Environmental Oceanography and Coastal Dynamics: Current Scenario and Future Trends 3031344219, 9783031344213

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Swapna Mukherjee Kaushik Kiran Ghosh Abhra Chanda

Environmental Oceanography and Coastal Dynamics Current Scenario and Future Trends

Environmental Oceanography and Coastal Dynamics

Swapna Mukherjee · Kaushik Kiran Ghosh · Abhra Chanda

Environmental Oceanography and Coastal Dynamics Current Scenario and Future Trends

Swapna Mukherjee Geological Survey of India Kolkata, India

Kaushik Kiran Ghosh Department of Geology University of Calcutta Kolkata, India

Abhra Chanda School of Oceanographic Studies Jadavpur University Kolkata, India

ISBN 978-3-031-34421-3 ISBN 978-3-031-34422-0 (eBook) https://doi.org/10.1007/978-3-031-34422-0 Jointly published with Capital Publishing Company The print edition is not for sale in India, Sri Lanka, Pakistan, Nepal, the Maldives, Bhutan, Bangladesh and Afghanistan. Customers from India, Sri Lanka, Pakistan, Nepal, the Maldives, Bhutan, Bangladesh and Afghanistan please order the print book from: Capital Publishing Company. © Capital Publishing Company, New Delhi, India 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 publishers, 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 publishers 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 publishers remain neutral with regard to jurisdictional claims in published maps and institutional affiliations. Disclaimer: Every effort has been made to contact the copyright holders of the figures and tables which have been reproduced from other sources. Anyone who has not been properly credited is requested to contact the publishers, so that due acknowledgment may be made in subsequent editions. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

‘Earth and Planetary Science’ is perhaps the oldest, most dynamic, and ever-evolving subject. Oceanography is one of its domains, which has become necessary today, given the ubiquitous and undeniable climate change we are experiencing. The subject domain of oceanography encompasses several environmental issues which need serious attention from the present scientific community. The ocean, having an infinite resource and the capability to modulate Earth’s climate, has tremendous potential in combating global phenomena like the rising sea level, global warming, melting of ice caps, and more. Despite its significant role in the collective well-being of the human race, many anthropogenic activities have drastically polluted and degraded several crucial oceanic ecosystems within a short span. At present, humankind is standing at a critical juncture where our knowledge of ocean-derived services needs expansion, and we are polluting the oceans too. Thus, studying environmental oceanography as a discipline has become an urgent need of the hour. Conserving the oceans and marine habitats has become a top priority for several regional to international organizations. Devising proper management strategies to preserve and protect the oceans effectively would require a tremendous human workforce in the future. Hence, subjects like environmental oceanography would become more relevant in the days to come. Oceanography as a subject has four significant classifications, physical, chemical, biological, and geological oceanography. However, the present book did not follow the classical approach to studying oceanography. The authors felt the necessity to indulge in the most crucial aspects linked to oceanography that can potentially alter the present-day environment. Hence, instead of the fundamental processes of oceanography, which several authors have covered in the past, this book tried to link the environmental processes and phenomena related to the oceans. The book’s first part furnished a concise introduction to the realm of oceanography, its ecosystems, anthropogenic activities, and the basic oceanographic parameters that we usually measure to monitor the overall health of marine ecosystems. Many early career researchers and post-graduate scholars grow up thinking that oceanography encompasses only those activities or phenomena in the mid-oceans. However, the coastal sector also comes under the purview of environmental oceanography. Most signatures of anthropogenic activities are visible in inshore and nearshore waters v

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worldwide. Thus, coastal pollution has emerged as a subdiscipline requiring an interdisciplinary approach to understanding and studying these processes. In this regard, this book’s second part deals with the various aspects of Coastal pollution. Nutrients, heavy metals, persistent organic pollutants, oil, and plastics are some active pollutants in the global coastal periphery that require rigorous scientific attention. The book’s third part focussed on marine resources and renewable energy extraction mechanisms based on the ocean. This part also dealt with the coastal hazards vis-à-vis that is relevant to the present-day scenario. The authors were aware while writing this book that students from varied disciplines pursue specialized subjects like oceanography at higher levels. Thus, the authors tried to keep the language and content of the book as lucid as possible, keeping the diversity of interested readers in view. Overall, this book tries to be an eye-opener for future interdisciplinary researchers. Apart from academicians, policy managers and environmental practitioners might also find this book interesting to develop some ground knowledge on environmental oceanography. We hope that this book can intrigue the eager young minds of tomorrow. Kolkata, India

Swapna Mukherjee Kaushik Kiran Ghosh Abhra Chanda

About This Book

This book aims to present a concise yet succinct introduction to Oceanography as a subject and, at the same time, highlight the cutting-edge topics of research encompassing marine pollution, coastal processes, and many other associated phenomena. This volume deals with every aspect of oceanography in detail, including physical, chemical, geological, and biological discourse. Long sections are devoted to ocean-atmosphere interaction, tides, waves, and related coastal processes. It helps to understand marine pollution and the behavior of oil, plastic, and other agents in the light of real-world examples and empirical models. The ocean’s vast resources, like oil, mineral, and methane hydrate, and their proper estimation and exploitation, is the topic of discussion in the volume’s third part. The book is designated to meet the essential needs of the students studying oceanography and marine science.

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Contents

1

An Introduction to Oceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 The Term Oceanography and Its Scope . . . . . . . . . . . . . . . . . . . . . 1.2 Historical Evolution of this Subject . . . . . . . . . . . . . . . . . . . . . . . . 1.3 The Broad Categorization of Oceanography . . . . . . . . . . . . . . . . . 1.3.1 Geological Oceanography . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Physical Oceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3 Biological Oceanography . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.4 Chemical Oceanography . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Oceans and Global Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Oceanic Circulation System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Global Biogeochemical Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.1 Water Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.2 Carbon Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.3 Nutrient Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Ice Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 Coastal Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8.1 Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8.2 Tides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8.3 Coastal Geomorphological Dynamics . . . . . . . . . . . . . . . 1.9 Renewable Energy and Resources from the Ocean . . . . . . . . . . . 1.10 Advancements in Oceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 4 5 5 6 7 8 10 11 12 14 15 17 18 18 18 19 20 22 24

2

Marine Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Classification of Marine Water Bodies . . . . . . . . . . . . . . . . . . . . . . 2.2 Neritic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Pelagic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Epipelagic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Mesopelagic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Bathypelagic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4 Abyssalpelagic Ecosystems . . . . . . . . . . . . . . . . . . . . . . .

27 27 28 29 30 32 33 33

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2.3.5 Hadalpelagic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.6 Benthic Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Photic and Aphotic Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Intertidal and Littoral Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Coastal Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.1 Estuaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.2 Mangroves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.3 Seagrass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.4 Salt Marshes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.5 Coral Reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.6 Seaweed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.7 Tidal Flats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.8 Lagoons and Backwaters . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Marine Ecosystem Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.1 Provisioning Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.2 Regulating and Supporting Services . . . . . . . . . . . . . . . . 2.7.3 Cultural Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Scope of Research in Marine Science . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

33 34 34 35 37 37 37 39 40 42 43 43 44 45 45 46 46 47 47

3

Oceans and Human Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Shipping and Trade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Ports and Harbours . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Offshore Mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Petroleum and Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Submarine Cables and Pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Tourism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7 Desalinization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8 Capture Fisheries and Seafood . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Genetic Resources and Pharmacy . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

53 54 55 56 57 58 60 60 61 62 63

4

Basic Oceanographic Parameters and Their Significance . . . . . . . . . . 4.1 General Physicochemical Parameters . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Water Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.4 Dissolved Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.5 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.6 Suspended Particulate Matter . . . . . . . . . . . . . . . . . . . . . . 4.2 Water Column Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Secchi Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Euphotic Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Turbidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.4 Underwater Photosynthetically Active Radiation . . . . . 4.2.5 Mixed Layer Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

67 67 68 69 70 71 72 73 73 74 75 76 77 78

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4.2.6 Thermocline Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.7 Pycnocline Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.8 Halocline Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Carbonate Chemistry Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Dissolved Inorganic Carbon . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Total Alkalinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 The Partial Pressure of CO2 . . . . . . . . . . . . . . . . . . . . . . . 4.3.4 Dissolved Organic Carbon . . . . . . . . . . . . . . . . . . . . . . . . 4.3.5 Particulate Organic Carbon . . . . . . . . . . . . . . . . . . . . . . . . 4.3.6 Calcium Carbonate Saturation State . . . . . . . . . . . . . . . . 4.3.7 Air-Water CO2 Fluxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Biological Productivity Parameters . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Gross Primary Productivity . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Community Respiration . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Net Primary Productivity . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.4 Phytoplankton Abundance . . . . . . . . . . . . . . . . . . . . . . . . 4.4.5 Chlorophyll Concentration . . . . . . . . . . . . . . . . . . . . . . . . 4.4.6 Zooplankton Abundance . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.7 Trophic State Index (TRIX) . . . . . . . . . . . . . . . . . . . . . . . 4.5 Essential Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Nitrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Nitrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.3 Ammonia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Total Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Soluble Reactive Phosphorus . . . . . . . . . . . . . . . . . . . . . . 4.5.6 Total Phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.7 Reactive Silicate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

78 78 79 79 79 80 80 81 82 82 83 84 84 85 85 86 86 86 87 87 88 88 89 90 90 90 91 91

Coastal Pollution—An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 What is Marine Pollution? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Coastal Geography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Sources of Marine Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Types of Inputs for Marine Pollution . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Direct Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Sewage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Surface Runoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.4 Hydrocarbon in the Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.5 Shipping Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.6 Deep Sea Mining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Impacts of Marine Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6 Human Impacts on Marine Environments . . . . . . . . . . . . . . . . . . . 5.7 Coastal Zone Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

99 99 101 101 101 102 102 103 103 103 103 104 105 106 106 107

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Nutrient Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.1 Nutrient Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.2 Problems of Nutrient Imbalance . . . . . . . . . . . . . . . . . . . 6.1.3 Ecological Impact Due to Nutrient Over-Enrichment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.4 Role of Seagrass Habitat and Their Impact on the Ecosystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Eutrophication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Cultural Eutrophication . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Factors Affecting Eutrophication . . . . . . . . . . . . . . . . . . . 6.2.3 Harmful Algal Bloom (HAB) . . . . . . . . . . . . . . . . . . . . . . 6.3 Limiting Nutrients and Their Biological Role . . . . . . . . . . . . . . . 6.3.1 Redfield Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 High Nutrient-Low Chlorophyll (HNLC) Regions . . . . 6.4 Dead Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Effects of Hypoxia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.3 Impact on Coral Reef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Strategies to Combat Nutrient Over-Enrichment . . . . . . . . . . . . . 6.6 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

109 109 109 110

Organic Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Biochemical Oxygen Demand (BOD) . . . . . . . . . . . . . . . . . . . . . . 7.2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Wastewater Quality Indicators . . . . . . . . . . . . . . . . . . . . . 7.2.3 BOD as Wastewater Quality Indicators . . . . . . . . . . . . . . 7.2.4 Standard Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.5 Measuring Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Chemical Oxygen Demand (COD) . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Standard Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Measuring Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.4 COD as Wastewater Quality Indicator . . . . . . . . . . . . . . 7.4 Coliform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Indicator Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Coliform Group of Bacteria . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 The Membrane-Filter (MF) Technique . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

127 127 127 127 128 130 130 131 131 131 132 133 133 134 134 134 135 135

110 111 112 113 113 115 115 116 116 117 118 119 119 120 122 123 125

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Persistent Organic Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 A Brief History of the POPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Types of POPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 The Dirty Dozens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Sources of POPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Chemical Properties of POPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7 Environmental Behaviour of POPs . . . . . . . . . . . . . . . . . . . . . . . . . 8.7.1 Transportation/Long-Range Atmospheric Transportation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.7.2 Bioaccumulation and Biomagnification . . . . . . . . . . . . . 8.8 Global Distribution of POPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.9 Environmental Impacts of POPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.10 Silent Spring—The Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.11 Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.12 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

137 137 137 138 138 142 143 143

Heavy Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 General Principles of Metal Toxicity . . . . . . . . . . . . . . . . . . . . . . . 9.3 Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.1 Sources of Arsenic in Nature . . . . . . . . . . . . . . . . . . . . . . 9.3.2 Toxicokinetics of Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.3 Impact of Arsenic on Living Beings . . . . . . . . . . . . . . . . 9.4 Copper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.1 Toxicokinetics of Copper . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.2 Impact of Copper on Living Beings . . . . . . . . . . . . . . . . 9.4.3 Chronic Copper Poisoning . . . . . . . . . . . . . . . . . . . . . . . . 9.5 Chromium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.6 Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Mercury . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7.1 Sources of Mercury and Health Impacts . . . . . . . . . . . . . 9.7.2 Minamata Bay Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

151 151 151 152 152 153 153 155 155 155 156 157 157 159 160 160 161 162

10 Marine Oil Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Composition and Classification of Oils . . . . . . . . . . . . . . . . . . . . . 10.3 Oil Spillage and Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Effects of Oil Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Remediation of Oil Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6 Physical Remediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.1 Booms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.2 Boom Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

163 163 163 164 168 168 170 171 172

9

145 145 146 147 147 147 147 149

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Contents

10.6.3 Skimmers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6.4 Sorbent Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7 Chemical Remediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7.1 Dispersants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7.2 Solidifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.8 Thermal Remediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9 Bioremediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.10 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.11 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

173 174 174 175 176 176 176 177 178 179

11 Plastic Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Classification, Sources, and Effects of Plastics . . . . . . . . . . . . . . . 11.2.1 Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2.2 Sources of Plastics in the Marine Environment . . . . . . . 11.2.3 Harmful Impact of Plastic on the Marine Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Macroplastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3.1 Macroplastic Pollution Pathway . . . . . . . . . . . . . . . . . . . 11.3.2 Effects of Macroplastics on the Marine Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3.3 Agreement and Measures to Prevent and Combat Macroplastics in the Marine Environment . . . . . . . . . . . 11.4 Microplastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4.2 Types, Sources and Distribution . . . . . . . . . . . . . . . . . . . . 11.4.3 Effects of Microplastics on Marine Organisms . . . . . . . 11.4.4 Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5 Case Study: The Great Pacific Garbage Patch . . . . . . . . . . . . . . . 11.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

181 181 182 182 184

12 Ocean Acidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.2 Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3 Causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.4 Impacts of Ocean Acidification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5 Remedies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.5.1 Reducing CO2 Emissions . . . . . . . . . . . . . . . . . . . . . . . . . 12.5.2 Managing Solar Radiation . . . . . . . . . . . . . . . . . . . . . . . . 12.6 Case Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.1 Norwegian Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.2 Barents Sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.3 Western Canadian Arctic Sea . . . . . . . . . . . . . . . . . . . . . .

205 205 205 206 206 207 207 207 207 209 211 211

185 188 189 191 191 192 192 193 196 199 200 201 203

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12.6.4 Greenland . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.6.5 Alaska . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

211 211 211 212

13 Energy From the Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.2 Marine Renewable Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.3 Principles of Energy Generation From Ocean Resource . . . . . . . 13.4 Wave Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.4.1 Wave Energy Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.4.2 Wave Energy Conversion Technologies . . . . . . . . . . . . . 13.5 Wind Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5.1 Wind Energy Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.5.2 Wind Energy Conversion Technologies . . . . . . . . . . . . . 13.6 Tidal Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6.1 Tidal Resource Potential . . . . . . . . . . . . . . . . . . . . . . . . . . 13.6.2 Tidal Power Conversion Technologies . . . . . . . . . . . . . . 13.7 Ocean Thermal Energy Conversion (OTEC) . . . . . . . . . . . . . . . . . 13.7.1 OTEC Resource Potential . . . . . . . . . . . . . . . . . . . . . . . . . 13.7.2 OTEC Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.8 Energy From the Salinity Gradient . . . . . . . . . . . . . . . . . . . . . . . . . 13.8.1 Salinity Gradient Energy Potential . . . . . . . . . . . . . . . . . 13.8.2 Technologies Related to Salinity Gradient Energy (SGE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.9 Other Forms of Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.9.1 Marine Biodiesel as an Energy Source . . . . . . . . . . . . . . 13.9.2 Concept of Artificial Energy Island . . . . . . . . . . . . . . . . . 13.9.3 Geothermal Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.10 Benefits and Disadvantages of Using Ocean Energy . . . . . . . . . . 13.11 Environmental Interactions and Consequences of Ocean Renewable Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

213 213 214 216 218 220 220 228 230 231 235 236 238 246 249 251 253 253

14 Marine Mineral Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.2 Polymetallic Nodules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.3 Ferromanganese Crusts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.4 Sea Floor Massive Sulphides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.5 Oil in the Offshore Basins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.6 Offshore Oil of India . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.7 Natural Gas Hydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8 Other Mineral Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8.1 Offshore Coal Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8.2 Marine Placer Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8.3 Construction Material . . . . . . . . . . . . . . . . . . . . . . . . . . . .

269 269 273 277 280 284 288 291 302 302 303 305

254 255 255 257 258 258 260 262

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Contents

14.8.4 Evaporites and Salts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.8.5 Marine Phosphorite Deposits . . . . . . . . . . . . . . . . . . . . . . 14.8.6 Hot Brines and Metalliferous Muds . . . . . . . . . . . . . . . . 14.9 Seabed Mining and Its Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14.10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

306 309 311 311 313 315

15 Coastal Hazards: Climatic and Hydrogeological Hazards . . . . . . . . . 15.1 Coastal Hazards—An Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 15.2 Cyclone and Cyclone Related Surge . . . . . . . . . . . . . . . . . . . . . . . 15.2.1 Condition for the Formation of Tropical Cyclone . . . . . 15.2.2 Development of a Tropical Cyclone . . . . . . . . . . . . . . . . 15.2.3 Structures of Tropical Cyclones . . . . . . . . . . . . . . . . . . . . 15.2.4 Impact of Tropical Cyclones . . . . . . . . . . . . . . . . . . . . . . 15.2.5 Global Distribution of Tropical Cyclone and the Scenario in Coastal India . . . . . . . . . . . . . . . . . . . 15.2.6 Prediction and Mitigation of Tropical Cyclone . . . . . . . 15.2.7 Extratropical Cyclone . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.8 Difference Between Tropical and Extratropical Cyclone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.2.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3 Coastal Flood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3.1 Types of Floods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3.2 Causes of Coastal Flood . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3.3 Consequences of Coastal Flood Hazard . . . . . . . . . . . . . 15.3.4 Coastal Flood Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . 15.3.5 Coastal Flood Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . 15.3.6 Urbanisation and Floods in Coastal Cities . . . . . . . . . . . 15.4 Coastal Groundwater Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15.4.1 Salinity Problem in Groundwater . . . . . . . . . . . . . . . . . . 15.4.2 Remediation of Coastal Salinity . . . . . . . . . . . . . . . . . . . 15.4.3 Other Problems of Groundwater . . . . . . . . . . . . . . . . . . . 15.4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

325 325 333 333 334 336 337

16 Coastal Hazards: Geomorphic and Tectonic Hazards . . . . . . . . . . . . . 16.1 Coastal Erosion and Beach Degradation Process . . . . . . . . . . . . . 16.1.1 Beach Profile and Morphology of a Coast . . . . . . . . . . . 16.1.2 Source of Beach Sands and Coastal Sediment Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.1.3 Process of Coastal Erosion . . . . . . . . . . . . . . . . . . . . . . . . 16.1.4 Remedial Measures to Coastal Erosion . . . . . . . . . . . . . . 16.1.5 Coastal Protection Activities in India . . . . . . . . . . . . . . . 16.2 Coastal Land Subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.3 Coastal and Submarine Landslide . . . . . . . . . . . . . . . . . . . . . . . . . .

