety of landscapes is also extensive.

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Fig. 6 a Limestone forms (Penedos de Oulego, Rubiá, Ourense). b “Lapiaces” (Mercurín, Folgoso do Courel, Lugo). c “Dolina” (O Seixo, Pedrafita, Lugo). d Slope of Taro Branco (Folgoso do Courel, Lugo)

3.1 Landscapes Shaped by Water The flow of water on the earth’s surface varies depending on climatic conditions and tectonic dynamics. This explains two types of forms that can be found in Galicia: alluvial fans and fluvial terraces. Both can appear in different spaces or in the same area. Good examples of this are the depressions of Monforte, Valdeorras or San Clodio-Quiroga. An alluvial fan is an accumulation of sediments showing that expanding shape (fans out) from a higher level to a lower one. In the case of Galicia, they are associated

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Fig. 7 a Limestone forms. Os Grobos (Becerreá-As Nogais, Lugo). b Limestone forms. Baralla (Lugo). c Collapse “dolina” (Millares, Folgoso do Courel, Lugo)

with climates that were more arid than the current ones and, very often, attached to faults. This is the case of those found on the western margin of the Quiroga basin, in the Hermida area, associated with a NNE-SSW tearing fault (Pérez Alberti 2018) or those found in Caldesiños (Ourense) (Fig. 8). Sediments in an alluvial fan are usually thick and poorly classified as a result of high-energy transport. They are associated not with continuous water currents but with discharges related to debris flows, transporting clasts of all sizes (from blocks and pebbles to clay). Fluvial terraces are stepped forms that can be seen on the riverbanks. They are formed due to the continuous erosion and deposition of sediments by a river. In a very simple way, they could be classified into two types: filling, or accumulation (fill terraces), and erosive (strath terraces). The former type is observed in river valleys filled with sediment during cold periods or due to an increase in bed load. The flow

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Fig. 8 Alluvial fan deposits (Caldesiños, Ourense)

of the river will continue depositing the material in the valley until the bed becomes embedded, which would be due to changes in the erosive capacity of the river, or due to increased water flow or tectonic movements. At the end, in the valley, flattened levels of extension and height are observed on the variable bed. This fact is visible, for example, in the valleys of the Avia and Miño rivers, in the Ribeiro region, or in the lower Miño (Viveen et al. 2013), or in the valley area of Cabe river, in the Monforte or Sil depression, and the Quiroga river valley, in that of Quiroga-San Clodio, and that of the Sil river, in Valdeorras. Good examples of fluvial terraces can be seen in the Monforte de Lemos depression, associated with the Cabe river (Fig. 9a) and in the San Clodio-Quiroga depression, related to the Sil and Quiroga rivers (Fig. 9b). In the studies carried out so far (Cunha and Pérez-Alberti 2022) five terrace levels have been differentiated in Monforte, at +4 m, +13 m, +17 m, +21 m, and +26 m high above the current bed of the river, and similar levels were found in Quiroga-San Clodio (at +7, +10,+14, +19 and +35 m). Downstream, in the case of the Ribeiro region, the works by Pérez Alberti (1978) and Pérez Alberti et al. (2013) have differentiated four levels of cumulative terraces located at around 40–46 m (T1), 30–33 m (T2), 20–26 m (T3), and 4–10 m (T4). The T1 level is preserved between the localities of Fea and Puga and, to a lesser extent, in Troncoso, Prado and Vide-Astariz, on the left bank of the river (Fig. 10a), or in Laias and Sanín, on the right bank. In the outcrops, boulders of quartz and quartzite are observed, embedded in a sandy matrix. The T2 level is more extensive and can be seen in Santa Cruz de Arrabaldo (Fig. 10b), Laias, Razamonde and Sanín, on the

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Fig. 9 a Terrace level in Parada Seca (A Gudiña. Ourense). b Terrace level in the Ser River valley (Cervantes, Lugo)

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right bank of the river, and in Oleiros, Prado and Vide-Astariz, on the left. It is made up of pebbles and gravel embedded in a sandy matrix. As in the previous level, it has an intense reddish color. Lower down lies the T3 level, which is well represented in Laias, Razamonde, Sanín and Ventosela, on the right bank of the river, and in Oleiros and Vide-Astariz, on the left bank, while the T4 level can be seen in Santa Cruz de Arrabaldo, BarbantesEstación, Laias or Sanín, on the right bank of the river, and in Fea, on the left. Formerly it could be seen in the alluvial plain of Castrelo, today flooded by the Castrelo reservoir. At a general level, it is composed of pebbles and gravel of heterometric size embedded in a sandy matrix. The pebbles are well rounded, composed of quartz and quartzite, and the overall dominant color is brownish grey. On the other hand, Viveen et al. (2013) have differentiated up to 9 levels in the lower Miño: at 11–13, 16–18, 23, 30–36, 41, 48–50, 60, 65–70, 80 and 85 m above the current level of the riverbed. According to these authors, different levels are visible in the surroundings of Caldelas or O Rosal.

3.2 Landscapes Shaped by Glacial Ice In the mountains of Galicia, from the coast to the border with Asturias and León, there is a great diversity of forms and deposits of glacial origin generated during the Upper Pleistocene. The imprint of the ice is evident in the extension and magnitude of the forms of erosion and accumulation. Among the former, glacial valleys, cirques, amphitheaters, shoulder pads, excavation buckets and fleecy or striated rocks stand out, with moraines being remarkable within the latter. Based on the distribution of these geo-forms, Pérez Alberti et al. (1993) differentiated four types of ancient glaciers: (1) Cap glaciers with prolongation in tongues, (2) Complex glacial systems with coalescing tongues, (3) Simple glaciers with head and well-developed tongue, and (4) Circus glaciers with incipient tongues. The first type is characteristic of the Manzaneda and Trevinca massifs. The second and third are the dominant ones, for example in Ancares and Courel. The fourth is located on the southern edge of the Manzaneda Massif or in the Cebreiro mountains. In Serra da Capelada various authors (Oliva et al. 2019; Pérez Alberti 2020) found traces of glacial activity at sea level, in three sectors: Valle de Teixidelo, in the surroundings of the Teixidelo village, Valle de Santo André de Teixido, where this town is located, and Enseada de Cortes, slightly further south. The first one has its head at 506 m altitude, while the second is at 571 m. In the Santo André valley, stepped morainic arches stand out towards the sea (Fig. 11a). In that of Teixidelo the moraines of the left margin are clearly seen (Fig. 11b), as well as those from the front of the valley, being more diffuse on the right. Several valleys of glacial origin have been described in the Serra do Xistral (Valcárcel-Díaz and Pérez-Alberti 2022). The forms of glacial accumulation are visible, for example, in the Pedrido river valley, where two parallel moraines with a front-lateral arrangement appear, which are connected to a fluvial-glacial terrace,

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Fig. 10 a Staggering of terraces between Laias and Troncoso (Ourense). b Terrace outcrop in Laias (Ourense). c Terraces in Santa Cruz de Arrabaldo (Ourense)

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Fig. 11 a Moraines in Santo André de Teixido (Cedeira, A Coruña). b Morrenic arches in Teixidelo (Cedeira, A Coruña)

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at an altitude of 700 m. However, the most developed moraine complex in Serra de Xistral is that of Rego do Esterco. These are two parallel moraines that begin in the highest sector of the O Carranco peak (935 m). From there they descend attached to the slope of Rego do Esterco until reaching 650 m of altitude in contact with the bottom of the valley. In the Eume glacial valley, there are three moraine alignments that occupy the central section of the valley in a longitudinal direction. In Montes do Cebreiro and in Serra de Oribio (Valcárcel-Díaz and Pérez-Alberti 2022) a group of small individual circus or incipient valley glaciers is also visible. The structural layout facilitates the presence of extensive slopes oriented to the NE, as well as elongated summit lines in the same course, at altitudes ranging between 1350 and 1474 m. Others are situated in Montes de O Cebreiro, from E to W, those of Poza do Carballal (Fig. 12a), Padornelo, Vilar and Vella Morta, Traschancia, Val de Pradela, Navallos and Bouza do Río. In Serra de Oribio are situated those of Queixadoiro (Fig. 12b), Poza do Lacelo, Arroyo de Lombán, Penedo do Lobo, Arroyo de Abrairal, Arroyo de Reigosa and Arroyo de Gandarela. The characteristic forms are the glacial cirques, oriented to the NW, as well as moraines. The presence of morainic ridges stands out both in a lateral, lateral-frontal or frontal position, with fronts that oscillate at altitudes between 1000 and 1320 m. The glaciers had a thickness between 50 m (Queixadoiro) (Fig. 12a) and the 80 m reached in Poza do Carballal (Fig. 12b), or in Penedo do Lobo. Its length varies between up to 1.96 km in Serra de Oribio (Penedo do Lobo), up to 800 m in the Queixadoiro valley, or 500 m in the small circus glaciers of Rigosa and Gandarela. The most abundant lengths vary between 1.14 and 1.30 km. The total surface occupied by the ice is 6.11 km2 . In Serra de Ancares (Pérez-Alberti and Valcárcel-Díaz 2022) numerous glacial valleys have been differentiated that in total occupy 141.6 km2 . According to their longitudinal development, as well as the thickness of the ice, those located on the western slope were very different from those located on the eastern one. The glacial tongues reached a development that was greater in the eastern valleys [in the case of Ancares (14.6 km), Burbia (9.8 km) or Porcarizas (7 km)] compared to the western ones, such as Suárbol (6.5 km), Balouta (5.5 km) or Piornedo (5.3 km). The thicknesses varied from one valley to another, reaching 128 m in the Suárbol valley and 130 m in Piornedo, both located on the western slope, and 247 m in Porcarizas, or 310 m in the eastern Ancares valley. This is due to the already mentioned asymmetry between the western slope, which has its base level in the tributaries of the Navia River, at an altitude of 600 m, and the eastern slope that drains towards the Sil River, with a base level close to 900 m. The glacial deposits located at a lower altitude are found on the eastern slope, specifically in the Burbia valley, at an altitude of 790 m, the general rule being that, on average, they are located between 800 and 1000 m. Good examples of glacial valleys with a trough profile are found in the Ancares, Balouta (Fig. 13a), Burbia, Porcarizas and Teixeira valleys. Other valleys present a cradle profile, among which those of Piornedo, Suárbol (Fig. 13b), Ortigal and Brego stand out. The most representative cirques are located at the headwaters of the Ancares, Suárbol, Burbia and Teixeira valleys. On the other hand, the existing amphitheaters that present semicircular and open shapes, with gentle slopes, as well as a generally flat bottom, and appear connected to the valley by means of thresholds.

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Fig. 12 a Lagoon closed by moraines (Poza do Carballal, Montes do Cebreiro, Lugo). b Lateral moraine of the Queixadoiro valley (Triacastela, Lugo)

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They are found in the headwaters of the Piornedo valley (Fig. 13c). Good examples of striated rocks appear in the Piornedo valley. In both the Ancares and Porcarizas valleys, some sectors with glacial shoulder pads on the slopes have been preserved. In all the Ancares valleys there are numerous morainic systems located between 824 and 1788 m. Due to their importance, the southern lateral moraines of the Suárbol valley (Fig. 13d) and the front-lateral moraines of Piornedo are noteworthy. In Serra do Courel (Pérez-Alberti 2018, 2021) other glaciers have also been described, covering a total of 19.2 km2 . The glaciers do not reach 6 km, being the longest (4.8 km) that of A Seara (Fig. 14a), with that of Vilarbacú measuring 2.5 km, and that of Ferreirós achieving 2.9 km. The ice layer reached thicknesses of 130 m on the A Seara glacier, 65 m on the Ferreirós glacier, or 50 m on the Folgoso glacier. The cradle valleys and amphitheaters dominate in the valleys of Folgoso, Ferreirós and A Seara. There are small circuses in the A Seara valley. The thresholds are less clear, as well as the furrowed and striated rocks. The moraines are staggered between 900 and 1,518 m. Among them, the frontal-lateral ones at a lower altitude of A Seara, and the frontal ones of the head of this valley and that of Ferreirós, stand out (Fig. 14b). In the Manzaneda Massif, ancient glacial valleys have been identified covering 139.2 km2 (Pérez-Alberti and Valcárcel-Díaz 2022). Its length varies from 16.6 km for the Pradoalbar glacier (Fig. 15a) or 11.5 km for the Cenza glacier, to 2.7 km for the Seixo Norte. Regarding the thickness of the ice, it varies from one valley to another, reaching, for example, 206 m in the As Lamas-Prada-Requeixo valley, 187 m in the Pradoalbar valley, or 111 m in the Cenza valley. The cradle valleys dominate in As Lamas-Prada, Cenza and Pradoalbar. The clearest cirques are found in the southern sector of the massif, in the Forcadas-Requeixo and Ribeira Grande valleys, and in the northern sector, in the As Lamas-Prada valley (Fig. 15a). Fleece and striated rocks are abundant in the valleys where granite dominates, such as the Cenza (Fig. 15b) and As Lamas valleys. The morainic systems are located between 812 and 1612 m above sea level. In some places they are highly developed, especially in the Cenza valley (Fig. 15c) and in the As Lamas-Prada valley. Built by the accumulation of heterometric blocks of granite, they are very visible in the landscape. In the Galician sector of the Trevinca Massif (Pérez-Alberti and Valcarcel-Díaz 2022) some glaciers have been identified, covering 326.5 km2 at the time of maximum glacial advance. The tongues reached 8.6 km in the A Morteira valley, 11 km in the Barxacoba valley, and 30 km in the Bibei valley. In this valley the ice layer reached a thickness of 425 m. In the Barxacoba valley it reached 353 m, and it was 289 m in A Ponte. Excellent examples of cradle valleys exist at A Ponte, Canda, Chanos (Fig. 16a) or Bibei. To note other examples, corresponding to circuses, in that of Meladas, shoulder pads in that of A Ponte and A Morteira, and thresholds in all the valleys. Also noteworthy are the glacial excavation lagoons, favored by the extensive network of fractures, and plugging, generated as the glacial tongues receded (Fig. 16b). They exist in most of the valleys. The morainic deposits are very abundant in all the valleys. They are staggered between 998 and 1930 m of altitude. Due to their spectacular nature, the morainic arches on the right bank of the Bibei

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Fig. 13 a Balouta Valley (León). b Valleys of Suárbol (León), in the foreground, and Piornedo (Cervantes, Lugo), in the background. c Piornedo valley headwaters. d Lateral moraines of the Suárbol valley

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Fig. 14 a Glacial moraines at the head of the A Seara glacial valley (Quiroga, Lugo) around Lucenza Lake (Quiroga, Lugo). b Morainic ridges at the head of the Ferreirós glacier (Folgoso do Courel, Lugo)

valley in the Cepedelo area are worth noting (Fig. 16c). Also noteworthy in this valley are the glacio-lacustrine deposits existing at the Pias site (Fig. 16d).

3.3 Landscapes Performed by Periglacial Dynamics Ice/thaw processes, periglacial processes, are also present in all the Galician mountains, becoming more evident where the slopes are steeper and where the rocky

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Fig. 15 a As Lamas glacial cirque (Manzaneda, Ourense). b Sheepback rocks in the Cenza glacial valley (Vilariño de Conso, Ourense). c Glacial moraines at Chaguazoso. Cenza Glacier (Vilariño de Couso, Ourense)

substrate offers a greater degree of jointing or a greater number of exfoliation planes. This means that are more evident in those sectors with dominance of metamorphic rocks, especially slates, schists and quartzites, being less frequent on areas with limestone, dolomites, and granites. Layered or amorphous slope debris with evidence of soli-fluid movements, boulder fields and slopes, and rock glaciers, have been mapped. In the landscape, the latter stand out, as they are relatively abundant in the sectors where quartzites dominate. Within them, they can be differentiated, depending on their topographic location (Pérez-Alberti and Rodríguez-Guitián 1993; Pérez-Alberti 2021) into: (a) Block slopes, (b) Summit block fields, (c) Fields of blocks of slope with preferential movement (rivers of blocks), and (d) rocky Glaciers.

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Fig. 16 a Glaciar valley of Chanos (Zamora). b A Serpe Lake (A Veiga, Ourense). c Cepedelo moraines (Viana do Bolo, Ourense). d, e Glacio-lacustrine deposits in Pias (Zamora)

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Fig. 17 a Block slope. Ancares (Cervantes, Lugo). b Block slope. Courel Mountains (Quiroga, Lugo). c Block field. Ancares (Cervantes, Lugo). d Blocks field. Cabeza Grande de Manzaneda (Manzaneda, Ourense)

3.3.1

Block Slopes

They can be found in different places in the Northwest mountains. They are clean castings (without matrix), which have not been formed by simple gravity, as attested by the existing overlap between the blocks and which, generally, interbedded or covered other stratified deposits. Block slopes located in places with inclinations that fluctuate between 16° and 32° and in different orientations are very frequent in the Ancares mountains (Lugo and León) (Fig. 17a), especially above 1000 m, and in Serra do Xistral (Lugo), between 600 and 1000 m, in Serra do Courel (Lugo) above 450 m, in Serra da Queixa (Ourense), above 1300, and in the peaks of Serra do Eixe, above 1000 m. At lower altitudes they can be observed in the Courel Mountains (Fig. 17b).

3.3.2

Summit Block Fields

They have been generated on the summits of Serra de Ancares (Fig. 17c), Serra de Queixa, Serra do Xistral, or Trevinca Massif, at elevations ranging from 1200 to 1800–1900 m. They present evident traces of imbrication, which implies processes of

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fragmentation, uplift and incipient movement with interstitial ice. Towards the edges of the summit zone, downslope, these formations tend to gradually form block slopes. This can be very well seen in the peaks of Cuiña (1998 m), Penalonga (1890 m) or Corno Maldito (1848 m), in Serra de Ancares. They are frequent in areas dominated by quartzite but have also been detected in granitic areas, in the case of Cabeza de Manzaneda (1778 m), within Serra de Queixa (Fig. 17d).

3.3.3

Block Fields with Preferential Movement: Rivers of Blocks

Halfway between the boulder slopes and the boulder fields, practically horizontal, are these formations that, in some cases, are highly developed. These are large stone quarries, associated with quartzites, which spread down the slope forming flows. In all cases they appear on hills with a slope that does not reach 16°. The best examples are found in the Pedregal de Irimia (Fig. 18a), within Serra de Meira, which rises to 896 m altitude, and in Os Carballoes, in Serra do Courel (Fig. 18b). In the first case, it is a deposit 617 m long and 170 m wide, made up of quartzite clasts up to 1.5–2 m long on its longest axis, which descend from approximately 800–700 m. The slopes do not exceed 16°. In the case of Os Carballoes, its length is 450 m, and its width is 115 m.

3.4 Coastal Landscapes The Galician coastline is over 2100 km long (POL Galicia 2010). Two major coast types may be distinguished: those with estuaries (“rías”) inside, and those without estuaries. In the first type, marine inlets dominate, while in the second, straight sections prevail, and only small inlets or estuaries open up. In general, the modeling responds genetically to different factors: the tectonic one marks its general design and its direction; the lithology causes differential erosion processes, which define the broad features of its coastline; and, finally, the succession of geomorphological processes over time has conditioned the detail forms and the distribution of the different environments. In addition, human activity has affected many sectors, mainly on the low coast. Considering lithology, an important part of the coasts of Galicia are modeled on granite rocks, although there are sectors in which other types of rocks emerge. This is the case of the dominant basic and ultrabasic rocks in the Cabo Ortegal Complex found in Serra da Capelada, or the slates and schists around the Ría de Ortigueira and to the north of the Ría de Vigo. Thus, the type of rock, its mineralogical composition, and its degree of fracturing, together with the degree of alteration, are of vital importance in coastal modelling. At any scale of analysis, the arrangement of the rocky outcrops establishes many of the lines of the plan layout of the coast and, similarly, a relation can be established between the shape of the vertical profile and the structural arrangement of the materials. However, the effectiveness and action of

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Fig. 18 a Pedregal de Irimia. Serra de Meira (Lugo). b Os Carballoes, Vilarbacú (Quiroga, Lugo)

erosive processes does not only depend on the type of rock, but also on the geometry and the pattern of discontinuities, which establish the lines of weakness in favor of which erosion preferentially occurs.

3.4.1

The Cliff Shores

A sea cliff is understood as any slope that is on the seashore and is directly or indirectly affected by the dynamics of the waves. However, the multiple factors involved in its dynamics, current or past, make it very difficult to create a clear and unequivocal

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classification. The profile of a cliff is the result of the interaction between geological, climatic, oceanic and biogeographic variables together with the depth of the water, the type and amount of material at the base, the topography of the cliff-top or changes in the level relative to the sea. The conjunction of all this is reflected in the fact that the profile of the cliffs is related to the relative indices of erosion by marine or subaerial agents, and the duration of the period during which they operate. In marine erosion, processes of abrasion, alteration, mechanical attack and biological activity intervene, but in turn, the effects of marine erosion determine the implementation of other types of processes, such as mass movements, which can also be a direct consequence from continental factors. Coastal morphogenetic processes therefore do not present a linear character, nor are cumulative, but rather vary according to a previous system. Although they can act at the same time, overlapping or juxtaposing spatially, there is also a temporal succession. Thus, many cliffs draw profiles that are inherited and are currently affected by other phenomena, so that most of the cliffs can be characterized as polygenic forms. What has been indicated above leads to the possibility of differentiating the cliffs based on different characteristics, such as their shape, the type of dominant rock, the composition of their base, their height, slope and orientation, and their degree of stability. All this means that, as new elements of analysis are introduced, the number of typologies increases. The variety of cliff coasts is high (POL Galicia 2010; Pérez-Alberti and GómezPazo 2019). Synthetically, they can be differentiated by their height, by their design, by the materials on those they have been modeled, and even by the type of deposit they have at their base. By their height, it is possible to differentiate among high, medium and low cliffs. The first may exceed 200 m in height, in the case of those on the façade of Serra da Capelada (Fig. 19a) or of Montes da Lagoa (Fig. 19b). Due to their design, it is possible to identify, among others, the following: (a) cliffs with associated convex or concave slopes that can be observed in many places, from the coast of the Rías Baixas, to the north of Ferrol (A Coruña) (Fig. 19c); (b) flat-topped cliffs without associated plain that are characteristic of places where schist materials dominate, in the case of the north coast in the case of Valdoviño (A Coruña) or Costa de Dexo (A Coruña) (Fig. 19d); (c) flat-toped cliffs with associated plain, which appear on the Galician Cantabrian coast, in its eastern sector, between Fazouro and Ribadeo (Lugo) (Fig. 20). When analyzed based on lithology, it is possible to differentiate the following: (a) cliffs modeled on granitic rocks, which have a wide distribution along the Galician coast, highlighting those of the north coast, with higher height, or sectors of the Camariñas coast (Fig. 21a), or from the south of Galicia, case of the Cies Islands (Pontevedra) (Fig. 20a) or between Cabo Silleiro and A Guarda (Pontevedra), where the granitic forms present less power and are frequently found linked to accumulations of heterometric materials at their base; (b) cliffs modeled on dominant metamorphic rocks of the Galician Cantabrian coast, where the most notable examples of this category are found with flat-topped profiles on schist materials in the area between Viveiro and Ribadeo (Lugo) or in the surroundings of the Ortigueira Ría (Fig. 20b); (c) in other sectors, such as those in the north of Galicia, metamorphic

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Fig. 19 a A Capelada (Cedeira, A Coruña). b Montes da Lagoa (Narón, A Coruña). Source POL (Xunta de Galicia). c Monte Louro (Muros, A Coruña). Source POL (Xunta de Galicia). d Punta Frouxeira (Valdoviño. A Coruña). e Augasantas Beach. (Ribadeo, Lugo). Source POL (Xunta de Galicia)

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Fig. 20 a Cies Islands (Vigo, Pontevedra). b Picón (Ortigueira, A Coruña). c Espasante (Ortigueira, A Coruña)

rocks are associated with profiles with variable slopes and in which landslides gain importance (Fig. 20c).

3.4.2

Shore Platforms

Shore platforms are plains, generally narrow, located in the intertidal zone. They are not very abundant and are found both inside the estuaries and outside them (PérezAlberti and Gómez-Pazo 2019), both in high and low energy sectors, being modeled on metamorphic rocks (Fig. 21a), or on granitic rocks (Fig. 21b). In some places, the platforms are barely 5 m wide. They are sub-horizontal and with a low uniformity,

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Fig. 21 a Caamaño (Porto do Son, A Coruña). b Oia (Pontevedra)

presenting even projections of about 1 m. In other cases, there are better developed platforms, up to 50–100 m wide, with a notable uniformity and an approximate slope between 0° and 2°, and they are covered by debris that form deposits of variable amplitude and strength, composed of materials with diameters ranging from those of gravels to metric blocks. Sometimes abrasion processes are responsible for its modeling, but there is evidence that in many cases weathering processes and, consequently, differential dissection, are responsible for its construction (Gómez-Pazo et al. 2021).

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Boulder Beaches

The existing block beaches on the Atlantic coast are relatively abundant sectors in which large accumulations of blocks dominate. They are called “coidos” in Galician, and constitute one of the most unique elements of the Galician coastline, both for its configuration and its dynamics (Pérez-Alberti et al. 2012; Pérez-Alberti and Trenhaile 2015a, b; Gómez-Pazo et al. 2021). The variety of typologies of block beaches is high (Pérez-Alberti and LópezBedoya 2004; Pérez-Alberti and Gómez-Pazo 2019). Within them, there are those that are the result of washing the granite alteration layer, those resulting from the dismantling of the granite platforms, or those resulting from the remobilization of the deposits generated by mass movements that have occurred on the façade, or those resulting from cliffs or from the destruction of ancient deposits, mostly of periglacial or snowy origin. In the case of the former, an initial phase of sub-surface alteration of the rock has been followed by another phase of washing by marine or continental waters. The alteration of the granite has been marked by the already mentioned existence of an extensive network of fractures that has directed the advance of the alteration and by the genetic predisposition of some types of granites (in the case of granodiorites) to decompose in a spheroidal manner. In any case, the presence of unaltered rock cores embedded in the alterite has favored the accumulation of blocks of heterometric size. Good examples of these accumulations are found at the mouth of the Ferrol and O Barqueiro estuaries (A Coruña) or at Punta do Couso, in Corrubedo (A Coruña) (Fig. 22). Block accumulations have different shapes. Longitudinal block beaches are located on the upper level of narrow and irregular coastal platforms, about 50–75 m wide, depending on where they extend longitudinally, in sectors such as the one between Cabo Silleiro and A Guarda (Fig. 23a). The double-pointed blocky beaches in the coastal sector that extends between Cabo Vilán and Camelle (Camariñas, A Coruña) (Fig. 23b). Arched boulder beaches appear in some sectors, such as in Laxe Brava (Ribeira, A Coruña) (Fig. 23c). There are corridor block beaches that are emplaced in corridors, between 30 and 50 m wide and 70–80 m long, opened from the wide network of fractures that follow an N–S direction (Fig. 23d), and are very similar to the previous type, in terms of the size of the clasts and their distribution from the low tide level. However, they are characterized by presenting a mushroom shape, with a lower level framed by rocky walls and an upper level on the coastal plain (Pérez-Alberti et al. 2012). The simple point boulder beaches are rare, standing out in Punta Corrubedo (Ribeira, A Coruña) (Fig. 23e). The beach reaches 40 m wide and 5 m high. It is made up of well-rounded and overlapping edges that usually have lengths of less than 1 m on their longest axis.

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Fig. 22 Punta do Couso (Ribeira, A Coruña)

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Fig. 23 a Portecelo (O Rosal, Pontevedra). b O Trece (Camariñas, A Coruña). Source POL (Xunta de Galicia). c Laxe Brava (Ribeira, A Coruña). d O Trece (Camariñas, A Coruña). e Punta Corrubedo (Ribeira, A Coruña). Source POL (Xunta de Galicia)

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381

Sandy Beaches

There are different types of sandy beaches (López-Bedoya and Pérez-Alberti 2006) that, although with similar shapes, have sizes that vary from one place to another. Some examples can be characterized synthetically. For example, the beaches anchored at two points correspond to those sandbanks located in open coastal inlets with sparsely developed points that constitute simple cuts to the intense longitudinal drift that deposits part of its load (Fig. 24a). Those at the bottom of the bay are represented by those sandbanks, generally of intermediate or large dimensions, located at the bottom of bays with sufficient continental development, which present sandy arcs with differentiated dynamics from the nearby coast. This is the case of those of Vilarrube or Pantín (Fig. 24b), each with its own dynamic.

Fig. 24 a Soesto (Laxe, A Coruña). Source POL (Xunta de Galicia). b Pantin, Valdoviño (A Coruña). Source POL (Xunta de Galicia). c “Calas” around Cariño (A Coruña). Source POL (Xunta de Galicia)

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Cove beaches (“calas”) are located in small inlets that act as a sediment trap without significant longitudinal circulation. These are small sandbanks, enclosed between elongated rocky promontories. There are good examples in the area of Cariño (A Coruña) (Fig. 24c). The spits beaches are anchored at one end to the mainland and stretch out in the opposite direction, built by sedimentary drift, and their development is highly conditioned by fluvial discharges. Those of Ladeira, in Baiona (Fig. 25a), or that Miño beach (Fig. 25b) or Barra, at the mouth of the Anllóns river may be very good examples. There are those that draw a double arrow and are anchored to a projection in their central sector. Located at the mouths of two rivers with a similar discharge capacity and a characteristic marine action, they develop two growths in an opposite direction. They are not very abundant because they develop only in very specific environments. They appear in ramified estuaries in large sections, as is the case of the Morouzos de Ortigueira (Fig. 25c) or Vilarrube (in Valdoviño) (Fig. 25d). Beaches on a rocky platform are those whose sedimentary deposition and plan shape depend to a large extent on the existence of a lower platform that acts as a sediment trap and conditions its morpho-dynamics. They can be observed in the stretch of coast that stretches between Monte Louro and Carnota, for example in Lariño (Fig. 26a).

Fig. 25 a Ladeira beach (Baiona, Pontevedra). Source POL (Xunta de Galicia). b Miño beach (A Coruña). Source POL (Xunta de Galicia). c Morouzos beach (Ortigueira, A Coruña). Source POL (Xunta de Galicia). d Vilarrube beach (Valdoviño, A Cofruña). Source POL (Xunta de Galicia)

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Fig. 26 a Lariño (Carnota, A Coruña). Source POL (Xunta de Galicia). b Esteiro (Masñón, A Coruña). Source POL (Xunta de Galicia). c Meirás (Valdoviño, A Coruña). Source POL (Xunta de Galicia)

The beaches at the mouth are in the final course of small valleys carved by rivers of little entity. The Esteiro beach, south of Cape Estaca de Bares (Fig. 26b) or Praia do Río (Meiras, Valdoviño, A Coruña) (Fig. 26c) are the best examples. Tombolo beaches evolve from the loss of wave energy by refraction in spaces between an islet -which acts as an anisotropic obstacle- and the continental coastline or another islet. But the sedimentary forms resulting from the deformation of a sandbank due to the existence of a cliff with a distal prominence that acts as an obstacle to the drift closest to land are also included. Many of these beaches have in the tombolo characteristic a partial attribute of a sector, responding in reality to another morphogenetic typology causing the greatest cumulative volume. The best example is that of A Lanzada (Pontevedra), although due to its size it is difficult to capture with oblique photography, or that of San Cibrao (Lugo) (Fig. 27).

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Fig. 27 Tómbolo of San Cibrao (Lugo). Source POL (Xunta de Galicia)

3.4.5

The Coastal Dune Landscapes

At a general level in Galician dune systems (Pérez-Alberti and Vázquez-Paz 2011) there are different geo-forms: embryonic or incipient dunes, sand tails, linguiform, coastal dunes, pyramidal dunes, parabolic dunes, barjanoid dunes, rising or rampant, etc., which build landscapes of great value. The embryonic or incipient dunes (Fig. 28a) show little development. They have formed on the high beach from berms or from material deposited in front of dune micro-cliffs. They are present in practically all sandbanks. Sand shadows are elongated shapes, accumulated to the lee of vegetation obstacles (Fig. 28b). They have been generated in places where there is a flat topography and vegetation. They usually present little development. The best examples have been observed in the Caldebarcos sandbank (Carnota, A Coruña), in A Frouxeira (Valdoviño, A Coruña), and in Monte Branco (Ponteceso). The linguiform dunes are elongated shapes with decametric dimensions in length and metric in width and height. They draw a longitudinal geometry and are behind the dune cord. They have been mapped in the Santa Mariña sector, after the rising dunes of O Trece (Camariñas), in Caldebarcos (Carnota) Fig. 28c), and in Covas (Ferrol).

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Fig. 28 a O Trece (Camariñasd, A Coruña). b Caldebarcos (Carnota, A Coruña). c Caldebarcos (Carnota, A Coruña). d Traba (Laxe, A Coruña). Source POL (Xunta de Galicia)

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The dune cords (foredunes) are in contact with the beach. They represent a more advanced stage in dune development. They present a pronounced escarpment on the flank towards the sea and a greater accumulation of sand on the internal side, generally oriented in a SW-NW direction, parallel to the prevailing winds. The best examples are found in Carnota Louro (Muros), Traba (Laxe) (Fig. 28d), Vilarrube (Ferrol), and Baldaio (Carballo), in the province of A Coruña. The so-called pyramidal dunes or vegetated mounds draw sharp profiles and can reach 2–4 m in height. They are formed when encountering an obstacle, generally plants. These are elementary forms that can favor a later accumulation stage or form on other dunes. They have been mapped in different places, highlighting the dune system of Corrubedo (Ribeira), Caldebarcos (Carnota), Traba (Laxe) or Cobas (Ferrol), in the province of A Coruña. Parabolic dunes appear associated with inlets in which a large amount of sand has accumulated. Semicircular in shape and with a concave profile, they are usually active in many places on the Galician coast. Trampling becomes the main factor of alteration of this type of dunes, in which landslides and detachments of large masses of sand are frequent, favored by the slope and the scarce vegetation cover, which is restricted to the dune crest. The dune field of Lourido (Muxía) is totally inactive, and those of A Frouxeira (Valdoviño) and O Trece (Camariñas) are active (Fig. 29a), in A Coruña. In many cases it is difficult to decide when they are classic parabolic dunes, with their fronts open towards the sea, or when they are elongated deflation troughs. Different landscapes generate rampant or rising dunes (climbing dunes) that are relatively abundant and are characterized by ascending the slopes. They usually present steep slopes and, occasionally, overflow the crest, giving rise to linguiform dunes in the lee. This is the case of the Ensenada de O Trece (Camariñas, A Coruña) (Fig. 29b) or the Monte Branco (Ponteceso) (Fig. 29c). Another example, on a smaller scale, is found on the southern slope of Monte Siradella (O Grove). Finally, it should be noted that the great dune of Corrubedo (Ribeira, A Coruña), the largest of those existing in Galicia, has been considered as a transversal dune. It is an accumulation that designs an elongated shape from NE to SW, cut by different deflation channels (Fig. 30a and b).

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Fig. 29 a Parabolic dunes in O Trece (Camariñas, A Coruña). Source POL (Xunta de Galicia). b O Trece (Camariñas, A Coruña). Source POL (Xunta de Galicia). c Monte Branco (Ponteceso, A Coruña)

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Fig. 30 a The transversal dune of Corrubedo (Ribeira, A Coruña) around of 1990. b The dune in 2011

References Cunha PP, Pérez-Alberti A (2022) Discussion of the transition of endorheic to exoreic drainage of Cenozoic Basins in Galicia (NW of Iberia), the development of the ancestral transverse drainage to the Atlantic and the later stage of fluvial incision; Gómez-Pazo A, Pérez-Alberti A, Trenhaile A (2021) High resolution mapping and analysis of shore platform morphology in

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Galicia, northwestern Spain. Marine Geol 436:106471. ICG2022-322. https://doi.org/10.5194/ icg2022-322 De Vicente G, Vegas R (2009) Large-scale distributed deformation controlled topography along the western Africa-Eurasia limit: tectonic constraints. Tectonophysics 474(1–2):124–143 Gómez-Pazo A, Pérez-Alberti A, Trenhaile A (2021) Tracking clast mobility using RFID sensors on a boulder beach in Galicia, NW Spain. Geomorphology 373:107514 López Bedoya J, Pérez-Alberti A (2006) Clasificación morfogenética de las playas de arena en Galicia como herramienta para abordar el uso sostenible de los complejos sedimentarios costeros. In: Geomorfología y territorio: actas de la IX Reunión Nacional de Geomorfología, Santiago de Compostela, 13–15 de septiembre de 2006. Universidade de Santiago de Compostela, pp 843–860 Macías-García I, Pérez Alberti A, Martínez Cortizas A, Nieto C, Otero Pérez XL (2007) 11 millones de años de ciclos de biostexia-rexistasia en la cuenca Oligoceno-Mioceno de As Pontes en Galicia. Edafologia 14(1–3):67–98 Migo´n P (2004) Structural control in the evolution of granite landscapes. Acta Universitatis Carolinae Geographica 39-1 Oliva M, Palacios D, Fernández-Fernández JM, Rodríguez-Rodríguez L, García-Ruiz JM, Andrés N, Carrasco RM, Pedraza J, Pérez-Alberti A, Valcárcel Díaz M, Hughes PD (2019) Late quaternary glacial phases in the Iberian Peninsula. Earth-Sci Rev 192:564–600 Pérez Alberti A (2021) El patrimonio glaciar y periglaciar del Geoparque Mundial UNESCO Montañas do Courel (Galicia). Cuaternario y Geomorfología 35(1–2):79–98 Perez Alberti A, Rodriguez Guitian M (1993) Formas y depósitos de macroclastos y manifestaciones actuales de periglaciarismo en las sierras septentrionales y orientales de Galicia. In: La evolución del paisaje en las montañas del entorno de los caminos jacobeos, 01/1993. Xunta de Galicia, pp 91–105. ISBN: 84-453-0885-8 Pérez Alberti A, Rodríguez Guitián M, Valcárcel Díaz M (1993) Las formas y depósitos glaciares en la sierras orientales y septentrionales de Galicia (NW Península Ibérica). La evolución del paisaje en las montañas del entorno de los caminos jacobeos, Xunta de Galicia 01/1993, pp 61–90. ISBN: 84-453-0885-8 Pérez Alberti A (1978) Los depósitos sedimentarios del valle del Miño dentro de la Comarca del Ribeiro. Miscelanea de Geografía de Galicia en homenaje a Otero Pedrayo. Universidad de Santiago de Compostela, pp 253–272 Pérez Alberti A (2018) Xeomorfoloxía das Montañas do Courel. Edita Grupo de Desenvolvemento Rural Ribeira Sacra-Courel Pérez Alberti A (2020) El glaciarismo de baja altitud en la Serra da Capelada en el contexto del Noroeste de la península Ibérica. In: Ruís-Fernández J et al (eds) Socio-ecología, arqueología y geohistoria de los paisajes de montaña ibéricos: una mirada multidisciplinar. Servicio de Publicaciones de la Universidad de Oviedo. In press Pérez-Alberti A (2022) A paisaxe protexida dos Penedos de Pasarela e Traba (Costa da Morte, Galicia). Nemus 12:31–47 Pérez-Alberti A, López Bedoya J (2004) Caracterización de las playas de Cantos y bloques (coídos) en el noroeste de la Península Ibérica. In Procesos geomorfológicos y evolución costera: actas de la II Reunión de Geomorfología Litoral, Santiago de Compostela, junio de 2003 (pp 371–400). Universidade de Santiago de Compostela Pérez-Alberti A, Blanco-Chao R (2005) Controles y balances geomorfológicos en costas rocosas de macizos antiguos. Geomorfología litoral i Quaternari. Publicaciones de la Universitat de Valencia, El ejemplo de Galicia (Noroeste de la Península Ibérica) Pérez-Alberti A, Trenhaile AS (2015a) An initial evaluation of drone-based monitoring of boulder beaches in Galicia, north-western Spain. Earth Surf Proc Land 40(1):105–111 Pérez-Alberti A, Trenhaile AS (2015b) Clast mobility within boulder beaches over two winters in Galicia, northwestern Spain. Geomorphology 248:411–426

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Pérez-Alberti A, Trenhaile AS, Pires A, López-Bedoya J, Chaminé HI, Gomes A (2012) The effect of boulders on shore platform development and morphology in Galicia, north west Spain. Cont Shelf Res 48:122–137 Pérez-Alberti A, Gomes A, Trenhaile A, Oliveira M, Horacio J (2013) Correlating river terrace remnants using an Equotip hardness tester: an example from the Miño River, northwestern Iberian Peninsula. Geomorphology 192:59–70 Pérez-Alberti A, Sanchiz M, Rodríguez F, Pérez M (2014) Metodología y clasificación de tipos de paisaje en Galicia. Revista De Geografia e Ordenamento Do Território 1(6):259–282 Pérez-Alberti A, Gómez-Pazo A (2019) The rocky coasts of Northwest Spain. In: The Spanish coastal systems. Springer, Cham, pp 27–47 Pérez-Alberti A, Valcarcel M (2022) The glaciers in Eastern Galicia. In: Iberia, land of glaciers. Elsevier, pp 375–395 Pérez-Alberti A, Vázquez Paz MC (2011) Caracterización y dinámica de sistemas dunares costeros de Galicia. In: Las dunas en España. Sociedad Española de Geomorfología, pp 161–185 POL Galicia (2010) Xunta de Galicia. http://webpol.xunta.gal/web/index.php/introduccion/gl Valcarcel M, Pérez-Alberti A (2022) The glaciers in Western Galicia. In: Iberia, land of glaciers. Elsevier, pp 353–373 Viveen W, Schoorl JM, Veldkamp A, Van Balen RT, Desprat S, Vidal-Romani JR (2013) Reconstructing the interacting effects of base level, climate, and tectonic uplift in the lower Miño River terrace record: a gradient modelling evaluation. Geomorphology 186:96–118. http://web pol.xunta.gal/web/index.php/descargables

‘The Cultural Landscape of Galicia: A History of the Inappropriable’ A Scientific Story of Galicia’s Landscapes Federico López-Silvestre

Abstract In this chapter, our aim is to present a concise history of the landscape in Galician culture. To do this, we begin by defining the idea of ‘landscape’ in relation to the philosophical notion of the ‘inappropriable’ in order to clearly distinguish it from the concepts of ‘environment’, ‘country’ and ‘pagus’. Then, we set out to determine when the set of practices that produced what is known as a ‘landscape society’ emerged in Galicia. These practices include paintings of stand-alone landscapes, poems and anacreontics about the environment, ornamental gardens and the Galician word paisaxe. Finally, we draw on and question our own research as we ponder the history of the landscape in Galicia that has yet to be written; a history of what could be referred to as the ‘ante-landscape’. Keywords Cultural landscapes · Paisaxe · Antepaisaxe · Galician landscapes · Art · Literature · Gardens · Environment · Pagus · Country · Property · Inappropriable

1 Introduction: Why Insist on a History of the Inappropiable? 1.1 Landscape is Not Only Environment Ten or fifteen years ago, I met a best-selling German author by chance in Pamplona. After telling her how fascinated I was by good writers’ ability to hook readers in just a few sentences, we chatted for several hours. I asked her about the ins and outs of her profession and she told me that, despite her youth, two of her novels had already been translated into six or seven languages (including Japanese) and that she was in the middle of writing a new book. She was travelling with a Galician guide, who she had hired for three weeks to take her to a series of spots along the Camino F. López-Silvestre (B) Universidade de Santiago de Compostela, Santiago de Compostela, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_20

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de Santiago (Way of Saint James) from the Pyrenees to Santiago and Finisterre, so that she could make notes for her forthcoming novel. Of course, I asked her what the book was about. She told me the story of a young woman, who, dressed as a pilgrim, had travelled the Camino de Santiago in the Middle Ages to carry out a secret assignment for the Templars at a time when they had ceased to be considered upstanding protectors of the holy places and Christian faith (1119–1291) and were accused of heresy by Clement V and tortured by Philip the Handsome, King of France, in 1307. This topic was very relevant because there were several Templar establishments along the Camino de Santiago in both France and Spain (especially in Navarre and Castile and León), which had in many cases been built to defend border regions and made up part of the Camino de Santiago’s Romanesque heritage. Continuing our conversation, I asked her about the main character in the novel and she told me that the notes she was taking during her travels would become the fourteenth-century pilgrim’s impressions of the journey. She mentioned the Navarran people’s character and Spain’s landscapes, explaining that she was recording all her observations in notebooks for later use. I told her that, like Dilthey, I found empathy to be an excellent starting point for literature and the history of art so her method seemed exemplary to me. As a specialist in landscape matters, I could not help but ask her the question that is eternally present in my thoughts. Wouldn’t pilgrims in the Middle Ages have been too hungry and thirsty to see what we see when we talk about landscapes? This question would be of little importance had the editors of this book not sought to make a distinction between the book title ‘Environment in Galicia’ and the title of the fifth section, ‘Geomorphology and Landscapes’, in which this chapter appears. This distinction is far from trivial and prompts us to reflect on a series of considerations that underpin the research we have been carrying out since we began to read, write and work with experts such as Augustin Berque, Raffaele Milani, Javier Maderuelo and Joan Nogué a quarter of a century ago. In short, what do we actually mean when we talk about ‘landscapes’? The first question is not whether what pilgrims to Santiago de Compostela saw in the Middle Ages was landscape, but whether the expanding galaxy that began to blossom 300,000 years after the Big Bang was landscape. Some scholars confuse ‘space’, ‘territory’ and ‘landscape’, leading them to the conclusion that the ‘landscape’ is simply the ‘environment’ and that everything that surrounds us is therefore ‘landscape’. As a result, they are forced to accept that whatever constituted the galaxy after the Big Bang was landscape. To address this, we must begin by differentiating between the two concepts (López-Silvestre 2009b). No matter how vehemently some scholars believe otherwise—on that subject, the criticisms made by Martínez de Pisón (2009) have always seemed unfair to us—, insisting on the conceptual difference between ‘landscape’ and ‘environment’ is not the same as insisting that ‘landscape’ relates solely to questions of ‘aestheticism’; rather, it reminds us that the concept cannot be defined without perception by a subject (human or otherwise). In other words, what emerges when we talk about ‘landscape’ is not a matter solely of art or of aesthetic ideas, but, above all, a concern

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with what Kant refers to in Critique of Pure Reason as a “transcendental aesthetic” or what Berque describes as “the institution of reality” (Berque 2009). It is clear, then, that ‘landscape’ is neither a thing-in-itself—ding an sich—nor a purportedly objective ‘environment’ that is separate from the observer; instead, the etymology of the word hints at a gaze [-scape] or manner of perceiving. As we have noted elsewhere (López Silvestre 2009c, 2009d, 2010, 2011), a dramatic, complex environment is undoubtedly required to draw the observer’s attention and allow us to see ‘landscape’. The concept always refers to the relationship between this abundance and those who experience, contemplate and synthesise it. A certain “disjunctive synthesis”—not solely due to the presence of a particular object or a specific subjective image—makes it appropriate to continue to define the landscape as an expanse of land that takes on unity and autonomy as a result of a gaze that appreciates it in and of itself and, as Roger argued years ago, to distinguish between ‘landscape’ and ‘environment’ (Roger 1996).

1.2 Paisaxe is Not Only Country That said, the question of the type of human gaze that must be taken into consideration when we ponder the idea of ‘landscape’ remains unanswered. Could pilgrims to Santiago in the Middle Ages appreciate the ‘landscape’ itself? Did Galicians at that time think of the ‘landscape’ in the same way as we do? These days, the notions of ‘nature’ and ‘landscape’ are often confused and it has become fashionable to view both farmland and ‘native land’ as synonymous with ‘landscape’, or even as a more inclusive, democratic type of landscape. This confusion originated in the English-speaking world and the Germanic languages for obvious reasons. The term Landschaft emerged in High German in the eighth century, before it appeared in the English language; for a long time, it was translated into Latin as patria, provincia or regio, or in other words, as ‘country’. Echoing such interesting scholars as Jackson (2010), it is this ‘landscape’ or ‘country’ constructed over centuries by human labour and toil that should be studied when we research ‘landscape’. It is important to divert attention from what Clark (1971/1949) studied in Landscape into Art to explore a broader set of works and affects and to examine subaltern spaces from a ‘landscape infrahistory’ perspective that encompasses the working class and disadvantaged sectors of the population. Despite the benefits of such a shift and the central focus placed upon it in Galicia by Otero-Pedrayo (1928) and Villares (1982), we maintain that this approach is not without risks. No matter what Castelao thought (Image 1). The fact that rural dwellers worked and cherished their fields and farmland and continued to recall the land they had left behind with affection or longing after or even before they had been forced to emigrate does not imply that ‘landscape’ should be reduced to crop fields and the motherland.

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Image 1 Castelao: The emigrant, 1916, oil on canvas, 200 × 410 cm. Source Colección AFundación. Inv. 252 (Vigo)

In this regard, we know that ‘pagus’, ‘country’ and ‘landscape’ were separate concepts in the Romance languages at least and it is important to bear this in mind as we seek to demonstrate the ‘inappropriable’ dimension of the ‘landscape’. (a) Of these three notions, the earliest and simplest was ‘pago’, which is associated with farmland in Galicia. The term ‘pago’ is believed to have emerged in the Middle Ages from the Latin pagus and to have been employed in Old Spanish to refer to properties used for farming, which were created to meet demand and had a use and exchange value—they had to be paid for (pagado) (Pitte 2003, 14). The notion spread so widely that, even today, the best vineyards in Spain are known as pagos (Calvo-Serraller 1993). In short, what is relevant here is the productivity of the land, its capacity to supply food and the economic potential apparent in some valleys long before the emergence of physiocratic thought. This cultivated land first had to be forged by generations and generations of farming endeavours that transformed the world. There can be no doubt as to the value of these efforts, which, as Otero-Pedrayo and Colmeiro demonstrates, are driven by feelings and emotions (Image 2). But is landscape only this bond with the land? (b) Etymologically speaking, the term pago appears to have given rise to the Spanish word país or country. This notion emerged in response to the shift from a narrow, economic, purely productive perspective to a pre-political and political understanding. Like ‘motherland’, ‘homeland’ and Landschaft in Germanic languages, país linked kinship communities to pagos and communal land. This was a distinct, apparently loftier concept than the earlier pago, which, according to Olwig, serves as a cultural “mirror” of a particular “system of governance” (Olwig 2002, 9–20). However, as scholars of Nazi geography and landscape design have shown, some extremely primal elements can also be perceived within the concept with the emphasis on Heimat: the sublimated instincts in the

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Image 2 Manuel Colmeiro: Collecting leaves, oil on canvas, 60 × 74 cm. Source Museo de Pontevedra (Pontevedra)

“basic teleonomic programme” present in many animal species drive us to mark our territory in order to control the supply of nutrients and areas for reproduction and protecting descendants (Gröning 1997). When we leave the land we grew up in, the land where we toiled, we all feel a sense of nostalgia. But once again, can landscape be reduced to these sentiments? (c) Finally, the eternally ambiguous community/immunity notion of ‘country’, ‘motherland’ or ‘homeland’ is believed to have given rise to the concept of ‘landscape’. In the Romance languages, the term ‘landscape’ (paysage) initially emerged in French from the word pays and was used among artists in the sixteenth century (Franceschi 1997). It referred to an expanse of land viewed from a specific point that was bounded not by utilitarian, economic or political borders but solely by phenomenological or perceptual limits, an appealing ensemble appreciated for reasons that went beyond nutritional, economic, political or family interests. It is likely that the Anglo-Germanic notion of Landschaft/landscape was used in the sense of ‘pagus’ and ‘country’ before taking on any other meaning. However, when the word ‘landscape’ came into use in the Romance languages in the sixteenth century, it referred above all to an expanse of rural, urban or wild land appreciated in and of itself. In other words, a mountain, plot, valley or neighbourhood appreciated not because they inspired longing or allowed extraction of some resource but because they triggered a sense of pleasure or displeasure that went beyond any ‘thing-in-itself’ or ‘environment’, beyond any immediate purpose such as food, protection or reproduction and

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beyond any nostalgia for the comfort of the familiar and known—in short, beyond any morriña or saudade. What value or purpose lies in continuing to make this argument after twenty five years in the light of emerging historiographic trends? The answer, in our view, has always been obvious. Firstly, should we forget the distinction between ‘landscape’ and ‘pagus’ entirely, we would be giving our governments and corporations carte blanche to designate all our wild and artistic reserves and all our cultural and natural areas as exploitable landscapes. Secondly, should we forget the distinction between ‘landscape’ and ‘country’ or ‘motherland’, we would be incapable of grasping the difference between the landscape and heritage, leaving us ill-equipped to appreciate landscapes belonging to the Other, transforming the great Humboldt into a strange, misunderstood creature and making us all a little more parochial than before. There have been periods in history when human beings have only been capable of understanding that our destiny is never a place and of appreciating our environment on the basis of elements that are neither productive nor familial at very specific times. In neo-Marxist historiography, which we respect because of its consideration for the poor and displaced, it is argued that disinterested appreciation of the ‘landscape’ was the preserve of monks, nobles and the bourgeoisie, whose appreciation rarely extended beyond their properties, which they ordered their artists to paint (Berger 2000). Meanwhile, postcolonial historiography, which we value for its commitment to hearing the voice of the Other, maintains that, even in cases like that of Humboldt, the gaze on the ‘landscape’ exported around the world in the nineteenth century merely endorsed colonial expansion by cloaking it in art and science (Mitchell 2002; Coetzee 2013). Like Dürer and Bruegel in Italy, Petrarch on Mont Ventoux neither coveted, inherited nor owned anything that he saw yet he was fascinated by it nonetheless, an emotion that is deeply human and that we can all understand (López-Silvestre 2021). Echoing Otero-Pedrayo, we believe that exploring every phase of the landscape (planetary, vital and historic) enriches our understanding and study of it (OteroPedrayo 1955, 11–59). Consideration of the geomorphological, edaphological and botanical dimensions of the ‘landscape’ (its ‘environment’ dimension) can help us to situate the ‘pre-human territorial structures’ that shaped the type of gaze on the ‘landscape’ that emerged. By focusing on the ‘structure of property’ and the farms and ‘pagos’ or on love for the ‘country’ and motherland, we can explore more of the social values that underpin the history and theory of the landscape, as reflecting the ideas present in these historiographic trends entails taking the feelings of the Third Estate into consideration where traditional European histories of art and literature did not. However, alongside this consideration of the ‘environment’ and basic needs, it is important to note that only an idea of the landscape capable of transcending appreciation for merely nutritional, economic, family or political reasons allowed us to learn to value: (a) the glacial wastelands that provide no sustenance; (b) the distant, foreign lands that are just as immense and fascinating despite belonging to others, and (c) the Third Landscape of tiny plants and animalcules deemed useless and unproductive, which comprise and enrich the world as landscape just as much

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as far-reaching deserts. Although it may appear somewhat elitist and classist, this is why the deteleologised, deterritorialised notion of an inappropriable landscape is more inclusive and less patriotic and anthropocentric than the concepts proposed by certain contemporary currents in Landscape Studies. What makes us human is our ability to sense the imprint of the inappropriable, even in our own bodies (Lévinas 1999), and, if we are capable of discovering something unfamiliar even in our bodies’ frequent losses of control, what might we discover in the complex world that surrounds us every day (Agamben 2017, 173–178)? By portraying it as a property either inherited or at our service, the living, evolving landscape is essentialised and made comforting and manageable. In doing so, it becomes detached from the infinite, inappropriable processes of which we sense only part and about which we constantly seek to know more, precisely because we have clumsily condensed them to fit our ideas and gaze. In short, for human beings, there is always something beyond property and ownership and beyond hunger, farms and inherited homelands. Were this not the case, we would be incapable of appreciating the glorious spectacle of the sun setting on foreign ‘pagos’ and ‘countries’ or the appeal of deserts and wastelands and high mountains (Image 3). As Otero-Pedrayo acknowledged, “a single path through a wasteland imprints history upon it. The ruins of a monastery or ‘stately home’ enhance the perspective” (Otero-Pedrayo 1945, 174). Taking this idea to the extreme, it could be argued that even the idea of Galicia was too vast and of Galicians too strange and arcane, as, to give just one example, people from inland Ourense would have been incapable of appreciating Atlantic landscapes of Portugal (Image 4).