375 377 378

339 342 344 345 346 346 346 349 349 352 353 355 357 359 364 367 369 369

382 384 385 390 390 394

Contents

16.4

xvii

Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.4.1 Mechanism of Tsunami Generation . . . . . . . . . . . . . . . . 16.4.2 Global Distribution of Tsunamis . . . . . . . . . . . . . . . . . . . 16.4.3 Tsunami in the Light of Plate Tectonics . . . . . . . . . . . . . 16.4.4 Tsunami Warning, Forecasting and Mitigation . . . . . . . 16.4.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16.5 Coastal Radioactivity and Hazard Related to Radionuclides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

399 400 404 404 406 408

17 Global Sea-Level Rise and Associated Problems . . . . . . . . . . . . . . . . . . 17.1 Causes of Sea-Level Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.2 Quantification of Sea-Level Change . . . . . . . . . . . . . . . . . . . . . . . . 17.3 Problems of Sea-Level Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17.4 Solution to SLR and Adaptation Strategies . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

419 420 420 423 425 425

410 413

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429

About the Authors

Dr. Swapna Mukherjee is a retired Director of the Geological Survey of India. She completed her Ph.D. at the Saha Institute of Nuclear Physics, Kolkata, India. She has authored four books with Capital Publishing Company, two co-published by Springer. These books covered clay basics and industrial aspects, applied clay science, and environmental soil science. Dr. Mukherjee is a member of the Clay Mineral Society of India, Soil Society of India, Indian Chemical Society, Centre of Interdisciplinary Research and Education (CIRE), Institute for Science Education and Culture, World Science Congress, and Indian Science Congress. Dr. Kaushik Kiran Ghosh is an Associate Professor in the Department of Geology at Jogamaya Devi College, Kolkata. He received his bachelor’s degree in Geology from the Presidency College, Kolkata, and his master’s and Ph.D. degree in Geology from the University of Calcutta, Kolkata. Dr. Ghosh has been engaged in teaching for around 25 years. His research fields cover major areas in geochemistry, petrology, and ore geology, with a special emphasis on iron ore. He has also served as Guest Faculty at Presidency University (formerly Presidency College), Vidyasagar University, Asutosh College PG Centre, and Meghnad Saha Institute of Technology of Kolkata. Dr. Abhra Chanda is an Assistant Professor in the School of Oceanographic Studies at Jadavpur University, Kolkata, India. In his brief eleven years research career, he has actively conducted interdisciplinary research in greenhouse gas dynamics and coastal and marine pollution. His research interest encompasses lentic and lotic biogeochemistry, air pollution, wetland ecology, and chemical oceanography. Dr. Chanda has 105 publications to his credit, including national and international journal articles and edited book chapters. He has authored two books with Springer that discussed the pond ecosystems of the Indian Sundarban and the blue carbon dynamics of the Indian Ocean, respectively.

xix

Chapter 1

An Introduction to Oceanography

1.1 The Term Oceanography and Its Scope Oceanography (also referred to as oceanology) is a scientific study that focuses on the oceanic realms of the world. The gradual advent of several Earth science disciplines led to the emergence of oceanography as a subject. Since our elementary days, we have known that oceans comprise almost 71% of the Earth’s surface. However, in the recent past, these massive water bodies have received increasing scientific attention due to their role in regulating the global climate and atmospheric gaseous composition and provisioning food resources. Oceans play a crucial role in regulating the greenhouse gases in the atmosphere. They act as an abode to neverending biodiversity, most of which remain undiscovered, even at the present date. Several crucial climatic phenomena (like the monsoon) and disasters (like cyclones, tornados, and hurricanes) originate in the oceans. The oceans also offer an incredible potential to harness renewable energy through several mechanisms, like tidal energy, wind energy and ocean thermal energy conversion (Table 1.1). According to the common perception, only the vast blue stretch that one beholds while standing on a beach encompasses the oceans. However, the coastal periphery that bestows several crucial marine ecosystems plays an equally significant role, and thus, rightfully comes under the purview of this subject. As we go deep into the matter, we would realize that oceanography is a subject that is worth studying. The oceans can provide many solutions to the already existing problems that humankind is facing at present. However, unlike many other disciplines, oceanography requires an interdisciplinary approach to develop a holistic understanding. Studying oceanography requires knowledge of fundamental subjects like physics, chemistry, biology, geography, geology, and specialized subjects like climatology, meteorology, hydrology, and biogeochemistry.

© Capital Publishing Company, New Delhi, India 2023 S. Mukherjee et al., Environmental Oceanography and Coastal Dynamics, https://doi.org/10.1007/978-3-031-34422-0_1

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Table 1.1 The fundamental role of oceans in a nutshell Category

Specific importance

Climate regulation

Ocean-atmospheric coupled phenomena like the monsoon and El Niño-Southem Oscillation (ENSO) regulate the climate Acts as a sink for several greenhouse gases like CO2 and helps alleviate global warming Plays a crucial role in regulating the heat budget of Earth

Resource provisioning

An abode for marine biodiversity, including fishes and crustaceans, which human beings consume as food Source of several ethnobotanical and medicinal compounds Source of petroleum, hydrocarbons and several minerals

Atmospheric composition

Provides more than half of the global atmospheric O2

Energy

Tidal energy, oceanic wind energy and ocean thermal energy conversion, generate renewable energy

Trade

Oceans offer navigational routes that enable shipping and trade between countries

Waste repository

Selected oceanic sites are used for disposing of low-level radioactive wastes

Livelihood

A large section of the global population relies on ocean-derived products to earn a decent livelihood

Plays a crucial role in the biogeochemical cycle of several crucial gases and compounds, like carbon, nitrogen, phosphorus, water and many more

1.2 Historical Evolution of this Subject At times immemorial, human beings believed that the sea-level horizon marks the boundary of Earth. They also used to consider Earth as a flat surface. Later some of the brave sailors of the ancient past ventured to know what lies beyond those horizons. Their courageous voyages were perhaps the most significant step forward to learn about the oceans. However, the inquisitive nature of various navigators and explorers led them to critically observe the coastal oceanic activities tens of thousands of years ago. The periodic encroaching and retreat of waters on the coastlines (tidal activities), wave patterns, and storm surges were their basic observations. They also realized that the seawaters are salty and not fit for drinking (unlike the rivers and streams). It is only 3000 years ago when philosophers started trying to understand the significance of these vast water bodies on our daily life and climate. The fifteenth century witnessed many sea ventures, which eventually established that Earth is spherical (not flat), and the oceans approximately encompass three-fourths of the Earth’s surface. However, in the late nineteenth century, several oceanic expeditions led to the emergence of modern oceanography. The second world war compelled many countries, especially the United States of America, to learn more about the

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characteristic traits of the oceans to gain an advantage in Navy warfare. Table 1.2 gives a snapshot of the chronological events that were milestones in the development of this subject. Table 1.2 The list of significant events in the historical time-scale related to the evolution of the subject of Oceanography Time

Events

4000 B.C.

The Egyptians developed raft-like structures to navigate in the coastal waters

1000–600 B.C.

The Phoenician civilization used landmarks and stars to navigate in the Atlantic Ocean

325 B.C.

The Greek geographer Pytheas indicated a possible relationship between lunar phases and tidal amplitude Aristotle wrote Meteorologica, which had initial information on a few of the marine biological aspects

54 B.C.-30 A.D.

Roman philosopher Lucius Annaeus Seneca observed that riverine flow is unable to alter the sea level

725 A.D.

The Northumbrian monk Bede wrote De temporum ratione (The Reckoning of Time), where he discussed tidal variability and the effect of winds on tide-driven wave surges

982 A.D.

The Norwegian explorer Erik Thorvaldsson ventured across the Atlantic and discovered Baffin Island in the Arctic Ocean

1452–1519 A.D.

Leonardo da Vinci commented on waves, currents, and pre-historic sea levels

1492 A.D.

Italian explorer, Christopher Columbus discovered North America

1500 A.D.

Portuguese explorer Pedro Álvares Cabral discovered Brazil

1513 A.D.

Spanish explorer, Juan Ponce de León studied the Florida Current

1513–1518 A.D.

Spanish explorer, Vasco Núñez de Balboa sailed into the Pacific Ocean for the first time

1519–1522 A.D.

Ferdinand Magellan and Juan Sebastian Elcano completed the circumnavigation of the world through the oceans for the first time

1674 A.D.

Robert Boyle studied the relationship between water temperature, salinity, pressure, and water depth in the oceans

1725 A.D.

Luigi Ferdinando Marsili wrote a book on the scientific aspects of the sea named L’Histoire physique de la mer

1768–1779 A.D.

Captain James Cook carried out many voyages exclusively to collect oceanographic data

1831–1836 A.D.

Physician Alexander Marcet derived the law of constancy in composition in all the oceans of the world

1839–1843 A.D.

Sir James Ross carried out an expedition to the Antarctic Ocean and collected ocean-bottom samples

1873 A.D.

Charles Wyville Thomson wrote a book on oceanography named The Depths of the Sea (continued)

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Table 1.2 (continued) Time

Events

1872–1876 A.D.

The first official oceanographic expedition to collect data from the world oceans was named the Challenger Expedition

1888 A.D.

Woods Hole, Massachusetts, witnessed the first marine biological laboratory

1902

The International Council for the Exploration of the Sea (ICES) came into existence

1912

Alfred Wegener proposed the continental drift theory

1958

Submarine USS Nautilus reached the North Pole under ice cover

1959–1965

The International Indian Ocean Expedition

1972

The Geochemical Ocean Sections Study (GEOSECS) Expedition to accurately measure seawater chemical parameters

1992

NASA launched the TOPEX-Poseidon satellite to monitor sea level and currents

1998

International year of the Ocean to spread awareness on the significance of oceans among the common mass

2006

Japan and the USA launched the Integrated Ocean Drilling Programme (IODP)

See The Growth of Oceanography (n.d.) for more details

1.3 The Broad Categorization of Oceanography The subject of Oceanography has four broad subdisciplines (Fig. 1.1). Geological oceanography forms the foundation of this subject. It deals with the structural aspects like the sediments and rocks of the abyssal plain and the coastal periphery. Physical oceanography encompasses all the oceanic motion-related features and focuses on current, wave, tide, and energy dynamics. The marine biodiversity and its interaction with the oceanic water column and the ambient atmosphere deserve a separate subdiscipline. Biological oceanography covers these issues. The chemistry of the oceans plays a crucial role in regulating several biogeochemical phenomena and governs air-sea gaseous exchange and hence, the global climate. This sub-section comes under the head of chemical oceanography. Though these sub-branches are distinct in their area of coverage, they often share common domains. Besides these four fundamental subdisciplines, some specialized branches have evolved in the recent past. Satellite oceanography is one of them. With the advent of remote sensing tools, it is possible to acquire synoptic-scale data from the ocean’s surface and subsurface. Satellite oceanography is that branch of remote sensing that focuses exclusively on the oceans. Paleoceanography is another specialized branch that enquires about the geological past events in the oceans and the oceanic sediments.

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Fig. 1.1 The broad categories of oceanography

1.3.1 Geological Oceanography Geological oceanography, also known as marine geology, principally deals with the formation and evolution of the structure of the ocean basins. This subdiscipline of oceanography interconnects several aspects like stratigraphy, solid-earth geophysics, sedimentology, geochemistry, and coastal processes (Table 1.3). This subject mainly discusses the evolution of the earth and the ocean basins, followed by interlinked aspects like volcanism, plate tectonics, hydrogeodynamics, and petrogenesis (Shepard 1977). The shape, size and depth of the oceans and the characteristic features of the coastal periphery like the continental shelf, slope, and beach properties also come under the purview of this branch. The geomorphology of the coastlines, morphodynamics of the coastal features, and sedimentation are some of the crucial topics studied under this sub-branch of oceanography. Paleoceanography, though often considered a specialized discipline, is strictly a part of geological oceanography.

1.3.2 Physical Oceanography Physical oceanography, also referred to as marine physics, focuses on the physical properties of oceans and their role in regulating the global climate (Table 1.4). This sub-discipline of oceanography considerably involves meteorological sciences, as many of the topics orient around ocean-atmospheric coupled processes (Stewart 2008). This subject covers the physical setting of the oceans and the atmospheric

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Table 1.3 The broad topics that come under the sub-discipline of geological oceanography Evolution of earth and ocean basins

Solid earth geophysics

Sedimentation and coastal processes

Paleoceanography and climatology

Petrogenesis

Structure of Earth

Sediment transport and deposition

Climate changes in the geological past

Volcanism

Lithosphere formation

Coastal landscapes and morphodynamics

Pleistocene ice ages

Cosmochemistry and the evolution of the universe

Continental plate tectonics

The Anthropocene

Glacial maxima and deglaciation

Geologic time-scale

Seismology

Coastal geomorphology Paleoclimatic record characterization

Mid-oceanic ridges and Subduction

Hydrogeodynamics

Table 1.4 The broad topics that come under the sub-discipline of physical oceanography Physical setting

Motion physics

Ocean–atmosphere coupled phenomena

Wave dynamics

Atmospheric influences

Equation of motion

Equatorial processes

Various categories of waves

Oceanic heat budget

Motion and viscosity

Walker cycle

Coastal processes

Thermohaline circulation

Geostrophic currents

ENSO

Tide dynamics

Upper-ocean and winds

Wind-driven ocean circulation

Numerical modeling

Tsunamis

Deep-oceanic circulation

Physical forcing events

Storm surge modeling

influences governing them. The oceanic heat budget and the role of temperature, salinity and density in oceanic circulation, come under the purview of this branch of oceanography. Motions of any kind and the effect of wind on the upper surface of oceans are some of the critical topics covered by this subject. Besides, wave and tide dynamics, coastal processes, ocean-related disasters, and physical forcing events are a part of this broad sub-head.

1.3.3 Biological Oceanography Biological oceanography, also known as marine biology, focuses on the life forms in the oceans (Table 1.5). It also encompasses the interactions of living organisms with the abiotic environment and among one another (Lalli and Parsons 1997). The marine

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Table 1.5 The broad topics that come under the sub-discipline of biological oceanography Broad topics

Areas covered

Interaction with the abiotic environment

Role of salinity, temperature, solar radiation, pressure, and current in regulating marine life forms

Phytoplankton and primary production

Species diversity, photosynthesis, nutrients, and physical control of autotrophic activities

Zooplankton dynamics

Species diversity, distribution, spatiotemporal variation

Marine ecological food chain

Food web, energy flow, ecological pyramids, trophic structure

Nekton and fisheries

Crustaceans, cephalopods, reptiles, mammals, fisheries, and mariculture

Benthos and benthic communities

Phytobenthos and coastal vegetations like mangroves, seagrass, seaweeds, kelps, and corals

Anthropogenic impacts on marine biota

Effect of marine pollutants like heavy metals, pesticides, plastics, sewage, radioactive wastes, and thermal effluents on marine life forms

biodiversity remains only partly explored even in the current date. With each passing day, newer information is enlightening us all in this regard. This subdiscipline focuses on the phytoplankton communities, which form the base of the marine ecological food chain. Zooplankton also comes under the purview of this subject. Energy flow through the different ladders of the food chain and the food web are the prime areas of interest. Nektons and fisheries comprise a bulk volume of this domain. Several marine scientists consider fisheries oceanography as a specialized subdiscipline of marine biology. Biological oceanography also covers the benthic communities and the coastal vegetation that play a crucial role in regulating the Earth’s greenhouse gas concentrations. Lastly, the anthropogenic impacts on marine biota have emerged as one of the topics of this subject.

1.3.4 Chemical Oceanography Chemical oceanography, also known as marine chemistry, principally focuses on the chemical composition of seawater (Table 1.6). This subject often encompasses the estuarine, nearshore, and riverine sectors that do not strictly qualify in the realm of oceanography. This subdiscipline deals with the plethora of compounds and chemical substances that are available in the oceans (Pilson 2013). The evolution of the present chemical composition, geochemical history of the oceans, dissolution of atmospheric gases, and atmosphere-hydrosphere gaseous exchange are a few broad subtopics of this discipline. The geochemical extraction of materials from the oceanic water column and benthic sediments also comes under the purview of this subject.

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Table 1.6 The broad topics that come under the sub-discipline of chemical oceanography Broad topics

Areas covered

Basic chemical composition of seawater

Major and minor constituents of seawater and the law of constancy of composition; definition of salinity

Gas dynamics

The gaseous composition that plays a role in the biological phenomena, greenhouse gas dynamics, solubility, atmosphere-hydrosphere gas exchange

Nutrient dynamics

The microelements, compounds and ionic radicals that play a crucial role in the autotrophic production of organic matter

Marine pollution

Organic pollution, plastic pollution, eutrophication, heavy metal pollution, persistent organic pollutants, and ocean acidification

Geochemical extraction of substances

Methodologies dealing with the extraction of several useful substances from the water column and benthic sediments; some aspects of offshore mining

Radioactive substances and paleoceanography Role of radioactive substances in analyzing several biogeochemical phenomena and long-term historical past of the oceanic systems

Marine pollution is a burning topic that is primarily interdisciplinary. However, chemical oceanography explains the lion’s share of this topic on this date. Certain areas of oceanography intersect the domain of chemical oceanography with other subdisciplines like geological, biological, and physical oceanography. However, in most cases, a conceptual understanding of the chemistry of the seas becomes essential to developing a holistic understanding of such common domains.

1.4 Oceans and Global Climate The Earth as we know it in the present day would not have been possible without the oceans. These vast aquatic stretches play a crucial role in shaping the global climate (Voldoire et al. 2013). Now one might wonder how these water bodies influence the weather even near the continental landmass. The answer lies in the plethora of physicochemical properties of water molecules that encapsulate this planet. Water as a compound has a very high specific heat capacity that enables the oceans to store a substantial amount of heat. The oceanic water mass absorbs a substantial portion of the incoming solar radiation near the tropical belts. The land surface also receives such radiation; however, it quickly emits energy toward the atmosphere. The oceans distribute the heat retained in the water column throughout the nooks and corners of the globe. Evaporation takes place at a much higher rate in tropical regions.

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It leads to the formation of clouds and wind systems in the atmosphere through the high-pressure-low-pressure systems. These winds carry the clouds to various places all around the continental landmass. Wherever these clouds face obstruction and undergo condensation in higher altitudes (with the help of cloud condensation nuclei), they burst out and lash in the form of rain (Spracklen et al. 2008). Besides, the equatorial waters dissipate heat to the adjoining water mass. In this way, heat from the equator passes towards the poles, and the cold polar waters return to the equator. This mechanism is known as thermohaline circulation (Fig. 1.2). The differing salinity and temperature induce such a kind of motion in the oceans. Previously the global scientific community believed that oceans are still water masses that do not mix well spatially and vertically. However, advanced pieces of research in

Fig. 1.2 The thermohaline circulation or conveyor belt mechanism of global oceanic circulation (top) and the current systems in the global ocean (below). The blue and red lines indicate the cold and the warm currents, respectively. Credit European Space Agency and David Bice © Penn State University, NASA

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this domain proved these concepts wrong. If this would have been the scenario, then the equatorial waters would have been boiling, and the subtropical to polar waters would be frozen, leaving a much smaller habitable area on this planet. The oceans play a crucial role in regulating the climate by altering the chemical composition of the atmosphere. The oceans in the present date act as a significant sink for CO2 , which is a greenhouse gas (Le Quéré et al. 2010; DeVries 2014). The global scientific community unequivocally accepts that the greenhouse gases emitted due to anthropogenic activities have led to phenomena like climate change and global warming. However, the oceans alleviate to a large extent the atmospheric greenhouse gas load. The present understanding strongly indicates that the very concept of weather and climate would not have existed in oceanic absence.

1.5 Oceanic Circulation System Ocean circulation refers to the process of large-scale movement of voluminous water mass across the global oceanic system. Physical forcings like wind lead to the formation of oceanic currents, which lead to gyre formation. The gyres can be subtropical (equator to 50 °N/S) or subpolar (50 °N/S to 90 °N/S) depending upon the latitudinal position of these current systems. The wind-driven currents usually exert water movement in the surface layers. However, the depth up to which winds can promote water movement depends on the degree of stratification. In the equatorial region, the water column remains substantially stratified, and there the currents are available in the top 1000 m depth. However, in the polar regions where stratification is almost absent, these currents reach the abyssal plain. Other factors like Coriolis force, vertical and horizontal friction, and planetary vorticity also regulate these gyres (Table 1.7). The wind-driven stress is primarily responsible for the lateral movement of water mass, whereas the water temperature plays a crucial role in the vertical motion of water. The heat acquired in the equatorial region moves towards the poles, and during the winter, it sinks to the bottom and moves back towards the equator. The scientific community often refers to this movement as a conveyor belt mechanism. The salinity and temperature regulate the density difference between two adjacent water masses within the same system. The cold denser water tends to reach the abyssal plain and spread across the plain. This type of water movement is referred to as deep ocean circulation. Since a combination of phenomena driven by salinity and temperature spreads the water mass across the ocean, this type of motion is known as thermohaline circulation (thermo stands for temperature, and haline stands for salinity) (Wunsch 2002). The North Atlantic Ocean and Antarctica are the most significant regions that give rise to deep water masses. Two other phenomena, known as upwelling and downwelling, also add to this global water movement mechanism.

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Table 1.7 Few important terms and their lucid definitions concerning global oceanic circulation Thermohaline circulation

It is a synoptic scale ocean circulation process that is governed by the density gradients created by surface heat and freshwater flows from the terrestrial regimes

Gyres

It is a large system of circular ocean currents formed by global wind patterns and forces created by Earth’s rotation

Subtropical gyres

The oceanic gyres that exist between the equator and 50°N in the northern hemisphere rotate in a clockwise direction, and the ones in the same latitudinal ranges in the southern hemisphere rotate in a counter-clockwise direction

Subpolar gyres

The cyclonic ocean circulation gyres that form in the polar regions and center around a low atmospheric pressure system unlike the subtropical gyres which circle a high atmospheric pressure system

Currents

An incessant, predictable, directional movement of seawater governed by gravitational forces, wind (Coriolis Effect), and water density

Upwelling

An oceanographic process (mostly wind-driven) under which cold, dense, and nutrient-rich waters from the bottom of the ocean come up to the air–water interface

Downwelling

It is the reverse of upwelling where cold and dense water accumulates in a region and sinks below the warmer less dense freshwater

Coriolis effect

From the perspective of oceanography, the deflection of oceanic currents in a particular direction based on the hemispherical positions due to the rotator motion of the Earth

Frictional forces

Water masses in the ocean have different velocities. These masses when encountering each other transfer momentum from one layer to another, which gives rise to frictional forces

Geostrophic current

Keeping aside the frictional forces that mostly prevail in the upper oceanic layers, the oceanic currents develop out of the horizontal pressure gradient and Coriolis force

Equatorial current

The westward wind-driven current is mostly situated near the equatorial regions of the global oceans

Antarctic circumpolar current

The ocean current that flows clockwise from west to east around Antarctica

Ekman transport

The oceanic currents usually deflect due to the ambient wind vector and form a spiral in the oceanic depths. At some depth, the direction of the current becomes antiparallel to the wind vector leading to a spiral of currents that enables matter and energy transport from the upper surface to the deeper layers

1.6 Global Biogeochemical Cycles The oceans are reservoirs of several substances and chemicals. Matters exchange between the hydrosphere, atmosphere, and lithosphere via several phenomena (Hedges 1992). Many of these elements are integral to various life forms on earth. Carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur are some crucial elements that remained under the lenses of the scientific communities. Water is also a

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critical compound that cycles around the spheres of this planet. These subtopics come under the umbrella of Environmental Science in general. However, from the point of view of oceanography, we are interested in studying the avenues through which these crucial elements and compounds leave the oceans or any other linked aquatic ecosystems and how they come back. Even within the water-based ecosystems connected to the oceans, a substance can exist in several forms, known as chemical speciation. The interchange of chemical species among one another is also a part of these biogeochemical cycles. The rate of such changes and the phenomena through which these biogeochemical substances exchange phases are of immense significance. Such changes affect the global climate and the well-being of several life forms. The term biogeochemistry evolved for studying those phenomena which involve biological, geological (often physical), and chemical pathways in altering or shifting any matter within natural ecosystems. The exchange of natural substances within a particular phase (gas, liquid, or solid) or between different spheres takes place through a combination of biological and non-biological processes. Together these processes led to a new regime of biogeochemistry. This subject often encompasses several pollutants that are either natural or have an anthropogenic origin.

1.6.1 Water Cycle We came across the term and concept of the water cycle in our elementary days. The movement of water through the aquatic ecosystems and their subsequent phase change to the atmosphere and back to the hydrosphere led to the formation of the global climate as we know it today. Those who are reading this book are already aware that water molecules from oceans, lakes, reservoirs, and rivers evaporate in the tropics and enter the atmosphere as water vapour. These water vapours move towards the higher altitudes and higher latitudes as well, where they condense and return to the earth’s surface in several forms of precipitation, like rain, snow, hail, etc. A substantial part of the down poured water on the terrestrial sectors ends up as runoff and meets the nearby rivers and streams that flow back to the ocean (Fig. 1.3). Another part percolates through the lithosphere to the subsurface aquifers. Several studies have shown that groundwater discharge directly takes place in the lotic ecosystems like rivers and estuaries, thus, contributing to the oceanic water mass (Taniguchi et al. 2002; Moore 2010). Environmental scientists carry out numerous pieces of research focusing on the water cycle even in the present date to understand several climatic and ocean–atmosphere coupled phenomena. From the perspective of oceanography, the water cycle is observed from a slightly different viewpoint. Oceanographers are interested in studying the water movement within the ocean. The early philosophers used to believe that the vast oceans are static bodies of water. However, advancements in the field of oceanography explored that oceanic waters move all around the earth. Two types of principal movements give rise to the dynamism of the oceanic water column: (i) the lateral movement of water mass across the latitudes from the tropics to the poles and back, and (ii) the vertical movement of water from the ocean surface to

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the bottom and back. Due to such movements, water acts as a carrier and transports several essential gases and compounds to the depths of the ocean and all corners around this planet. Previously oceanographers used to have a perception that the benthic depths of oceans where light cannot penetrate are devoid of any oxygen as photosynthetic activities are not possible in such depths without any light. However, depth profiles show a fair bit of dissolved oxygen concentrations in the deepest layers of the ocean. This observation indicated that oxygen produced in the surface layers of the ocean goes deep down due to the vertical movement of water mass (Atamanchuk et al. 2020). Processes like thermohaline circulation, upwelling, downwelling and oceanic current formation driven by wind vectors, evaporation, and precipitation, all contribute to the dynamics of water within the oceans. The ocean–atmosphere give and take of water lead to the formation of high/low-pressure systems around the globe, which in turn, gives rise to several natural climatic events, like monsoon rain, storms, surges, and many more. Many of these events turn out to be hazards and disasters for humankind. Thus, understanding the water cycle with special emphasis on the oceans has become a dire need of the hour.

Fig. 1.3 A snapshot of the hydrological cycle as portrayed by Trenberth et al. (2011). The units are in thousand cubic kilometers signifying storage and thousand cubic kilometers/year for exchanges

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1.6.2 Carbon Cycle Carbon is an element that is integral to various life forms on this planet. Carbon circulates from the biotic life forms to abiotic materials through several biochemical processes on earth. Since the Industrial Revolution, carbon came to the forefront, as a plethora of anthropogenic activities potentially disrupted the natural equilibrium of the carbon-containing greenhouse gases like carbon dioxide (CO2 ) and methane (CH4 ), and it is held responsible for phenomena like global warming and climate change. The fundamental process that regulates carbon in the atmosphere is photosynthesis, wherein atmospheric CO2 is utilized by the plant communities to form organic carbon-containing molecules (Falkowski 1994). These life forms also respire CO2 back into the atmosphere. Fossil fuel combustion has been a significant factor for the last two centuries that introduced gaseous CO2 and CH4 molecules at a much faster rate than ever experienced by this planet. The greenhouse properties of these gases enable the earth’s surface and the lower troposphere to retain the heat that should have otherwise been emitted back to space. This phenomenon leads to the increase in temperature of the atmosphere as well as the oceans and has some serious deleterious consequences. The significance of the carbon cycle has increased manifold since it has been responsible for all the manifestations of climate change that we are experiencing at the present date. It might seem that all the carbon-centric reactions and phenomena take place in the terrestrial sector; however, the oceans are the principal regulators of carbon. Oceans at present act as a net sink for atmospheric CO2 , though the sink strength varies spatiotemporally throughout the globe (Bates et al. 2006; Roobaert et al. 2019). The oceans process the carbon through several mechanisms, like the biological carbon pump and the physical pump. The carbonate chemistry of the ocean transforms carbon into several chemical species that regulate the atmosphere–ocean carbon equilibrium. In the oceans and almost all aquatic bodies, carbon remains in the inorganic and organic forms that can be particulate and dissolved. The interchange of carbon among the different forms takes place through several biogeochemical reactions within the ocean (Fig. 1.4). Dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), particulate inorganic carbon (PIC), and particulate organic carbon (POC) comprise the carbon universe in aquatic ecosystems. DIC is mainly composed of bicarbonate ions (HCO3 − ), carbonate ions (CO3 2− ), and gaseous CO2 . The pH of the water column determines the amount of gaseous CO2 on the ocean surface. Higher pH facilitates lower partial pressure of CO2 in water [pCO2 (water)] and vice-versa. If the pCO2 (water) is higher than the partial pressure of CO2 in the air [pCO2 (air)], CO2 escapes from the water surface towards the atmosphere, and hence, acts as a source of CO2 . Under the reverse scenario, the water surface acts as a sink for CO2 . Most of the open oceanic waters act as a sink for CO2 , as the pCO2 (water) remains less than pCO2 (air). A diversity of autotrophic organisms assimilate bicarbonate and carbonate to carry out photosynthesis and thus, shift the equilibrium in favour of sinking CO2 . However, processes like biotic respiration and mineralization of organic carbon to inorganic carbon provide positive feedback to carbon emission.

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Fig. 1.4 The carbon exchange within the oceanic water mass through several phenomena. Credit David Bice © Penn State University, NASA

The rivers and estuaries drain significant quantities of carbon in both inorganic and organic forms that enhance the carbon load in the ocean. A small fraction of this carbon sinks to the abyssal plain; however, a substantial portion remains embedded in the coastal vegetated ecosystems, like the mangroves, seagrasses, salt marshes, kelps and marine wetlands. These ecosystems are collectively referred to as the blue carbon ecosystems. These ecosystems store and sequester organic carbon for hundreds and thousands of years and act as long-term sinks of carbon. However, their anthropogenic destruction in the name of coastal development has become a point of concern at the present date. Thus, understanding the carbon balance and the global carbon budget in the oceans has become a priority to combat the evil posed by climate change.

1.6.3 Nutrient Dynamics The biological fixation of carbon in the oceans by the phytoplankton plays a crucial role in governing the global climate. The ecological food chain in the marine domain critically depends on autotrophic carbon production. Autotrophs utilize CO2 and water to build organic biomass; however, they require some essential micronutrients to carry out photosynthesis. Nitrogen, phosphorus, silica, and to some extent iron, are the primary micronutrients. These nutrients usually exist in scanty and essentially in the inorganic form in oceanic water mass. Nitrogen mainly exists as nitrate, nitrite, ammonia, organic nitrogen, dissolve nitrogen gas and nitrous oxide (Fig. 1.5). The

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Fig. 1.5 The nitrogen dynamics in the oceanic waters. Credit Webb (2021)

terrestrial sectors act as the fundamental source of these nutrients. Rivers and streams through denudation and weathering bring in nitrogenous and phosphorus-rich materials to the sea. However, at the present date, anthropogenic nutrient delivery into the natural aquatic systems including the oceans has caused severe concern. Excessive nutrients in the ocean lead to an enhanced growth of phytoplankton that forms algal blooms and lead to eutrophication. Eutrophication takes place naturally; however, when it occurs due to anthropogenic input, it is referred to as cultural eutrophication. The formation of algal bloom is detrimental to all life forms that thrive in the oceans as the bloom layer cuts off the gaseous and energy exchange between the surface ocean and the atmosphere. The nutrients often maintain a particular ratio in the oceanic water column and the phytoplankton biomass, known as the Redfield ratio (C: N: P ≈106: 16: 1) (Takahashi et al. 1985). It is argued by several scholars that a nutrient ratio of this magnitude is ideal for phytoplankton to conduct photosynthesis. However, some regions of the ocean suffer from nutrient limitations too. The deficiency of nitrogen compared to phosphorus levels gives rise to a nitrogenlimiting condition and vice-versa to a phosphorus-limiting condition. Often despite the adequate presence of both nitrogen and phosphorus, nutrient limitation occurs due to a deficiency of iron. An absence of less availability of photosynthetically active radiation in places with minimal sunlight leads to light limitation. With the increased use of agricultural fertilizers and aquaculture farming practices, the nutrient load has increased substantially in the rivers and estuaries. This effect sometimes leads to algal blooms in the nearshore plumes adjacent to river mouths. Airborne nutrient supply to the nearshore oceanic margins is also reported by several studies. Excessive inorganic nitrogen that is introduced to the aquatic systems often undergoes microbial activities

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that lead to the production of greenhouse gases like nitrous oxide (N2 O) (MartinezRey et al. 2014). Thus, nutrient concentrations should ideally remain confined to a limit so that it does not become deficient or surplus. These critical aspects of nutrients need special emphasis in the field of environmental oceanography.

1.7 Ice Dynamics The polar oceans comprise a substantial part of the cryosphere that shelters some of the fascinating biomes of this planet. There has been a growing concern about the spatial extent of these polar ice covers as the ongoing global warming has severely impacted these ecosystems. Ice in the oceans exists naturally in the north and the south poles. The Arctic and the Antarctic Oceans have always amazed oceanographers. These polar regions play a crucial role in the well-being of Mother Earth. The temperature in the polar regions is substantially lower than in the tropics and the subtropics that facilitate the formation of sea ice and polar ice caps. The sea ice comprises a small portion of the global ocean; however, plays a crucial role in regulating the Earth’s climate. The sea ice owing to its bright white texture effectively reflects the sun’s incoming rays in space and thereby, reduces the global temperature. However, in the wake of global warming, the polar ice caps are continuously reducing in the area, and they are melting rapidly. The manifestation of polar ice melting can be witnessed throughout the globe, as it is considered one of the primary drivers of climate change. The sea ice exhibits significant seasonality. Some regions are covered by ice throughout the year, whereas the peripheral regions of these permanent frost zones are covered by regions where ice remains only during the winter season. The polar regions are also crucial as these portions absorb substantial quantities of atmospheric CO2 due to the cold temperature. CO2 , like any other gas, exhibits higher solubility at lower temperatures and vice-versa. The decrease in the area cover of polar ice regions implies a reduction in the net sink strength of the global oceans. However, due to excessive absorption of CO2 in the polar regions, these regions are more susceptible to ocean acidification. The seasonal sea ice dynamics have far-reaching impacts on the plankton ecology and ocean surface stratification. The cold waters usually sink in the polar regions that regulate the global conveyor belt mechanism or thermohaline circulation. Any change in the temperature regime of this region can affect global oceanic circulation. The polar regions experience the lowest anthropogenic disturbance. However, in recent days, human intervention has substantially increased in the Arctic and Antarctic circles. Such human encroachment for various reasons is also argued to have a deleterious impact on the stature of the ice cover in the poles. The melting of polar ice and glaciers has a direct contribution to the global sea-level rise (Mitrovica et al. 2001). The coastal population has increased at an alarming rate in the last few decades. With each millimeter of rising sea level, thousands and millions of people become vulnerable. Sea-level rise directly hampers

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the life and livelihood of many, especially the marginalized section of the coastal communities in developing and underdeveloped countries. The polar regions shelter endemic biodiversity that continues to be under threat due to the incessant retreat of ice cover. Thus, ice dynamics altogether form a critical component of oceanography that requires substantial attention from the scientific community.

1.8 Coastal Processes 1.8.1 Waves Tides and waves are two crucial intrinsic properties of an oceanic system that govern the dynamism in these lotic water bodies. The upper surface of the ocean that remains in contact with the atmosphere, experiences winds and the winds lead to the formation of waves. The nature of waves varies in size and shape depending on a plethora of physical factors. The sea waves occur in the open as well as the coastal ocean. However, the coastal regions that are usually much shallower than the open oceanic regions, exhibit a stronger form of waves. The amplitude of the waves usually increases in the coastal periphery, and it breaks in these zones that we often enjoy on a sea beach (Fig. 1.6). The sea waves attract millions of tourists all over the world. The waves play a crucial role in shaping the coastal landscape that is a part of the marine ecosystems. Through the formation of waves and their breaking in the coastal periphery, physical energy acquired by the oceanic water mass is transported and dissipated, respectively. Waves are also produced due to strong physical forcing events like tropical cyclones, tornados, typhoons, and hurricanes (Thomas and Dwarakish 2015). Such phenomena lead to storm surges that wreak havoc on the coastal set-up. Almost all these storms that generate in the oceans make landfall in any coastal periphery and often inundate the coastal sectors and cause coastal flooding. A tsunami is another cataclysmic disaster that produces high waves and leads to devastation in the coastal regions. Thus, understanding wave dynamics is of prime importance in coastal regions. This topic comes under the purview of physical oceanography. Oceanographic modelers predict wave movement depending on the climatic scenario. Such information can save thousands of lives and property from ocean-induced climatic hazards.

1.8.2 Tides Tides, on the other hand, are oceanic water movements created due to the periodic rise and fall of the water column driven by the gravitational forces of the sun and moon. The tidal dynamics are visible in the nearshore coastal reaches and the adjoining estuaries (Haigh et al. 2020). Like waves, the tides also vary in nature and amplitude.

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Fig. 1.6 A schematic diagram showing a typical wave and some associated terminologies. Credit https://cdip.ucsd.edu/m/documents/wave_measurement.html

It is predominantly dependent on the lunar cycle. The new moon and the full moon mark the spring tide sessions and the first and the third quarter mark the neap tide sessions. The tidal amplitude varies spatially and temporally. The regular ingress and retreat of oceanic water in the coastal set-up gives rise to several typical ecosystems like mangroves, seagrasses, salt marshes, kelps, and corals in the coastal setting. The tidal processes play a crucial role in regulating the biogeochemistry of the coastal water mass. This phenomenon enhances the residence time of water in the estuarine to the offshore transition zone and makes this region a biogeochemically active lotic ecosystem on earth (Yuan et al. 2007). Tides can be of the diurnal type, semidiurnal type, and mixed type (Fig. 1.7). Diurnal tides refer to those regions which experience only one high tide and one low tide in a day. Semidiurnal tides refer to almost equal amplitudes of two high tides and two low tides in a day, whereas mixed tides denote a semidiurnal tide with different amplitudes of high tide and low tide during a day.

1.8.3 Coastal Geomorphological Dynamics Coastal geomorphology is a crucial subdiscipline of oceanography as it is linked to millions of people and their livelihoods. Phenomena like coastal erosion and accretion are of significance in the present era where almost all coastlines of the world are experiencing a regional sea-level rise. Unlike the terrestrial systems, the coastal landscape and the seascape undergo rapid changes. The continental shelves, slopes, and beaches are some of the dynamic regions of the coastline (Fig. 1.8). The thrust of waves and the absence of adequate sediment supply often led to coastal erosion that forces thousands of people every year to leave their homes and move places. Problems of coastal erosion often sacrifice agricultural fields, aquaculture plots, ports, jetties, and several coastal infrastructures (Mentaschi et al. 2018). Population residing in unstable coastal geomorphic regimes pay a heavy price each year due to this

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Fig. 1.7 A diagram showing the three different types of tides observed in the coastal periphery of the world. Credit https://gotbooks.miracosta.edu/oceans/chapter11.html

phenomenon. The deltaic fronts exhibit a typical dynamism based on sediment flow. Depending on the nature of erosion/accretion, deltas can be prograding (enhances in size) and degrading (reduces in size). Several deltas all over the world shelter a wide range of biodiversity and are thickly populated. Thus, coastal processes altogether deserve their due attention from policy managers and researchers.

1.9 Renewable Energy and Resources from the Ocean Ever since the ill-effects of fossil fuel combustion on the global environment have been realized, humankind has been desperately looking for all renewable energy options and cultivating their potential to meet the energy demands of the everincreasing global population. Harnessing energy from the oceans is also possible. The wave energy, tidal energy, and thermal energy of the oceans can be effectively utilized (Vega 2002; Leijon et al. 2006; Rourke et al. 2010). However, most of the

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Fig. 1.8 A diagram showing the lateral cross-section of the significant oceanographic features. Credit https://www.tulane.edu/sanelson/eens1110/oceans.htm

technology used in this sector is still in its infancy and has not been commercialized to the desired extent. Besides, electrical energy, oceans can act as a renewable source of potable water as well. Several desalinization protocols for ocean water have been formulated and many are in action in different parts of the world. However, still today, it is a costly technology and beyond the affordability of many. Cheaper and eco-friendly technology for producing potable water from seawater can solve the burning problem of water scarcity that has remained in the pages of human history and continue to bother millions all over the world. The marine ecosystems that thrive in the coastal periphery, like mangroves, seagrasses, salt marshes, kelps, and corals provide a plethora of ecosystem services to humankind. These services range from provisioning (food resources, nursery ground for rearing fishes, medicinal resources, ornamental resources, water provisioning, etc.) to regulating (climate regulation, prevention from natural hazards, air and water purification, etc.). The cultural ecosystem services include an opportunity for tourism, their aesthetic beauty, mental well-being, and many more. The oceans and benthic bottoms are storehouses of several minerals and gases that are mined to meet the multifarious needs and demands of the growing population. However, these actions of human beings have led to marine pollution that can have far-reaching consequences on the hydrosphere of this planet. The oceans can act as a huge source of medicine and food if cultivated properly and sustainably. However, a substantial part of the ocean remains unexplored, and its potential remains largely unutilized. Several pieces of research are trying to characterize the genetic resource of the oceans that can benefit humans. However, the entire subdiscipline of sustainable ocean utilization has so many avenues that need to be explored in the days to come (Fig. 1.9).

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Fig. 1.9 The oceanic resources in a nutshell

1.10 Advancements in Oceanography Environmental oceanography is a vast discipline altogether and so many aspects come under the purview of this subject. The good news is that due to the growing urge to cater to the global environment, the scientific community has diverted its attention to disciplines like this for the betterment of this planet and its sustainable future. Oceanography as a subject has evolved; however, it is yet to mature completely as each passing day is contributing to the advancement of this subject with newer discoveries being reported each day. Environmental oceanography is an interdisciplinary subject that can utilize the expertise of several branches of science. The below-mentioned list (Table 1.8) indicates some of the fascinating domains of oceanography which has advanced in the last few decades and remain an active area of research.