1.3 A Method for Studying the History of Landscape The comments made in the previous sections hint at the type of history of the landscape in Galicia that we have always been keen to explore. Our hesitations surrounding the excessively short list of practices that may be considered ‘landscape practices’ and the developmental, progressive approach that makes a clear distinction between the time of the ‘pagus’, the ‘country’ and the ‘landscape’—indeed, we no longer consider the theory that appreciation of the landscape ‘appeared’ thousands of years after humankind to be valid—will be presented in the conclusion. Nevertheless, we remain convinced of the need to show that the idea of ‘landscape’ overlaps with but must be distinguished from mere ‘environment’ and from ‘pagus’ and ‘country’. Therefore, we believe that landscape historians must move beyond topics such as the land itself, the structure of property systems or nostalgia for a beloved country and dedicate their attention to studying practices that flourish only in certain eras and places and that elude a proprietary understanding of the land. With a focus on Europe, von Humboldt (2005, I, 17 & II, 3), Burckhardt (1941, 186), Ritter (1986, 125–158), Berque (1995), Roger (2007) and Maderuelo (2005) draw on multiple sources to confirm that landscape practices did not become apparent

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Image 3 Serafín Avendaño: Procession, oil on canvas, 29 × 20 cm. Source Fundación María José Jové (A Coruña)

until the Renaissance. Meanwhile, Milani (2007) argues that there are many signs of the existence of a gaze capable of appreciating the poetic and pictorial value of the landscape even in ancient times. The presence of this type of gaze in the Middle Ages in Europe is less certain, but Baridon’s (2006) book Naissance et renaissance du paysage shows clear evidence of the development of the landscape in thirteenth and fourteenth-century Italy. In any case, our focus here is on Antiquity and the Middle Ages in Galicia rather than in Italy. What do we find here? Between 1996 and 2005, we studied sources with the potential to show the emergence of a mature cultural ‘landscape’ in Galicia; a ‘landscape’ that differs from ‘country’ and ‘pagus’ according to established definitions. During this nine-year period, we dispensed with sources such as those mentioned in the conclusion. We adopted Berque’s approach, whereby any discussion of the maturity of a ‘landscape society’ requires the concurrent presence of a word meaning ‘landscape’, ornamental gardens, poems praising the beauty of the surroundings and pictures depicting it (Berque 1995; Donadieu 2006). This led us to the conclusion that there is no evidence of the development of a ‘landscape society’ in Galicia prior to the eighteenth century (López-Silvestre 2005, 2008).

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Image 4 Castelao: On the banks of the Miño river…—And those on the other side of the river are more foreign than those in Madrid? [«Na veira do Miño…—E os da banda d´alá son máis estranxeiros que os de Madrí?»], from Álbum Nós, 1916–1919, gouache on paper. Source Museo de Pontevedra (Pontevedra)

2 A Concise History of the Landscape in Galicia 2.1 The Word Paisaxe in Galician As noted above, the term ‘paisaje’ did not exist in Spanish in the Middle Ages. It appeared in the sixteenth century as a derivative of the French word ‘paysage’ and was applied initially to painting. In the Latin countries, ‘landscape’ referred to a pictorial representation of a particular, well-defined geographical area before it came to take on any other meaning. As a result of its origin and its early use in artists’ studios, the term ‘landscape’ was primarily aesthetic in nature. This meaning persisted until the early twentieth century. However, in the eighteenth and nineteenth centuries, travellers, geographers and writers had already begun to bring new meaning to the term. Initially used to refer to an accessible pictorial representation of the ‘country’, ‘landscape’ became a kind of synonym for that word. However, the eighteenth-century Diccionario de

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Autoridades indicates that, even in this case, it was used to denote a ‘pleasant place’ (pays ameno). In subsequent decades, from eighteenth-century engineers in Ferrol to OteroPedrayo, the territory known as ‘landscape’ retained a special connotation and a value that was both gnoseological and aesthetic; it is no coincidence that the first person to speak of ‘paisaxe’ in Galician was a poet, Rosalía de Castro, in the nineteenth century (Castro 1863; López-Silvestre 2005, 492; López-Silvestre 2007; López-Sández 2008).

2.2 A Medieval ‘Landscape’? As Peter Burke observed some years ago, periegetic or travel literature constitutes one of the best sources available to historians of tastes and attitudes. There is no need to read Marco Polo to realise that travellers receive such an overwhelming amount of new information during a journey through distant lands that they can do little more than write about what they know or what particularly catches their attention. More than one hundred historical texts written by travellers about the Camino de Santiago have been preserved to this day. What did pilgrims report when travelling along the Camino in the Middle Ages? Although a certain ‘feeling for nature’ has been identified in some of the pilgrims’ texts, their use of the epithet pulcher or the expression malariis obtimis almost always related to places of peace and nourishment, such as establishments providing shelter for pilgrims (Deluz 1979). Generally speaking, the only spot worthy of great praise tended to be the peaceful, cosy monastic garden that offered a refuge from the very real dangers facing travellers on the Camino. The most well-known text about the pilgrimage to Santiago, Book V or ‘Liber Peregrinationis’ from the Codex Calixtinus compiled by Aymeric Picaud in around 1140, is similarly restrained when it comes to the landscape. Besides references to the fertility or barrenness of some lands and their people—Galicia is reported to be extremely fertile, while Palas is said to be a region of whores—, the only landscape extolled in the book is that of Compostela. The city of Santiago is described in unambiguously artistic and aesthetic terms; this was most likely because the ‘Book of Pilgrimages’ was commissioned by Archbishop Gelmírez and the writer was expected to portray his work in a flattering light. For example, the text notes that the cathedral was incredibly beautiful and that Gelmírez: “Built houses arranged prettily around it, in the midst of which [there was] a very lovely, skilfully painted church” (Picaud 1989; López-Silvestre 2005, 37). Moving away from this urban ‘paradise’, the texts produced in the twelfth and fourteenth centuries made only very rare references to the wooded, untouched valleys that modern-day observers would consider idyllic, the rough seas and rugged coasts, the mountain peaks, the Castilian plateau and the cliffs. As for the images used, depictions of the passing seasons on church porticoes have been widely studied and are highly significant in terms of the symbolism associated with the exploitation of the ‘pagos’ (Castiñeiras 1996). The miniatures of the Cantigas de Santa María

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by Alfonso X the Wise, which relate in some cases to pilgrims and the pilgrimage along the Camino, have also been analysed. However, these images never depict pure landscapes that are appreciated in and of themselves; instead, they show landscapes that are contingent upon or subordinate to human or divine stories. One example is Cantiga 49 in Codex T.I.1 at the Monastery of San Lorenzo de El Escorial (Image 5), which narrates the story of several pilgrims who got lost and were shown the way by an apparition of the Virgin Mary (Filgueira-Valverde 1979).

Image 5 Cantiga n. 49. Cantigas de Santa María, attributed to Alfonso X el Sabio (1250–1280). Source San Lorenzo del Escorial (El Escorial)

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Although the quality of these miniatures makes them rather exceptional for the era, the landscape is present but is always in the background and subordinate to the story being told rather than depicted independently. The case of some of the Cantigas do Mar appears to differ: although there are no images or miniatures accompanying them, they contain references to the landscape that we will analyse in the conclusion to this chapter.

2.3 Licenciado Molina and Descriptions of the Land and Landscape in the Modern Age In the Modern Age, descriptions of the land were mostly utilitarian in nature. This is no different in the work that may be viewed as the origin of all the texts written in praise of Galicia in the sixteenth, seventeenth and eighteenth centuries: Descripción del Reyno Galizia by Licenciado Molina (López-Silvestre 2008, 44–47), published in 1550. Although Licenciado Molina does not mention the village of Palas, he does refer to other locations on the French Way such as Portomarín. What draws his attention to them? Purely utilitarian concerns. Molina does not describe the beautiful riverbanks around Portomarín, focusing instead on the local practice of farming eels, which would be salted and sold all over Galicia. Similarly, the Ría de Viveiro appeals to him because it is covered in grapevines and offers abundant fish stocks. This was the usual approach in the Modern Age when it came to referring to the land: ‘pagus’ and ‘country’ came first, with the ‘landscape’ only sensed in the distance. Licenciado Molina also mentions Finisterre, a spectacular location on the Costa da Morte billed by modern tourism agencies as the endpoint of the Camino de Santiago, which was visited by a small number of devotees in the sixteenth century. However, rather than describing the sublime marine landscapes on stormy nights, Molina speaks of the “marvellous” crucifix in Finisterra [sic.] and observes that “following a passage away from the point made here by the land: there is no more navigation nor place to stop in the world” (Molina 1949, fo. xxiii). His observations hint at a reverential fear that Alain Corbin describes as leading to centuries of “ante-landscapes” of fear and repulsion, which made way for the sublime “landscapes” we perceive today (Corbin 1988). Meanwhile, no matter how wonderful they might appear, the representations produced by travellers like Baldi were always a rare exception (Image 6) (Vigo et al. 2004). The issue is clear when we consider the available information on local painters. Of the 101 painters cited by Pérez-Costanti in his Diccionario de artistas que florecieron en Galicia durante los siglos XVI y XVII, the vast majority (98) worked for the church or for brotherhoods or nobles seeking to invest in religious art. Unless there is hidden information of which we are unaware, this means that almost all the paintings produced in Galicia at that time were religious in nature and featured neither landscapes nor still lifes (Pérez-Costanti 1988).

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Image 6 Pier Maria Baldi: Santiago de Compostela, from Il viaggio a Compostela di Cosimo III de Medici (1668–1669). Source Biblioteca Medicea Laurenziana (Florencia)

2.4 The Development of an Empiricist Gaze and a ‘Landscape Society’ in Galicia Although not many sources are available to prove this theory, it is entirely possible that our human condition brings with it an innate ability to be enraptured by the night sky or a breathtaking landscape. However, this is an entirely separate debate from the development of a ‘landscape society’. In order for such a society to emerge, not only must an individual cease to be hungry and focus on the inappropriable properties of everything that surrounds them but there must also be others like them who share a series of impressions and values that prompt them to take an interest in discussing and writing about all kinds of landscapes—including barren landscapes— , recording their contemplative ecstasy in pictorial representations and even nurturing this ecstasy through gardens and architecture (Berque 1995; Roger 2007; Maderuelo 2005; Donadieu 2006). In Galicia, this society did not develop until an audience with sufficient interest in reading more nuanced verses than those focusing on ‘payses’ and ‘pagos’ began to emerge at the turn of the eighteenth century. This shift in sensibilities can be observed in Galicia between 1724 and 1845. Early indications include Governor General of the Kingdom of Galicia Rodrigo Álvarez Caballero y Llanes’s proposal to plant a pleasant boulevard in La Coruña and Father Feijoo’s celebratory descriptions of the environment in several paragraphs of his work. At that time, a proliferation of gardens, paintings and poems pointed to the growing success of the ‘landscape’ in Galicia. The affluence of noble families with their country estates, the empiricist vision of the engineers at the Arsenal de Ferrol, the illustrated texts by Fathers Sarmientos and Feijoo and the way in which all these factors opened Galicia up to the world played a key role in this regard. It was only after a handful of reformers began to observe their environment more closely that it could begin to be exploited as a source of pleasure and knowledge far-removed from any purpose or property system.

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Generally speaking, the learned took a more ambiguous stance on the matter, which straddled utilitarianism and aesthetics. At the Academia de San Fernando in Madrid, which trained Galicians including Gregorio Ferro (1742–1812), Melchor de Prado (1760ca.–1834), Juan Alonso (1768–1839), and later on, Cancela del Río (1829–1835), vistas and perspectives were drawn and engraved from the outset due, among other aspects, to the pioneering influence of engineers, architects, scientists and mathematicians, who set aside traditional approaches and methods for clearly practical purposes. The art of the landscape was further bolstered by the engraving classes that began on 12 April 1752 and the creation of a Perspective professorship on 3 May 1766. Meanwhile, in Ferrol and La Coruña, landscape classes also began to be taught to allow seafarers of all kinds to plot their course. In Santiago, those who did not train at San Fernando for one reason or another, including Ángel and Luis Piedra (1735–1800; 1769–1818) and Miguel Ferro Caaveiro (1740–1807), attended the Escuela Patriótica de Dibujo run by the RSEAP and the Colegio Militar. The older artists tended to continue to produce very sparse images that displayed mediocre workmanship. Others, like Miguel Ferro (director of the Escuela de Dibujo from 1799, master builder, set designer and “map surveyor”) and Melchor de Prado (who taught at the institution from 1804 to 1809), were able to improve on their work (López-Silvestre 2009a, 257–281). The notes produced by certain prominent travellers are of greater interest. For example, Cornide’s notes and Vicente del Seixo’s travel guide contain one or two sentences describing beautiful, picturesque locations. However, practical concerns such as discovering new places to improve transport and facilitate transit remain the priority here. The Mapa del Pais y del Camino entre La Coruña y Lugo plotted by Carlos Lemaur in 1769 to facilitate construction work on the new Camino, provides clear evidence of these preferences (Image 7) (Nárdiz 1992, 361–400; López-Silvestre 2009a, 78–87). Another example of the slow pace at which what we now refer to as ‘landscape’ emerged can be found by comparing the poetry of the two priests of Fruime. In the eighteenth and nineteenth centuries, the small, humble parish of Fruime had two parish priests who became poets. The eldest of the two continued to refer more to the ‘pagus’ than to any other concept in his verses, while the younger adopted a looser, more landscape-driven gaze. The poetry written in 1778 by the first priest of Fruime, Diego Antonio Cernadas, includes graphic descriptions such as the verses reproduced below: Valley upon valley of placid countryside,/ delicious ham, carefully selected beef,/ tender capons, splendid chicken,/ fine fabrics, and uncomplicated dealings:/ there are hills, but they are all productive,/ wheat from other Kingdoms is not coveted,/ generous wines are found in abundance:/ delicious fish from the river and sea…. (Cernadas 1988, 214–215)

Meanwhile, the texts written by the second priest of Fruime, Antonio Francisco de Castro, most likely between 1805 and 1820, include poems that speak of the natural world in contemporary or romantic terms: From the upright poplar/ To the smallest bush and weakest herb:/ From the proud oak and tall pine/ To the humble willow: preserved/ In my memory the pompous alder,/ And the

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Image 7 Carlos Lemaur: Detail from “Mapa del Pais y del Camino proyectado y construido entre La Coruña y Lugo”, 26 June 1769, pen and watercolor. Source Biblioteca Virtual de Defensa [Ar.E-T.3-C.1–12] (Madrid)

crawling restharrow:/ The broom and gorse standing side-by-side/ And the fragrant, faded laurel./ The stream and the meadow,/ The hill, the cave, the plain,/ It is all imprinted on my mind. (de Castro 1841, 224)

It was not until the time of the second priest of Fruime that Galician artists capable of appreciating not only the coastal landscape but also the ‘sublime’ depths of the woodland bordering the Eume and the Ancares began to emerge. In the visual arts, these artists include Jenaro Pérez Villaamil († 1854) and Ramón Gil-Rey († 1844), who trained under an empiricist, pictorial model focusing on topographic vistas, which were intended to record sites of particular cultural or military value. After training in Santiago, flawed yet precocious artist Ramón Gil-Rey studied drawing and painting at the Academia de San Fernando from 1839 to 1840, just five years before the Landscape professorship was created in 1845 and awarded to Villaamil (López-Silvestre 2009a, 281–327). The text recounting Ramón Gil-Rey and his brother José’s travels around Galicia, which was written in 1842, points to the spread of a more subtle ‘landscape sensibility’ among the Galician cultural elites. José’s notes contain several references to the tranquil beauty of the landscapes and their gardens and incipient praise for the picturesque forests, as well as explicit descriptions of more sublime locations, such as the path through San Xoán da Cova (Image 8) (Díaz-Fierros 2013) and the route followed by the Camino through the Ancares and Cebreiro. “All this”, writes José Gil-Rey, “is a magnificent backdrop to a terrible drama, especially when you consider that it leads to the Ancares mountains shining far away in a beautiful pink hue cast by the sun from its grave to the snow on the pointed peaks. Oh! it is a sublime backdrop that our senses cannot comprehend, a new world that we experience for the first time, an incomprehensible creation that God shows man to make him poor in spirit....” (Gil-Rey 1946, 118–130).

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Image 8 Ramón Gil Rey: Passage of the River Ulla through San Juan da Cova, 1842, lithograph. Source Colección Puertas (Santiago de Compostela)

Villaamil, who trained at the academies in Ferrol, the Colegio Militar in Santiago and the Academia de San Fernando in Madrid, also described the River Eume as it passes through San Xoán de Caaveiro as “sublime” (Image 9) (Arias 1986, 37–48 & 180; Yáñez 2019, 140). Finally, it is in the gardens planted at manor houses for recreation and botanical research, separate from the vegetable gardens, that we encounter the first Galician readers of Linnæus and the most visible progress of the ‘landscape society’ in Galicia (lópez-Silvestre 2009a; Sánchez-García 2010). This new pastime, which quickly became fashionable, was enjoyed in groups (Image 10). The gardens underwent a similar evolution to the new perspectives, vistas and panoramas used in art; it suffices to compare the names of the gardens’ owners prior to the Napoleonic wars with the paintings produced at the great Galician educational institutions or the lists of Galicians who lived and worked at the Court in order to see the links between them. Once Spain had regained its independence and despite the fall from grace of those who had opted for French-style gardens, ornamental gardens continued to proliferate.

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Image 9 Jenaro Pérez Villaamil: San Juan de Caabeiro, 5 September 1849, pencil on paper, 30 × 40 cm. Source Museo de Bellas Artes (A Coruña)

Image 10 Garden at Pazo de Oca. Photo Alberto Valle Souto

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2.5 The Landscape Myth: Success of the Landscape and Reinforcement of Stereotypes The heartfelt verses by Añón, Rosalía de Castro and Pondal (the generation of the 1862 Álbum de la Caridad), the more ingenious texts by Otero-Pedrayo and Risco (the Xeración Nós), the paintings by Dionisio Fierros (1827–1894), Serafín Avendaño (1836–1916), Ovidio Murguía (1871–1900) and Francisco Llorens (1874– 1948) (López-Silvestre 2005, 535 & 587), and, more generally, freer expressions of walking and wild nature did not appear until after the drawings and paintings by Ramón Gil Rey and Pérez Villaamil that sought to depict the sublime beauty of the landscape (Díaz-Fierros 2006). The ‘landscape society’ continued to consolidate in Galicia until 1936, as evidenced by three main factors that go far beyond the subjects explored by a handful of pioneering painters and poets: the gradual increase in the number of painted landscapes at exhibitions in Galicia, the emergence of a market for purchasing landscapes and the rising number of professional and amateur landscape artists. The most vivid indicator of the spread of these sensibilities, values and practices was the gradual increase in the genre’s presence at large group exhibitions. The catalogue for the Agricultural, Industrial and Artistic Exhibition of Galicia held in Santiago in 1858 shows that only around ten works, including several by Serafín Avendaño, depicted landscapes; in other words, approximately 10.1% of the total on display. Meanwhile, at the Galician Art Exhibition in Santiago in 1926, 70.2% of the painters whose work was exhibited presented one or several landscapes (Table 1) (Planellas et al. 1858; Vilanova 1998, 337–350). Table 1 Evolution of the percentage of landscape paintings on display at the largest Galician exhibitions held from 1858 to 1928

Source Compiled by the author using exhibition catalogues

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Not long before, in 1922, Francisco Llorens won first prize at the National Exhibition in Madrid (Image 11) for a beautiful landscape of the Rías Baixas, which belongs to the Museo del Prado collection but is currently held at the Faculty of Geography and History at the University of Santiago de Compostela. Following his success, a journalist asked Llorens if he believed that landscape painting had reached its peak. He replied: “I believe so. Landscapes are the future. Figure paintings have come and gone, history painting no longer exists, genre painting is no longer in vogue… Landscapes are the future” (Luna 1988, 74, citing an interview with Llorens published in Diario Español, Buenos Aires, July 1922). It is no coincidence that the landscape depicted by Llorens in 1922 was the Rías Baixas. Until the last decade of the nineteenth century, the future of the theme of the landscape in Galicia remained uncertain, reflecting the limitless diversity of the world and of Galicia. Yet, in the early twentieth century, tourist clichés and stereotyped regional archetypes emerged and were promoted from all kinds of quarters. Since then, rural and cultural landscapes have prevailed in painting, literature and the media, taking precedence over wild landscapes. In the cultural sphere, views of Santiago, farmland, traditional granaries, palleiros (haystacks), cruceiros (stone crosses) and Romanesque chapels, as well as marine landscapes featuring ports, rias and small boats, especially locations such as O Berbés, were repeated over and over (López-Silvestre 2019). Meanwhile, natural

Image 11 Francisco Llorens: Rías Baixas, 1922. Source Museo del Prado (held at the Faculty of Geography & History at USC)

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landscapes depicted “thick chestnut woods”, “blue mists”, “pine” or “oak” woods and the “wild valley” (López-Silvestre 2005, 653–727; López-Sández 2008). Despite Noriega Varela and Novoneyra’s affirmations, these motifs were encouraged at the expense of the mountains and ermo (wilderness). Despite the early progress made in the Gil Reys’ sublime work, Galicia’s wild massifs were the last of its landscapes to attract attention. For decades, the majority of those depicting the Galician landscape set their sights on coastal and rural areas rather than the high mountains to the east (Paül 2019). Of course, these were clichés. Cultivating them further, Unamuno contrasted the feminine picturesqueness of the Galician landscape with the sublime masculinity of the Castilian plateau (Pena 1984, 141–148). However, this is a rather unnuanced, stereotyped vision and the nub of the issue can be found in the ‘Oterian psychodrama’. The internal dilemmas found in Otero-Pedrayo’s work provide the clearest illustration of the tensions that were present. On the one hand, the precision of his meticulous, scientific gaze on the landscape prompted him to criticise tourist postcards in the first edition of his Guía de Galicia in 1926 and he constantly advocated a more sophisticated Galician geography (Otero-Pedrayo 1945, 172). On the other, his nationalism pushed him to look for distinctly Galician characteristics that he could use in his more literary work and identity-building project (Villares 2008; LópezSández 2008). Although they may appear to be diametrically opposed, it is clear that tourist marketing and nationalism shared certain common interests (López-Silvestre and Lois-González 2007).

3 Concluding Remarks: The Future of Landscape History in Galicia Despite our research helping to shape the modern and contemporary Landscape History analysed here, we maintain that it would be erroneous to present the interaction between ‘pagus’, ‘country’ and ‘landscape’ as a gradual succession over time. The claim that economic culture preceded political culture and that both emerged before the ‘landscape society’ is symptomatic of an excessively teleological, Hegelian understanding of human history. From this perspective, everything fits together in a great linear narrative that makes us believe that, since our species appeared on Earth, we have undergone a process of elevation in which our crossborder sensitivity and tolerance have grown unceasingly in pursuit of the common good and world peace. However, as Giorgio Agamben acknowledged not long ago (Agamben 2017, 173–178), the notion of ‘landscape’ used here possesses universal, anthropological value, as only this notion is capable of contrasting a way of viewing the world based exclusively on production, exploitation, family and ownership with a more adventurous, deteleologised, exaggerated and ‘inappropriable’ manner of appreciating it.

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Based on these reflections, we believe that the most important question that landscape theorists must ponder these days is the one posed by J.-F. Lyotard when he speaks of the estrangement of “scapeland” (Lyotard 1998; Besse 2018, 21): as they moved slowly across the globe, were humans already capable of appreciating the world’s excess when they came across vast expanses of foreign land? In other words, were they driven solely by fear and hunger or did a sense of adventure and the appeal of the inappropriable and inobjective (Besse 2021, 160) play a central role in the incessant movement of the human race even at that time? If this hypothesis is confirmed, the landscape cannot have been a modern invention in Galicia either. The author of Mito e realidade da terra nai, Juan Rof-Carballo, never doubted this and insists that a certain spiritualised perception of the environment has always been apparent in these lands, arising spontaneously as a result of an intimate coexistence with the land and preceding any form of modern aesthetic contemplation (Rof-Carballo 1966). In order to distinguish it from an emerging notion capable of producing infinite representations of the environment, Rof-Carballo labelled this spiritual perception “ante-landscape” long before Berque and Roger began to speak of a “proto-landscape” (Berque 1995, 39–42; Roger 2007, 55–70). If we set these labels to one side, what kind of evidence can historians and prehistorians draw on to support the argument that something akin to an “ante-landscape” has always been present in Galicia? Put differently, before the rise of landscape painting, what cultural practices point to the existence of a gaze unrestricted by the instinct to survive and reproduce and concerned only with the land’s potential to provide sustenance or assets? We have identified at least four possible answers to this question. (a) First of all, from an anthropological perspective, the recent research into the “living landscapes” of people in the Ancares by Vanessa Fernández is very interesting (Fernández 2019). Another relevant area of study is Marcial Gondar’s work on folk cantigas, which he believes to contain hidden information about traditional ways of interacting with the land among the community (Gondar 2007). This relates to some of the ideas expressed by Filgueira-Valverde and explored further by Mercedes Brea and other researchers, whereby references to the landscape in courtly cantigas in the Middle Ages took traditional motifs drawn from nature and recreated them (Brea 1998; Castro 1996). Yet in all these cases, the devil is in the detail. Most of these more vital traditions and folk cantigas revolve around the productivity of the land or sea, the sadness felt at losing a loved one or the morriña and saudade provoked by the loss of a beloved place. In other words, they focus on the ‘pagus’ and ‘country’ or ‘motherland’; even love songs may be reduced to an instinct to reproduce, as Schopenhauer suggested. However, in our view, these new studies are likely to point to other gazes that remain authentically homegrown but are able to hint at the dancing waves of the sea or the radiance of the sun without any underlying motive or purpose. (b) Secondly, another element that can help us to understand the likelihood that this appreciation was present in Galicia prior to the nineteenth century are the modern ascetic texts preserved to this day, which served as inspiration for parish priests’

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sermons. Over the course of years of exhaustive research into the Galician landscape, we have compiled a large number of transcriptions of anti-sensualist, Counter-Reformist ascetics who attacked all forms of recreation in the landscape. At that time, these texts appeared to provide evidence that a sensibility towards the landscape had not yet emerged in Galicia, but the opposite now seems to be true: in reality, these theologians’ insistence on the importance of self-control to avoid enjoying the landscape demonstrates the very existence of this landscape. Pedro de Oña, a Mercedarian and professor at the University of Santiago in the early seventeenth century, is a good example. He parodied the attitudes of sinners, speaking of their approach to nature as well as their fondness for food and drink: “let there be no taste that we do not seek, let us be the keepers of our bodies, let us seek what appeals to our eyes, what is flavoursome to our palate, what sounds good to our ears, what is soft to our touch, what is fragrant to our nostrils, let there be no meadow that we do not wander, nor flowers that we do not pick: let God be in heaven, and let us have a good time on earth” (Oña 1603, 816–818). Does this critical text really prove that the landscape gaze did not exist in Galicia at that time or does it show instead that this gaze was so widely present that it had to be repressed? (c) Thirdly, it would also be interesting to apply the method used by Gonzalo Barrena in the Picos de Europa (Asturias) or by Maria Vicentina Dick in Brazil to Galicia: the toponymy method (Dick 1990). The microtoponymy used by shepherds in the Picos de Europa dates back to time immemorial and offers a wealth of information about their relationship with the land as landscape (Barrena and Izquierdo 2006; Barrena 2007). A similar phenomenon may be observed in Galicia, where the names of the capes along the coast are enveloped in the rhythm of the waves, according to Rosselló’s paraphrasing of OteroPedrayo (Rosselló 2010). Indeed, Galicia contains half of all Spain’s settlements and has such a rich toponymy that there are 45–50 names per square kilometre. These names highlight physical (dangerous or unproductive locations), cultural, phenomenological and emotional features: As Furnas, Os Outeiros da Mariña, O Pozo do Inferno, etc. When the origins of the 400,000 Galician toponyms that are believed to exist are studied in earnest and the initiative launched by researchers at the Instituto da Lingua Galega at the University of Santiago de Compostela to explore medieval toponymy is revived, it is likely that many interesting facts about the history of the Galician landscape will emerge (Martínez-Lema et al. 2010). (d) Finally, echoing Rof-Carballo, it is important to continue to study pre-Roman myths and rituals, as well as the spatial layout of certain petroglyphs, monuments and fortifications. Reports on Galician archaeology published in the twentieth and twenty-first century point to the need for in-depth research into accounts of the worship of trees and stones, high crossroads and the sacralisation of the landscape by local people in the past (Taboada 1957, 1965; Criado et al. 1998; Bermejo 1986; García-Quintela and Santos 2008). At Fondazione Benetton, the Landscape Studies centre in Treviso, the very picturesque locations of many

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shrines around the world are already being explored from a universal perspective (Luciani 2012). Drawing on this research and on other, more local studies focusing on places such as San Pedro de Rocas in Esgos (Ourense) and San Andrés de Teixido (Ortegal), it is possible to demonstrate—in a hypothesis defended by Murguía, Maciñeira and Otero-Pedrayo—that the Christianisation of old pagan shrines rarely entailed surrendering locations strategically positioned high up or in communion with nature and instead reaffirmed them (Maciñeira 2011). Indeed, the broad vistas that can often be seen from structures such as the Temple of Apollo in Delphi, the Church of Santa Maria Nuova in Cortona, Tuscany, and the top of Uxmal in Yucatán hint at a freer gaze than that associated with high defence towers in the Middle Ages and earlier royal rituals and inaugurations where aristocrats would climb to the top of their buildings to gaze over their properties and confirm their power (Bak 1990). Was that gaze that preceded worshippers’ enclosure in churches and was capable of taking in the celestial landscape driven by greed for power and Nietzsche’s promesse de bonheur or can it be associated with other kinds of feelings and emotions? To what extent did the nocturnal spectacle seen from these sacred places offer teleonomic compensation when linked to prayer? There is no need to look as far as the tablets of Enuma Anu Enlil or Chatwin’s descriptions of Australian aboriginal rituals to perceive the human ability to gaze at the sky or the surrounding spectacle with the sense of inappropriable excess that we have discussed here. Until this new evidence is gathered, there will always be historians who maintain that we run the risk of applying a modern scale of values anachronistically by seeking signs of the idea of ‘landscape’ in the past and who argue that pilgrims and peasants from Antiquity to the Modern Age did not perceive the ‘landscape’ as such, instead using the stars to navigate at night so that they could reach their destinations and the fields to plant cabbages or potatoes. No matter where it crops up, historic enjoyment of the spectacle of the world and the prehistoric relationship between shrines, the sky and broad panoramic vistas unequivocally reveal the admiration felt by tiny human beings as they gaze upon a strange, plentiful world offering something rich and inappropriable that goes beyond their basic needs, structures and conceptualisations. The information on the history of the landscape in Galicia that we have compiled over the last twenty-five years demonstrates that some ‘societies’ move beyond the intimate experience and learn to verbalise, represent and even foster those moments of appreciation of the landscape in which we all appear capable of grasping the inappropriable, while other societies are unable to do so for a number of simple yet diverse reasons. Just like today’s young unemployed, the hungry peasants of yesteryear were unable to think about promises or mystical or aesthetic experiences (Prada 2007). In other words, certain minimum basic needs must be met before a ‘landscape’ detached from conflicts of interest and property can emerge and this is just as true today as it was four thousand years ago (Aneiros 2007). Until these basic needs are fulfilled, there is no room for the recent gaze that is finally exploring the Ancares, the geological paleoenvironment and long-term geomorphological processes (Pérez-Alberti

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Image 12 Ovidio Murguía de Castro: Detail from “Winter landscape”, 1899, Oil on canvas, 80 × 109 cm. Source Colección AFundación. Inv. 814 (Vigo)

et al. 1993; Pérez-Alberti and Valcárcel 2022), nor the more established gaze that patiently analyses the ancient structure of farmland (Otero-Pedrayo 1928; Bouhier 1979; Villares 1982; Saavedra 2015; Fernández-Prieto 2015), nor the nature-loving gaze that focuses on ecological issues (Díaz-Fierros 2006; Pérez-Moreira 2012; Paül 2017; Ramil-Rego et al. 2017), nor the gaze that dwells on local architecture and heritage (De Llano 1981; Seara 2017), nor the more aesthetic gaze delving into literature and art (López-Silvestre 2005, 2007, 2008). Once these needs are met, any human being is capable of lingering on the characteristics of the landscape and experiencing its excess as a living, inappropriable process, the enemies of which are traditionally associated with fear and hunger (Image 12). Acknowledgements With thanks to Eleanor Staniforth for her excellent translation.