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Table 1.8 A list of several aspects of environmental oceanography that are active areas of research and innovation Study field

What is happening

Satellite oceanography

Ocean monitoring has become essential to study the global climate. Remotely sensed images have come up as an effective tool to study the oceans from a synoptic scale. Oceanographer communities have formulated several region- specific models and empirical equations to interpret satellite- acquired data on the oceans

Ground observations Sampling in oceans has always been a tedious and costly endeavour. However, to develop holistic knowledge, we require a full-proof database of several physical, chemical, biological, and geological parameters. Scientific cruises, research vessel operations, mooring, depth sampling, innovative sensors to measure real-time data, and long-term data storage have seen substantial advancements in the last few decades. However, several parameters are still difficult to measure and require more attention Characterizing biodiversity

It is believed that the oceans shelter a much greater number of species than that observed in the terrestrial parts of this planet. However, our confidence level in the biotic life forms and species count in the oceans remains low. Thus, oceanographic exploration from the biological point of view continues to be an active area of research. Sampling and observation in the difficult most parts of the ocean remain a challenge. Very recently deep oceanic benthos like the Mariana Trench has been explored by NOAA. Similar endeavours are encouraged by many other oceanographic institutions

Computational oceanography

Physical oceanographers are studying the ocean–atmosphere coupled processes and phenomena as they govern the global climate and its spatiotemporal variability. These scientists are trying to predict the short-term as well as long-term changes in these phenomena that we can expect shortly. Such predictions help us save thousands of lives from ocean-induced disasters like storms and surges. Portraying the long-term changes enables us to prepare proper climate action plans and prioritize the areas that require attention to achieve a sustainable earth

Paleoceanography

Understanding the core nature of Mother Earth and the geological past events witnessed by this planet enable us to predict the future of this planet. Thus, palaeoceanographic studies involving both radio and stable isotopes have emerged as a special subdiscipline in this field

Geological exploration

Oceans have always been a point of interest for the geologists. These vast water bodies are considered storehouses of several minerals and other earthly resources. Exploring the geological resource potential of the oceans continues to be an active area of research

Energy extraction

Technologies to harness electrical energy from renewable resources like oceans have always been prioritized ever since the concept came into action. Ocean thermal energy conversion, the piezometric potential of ocean, tidal energy, and wave energy are under the lenses of both physical oceanographers and marine technologists. These subdisciplines require the involvement of more people to enhance the sustainability of this planet in the days to come

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References Atamanchuk, D., Koelling, J., Send, U. and Wallace, D.W.R. (2020). Rapid transfer of oxygen to the deep ocean mediated by bubbles. Nature Geoscience, 13(3): 232–237. Bates, N.R., Pequignet, A.C. and Sabine, C.L. (2006). Ocean carbon cycling in the Indian Ocean: 1. Spatiotemporal variability of inorganic carbon and air-sea CO2 gas exchange. Global Biogeochemical Cycles, 20(3). DeVries, T. (2014). The oceanic anthropogenic CO2 sink: Storage, air-sea fluxes, and transports over the industrial era. Global Biogeochemical Cycles, 28(7): 631–647. Falkowski, P.G. (1994). The role of phytoplankton photosynthesis in global biogeochemical cycles. Photosynthesis Research, 39(3): 235–258. Haigh, I.D., Pickering, M.D., Green, J.M., Arbic, B.K., Arns, A., Dangendorf, S., ... and Woodworth, P.L. (2020). The tides they are a-Changin’: A comprehensive review of past and future nonastronomical changes in tides, their driving mechanisms, and future implications. Reviews of Geophysics, 58(1): e2018RG000636. Hedges, J.I. (1992). Global biogeochemical cycles: Progress and problems. Marine Chemistry, 39(1–3): 67–93. Lalli, C., and Parsons, T.R. (1997). Biological oceanography: An introduction. Elsevier. Le Quéré, C. Takahashi, T., Buitenhuis, E.T., Rödenbeck, C. and Sutherland, S.C. (2010). Impact of climate change and variability on the global oceanic sink of CO2 . Global Biogeochemical Cycles, 24(4). Leijon, M., Danielsson, O., Eriksson, M., Thorburn, K., Bernhoff, H., Isberg, J., ... and Wolfbrandt, A. (2006). An electrical approach to wave energy conversion. Renewable Energy, 31(9): 1309– 1319. Martinez-Rey, J., Bopp, L., Gehlen, M., Tagliabue, A. and Gruber, N. (2014). Oceanic N2 O emissions in the 21st century. Biogeosciences Discussions, 11: 16703–16742. Mentaschi, L., Vousdoukas, M.I., Pekel, J.F., Voukouvalas, E. and Feyen, L. (2018). Global longterm observations of coastal erosion and accretion. Scientific Reports, 8(1): 1–11. Mitrovica, J.X., Tamisiea, M.E., Davis, J.L. and Milne, G.A. (2001). Recent mass balance of polar ice sheets inferred from patterns of global sea-level change. Nature, 409(6823): 1026–1029. Moore, W.S. (2010). The effect of submarine groundwater discharge on the ocean. Annual Review of Marine Science, 2: 59–88. Pilson MEQ (2013). An introduction to the chemistry of the sea, Second edition. Cambridge University Press, Cambridge. Roobaert, A., Laruelle, G.G., Landschützer, P., Gruber, N., Chou, L. and Regnier, P. (2019). The spatiotemporal dynamics of the sources and sinks of CO2 in the global coastal ocean. Global Biogeochemical Cycles, 33(12): 1693–1714. Rourke, F.O., Boyle, F. and Reynolds, A. (2010). Tidal energy update 2009. Applied Energy, 87(2): 398–409. Shepard, F.P. (1977). Geological Oceanography: Evolution of Coasts, Continental Margins & the Deep-sea Floor. Crane, Russak and Co. Spracklen, D.V., Carslaw, K.S., Kulmala, M., Kerminen, V.M., Sihto, S.L., Riipinen, I., et al. (2008). Contribution of particle formation to global cloud condensation nuclei concentrations. Geophysical Research Letters, 35(6). Stewart, R.H. (2008). Introduction to Oceanography. Department of Oceanography Texas A & M University. Takahashi, T., Broecker, W.S. and Langer, S. (1985). Redfield ratio based on chemical data from isopycnal surfaces. Journal of Geophysical Research: Oceans, 90(C4): 6907–6924. Taniguchi, M., Burnett, W.C., Cable, J.E. and Turner, J.V. (2002). Investigation of submarine groundwater discharge. Hydrological Processes, 16(11): 2115–2129. The Growth of Oceanography 1 - Jones and Bartlett Learning, Jones & Bartlett Publishers. Available at: https://samples.jblearning.com/0763759937/59933_CH01_001_029.pdf.

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Thomas, T.J. and Dwarakish, G.S. (2015). Numerical wave modelling: A review. Aquatic Procedia, 4: 443–448. Trenberth, K.E., Fasullo, J.T. and Mackaro, J. (2011). Atmospheric moisture transports from ocean to land and global energy flows in reanalyses. Journal of Climate, 24(18): 4907–4924. Vega, L.A. (2002). Ocean thermal energy conversion primer. Marine Technology Society Journal, 36(4): 25–35. Voldoire, A., Sanchez-Gomez, E., y Mélia, D.S., Decharme, B., Cassou, C., Sénési, S., et al. (2013). The CNRM-CM5. 1 Global Climate Model: Description and basic evaluation. Climate Dynamics, 40(9): 2091–2121. Webb, P. (2021). Introduction to Oceanography. Pressbooks Publishers. Wunsch, C. (2002). What is the thermohaline circulation?. Science, 298(5596): 1179–1181. Yuan, D., Lin, B. and Falconer, R.A. (2007). A modelling study of residence time in a macro-tidal estuary. Estuarine, Coastal and Shelf Science, 71(3–4): 401–411.

Chapter 2

Marine Ecosystems

2.1 Classification of Marine Water Bodies All the oceans of planet Earth are inter-connected and comprise one huge water body. Due to wind-driven forces and thermohaline circulation, all the water molecules get circulated to every nook and corner of this giant water body. However, based on several physical and chemical properties, as well as geomorphological features, marine water bodies can be classified into several smaller dimensions. If we investigate the lateral cross-section of the oceanic regime, the zones can be broadly divided into pelagic and neritic zones. The neritic zone refers to the shallow water mass that exists in between the low tide line in the coastal periphery of an ocean and the continental shelf break. The pelagic zone, on the other hand, refers to the entire open oceanic water column. This zone is further subclassified into five categories based on depth and solar incidence penetrability, namely epipelagic, mesopelagic, bathypelagic, abyssalpelagic and hadalpelagic zones (Fig. 2.1). The ocean bottom is usually referred to as the benthic zone, which again has several subclassifications that mostly conform to the pelagic subcategories. Most of the rivers in the world drain into the oceans and this gives rise to regions that are partly terrestrial and partly marine. Water salinity is considered a key parameter that defines the marine water regime throughout the globe. A typical salinity of 35 is considered a true signature of oceanic water. However, in the coast adjoining regions, the effect of terrestrial zero salinity freshwater and their admixture with the marine water, especially in the tail end of the rivers, gives rise to estuaries. Closed marine water systems with small outlets and connections to the ocean (in the coastal sector) give rise to aquatic bodies like lagoons and backwater. Based on the shape of the oceanic water mass in the coastal periphery, some regions are categorized as gulfs, bays, straits, etc. The gulfs are usually the large inlets from the oceans having a deep but narrow opening, rendering most of the water body covered by land borders. On the contrary, when such openings are wide-mouthed and the land surface borders almost three sides of the oceanic water body, it is referred to as a bay. Sometimes, two

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Fig. 2.1 The lateral cross-section of the oceanic water body showing the various subcategories of the oceanic water column

large oceanic water bodies remain connected to each other through a very narrow passage where water moves freely. Such narrow passages are often referred to as straits.

2.2 Neritic Ecosystems The neritic ecosystem encompasses the shallow water mass that lies above the continental shelf throughout the continental margin of this planet (Fig. 2.2). This region has some unique character compared to the other vast open oceanic stretches of the world. The depth of the neritic zone exhibits significant spatial variability; however, an average depth of 200 m is observed all around the world. This zone is one of the biogeochemically active regions of the global oceans. The vicinity to the landmass is one of the prime reasons behind such active nature of this zone. Land-driven runoffs and estuarine discharges make this region abundant in a plethora of chemical compounds. Some of these chemical constituents are useful for the marine ecological food chain to flourish. The nutrients like nitrate, nitrite, phosphate, and silicate are usually in higher concentrations in the neritic zone compared to the open oceanic regimes (Jickells 1998). The planktons and autotrophs make good use of these nutrients to grow. Being shallow, this region experiences solar insolation down to the depths of the water column. Thus, bottom dwellers as well as planktonic groups receive ample sunlight to carry out photosynthesis (Cahoon 2002). However, the degree of photosynthesis depends on the intrinsic turbidity of the water column that

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Fig. 2.2 The lateral cross-section of the oceanic water column showing the location neritic zone

varies across space. Some of the unique and productive marine ecosystems thrive in this zone and the periphery of this zone, like the mangroves, seagrasses, salt marshes, corals, kelps, and more. The neritic zone is also known for carbonate deposition in many places of the world (Pomar and Hallock 2008). Besides the floral biodiversity, the neritic zone of the ocean shelters some of the unique faunal life forms as well. Dugongs, sponges, sea anemones, crabs, oysters, clams, scallops, shrimps, dolphins, lobsters, jellyfish, sea snakes, eels, and tunas are some of the widely abundant neritic fauna in the global oceans. Apart from receiving essential micronutrients, this region is also a potentially polluted region of the ocean due to multifarious anthropogenic activities. Several manmade chemical by-products like heavy metals, plastics, oils, and persistent organic pollutants end-up in this domain and are often found to be present at substantially elevated concentrations (Cabral et al. 2019).

2.3 Pelagic Ecosystems The pelagic zone of the oceans comprises the lion’s share of the entire oceanic regime on this planet. This zone encompasses greater than 70% of this planet’s surface. This region shelters a mammoth species diversity and many of such species are yet to be explored to date. The species diversity is not homogeneous though and exhibits significant spatiotemporal variability depending on the associated biogeochemical processes that govern them (Belgrano et al. 2013). The pelagic biodiversity has evolved over a large time and its complex food web structure is a result of such longterm evolution. However, several pieces of research unequivocally argued that the phytoplankton that forms the base of the marine ecological food chain plays a crucial role in delineating the immediate-next trophic level organism like the micronekton, zooplankton, and the large nektonic faunas, and hence the entire food web structure

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(Sheppard 2018). Pelagic fishes deserve a special mention under this category as the fish diversity feeds and provides livelihood opportunities to millions throughout the world. More than 16% of the animal-derived protein of the global human population comes from fishes (Tacon and Metian 2013), where pelagic fishes caught through capture fisheries sectors contribute the most. The global atmosphere-hydrosphere coupled phenomenon like that of El Nino Southern Oscillations plays a crucial role in governing the species composition and structure of the pelagic zones and their spatial and temporal variability (Ruiz-Cooley et al. 2017; Santora et al. 2017). With the advent of modern oceanographic tools and scientific explorations, we have started understanding the nuances of the pelagic ecosystems as a whole; however, still, a lot of endeavours are required to develop a holistic grasp on this subject. Several groups of scholars prepared pelagic ecosystem models trying to characterize the flow of carbon, oxygen, and nutrients among the floras and faunas of this region. Kitazawa and Zhang (2015) portrayed a schematic in their study (Fig. 2.3) which exhibited the complicated dynamics of photosynthetic assimilation potential of the planktonic communities and the grazing and excretion by the zooplankton along with the interlinkages of carbon flow from one compartment to the other in the pelagic domain of the oceans.

2.3.1 Epipelagic Ecosystems The epipelagic zone of the oceans demarcates that part of the ocean which receives abundant sunlight. The light penetrability usually occurs up to depths of 200 m or more depending on the transparency of the water column (Fig. 2.4). The open oceanic water column is seldom bothered by turbid waters anywhere in the world. This zone of the open ocean is principally responsible for all the oceanic photosynthetic processes as light availability below the epipelagic zone is not decent enough to facilitate photosynthesis. Here lies the prime significance of this zone to the entire oceanic domain as the algae and autotrophs that concentrate these waters are the primary producers in the marine food chain and are also responsible for contributing a lion’s share of this planet’s oxygen levels in the lower troposphere. The biological pump that enables the atmospheric CO2 to sink into the oceanic waters is also mediated by the autotrophic organisms thriving in this layer. The epipelagic layer encompasses only 2–3% of the global oceanic volume, yet this region plays some fundamental roles in governing life and several other biogeochemical cycles throughout the planet. Several researchers believe that more than 90% of the marine life forms thrive in the epipelagic zone of the oceans.

2.3 Pelagic Ecosystems

Fig. 2.3 A glimpse of the pelagic ecosystem model (after Kitazawa and Zhang 2015)

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Fig. 2.4 The figure showing the variation of water temperature in the thermocline zone that coincides with the mesopelagic zone

2.3.2 Mesopelagic Ecosystems The end of the epipelagic zone marks the beginning of the mesopelagic zone. It usually reaches up to 1000 m depth on average. This zone is also known as the twilight zone as it remains sandwiched between the epipelagic zone that receives most sunlight and the bathypelagic zone that receives no sunlight at all. This zone does not receive sufficient sunlight to facilitate photosynthesis (Baumas et al. 2021). This water mass encompasses a substantially higher volume of water than the epipelagic zone. The ambient conditions in these depths are quite difficult for many species to sustain. Usually, the mesopelagic zone coincides with the thermoclines of the water depths. With increasing depth, a reduction in temperature, light, and oxygen is observed in this zone along with a concomitant rise in water pressure and salinity. However, the depth of the thermocline usually varies with seasons and across the globe depending on the latitudes (Yang et al. 2019). Despite the harsh living conditions, several invertebrates and fish species thrive in this layer of the ocean. Pieces of research indicated that many of these marine animals travel to the epipelagic depths in search of food but only during the night-time. The fauna and marine bacteria found in these depths play a crucial role in governing the global carbon cycle, as they are principally responsible for sinking the organic carbon produced in the epipelagic layers to the depths of the abyss. Several adaptation features are observed among mesopelagic animals, especially fish. Bioluminescence is one of them. Salps, a creature like jellyfish is one of the most abundant bioluminescent fauna available in this zone. Anglerfish is another example. These bioluminescent organisms provide minimal light in these depths. The fish residing in this water has large eyes and silvery scales that enable them to have a close watch on the predator as well as prey base and make use of the dim available light, respectively.

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2.3.3 Bathypelagic Ecosystems The zone just below the mesopelagic zone up to the depths of around 4000 m marks the bathypelagic zone. This zone is also known as the “bathyal zone” or the “midnight zone”. The temperature remains very low in this zone (Dong et al. 2019). In most open oceanic regions at lower latitudes, the temperature in this zone varies between 5 and 15 °C. However, near the polar sectors water mass having temperatures of 3 to −1 °C also prevails in these depths. This region is characterized by a sluggish movement of water mostly due to the thermohaline circulation and happens to have very low dissolved oxygen levels. This zone is comparatively the most fauna-deficient zone of the global oceanic water column. This zone experiences a very narrow range of salinity (34–36) and temperature fluctuations. This zone of the ocean remains permanently in dark conditions. Only the blue end of the electromagnetic spectrum can reach these depths. As this zone is principally devoid of any primary production, the life forms available in these depths are mainly carnivorous. Hagfish, viperfish, dragonfish, and scavenger sharks are common in these depths (Cousteau et al. 2021). Eels are also quite abundant in this zone. Swallower eel, monognathid eel, and the gulper eel are some of the common eel species that reside in this zone.

2.3.4 Abyssalpelagic Ecosystems The shallow bottom layer of water from the depths of 4000 m up to 6000 m refers to the abyssalpelagic zone or simply the abyssal zone. Abyss is a Greek word that means bottomless. This zone of the ocean has the coldest and densest of waters in the entire ocean that sinks to these depths. This zone is deficient in life forms. The temperature and salinity ranges are very narrow in this zone, 34.6 to 35.0 and 0 °C to 4 °C, respectively. The atmospheric pressure is enormous in these strata varying from 200 to 600 atmospheres. The very few marine life forms that prevail in these waters have adapted to these high-pressure conditions to survive. It is interesting to note that the abyssal depths of the ocean usually have a high nutrient concentration as most of the dead and decaying sinks of organic matter degrade and release the essential nutrients (Holzer et al. 2021). However, due to the utter lack of light in these depths, these nutrients accumulate and remain unexploited. Oxygen is not produced in these depths by autotrophic activities; however, there is sufficient oxygen dissolved in these depths, and oxygen consumers are very few (Gamo and Shitashima 2018).

2.3.5 Hadalpelagic Ecosystems This special zone of the oceanic water column is available only at a few places where the water column extends beyond the depths of 6000 m. This zone is also known

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as the hadopelagic zone. The deepest trenches in the ocean bottom like the famous Mariana Trench in the Pacific are filled with waters that exist below 6000 m depth and extend up to depths of around 11,000 m. Recent advances in marine sciences have discovered around 46 hadal habitats throughout the global oceans, and most of them are found in the Pacific Ocean. This term originated after the name of the Greek God, Hades, who was known to be the god of the underworld. This part of the ocean remains largely unexplored to date. However, pieces of research indicated that life forms do exist even in these harsh conditions (Liu et al. 2018). Very few fish species like grenadiers, pearlfish, cutthroat eels, snailfish, cusk-eels, and eelpouts are known to thrive up to depths of 8500 m in the hadopelagic zone. Astrorhizana foraminifera, myriotrochid sea cucumbers, polynoid worms, pardaliscid amphipods, and turrid snails are some of the invertebrates that are found to exist at depths even below 10,000 m (Jamieson et al. 2010).

2.3.6 Benthic Ecosystems The benthos refers to the biome that is located at the bottom of any aquatic ecosystem. In the case of oceans, the benthic zone refers to the ocean bottom irrespective of the depths where the bottom is located. Many of the benthic organisms remain attached to the sediment surface of the benthos, whereas several other organisms remain mobile but dwell close to the bottom of the ocean. Though benthic zones can be at shallow depths in the continental shelf and slope regions, most of the oceanic benthos experience low temperature, high pressure, and an absence of solar insolation. The soil-water interface in the benthic region facilitates the recycling of nutrients and thus facilitates the flourishment of several life forms. Coral reefs and seagrass beds are examples of benthic ecosystems in shallow coastal waters. Deep-sea corals are also reported from various regions of the global oceanic realm. The benthic ecosystem can be subclassified into several typical ecological regimes based on the topography of the ocean bottom, depth, and water column variability of biogeochemical variables. The deepest benthic ecosystems occur in the hadal zone followed by the abyssal, bathyal, sublittoral, littoral, and supralittoral zones.

2.4 Photic and Aphotic Zones Based on the degree of light penetration and the reaches of solar insolation, the water column of the ocean basin has been classified into several strata. The photic zone is referred to the upper oceanic layers where solar insolation reaches and can penetrate up to varying depths. The exact depth of the photic zone varies in spatial and short-term temporal scales depending on external factors like seasonality and intrinsic factors like turbidity of the water column. However, in the open oceanic realm, this depth is constant and is found to be around 200 m. The upper 80 m of

2.5 Intertidal and Littoral Zones

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Fig. 2.5 The diagram showing the euphotic, disphotic, and aphotic zones in the marine realm

the photic zone that is perfect for photosynthesis is known as the euphotic zone that extends from the air-sea interface (Fig. 2.5). The remnant depths of the photic zone, i.e., from 80 m depth to almost 200 m, which receive light; however, not sufficient to carry out unhindered photosynthesis is known as the “disphotic zone”. The water mass under the photic zone which mostly remains in perpetual darkness all around the year is known as the “aphotic zone”. Almost 90% of the global oceanic water volume falls under the domain of the aphotic zone.

2.5 Intertidal and Littoral Zones Near the coastline where the land and oceanic water mass meet, the micro-ecosystems have been classified into several categories. The term “littoral zone” in the field of oceanography is referred to as the nearshore coastal environment where the water level incessantly varies with changing tidal regimes. Figure 2.6 indicates that the classification of littoral zones varies depending on the ecological and geological perspectives. From an ecological standpoint, the littoral zone varies between the high tide line and the low tide line of the spring phase. According to oceanographic definitions, the extent of the littoral zone is sometimes referred to as the region from the base of the sea cliff to around 20 m water depth, or the high tide line to around 200 m depth. The high tide line to the low tide line region is often referred to as the eulittoral zone from the oceanographic viewpoint. Similarly, the region from the low tide line to around 50 m depth and from 50 m depth to around 200 m depth are termed infralittoral and sublittoral zones, respectively. However, from the ecological standpoint, the region lying just above the hide tide mark of the spring phase is known as the supralittoral zone or the splash zone. This zone receives sprinkles of water due to wave-breaking action and scarcely remains submerged. Ecologically,

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Fig. 2.6 The various classification of littoral zones according to ecological and geological/ oceanographic perspectives

the regions from the high tide mark to the zone of the groundwater outcrop and from this zone to the low tide line are referred to as the midlittoral and the infralittoral zones, respectively (Fig. 2.6). Contrary to the definition of the eulittoral zone in the field of oceanography, ecologists prefer to refer to the region between the low tide line and the 50 m water depth as the eulittoral zone. The geomorphologic setting and the benthic substratum of the coastline exhibit a wide variation throughout the world. The nature of the ecosystem and the floras and faunas vary accordingly. However, on the whole, the littoral zones of the world experience sufficient sunlight, plenty of dissolved oxygen, and essential micronutrients in the shallow adjacent water mass. These zones are usually dynamic as wave actions often maintain an incessant disturbance. The region of submergence and exposure continually vary in the intertidal zones. The coastal sediment substratum and the degree of wave-based disturbances are the two fundamental parameters that govern the floral and faunal diversity in the littoral zones. Sandy beaches usually exhibit very few populations, whereas the rocky substratum often shelters several organisms that remain cemented with the bottom. Protected regions from wave disturbance often have substantially high biodiversity compared to those regions of prolonged disturbances. Sheltered muddy and sandy shores act as abodes for echinoderms, worms, and mollusks, whereas rocky substratum in a protected environment often facilitates the flourishing of barnacles, mussels, and seaweeds.

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2.6 Coastal Ecosystems 2.6.1 Estuaries Estuaries are one of the most biogeochemically dynamic regions in the marine domain. Whenever a river or a stream or collection of rivers and streams (often in the case of deltas) meet the open ocean, the transition zone formed by the semienclosed water mass is termed an estuary. Pure riverine stretches usually exhibit zero salinity, i.e., no salts are present, whereas the exclusively marine water mass usually has a salinity of 35 or sometimes more. The estuarine reaches exhibit a varying salinity regime lying between 0 and 35. The inner estuarine regions where the marine dominance is low exhibit low salinity and the outer estuarine regions close to the open ocean have substantially higher salinity. The magnitude of salinity in the estuaries acts as a proxy of the freshwater-saltwater admixture. Estuaries are of various types depending on the geomorphological attributes, tidal nature, and freshwater flow (Table 2.1). These ecosystems receive substantial quantities of nutrients from the upper riverine reaches and runoffs from terrestrial sectors rendering them rich in nutrients. However, due to the same reason, estuaries in the present day have become highly polluted too. Industrial effluents mostly the ones that are untreated end up in the estuaries and these effluents bring them a plethora of chemical constituents that leaves a deleterious signature on all sorts of life forms. Heavy metals, persistent organic compounds, polychlorinated biphenyls, polyaromatic hydrocarbons, antibiotics, and many more pollute the estuaries all over the world (Barletta et al. 2019; Rodgers et al. 2019; Zhang et al. 2020). These estuaries are usually net heterotrophic, and thus, unlike the open ocean, the estuaries mostly act as a source of CO2 in the present date. The organic substrates are acted upon by the microbial communities and the water column respiration coupled with mineralization of organic carbon to inorganic carbon results in the net CO2 emissions toward the atmosphere (Cai et al. 2021). As the estuaries have a dynamic salinity regime, several types of euryhaline species and anadromous fishes populate these regions of the coast throughout the world.

2.6.2 Mangroves Mangroves are one of the most significant coastal vegetated ecosystems that flourish in the tropical and subtropical land-sea interfaces like estuaries, beaches, lagoons, and sheltered bays (Fig. 2.7). These tidal halophytic floral assemblages can withstand harsh environmental conditions like high salinity, strong wind, and wave action. These plants have adapted themselves over a long time to acclimatize to this setup with several morphological features like viviparous germination, stilt root systems, pneumatophores (breathing roots), and thick cuticle to prevent evapotranspiration losses. These plants withstand the strong wind and wave disturbances through

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Table 2.1 The various types of estuaries and their characteristics Types

Characteristics

Drowned river valley

This type of estuary forms when the sea level adjoining the river mouth rises at a comparatively higher rate than the adjacent landmass and thus facilitates the gradual progression of seawater towards the river. This type is also referred to as a coastal plain estuary

Bar-built

This type of estuary is usually shallow, unlike the coastal plain estuaries that are deep enough. This type of estuary forms in regions where the rising sea level and the sediment deposition go hand in hand. The river-sea connection is disjointed at places leading to the formation of sediment bars that breaks the direct connection with the riverine end

Fjord

These estuaries took shape through the deepening and widening of river valleys by the Pleistocene glaciers. These estuaries usually have a U-shape and have rocky bottoms and sharp inclined rocky cliffs on the banks

Tectonically formed

The estuaries came into existence due to some tectonic activities like landslides, volcanoes, or faulting. When the fissures created by such tectonic events are filled with seawater, they take the shape of an estuary

Salt wedge

In this type of estuary, the predominance of freshwater from the river supersedes the oceanic water. The dense marine water sinks and flows towards the river close to the bottom of the estuary, whereas the riverine freshwater flows on the top in an opposite direction. The column depth of freshwater near-surface minimizes in the estuary to the offshore transition zone

Mixed

In regions where the tidal encroachment of marine water has enough force to create turbulence that can break the seawater-freshwater boundary, the entire water column remains well-mixed by the two water types

Inverse

In estuaries where evaporation rates supersede the freshwater flow input to the estuary, the salinity rises sharply. The high saline water sinks and near the bottom of the estuary, water movement towards the sea and land, can be observed

Macro-tidal

An estuary that experiences substantially high tidal amplitude

Meso-tidal

An estuary that experiences moderate tidal amplitude

Micro-tidal

An estuary that experiences minimal tidal amplitude

several types of root structures like the stilt roots, knee roots, root buttresses, prop roots, etc. These floral assemblages developed physiological mechanisms like salt exclusion and salt excretion to combat the high saline waters where they grow (Esteban et al. 2013). The mangroves in many parts of the world have dense forest canopies, whereas in some regions they sparsely occupy the coastlines and occur in patches. Mangrove species are classified as true mangroves (that possess all the morphological features of mangrove plants) and mangrove associates (that possess some of the qualitative traits of mangroves and thrive in and around the true mangrove vegetation). Mangroves encompass approximately 70 species throughout the world (Friess 2016). Avicennia sp. belonging to the Acanthaceae family is perhaps the most dominant mangrove genus that is found throughout the coastlines where mangroves are prevalent (Thatoi et al. 2016). Excoecaria sp., Sonneratia sp., Bruguiera sp., Ceriops sp., Rhizophora sp., Heritiera sp., Acanthus sp., Phoenix sp., Nypa sp.,

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Fig. 2.7 The important salient features of mangroves

and Xylocarpus sp. are some of the widely abundant mangrove floras. Mangroves provide a lot of ecosystem services to humankind and other coastal life forms (Vo et al. 2012). The mangrove adjacent waters and estuaries are rich in nutrients that act as a nursing ground for several fishes. These stands offer storm protection to coastal communities. The mangroves are of the most productive ecosystems of the world and can sequester substantial quantities of carbon in their aboveground biomass, below-ground root system, and the pedosphere. The carbon stored by the coastal vegetated ecosystems is referred to as “blue carbon”. The blue carbon repository on earth plays a crucial role in combating the enhanced carbon emission of the post-industrial revolution era. The mangrove forests act as an abode for several faunas like the mud crabs, fiddler crabs, mudskippers, mollusks, and gastropods. The Sundarbans mangrove forest shared by Bangladesh and India shelters the majestic Royal Bengal Tiger. Several mangrove-adjacent waters are populated by crocodiles as well. At the present date, Indonesia holds the largest mangrove cover in the world.

2.6.3 Seagrass Like mangroves, seagrasses are also found in the coastal periphery of the global oceans. Unlike the mangroves, these floral communities are not restricted to the tropics and subtropics but also flourish in the temperate regions of this planet. Their growth and abundance depend on several biogeochemical characteristics of the water column, out of which light penetration (i.e., a clear water column) and a suitable substrate on which the seagrasses grow are the most crucial. The water depth at which

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seagrasses flourish depends upon the clarity of the water column. The seagrasses resemble the looks of grasses that we encounter in the terrestrial sector; however, they prefer to always remain submerged under the water. The buoyant forces of the adjacent water keep these grasses always afloat. These floral communities can perform photosynthesis by utilizing dissolved CO2 in the water. Several studies tried to make a list of the global species count of these remarkable floral stands. The figures range from 60 to 72 species (Short et al. 2007). The area covered by seagrasses throughout the world continues to be of a debatable magnitude ranging from 177,000 to 600,000 km2 (McKenzie et al. 2020). Latest advancements in remote sensing technologies are incessantly trying to come up with solutions to overcome the intrinsic challenges of mapping vegetation that remains submerged underwater. Zostera marina, Posidonia oceanica, Thalassia testudinum, Ruppia maritima, and Halophila sp. are some of the most abundant seagrass species. The seagrass beds offer refuge to a multitude of faunal species that are unique to this habitat like the sea turtles, dugongs, Queen conch, West Indian manatee, Oreaster reticulatus, Blue stripped grunt, Asian date mussel, and many more. Seagrasses provide a bundle of ecosystem services not only to humans but also to other marine life forms. The roots of the seagrasses grip the coastal soil, and this prevents coastal erosion and provides protection against coastal flooding. The seagrass beds act as nursing grounds for several fish, which in turn provide food provisioning to human beings (Wahyudin et al. 2018). Seagrass beds are a strong sink for CO2 and the pedosphere lying beneath the beds sequesters substantial quantities of carbon that provide negative feedback to climate change (Zou et al. 2021). The seagrasses owing to their structure and position can absorb the physical disturbances caused by near-shore wave action and thus, provides a calm environment on the coastal side for the mangroves and other coastal vegetations like salt marshes to flourish. However, despite so many crucial aspects, seagrasses throughout the world face severe threats from multiple natural and anthropogenic factors (Unsworth et al. 2019). Regional sea-level rise is one of the fundamental natural threats though it is being triggered by anthropogenic causes. Marine pollution, coastal construction activities that increase the turbidity of the water column, boat anchoring, and destructive fishing techniques are some of the most significant threats that these ecosystems experience throughout the world (Table 2.2).

2.6.4 Salt Marshes Salt marshes grow mostly in intertidal habitats like coastal wetlands where the substratum is muddy and has peat formations. At some point in time, not too many decades back, these marshy lands were considered wastelands that provided no benefits to humankind (Boorman et al. 1999). However, the perspectives have undergone drastic changes in the last two to three decades. Now, the salt marshes are unanimously recognized as a provider of wildlife habitat to several marine organisms. Their role in regulating the organic carbon and nutrient stoichiometry in the coastal

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Table 2.2 Characteristic features of seagrass communities observed throughout the world Number of species

6072

Global extent

1,77,000–6,00,000 km2

Most dominant Zostera marina, Posidonia oceanica, Thalassia testudinum, Ruppia maritima, species and Halophila sp. Faunal assemblages

Sea turtles, dugongs, Queen conch, West Indian manatee, Oreaster reticulatus, Blue stripped grunt, Asian date mussel, etc.

Ecosystem services

Flood protection, carbon sequestration, nursing grounds for fish

Threats

Marine pollution, destructive fishing, boat anchoring, construction activities that increase turbidity

regimes has been studied in detail in many places. These marshes also act as a coastal defence mechanism that prevents the coastline from being eroded by extreme events. These marshes are widely used for livestock grazing too (Davidson et al. 2017). The vegetation mostly comprises herbs and low shrubs; however, these communities encompass around 500 species throughout the world (Silliman 2014). These marshes are prevalent all through the world and prefer to thrive in sheltered regions with minimal physical disturbances (Mcowen et al. 2017). Salicornia spp., Spartina spp., Limonium spp., and Plantago spp. are some of the most abundant salt marsh floras observed in the coastal periphery. Mcowen et al. (2017) recently reported a mapped vegetation cover of nearly 55,000 km2 for the salt marshes; however, uncertainties remain about some localities due to a dearth of ground-truthed data. The salt marshes are occupied by a plethora of faunas such as the fiddler, hermit, stone crabs, worms, mussels, and snails (Table 2.3). Occasionally larger mammals are found to inhabit the marshlands. Despite providing valuable ecosystem services, these ecosystems face severe threats from factors like regional sea-level rise, marine pollution, over-grazing, and a primary lack of awareness among the coastal inhabitants (Gedan et al. 2011; Gu et al. 2018). Table 2.3 Characteristic features of salt marsh communities observed throughout the world Number of species

Nearly 500

Global extent

Approximately 55,000 km2

Most dominant species

Salicornia spp., Spartina spp., Limonium spp., and Plantago spp.

Faunal assemblages

Fiddler, hermit, stone crabs, worms, mussels, and snails

Ecosystem services

Wildlife conservation, binding sediments, coastal erosion prevention, and organic carbon and nutrient cycling

Threats

Regional sea-level rise, marine pollution, lack of awareness

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2.6.5 Coral Reef Corals are perhaps the most scenic and beautiful elements of the coastal sector that are cherished and enjoyed by anyone and everyone. The colourful structures of the corals always attract millions of tourists and thus, the coral tourism industry has flourished in almost all the places where these are abundant. Corals are oceanic invertebrates that secrete calcium carbonate and form colonies by occupying the benthic bottom mostly near the coastline. However, deep-sea corals are also reported by several scholars (Roberts and Hirshfield 2004) and they usually exhibit comparatively higher longevity than nearshore corals (Roark et al. 2009). The calcareous depositions of these organisms have in many places created reefs that are known as coral reefs. Patchy coral masses are also found in places; however, it is the giant reefs that are considered to have immense ecological significance. The reefs are primarily of three types: the atoll type, the barrier type, and the fringing type. The coral reefs are one of the most productive and biodiverse regions of the marine domain. These reef structures act as the abode of a plethora of marine organisms that leads to very high species diversity in these regions. Like many other marine systems, corals also furnish a bundle of ecological goods and ecosystem services (Moberg and Folke 1999). Fishes remain abundant adjacent to corals, and thus, coralline fishing comprises a substantial part of the global total marine capture fisheries. Their physical structure and position near the shoreline act as wave-breakers and furnish a calm environment towards the coast where other vegetated ecosystems can grow in sheltered environments. Coral mining for the extraction of lime and cement is also practiced in many places; however, it is strongly discouraged as such activities often damage the reefs irreversibly. Ornamental fishes are also quite prevalent among the corals. In addition, coral-related tourism industries provide livelihood opportunities to millions of people throughout the world. Globally, coral reefs occupy an area of about 2,284,300 km2 (Majumdar et al. 2018). However, uncertainties in these estimates exist as it is quite challenging to map any underwater structure with absolute certainty (Vecsei 2004). Almost 6,000 coral species have been recorded so far. The corals by their shape, size, and structure can be classified into massive, sub-massive, branching, foliose, encrusting, table, digitate, corymbose, bottle crush, and many other types (Majumdar et al. 2018). Mustard Hill, Boulder Star, Massive Starlet, Grooved Brain, and Great Star are some of the common hard coral species. The coral reefs are home to a multitude of organisms like sea urchins, sponges, clams, oysters, crabs, sea stars, and many species of fish. Like many other marine ecosystems, corals are also suffering from severe threats due to sea-level rise, ocean acidification, destructive fishing, unsustainable tourism, etc. (Table 2.4).

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Table 2.4 Characteristic features of corals observed throughout the world Number of species

Nearly 6000

Global extent

Approximately 2,284,300 km2

Most dominant

Mustard Hill, Boulder Star, Massive Starlet, Grooved

Species

Brain, and Great Star

Types of corals

Massive, sub-massive, branching, foliose, encrusting, table, digitate, corymbose, and bottle crush

Types of reef

Fringing, atoll, and barrier

Faunal assemblages

Sea urchins, sponges, clams, oysters, crabs, sea stars, and many species of fish

Ecosystem services

Fish, tourism, wave protection, marine habitat for many organisms

Threats

Sea-level rise, ocean acidification, destructive fishing, unsustainable tourism, etc.

2.6.6 Seaweed The coastal periphery having a hard substratum is often occupied by large algae of red, brown, or green colour that are known as seaweeds. The seaweeds just attach themselves to the rocky substrates like rocks and boulders; however, they do not draw any nutrition from the underlying pedosphere like seagrasses or terrestrial plants. Some of these seaweeds grow in deep waters where they remain submerged, whereas some grow at shallower depths where they occasionally remain exposed to the atmosphere. Many of these seaweeds are edible and are commercially produced throughout the world for human consumption (Buschmann et al. 2017). Seaweeds are being increasingly used as fertilizers, mainly in the aquaculture fishing practice (van Hal et al. 2014). Many of the brown algae encompass special groups like kelps and fucus. These are not found to thrive in tropical waters but are much more prevalent in temperate regions and higher latitudes. These are one of the largest algae that are often found to be more than 30 m in length. Seaweeds, like several other marine ecosystems, provide substantial ecosystem services to humankind (Hasselström et al. 2018). Seaweeds provide food, medicine, fertilizer, and polysaccharides, and have the capability of strong nitrogen and phosphorus uptake that helps in alleviating eutrophication. Due to the increased use of seaweeds, these algae are being cultured on large scale in many parts of the world (Alemañ et al. 2019).

2.6.7 Tidal Flats Those unvegetated regions adjoining the coastal periphery where sediment deposition takes place in the form of either mud or sand carried by the riverine freshwater flow or by the tidal action are referred to as tidal flats. Depending upon the soil texture, they are sometimes referred to as sand flats or mudflats. The tidal flats though devoid of any

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vegetation have substantial ecological significance. These landmasses stabilize the coastal sediments, protect us from atmospheric disturbances like storms, and provide food for human beings as well as other marine life forms. Moreover, the formation of these tidal flats allows other coastal vegetations to flourish using these flats as the substratum. Murray et al. (2019) estimated around 1,28,000 km2 of coastal tidal flats throughout the globe. These terrains like many other coastal ecosystems face severe threats from factors like sea-level rise, coastal pollution, human encroachment, erosion, sediment deprivation due to blockades upstream, and many more. These flats are very crucial to sustain avifauna as several birds acquire their foods from these regions by scooping foods (Jackson et al. 2021). Thus, their conservation and management should be prioritized in the days to come.

2.6.8 Lagoons and Backwaters Coastal lagoons are shallow water bodies that remain adjacent to the oceans or sometimes estuaries, but they are secluded from each other through a narrow opening that often remains guarded by reef structures or sand bars. The lagoons thus possess the qualities of being a lentic as well as a lotic ecosystem. Depending upon the freshwater-seawater admixture, lagoons can be of the freshwater type, brackish, or salty. However, most of the coastal lagoons are brackish to hypersaline. Usually, these water bodies exhibit high species diversity and are counted as one of the most productive marine ecosystems (Boudouresque and Verlaque 2012). As the coastal lagoons share both terrestrial and marine characteristics, they offer a suitable habitat to a plethora of floras and faunas. Several scholars have argued that the coastal lagoons play a crucial role in regulating the atmospheric CO2 load and thus, can provide negative feedback to climate change (Anthony et al. 2009). The shallow nature and the mostly lentic stature of the lagoons provide a disturbance-free ambiance and thus, several coastal floras such as mangroves, seagrass, and salt marshes often coexist altogether leading to a high rate of primary productivity in the entire region. The coastal lagoons provide a bundle of ecosystem services in the form of food (fish assemblages), storage of freshwater, water balance, protection from floods and storms, buffering several pollutants, ecotourism, and recreation (Newton et al. 2018). However, like all other coastal ecosystems, the coastal ecosystems are also facing incessant threats from factors like the regional sea-level rise that alters the salinity regime of these ecosystems, coastal eutrophication, marine pollution of all kinds, and climate change-induced alterations in water temperature and rainfall pattern (Esteves et al. 2008). When an array of lagoons remain interconnected with each other, it gives rise to a large water body, often referred to as backwaters. The backwaters possess all the characteristics as that of a lagoon; however, these are scarcely found in the coastal setup, unlike the lagoons which are more common.