References Agamben G (2017) Lo inapropiable, pp 159–184. In: El uso de los cuerpos. Homo sacer, vol IV, 2. Adriana Hidalgo, 512 p. ISBN 978-987-4159-03-8 Aneiros R (2007) Cosmicidad. In: El País, 17/04/2007. ISSN 1576-3757 Arias E (1986) El paisajista romántico Jenaro Pérez Vilaamil, Madrid, Ed. CSIC. 582 p. ISBN: 84-00-06396-1 Bak J (ed) (1990) Coronations medieval and early modern monarchic ritual. University of California, 256 p. ISBN 0-520-06677-4 Baridon M (2006) Naissance et renaissance du paysage. Actes Sud. ISBN 9782742763733

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The Geological Landscape. 1. Geoforms in the Inland Galicia Rogelio Pérez Moreira and María Teresa Barral Silva

Abstract The geological action is essential in the conformation of the relief and the landscape since it is the constitutive of the rocks and of the most apparent forms of the orography. The geological landscape would be inexplicable without considering its geological history, through the interpretation of lithology, tectonics, and the successive cycles of carving by erosive agents. Considering these determinants, in this first chapter the genesis and main geoforms of the inland Galician landscape will be explained. Keywords Geomorphology · Landscape · Geological history

1 Introduction Landscape is a process, because it is not something static, but changing, dynamic; the always unfinished result of transformations that have occurred from the beginning of time to the present. At each moment of this transformative sequence, very diverse geological, biological, edaphic, and climatic conditions interacted, including, more recently, humans. All of them have participated in different ways and on different scales in the landscape shaping. But is Geology, among all these determining factors, which manifests as the most primitive and primordial, since the geological action determines the origin of rocks, the forms of the relief and the most apparent landscape units. Internal and external geological processes interacted in the landscape morphogenesis. Titanic forces from the entrails of the Earth operate, while the sculptural erosive action acts day by day, modelling on the surface. And, in this way, the current forms of the landscape have been carved out after a prolonged sequence of events that occur slowly but continuously (Fig. 1). R. P. Moreira (B) · M. T. B. Silva Department of Soil Science and Agricultural Chemistry, Universidade de Santiago de Compostela, Santiago, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_21

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Fig. 1 Landscape is a process, it is not static, by changing and dynamic

Galicia has a long history of geological processes that, from very remote times, preconditioned the current forms of relief and landscape. However, although the lithological substrates that constitute the Galician basement had a Precambrian or Paleozoic origin, its relief has been formed from the Mesozoic, and the main orographic forms observed today are from the Tertiary and Quaternary. So many authors distinguish two stages in such a long shaping history, one geological and one geomorphological, considering that the modelling of the forms that now prevail would have occurred from the last 200–65 million years, depending on the moment chosen as the starting point (Parga Pondal 1970; Vidal Romaní 2012). The existing geodiversity and its landscape expression would be inexplicable without considering the geological history, the lithology, tectonics, and the successive cycles of erosion. The geomorphology explains not only the forms but their genesis, and for this reason it is necessary to describe the geological landscapes together with the possible interpretation of their origin. Consequently, we will observe the landscape from a geological point of view and with necessary brevity, only pointing out its main conditioning factors and its most significant morphological traces, while trying to explain its geological or geomorphological genesis.

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2 Determining Factors 2.1 Lithological Factors Rocks are part of the landscape, sometimes even constituting the entire landscape panorama. In the Galician territory the crystalline substrate dominates, formed by igneous and metamorphic rocks of stony consistency. The oldest ones are from the end of the Precambrian and the beginning of the Paleozoic, among them the so-called Ollo de Sapo (Parga et al. 1964), but the dominant rocks are slates and granites, formed in the Paleozoic Era; overlaid in some areas is a Cenozoic cover of poor consistency, made up sediments from the Tertiary and Quaternary (Fig. 2). The various types of substrates differ in their composition, conformation and consistency characteristics; thus, they also vary in their weathering and erosive modes, and give rise to diverse landscapes. The weathering and erosive action will be facilitated by the regional fracturing and that of the rock itself, as well as by its stratification planes. Moreover, differential erosion will leave as relieved areas the rocks more resistant to weathering, which therefore will be those that normally constitute the rocky promontories on the crests of the mountains or the headlands in the coast. Likewise, the arrangement of these rocks, the dip and the folding of the geological strata influence the relief, also predrawing the landscape orography.

Fig. 2 Rocks are part of the landscape. O Pindo

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Each geological substrate, then, is modelled in a different way, giving rise to different landscapes. We will describe the most significant in Galicia: (Fig. 3) The granitic landscape is generally abrupt and frequently very rocky. The different types of granites, together with their different degrees of fracturing and modes of disjunction, give rise to very diverse forms and microforms, such as domes, tors, castellated rocks, balancing rocks, gnammas, taffoni, etc., sometimes forming stony fields and authentic rocky labyrinths. The schists and slates landscapes are also abrupt, with sharp peaks, angular and asymmetrical slopes, and parallel valleys, conditioned by the orientation and the dip of their strata. Frequently, the most pronounced orographic ridges correspond to other intercalated rocks, of greater consistency, which form the crests of the relief. The calcareous landscape is characterized by steep reliefs where deep river gorges are excavated. Its weathering is peculiar, giving rise to the characteristic karstic modelling, with a variety of unique forms such as lapies, sinkholes or underground cavities, resulting from the dissolution of limestone. The landscape of quartzites and other quartz-rich rocks shows scabrous ridges and narrow valleys. They are normally traced in veins or bands between other less firm rocks, which favours their rough protrusions. The landscape of the more weatherable rocks, such as amphibolites, gabbros or biotite schists, is expressed in smooth reliefs, because of their intense weathering, with few rocky outcrops. The landscape of serpentinites, which can be serpentinized amphibolites or peridotites, shows singularities derived from the serpentinization process. Their mineral composition is problematic for many plants, determining a scarce vegetal cover that favours erosive processes. Rockiness is common, showing gullies and very irregular forms of relief. The landscape of sedimentary materials is generally observed in orographic depressions, sometimes forming wide valleys with a flattened bottom. This location in basins and depressions has favoured the accumulation and conservation of sediments, which are usually poorly compacted deposits, with low resistance to erosive agents.

2.2 Tectonic Factors Plate Tectonics is the explanatory basis for orogenic processes, as well as of the crustal movements that have their expression in the landscape. The most relevant episodes were: First, the Hercynian orogeny, dated between 380 and 370 BP, in the Paleozoic, mainly due to the collision of the Laurussia and Gondwana plates; afterwards, the opening of the Atlantic occurred, leading to the separation of the Iberian and American plates, which began in the Mesozoic, since 200 million years ago. Later, the Alpine orogeny occurred, at the beginning of the Cenozoic, between 65 and 35 million years BP. And even later, a late neotectonic occurred, as well as a

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Fig. 3 a The granitic landscape; b the schists landscape; c the calcareous landscape; d the landscape of quartzites; e the landscape of the more weatherable rocks; f the landscape of serpentinites; g the landscape of sedimentary materials

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general epirogenesis in subsequent times, which affected the entire Galician massif from at least 25 million years. The Hercynian orogeny caused folding, thrusting and slipping, as well as metamorphism, magmatism and fracturing. But the most outstanding Hercynian megastructure is the commonly called Arco o Rodilla Astúrica, in which the geological structures are folded in a great curvature, from the northern to the southern parts of Galicia, continuing towards the interior of the Iberian Peninsula along the Hesperian Massif (Matte 1968; Parga Pondal et al. 1982). The arrangement of this structure will have important morphological consequences, since it is that of the lithological substrates and some important fractures, with repercussions in the fluvial orientations and in the indented profile of the coastline (Fig. 4). Other relevant Hercynian folds show remnants of their traces that are clearly visible in the landscape. This is the case of the large recumbent folds, of kilometric dimensions, found in some eastern Galician areas, of which the most spectacular is the so-called Courel or Campodola-Leixazós Fold, an eloquent testimony to the magnitude of this orogenic convulsion in the Galician area. This orogeny has also left its mark in the collision zone between the lithospheric plates Laurussia y Gondwana, evidenced in the orography. This line of suture was previously associated with the Ollo de Sapo region or the southern limit of the Ordes Unit (Vidal et al. 1998; Martínez Catalán et al. 2010), but nowadays it is interpreted that it could be marked by a hypabyssal injection of quartz, intruded in favour of that geological discontinuity, which today stands out in relief in the quartzite dike of Pico Sacro (Vence and Vidal 2018; Vidal Romaní 2022) (Fig. 5).

Fig. 4 The Hercynian convulsion has left eloquent testimonies. Campodola- Leixazós Fold

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Fig. 5 The fractures cracked in various directions. Sil Canyon

The Hercynian and late-Hercynian fractures cracked the Galician basement in various directions, and many of them would reactivate, along with new ones, during the subsequent Alpine tectonics. Some fractures reached a regional entity, mainly those traced in NE-SW, ENE-WSW and N-S directions, while many others are local (Parga 1969; Yepes and Vidal 2004). Some of these fractures have a great structural importance, for example the so-called Valdoviño and Viveiro faults. Also, other fractures running N-S in western Galicia, including those that later fragmented the Atlantic coastline during the Mesozoic (Vanney et al. 1979; Santanach 1994), as well as the fracture that formed the so-called Fosa Meridiana (Carlé 1949), going from Baldaio/Carballo to Tui in the same direction. In many cases, the fractures marked the lines for the subsequent formation of horsts and grabens, or for the erosive excavation of the basins and the fluvial network, as well as the rías. The opening of the Atlantic, when the Pangea supercontinent fragmented and Iberia and America consequently were pull apart, began during the Mesozoic, in the Jurassic-Lower Cretaceous interval; and other opening took place in the Cantabrian zone, when the Bay of Biscay formed, and the Iberian Plate was individualized. These Atlantic and Cantabrian openings would define the future coast of Galicia. The Alpine orogeny caused a tectonic reactivation. It took place at the beginning of the Cenozoic, during the Paleogene, due to the compression of the Iberian microplate against the Eurasian plate, under the push of the African plate. A continental collision occurred in the Pyrenees area and a shortening of the Bay of Biscay, which also caused subduction to begin under the Iberian plate. This new orogenesis turned the Cantabrian zone into a compressive border. Consequently, the Cantabrian Mountain

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Fig. 6 The Alpine orogeny caused a tectonic reactivation. Quinxo Hills, O Xurés

Range rose, including its Galician extensions, as well as the entire northern coastal cornice. Over time, the entire Galician territory, both the coast and the inland, would be affected by this Alpine epirogeny (Fig. 6). After the repercussions of the Paleogene, other geological events occurred during the Neogene. It is possible that, after the strong compression, a relative tectonic relaxation would take place, giving rise to a reactivation of the old Hercynian fractures and the opening of new ones. Moreover, according to some authors, a tectonic block rearrangement (“juego de bloques”) was produced, generating horsts and grabens (Pérez Alberti 1993a, b). Other authors, however, dismissed this interpretation of the relief, fundamentally based on block movements, restricting its validity to the now submerged western areas, subjected to distensive tectonics. These authors consider that, in the Galician interior, compressive tectonics predominated, and that weathering and erosional degradation were more decisive than vertical tectonics in the general configuration of the relief (Vidal Romaní et al. 1998; Vidal Romaní 2002). Anyway, both mechanisms, block rearrangements and erosive corrosion, are accepted as true and may even act simultaneously in the formation of the orography. Moreover, it is likely that the entire Galician territory is since then in a geodynamically opposed location, between the Cantabrian compressive border and the Atlantic distensive border (Vidal Romaní 2002). However, this produces the same geomorphological effect, since both processes cause the incision and rejuvenation of the fluvial network, either by compression from the north caused by epirogenic impulses, or by distension from the west causing a drop in the base level and the consequent upstream remounting erosion (Vidal et al. 1998).

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Fig. 7 The horizontal/vertical dichotomy. Sil Canyon

As a result of the relief readjustments, rivers must adapt, either changing their course direction, or downcutting into the raised areas and flowing slowly in the depressed ones. The strong incision of the rivers in the terrain generates one of the Galician orographic peculiarities, the horizontal/vertical dichotomy (Fig. 7).

2.3 Orographic Factors The Galician relief generally shows an appearance that is both flat and excavated. These are the simultaneous fingerprints of senescence and youth that result from its geological history: the old country, denudated and softened, together with the jovial country, rejuvenated by the incisive downcutting of the fluvial network (Otero Pedrayo 1926; Pérez Alberti ). In other words, it shows the erosive actions typical of maturity and rejuvenation, respectively expressed in that clear dichotomy of horizontality and verticality. As a result of the geological history, the main geoforms were traced in the relief, shaped by the different types of geomorphological modelling. Below, these principal morphological units, manifested in the geological landscape, are described.

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3 Geoforms 3.1 Planation Surfaces In a large part of the Galician country flattened surfaces dominate because of prolonged erosive denudation along its geological history. Such surfaces are gradually stepped at different heights, from the high flattened peaks to the coastal plain, and even some submerged steps have been described covered by the sea (Fig. 8). Names and dates were given to the main surfaces. For example, in the Ourense Central Massif, Hernández Pacheco (1949) describes a Summit Peneplain, an Inferior Peneplain and a Low Peneplain. In turn, what is considered the more general surface has been called the Chantada Surface or Fundamental Peneplain or Fundamental Surface of Galicia (Birot and Solé 1954; Nonn 1966), since the traces of this flattening can be recognized from the central Galician zone to the coastline (Pérez Alberti 1993a; Vidal Romaní 1996, 2002). Thus, this is the surface observable around the Miño river, around the Chantada area, where it was defined, and also in the Terra Chá, Lugo Plateau, Melide area, Ulla contour, Ordes Plateau, Santa Comba Plateau, Xallas Plateau, and even in the various coastal mountain ranges raised to about 600 m of altitude, such as those of A Capelada, O Pindo, O Barbanza, O Castrove, O Galiñeiro, A Grova, etc.

Fig. 8 Flattened surfaces are gradually stepped at different heights. Surface of Castro Caldelas raised on the A Limia depression

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Fig. 9 Two types of surfaces, erosive and accumulative, could be differentiated. Terra Chá

And there are many more flattenings spread throughout the Galician geography. Some examples are those recognizable in the contour of the Ribeira Sacra (Pérez Alberti 1993b; Vidal et al. 1998), where up to eight levels of planation have been identified. Other flat surfaces, located at lower levels, are those found in depressed basins, which could be of various origins. Therefore, two types of surfaces, erosive and accumulative, could be differentiated (Fig. 9). The genesis of the different planation surfaces and depression basins is still debated. Their location at different heights was given two interpretations: either they were uneven due to tectonic causes, or they were excavated by weathering and erosional degradation, in successive corrosive phases. However, since there are a greater number of flattened surfaces than recognized erosive cycles, it is most likely that they are due to both actions, a combination of corrosive action and vertical tectonics (Pérez Alberti 1993a; Vidal Romaní 2002; Pérez Moreira and Barral Silva 2019).

3.2 Reliefs and Basins Some defining features of the Galician landscape are, in short, the horizontal/vertical dichotomy and the stepping of the relief forms (Pérez Alberti 1993a, 2001a). In addition to the planation surfaces at different heights, there are mountainous elevations above the general level and depressions below the surrounding territory; however,

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Fig. 10 Some flattened peaks are residues of an old erosive denudation. Candán Range

the flattened morphology is generally maintained, with smoothed summits and wide flat-bottomed valleys. The controversy about this irregular morphology was previously exposed and its origin interpreted as a combination of corrosive degradation and tectonic causes. The erosive action already begun in the Mesozoic, lasting for much of the Cenozoic, leaving remnants of the old surface only on the summits of some mountain ranges (Birot and Solé 1954; Nonn 1966; Torre Enciso 1970; Vidal Romaní 1996, 2002), while the vertical displacements occurred throughout the Cenozoic, because of the Alpine orogeny (Pérez Alberti 1993a) (Fig. 10). The raised blocks are represented by most of the dominant mountain ranges, without ruling out that they were also residual reliefs of an old denudation. This is the case of the high mountains of Ancares, Courel, Manzaneda, Trevinca, Xistral, Xurés, Dorsal Galega, etc. The Dorsal Galega (Birot and Solé 1954) is a chain of consecutive mountain ranges, about 500–1150 m high, which crosses Galicia in a meridian sense; it is a clear example of this dual explanation: undoubtedly, it is a horst raised by the Alpine tectonics, but, at the same time, its summits can be residuals of a previous erosive denudation (Figs. 11 and 12). The depressed basins could be in some cases of tectonic origin, and in others due to weathering corrosion, or even both simultaneously (Pérez Alberti 1993b; Vidal Romaní 2002; Uña et al. 2004), favoured by the previous existence of geological fractures. In general, their genesis has been interpreted as tectonic in the case of the Ourense basins (Verín, Maceda, A Limia, for example), and as erosive in the Lugo basins (Monforte, Sarria, Terra Chá, for example). To the W, there is the Meridian

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Fig. 11 The raised blocks are represented by most of the dominant mountain ranges. O Courel

Fig. 12 The depressed basins could be of tectonic origin or due to weathering corrosion. A Limia

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Depression, which is currently interpreted as originating from erosive corrosion (Pagés Valcarlos and Vidal Romaní 1997). To the NW, other basins are associated with directional faults (Meirama Xanceda, Roupar, As Pontes, for example). In the SE, the Sil basins (O Barco, A Rúa, Quiroga) are the oldest in this area, formed in association to fracture lines, before they were affected by the Pyrenean Basal Thrust, during the Alpine tectonics (Santanach 1994; Vidal et al. 1998). The more recent Monforte basin is an example of a non-tectonic but degradative basin (Yepes 2002). And good examples of tectonic basins is that of Verín, extended with a flat bottom at 400 m altitude, below a planation surface at about 800 m above sea level; as well as the Maceda trench, surely the last to form (Vidal et al. 1998), located at about 550 m, well below a higher surface at about 1000 m altitude. In all these basins, sedimentary formations of different facies have been preserved, either lacustrine, alluvial or colluvial, indicative of different environmental conditions, from hot and humid to hot and dry. Consequently, they allow to reconstruct the geography of the area and the paleoenvironmental conditions at the time of their sedimentation (Pérez Alberti 1993b, 2001a).

3.3 Glacial Morphology Quaternary glaciarism developed with singular features in the highest mountains of the peninsular NW, clearly differentiated from the rest of the glacial systems of the Iberian Peninsula and even from those of the northern hemisphere. During the Pleistocene (between 2.58 million years and 15,000 before now) at least twenty glacial episodes occurred (Vidal Romaní 2015). Each glacial cycle totally or partially erased the traces of the previous ones, and only remains of the last glacial phases are preserved (Fig. 13). There were undoubtedly different glacial episodes, with extreme conditions of humid cold or dry cold; for this reason, the most extensive ice did not coincide in time with the most intense cold, and it was also different in the reliefs closest to the coast that in those of the most remote areas (Pérez Alberti 1993a, 2004; Pérez Alberti and Valcárcel Díaz 1998; Pérez Moreira 2004). In addition, some studies have revealed the existence of very expansive phases of glaciarism much older than those of the last glacial cycle (Vidal Romaní et al. 1999). Thus, as was observed in a mountainous area near the coast, in the Xurés-Gerês, the greatest expansion of ice would have occurred between 300,000 and 238,000 years BP, decreasing its thickness from 130,000 years BP (Vidal Romaní et al. 1999; Vidal Romaní 2002). And in studies made in more interior mountains, such as Ancares, Courel and Manzaneda (Vidal Romaní et al. 1995, 1999; Valcárcel Díaz 2001; Vidal Romaní and Fernández Mosquera 2005; Pérez Alberti 2021; Pérez Alberti y Valcárcel Díaz 2021), referred to more recent times, two glacial phases were identified, one “oceanic” of humid cold, from about 44,000 years BP, and a greater advance of the ice between 29,000 and 22,000 years BP, and another “continentalized”, of dry cold but more intense, which corresponds to the Global Glacial Maximum, about 22,000–18,000 years BP,

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Fig. 13 Quaternary glaciarism developed with singular features in the mountains of the peninsular NW. Os Penedois, Os Ancares

when glaciers were restricted to the highest peaks, but with permafrost and a most widespread periglacial action (Vidal Romaní et al. 1990; Pérez Alberti 2001b, 2004; Pérez Alberti and Valcárcel Díaz 1998; Viana Soto and Pérez Alberti 2019). Since then, the deglaciation would take place, which ended about 15,000 years ago. Evidence of glaciarism is clear in the mountains of Ancares, Courel, Manzaneda, Trevinca-Segundeira and Xurés-Guêres, and more doubtful in other less elevated areas, such as those of Xistral or Faro de Avión, where it is debated the greater or lesser spreading of glaciarism or periglaciarism (Pérez Alberti et al. 1993a, b; Valcárcel Díaz 1996, 2002; Pérez Alberti and Valcárcel Díaz 1998, 2021; Vidal Romaní 2002, 2015; Valcárcel Díaz and Pérez Alberti 2021) (Fig. 14). The glacial action generally occurred at heights above 1000 m. The accumulations of snow and ice would concentrate on the contour of the summits, from where they would slide towards the valleys, descending in some places with steep slopes to heights of only 600–750 m. The level of perpetual snow varies in altitude from one mountain to another, as well as from western to eastern slopes. In general, the glacial formations are more evident in the eastern part than in the western part, probably due to a greater accumulation and snow overfeeding, however the perpetual snow level is lower in the western part than in the eastern part, possibly due to their different insolation (Pérez Alberti 1993a; Pérez Alberti and Valcárcel Díaz 1998, 2021). For example, in the Manzaneda Massif this level would be situated around 1000–1100 m in the western part and between 1150 and 1300 m in the eastern part, the ice descending to a minimum of 900 m (Pérez Alberti 1993a; Vidal Romaní

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Fig. 14 The level of perpetual snow varies in altitude from one mountain to another, as well as from western to eastern slopes. Tres Bispos, Os Ancares

et al. 1995; Pérez Alberti and Valcárcel Díaz 1998; Vidal Romaní and Fernández Mosquera 2005). In Os Ancares, the ice also spread further and got thicker at the east than at the west, and the excavation of the glacial valleys was more pronounced in the eastern than in the western zone, although ice ablation occurred in both parts at an identical level, below 900 m high (Pérez Alberti et al. 1993, 1993a; Valcárcel Díaz 1996, 2001; Rodríguez Guitián et al. 1996a; Kossel 1996; Pérez Alberti and Valcárcel Díaz 1998; Pérez Moreira 2008). In O Courel, there is no clear evidence of where the ice flowed on the western slope, but marks are evident and extensive on the eastern part, descending to a level below 900 m (Rodríguez Guitián et al. 1996b; Pérez Alberti 2021). However, on the Galicia side of Trevinca, the Bibei glacier descended to its ablation level of 900 m after having covered a length of 28 km (Rodríguez Guitián and Valcárcel Díaz 1994). There where glacialism acted, we observe its traces, its different forms of erosion and accumulation (Fig. 15). The main erosive landforms are U-shaped valleys, glacial cirques and overexcavated basins, as well as other signs of erosion, as glacier thresholds, fleecy rocks (roches moutonnées), glacial polish, striae, etc. Trough valleys are clearly observed in some areas of Ancares, Trevinca and Xurés, but are less evident in other places. In Manzaneda, at some places the ice was settled on a previously flattened morphology, which favoured its disfluency from one valley to another, without forcing excavation; this is especially evident over a plain of about 8 km in the Cenza glacial valley, another of the largest in Galicia. The most striking cumulative forms are the moraines, which are of various types, mainly fronto-lateral. The moraines corresponding to the last glacial advance are rather scarce; somewhat more frequent are the moraine arcs, staggered in the valleys, indicative of final pulses during the general retreat of the glaciers. However, there are also conspicuous deposits, such as those formed by large boulders, up to 4 m

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Fig. 15 The main erosive landforms are U-shaped valleys. Val de Burbia, Os Ancares

wide, above the town of Piornedo, in Os Ancares, or the spectacular frontal moraine, about 40 m high, above the village of Chaguazoso, at the end of the Cenza glacial valley in Manzaneda, both accumulations located at 1300 m high (Fig. 16). Other singular forms of glacial action are the pyramidal peaks, as horns, that can be found in the tops of some mountains, such as that of Penarrubia peak, in Os Ancares. Also frequent are the lakes of glacial origin, usually formed by overexcavation of the glacier bed and moraine-damming, where waters are retained after ice melting. Remarkable examples are the lakes of A Lucenza in O Courel, As Lamas in Manzaneda, and A Serpe, Ocelo and many others in Trevinca (Fig. 17). Periglaciarism is evidenced in diverse deposits widely distributed in the Galician territory, from the high mountains to the coast (Pérez Alberti 1984, 1993a, 2021; Asensio Amor and González Martín 1992; Costa Casais et al. 1996; Pérez Alberti et al. 2001; Valcárcel Díaz 1996), although they are less evident at intermediate altitudes, where the existence of a greater vegetation cover surely stopped the periglacial processes (Nonn 1966; Pérez Moreira et al. 1988). Some of these deposits are limited to the high peaks and others cover the slopes at lower altitude. The most characteristic are rock glaciers, boulder slopes, screes, stratified slope deposits, gelifluction lobes, etc. (Pérez Alberti and Rodríguez Guitián 1993; Valcárcel Díez 2001; Viana Soto and Pérez Alberti 2019). In some places, the boulder fields are channelled downslope and move immersed in an iced mass, taking advantage of the valleys, thus forming block streams, sometimes with boulders of great size, of which the most spectacular is the Pedregal de Irimia (Figs. 18 and 19).