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2.7 Marine Ecosystem Services Humankind and several other life forms benefit substantially from the ocean and ocean-derived resources and services. United Nations, in the year 2015, proposed 17 sustainable development goals (SDGs) that the entire world needs to focus on, to achieve sustainability in the development of humankind in the long run. One of these SDGs concentrates on the “Life below water” with the main aim of conserving the marine domain of this planet through sustainable use of the marine resources for sustainable development (van Zanten and van Tulder 2021). Marine resources provide livelihood options to millions, especially to those based near the coastline (Ferrol-Schulte et al. 2015). Besides, the oceans are fundamentally responsible for regulating the global climate, and hence, if managed properly, can indirectly benefit the total global population. It has been identified and unanimously realized by the global scientific community that each type of natural ecosystem provides a bundle of benefits in the form of services provided to humankind (Portman 2013). The oceanic ecosystem services comprise a lion’s share of the global natural ecosystem’s services. According to Millennium Ecosystem Assessment Report (2005), principally four types of ecosystem services have been recognized, namely, the provisioning, regulating, supporting, and cultural services. The following subsections discuss the various types of ecosystem services provided by the oceans and seas that need to be maintained for future generations to come.

2.7.1 Provisioning Services Provisioning ecosystem services refer to any type of benefits that can be extracted from nature in the form of material or resources. The fundamental provisioning services provided by the open oceanic realms of this planet are the plethora of food sources that are consumed by human beings. Fish resources are one of the principal provisioning services provided by the oceans. The marine fisheries sector provides a substantial part of the global protein demand to the human population and job opportunities to meet livelihood requirements for millions (Johnson and Welch 2009). Globally, almost 260 ± 6 million people are engaged in the marine fisheries sector excluding an approximate count of another 22 ± 0.5 million people engaged in the small-scale fishing sector (Teh and Sumaila 2013). Besides fishes, several other seaderived foods include seaweeds, crustaceans, shrimps, crabs, shellfish, and others. The trading of marine ornamental fishes also provides livelihood opportunities to many in the world (Townsend 2011). Recent biotechnological advancements have paved the way for recovering several medicinal products, dietary, and health products from ocean-derived resources that have become a part of our daily life consumption (Jaspars et al. 2016). Deep sea bed mining offers an avenue to extract a plethora of minerals, petroleum, and natural gases (Leal Filho et al. 2021). Desalination of oceans though remains quite expensive, appears to be one of the promising avenues

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to furnish potable water to the growing human population of the world (Youssef et al. 2014). The kinetic and thermal energies of the oceans driven by solar insolation can be effectively utilized to extract renewable energy options (Bahaj 2011), though a substantial level of research is still required to enhance the efficacy levels. Thus, the oceans can provide a bundle of provisioning services and most of it can be renewable if the oceanic domain, on the whole, is conserved properly following the guidelines for SDG 14.

2.7.2 Regulating and Supporting Services Like the endless provisioning ecosystem services provided by the oceans, there is a long list of regulating services that the oceanic bodies furnish to humankind. One of the most significant regulating services of the ocean is that these vast water bodies act as the principal sinks of carbon like the terrestrial greenbelt. According to the latest estimates, oceans absorb around −2.0 ± 0.5 PgC as CO2 per year (1 Pg = 1012 kg) (Iida et al. 2021). This absorption of CO2 is mainly mediated by autotrophic conversion of CO2 to organic carbon, which alleviates the atmospheric burden of anthropogenically emitted CO2 . The coastal vegetated ecosystems, such as the mangroves, seagrasses, and saltmarshes also play a crucial role in sequestering carbon, collectively referred to as the blue carbon ecosystems (Pham et al. 2019). These peripheral coastal systems and the nearshore water bodies act as filters that naturally purifies a plethora of pollutants discharged by several anthropogenic activities that flow through the rivers and finally end up in the oceans. These vegetated ecosystems also protect us from storms that mostly originate in the oceans in the form of cyclones, tornados, typhoons, hurricanes, etc. (Dasgupta et al. 2019) Their role in preventing coastal erosion and moderating extreme events is also undeniable. The oceans are also principally responsible for governing the global climate by circulating the heat absorbed in the tropical belt to the other parts of the world through mechanisms like gyres, eddies, and thermohaline circulation. The oceans and the peripheral ecosystems furnish several types of wildlife to accommodate typical faunas in those regions. Several coastal lotic ecosystems act as nursing grounds for fishes, prawns, and crabs. The specificities of the ecosystem services vary across the different types of marine ecosystems; however, overall, the marine domain provides a lion’s share of the global total ecosystem services from natural ecosystems (De Groot et al. 2012).

2.7.3 Cultural Services Apart from the most tangible services discussed above, the oceans and several adjoining oceanic ecosystems provide an array of intangible ecosystem services such as cultural services. The aesthetic beauty of the ocean has always remained appealing to millions. People throughout the world engage themselves in several

References

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beach activities for fun and recreation. Ocean-related tourism is perhaps one of the large giants in the overall tourism industry of the world. Several coastal ecosystems also furnish recreational values such as the pristine mangrove forests and the coral reefs. Reef diving is very popular in many parts of the world. The oceans have been of immense educational and scientific value as well. The young eager minds are tutored on the significance of nature by exemplifying the services provided by the oceans. The oceans still act as one of the best possible avenues for maritime trade and communication. Besides the entertainment furnished by the oceanic domain, several regions have ethnic cultural heritage values. In many places and across several religions, oceans are still worshipped via several cultural rituals. Oceans are considered sacred and divine by many, and the different types of oceanic realms are intricately bound to the belief system of millions of people.

2.8 Scope of Research in Marine Science The significance of studies on marine ecosystems and advanced-level research is gaining impetus day by day. At present, we are living in an era where the evil of climate change is bothering all of us, and we seek to explore the role of oceans and their ecology to mitigate this phenomenon. Several scholars argue that the biological potential of the oceans remains unexplored to a large extent. Apart from the conventional food sources that the marine domain furnishes to humans, scientists believe that several other food resources can be generated from this sector. A plethora of medicines, antibiotics, and drugs can be synthesized from marine products. Besides, the marine sector has already exhibited promising potential in harnessing renewable energy. Desalination of ocean water with cost-effective and robust technologies can solve a long-standing problem of potable water scarcity in many regions of the world. Many scholars from varied backgrounds are engaging themselves in research related to marine ecosystems. A strong sense of interdisciplinarity is quite essential to pursuing research in this domain and exploring the scopes and avenues. Thus, interested candidates who are going through this book are urged to develop a holistic understanding of the marine domain altogether to contribute meaningfully to this field.

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Portman, M.E. (2013). Ecosystem services in practice: challenges to real-world implementation of ecosystem services across multiple landscapes–a critical review. Applied Geography, 45: 185–192. Roark, E.B., Guilderson, T.P., Dunbar, R.B., Fallon, S.J. and Mucciarone, D.A. (2009). Extreme longevity in proteinaceous deep-sea corals. Proceedings of the National Academy of Sciences, 106(13): 5204–5208. Roberts, S. and Hirshfield, M. (2004). Deep-sea corals: Out of sight, but no longer out of mind. Frontiers in Ecology and the Environment, 2(3): 123–130. Rodgers, K., McLellan, I., Peshkur, T., Williams, R., Tonner, R., Hursthouse, A.S., ... and Henriquez, F.L. (2019). Can the legacy of industrial pollution influence antimicrobial resistance in estuarine sediments? Environmental Chemistry Letters, 17(2): 595–607. Ruiz-Cooley, R.I., Gerrodette, T., Fiedler, P.C., Chivers, S.J., Danil, K. and Ballance, L.T. (2017). Temporal variation in pelagic food chain length in response to environmental change. Science Advances, 3(10): e1701140. Santora, J.A., Hazen, E.L., Schroeder, I.D., Bograd, S.J., Sakuma, K.M. and Field, J.C. (2017). Impacts of ocean climate variability on biodiversity of pelagic forage species in an upwelling ecosystem. Marine Ecology Progress Series, 580: 205–220. Sheppard, C. (ed.). (2018). World seas: An environmental evaluation: Volume III: Ecological Issues and environmental impacts. Academic Press. Short, F., Carruthers, T., Dennison, W. and Waycott, M. (2007). Global seagrass distribution and diversity: A bio-regional model. Journal of Experimental Marine Biology and Ecology, 350(1– 2): 3–20. Silliman, B.R. (2014) Salt marshes. Current Biology, 24(9): R348–R350. Tacon, A.G. and Metian, M. (2013). Fish matters: Importance of aquatic foods in human nutrition and global food supply. Reviews in Fisheries Science, 21(1): 22–38. Teh, L.C. and Sumaila, U.R. (2013). Contribution of marine fisheries to worldwide employment. Fish and Fisheries, 14(1): 77–88. Thatoi, H., Samantaray, D. and Das, S.K. (2016). The genus Avicennia, a pioneer group of dominant mangrove plant species with potential medicinal values: A review. Frontiers in Life Science, 9(4): 267–291. Townsend, D. (2011). Sustainability, equity, and welfare: A review of the tropical marine ornamental fish trade. SPC Live Reef Fish Information Bulletin, 20: 2–12. Unsworth, R.K., McKenzie, L.J., Collier, C.J., Cullen-Unsworth, L.C., Duarte, C.M., Eklöf, J.S., ... and Nordlund, L.M. (2019). Global challenges for seagrass conservation. Ambio, 48(8): 801–815. van Hal, J.W., Huijgen, W.J.J. and López-Contreras, A.M. (2014). Opportunities and challenges for seaweed in the biobased economy. Trends in Biotechnology, 32(5): 231–233. van Zanten, J.A. and van Tulder, R. (2021). Towards nexus-based governance: Defining interactions between economic activities and Sustainable Development Goals (SDGs). International Journal of Sustainable Development and World Ecology, 28(3): 210–226. Vecsei, A. (2004). A new estimate of global reefal carbonate production including the fore-reefs. Global and Planetary Change, 43(1–2): 1–18. Vo, Q.T., Künzer, C., Vo, Q.M., Moder, F. and Oppelt, N. (2012). Review of valuation methods for mangrove ecosystem services. Ecological Indicators, 23: 431–446. Wahyudin, Y., Kusumastanto, T., Adrianto, L. and Wardiatno, Y. (2018). A social ecological system of recreational fishing in the seagrass meadow conservation area on the east coast of Bintan Island, Indonesia. Ecological Economics, 148: 22–35. Yang, G., Liu, L., Zhao, X., Li, Y., Duan, Y., Liu, B., ... and Yu, W. (2019). Impacts of different types of ENSO events on thermocline variability in the southern tropical Indian Ocean. Geophysical Research Letters, 46(12): 6775–6785. Youssef, P.G., Al-Dadah, R.K. and Mahmoud, S.M. (2014). Comparative analysis of desalination technologies. Energy Procedia, 61: 2604–2607.

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Chapter 3

Oceans and Human Activities

Oceanic domains and their vast resources have been long used by humankind for their benefit. Ever since the earlier historic explorations of oceans and times before that, humans have been reaping the benefits of several oceanic resources either via extraction or by depending on ocean-derived products (Blum 2013). Global transport from one region to the other has always been done through the oceans (Seland 2008). Even at present, the lion’s share of global trade and commerce is carried out through oceans (Cobb 2018). Several ports and harbours have been built on the oceanic margin for both human transport and trade purposes (Rodríguez et al. 2021). Besides the sea routes, the estuarine reaches of several major coastal regions exploit the water bodies as means of transport and commerce. Geologists have long realized that the open oceanic beds shelter several minerals and mines that have varied uses in present-day life. Offshore mining and drilling for extracting minerals and hydrocarbons have long been practiced meeting the demands of the growing population (Jouffray et al. 2020). Oceans have also been used to lay submarine cables and pipelines that spread internet connectivity throughout the world, and this revolutionary step brought the entire world to our finger points. Oceanic tourism has always been one of the major sectors of global tourism industries that provide livelihoods to millions and act as a means of refreshment for billions of people (Gössling et al. 2018). Ocean-derived food resources like fish, shrimps, crabs, squids, octopuses and many others have long served as a source of nutrition to the human population. In an era, when the global population is rising at an exponential rate, oceanic water mass is eyed to be a constant source of fresh and potable water through mechanisms like desalinization (Li et al. 2018). Besides the sea-derive direct food resources, the oceans provide us with several resources that include cosmetics products, pharmaceutical products, various types of genetic resources, and many others (Zhang et al. 2021). This chapter gives a brief overview of the major human activities related to the global oceans. It has become imperative to understand and research all these activities centered around the global oceans, as almost all these activities leave an irreparable mark on the overall health and wellbeing of the oceanic ecosystems. The more humans have engaged themselves in drawing oceanic resources, the more polluted the oceanic © Capital Publishing Company, New Delhi, India 2023 S. Mukherjee et al., Environmental Oceanography and Coastal Dynamics, https://doi.org/10.1007/978-3-031-34422-0_3

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realms have become. Thus, to understand the holistic scenario that comes under the purview of environmental oceanography, it is essential to understand the oceanic exploitation in the present date (Swing 2003). Unless we properly know the inevitable harm that we are doing to the oceans, we would not be able to frame effective management strategies to revive this crucial ecosystem for the coming generations to enjoy (Fanning and Mahon 2020).

3.1 Shipping and Trade Had there been no oceans, we still perhaps would not have witnessed the phrase “global trade and commerce”. Oceans act as the transport routes for more than 75% of products and goods manufactured and exported by the countries on this planet (Heiberg et al. 2012). The fuel efficiency in carrying the volumes and weights of goods and products is still the best for oceanic transport compared to all other means like road or aerial transport. Thus, in other words, maritime trade forms the backbone of the global economy (Lane and Pretes 2020). Thus, countries having access to navigable open ocean waters are always at an upper hand compared to the landlocked countries that face several difficulties and bear additional costs to maintain global trade and commerce (Carmignani 2015). United Nations have formed a specialized agency known as the International Maritime Organization that is principally formulated to look after the issues that encompass the security and safety of international shipping and preventive measures against marine pollution induced by such shipping. Several oceanic trade routes have been followed by humankind dating back to almost the third century BC. These trade routes continue to play an integral role in the global transport of goods and products from one corner to the other. The early twentieth century marked the beginning of an era of airplanes, and it has been essentially the primary means of human transport. However, given the bulk quantity of the goods and products, airplanes cannot be cost-efficient. Thus, oceans continue to be our only resort. South Atlantic oceanic route, North Atlantic oceanic route, Mediterranean Sea oceanic routes, Cape of Good Hope route, North Pacific oceanic route, South Pacific oceanic route, and Indian Ocean routes are the most significant and busiest trade routes in the world. At present date, almost one million merchant fleets roam over the global oceans (Clarksons 2021). As of 2019, more than 11,000 million tons of goods are being transported through the oceans (United Nations Conference on Trade and Development 2019). Shortly, with a projected rise in the population, trade and ship movement are expected to increase manifold. Shipping is undoubtedly the cheapest means of international export and import. However, shipping is responsible for various facets of pollution (Fig. 3.1). Shipping leads to the inevitable leakage of oils that forms a thin film on the air–water interface and can be detrimental to various marine floras and faunas. These oils often have a very high residence time and persist in open water for a long time (Tansel 2014). Accidental oil spills leave a disastrous signature in the oceanic ambiance for a long time too (Prabowo and Bae 2019). Several pieces of research indicated that shipping-induced noise leaves

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Fig. 3.1 The harmful impacts of the shipping industry on the marine environment

severe impacts on marine animals as these noises create troubles in communication, behavioural patterns, physiology, and overall well-being of these faunas (Yan et al. 2021). The global ship movement is held accountable for almost 8% of the total greenhouse gas emissions (Atilhan et al. 2021). The shipping industry is also responsible for a substantial share of global sulfur oxide (SOx) and nitrogen oxide (NOx) pollution (Ni et al. 2020). Keeping in view the environmental pollution caused by the ships, several effective technologies are being discussed to implement to curb the emissions from this industry (Balcombe et al. 2019).

3.2 Ports and Harbours Another crucial aspect related to the shipping industry itself which has become an integral part of almost all of the coastal belts of the world is the construction of ports and harbours. Ships require special facilities in the coastal margin for docking, loading, and unloading materials. Such specialized constructed structures with cranes, pulleys, and warehouses are termed ports, whereas the constructed structures used for docking the ships are termed harbours. Ports have comparatively much higher facilities than harbours and require larger space. In several coastal regions, jetties are also constructed mainly for human navigation over smaller distances within a locality. All these anthropogenic constructions are essential for smoothly carrying out shipping and transport of both humans and goods; however, these structures often change the overall geomorphology and hydrodynamics of the nearshore regions (Zarzuelo et al. 2015) (Fig. 3.2). At the same time, maintaining harbours and ports in an era of constant environmental change and regional sea-level rise has become a nuisance (Giaime et al. 2019). At present, there are close to a thousand seaports that are active and remain busy all around the year. Apart from that, there could be

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Fig. 3.2 The harmful impacts of the port’s and harbour’s construction and operation on the marine environment

several thousands of harbours and jetties constructed in the land-ocean interface. Port and harbour regions remain overcrowded and several anthropogenic activities in and around these regions often lead to heavy metal pollution in the port’s adjacent sediment and water column (Idris et al. 2007). Loading and unloading various types of containers and goods generate particulate matter that leads to severe health impacts on humans (Weli 2014). The ballast waters used in ships for their proper maneuvering upon discharge lead to a wide range of pollution including the spreading of invasive microorganism species (Kumar et al. 2021). Several types of volatile organic compounds are discharged in port regions from these ballast waters that can lead to harmful impacts on the ship crews and port dwellers (Romanelli et al. 2019; Dock et al. 2020). The International Convention for the Prevention of Pollution from Ships (MARPOL) is the only organization that looks after the issues of shipping industry-oriented pollution and its prevention. However, at present, this aspect requires further scientific and administrative attention, as this industry is expected to flourish further and if kept unchecked the pollution from this sector can have farreaching environmental consequences (García-Onetti et al. 2018; Teerawattana and Yang 2019).

3.3 Offshore Mining The concept of offshore mining came into existence in the 1970s. Geological oceanographers have long identified the presence of ferromanganese nodules in the deep sea sediments that are rich in rare earth minerals like copper, nickel, cobalt, molybdenum, yttrium, lithium, etc. (García et al. 2020; Toro et al. 2020). Offshore mining has been carried out by many countries, especially the ones that have their

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exclusive economic zones bordering their country’s land mass. However, most of these mining activities are centered close to the continental shelf and shallow waters. At present, a new venture of deep sea mining is coming to the surface under immense demand for minerals among the growing population of the world. As most of the land-based mining sites have been identified and exhausted, growing interest in deep sea mining has emerged consequently. Polymetallic sulfide deposits and cobalt-rich crusts near hydrothermal vents are the principal objects of interest (Knorsch et al. 2020; Qiao et al. 2022). The United Nations Conventions on the Law of the Sea formulated the International Seabed Authority, which is principally responsible for governing all the mining activities in the international waters beyond the exclusive economic zones of the respective countries bordering the oceans. Though the benthic substratum of the oceans offers an excellent deposit of several valuable minerals, the scientific community, as well as the industrialists, are divided into two, where larger schools of thought believe that it is best not to disturb the seabed at any cost by performing deep sea mining. Even with advances in every field of oceanography, very little is known about the deep sea faunal communities and the likely impacts of such large-scale mining in deep oceans can most presumably leave disastrous longterm signatures on the deep ocean environment (Zhou et al. 2022). Several scholars argued that deep sea mining can not only disturb the benthic bottom of the open oceans but also disturb the ecological equilibrium of the mid-waters that range from 200 to 5000 m down the water column of any ocean (Drazen et al. 2020). Deep sea mining activities would inevitably create large plumes and produce substantial noise on the ocean bottom that can be detrimental to several pelagic and benthopelagic biota which has remained in an undisturbed environment for millennial time (Christiansen et al. 2020). The after-effects of such mining if comes into operation are largely unpredictable but could be severe enough to disrupt the entire marine ecological food chain. In the days to come, managing the environmental impacts due to offshore mining would be one of the prime challenges in the field of environmental oceanography.

3.4 Petroleum and Hydrocarbons Besides offshore mining or deep sea mining, which is still in its infancy in terms of execution, humankind has long been harnessing crude petroleum and hydrocarbons in the sea beds lying close to the continental shelves of the world. The offshore drilling technique involves the deployment of either a moving body or a stable platform in the near-shore seas and penetrates the sea bed with a borer that extracts oil and crude petroleum from the deposits that lie under the sea bed. The segregation of crude petroleum into the respective finished products is carried out on the surface. Not only oil but natural gases are also extracted through such drilling techniques and brought to the surface (Wu et al. 2016). Offshore drilling provides close to 30% of the world’s crude petroleum and more than 24% of the natural gas produced per annum (Kaiser 2022). Currently, there are more than 650 offshore drilling sites in the coastal

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Fig. 3.3 The harmful impacts of the offshore mining and drilling operations on the marine environment

periphery of this planet. However, these activities like all other anthropogenic activities have far-reaching consequences (Fig. 3.3). The drilling operations are often held responsible for the depletion of onshore aquifers and enhanced submarine groundwater discharge to the oceans leading to local subsidence (Yu and Michael 2019). Oil pollution in the marine sector is one of the prime challenges that offshore drilling operations pose at the present date (Carpenter 2019). Oil spills not only destroys marine habitats and lead to mortality in various marine floras and faunas but also cause severe health risks to workers involved in this industry (D’Andrea and Reddy 2018). To make things worse, it has been identified that the ongoing climate change manifestations in the form of regional sea level rise, and strong physical forcing events like storms and surges enhance the likelihood of damage to the offshore drilling infrastructures and lead to more oil pollution (Dong et al. 2022). Offshore drilling is also responsible for the destruction of several marine habitats, as oil deposition on air-exposed coastal landscapes becomes unfit for all types of marine floras and faunas (Scanes 2018). Oil and gas exploration can lead to significant disturbance of the benthic substratum, which in turn can lead to loss of biodiversity of essential submerged marine ecosystems like coral reefs (Zimmerman et al. 2020) and seagrasses (Morton et al. 1986).

3.5 Submarine Cables and Pipelines The oceans have long been utilized to transfer data from one part of the world to the other. In other words, the oceanic bottom is used to lay cables for communication, and in this way, dissemination of data from one continent to other became possible. The first such kind of endeavour dates back to the 1850s when submarine cables

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were placed all across the Atlantic Ocean for the proper functioning of the telegraph network. With the advent of newer technologies, the cables that lay across the oceans and seas were used for telephone services and now act as the backbone of the global internet connection. These cables connect the land-based stations of one region to the other utilizing wired connections that remain on the sea bed (Fig. 3.4). Optical fibers are used now-a-days that can transmit digital data at lightning speed. Thus, surfing the internet or server of other countries sitting in another country has become a matter of a few microseconds. Unlike the other cases where oceans are exploited, this service causes very little damage to no damage at all to the oceanic ecosystem. Almost 3,20,000 km of telecommunications cable exist in international waters at the present date (Burnett and Carter 2017). Previously these cables used to get strangled by several bottom-dwelling large faunas like whales; however, in the present date, such cables have been replaced with materials that scarcely self-coil to do any harm to any large marine fauna. However, besides the telecommunications cables, submarine pipelines are also being used to transfer oil and gas. The environmental consequences of such transfer through the seas are yet to be studied properly and might lead to severe disasters if such pipelines get disrupted due to any accident (Davenport 2018).

Fig. 3.4 A map showing the world’s major submarine cable network. Courtesy https://www.sub marinecablemap.com/

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3.6 Tourism The tourism industry is one of the booming ones of all the different service-oriented industries that exist at the present date. Within this industry, ocean-centric tourism has accelerated at an exponential scale, especially in the last century (Miller and Auyong 1991). Sea beaches, estuarine boat travel, houseboat night stay, coral diving, underwater walks, and many more activities attract millions of tourists every year to the coastal margins, and it has become primary livelihood options for a substantial number of people worldwide. Thus, in a way, oceans provide us with one of the best possible recreational ecosystem services that have led to the flourishing of this industry (Hall 2001). However, the indiscriminate expanse of tourism and tourism-induced changes in the land use and land cover in the coastal belt has led to severe concerns all around the globe (Gössling et al. 2018) (Fig. 3.5). Coastal tourism has accelerated the construction of hotels, resorts, and several other manmade infrastructures in the land-ocean interface that is taking a heavy toll by altering the coastal geomorphology altogether (Wong 1993). Scuba diving in coral regions leads to several diseases among the coralline communities and direct damage to the coral structures (Lamb et al. 2014). Similar kinds of tourism activity and boat movement and anchoring in shallow seagrass beds are also held responsible for substantial damage to seagrass communities in many parts of the world (Dewsbury et al. 2016). In several instances, tourism infrastructures are built at the coast of crucial marine ecosystems like mangroves, seagrass, and salt marshes (Bennett and Reynolds 1993). Irresponsible tourism activities lead to littering of coasts and beaches that pose severe problems to the marine floras and faunas thriving in those regions and disturb the overall ecological balance of such regions (Panwanitdumrong and Chen 2021). Plastic pollution in the marine sector has increased at an alarming rate and the tourism sector is one of the growing concerns behind such an accelerated rate of plastic pollution (Thushari and Senevirathna 2020). Due to all these factors and many more, sustainable tourism and the promotion of responsible tourism keeping the environment intact has become a challenge for the coastal sectors of this planet.

3.7 Desalinization Oceans have a vast water mass; however, they cannot be used for drinking or any other purposes owing to intrinsic salt content. Hence, desalinization of ocean water evolved as an option long ago. This process is quite energy-intensive and not very cost-effective at present, but several newer techniques are getting introduced to reduce the cost of manufacturing potable water from saline seawater (Ng and Shahzad 2018). Even then almost 150 countries have installed a total of 18,000 desalinization plants to prepare an estimated total of 38,000 million m3 of potable water using seawater (Elimelech and Phillip 2011; Ghaffour et al. 2013). Despite its high energy requirement, desalinization plants are expected to increase in number

3.8 Capture Fisheries and Seafood

61

Fig. 3.5 The harmful impacts of unsustainable tourism on the marine environment

in the days to come to meet the ever-increasing water demand of the growing global population (Plappally 2012). The conventional desalinization process produces substantial amounts of greenhouse gas as well, which makes it quite challenging to make this way of meeting the water demand sustainable in the long run. Desalinization is mainly followed by either reverse osmosis or evaporation-condensation methods. Both methods require technological advancements to reduce the GHG footprints of such plants. A prominent area of research at the present date is utilizing ocean energy (thermal gradient or salinity gradient) to produce desalinized water from seawater; however, the effective output level is still quite low to replace the conventional treatment options (Li et al. 2018). As freshwater resources are steadily getting depleted due to several anthropogenic activities, reliance on seawater is inevitable and this science needs to be nurtured with utmost importance.

3.8 Capture Fisheries and Seafood Fishes are consumed by the non-vegetarian community almost all over the world. A substantial number of people residing in the coastal sectors, especially in developing countries, rely on fish for protein, micronutrients, and essential vitamins (Garcia and Rosenberg 2010). In several places, fish is a part of the regular diet and in this regard, the marine capture fisheries play a fundamental role in meeting this demand (Stentiford et al. 2012). At some point in time, people used to believe that the fishery resources in open oceans would never get exhausted, and we can keep on catching as much as we need. However, recent trends prominently show that marine capture fisheries are declining in several parts of the world (Brander 2007). Overexploitation of fishing in open oceans without putting a threshold margin (restricting total fish catch to a decided amount understanding the fish standing stock of a particular region) is one

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of the fundamental reasons for this decline (Ding et al. 2017). Unsustainable fishing techniques like bottom trawling seizing a bulk quantity of juvenile fish and destroying the food zone for the fish are also held accountable by many scholars (Kularatne 2020). With each passing day, marine capture fisheries are becoming both labour and as well as a cost-intensive endeavour. Moreover, in the era of climate change, offshore fishing productivity has become unpredictable, and the uncertainties involved in this business often lead to a massive loss of capital too (Freer et al. 2018). These factors are to a large extent responsible for the boom of the aquaculture industries in several countries of the world, where profitability is comparatively less uncertain than open capture fisheries in the oceans. Besides fish, seafood includes a wide variety of organisms like echinoderms (sea cucumbers and sea urchins), mollusks (cockles, clams, oysters, mussels, scallops, whelks, periwinkles, snails, limpets, and abalones), cephalopods (octopuses, squids, edible jellyfish, cuttlefish, frogs, and sea turtles), and crustaceans (shrimps, lobsters, crabs, crayfish, and prawns). Many of these kinds of seafood are being produced now-a-days through practicing aquaculture (Shamshak et al. 2019). Several pieces of research indicated that consuming seafood can be beneficial for human beings as these foods contain several ingredients that are not found in any terrestrial organisms (Hosomi et al. 2012). At the same time, consuming seafood can be risky too, as many of these organisms bioaccumulate substantial amounts of toxic substances in their body, which upon ingestion can lead to detrimental results in human beings (Hellberg et al. 2012). Thus, at the current date, maintaining sustainable fish catch and eliminating health risks from the consumption of such fish and seafood has become a prime concern (Cohen et al. 2005; Pauly and Palomares 2019).

3.9 Genetic Resources and Pharmacy Scientists have long realized the potential of the ocean in serving humankind. Besides providing food, either in the form of flora or fauna, it is a storehouse of several genetic resources that can have multiple uses. Several pieces of research showed that various biochemicals can be found in marine floras and faunas that can be effectively utilized in pharmaceutical, cosmetic, beauty, and many other types of products (Jaspars et al. 2016). Many of these products have industrial applications too (Ferrer et al. 2009). Though these discoveries can solve several problems related to human health and well-being, it is feared that such discoveries can put marine biodiversity at stake, as a widespread collection of marine organisms can destroy their habitats and incur long-term damage to the marine resources (Miller et al. 2018). To ensure a global benefit-sharing approach from any marine genetic resource and safeguard the overall interest of the marine realm, several protocols are being formulated (Lallier et al. 2014). This field of oceanography is still evolving, and several regions of the oceanic volume are yet to be explored. However, the more we explore the more the chances of exploitation and eventual destruction of oceanic resources. The prime challenge

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that lies before humankind is to formulate strategies to sustainably extract oceanic resources keeping in view the targets of the sustainable development goal (SDG) number 14 laid by the United Nations.

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Chapter 4

Basic Oceanographic Parameters and Their Significance

4.1 General Physicochemical Parameters Oceanic water columns, their overall health, and the ongoing biogeochemical processes in these oceanic masses are integral in regulating several global phenomena and providing ecosystem services to humankind. Ever since the potential of oceanic water bodies and the significance of all the biotic life forms in this hydrosphere have been realized by the global scientific community, measuring and monitoring these water masses have become imperative. In this regard, the worldwide marine research community identified several parameters that give us an idea of the holistic state of the art of any oceanic waterbody. Ocean biogeochemistry includes a plethora of parameters that are either physical, chemical, biological, or geological (Chai et al. 2020). However, a few parameters are recognized as the basic types that give us an elementary knowledge of the present state of the aquatic ecosystem. Water temperature, density, salinity, dissolved oxygen, pH, and suspended particulate matter are some such parameters. Water temperature is a crucial parameter that governs the well-being of many floras and faunas in the water column (Yasuhara and Danovaro 2016). Some species prefer to thrive in a particular range of temperature regimes. Moreover, innumerable biogeochemical processes are essentially temperature-dependent (Kirchman et al. 2009). The density of seawater plays a crucial role in the thermohaline circulation of the global seawater mass. Similarly, salinity plays a critical role in fragmenting oceanic sub-ecosystems (Telesh and Khlebovich 2010). The admixture of freshwater and seawater leads to varying salinity regimes that facilitates a typical ambiance for various floras and faunas to perform their life functions. Almost all marine organisms require oxygen for their survival like terrestrial organisms. However, marine organisms have to rely on the oxygen that remains dissolved in the water column. The abundance of oxygen depends on physical as well as biological factors and it plays a significant role in maintaining life below water (Juranek and Quay 2013). pH is another important parameter that tells us about the abundance of the freely available hydrogen ion, and hence the acidity and alkalinity of the water medium. Like temperature, several biogeochemical parameters are pH-dependent. In the era of © Capital Publishing Company, New Delhi, India 2023 S. Mukherjee et al., Environmental Oceanography and Coastal Dynamics, https://doi.org/10.1007/978-3-031-34422-0_4

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climate change, sinking CO2 is found to elevate the acidity levels in various parts of the ocean (Hofmann and Schellnhuber 2010). Thus, pH measurements have become imperative. Lastly, suspended particulate matter is a crucial parameter that depicts the clarity of the water column. This parameter is particularly critical in the upper surface waters of the ocean, where photosynthetic activities primarily take place (Price et al. 1999). These parameters, their significance, importance in the branch of marine science, and their measurement protocols are introduced in the following sub-sections.

4.1.1 Water Temperature Water temperature is one of the most crucial physicochemical parameters in the field of oceanography. The temperature of the water column governs several biogeochemical processes and biological activities. The sustenance of several floras and faunas in the oceanic realm depends on the temperature of the microhabitat (Helmuth 2009). Some species prefer to thrive in colder waters whereas others in warmer regions (Hurst 2007). Thus, temperature variability plays a crucial role in regulating the environmental niche of various organisms that inhabit the oceans. Sea water temperature is also one of the most significant physical properties that have far-reaching consequences on the global climate (Deser et al. 2010). Due to increasing greenhouse gas concentrations in the lower part of the Earth’s troposphere, this planet is experiencing global warming, and that has led to increased sea surface temperature and an increase in the volume of global seawater mass. Such an enhancement in global oceanic volume is believed to be responsible for a phenomenon like sealevel rise (Willis et al. 2010). The rise in oceanic temperature has implications for the solubility of several crucial gases. With the rising temperature, the solubilities of gases reduce, and the dissolved gases in the oceans tend to leave the hydrosphere and escape towards the atmosphere (Marinov and Sarmiento 2004). Such a phenomenon hampers the CO2 sink capacity of the oceans and depletes the dissolved oxygen levels in several regions that are key to underwater life. Thus, due to the reasons discussed above and many other factors, the monitoring of water temperature has always been routine work in oceanographical and limnological studies. Temperature is usually measured by a thermometer; however, thermocouple probes having thermistors or resistors are mostly used in oceanographic sampling. These types of sensors record the minute changes in voltage that arises due to the changes in water temperature. Water temperature measurements can be discrete or sometimes carried out continuously. Now-a-days, data loggers capable of logging high-frequency data are easily available that can store long-term data. These sensors are usually deployed from a ship or static platform. Depth profiling of temperature is also practiced for some types of research, especially in the open ocean, where the temperature across the varying depths of the water column is measured at any

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Table 4.1 The salient features of water temperature measurement Features

Particulars

Measurement unit

°C, °F, Kelvin

Types of sensors used

Thermometer, thermocouple probes, thermistor, resistor

Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1–0.001 °C

Calibration

Usually, factory calibration lasts long enough if the sensors are handled well and do not require frequent calibration

location. The analytical resolution of the instruments varies across a wide range (Table 4.1). The researcher deploys the type according to his/her needs. Usually, these sensors are robust and do not require frequent calibration.

4.1.2 Density The density of seawater is a crucial parameter that principally governs the thermohaline circulation of water throughout the global oceans. Cool dense waters sink in the polar regions and travel towards the equator and rise. This conveyor belt-like mechanism is responsible for disbursing heat and energy to all the corners of Mother Earth and potentially regulating Earth’s climate (Clark et al. 2002). In the open ocean, the density fluctuations throughout the water column mainly take place due to temperature changes (Sharqawy et al. 2010). However, near the coastline, the admixing ratio of freshwater and seawater leads to a wide range of densities. Apart from the physical significance of this parameter, it has been recorded that marine biota also prefers to thrive at a particular density level. Thus, density has long been realized as a crucial oceanographic parameter that needs monitoring. The density of any liquid is usually measured with the help of a specific gravity bottle. Ocean water is not an exception in this regard. Hydrometers are also quite popular for measuring density. These sensors are usually robust and do not require much calibration (Table 4.2). However, most of these sensors are capable of logging discrete data and cannot monitor continuously. However, a few sophisticated instruments are available that use the principle of the changing refraction level of light under changing density levels to measure density continuously.

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Table 4.2 The salient features of water density measurement Features

Particulars

Measurement unit

g/cm3 is the most widely used unit

Types of sensors used

Specific gravity bottle, hydrometer

Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1–0.001 g/cm3

Calibration

Usually, factory calibration lasts long enough if the sensors are handled well and do not require frequent calibration

4.1.3 Salinity Salinity is a critical parameter in the field of oceanography that governs several physical and biological activities incessantly taking place in the marine sector (Velasco et al. 2019). Salinity simply means the salt content of the water column. It is also a metric of the total dissolved solids (TDS) in the ocean water mass. As the dissolved solids are the fundamental substances that cause density changes in the water mass, salinity is also considered a proxy of the density of the water column. Salinity signifies the ratio of freshwater and seawater in any water mass. Salinity is usually zero in the exclusively freshwater mass and close to 35 ppt in the open ocean water mass. In the estuarine and nearshore waters, the admixture of riverine freshwater and seawater gives rise to a varying salinity regime (Iglesias et al. 2020). Even in the open ocean, salinity fluctuates to a little extent across the spatial and vertical column of the water mass. The osmoregulatory functions of several floras and faunas in the marine sector depend on the varying salinity (Takvam et al. 2021). Thus, salinity plays a crucial role in governing the species composition and several life processes. Therefore, any drastic change in salinity can lead to serious consequences on the marine ecological food chain (Wang et al. 2018a, b). Salinity is a robust parameter that can be measured in-situ and can be sampled and returned to the laboratory without adding any preservatives. Salinity in the earlier days was measured by performing argentometric titration; however, now-a-days, researchers usually measure the electrical conductivity of the water that can be converted to salinity. Previously, salinity was reported in the unit of parts per thousand (ppt). In the present day, salinity is regarded as unitless as it is measured as a ratio of two electrical conductivities of which one is a known standard solution (Table 4.3). Salinity sensors can continuously monitor salinity and can record discrete data as well. Usually, these sensors are quite robust and do not require regular calibration if maintained properly.

4.1 General Physicochemical Parameters

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Table 4.3 The salient features of salinity measurement Features

Particulars

Measurement unit

ppt; unitless (in the present day)

Types of sensors used

Argentometric titration, Electrical conductivity meters

Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1–0.001

Calibration

Usually, factory calibration lasts long enough if the sensors are handled well and do not require frequent calibration

4.1.4 Dissolved Oxygen The oxygen molecules that remain dissolved in the oceanic water mass is the key to the sustenance of life underwater. The concentration of dissolved oxygen varies across the spatial and vertical extent of the oceans that governs the abundance and types of life below water (Matli et al. 2020). Almost all living organisms below make use of the dissolved oxygen to carry out life processes and in its absence or concentrations below a certain threshold, maintaining life is nigh impossible. Thus, dissolved oxygen is a crucial parameter that needs to be monitored to develop a basic idea about the health of any marine ecosystem. Dissolved oxygen levels not only depend on the autotrophic potential of the ambiance but also on physical factors like wind, turbulence, temperature, etc. (Li et al. 2020). Thus, both physical as well as biological attributes can alter the dissolved oxygen levels of any region. Dissolved oxygen is usually measured by the modified Winkler’s titrimetric method (azide modification method), where manganous sulfate solution and an alkali-azide solution are used to trap the dissolved oxygen, and the same is titrated iodometrically with the help of standard sodium thiosulphate solution (Carvalho et al. 2021). However, this process requires discrete sampling and continuous monitoring requires a lot of manual labour in this way. However, now-a-days dissolved oxygen probes have been introduced that can continuously measure dissolved oxygen and record the data as well. Dissolved oxygen sensors can be of the electrochemical type or the optical type. Electrochemical sensors make use of the dissolved oxygen to generate an electric voltage that is measured by the sensor (Table 4.4). This type of electrochemical sensor can be of two types: polarographic (requires a constant supply of voltage) and galvanic (does not require a constant voltage supply). Optical sensors, on the contrary, utilize some photo dyes and oxygen’s potential to interfere with the luminescent properties of the dye.

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Table 4.4 The salient features of dissolved oxygen measurement Features

Particulars

Measurement unit

mg/l; mmol/l

Types of sensors Winkler’s titration; Electrochemical sensors (polarographic and galvanic); used Optical sensors Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1–0.01 mg/l

Calibration

Regular calibration in 100% oxygen saturated water and water devoid of any oxygen (0% saturation) is required for better functioning

4.1.5 pH Oceanic pH indicates the measure of free and mobile hydrogen ion concentrations in any seawater mass. This parameter is linked to several atmospheric and biological processes (Carstensen and Duarte 2019). Oceans in the present date behave as active sinks of CO2 . In the era of ever-increasing CO2 emissions, oceans keep on absorbing a substantial part of the anthropogenically emitted CO2 . CO2 thus dissolved in the ocean forms a weak acid namely the carbonic acid that dissociates into bicarbonate and carbonate ions and releases hydrogen ions. The bicarbonate and carbonate ions participate in several biological processes and get deposited as shells and many other forms by calcareous organisms living below water. However, the excess hydrogen ions reduce the pH levels. This phenomenon is referred to as ocean acidification (Kapsenberg and Cyronak 2019). Moreover, several metabolic pathways, absorption, adsorption, and release or dissolution of several pollutants are found to be pH-dependent (Middelburg et al. 2020; Baker et al. 2021). Due to all these factors, pH has been realized as one of the crucial factors that indicate the overall health of an aquatic ecosystem. pH is typically measured by carrying out a pH-metric titration by measuring the cell potential concerning a standard hydrogen electrode. This method has been used for long; however, it requires the sample to be carried to the laboratory. Or in other words, ex-situ sampling is required to measure pH in this way. Now-a-days, several glass calomel electrodes are available that can be attached to a data logger that can measure pH in-situ. Depending on the type of buffer used to calibrate the pH sensor, pH measurements can be based on different types of scale, like NBS scale, free scale, seawater scale, total scale, etc. The analytical resolution of pH sensors usually varies from 0.1 to 0.001 (Table 4.5).