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Fig. 16 The main cumulative landforms are the moraines. Chaguazoso, Manzaneda

Fig. 17 Also frequent are the lakes of glacial origin. a Lagoa da Lucenza, O Courel; b Lagoa da Serpe, Trevinca

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Fig. 18 Block slopes. Cuiña Peak, Os Ancares

Fig. 19 Block streams. Pedregal de Irimia

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Fig. 20 In many places the fluvial network is strongly embedded. Sil Canyon

3.4 Fluvial Morphology Galician rivers usually show discontinuities in their equilibrium profile, with breaks in slope and sections with a marked unevenness, which correspond to erosive cycles due to rising erosion (Río Barja and Rodríguez Lestegás 1992), which together with epirogenic movements has determined the incision of a large part of the fluvial network. River downcutting receives different interpretations depending on whether it occurs close to the Atlantic or Cantabrian coast, or in the interior of Galicia (Fig. 20). In the case of Atlantic rivers, incisions of up to 180 m below the dissected surfaces are observed in their final course. This can be clearly seen, for example, in the Eume, Tambre or Ulla rivers, which carve out river gorges in their final sections. The incision of the Atlantic network would take place since the Mesozoic; by then, there would be rivers longer than the current ones, flowing in an E-W direction after the opening of the Atlantic and the formation of the western coast. As the coastal base level was modified, these rivers excavated their valleys on the old surface and the upstream erosion progressed from their mouth to the interior of Galicia. Later, the Tertiary epigenic movements and the Quaternary glacio-eustatic oscillations would accentuate the fluvial excavation, especially on the coastal edge, deepening the valleys that would later be flooded forming the rías. The excavation of the Cantabrian network took place from the Cenozoic, after the Alpine compression and the consequent elevation of the mountains and the entire northern coastal cornice. This fact conditioned the short course and abrupt incision of the rivers in this region, which appear very erosive, as evidenced, for example, in the Navia, Eo, Masma and Sor rivers. Furthermore, this was the cause of the lower development of these Cantabrian rías (Fig. 21).

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Fig. 21 The fluvial incision is very explicit in the a Miño Canyon and b Sil Canyon

Tertiary tectonics had other important repercussions that interfered with the fluvial network, mainly due to the rise of the mountain ranges, the subsidence of tectonic basins, and the general epirogenesis that has affected the country ever since. One of its consequences was the accentuation of the fluvial network downcutting, explicitly evidenced in the Miño and Sil river canyons. But there was also a reorganization of the drainage, caused by the elevation of the terminal reliefs of the Cantabrian Range and the depression of the so-called Ourense Corridor; in this way, mountain ridges and depressed areas formed, framed by Tertiary faults oriented in N-S or NE-SW directions. Consequently, the course of some of the long Atlantic rivers flowing E-W were cut at their heads, and part of their drainage was captured by a new river that would run in a N-S direction, channelled in favour of a fracture and between the mountain ranges of the Dorsal Galega and the eastern mountains. This new river is now the current Miño from its source to its confluence with the Sil (Vidal Romaní 2012, 2015). The Sil river already existed for at least 100 million years, while the Miño could only be established at the end of the Tertiary, in the Pliocene, about 5 million years ago, and is therefore, curiously, the youngest of the Galician rivers (Vidal Romaní 2015). The Galician fluvial network usually shows an antecedent character, as in many cases it does not follow the disposition of the geological structures. An obvious example is observed in how the Atlantic rivers cross the Fosa Meridiana and the Hercynian structures without being affected by them. Another eloquent example can be seen in many morphological features of the Sil River, evidencing both its antiquity and its antecedence: it cuts through the structures of the Cantabrian Mountains, downcuts the old erosion surfaces, eludes some Tertiary basins (Monforte and Maceda) but crosses others in its layout (El Bierzo, O Barco, A Rúa, Quiroga), and strongly entrenched crosses some Hercynian and Alpine structures (Vidal et al. 1998; Yepes and Vidal 2004). The antecedence of the Miño and Sil rivers -the main Galician rivers- is especially evident in some sections, due to their strong incision and the existence of epigenic meanders, the most notable examples of which are the O Cabo do Mundo meanders in the Miño River and A Cubela in the Sil River, where these rivers sink in the relief 335 and 400 m, respectively. In nearby areas, the incisions in the substrate

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are manifested by a succession of erosive and cumulative terraces; a last stage of strong vertical excavation is notorious, which should be interpreted as the result of a modern tectonic pulse rather than an old upstream erosion that, however, could be more effective in the general downcutting because it was active for a longer time (Vidal et al. 1998) (Fig. 22). As a final observation, it should be noted that most Atlantic rivers in Galicia do not usually follow the common rule that rivers have a torrential character at their headwaters and are mature at their mouth. Instead, they generally show a slow course in their initial stretch, as they cross the flattened mountainous surfaces, and rush with rapids in the middle and final stretches (Carlé 1949). The Galician geological conditions, previously pointed out, explain this singular morphology. And there is even a river that flows into the sea in a waterfall, in the case of the Xallas river. There are many waterfalls in Galicia. Among the most outstanding, in addition to the Xallas river, are those of the Toxa, Belelle, Cerves, Selmo rivers, or the so-called Seimeira de Vilagocende and Corga da Frecha, which is the one with the highest waterfall. They originate, either by differential erosion or by tectonic causes, and they are often justified by both reasons. For example, the Xallas waterfall is partly explained by the extraordinary hardness of the O Pindo granite, which makes the river carve a deep gorge, but it is also due to the general epirogenesis that occurs since the Cenozoic; in the Fervenza de O Toxa, the most noticeable thing is the hardness of the granite; in the Seimeira de Vilagocende, the existence of a quartzite dike is evident; and in the Corga da Frecha, the waterfall falls from the raised block

Fig. 22 The antecedence of the fluvial network becomes evident in the existence of epigenic meanders. A Cubela meander, Sil River

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Fig. 23 Waterfall at the mouth of the Xallas river. O Ézaro

of the Serra do Xurés to the Caldo river, in the lower Baixa Limia, being evident its tectonic conditioning. These waterfalls produce logical breaks in the equilibrium profile of the rivera (Fig. 23).

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Pérez Alberti A (2004) El análisis geomorfológico en la reconstrucción paleoambiental. El ejemplo de los procesos de origen frío en el noroeste de la Península Ibérica. Polígonos, 14:139 Pérez Moreira R, Barral Silva MT (2019) Xeoloxía e xeomorfoloxía da Ribeira Sacra. In: Arias M, Álvarez E (eds) Ribeira Sacra. Conservación do solo e construción da paisaxe. Deputación de Ourense, pp 15–42 Pérez Moreira R, Barral Silva MT, Díaz-Fierros Viqueira F (1988) Depósitos detríticos de origen periglaciar bajo un suelo orgánico coluvial en una ladera de Serra da Loba (Galicia, España). Caracterización y génesis. Cadernos do Laboratorio Xeolóxico de Laxe 12:59 Pérez Moreira R (2004) Diversidade Natural de Galicia. SOGAMA, Xunta de Galicia. Cerceda, A Coruña, p 245 Pérez Moreira R (2008) Acariciando el cielo/Caressing the sky. Texto y Fotos/Texts and Photos. In: Ancares, Parque Natural/Ancares, Natural Park (ed) Lunwerg, Madrid, pp 39–107, 203–217 Río Barja FJ, Rodríguez Lestegás F (1992) Os ríos galegos. Consello da Cultura Galega, p 333 Rodríguez Guitián MA, Vacárcel Díaz M (1994) Contribución al conocimiento del glaciarismo pleistoceno en la vertiente suroccidental del Macizo de Pena Trevinca (Montañas GalaicoSanabrienses, NW Ibérico). In: Arnáez-Vadillo J, García Ruíz JM, Gómez Villar A (eds) Geomorfología de España, III Reunión de Geomorfología, Tomo I, pp 241–251 Rodríguez Guitián MA, Valcárcel Díaz M, Pérez Alberti A (1996a) El último ciclo glaciar en el valle de Piornedo (Serra dos Ancares, Lugo): hipótesis sobre la deglaciación basada en la cartografía de formas y depósitos glaciares y periglaciares. In: Pérez Alberti A, Martínez Cortizas A (Coords.), Avances en la reconstrucción paleoambiental de las áreas de montaña lucense, Monografías GEP, 1, pp. 39–52 Rodríguez Guitián MA, Valcárcel Díaz M, Pérez Alberti A (1996b) Morfogénesis glaciar en la vertiente meridional de la Serra do Courel (NW Ibérico): el valle de A Seara. In: Pérez Alberti A, Martínez Cortizas A (Coords). Avances en la reconstrucción paleoambiental de las áreas de montaña lucense, Monografías GEP 1, pp 77–88 Santanach Prat P (1994) Las cuencas terciarias gallegas en la terminación occidental de los relieves pirenaicos. Cadernos Do Laboratorio Xeolóxico De Laxe 19:57 Torre Enciso U (1970) Avanzos no coñecimento da xeomorfoloxía de Galicia. Discurso de ingreso na Real Academia Galega. Real Academia Galega (A Coruña) Uña Álvarez, E., Yepes Tomiño, J., Vidal Romaní, J. R. 2004. Cuencas del Limia y Támega. 302–323 pp. In: Patrimonio Geológico de Galicia. R. Nuche del Rivero, ENRESA (Eds.). Madrid. Valcárcel Díaz M, Pérez Alberti A (2021) Los glaciares de Galicia occidental. In: Oliva M, Palacios D, Fernández JM (eds.). Iberia, Land of Glaciers. Elsevier, pp 353–373 Valcárcel Díaz, M. 1996. Aportaciones al estudio de los procesos glaciares y periglaciares en Galicia (NW de la Península Ibérica): estado de la cuestión. In: Pérez Alberti A, Martínez Cortízas A (Coords.), Avances en la reconstrucción paleoambiental de las áreas de montaña lucense. Monografías G.E.P., I, pp 11–37 Valcárcel Díaz M (2001) As paisaxes das serras dende unha perspectiva xeomorfolóxica. In: Pérez Alberti A (Coord.) Galicia fai dous mil anos. O feito diferencial galego. IV: As paisaxes de Galicia, vol 2. Museo do Pobo Galego, pp 237–267 Vanney JR, Auxietre JL, Dunand JP (1979) Geomorphic provinces and evolution of northwestern Iberian continental margin. Ann Inst Océanographique De París 55(1):5 Vence M, Vidal Romaní JR (2018) “Top ten” geológico de Galicia. (M. Vence, citando a J. R. Vidal Romaní, com. pers.). GCiencia, Xornalismo and Divulgación, 17/10/2018. Viana Soto A, Pérez Alberti A (2019) Depósitos periglaciares como indicadores de paleotemperatura. Un estudio de caso en la Península Ibérica: las montañas de Galicia. Permafrost and Periglaciar Processes, 30(4):374 Vidal Romaní JR, Fernández Mosquera D (2005) Glaciarismo pleistoceno en el NW de la Península Ibérica (Galicia, España, Norte de Portugal). Enseñanza De Las Ciencias De La Tierra 13(3):270 Vidal Romaní JR, Villaplana JM, Brum A, Zêzere JL, Rodrigues L, Monge C (1990) Los tills de la Serra de Gerês-Xurés y la glaciación pleistocena (Minho, Portugal, Ourense, Galicia). Cuaternario y Geomorfología 4:13

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Vidal Romaní JR, Fernández D, Marti K, Brum A (1999) Nuevos datos para la cronología glaciar pleistocena en el NW de la Península Ibérica. Cadernos Do Laboratorio Xeolóxico De Laxe 24:7 Vidal Romaní JR, Santos ML, Jalut G (1995) Cronología relativa del máximo glaciar finipleistoceno en el sector Nor-Oriental de la Serra de Queixa (Ourense, Galicia, España). In: Actas III Reunión del Cuaternario Ibérico. Coimbra, 1993, pp 215–222 Vidal Romaní JR, Yepes Temiño J, Rodríguez Martínez-Conde R (1998) Evolución geomorfológica del Macizo Hespérico Peninsular. Estudio de un sector comprendido entre las provincias de Lugo y Ourense (Galicia, NW de España). Cadernos do Laboratorio Xeolóxico de Laxe 23:165 Vidal Romaní JR (1996) Geomorfología de Galicia. In: Geografía de Galicia. F. J. Río Barja (Coord.), vol. XVII. Hércules de Ediciones, A Coruña, pp 37–63 Vidal Romaní JR (2002) El relieve actual de Galicia. In: Díaz-Fierros Viqueira F (Coord.), Galicia, Naturaleza, vol XXXVI: Historia Natural, Geología, Hércules de Ediciones. A Coruña, pp 304–341 Vidal Romaní JR (2012) Por qué Gallaecia Petrea. In: Gallaecia Petrea I: Xeoloxía. Cidade da Cultura de Galicia. Xunta de Galicia, Santiago de Compostela, pp 22–33 Vidal Romaní JR (2015) Geología de Galicia: cómo armar un rompecabezas. Discurso de ingreso en la Real Academia Galega de Ciencias, 25-III-2015. Vidal Romaní JR (2022) A xeoloxía de Galicia, un vello país que non é tan vello. Conferencia en Universidade de Verán, A Xeoloxía: una ciencia para a Sociedade. Universidade de Santiago. Santiago de Compostela Yepes Temiño J, Vidal Romaní JR (2004) Indicios de antecedencia en la red fluvial del sureste de Galicia. Estud Geol 60:21 Yepes Temiño J (2002) Geomorfología de un sector comprendido entre las provincias de Lugo y Ourense (Galicia, Macizo Hespérico). Serie Nova Terra, Edicións do Castro, p 272

The Geological Landscape. 2. Geoforms in the Coastal Galicia Rogelio Pérez Moreira and María Teresa Barral Silva

Abstract In the preceding chapter, the lithological, tectonic, orographic and erosive factors determining the general forms of relief and landscape were described, in particular pointing out the morphology of inland Galicia. This chapter refers to the main geoforms of the Galician shoreline. The Galician coast is uniquely sinuous and contrasted. The genesis and main existing coastal landforms are indicated. Continental and marine geological action have been a determinant of its morphological and landscape conformation. Structural, lithological, tectonic and erosive factors shaped the current profile of the coastline. Finally, a global reflection on the valuation and sustainability of geological heritage is added. Keywords Galician coast · Rías · Coastal morphology · Geological heritage

1 The Galician Coast 1.1 Coastal Morphology The Galician coast is extremely indented and contrasted. It shows a very sinuous profile, with numerous inlets and outlets where erosive or sedimentary sections alternate, producing very diverse morphologies. Along the coast, there are rías and estuaries, cliffs and coastal plains, sandbanks and dunes, marshes and tidal flats, coastal lagoons, islands, etc. Such morphological diversity is one of the peculiarities of the Galician coast, but the greatest is undoubtedly the existence of the rías (Fig. 1). The main observed coastal geoforms are the legacy of a long geological history, whose origins go back to the Mesozoic, when the primitive limits of the Galician coast were defined after the opening of the Atlantic Ocean and the Bay of Biscay. In western Galicia, a lithospheric stretching took place that would produce its fragmentation R. P. Moreira (B) · M. T. B. Silva Department Soil Science and Agricultural Chemistry, Universidade de Santiago de Compostela, Santiago de Compostela, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_22

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Fig. 1 The Galician coast is extremely indented and contrasted, its greatest singularity being the existence of the rías. Corcubión ría and Fisterra Cape

into staggered blocks, due to N-S faults, which will later be submerged and now form submarine reliefs (Vanney et al. 1979; Santanach 1994). Thus, the original coastline, which was some 200–600 km from the current one, is now represented by various submerged horsts, such as the so-called Banco de Galicia (Vidal Romaní 1996, 2002). In this way, new limits were established for the Galician western coast. Other consequence is the existence of large coastal cliffs of tectonic origin (Vidal Romaní 2015); and the fluvial excavation of the Atlantic coastal edge also began, which would prefigure the future formation of the rías (Pagés Valcarlos 2000; Vidal Romaní 2015; Pérez Alberti 2021). On the other hand, subduction in the southern edge of the Bay of Biscay originated an oceanic trench that would also determine the true limits of the Cantabrian coastal zone. Its conformation continued during the Cenozoic, with Tertiary tectonic and epirogenic movements that contrasted the relief and raised the coastline, affecting the drainage network and its incisive work, to which were added the effects of the Quaternary variations in the sea level. In the Quaternary there were glacio-eustatic oscillations in the sea level, which descended during the glacial phases to about −120/−200 m below the current average level and rose during the interglacial phases up to about 15 or perhaps 40/60 m above today’s level (Vidal Romaní 2015; Vidal Romaní et al. 2018). This alternation of sea level rise and retreat occurred at least 20 times throughout the Pleistocene (Vidal Romaní 2015). In the stages of marine regression, the limits of the coast were up to 40 km away from their current position, favouring a greater excavation of the valleys in the final stretch of the fluvial courses. The marine transgression corresponding to the last interglacial period was the Eemian, about 140,000 years ago, when the sea rose about 4–6 m above its current level. And the last rise in sea level corresponded to

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Fig. 2 During the Quaternary there were glacio-eustatic oscillations of the sea level. Areagrande Beach

the Holocene postglacial transgression, between 15,000 and 4000 years before now, when the maximum sea level of recent times was reached, slightly above current level. At present, there is a new uplifting trend in the sea level, recorded in the last 150 years (Blanco Chao et al. 2001; Vidal Romaní and Grandal 2018) (Fig. 2). Petrological and structural characteristics also influenced the coastline shape (Pérez Alberti 2001; Blanco Chao et al. 2001; Gómez Pazo and Pérez Alberti 2017). In this sense, there is a clear differentiation between the Cantabrian and Atlantic coasts. On the one hand, in the Cantabrian sector metamorphic rocks such as slates, schists and quartzites usually predominate, while in the Atlantic sector igneous rocks such as granites dominate; and, in an intermediate position, some outcrops of basic rocks exist, such as those of the Cabo Ortegal comple On the other hand, the geological structures show different orientations; they are perpendicular to the coastline in the Cantabrian zone and parallel in the Atlantic zone. The lithological contrasts and structural layouts affect the differential erosion, since the marine erosive action advances through the areas of greatest weakness, conditioned by the rock type or the orientation of the stratification planes, also facilitated by the existing fracture network. In the littoral, continental and marine processes interact, which are extremely dynamic and changing. As an example, the configuration of a beach or the ripples formed on the sand can change significantly within hours. And, sometimes, a balance between erosive and cumulative stages is established over time in the same area, completely changing its physiognomy (Fig. 3).

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Fig. 3 The coastal space is extremely dynamic and changing. Ripples, Carnota Beach

The Galician coastline is situated in a context of high marine energy, and its most exposed areas are subject to frequent maritime storms. Waves and currents follow a dominant pattern (Asensio Amor and Iglesias Vidal 1989; Gómez Pazo and Pérez Alberti 2017). Regularly, waves come from the northwest, especially in large storms, while surface drift currents vary circumstantially, depending on the changing wind regime; during the winter, these go from south to north in the Atlantic part and from west to east in the Cantabrian part, while during the summer they are weaker and tend to move in the opposite direction. In episodic moments, strong Atlantic storms that generate giant waves occur. These large waves are capable of accumulating and removing rocky boulders in the supralittoral zone, as well as eroding and receding the dune fronts, as was observed during the great storms of the 2013–2014 winter (Flor et al. 2015; Pérez Alberti 2019). The highest waves recorded so far in Galicia (even in Spain) were in that winter, in the Costa da Morte, reaching a significant height of 13 m, one of the waves reaching 27.81 m (Fig. 4).

1.2 Rías Rías are tongues of sea that are introduced inland. The term was initially of local use as a generic toponym, until it was coined in 1886 by the German geographer Ferdinand von Richthofen when he described the rías as a singular formation that,

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Fig. 4 Retreat of the dune front. Morouzos Beach

already at that time, he associated with valleys carved out by rivers and flooded by the sea (Méndez and Rey 2000). Since then, many authors have addressed their origin, prevailing the original idea but with new contributions and reflections that still generate controversy today (Torre Enciso 1958, 1970; Carlé 1949; Pannekoek 1970; Vidal Romaní 1983, 1984, 2015; Pagés Valcarlos 2000; Méndez and Rey 2000; Pérez Alberti 2021). Their genesis was determined by plate tectonics, the orientation of fractures, the incision of fluvial courses and, finally, by marine action. Three sections of rías can be distinguished, which in turn correspond to three different sections of the coast: Rías Altas, Rías Medias and Rías Bajas (Torre Enciso 1958). They differ in various aspects, as, for instance, in their orientation, morphology, extension of the penetration of sea into the land, and formation age. Chronologically, the formation of the Rías Bajas was first, about 110 million years ago; later, the formation of Rías Altas initiated, about 24 million years ago; and then the Rías Media began to form, just 5 million years ago (Vidal Romaní et al. 2018) (Fig. 5). There is a clear distinction between the Cantabrian and Atlantic rías. They differ, for example, in their amplitude, the Cantabrian ones shorter, between 7 and 20 km in length, and the Atlantic ones larger, between 20 and 35 km in length. The Cantabrian ones are also shallower than the Atlantic ones, which may reach up to 50 m deep. Structural, petrological and tectonic factors, previously explained, conditioned the orientation, shape and length of the rías (Fig. 6). In the Atlantic part, the incision of the valleys that gave rise to the future rías began sometime after the opening of the Atlantic Ocean and the isostatic recovery of the old plate border. Thus, the fluvial excavation would begin about 100 million years ago, in the Cretaceous, when the sea reached the Galician coast for the first time (Vidal Romaní 2015). Later, in the Lower Paleogene, when the immersion of the continental shelf occurred, as well as epirogenesis of the general relief and the

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Fig. 5 Three sections of Galician rías can be distinguished: Rías Altas, Rías Medias and Rías Baixas. Muros-Noia Ría

Fig. 6 There is a clear distinction between the Cantabrian and the Atlantic rías. a Viveiro Ría; b Arousa Ría

coastal edge, a new cycle of fluvial incision was triggered (Torre Enciso 1958, 1970; Pagés Valcarlos 2000). This elevation of the coast is happening from at least 25 million years (Vidal Romaní 2012). Proofs of this uplift of the coast are the existence of elevated fluvial terraces in the final section of the Miño river (Viveen et al. 2013), and sea levels located along the entire coast up to 60 m above sea level (Vidal Romaní 1979; Vidal Romaní et al. 2018), as well as the mouth of the Xallas river, flowing into the sea in the form of a waterfall. The glacioeustatic oscillations of the Pleistocene, which lowered the sea level, activated the last phase of excavation, especially in the final outer stretch of the rivers. Finally, the post-glacial marine transgression would flood the previous fluvial valleys, originating the rías. In the Cantabrian part, the Alpine rising caused the rivers in this area to become strongly entrenched and short, which in turn limited the widening of their valleys and

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explains why the Cantabrian rías have not reached the dimensions of the Atlantic ones. However, the excavation that finally gave rise to the rías did not take place in the final stretch of the Miño river, despite being larger than other Galician rivers, so a ría did not develop here. This was because the tectonic movements that occurred in the Tertiary, due to the Alpine orogeny, extended the elevation of the Cantabrian Range to this Atlantic end, preventing the final section of this river from being flooded by the sea (Santanach 1994; Vidal Romaní 2012, 2015), and giving rise, in the south of Galicia and the north of Portugal, to the so-called Rías Secas.

1.3 Estuaries Galician rivers sometimes flow into estuaries, where fluvial and marine dynamics are juxtaposed, mixing fresh and marine waters, under the influence of river currents and tidal oscillations. The depth of the estuaries is limited, no more than 5–10 m, much less than that of a ría. In the estuaries there are zones differentiated by their morphology and hydrodynamics, with different biotopes and ecotopes, varying between the innermost and outermost zones that often open to a ría (Rey et al. 2000; Galván Arbieza 2014). From one area to another, the characteristics of salinity, currents and sedimentation conditions vary, being a very changing medium on the spatial and temporal scales. There are commonly subtidal and intertidal sedimentary complexes, due to discharges from fluvial currents, forming sandbanks and sandy-muddy tidal plains in various areas inside the estuary (Asensio and Teves 1965; Teves 1965; Vilas and Nombela 1985; Rey et al. 2000; Flor Rodríguez and Flor Blanco 2011). In certain places, the accumulation of these deposits becomes islands. In the more sheltered areas and where the deposition is finer, marshes also tend to form. Sometimes, the origin of these complexes is due to the existence of sandy arrows that partially close the estuary, as is quite evident, for example, in the cases of the mouths of the Masma, Eume, Mandeo, Mero, Anllóns, Miñor, and particularly obvious in the Miño (Fig. 7). The Miño estuary is a clear example of this morphology. It is the widest and one of the large European estuaries due to its extension and the flow of fluvial contributions. It is about 30 km long, which is as far as tidal influence normally reaches, widening to 2 km in the last 15 km before its mouth, where it narrows to only 400 m, partially enclosed by a sandy arrow. It is not very deep, since at the mouth of the estuary it does not exceed 4 m of depth below the mean tidal level, and at its opening to the sea it develops sandy bars parallel to the external coastal beach (Vilas and Somoza 1984). In various areas of this estuary there are alluvial plains, sandbars, islands and marshes.

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Fig. 7 The Miño estuary is one of the great European estuaries

1.4 Marshes Marshes are formed in protected areas of the coast, mainly at the inner part of the rías and estuaries, or sheltered by coastal lagoons, or protected by sandy arrows that partially slow water currents and protect from sea waves. Due to their location, they are subject to fluvial and marine influence, both continental and oceanic, affected by tides while receiving the contributions of the rivers, and located where the deposition of usually fine sedimentary materials predominates (Fig. 8). These are muddy areas, on which a specific vegetation of rushes and reeds extends, zoned in strips or levels, according to their tolerance to changing environmental conditions of salinity gradation, adaptation to the tidal regime and to the generally brackish waters. An irregular network of shallow channels is traced through them, forming narrow meanders that are flooded or dry following the periodic tide rise and fall. Their muddy soils are highly enriched in organic matter and nutrients, contributing to the high biological productivity of these systems. Marshes are common along the entire coastline; however, stand out for their extension those existing at the inner part of the Ribadeo, Ortigueira-Ladrido, Betanzos and Noia rías, and in the Corrubedo Complex. Also, in other areas there are wide intertidal plains, whose dynamics are exclusively due to the tide flow; they are also muddy, with channels excavated by the tide ebb and flow. Good examples are those of Arcade, inside the Vigo estuary; in Ponte

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Fig. 8 Marshes are formed in protected areas of the coast. Corrubedo

Nafonso, inside the Noia estuary, and in the O Bao cove, in the Umia-O GroveCarreirón Complex. In all these areas there are mudflats and marshes. However, the current uprising trend in sea level can cause these ecosystems to disappear.

1.5 Cliffs The Galician coast is mostly rocky, rising to different heights above the sea, even reaching several hundred meters in height on some cliffs. There are various types of sea cliffs, affected by processes of intense instability (Pérez Alberti et al. 1997, 2000). The limits of many mountain ranges near the coast are also interpreted as cliff morphologies, as they were considered intraplate cliffs of tectonic origin and not due to marine erosion; they represent the edge of the fissure created when Pangea opened during the Mesozoic, subsequently raised by isostatic recovery (Vidal Romaní, 2015). This is the case of the hills of A Capelada, O Pindo, O Barbanza, A Grova, etc. It is the existence of these coastal elevations with heights up to 600 m that constitutes another of the characteristic features of the Galician coast (Blanco Chao et al. 2001). One of these cliffs is Vixía Herbeira, near Cabo Ortegal, considered the highest in southern continental Europe, with an almost vertical drop of 617 m. “Costa da Morte”, the most western coast of Galicia, is also a renowned cliff area, in general over 100 m high, as is the case at the terminal Cabo Fisterra.

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Fig. 9 The limits of mountain ranges near the coast are considered intraplate cliffs of tectonic origin and not due to marine erosion. Herbeira Cliff

The marine action erodes the foot of the cliffs and causes their dismantling and the inland retreat of the coastline. In certain cases, detached rocky blocks accumulate at the base of the cliff, serving as testimony to the coastline retreat; sometimes, they protect the cliff, slowing down the direct action of the waves, but on the contrary, on other occasions the detached material increases the abrasive action of the waves. It also happens that many escarpments are preceded by intertidal rocky platforms that dissipate the energy of the waves before reaching the base of the cliff that only reached in strong storms (Figs. 9 and 10). Sometimes, the favorable spatial arrangement of fracture lines and stratification planes facilitates the excavation by the sea, taking advance of the areas of greatest weakness, and creating hollows such as “furnas”, arcs, etc. (Perez Alberti et al. 2000). A singular example can be found in the Mariña Lucense coastline, where vertical fractures and horizontal pleated strata of quartzite, schist and slate allowed the sea to carve surprising caves and arcs, as observed in the so-called Cathedral’s Beach (Fig. 11).

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Fig. 10 Blocks falls evidence the retreat of the cliff. As Lagoas Beach

Fig. 11 Generally, the sea excavates in favor of the areas of greatest lithological and structural weakness. Catedrais Beach

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1.6 Coastal Plains In the perimeter of the Galician coast there are some rocky platforms and flattened surfaces, placed slightly above sea level. In many cases, they are ancient marine abrasion surfaces, possibly eroded by the sea in the Tertiary period or in later interglacial period(s) (Blanco Chao et al. 2003). In other cases, their origin is more doubtful or is clearly of continental genesis. In those caused by marine erosion, their elevation above current sea level and their conservation often depend on lithological and structural factors (Gómez Pazo et al. 2021), but sometimes tectonic causes have influenced (Mary 1992). The most discussed origin has been that of the so-called Rasa Cantábrica (Fig. 12). The Rasa Cantábrica, although it has the appearance of a marine abrasion platform and probably was covered by the sea at some point, would have an essentially continental genesis, as more terrestrial than marine deposits exist on it (Hernández Pacheco and Asensio Amor 1959, 1960; Asensio Amor 1985; Mary 1983; Barral Silva et al. 1985; Asensio Amor and González Martín 1987). It is likely that it was an ancient erosion surface or perhaps a chemical corrosion surface (Vidal Romaní 2015). It would surely have a polygenic origin and complex evolution, in which various continental processes and briefly some marine processes are mixed. Its current position above sea level can be explained by a tectonic uplifting due the Alpine compression episode (Mary 1992). This uplifting is not uniform, as it is slightly tilted, increasing its height from west to east as it widens: it is a narrow

Fig. 12 Continental and marine processes are mixed in the genesis of some rasas. Cantabrian Rasa

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strip of only 5–20 m above the sea near Burela, it is about 40–60 m high in Ribadeo, but reaches 110 m high near Cabo Peñas in Asturias. A marine abrasion platform is currently being carved in the infralittoral zone, at the foot of this Rasa Cantábrica.

1.7 Boulder Beaches On the coastline, accumulations of rocky blocks are very frequent, especially in areas of high wave energy. They are generally settled on rocky platforms or deposited at the foot of stony cliffs, usually above the mean tide level and sometimes at some height above sea level. At some places they reach a considerable thickness, up to 3 m, showing diverse arrangements (Pérez Alberti 2019), and constituting the so-called boulder beaches or “coídos”. They originate from the erosive dismantling of the rocks of the cliffs and the coastal platforms, or by the marine erosion of slope deposits, although they may also come from old coastal deposits, possibly of Eemian origin, located above the current sea level and now eroded by the sea (Costa Casais et al. 1996; Alonso and Pagés 2000; Blanco Chao et al. 2003). These boulders are of variable size, heterometric, generally rounded or slightly angular because of the abrasive action of the waves. The blocks closest to the sea show great mobility, whereas those located at higher levels and larger, although they were considered relics of other times, were shown to move at present, but only occasionally during marine storms (Pérez Alberti 2019) (Fig. 13).

1.8 Sandy Beaches and Dunes Beaches are sand accumulations deposited in areas favorable to its sedimentation, because of the reduction of the wave and littoral drift current energy. However, the indented nature of the coast hinders the existence of large longitudinal currents that could generate long and rectilinear beaches; therefore, the sandbanks are basically located in restricted areas between defined limits. Beaches are usually attached to inlets of the coast, showing a concave or half-moon shape, but may also form arrows and other sandy formations, usually associated to river mouths. Crosswise, the beaches present a typical profile, often with a small elevation or berm. Anyway, the conformation and profile of a beach are highly variable, both seasonally and daily, depending on the waves, tides and currents, as well as on episodic storms. Beach-dune complexes are common along the Galician coast. Some beaches are relatively long, of kilometric dimensions. There are about 50 beaches with a length greater than 1 km, among the largest are those of Carnota, Corrubedo and A Lanzada (Fig. 14). At the origin, the sands of the beaches and dune fields were mostly of continental provenance, carried to the sea by river contributions; occasionally they come from

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Fig. 13 Block accumulations are generally located above mean tidal level

Fig. 14 Some beaches are relatively long, kilometric in size. Carnota Beach

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Fig. 15 In certain places rampant dunes would be formed that climb the immediate slopes. Veo Cape

the erosion of granitic weathering mantles or from cliffs destruction (Pérez Alberti and Vázquez Paz 2011). These sands were then redistributed along the continental shelf by drift currents. Later, during the ice ages, when the sea level dropped, this sandy coast would be exposed. Some coastal sand sheets already exist from 20,000 to 18,000 years BP (Martínez Cortizas et al. 1996). Subsequently, when the ice melted and the sea level rose again, as happened between 15,000 and 4500 years before now, during the Holocene postglacial transgression, the sand sheets were pushed by the sea and wind, and they mostly accumulated in the protrusions of the current coastline (Vidal Romaní 2015; Vidal Romaní and Grandal 2018) (Fig. 15). At many places the wind would create large dunes, and up to 71 dune systems are identified in the Galician territory (Pérez Alberti and Vázquez Paz 2011). At some places, the wind created big dunes, like the one in Corrubedo, and at other places, it formed climbing dunes rising the immediate slopes, as happened in Cabo Veo, next to the Trece sandbank, or at the mouth of the Anllóns river, where they climb up to 192 m, in the so-called Monte Branco. The Corrubedo Dune is the largest one, although it is becoming less and less voluminous. It measures approximately 1 km in length, about 250 m in width, and reached 18–20 m in height a few decades ago, which has now been reduced, although its shape and elevation varies from year to year (Pérez Alberti and Vázquez Paz 2011). It is a mobile dune, balanced between two opposite directions of dominant winds that vary seasonally, blowing from the SW in winter and from the NE in summer. The greater predominance of the first ones has contributed to its advance inland, while it

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Fig. 16 The Corrubedo Dune is large, its shape and elevation varying from year to year

decreases in height in a natural way, regardless of the impacts produced by anthropic action. Moreover, it is no longer possible to regenerate it with new contributions of sand, as was the case in past times, because the source area is already covered by the sea. Consequently, it will decrease in height and become covered with vegetation as it migrates inland. On the other hand, the progressive rise in sea level suggests the possible future disappearance of all these dune systems (Fig. 16).

1.9 Coastal Lagoons Along the western Galician seashore, coastal lagoons are frequent. The most relevant, listed from north to south, are those of A Frouxeira, Doniños, Baldaio, Traba, Caldebarcos, Xarfas, Xuño, Carregal, Vixán and Bodeira. They are separated from the sea by a dune ridge that completely or partially closes off the lagoon space, while marshes advance progressively towards the interior, connecting with the mainland (Fig. 17). Some lagoons are permanently closed and have no direct communication with the sea; others open through a channel and are influenced by tidal oscillation; and others may be temporarily open or closed, depending on whether the waves have opened in episodic storms, or occluded, the channel that connects them with the sea. Among the lagoons that are always—or almost always—closed there are those of Doniños, Traba, Xuño, Vixán and Bodeira; among those always open are those of Baldaio

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Fig. 17 There are numerous coastal lagoons on the coast. Xarfas lake

and Carregal; and among those that seasonally open or close there are A Frouxeira and Xarfas. All these lagoons receive very limited fluvial water contributions, as if these were larger, they would surely not exist, and are generally fed by underground aquifers or by seawater seepage. Their origin is associated to the last postglacial marine transgression. The progressive rise in sea level has moved upwards the fine sediments deposited on the coastal platform, which pushed by wind and waves have originated sandy bars and littoral arrows that closed the normal drainage of some small basins, giving rise to these lagoons. At present, they have a natural tendency to gradually filling up, as it is already observable in the old Pantín lagoon. In this filling process can participate both the continental contributions and the sands of the dune ridges confining the lagoons, which can migrate and invade the lagoon space.

1.10 Islands In the Galician maritime periphery there are numerous islands, about 70 counting islands and islets. Some of them, the smallest and most recent ones, testify the retreat of the coast, as they are originated by differential erosion because to their higher resistance to the devastating action of the sea. This is the case, for instance, of almost all the islands of the Cantabrian and Northern coast, as those of Coelleira, Ansarón, Os Aguillóns and As Sisargas (Figs. 18 and 19). Other islands, such as the largest and farthest older ones in the Atlantic and Western coast, also evidence the retreat of a distant coastline, but in this case the tectonics played a more decisive role than the erosive processes. This is the case of the Ons and Cíes islands; they also show a clear asymmetry, with a cliff zone that

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Fig. 18 Some islands are testimonials of the retreat of the coast due to differential erosion. Os Aguillóns

Fig. 19 In the genesis of some islands, tectonics played a determining role. Cíes Islands

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rises to more than 160 m on the western side facing the ocean, and a gently sloping area on the eastern side facing the coast, where sandbanks can be found. And there are also other islands sheltered inside the rías, which are old relief protrusions that rise above seawater after the last rise in sea level flooded part of the coastline and the valleys now occupied by the rías. The most illustrative example is that of the island of Arousa, with a large area but low height and smooth relief, located central in the wide interior of the ría, in the so-called Mar de Arousa.

2 Geological Heritage Galicia shows a great variety and singularity of geological landscapes, whose genesis has been exposed above in a synthetic way. In the Iberian Peninsula few territories have such antiquity, complexity, richness and interest in their geology, which constitutes one of the most exceptional values of our natural, cultural and landscape heritage. Consequently, our geological heritage is a multiple resource, with varied economic and social uses, among which it is worth highlighting its scientific, educational and informative attractions, as well as its interest as a landscape. Many sites of special geological singularity have been inventoried. Their merits can be diverse: for their lithological formations, tectonic structures, forms of erosion and sedimentation, mineral and paleontological deposits, exceptional paleogeographic evidence, or also for their current hydrological, conservation or geotouristic interest. In any country, whenever places of geological interest have been catalogued, a majority turned out to also be of scenic interest. In the Galician case, it would suffice to point out the well-known examples of As Catedrais Beach, Miño and Sil Canyons, Xallas Waterfall, Corrubedo Dune, Herbeira Cliff, Courel Fold, etc., some of which are the objective of massive visits. Moreover, with few exceptions, they are generally wide and panoramic, little vulnerable spaces, suitable for educational and geotourism use. A pioneering work was initiated by the IGME (1983), when it inventoried the “Puntos de interés geológico de Galicia”, limiting to the most representative or essential ones, ruling out including all the possible ones, since they could be infinite. From the very beginning it was kept in mind that such cataloguing would serve, among other purposes, for possible protection and for social, educational and tourist use of the inventoried sites. The inclusion of new geosites in the IGME inventory continues open. In addition, numerous studies and publications have described different types of geological landscapes as well as geo-routes (IGME 1983; Vidal Romaní 1991; Pérez Moreira 2002; VV. AA. 2004). It is very important that our geological heritage, besides being studied, be disseminated and known, and therefore valued by society (Fig. 20).

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Fig. 20 It is very important that our geological heritage be disseminated and known, and therefore valued by society. Catedrais Beach

3 Sustainability of the Geological Landscape “Paisaje” is a term that in our field has been introduced precisely by a geologist, Guillermo Schulz (López Silvestre 2007), who was also the introducer of the modern Geological Science in Galicia (Vidal Romaní 1985). Schulz, a German geologist and mining engineer, in his pioneering “Descripcion Geonóstica del Reyno de Galicia” (1835), refers to “variedad de paisages” surely using the term in a morphological sense, not as an aesthetic idea, the original of the word landscape. Evidence is that, when Schulz describes a route through coastal Galicia Cantabrian coast, where Praia das Catedrais is located, now highly appreciated for its aesthetic beauty, he refers to this area of islets and caves saying that “It is a coast with a sad appearance… of ruin” (Díaz-Fierros 2015). The idea of landscape is a cultural concept, historically forged by culture (Pérez Moreira 2010). It defines, at the same time, an objective reality and a subjective perception, whose assessment depends on the observer and the qualification of his gaze. This means that the gaze can also be educated culturally and aesthetically, to grant values and recognition to the landscape. Hence the importance that our geological heritage, in addition to being studied, be disseminated and known, and therefore valued by society. As far as the conservation of the geological heritage is concerned, the ideal would be its maintenance in its own degree of naturalness, for the benefit of the normal development of natural cycles, as well as for the optimization of the landscape. However,

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human actions have been intervening in the territory for a long time, taking advantage of, and altering the geological resources. For example, with mining, reservoirs, landfills, road infrastructure, port works, or sometimes, inadvertently, due to forest fires or other causes of erosion, water turbulence, etc. On other occasions, human interventions are in prevention of geological risks, trying to avoid landslides, floods, etc. Anyway, nowadays these anthropic interventions very often exceed the capacity of natural processes, which forces us to rethink their proper management within the framework of Environmental Geology. In the future, human activity will continue to intervene in the geology resource, but also the geological cycles will continue their course on another time scale. The truth is that the current forms of relief are only the last link, for the moment, of a chain of slow geological events, which will continue in the future, modifying the forms of the landscape. It may even happen, in the medium term, that the current processes are accelerated or modified due to natural or anthropic causes, for instance, that the climate and its geological action are altered or that the sea level rises worryingly. Also, in the long term, the push of plate tectonics and other natural geological processes will continue for the next few million years. We already started this work pointing out that is a “process”: the constitution of the landscape (Fig. 21).

Fig. 21 In the future, geological processes will continue, modifying the forms of the landscape

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References Alonso A, Pagés JL (2000) El registro sedimentario del final del Cuaternario en el litoral noroeste de la Península Ibérica. Márgenes Cantábrico y Atlántico. Rev Soc Geol España 13(1):17 Asensio Amor I (1985) Conexión entre terrazas prelitorales y litorales en las proximidades del límite galaico-astur. Cadernos do Lab. Xeolóxico de Laxe, 9:321 Asensio Amor I, González Martín JA (1987) Síntesis de procesos geomorfológicos en el límite galaico-astur. Cuad Lab Xeol Laxe 11:103 Asensio Amor I, Iglesias Vidal JC (1989) Procesos litorales. Las corrientes superficiales en la costa oriental de Lugo. Trabajos del Laboratorio Xeolóxico de Laxe 14:55 Asensio Amor I, Teves Rivas N (1965) El proceso de relleno con materiales arenosos y fangosoarenoso en la ría de Foz. Boletín de la Real Sociedad Española de Historia Natural, sección Geología 63(1):17 Barral Silva MT, Guitián Rivera F, Guitián Ojea F (1985) Estudio sedimentológico de un depósito arenoso de la Rasa Cantábrica: aplicación de la exoscopía del cuarzo. Cadernos do Laboratorio Xeolóxico Laxe 9:329 Blanco Chao R, Costa Casais M, Martínez Cortizas A, Pérez Alberti A, Trenhaile AS (2003) Evolution and inheritance of a rock coast: western Galicia, Northwestern Spain. In: John Willei & Sons (eds) Earth Surface Processes and Landforms 28(7):757–775, Chichester, New York Blanco Chao R, Costa Casais M, Vázquez Paz M (2001) As paisaxes da costa: a dinámica xeomorfolóxica na súa configuración. In: Pérez Alberti A (Coord.). Galicia fai dous mil anos. O feito diferencial galego. IV. As paisaxes de Galicia, Museo do Pobo Galego. 2:197–235 Carlé W (1949) Las Rías Bajas Gallegas. Traducción de J. Gómez de Llarena. Estud. Geográficos 35:323–330 Costa Casais M, Martínez Cortizas A, Pérez Alberti A (1996) Tipos de depósitos costeiros antigos entre o cabo de Fisterre e o cabo de Corrubedo. In: Pérez Alberti A, Martini P, Chesworth W, Martínez Cortizas A (eds) Dinámica y Evolución de Medios Cuaternarios. Xunta de Galicia, pp 417–430 Díaz-Fierros Viqueira F (2015) Xeoloxía e Paisaxe: na memoria de I. Asensio Amor (1915-2001). Conf. Inaugural de Curso. IES Dionisio Gamallo. Ribadeo, Lugo Flor Rodríguez GS, Flor Blanco G (2011) La influencia humana sobre las playas y estuarios de Galicia oriental y Asturias occidental. Geolodía 11. Depto. Geología Universidad de Oviedo & Sociedad Geológica de España (eds) Flor Rodríguez, GS, Flor Blanco G, Flores Soriano C, Alcántara Carrió J, Montoya Montes I (2015) Efectos de los temporales de invierno de 2014 sobre la costa asturiana. In: Malvárez G, Navas F, Guisado E (eds). VII Jornadas de Geomorfología Litoral, Geo-Temas 15, Sociedad Geológica de España, pp 17–20 Galván Arbieza C (2014) Clasificación de estuarios a diferentes escalas espaciales mediante la integración de modelos físicos y biológicos. Tesis Doctoral. Universidad de Cantabria, pp 494 Gómez Pazo A, Pérez Alberti A (2017) Vulnerabilidad de las costas de Galicia ante los temporales marinos en el contexto del cambio global. Sémata 29:117 Gómez Pazo A, Pérez Alberti A, Trenhaile A (2021) High resolution mapping and analysis of shore platform morphology in Galicia, northwestern Spain. Marine Geology 436:1 Hernández Pacheco F, Asensio Amor I (1959) Materiales sedimentarios sobre la rasa cantábrica, I. Tramo comprendido entre las rías del Eo y de Foz. Boletín de la Real Sociedad Española de Historia Natural, Sección Geología 57:75 Hernández Pacheco F, Asensio Amor I (1960) Materiales sedimentarios sobre la rasa cantábrica. Tramo comprendido entre la ría de Foz y el casco urbano de Burela. Boletín de la Real Sociedad Española de Historia Natural, Sección Geología 58(1):73 IGME (1983) Puntos de interés geológico de Galicia. Instituto Geológico y Minero de España, pp 103 López Silvestre F (2007) Nota erudita sobre a orixe do termo «paisaxe» en galego. Adra 2:119

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Martínez Cortizas A, Costa Casais M, Moares Domínguez C (1996) Niveles dunares pleistocenos y holocenos en la costa de Galicia: hipótesis cronológica en base a su grado de edafización. In: Pérez Alberti A, Martini P, Chesworth W, Martínez Cortizas A (eds) Dinámica y Evolución de Medios Cuaternarios. Xunta de Galicia, pp 391–404 Mary G (1983) Evolución del margen costero de la Cordillera Cantábrica en Asturias desde el Mioceno. Trabajos de Geología 13:3 Mary G (1992) Interacción entre la epirogénesis y el eustatismo en el escalonamiento de las áreas de abrasión marina neógenas y pleistocenas del segmento medio de la costa norte española. Vasconia, Cuadernos de sección Historia 20:135 Méndez G, Rey D (2000) Perspectiva histórica del conocimiento geológico de las rías gallegas. J Iberian Geol 26:21 Pagés Valcarlos JL (2000) Origen y evolución geomorfológica de las rías atlánticas de Galicia. Revista de la Sociedad Geológica de España 13(3-4):393 Pannekoek AJ (1970) Additional geomorphological data on the ria area of western Galicia (Spain). Leidse Geologische Modelingen 37:185 Pérez Alberti A (2001) A paisaxe como sistema: o exemplo de Galicia. In: Galicia fai dous mil anos. O feito diferencial galego. IV: As Paisaxes de Galicia. Museo do Pobo Galego. Santiago de Compostela 1:57–106 Pérez Alberti A (2019) Caracterización e dinámica dos coidos nas costas de Galicia. Nemus, 9:15–26 Pérez Alberti A (2021) Sobre el origen de las rías gallegas: Viejas teorías y nuevas reflexiones. In: Roig Munar FX, Gelabert Ferrer B, Martín Prieto JA Coords., Gómez Pujol L (eds). De la tierra al mar i de la mar a la tierra: Homenaje a Antonio Rodríguez Perea. Societat d’ Historia Natural de las Balears pp 149–164 Pérez Alberti A, Blanco Chao R, Castro Casais M, Valcárcel Díaz M (2000) O relevo da costa. Ed. Bahía. A Coruña, pp 66 Pérez Alberti A, Blanco Chao R, Costa Casais M (1997) La importancia de los balances de acumulación/erosión y fosilización/exhumación en la evolución geomorfológica de la costa gallega. In: Dinámica litoral-interior, Actas XV Congreso de Geógrafos Españoles, Depto. Xeografía, Univ. Santiago de Compostela, 1:205–219 Pérez Alberti, Vázquez Paz MC (2011) Caracterización y dinámica de sistemas dunares costeros de Galicia. In: Sanjaume Saumeell E, García Prieto FJ (Coords.). Las dunas de España. Soc. Esp. de Geomorfología, pp 161–185 Pérez Moreira R (2002) Geología y paisaje. In: Díaz-Fierros Viqueira F (Coord.). Galicia, Naturaleza, Vol. XXXVI: Historia Natural, Geología. Hércules de Ediciones, pp 569–577 Pérez Moreira R (2010) A descuberta cultural da paisaxe. In: Pérez Moreira R, López González FJ (Coords.). Cultura e Paisaxe. Universidade de Santiago, pp 19–51 Rey D, López-Rodríguez N, Rubio B, Vilas F, Monamed K, Pazos O, Bógalo MF (2000) Propiedades magnéticas de los sedimentos de tipo estuarino. El caso de las Rías Baixas. J Iberian Geol 26:151 Santanach Prat P (1994) Las cuencas terciarias gallegas en la terminación occidental de los relieves pirenaicos. Cadernos do Laboratorio Xeolóxico de Laxe 19:57 Teves Rivas N (1965) El proceso de relleno con materiales arenosos y fangoso-arenoso en la Ría de Vivero. Boletín de la Real Sociedad Española de Historia Natural, Sección Geología 63(2–3):119 Torre Enciso E (1958) Estado actual del conocimiento de las rías gallegas. In: Homenaxe a Ramón Otero Pedrayo. Galaxia, pp 237–250 Torre Enciso U (1970) Avanzos no coñecimento da xeomorfoloxía de Galicia. Discurso de ingreso na Real Academia Galega, A Coruña Vanney JR, Auxietre JL, Dunand JP (1979) Geomorphic provinces and evolution of northwestern Iberian continental margin. Ann. Inst. Oceanographique de París 55(1):5 Vidal Romaní JR (1979) Estado de los conocimientos sobre la variación del nivel del mar en Galicia durante el Cuaternario, Braña, 1:69 Vidal Romaní JR (1983) Origen y evolución de las Rías, Muros y Noia. Introducción. Guía de la VI Reunión de Cuaternario. GGQ & Grupo Esp. Trabajos de Cuaternario, Univ. de Santiago, pp 1–41

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Vidal Romaní JR (1984) A orixe das Rías Galegas. Estado da cuestión (1886–1983). Cuad. Área de Ciencias Mariñas, Seminario de Estudos Galegos, 1:13 Vidal Romaní JR (1985) Descripción Geognóstica del Reyno de Galicia de Guillermo Schulz, 1835. Edición facsimilar comentada. Publicacións da Área de Xeoloxía e Minería do Seminario de Estudos Galegos, Edicións do Castro, Sada, A Coruña, pp 133 Vidal Romaní JR (1991) Unidades paisajísticas de Galicia (textos). Serie: Territorio y Paisaxe. COTOP, Xunta de Galicia, pp 103 Vidal Romaní JR (1996) Geomorfología de Galicia. In: Geografía de Galicia. Río Barja FJ (Coord.), T. XVII. Hércules de Ediciones, A Coruña pp. 37–63 Vidal Romaní JR (2002) El relieve actual de Galicia. In: Díaz-Fierros Viqueira F (Coord.), Galicia, Naturaleza, Vol. XXXVI: Historia Natural, Geología. Hércules de Ediciones, pp 304–341 Vidal Romaní JR (2012) Por qué Gallaecia Petrea. In: Gallaecia Petrea, I: Xeoloxía. Cidade da Cultura de Galicia. Xunta de Galicia, Santiago de Compostela, pp 22–33 Vidal Romaní JR (2015) Geología de Galicia: cómo armar un rompecabezas. Discurso de Ingreso en la Real Academia de Ciencias de Galicia, 25-III-2015 Vidal Romaní JR, Grandal D’ Anglade A (2018) Nota sobre la última transgresión marina en la costa de Galicia. Cadernos do Laboratorio Xeolóxico de Laxe 40:229 Vidal Romaní JR, Vaqueiro Rodríguez M, Costas Vázquez R (2018) Ría de Aldán. Geolodía, 2018. Soc. Geológica de España & Univ. da Coruña Vilas F, Nombela MA (1985) Las zonas estuarinas de las costas de Galicia y sus medios asociados, NW de la Península Ibérica. Thalassas 3:7 Vilas F, Somoza L (1984) El estuario del Miño: observaciones previas de su dinámica. Thalassas 2:87 Viveen W, Schoorl JM, Veldkamp A, Van Balen RT, Desprat S, Vidal Romaní JR (2013) Reconstructing the interacting effects of base level, climate and tectonic uplift in the Lower Miño River terrace record: a gradient modelling evaluation. Geomorphology 186:96 VV AA (2004) Patrimonio Geológico de Galicia. Rafael Nuche del Rivero (ed). ENRESA, pp 475

Vegetation Cover Manuel Antonio Rodríguez-Guitián

Abstract Galicia is a complex territory from the environmental (lithology, relief, climate) and socio-economic (population, distribution of productive activities) perspectives. Its geographical position has determined its paleoenvironmental dynamics throughout the last glacial cycle (Würm), in whose final phase a large part of the territory was under glacio-nival conditions, and has favored the emergence of favorable conditions for the domain of deciduous forests throughout the last two thirds of the Holocene. However, as a result of human colonization of most of this territory over the last 5,000 years, its vegetation cover has been greatly homogenized, first favoring the expansion of agricultural crops and scrublands (particularly heaths) and, already in recent times, forest plantations with introduced species (pines and Eucalyptus). The best examples of the characteristic vegetation of this territory take refuge in the steepest mountains, certain slightly altered coastal stretches, and some wetlands. Nonetheless, Galicia still harbors important elements (species, habitats) for the maintenance of biodiversity on a European scale. Its long-term persistence requires territorial planning and management of land use consistent with this singularity and in line with the evolving scientific knowledge and environmental regulations. Keywords Current vegetation · Residual forests · Heaths · Coastal complexes · Wetlands · Biodiversity threats

1 Biogeographical Setting The environmental changes that occurred throughout the Cenozoic (65-0 million years) have decisively conditioned the native plant species that are currently found in Galicia (Gómez-Orellana et al. 2007; Muñoz-Sobrino et al. 2007; Ramil-Rego et al. 2008, 2009; González-Sampériz et al. 2010; Rodríguez-Sánchez et al. 2010). M. A. Rodríguez-Guitián (B) Department of Plant Production and Engineering Projects, Higher Polytechnic School of Engineering, Campus Terra, University of Santiago de Compostela, 27002 Lugo, Galicia, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_23

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This territory shares with other parts of the temperate areas of the European continent most of its native flora, although reinforced with a wide group of thermophilic plants that are common in western Mediterranean area. Only a small part is endemic and is mainly concentrated in coastal environments, the highest mountain peaks, or outcrops of non-frequent lithologies (Amigo et al. 2017). The distribution of this flora and the plant communities to which it gives rise allows the division of the territory into units with their own floristic ensembles. Although various authors (Rivas-Martínez 1987; Rivas-Martínez et al. 2017) have argued that Galicia is divided between two biogeographical units of higher rank (the Eurosiberian and Mediterranean regions), other more recent ones (RodríguezGuitián and Ramil-Rego 2007, 2008; Fernández-Prieto et al. 2020) advocate that all of it must be included in the first, while acknowledging the transitional character towards the second of a large part of this region (Image 1). The large number of delimited basic phytogeographic units (districts) gives an idea of the high botanical diversity that the Galician territory harbors. This floristicallybased territorial division is easily recognizable in the areas less affected by human activities (districts included in sectors 3–7), in which native forests and the shrub and herbaceous communities that replace them still occupy extensive surfaces. However, in the districts of sectors 1 and 2, the expansion of urban spaces and the intensification

Image 1 Phytogeographical units of Galicia. Adapted from Fernández-Prieto et al. (2020). The numbers included in circles indicate the location of the images inserted in this section

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Image 2 The abrupt relief and severe climatic conditions have favored the eastern mountains of the province of Lugo to maintain a considerable area of native forest, an ecosystem that has contributed to the survival of emblematic animal species, such as the brown bear, the capercaillie or the black woodpecker. Parish of San Fiz de Donís (municipality of Cervantes, province of Lugo)

of agricultural, livestock and forest production with exotic species mask the floristic particularities of these territories, which are evident only to people trained in the botanical field (Image 2).

2 Vegetation and Human Activity Even though Galicia has been occupied by Homo sapiens for at least the last 25,000 years, paleoenvironmental reconstructions do not recognize a significative influence of their activities on vegetation cover until about 5000–4500 years before present (BP), when agriculture and livestock began to expand throughout the region (Ramil-Rego et al. 2011, 2012). Previously, in the Middle Holocene (8500– 5000 years BP), the prevailing warm and humid climate allowed the development of deciduous forests in most of its surface. The result of the generalization of human activities (clearing land for cultivation, obtaining fuel, grazing, mining, etc.) in this part of Europe led to the near disappearance of the pre-existing forests and to the periodic alteration of their corresponding substitution communities (Ramil-Rego and

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Aira Rodríguez 1996; Ramil-Rego et al. 2011). This process has led to the regional extinction of the populations of several plant species in historical times, among which some tree species can be highlighted, such as hornbeam (Carpinus betulus) and lime trees (Tilia spp.), as well as the native populations of maritime (Pinus pinaster) and Scots (P. sylvestris) pines (Muñoz-Sobrino et al. 2007; Rubiales et al. 2008; Rodríguez-Sánchez et al. 2010) (Image 3). Paleoenvironmental reconstructions reveal that at the end of the Iron Age (about 2500 years BP), most of coastal and inland Galicia lacked wooded vegetation and was covered by vast expanses of scrub and herbaceous formations that served as food for herds of cows, horses, goats and sheep. Around the settlements (hillforts or castros in the Galician language), the communities worked the land and planted different cereals (wheat, barley) together with a small group of vegetables (turnips, cabbage, broad beans, peas, lentils) and collected some species possibly used in rituals (poppy). Romanization (218 B.C.–476 A.D.) contributed to the maintenance of pre-existing uses and the further reduction of forests for the supply of wood,

Image 3 Despite the great longevity of many of the existing native tree species in Galicia, old specimens are scarce in this land. Some of them have been preserved as ornamental elements in noble houses or public spaces, being extremely rare to find in the different types of forests that have been described in this territory. The ecological role of old trees within wooded ecosystems is well known and is linked to the supply of microenvironments necessary for certain forest mammals, birds, invertebrates, and fungi, unable to complete their life cycles in other habitats. Veteran sessile oak-tree in an old-growth forest in the western part of the Serra dos Ancares (municipality of Cervantes, province of Lugo)

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necessary for increasing construction and mining activities (Ramil-Rego et al. 2008; López-Merino et al. 2009; Tereso et al. 2013, 2016). Later, due to the socio-economic instability of the High Middle Ages, the landscape experienced a certain recovery of the tree cover. However, this trend was soon reversed and, by the Late Middle Ages, reforestation with Pinus pinaster had already begun in coastal areas and inland temperate valleys, following the example from the neighboring kingdom of Portugal. After the European colonization of the Americas, numerous plant species began to be brought to Europe, initially for ornamental purposes, but shortly afterwards to be integrated into agricultural systems and wood production in different parts of the continent. In the case of Galicia, the American plants that were first integrated into production systems were cereals (corn) and vegetables such as potatoes, corn, beans, peppers, tomatoes, and pumpkins. In the case of the first two, their high productivity favored the expansion of arable land to the detriment of other pre-existing crops (turnips, proso millet, traditional chestnut plantations, etc.) (Ramil-Rego et al. 2012) (Image 4). In the nineteenth century, pines from America (P. radiata) and the first eucalyptus trees were introduced. Several European conifers (Picea abies, Pinus sylvestris)

Image 4 The intensification of timber production in the coastal areas of Galicia with a mild climate has led to the expansion of pine and Eucalyptus plantations and the virtual disappearance of natural vegetation, such as the heaths that can be seen in the foreground, which only remains in marginal places from the productive point of view. Basin of the Baleo River (north of the province of A Coruña)

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were added to these, along with more North American (Chamaecyparis lawsoniana, Pseudotsuga menziesii, Quercus rubra, Robinia pseudoacacia), Asian (Ailanthus altissima, Castanea crenata, C. mollissima) and Oceanian (Acacia spp.) tree species during the twentieth century. Particularly remarkable is the generalization of the use of Eucalyptus species in forest plantations which took place from the middle of the twentieth century. In the present day, about ten species of this genus are used to produce mainly cellulose and wood for various purposes, occupying around 435,000 ha (almost 15% of the surface of Galicia) (Image 5). Currently, the data published by the MARM (2011) indicate that just over 2,000,000 ha (almost 70% of Galician territory) is occupied by wooded and open lands. Of these, almost half correspond to forest plantations of non-native fastgrowing species intended to produce cellulose and low-quality wood in short shifts (10–40 years). Only 17.1% of the surface of Galicia conserves wooded vegetation dominated by native species, although the majority of these are immature formations or ancient forests that show clear signs of human use until recent times. In the areas of high intensification of agricultural or forestry production, such formations have completely disappeared. Moreover, most of the introduced tree species are invasive and produce highly flammable chemical compounds, helping to spread forest fires with great speed and virulence. These characteristics make the most abundant forest

Image 5 In NW Iberia, anthropic deforestation has led the expansion of shrubs dominated by heather and gorse species adapted to the use of fire by humans. In the easternmost mountains of Galicia, the heaths are often dominated by Spanish heath (Erica australis), which blooms in midspring and stains the slopes of many ranges a striking pinky color. Valley of A Seara (municipality of Quiroga, province of Lugo)

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Image 6 Despite the demographic decline suffered since the middle of the last century, the traditional mosaic of croplands and hay meadows separated by hedges and stone walls, small native copses, riverside vegetation, and heathland patches could still be recognized in many areas of Galicia. This organization forming a mosaic of the different types of use around the inhabited places fits well within the concept of bocage. Noceda valley, municipality of Folgoso do Courel, province of Lugo

plantations in Galicia difficult to manage in a context of global climate change and biodiversity loss (Image 6).

3 Galicia: Ancient Land of Heaths Shrublands in a broad sense and in particular, heathlands- have been the dominant vegetation in large areas of Atlantic Europe not covered by ice during the last glacial period (Pleistocene: 100,000–10,000 years BP). After the arboreal recolonization that occurred in these areas during the first part of the Holocene (10,000–5000 years BP), anthropic deforestation favored the expansion of heathlands in this territory, which recovered, to a certain extent, an appearance similar to the one it had during the cold periods of the Pleistocene. Because of human-induced changes over the last few millennia, heaths are now a large group of plant communities that characterize the landscape of the Atlantic territories of Europe, often integrated into the traditional form of organization of the agrarian landscape known as bocage (GEMET 2021).

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The paleoenvironmental history of this part of the continent and the most widespread way of using the territory implanted by the human being since the Middle Ages, have led to the SW end of the Atlantic territories being the area with the greatest diversity of heaths in Europe. In fact, Galicia has the highest number of heathland communities described to date in this continent (Díaz 1998; Izco et al. 2006). However, this characteristic element of regional (and, consequently, continental) ecosystem biodiversity has been experiencing a significant reduction since the mid-twentieth century, both in terms of surface area and in its connection with other typical ecological units of its traditional landscape. Among the causes that have contributed to the loss of biodiversity in many areas of high ecological value, it is possible to recognize the intensification of agriculture and livestock, the expansion of forest plantations of non-native species, and the construction of wind farms. The available information (Izco et al. 2006; Ramil-Rego et al. 2013) shows that this accelerated loss does not affect the different types of heathlands described in the same way, since it is more accentuated in the coastal areas of the north of the provinces of A Coruña and Lugo and the Rías Baixas area. In these zones, heathlands are in danger of disappearing in the short term, a significant fact given that all the types of heaths present in Galicia (wet and dry) are included in the Annex I of the CD 92/43/ EEC (“Habitats” Directive) (Image 7).

4 Coastal and Wetland Habitats Galicia has a very indented and extensive coastline (2.100 km, POL 2010) that is home to a vast diversity of ecosystems (cliffs, beach-dune-coastal lagoon systems, estuaries, marshes) whose extension and limits have been changing since the end of the Pleistocene and throughout the Holocene (Méndez and Vilas 2005; ArceChamorro et al. 2022a, b) (Image 8). A considerable part of the Galician coast articulates around the rías (northern, central and southern), complex estuaries of polygenetic origin (tectonic processes, differential erosion and sedimentation) whose current configuration is due to the flooding of low river stretches along of the last 20,000 years (Méndez and Vilas 2005). The coastal morphology of these estuaries usually presents an internal sector with marsh ecosystems, a middle part with low cliffs interspersed between small beaches and coves of fine sand and an outer part with more abrupt forms, often with sectors of high cliffs that penetrate in the sea forming prominent capes or, in other cases, extensive boulder beaches. In the northern half of the province of A Coruña and in that of Lugo (Central and Northern Rías), the estuaries have less development and are separated by coastal stretches eminently cliffy, among which the area between the Ortigueira and Cedeira rías stands out (district 1a). In this sector, the Serra da Capelada falls abruptly into the sea from a height that exceeds 600 m, creating the highest cliffs on the Spanish Atlantic coast. These stretches of high cliffs present a great variety of ecological environments (caves or furnas, steep

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Image 7 After several decades of abandonment of agricultural and livestock practices, during the present century a reorganization of uses is taking place throughout Galicia, which often does not consider the productive aptitude of the land. The photograph shows a wet heath under heavy clearing to promote its use as cattle pasture. Lagoas do Chao (municipality of Begonte, province of Lugo)

rocky walls, rapid stretches of streams that flow into the sea via waterfalls, etc.) in which highly specialized plant and animal communities develop (Image 9). As we have already commented, the beach-dune systems constitute, together with the steep coasts and the marsh environments, one of the basic geomorphological and biological elements of the Galician coastline. Their special ecological conditions (mobile and highly permeable substrate, impregnated with salt; constant winds and high insolation) control the flora capable of colonizing the sandy sediment and have played a role in evolutionary selection, favoring the appearance of plants specially adapted to living in these environments (Image 10). The Holocene evolution of the Galician coastline has favored the formation of large beach-dune complexes on the northern coast of the Iberian Peninsula, some of which are several km long. However, since prehistoric times, these habitat complexes have suffered in a particularly virulent way the negative effects of human activities, so that only the stretch of beach for tourist use has reached our days. Thus, only the coastal sectors most exposed to intense winds and with the worst access have survived this dynamic. Among them, it is worth highlighting the stretch between the Fisterra and San Adrián capes, known as Costa da Morte (the “Coast of Death”, district 2b), in the westernmost portion of the province of A Coruña. Here it is

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Image 8 Some coastal sections of Galicia maintain a wild aspect despite the intense campaigns to encourage tourist use that have been carried out in the last 30 years. The image shows one of those almost unaltered stretches of coastline, between Ansarón Island and Punta Morás (municipality of Xove, province of Lugo)

still possible to observe the complexity that these systems have reached in this part of the European continent, where they appear as a mosaic of different types of dunes (embryonic, primary, secondary), humid depressions and different types of psammophilous woody formations (bushes, thorny scrubs, a variety of forests), in addition to beaches (Image 11). Marshes are another of the characteristic systems of the Galician coast and perform very relevant ecological functions, such as the physical and chemical purification of river water in its contact with the sea, control of erosion and flood processes or longterm storage of atmospheric CO2 , among others. They are, by far, the most altered coastal systems and from the oldest times in Galicia. Despite this, there are still some examples in an acceptable state of conservation. The detailed study of several of them has allowed us to understand their functioning and diversity at the botanical level, as well as their importance in maintaining the variety of vertebrate fauna present, especially wader birds (Image 12). Despite the great complexity of the Galician coast, access to a large part of its profile is relatively easy, particularly in the middle and inner sections of the rías. This fact has facilitated the settlement of human populations and, subsequently, the alteration, and even elimination, of coastal ecosystems along large stretches of coastline, especially in the interior parts of the Rías Baixas (Southern Rías, district 2c). In recent decades, the sharp rise in sea level caused by the increase in the planet’s global

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Image 9 The Serra da Capelada (north of A Coruña province) is a mountain range that drops steeply into the sea from 600 m above sea level, forming the highest coastal cliffs on the Iberian Peninsula. It is made up of various types of basic and ultrabasic rocks, very rare in the Iberian context, that give it high environmental value, both from a geological, botanical and zoological point of view

temperature threatens the survival of many of these ecosystems, since human modification of the coastal landscape, together with the topographical configuration of the territory, prevent their accommodation at pace with the speed of this phenomenon (Image 13). Both in coastal areas and in the interior of Galicia, wetlands have also suffered the impact of human action due to their predominant location in flat, accessible, and potentially cultivable areas. Several wetland drainage processes have been carried out in Galicia since the end of the nineteenth century for this purpose, but the economic benefits obtained have not been as expected. In return, they have meant a significant reduction in the ecological value of these areas as well as an appreciable reduction in the quality of the ecosystem services provided by these environments to humans (Gómez-Orellana et al. 2014a) (Image 14).

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Image 10 The most rugged coastal sectors with the worst weather conditions (strong winds and frequent fog) maintain the best-preserved beach-dune systems in the entire Iberian Atlantic biogeographic area. Among them, the section known as Costa da Morte (Coast of Death) in the extreme northwest of the province of A Coruña, stands out. Praia do Trece (municipality of Camariñas, province of A Coruña)

5 Vegetation in Extreme Environments The environmental factors that condition the configuration of the vegetation cover of Galicia are varied and, at times, extreme. In the areas with the strongest oceanic climate (north of the provinces of A Coruña and Lugo), recurring rain and mists feed extensive acidic bog systems, the southernmost in Europe and in which some endemic or rare invertebrates and plants at continental level can be found. In the north of the province of Lugo (district 1a), the summits of the Serra do Xistral are covered by the southernmost blanket bogs in Europe, in which peat formation, a process that dates back more than 9,000 years BP, is still ongoing to this day. In several areas of these peatland systems, the accumulation of organic matter reaches five meters thick, constituting a very valuable record of the environmental changes that occurred in this part of Europe throughout the Holocene (Izco and Ramil-Rego 2001) (Image 15). Its considerable extension (around 2700 ha) and the humid and cloudy environment that characterizes these mountains recalls similar places in some mountainous

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Image 11 Marshes are very stressful environments for many living beings, but highly productive in biological terms. This justifies that these are the preferred environments for a wide variety of waterfowl (waders), many of them from northern Europe and that congregate here in winter. Human activities have exerted strong pressure on these systems since ancient times and, together with the rise in sea level, are their main threats in the medium term. System of channels and associated vegetation (maritime reed beds, dark green; sea purslane communities, light green) in the middle section of the Betanzos Marsh (province of A Coruña)

areas of Ireland, NW France, or the Scottish Highlands. However, its southern location, isolated from the rest of the wetlands of this type existing in Europe, justifies its vegetation to be exclusive and clearly different from that which develops in more northerly European Atlantic territories (Brittany, Ireland, Great Britain), since endemic species from the Iberian NW are integrated in its characteristic flora (Avenella flexuosa, Carex duriei, Erica mackaiana, Eriophorum angustifolium, Molinia caerulea) (Izco and Ramil-Rego 2001; Rodríguez-Guitián et al. 2009a). Despite being a territory of exceptional landscape value, with well-studied botanical, faunal and ecological particularities, and an example of traditional livestock exploitation with local breeds of horses and cows, this unique enclave of Galicia’s natural heritage is deteriorating rapidly due to the construction of wind farms and the intensification of livestock and forestry (Gómez-Orellana et al. 2014b). At the opposite extreme, in the central-eastern part of the province of Ourense (sector 4), a very different climatic regime, characterized by low rainfall ( 20 (g m−2 min−1 ) (reproduced from Díaz-Fierros and Benito 1991)

where M is a parameter related to soil texture in the topmost 15 cm, OM the percent content in organic matter, a the texture class of the soil and b its permeability class. Image 3 illustrates the earliest approximation to the K factor for Spanish soils, based on the 1:1 000 000 soil map of the country (Díaz-Fierros and Benito 1996). As can be seen, Galician soils were classified as scarcely erodible (class 1, K < 0.1). The low erodibility of Galician soils can be ascribed to their high infiltration capacity, a result of their primarily coarse texture and, especially, their aggregate stability against the action of water. Organic matter contributes markedly to such stability given the low clay contents of the soils (Benito and Díaz-Fierros 1989, 1992b). The upper right image shows a characteristic profile of a Galician forest soil developed on acid rock, with a deep and very dark A horizon (umbric horizon). As

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Image 3 Soil erodibility classes for the chief FAO (1985) soil units of Spain. Class 1: < 0.1; 2: 0.1–0.2; 3: 0.2–0.4; 4: 0.4–0.6; 5: > 0.6 (Mg m2 h ha−1 hJ−1 cm−1 ) (reproduced from Díaz-Fierros and Benito 1996)

can be seen from the electron micrographs of Image 4, macroaggregate stability in forest soils was helped by rootlets and fungal hyphae acting as binders. Although organic matter is the main protector from disaggregation of Galician soils, it can have an adverse effect on erodibility when it favours the presence of severely water-repellent horizons by diminishing or arresting water infiltration in the soil (Benito et al. 2010). Galician soils are often naturally water-repellent (Varela et al. 2005; RodríguezAlleres et al. 2007, 2012; Benito et al. 2019). As can be seen in Image 5 water repellency is more prevalent in forest soils under pine or eucalyptus than it is under pasture or some crop. Also, repellency is more marked in coarse-textured soils, especially under the typically dry conditions of summer in the region (Rodríguez-Alleres et al. 2007; Rodríguez-Alleres and Benito 2011). The severe water repellency of soils under pine and eucalyptus trees can be ascribed to a combination the factors including the temperate–humid climate of Galicia which facilitates massive biomass production and increasing organic matter contents—and production of hydrophobic substances as a result (Rodríguez-Alleres et al. 2007; Benito et al. 2019). Also, the strongly acidic nature of the soils facilitates fungal growth, the presence of thick layers of dead leaves and the formation of mor humus, all of which have frequently been cited as major sources of hydrophobic

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Image 4 Upper images: general view of a pine forest and soil profile developed on schists (Nigrán, Pontevedra). Lower images: scanning electron micrograph of macroaggregates of pine forest soils (developed on micaceous schists—left—and on pelitic schists—right), showing a network of fine roots and hyphae holding soil particles together (× 2500) (reproduced from Benito and Díaz-Fierros 1992b)

organic compounds (Doerr et al. 2000). In addition, these species release substantial amounts of resins, waxes and oils, thereby further increasing water repellency (Rodríguez-Alleres et al. 2007, 2012; Benito et al. 2019). De Blas et al. (2010) found evidence that soil water repellency under these tree covers is governed mainly by the concentration of free lipids in hydrophobic coatings. Also, they found the proportions of humic substances and free particulate organic matter to influence the extent of soil water repellency, the effect depending on the particular type of vegetation. The portable rainfall simulator (Image 6) devised by Benito et al. (2001) has shown that water repellency in Galician soils increases surface runoff to unexpectedly high levels for their morphological characteristics and the associated vegetation. An experiment involving measuring surface runoff and the resulting erosion under simulated rainfall at 64 mm h–1 and a period of 30 min, 5 times was conducted from June 1998 to July 1999 at three different sites in steeply sloping woodland in Galicia.

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Image 5 Relative frequency of WDPT (water drop penetration test) classes measured on surface samples from soils of different texture beneath various vegetation types in summer (reproduced from Rodríguez-Alleres et al. 2007). Classes: 0 non repellent; 1 slightly repellent; 2 strongly repellent; 3 severely repellent; 4–6 extremely repellent

Two of the sites had recently been deforested (sites 2 and 3), and one of the two had been sown with grass (site 3), which was germinating at the onset of the study (Benito et al. 2003). Site 1, forested with conifers was used as a control (Image 7). At site 1, where the soil was plant-covered and had a stable structure and a high organic matter content (Benito et al. 2003), runoff and soil loss rates were low, but runoff increased slightly in dry periods as a result of increased water repellency (Table 1). Although deforestation (sites 2 and 3) greatly increased runoff and erosion rates, once the vegetation cover had developed to an adequate extent, it reduced erosion by 96% (Benito et al. 2003). Hydrological changes at the deforested sites were found to depend partly on the extent of recovery of the plant cover, and partly on the moisture content and water repellency of the soil (Table 1). In particular, the strong water repellency of the soils, especially in dry periods, led runoff to greatly

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Image 6 View of rainfall simulator and detail of the spray nozzle (reproduced from Benito et al. 2001)

to exceed the amount expected on the basis of soil morphology and the associated vegetation; in any case, the high structural stability of the soils prevented the high runoff from resulting in strong erosion (Benito et al. 2003). Simulated rainfall tests are also highly useful to examine the influence of water repellency in burned soils on various hydrological and erosion-related variables. In a study on burned soil under granite and a Pinus pinaster plantation in Padrón (A Coruña, Galicia), the authors examined the effects of a wildfire of medium–high intensity on soil water repellency and its consequences on surface runoff and soil erosion (Rodríguez-Alleres et al. 2005). To this end, water repellency in the burned area immediately after the fire was compared with that of a nearby unburned area by using the water drop penetration time (WDPT) test. As can be seen from Image 8, the unburnt soil exhibited extreme water repellency (WDPT > 6 h) down to 10 cm, strong repellency (WDPT 60–600 s) from 10 to 20 cm and no repellency below 20 cm. On the other hand, fire of medium–high severity completely suppressed repellency in the top 2 cm of soil, but repellency increased with increasing depth and was extremely severe between 2 and 20 cm. Applying simulated rainfall at 50 mm h–1 for 30 min over two 1 m2 plots with an average slope of 20% revealed that the extreme repellency of the burned soil to underground water considerably increased runoff (to levels near 50%) but failed to result in substantial erosion (Table 2). At the end of the experiment, only the topmost 2 cm of soil had been wetted—and were not water-repellent; also, the underlying soil remained highly dry (moisture content 2.9%) and extremely water-repellent (Image 9). At slope scale, the intense rainfall events occurring in the area three months after the fire resulted in intense erosion owing to the lack of a protective plant cover and the extreme soil water repellency of the sub-surface layer.

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Image 7 View of the forested and deforested sites used in the rainfall simulation study. The lower image shows the experimental plot at site sown with grass. Vigo University Campus, Vigo (Pontevedra) Table 1 Soil surface characteristics and hydrological-erosional response to simulated rainfall at each site during the study period (reproduced from Benito et al. 2003) Dates

Rate erosion (g m−2 h−1 )

Average runoff (mm h−1 )

Bare soil (%)

Site 1

Site 2

Site 3

Site 1

Site 2

Site 3

Site 1

Site 2

Site 3

Site 1

Site 2

Site 3

June-98

5.5

303

112

7.25

27.3

31.6

0

75

70

M

Sl

Sl

Sept-98

7.3

60

4.5

40.4

14.6

0

65

0

VS

VS

VS

Nov-98

1.3

328

5.8

46.0

11.2

0

30

5

M

Sl

S

Mar-99

4.1

137

15.9

13.1

48.8

18.3

0

50

5

S

Sl

S

July-99

0.9

28

11.2

20.5

45.5

35.8

0

10

20

VS

S

S

18.3 3.41

Water repellency (severity rating)

Severity water repellency: Sl (slight), M (moderate), S (severe); VS (very severe)

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Image 8 Median WDPT classes at five different depths in burned and unburned soils 15 days after fire (from Rodríguez-Alleres et al. 2012). Classes: 0 non repellent; 1 slightly repellent; 2 strongly repellent; 3 severely repellent; 4–6 extremely repellent

Table 2 Hydrological and erosion-related parameters after simulated rainfall (from Rodríguez-Alleres et al. 2005)

Plot 1

Plot 2

T e (s)

40

276

Em (mm h−1 )

19.69

27.1

Ce

0.39

0.54

f c (mm h−1 )

22.76

23.06

T s (g·m−2 h−1 )

8.79

11.07

T e: time to surface runoff, Em: mean runoff, Ce: runoff coefficient, f c: steady-state infiltration rate, T s: erosion rate.

Morphological analysis revealed clear signs of erosion including exposed rock fragments on the soil surface and partly exposed side pine roots emerging above the soil (Image 10a); the loss of water through a cascading effect near some trees (Image 10b); and accumulation of materials near obstacles or at the bottom of the hillside by effect of a gentler slope (Image 10c). A sound knowledge of soil erodibility following a wildfire is of crucial importance to prioritize post-fire restoration practices for mitigating soil erosion. A two-fold approach is followed for this purpose in Galicia. In one study, the effects of wildfire were assessed by comparing selected topsoil properties in recently burned soils and

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Image 9 View of rainfall simulator, experimental plot and subsurface soil after application of simulated rain. (Padrón, A Coruña)

unburned neighbouring soils (28 site pairs in all). The soil properties studied included particle and aggregate size distribution, aggregate stability, organic carbon and water repellency (Varela et al. 2005, 2010a, b, 2015). Heating effects were evaluated in controlled laboratory tests and compared with those of the wildfires in order to shed further light on the importance of differences in fire severity (García-Corona et al. 2004; Varela et al. 2005, 2010b, 2015; Benito et al. 2009, 2014). A comparison of burned and unburned soils revealed that wildfires had a considerable adverse effect on aggregate size distribution (Image 11a). The effects on aggregate stability were highly variable and primarily dictated by organic matter combustion—and hence by fire intensity and severity (Varela et al. 2010a). Thus, as can be seen from Image 11b, fire increased aggregate stability in 40% of soils, but decreased it in another 40%, in relation to unburned soils (Varela et al. 2010a, b). Differences in aggregate size and stability were ascribed to changes in organic matter by effect of fire (Benito et al. 2009; Varela et al. 2010a, b). As can be seen from Image 11c, fire increased organic carbon in 43% of all burned soils (by a factor of up to

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Image 10 Signs of erosion in a burned area three months after fire. Padrón, A Coruña (from Rodríguez-Alleres et al. 2005)

2 with respect to unburned soils at some sites) but decreased it by 17–44% in 30% and had no effect on the remainder. There were statistically significant relationships between the differences in organic carbon and MWD (Spearman’s r = 0.49, α = 0.01), and also between those in organic carbon and aggregate stability (Spearman’s r = 0.54, α = 0.01; Varela et al. 2010a, b). Fire induced surface water repellency in wettable unburned soils, and increased water repellency severity in slightly to moderately repellent soils, but did not alter severity in strongly or very strongly repellent soils (Image 12). Only at three sites did repellency severity decrease from strong or very strong to moderate at the upper sampling depth; however, all three soils were strongly to very strongly water-repellent in their 2–5 cm layer (Varela et al. 2005, 2010a).

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Image 11 Comparison of aggregate size distribution (MWD, mm), stable aggregates (%) and organic carbon content (g kg−1 ) in neighbouring long unburned and recently burned forest soils (reproduced from Benito et al. 2009, 2014)

Unburned

Burned (0-2 cm)

Burned (2-5 cm)

6 MED class

5 4 3 2 1 0 3 4 22 27 1 2 24 26 28 12 18 20 5 6 7 9 10 11 13 14 15 16 17 21 25 sites nº

Image 12 Repellency classes of burned soils at two different depths (0–2 cm and 2–5 cm) and of neighbouring unburned soils at 0–5 cm. Unburned samples appear in increasing order of water repellency. Results of the molarity of ethanol drop (MED) test. Classes: 1 very hydrophilic, 2 hydrophilic; 3 slightly hydrophobic; 4 moderately hydrophobic; 5 strongly hydrophobic; 6 very strongly hydrophobic (reproduced from Varela et al. 2005, Benito et al. 2014)

Based on the foregoing, the effect of changes in soil properties by effect of wildfire on soil erodibility depends largely on the intensity of the fire. The difficulty involved in assessing fire intensity in many cases requires using controlled heating laboratory tests to more accurately assess the influence of temperature on the specific soil properties most closely related to erodibility. Samples obtained from three different sites where the soil exhibited contrasting responses to wildfire were studied. Soils 1 and 2 were sandy loam and strongly water repellent; also, they exhibited a high aggregate stability. On the other hand, soil 1 was scarcely affected by the fire—which decreased aggregate stability and water repellency by 75%, and organic carbon by 45%, in soil 2. Soil 3 was silty and moderately water-repellent; also, it contained a low proportion of stable aggregates (31%). Fire increased organic carbon, the proportion of stable aggregates and water repellency in it by 30, 55 and 60%, respectively.

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Samples were heated at 25, 170, 220, 380 and 460 °C, at a rate of 3 °C min–1 for 30 min, prior to analysis for organic carbon content, aggregate stability and size distribution, water repellency and saturated hydraulic conductivity (García-Corona et al. 2004; Varela et al. 2010b). The results testify to the considerable differences among temperatures as determined by one-way ANOVA (Table 3). As can be seen, the organic carbon content exhibited no significant changes below 220 °C but decreased markedly at 380 and 460 °C, with losses of 55–75% at the former temperature and 83–94% at the latter relative to the control soils (García-Corona et al. 2004; Varela et al. 2010b, 2015). Although there were no substantial changes in aggregate size distribution below 220 °C, two of the soils exhibited a marked increase in aggregate stability at 170 and 220 °C. Heating at 380 and 460 °C dramatically reduced aggregate stability in the soils (García-Corona et al. 2004; Varela et al. 2010b). Soils 1 and 2, which were the most water-repellent, underwent no change in aggregate stability at 170 °C. On the other hand, soil 3 switched from moderately hydrophobic at 25 °C to very strongly hydrophobic at 170 °C. Soil water repellency increased at temperatures from 170 to 220 °C in this soil but disappeared at 380 and 460 °C in all three. The changes in aggregation caused by heating were quite consistent with those in organic carbon content, and also with heating-induced changes in water repellency. This suggests a close relationship between the two explanatory variables. Finally, the influence of temperature on hydraulic conductivity may have been a consequence of changes in soil aggregation and water repellency. As can be seen from Table 3, hydraulic conductivity decreased with increasing temperature up to 220 °C and then remained at very low levels at 380 and 460 °C. The decrease observed at 220 °C can be ascribed to the resulting increase in water repellency. Because repellency vanished at higher temperatures, the low hydraulic conductivity of the Table 3 Selected properties of soil samples heated at various temperatures (mean ± s.d.) Organic carbon (g

kg−1 )

Mean weight diameter (mm)

Stable aggregates (%)

T ºC

Soil 1

25

Soil 2

Soil 3

53.1 ±

6.6a

170

48.3 ±

10.4a

220

52.3 ± 9.8a

104.5 ± 11.1a

72.6 ± 9.2a

380

23.8 ±

25.5 ±

32.3 ± 2.5b

460

4.5 ± 3.2c

5.9 ± 1.1c

15.0 ± 5.8b

25

1.3 ±

0.1a

1.1 ±

0.1a

1.11 ± 0.39a

170

1.3 ±

0.2a

0.7 ±

0.0bc

1.09 ± 0.08a

220

1.4 ± 0.1a

0.9 ± 0.1c

0.98 ± 0.09a

380

0.4 ±

0.0b

0.5 ±

0.1b

0.30 ± 0.07b

460

0.4 ±

0.0b

0.6 ±

0.0b

0.24 ± 0.04b

25

52 ± 4a

1.9b

101.9 ±

3.2a

87.7 ± 17.5a

103.1 ±

15.6a

86.5 ± 18.8a

5.0b

69 ± 13a

31 ± 12a (continued)

Soil Erodibility: Influencing Factors and Their Importance in Post-fire …

611

Table 3 (continued)

Water repellency (ethanol %)

Hydraulic conductivity (cm

h−1 )

T ºC

Soil 1

Soil 2

Soil 3

170

89 ± 5b

52 ± 7ab

47 ± 19ab

220

84 ± 14b

64 ± 24a

56 ± 4b

380

8 ±

8c

19 ±

9 ± 10c

460

1 ±

2c

n.d

25

19.1 ± 2.3a

21.8 ± 1.5a

10.9 ± 2.0a

170

20.8 ±

1.6a

21.0 ±

1.3a

21.4 ± 0.8b

220

23.5 ±

0.8b

23.0 ±

3.1a

22.2 ± 0.9b

380

0.0 ± 0.0c

0.0 ± 0.0b

0.0 ± 0.0c

460

0.0 ±

0.0 ±

0.0 ± 0.0c

25

15.2 ±

170

11.5 ± 6.1a

14.4 ± 14.0ab

3.3 ± 2.9b

220

0.4 ±

5.0 ±

0.0 ± 0.0c

380

1.7 ± 0.6b

13.1 ± 5.3ab

1.9 ± 0.9c

460

1.4 ±

6.9 ±

1.8 ± 0.3bc

0.0c 7.8a

1.1b 0.2b

18b

0 ± 0c

0.0b

19.7 ±

21.0a 9.0b 2.0ab

7.6 ± 5.1a

In Table 3, within each column, the mean values designated with different letters, for each soil property, are significantly different at p 200

6437

18,932

2483

228

28,080

Erosionable surface (ha)

767,200

971,987

709,234

432,396

2,880,817

Total surface (ha)

795,938

985,619

727,338

449,451

2,957,446

Soil Erosion in NW Spain

619

2 Erosion by Forest Fires Since the 1960s the extent of fires in Galicia has been measured. Díaz-Fierros (2018) summarises them in the following periods: (1961–1971) From 5000 to 20,000 ha were burnt and less than 1000 fires occurred. (1972–1978) More than 3000 fires occurred and more than 20,000 ha. Were burnt. (1979–1989) Several years with more than 100,000 ha burnt and more than 5000 fires. (1990–2020) Background trend of 20,000 to 30,000 ha burnt, with exceptional years of 20,000–30,000 ha burnt, with exceptional years in which between 50.000 and 100.000 were burnt. From 5.000 to 10.000 occurred, but after 2005 there were less than 5.000 fires. This persistence and extent of fires in a forest area of around two million hectares, and whose origin was the dismantling of traditional agriculture in the 1960s (López 2018), had obvious consequences in terms of soil loss due to erosion that did not begin to be quantified until the 1980s. The first studies were carried out with pinerosion by Díaz-Fierros et al. 1987) and it was found that the limits of tolerable soil loss are generally far exceeded, losses of over 50 Tm year−1 having been recorded in extreme cases. By researching the USLE application (Wischmeier and Smith 1978), the LS factors were found to show not correlation whatsoever with the gross erosion suffered, whereas R and C factors (rainfall and coverture) seem to be appropriate erosion predictors. From 1988 onwards research started to be carried out in U.S.D.A plots (20 × 4 m.) with rain simulators which made it possible to assess more precisely the influence of K and C factors (K: soil erodibility: C: plant cover), as well as the soil hidrophobity that took place in burnt soils (Varela et al. 2005). From all these studies it could be concluded that the most important factor in erosion control was the loss of vegetation cover (trees, shrubs and herbs) as a consequence of fires and that, conversely, its spontaneous or forced recovery was the best protection against erosion. It was concluded that with a vegetation cover of 60% of the soil surface, erosion control was already very effective and that the creation of artificial mulches with straw and other materials enabled erosion prevention (Díaz Raviña et al. 2013). Finally, with the application of the WEPP model (Soto and Díaz-Fierros 1998), soil losses due to forest fires, currently estimated at between 5 and 20 tm ha−1 year, could be more strictly assessed. These studies were used to correct the initial data, since they were considered significantly higher. The most frequent external manifestations of erosion in burnt soils are mainly due to inter-rill erosion that in its initial or low intensity processes give rise to the formation of terracettes. In high intensity fires or in areas where there is a concentration of water flows, large rills (Fig. 4b), massive soil creep (Fig. 4a), or—very occasionally—the gully formation (Fig. 4c) may appear.

620 Fig. 4 Soil erosion by forest fires: a soil deposits, b rill formation and c gully formation

F. D.-F. Viqueira

Soil Erosion in NW Spain

621

Fig. 5 a Soil erosión by agricultural and mining practices. a Soil deposits, b gully formation in meadows establishment. c Gully formation in mining dump and d traditional “terrace” system

3 Erosion by Agricultural Practices The traditional practice of burn-and-slash may be largely responsible for the erosion suffered by many Galician soils in the course of their agricultural history (Bouhier 1979). This practice can mean soil temperatures of over 400 ºC being maintained for several days, with the resulting marked degradation of structural stability and consequent severe soil loss. During the experience with USDA erosion plots (Soto and Díaz-Fierros 1998), some these were subjected to slash and burn using traditional local methods; soil losses from these plots totalled 51 tm ha year−1 .

622

F. D.-F. Viqueira

Fig. 5 (continued)

Spring sowing of maize or potatoes, which removes plant cover during the months of April and May, makes the soil vulnerable to erosion by heavy rains, with can create downfill rills and soil deposits in the lower part of the field carrying considerable quantities of soil (Fig. 5a) what’s more, of the rills and gullies (Fig. 5b). Though there have yet been quantitative studies of this process, it appears that is general on long slopes with a gradient of over 5%. Since field length have increased progressively because of the land ownership redistribution put in effect in Galicia since 1960’s, it seems possible that steps may to be taken to ensure that erosion control measured accompany redistribution in the future.

Soil Erosion in NW Spain

623

In the Galician traditional agricultural landscape there are still systems of cultivation terraces that protected the soil from erosion (Fig. 5d). Finally, artificial soils made of slopes and mining dumps can also be subject to short relevant episodes of soil erosion with the formation of rills and gullies (Fig. 5c).

References Bouhier A (1979) La Galice: essai geographique d´analyse et d´ínterpretation d´un vieux complexe agraire. Impr. Yonnaise. La Roce-sur-Yon (Poitiers), 2 t, 1516 pp Díaz-Fierros F, Benito E, Pérez R (1987) Evaluation of the U.S.L.E. for prediction of erosion in burnt forest areas in Galicia (N.W.) Spain. CATENA 14:189–199 Díaz-Fierros F, Benito E, Soto B (1991) Soil erosion in NW Spain. In: Sala M, Rubio JL, García-Ruiz JM (eds) Soil erosion in Spain. Geoforma, Logroño, Spain, 228 pp Díaz-Fierros F (2018) Perspectivas históricas de los incendios forestales en Galicia. In: Hércules (ed) Incendios forestales. Reflexiones desde Galicia (coord. Díaz-Fierros F). A Coruña, 238 pp Díaz Raviña M, Martin A, Barreiro A, Lombao A, Iglesias L, Díaz-Fierros F, Carballas T (2013) Mulching and seeding treatments for post-fire soil stabilisation in NW Spain: short term effects and effectiveness. Geoderma 191:31–39 Ibañez AR (1802) (2009) Discursos Económicos-Políticos sobre la restauración de los montes y plantíos españoles. Editión: Joaquin Ocampo. Xunta de Galicia. Real Instituto de Estudios Asturianos. Oviedo, 190 pp López E (2018) Deestructuración del medio rural, usos del suelo y gestion del territorio. El contexto de fondo del problema de los incendios forestales en Galicia. In: Hércules (ed) Incendios forestales. Reflexiones desde Galicia (coord. Díaz-Fierros F). A Coruña, 238 pp Ministerio de Medio Ambiente (2002) Inventario Nacional Erosion de Suelos, 2002–2012. Galicia. A Coruña. Madrid, 201 pp Muncher HJ, Carballas T, Guitian F, Jungerius PD, Kroonenberg SB and VIllar MC (1972) Micromorphological analysis of effects of alternating phases of landscape stability and instability on two soil profiles in Galicia, N.W. Spain. Geoderma 8:241–266 Rodriguez Mourullo G (1956) Memorias de Tain. In: Monterrey (ed). Vigo, 113 pp Soto B, Díaz-Fierros F (1998) Runoff and soil erosion from areas of burnt scrub: comparison of experimental results with those predicted by the WEPP model. CATENA 31:257–270 Varela ME, Benito E, De Blas E (2005) Impact of wildfires on Surface wáter repellency in soils of northwest Spain. Hydrol Proc 19(18):3649–3657 Wischmeier WH, Smith DD (1978) Predicting rainfall erosion losses—a guide to conservation planning. USDA. Agric. Handbook Nº 337. Washington, 58 pp

Some Environmental Effects of Slate Exploitation and Palliative Treatments Avelino Núñez-Delgado

Abstract In this chapter, a scientific story is presented to illustrate some environmental issues related to the management of wastes and/or by-products derived from the exploitation of slate in Galicia, as well as some alternatives used to solve or palliate these kinds of problems. Photographs taken by the author are included as starting point and basic support to tell the story, which is complemented with comments as regards previous publications dealing with the overall thematic. Keywords Composting · Mulching · Slate fines · Slate quarries · Spoil tips

1 Introduction To introduce data on the relevance of slate in Galicia, as regards its use, extraction from quarries, and commercialization, an interesting and synthetic publication is the paper by Cárdenes et al. (2019), which is also useful as a source of historic and complementary information. Currently, Galicia is one of the main slate producers and exporters in the world, but elaborated materials derived from this rock have been used for centuries in this geographic area, and not just for roofing but also covering a diversity of services in construction. Figures 1, 2 and 3 show examples of both, old and recent buildings (or remaining structures that were parts of buildings in the past), situated in or close to some of the areas where slate has been classically extracted and used in Galicia. Specifically, Fig. 1 shows images from Valdeorras (Ourense province), Fig. 2 includes images from O Courel (Lugo province), and Fig. 3 shows some buildings situated in A Mariña (Lugo province), near Ortigueira (A Coruña province). In addition, Fig. 4 shows examples of both classical and last generation buildings using slate, placed in the city of Lugo (Lugo province). A. Núñez-Delgado (B) Department of Soil Science and Agricultural Chemistry, University of Santiago de Compostela, Engineering Polytechnic School, Campus Univ. s/n, 27002 Lugo, Spain e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 A. Núñez-Delgado et al. (eds.), The Environment in Galicia: A Book of Images, https://doi.org/10.1007/978-3-031-33114-5_29

625

626

A. Núñez-Delgado

Fig. 1 Images from Valdeorras (Ourense province), showing the use of slate for a diversity of construction services, including roofing, both for old buildings (or remaining structures) and for restored/recent ones

The paper by Cárdenes et al. (2019) includes some details related to environmental issues associated to slate extraction and processing, but this aspect has been covered by other authors in different publications. As examples, some of them were performed by means of rather classical methodologies (such as González Nicieza et al. 1997), whereas others were carried out using recent/new survey tools (such as Gerassis et al. 2021). With that background, this chapter will present a scientific story illustrating some environmental issues related to the exploitation and processing of slate in various zones of Galicia, as well as alternatives to palliate/restore degraded areas affected by these problems.

Some Environmental Effects of Slate Exploitation and Palliative …

627

Fig. 2 Images from O Courel (Lugo province), showing slate used for roofing and other construction services, both for old buildings (or remaining parts of old structures) and restored/recent ones

628

A. Núñez-Delgado

Fig. 3 Images from A Mariña (Lugo province), near Ortigueira (A Coruña province), showing examples of slate being used for a diversity of construction services (not just roofing), both for old buildings and for restored/recent ones

2 Some Environmental Effects Due to the Exploitation of Slate in Galicia, and Palliative Treatments To illustrate the start of this scientific story, below are included some photographs taken by the author of this chapter in Valdeorras (Ourense province) by the end of the 80’s of the XX century. These images can be seen as an example of what was happening by that time (and that had started years ago from that date) in the zone, where multiple spoil heaps were situated besides rivers and streams, receiving

Some Environmental Effects of Slate Exploitation and Palliative …

629

Fig. 4 Images from Lugo (Lugo province), showing examples of slate being used for a diversity of construction services (not just roofing), both for classical and recent buildings

dumping materials derived from slate exploitation/processing, but also from other activities (such as construction). In fact, in Fig. 5 the photograph situated upside, on the left, shows an overall view of a spoil heap, clearly indicating that a variety of waste materials go downslope. The photo placed upside, on the right, shows another view of the spoil tip, where, at the bottom of the image, it can be noted that there are trees broken. Downside, on the left, the big-size construction-spoil material that had gone displaced downward from the spoil broking trees is illustrated, as is in the image placed downside on the right, where a broken tree and a child can be seen, to remark that the water stream reached by the construction spoil was used for bathing up to the moment when that dangerous event (the waste materials going downslope) took place. Some of these images also show slate fines (which are generated during the processing of the rocks) that were transported by the stream (the Casoio river) and were deposited as sediments. More recently, the author of this chapter was involved in research projects focused on the treatment of a variety of waste materials (such as sewage sludge, wood ash, vegetable remains, or mussel shell) by means of technical mixing, both in the short

630

A. Núñez-Delgado

Fig. 5 Photographs showing a spoil heap (upside on the left), broken trees on the bottom after a big-size spoil material had gone downslope (image upside on the right), the big-size spoil material (downside on the left), and the same spoil material with a broken tree in front, and a child on its right. All these images are from Valdeorras (Ourense province) and dated by the end of the 80’s of the XX century

Some Environmental Effects of Slate Exploitation and Palliative …

631

term and after giving time enough to allow composting, and on the use of these mixtures to restore spoil tips and other degraded environments. Figures 6a, b and 7a, b illustrate some of the field experiments carried out in that regard in the zone of Quiroga (Lugo province), both before and after adding the technically-treated mixtures of waste materials to various spoil areas.

Fig. 6 a Images of a slate spoil heap in the zone of Quiroga (Lugo), showing different initial phases of preparation for receiving treatments to promote reclamation and restoration. b Images of the same slate spoil heap in the zone of Quiroga (Lugo), showing other views corresponding to initial phases of preparation for receiving treatments to promote reclamation and restoration, and some of the first positive results as regards plant growth

632

A. Núñez-Delgado

Fig. 6 (continued)

The photographs clearly show that adding the technical mixtures to the spoil tips had a very positive effect as regards plant implantation and growth, thus promoting reclamation/restoration of the degraded environments, as well as facilitating the recycling of the waste materials used to perform the mixtures.

Some Environmental Effects of Slate Exploitation and Palliative …

633

Fig. 7 a Images of another slate spoil heap in the zone of Quiroga (Lugo), showing different initial phases of preparation for receiving treatments to promote reclamation and restoration, and some of the first positive results as regards plant growth. b Images of the slate spoil heap in the zone of Quiroga (Lugo), showing more advanced positive results (as regards plant growth) after receiving treatments to promote reclamation and restoration

634

Fig. 7 (continued)

A. Núñez-Delgado

Some Environmental Effects of Slate Exploitation and Palliative …

635

Some of the works that were published in this regard by the team of the author of this chapter were those by Estévez-Schwarz et al. (2009, 2012), Pousada-Ferradás (2012), Núñez-Delgado et al. (2015, 2018). To note that some researchers obtained their Ph.D. degrees working on thematic fields related to these subjects, being supervised by the author of this chapter and other senior researchers. Some of these Ph.D. Thesis were those by Sueiro-Blanco (2010), Estévez-Schwarz (2015). Even, the research team of the author of this chapter has studied different potential applications for slate fines, such as those shown in the publications by FernándezPazos et al. (2013), Seco-Reigosa et al. (2013), Quintáns-Fondo et al. (2016), RomarGasalla et al. (2016), Núñez-Delgado et al. (2018), Quintáns-Fondo et al. (2018). However, in most of these cases the results for slate fines were not among the best as compared to other alternative low-cost waste materials or by-products. Table 1 shows details corresponding to the publications on the matter referenced in this chapter.

3 Final Remarks The most positive aspects, in relation to the scientific story that has been presented, are that many crucial data corresponding to the environmental issues associated to the exploitation/processing of slate in Galicia are available, and now mostly known and recognized in a clear manner by the Administration and those more directly involved in all the activities related. This should facilitate that all key actions needed would be implemented, thus allowing a sustainable and environmentally responsible slate extraction/processing and commercialization in Galicia, and specifically in classical slate production zones such as those illustrated by the photographs presented in Figs. 8, 9 and 10.

636 Table 1 Publications on overall and specific aspects corresponding to the scientific story covered, which were referenced in this chapter

A. Núñez-Delgado

Thematic

Authors

Slate in Spain

Cárdenes et al. (2019)

Slate-related environmental issues

González-Nicieza et al. (1997)

Slate-related environmental issues

Gerassis et al. (2021)

Composting/recycling of wastes

Estévez-Schwarz et al. (2009)

Waste recycling focusing on restoration

Sueiro-Blanco (2010)

Composting/recycling of wastes

Estévez-Schwarz et al. (2012)

Waste recycling focusing on restoration

Pousada-Ferradás et al. (2012)

Recycling waste, including slate fines

Fernández-Pazos et al. (2013)

Recycling waste, including slate fines

Seco-Reigosa et al. (2013)

Composting/restoration degraded areas

Estévez-Schwarz (2015)

Recycling waste, including slate fines

Núñez-Delgado et al. (2015)

Recycling waste, including slate fines

Quintáns-Fondo et al. (2016)

Recycling waste, including slate fines

Romar-Gasalla et al. (2016)

Recycling waste, including slate fines

Núñez-Delgado et al. (2018)

Recycling waste, including slate fines

Quintáns-Fondo et al. (2018)

Some Environmental Effects of Slate Exploitation and Palliative …

637

Fig. 8 Two sights of parts of Valdeorras (Ourense province), where most of the Galician slate quarries are situated

638

A. Núñez-Delgado

Fig. 9 Sights of parts of O Courel (Lugo province), where some Galician slate quarries are exploited

Some Environmental Effects of Slate Exploitation and Palliative …

639

Fig. 10 Two sights of parts of A Mariña—Lugo province—(above), near Ortigueira (A Coruña province), with the three photos below corresponding to sights of the latter zone, where some Galician slate quarries are exploited

Acknowledgements Special thanks to Ángel Méndez and to Adalberto Álvarez, who enthusiastically collaborated in research projects dealing with technical mixtures and composting to treat waste materials, promote recycling and facilitate reclamation/restoration of degraded areas.

640

A. Núñez-Delgado

References Cárdenes V, Ponce de León M, Rodríguez XA, Rubio-Ordoñez A (2019) Roofing slate industry in Spain: history, geology, and geoheritage. Geoheritage 11:19–34. https://doi.org/10.1007/s12 371-017-0263-y Estévez-Schwarz I (2015) Obtención y valorización de un producto elaborado a partir de restos verdes y otros materiales residuales. Ph.D. thesis. University of Santiago de Compostela, Spain Estévez-Schwarz I, Seoane S, Núñez A, López-Mosquera ME (2009) Characterization and evaluation of compost utilized as ornamental plant substrate. Compost Sci Util 17(4):210–219. https:/ /doi.org/10.1080/1065657X.2009.10702426 Estévez-Schwarz I, Seoane-Labandeira S, Núñez-Delgado A, López-Mosquera ME (2012) Production and characterization of compost made from garden and other waste. Pol J Environ Stud 21(4):855–864 Fernández-Pazos MT, Garrido-Rodriguez B, Nóvoa-Muñoz JC, Arias-Estévez M, FernándezSanjurjo MJ, Núñez-Delgado A, Álvarez E (2013) Cr(VI) Adsorption and desorption on soils and biosorbents. Water Air Soil Pollut 224:1366. https://doi.org/10.1007/s11270-012-1366-3 Gerassis S, Giráldez E, Pazo-Rodríguez M, Saavedra Á, Taboada J (2021) AI Approaches to environmental impact assessments (EIAs) in the mining and metals sector using AutoML and Bayesian modeling. Appl Sci 11(17):7914. https://doi.org/10.3390/app11177914 González Nicieza C, Taboada Castro J, Menéndez Díaz A, Alvarez Vigil AE (1997) Geological risks in slag heaps of roofing slate in Spain. Int J Surf Min Reclam Environ 11(3):145–150. https://doi.org/10.1080/09208119708944079 Núñez-Delgado A, Álvarez-Rodríguez E, Fernández-Sanjurjo MJ, Nóvoa-Muñoz JC, Arias-Estévez M, Fernández-Calviño D (2015) Perspectives on the use of by-products to treat soil and water pollution. Microporous Mesoporous Mater 210:199–201. https://doi.org/10.1016/j.micromeso. 2015.02.001 Núñez-Delgado A, Sueiro-Blanco P, Seoane Labandeira S, Cela Torrijos R (2018) Polycyclic aromatic hydrocarbons concentrations in a waste from fuel oil spill and its mixture with other materials: time-course evolution. J Clean Prod 172:1910–1917. https://doi.org/10.1016/j.jclepro. 2017.11.239 Pousada-Ferradás Y, Seoane-Labandeira S, Mora-Gutierrez A, Núñez-Delgado A (2012) Risk of water pollution due to ash–sludge mixtures: column trials. Int J Environ Sci Technol 9:21–29. https://doi.org/10.1007/s13762-011-0014-6 Quintáns-Fondo A, Ferreira-Coelho G, Paradelo-Núñez R, Nóvoa-Muñoz JC, Arias-Estévez M, Fernández-Sanjurjo MJ, Álvarez-Rodríguez E, Núñez-Delgado A (2016) F sorption/desorption on two soils and on different by-products and waste materials. Environ Sci Pollut Res 23:14676– 14685. https://doi.org/10.1007/s11356-016-6959-8 Quintáns-Fondo A, Santás-Miguel V, Nóvoa-Muñoz JC, Arias-Estévez M, Fernández-Sanjurjo MJ, Álvarez-Rodríguez E, Núñez-Delgado A (2018) Effects of Changing pH, incubation time, and As(V) competition, on F− retention on soils, natural adsorbents, by-products, and waste materials. Front Chem 6. https://doi.org/10.3389/fchem.2018.00051 Romar-Gasalla A, Rivas-Pérez I, Paradelo-Núñez R, Nóvoa-Muñoz JC, Arias-Estévez M, Fernández-Sanjurjo MJ, Álvarez-Rodríguez E, Núñez-Delgado A (2016) Phosphorus retention on forest and vineyard soil samples, mussel shell, pine-sawdust, and on pyritic, granitic and waste materials. Geoderma 280:8–13. https://doi.org/10.1016/j.geoderma.2016.06.003 Seco-Reigosa N, Bermúdez-Couso A, Garrido-Rodríguez B, Arias-Estévez M, Fernández-Sanjurjo MJ, Álvarez-Rodríguez E, Núñez-Delgado A (2013) As(V) retention on soils and forest byproducts and other waste materials. Environ Sci Pollut Res 20:6574–6583. https://doi.org/10. 1007/s11356-013-1730-x Sueiro-Blanco P (2010) Inertización y promoción del reciclado de restos pastosos de fuel mediante mezclado con encalantes, cenizas y lodos. Ph.D. thesis. University of Santiago de Compostela, Spain