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Table 4.5 The salient features of pH measurement Features

Particulars

Measurement unit

Unitless; sometimes referred to as pHu

Types of sensors used

Titration in a laboratory; glass-calomel electrodes

Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1–0.001

Calibration

Regular calibration in pH buffers of varying pH covering the pH range of measurements is required for accurate data collection

4.1.6 Suspended Particulate Matter Any natural aquatic ecosystem comprises a plethora of heterogeneous solid particles that does not readily dissolve in the water column and remain suspended. In the marine sector or any lotic ecosystem, physical disturbance does not allow these particles to completely settle down, and thus, these particles remain in motion in the water column. The presence of suspended particulate matter hampers the penetration of sunlight and thus it is a crucial parameter from the perspective of autotrophic production. Hence, in simple words, the suspended particulate matter concentration gives us an idea of the clarity of the water column altogether (Haalboom et al. 2021). The more the suspended particulate matter concentrations the higher would be the turbidity levels and the lesser would be the light penetration potential (Xiang and Lam 2020). Suspended particulate matter is commonly measured by the gravimetric method by collecting samples and analyzing them in the laboratory. In this method, a fixed volume of water is passed through a dry and pre-weighed filter paper. The suspended particulate matters settle down on the filter. The filter paper is dried and weighed again. The difference in the weight gives us the concentration of the suspended particulate matter (Table 4.6). In the present day, several optical sensors have also emerged that measure the backscattering of the light passed through a water column and measure in-situ suspended particulate matter (Yu et al. 2019).

4.2 Water Column Parameters Several parameters are measured or monitored in oceanographic research that exclusively tells us about the state of the water column. The changes in the physical properties across the water column from the water surface to the bottom of the water body have far-reaching consequences on different biological activities and phenomena.

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Table 4.6 The salient features of suspended particulate matter measurement Features

Particulars

Measurement unit

mg/l

Types of sensors used

Gravimetric filtration, optical backscattering sensors

Type of monitoring Discrete, continuous, surface, depth profiling Analytical resolution

0.1–0.01 mg/l

Calibration

Gravimetric method requires no calibration. The optical sensors are also robust enough and do not require regular calibration if maintained well

Changes in light penetration, varying temperature, and pressure across the vertical extent of a water body govern the autotrophic potential, mixing of nutrients, exchange of matter and energy between the surface and the bottom layers, and so forth. Several parameters have been designed and measured to address these factors.

4.2.1 Secchi Depth Secchi depth is one of the most primitive and robust parameters to measure the clarity of the water column near the water surface of any aquatic ecosystem (Kirby et al. 2021). This measurement technique was named after its inventor, an Italian astronomer, Pietro Angelo Secchi. This method utilizes a circular disk whose diameter usually ranges between 20 and 30 cm having four distinct quadrants painted alternately as black and white (Fig. 4.1). This is usually made up of iron or any heavier alloy so that it easily sinks into the water. This disk is tied with a graduated rope and slowly released into the water column from a stable platform like a boat or a raft. The disk is closely monitored while it is slowly released into the water column. As soon as the black and white quadrants become indifferentiable, we stop the downward movement and bring back the disk onboard. The depth at which the black and white colors become indifferentiable is considered the Secchi depth. The Secchi depth gives us an idea about the clarity and the light penetration potential in the upper strata of any water column (Opdal et al. 2019). This measurement exercise should only be carried out during daylight hours, and this method is not suitable for monitoring clarity continuously. This method cannot be applied for depth profiling too. This method is also susceptible to human errors and hence, always advised to record the data in triplicate and take a mean of the three values. The higher the Secchi depth the greater the clarity of the water column and vice-versa.

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Fig. 4.1 A Secchi disk for measuring the transparency of the water surface

4.2.2 Euphotic Depth This water column parameter is of immense interest, especially to the marine biologists or biological oceanographer community. In almost all aquatic ecosystems, photosynthesis takes place in the upper strata of the water body where the sunlight is abundant and the deeper waters where light cannot penetrate cannot facilitate photosynthesis despite the presence of autotrophs. Euphotic depth refers to the top layer of the seas, oceans, or any aquatic body, where photosynthesis can take place easily. Photosynthetically active radiation or photosynthetic available radiation (discussed in detail in Sect. 4.2.4) remains the highest just at the air–water interface and it gradually decreases down the water column. The depth at which the available photosynthetic radiation becomes 1% of the magnitude found at the air-water interface is termed the euphotic depth. This parameter can be measured easily by deploying underwater light sensors. Besides, this parameter can be estimated from the Secchi depth as well by using some simple conversion factor based on some empirical relationship observed between the Secchi depth and the euphotic depth. However, these empirical relationships are mostly region-specific and cannot be generalized to any water body. Like Secchi depth, the higher the euphotic depth the greater the clarity of the water column and vice-versa. Water columns with minimal suspended particulate matter load and physical disturbance like bottom churning and effluent discharge usually exhibit greater euphotic depths. The penetrability of the light in the water column is wavelengthdependent (Fig. 4.2) and thus the euphotic depth varies considerably in the ocean and coastal waters (Grubisic et al. 2019).

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Fig. 4.2 The variation of euphotic depth with varying wavelengths of the photosynthetically active radiation (after Grubisic et al. 2019)

4.2.3 Turbidity Often it is required to quantify the degree of transparency of a water column rather than measuring the depth of clarity. For such instances, turbidity is a crucial parameter that tells us about the degree of transparency of a water column in terms of quantifiable measures (Shi and Wang 2010). Turbidity is usually measured by using an optical sensor that passes light through a path length full of the sample and records the light intensity on the other end. Nephelometers are perhaps the most common turbidity meters used all over the world (Davies-Colley and Smith 2001). Some of these nephelometers require the samples to be collected in a container, whereas some advanced level nephelometers can measure turbidity in situ. Turbidity is reported in nephelometric units (NTU). A mixture of known strength of hydrazine sulfate solution and hexamethylenetetramine solution is used to prepare standard turbidity solutions of known values (Table 4.7). These solutions are used to calibrate the sensors (Münzberg et al. 2017). Unlike the parameters like Secchi depth and euphotic depth, turbidity can be measured throughout the water column, and successful depth profiling of the transparency of the water column can be done by measuring this parameter. Though one can measure the turbidity of the entire water column, this parameter is meaningful in the strata where sunlight is able to penetrate. Highly turbid waters restrict several

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Table 4.7 The salient features of turbidity measurement Features

Particulars

Measurement unit

NTU

Types of sensors used

Optical sensors; nephelometers

Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1 NTU

Calibration

Nephelometers require regular calibration for better functioning

underwater vegetation to thrive or at times hamper the growth of the existing underwater vegetation. Seagrasses and corals suffer a lot due to anthropogenic disturbances in the nearshore regions that enhance the turbidity of the water column. The primary productivity is also regulated to a large extent by this parameter, especially in estuaries and coastal waters that receive significant quantities of suspended particulate matter load as terrigenous inputs.

4.2.4 Underwater Photosynthetically Active Radiation Marine biologists and biogeochemists are interested to quantify the amount of photosynthetically active radiation available in the euphotic zone of the aquatic ecosystems (Baker and Frouin 1987). The amount of photosynthetically active radiation plays a significant role in governing the primary productivity of the water column (Oliver et al. 2018). This parameter is measured by light sensors specially designed to monitor the light intensity ranging between wavelengths 350 and 700 nm. The radiation in this wavelength window (350–700 nm) is considered photosynthetically active, as most autotrophs can only utilize the light of this wavelength range to carry out photosynthesis. The underwater light sensors measure the amount of light per unit area per unit time. Hence, this parameter is also sometimes referred to as photosynthetic photon flux (Table 4.8). The higher the flux the greater the possibility of photosynthesis and vice versa (Grant and Slusser 2004). Table 4.8 The salient features of underwater photosynthetically active radiation measurement Features

Particulars

Measurement unit

µ mol m−2 s−1

Types of sensors used Underwater light sensors Type of monitoring

Discrete, continuous, surface, depth profiling

Analytical resolution

0.1 µ mol m−2 s−1

Calibration

These underwater sensors are robust enough to be used on the field without any calibration Sometimes, these sensors are calibrated against a standard light intensity above the water

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4.2.5 Mixed Layer Depth In simple words, the depth of the water column near the surface of the ocean which experiences the atmospheric and wind-driven turbulences and where the temperature, salinity, and density remains perfectly mixed and uniform is known as the mixed layer depth (Kara et al. 2000). Water has a very high heat capacity, and the top few meters of this mixed layer depth can store as much heat as the entire atmosphere lying above. Thus, from the point of view of physical oceanography, the narrowing and widening of the mixed layer depths in the oceans and their spatial-seasonal variability have farreaching implications for the global climate (Sen Gupta et al. 2020). Conductivity, Temperature, Depth (CTD) Sensors are often deployed to characterize the mixed layer depths.

4.2.6 Thermocline Depth Just below the mixed layer depth the water temperature changes abruptly within a certain depth range and then below a certain depth it becomes constant. The depth of the water column in an open sea where the water temperature exhibits a steep change (usually lowering of temperature) as we go deeper in the water column is known as the thermocline (Chu and Fan 2019). Depth profiling using a temperature sensor can help us characterize the thermocline depth. This parameter is often used by physical oceanographers to study ocean-atmospheric coupled phenomena like hurricanes and cyclones.

4.2.7 Pycnocline Depth Similar to the thermocline, the depth of the water column where the density of the water exhibits an abrupt increase with increasing depth is known as the pycnocline (Chen et al. 2021). The changes in density in the pycnocline region separate the surface mixed layer depth from the waters that prevail below the pycnocline acting as a physical barrier for outright vertical transport of nutrients and other substances. Thus, the pycnocline acts as a regulator of nutrient replenishment to the surface waters and controls the rate of primary productivity in the euphotic zone of the water column (Wang and Yin 2021).

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4.2.8 Halocline Depth Like temperature and density, the depth up to which the water column exhibits a steep change in salinity is known as the halocline. This can be measured by performing a depth profile of salinity. This type of layering plays a crucial role in the formation of sea ice (Polyakov et al. 2020) and in preventing the escape of trapped CO2 into the deeper ocean waters (Esposito et al. 2019).

4.3 Carbonate Chemistry Parameters Ever since the importance of CO2 in the atmosphere and the role of oceans in sequestering atmospheric CO2 have been recognized, the significance of the parameters related to the inorganic carbon chemistry has increased manifold (Bushinsky et al. 2019). The carbon that exists in the gaseous form of either CO2 or CH4 in the atmosphere undergoes several biochemically mediated and physical reactions in the water bodies. Understanding the fate of carbon in the oceanic domain has become imperative in the present day. Carbon mainly exists either in organic forms or inorganic forms. The organic forms of carbon can be either dissolved or particulate. The inorganic forms of carbon give rise to several parameters and are regulated by various physicochemical parameters like temperature, salinity, pH, etc. (Cai et al. 2020). The parameters that fall within the purview of the air-sea CO2 equilibrium are collectively referred to as carbonate chemistry parameters.

4.3.1 Dissolved Inorganic Carbon The sum of all the carbonaceous forms available in the dissolved and inorganic state is referred to as dissolved inorganic carbon (DIC). This parameter includes the carbonate ion, bicarbonate ion, aqueous CO2 , and weak carbonic acid. CO2 once entering the hydrosphere dissociates into a hydrogen ion and bicarbonate ion which again dissociates into another hydrogen ion and a carbonate ion depending upon the pH levels of the water column (Keppler et al. 2020). The carbonate and bicarbonate ions are utilized by the autotrophs and the calcareous organisms. Thus, the CO2 solubility pump and the biological pump depend a lot on this parameter. Any CO2 emission or CO2 flux-related research essentially measures this parameter to understand the air-sea CO2 equilibrium. DIC measurement requires sampling and is not usually measured in-situ. Several methods are prevalent to measure DIC in any aquatic sample. DIC is often measured with the help of a TOC analyzer. However, high precision measurements rely on coulometric measurements (Peng et al. 2022). In the absence of sophisticated instruments, DIC is also often estimated from the data of pH and total alkalinity or pH and partial pressure of CO2 using the CO2 sys software (Humphreys et al. 2022) (Table 4.9).

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Table 4.9 The salient features of dissolved inorganic carbon measurement Features

Particulars

Measurement unit µ mol kg−1 SW; mmol kg−1 Types of sensors used

TOC analyzer, Coulometers

Type of monitoring

Discrete, surface, depth profiling

Analytical resolution

1 µ mol kg−1 SW

Calibration

This parameter is not easily measured with any type of sensors, and hence require laboratory measurements. Calibration of such instruments is essentially required to measure this parameter

4.3.2 Total Alkalinity The total alkalinity of seawater, as the term suggests, represents the total acidneutralizing potential of the seawater (Middelburg et al. 2020). It represents the sum of all the negatively charged radicals that can balance the oceanic hydrogen ion concentration. It is also sometimes looked upon as the oceanic buffering capacity (Jiang et al. 2019). Though the total alkalinity refers to the total of all the negatively charged radicals like carbonate, bicarbonate, borate, phosphate, silicate, etc., it is primarily composed of carbonate and bicarbonate. Thus, total alkalinity is sometimes referred to as carbonate alkalinity. This parameter is integral in understanding the buffering capacity of the seawater. Total alkalinity can be measured by simple potentiometric acid-base titration, known as the Gran titration technique (Sharp and Byrne 2020). However, now-a-days researchers mostly use automated titrators to run samples in batches and mark the endpoint of the titrimetric reaction by fixing the endpoint pH.

4.3.3 The Partial Pressure of CO2 The gaseous CO2 that remains dissolved on the water surface is the most susceptible to being emitted towards the atmosphere, and at the same time, the CO2 that enters the water column from the atmospheric through sinking activities also remains dissolved in the water column as aqueous CO2 before transforming to other forms of carbon species. This dissolved CO2 is measured as the partial pressure of CO2 in water [pCO2 (water)] (Takahashi et al. 2018). pCO2 (water) can be directly measured using a non-dispersive infrared (NDIR) gas analyzer (Table 4.10). In this method, a gas equilibrator is used to collect the dissolved CO2 in a headspace which is then circulated through the NDIR sensor to get the real-time data (Lee et al. 2022). In the absence of a CO2 analyzer, pCO2 (water) can be estimated using the CO2 sys software

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Table 4.10 The salient features of dissolved inorganic carbon measurement Features

Particulars

Measurement unit

µ atm

Types of sensors NDIR sensor; CO2sys software used Type of monitoring

Discrete, surface, continuous depth profiling

Analytical resolution

0.1 µ atm

Calibration patm NDIR sensors require regular calibration with zero CO2 gas (preferably pure nitrogen gas) and gases having standard known CO2 concentrations

from the data of water temperature, salinity, pH, total alkalinity, and DIC data. Water column pCO2 has its significance not only in terms of the CO2 source-sink dynamics but also as a regulator of the trophic status. The pCO2 (water) magnitudes and their variability help us to comment on the net autotrophic or heterotrophic status of an ecosystem.

4.3.4 Dissolved Organic Carbon This group of carbon comprises a plethora of organic substances that remains dissolved in the water column and essentially not in the particulate form. Operationally, the carbonaceous organic substances in water that pass through a filter paper of mesh size 0.22 µm are technically referred to as dissolved organic carbon (Broek et al. 2020). The term dissolved organic matter is also commonly used by oceanographers in this regard. The carbon component of the total dissolved organic matter is termed the dissolved organic carbon (DOC). The DOC forms an integral part of the marine carbon cycle and acts as a basic food source for many lower trophic level organisms. DOC is mainly produced by the autotrophs as a by-product of several life processes, whereas allochthonous sources in the marine systems range over various anthropogenic production processes. A part of this DOC can be easily mineralized to DIC by microbes and this DOC is termed labile. In contrast, the DOC that does easily participate in any kind of biogeochemical reactions is termed the recalcitrant DOC (Wang et al. 2018a, b). DOC can be easily measured with the help of a TOC analyzer. The most common approach is to oxidize the organic carbon dissolved in water with acid to form CO2 and then measure the same with the help of a gas chromatograph or NDIR sensor.

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Fig. 4.3 The carbon transformation pathways in marine systems through natural processes

4.3.5 Particulate Organic Carbon All the non-carbonate and combustible carbon that deposits on a filter paper of mesh size 0.22 µm is collectively referred to as particulate organic carbon (POC) (Kharbush et al. 2020). Like DOC, it also forms an essential part of the marine carbon cycle and most of the food sources for lower trophic level organisms. POC can undergo leaching or weathering through several biogeochemical processes and get transformed to DOC and eventually mineralized to DIC (Li et al. 2018). However, carbon in the form of POC has the capability to be locked and sequestered for a long time. In coastal vegetated ecosystems like mangroves, seagrasses, and saltmarshes, autochthonous POC and allochthonous POC from terrigenous sources are trapped in the sediment column. POC is also of fundamental interest in the sector of biological carbon pumps as this form of carbon is least susceptible to being emitted as CO2 . POC is generally analyzed by assessing the mass loss upon combustion method at elevated temperatures. These chemical species of carbon interchanges among one another through several natural processes (Fig. 4.3), which is of immense interest to the present-day researchers.

4.3.6 Calcium Carbonate Saturation State In an era of climate change, the ever-increasing CO2 emission due to various anthropogenic activities has ignited an evil named ocean acidification that can prove to be deleterious to almost all calcareous marine organisms (Choi et al. 2022). Ideally, the seawater should always be supersaturated with CaCO3 . Under such circumstances, all those organisms which use calcium and carbonate to make building

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83

blocks like the corals and calcareous phytoplankton communities can engage themselves to shell formation. However, under an undersaturated condition, these organisms cannot manufacture calcareous shells, and the existing shell structures exhibit decay (Eyre et al. 2018). To study the state of ocean acidification, the CaCO3 saturation state also sometimes referred to as the calcite or aragonite (two most common polymorphic forms of calcium carbonate) saturation state is assessed by the oceanographer community from several carbonate chemistry parameters (Sulpis et al. 2022). Using the data of pH, pCO2 (water), DIC, and total alkalinity, the calcium carbonate saturation state (y) can be computed with the help of the CO2 sys software.

4.3.7 Air-Water CO2 Fluxes Ever since the menace of global warming has been linked with the increasing atmospheric CO2 load due to fossil fuel combustion and de-greening of Mother Earth, endeavours trying to understand the CO2 source and sink potential of both natural and artificial ecosystems have gained impetus. Studying the source and sink nature of marine systems like estuaries, lagoons, continental shelf waters, and the open sea has also increased (Laruelle et al. 2018; Roobaert et al. 2019). Scientists worldwide are desperately trying to understand the role of the character of all these types of ecosystems to understand the global carbon budget and project the possible scenarios for the near future (Carroll et al. 2020). The air-water CO2 flux needs to be assessed to delineate the source or sink character of any marine system. This term refers to the unit exchange of CO2 across the air-water or atmosphere-hydrosphere interface per unit time per unit area. Several techniques are prevalent now-a-days to measure the air-water CO2 flux, which includes the eddy covariance technique, the chamber method, and the bulk formula method. The eddy covariance technique assesses the change in CO2 concentration across the vertical gradient above the air-water interface using a 3D sonic anemometer and CO2 gas analyzer framed on a stable platform like a ship or boat (Prytherch and Yelland 2021). The closed chamber method allows the CO2 gas to accumulate or reduce from an inverted chamber that floats on the air–water interface. The rate of accumulation or removal allows us to compute the fluxes (Huang et al. 2022). The bulk formula method separately measures the pCO2 (water) and the partial pressure of CO2 in the ambient air [pCO2 (air)] and computes the flux from their difference. The difference in the partial pressures of CO2 between air and water is usually multiplied by a set of constants like the gas transfer velocity and solubility coefficient (Watson et al. 2020) that considers the effect of external factors like the wind velocity, water temperature, and salinity on the exchange of CO2 between the atmosphere and the hydrosphere.

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4.4 Biological Productivity Parameters Primary productivity in the oceans is one of the essential biological activities that do not shape the carbon biogeochemistry of the marine sector but also govern the entire marine ecological food chain (Henson et al. 2019). This activity is also responsible for the biological carbon pump of the oceans that provides us perhaps the only natural respite from the ever-increasing atmospheric CO2 load caused by a wide variety of anthropogenic activities. There are several parameters related to biological productivity that needs to be monitored and measured for various types of oceanographic research. The autotrophic potential of a water body, its state of health to maintain a healthy trophic status, and the overall trophic state of an aquatic ecosystem are some of the most crucial areas where biological productivity parameters give us proper insight (Lacroix et al. 2021). This section discusses the three fundamental types of productivity rates usually measured in any natural aquatic ecosystem, namely the gross primary productivity (GPP), net primary productivity (NPP), and community respiration (CR) (López-Urrutia et al. 2006). Besides, other crucial parameters like chlorophyll concentration, phytoplankton and zooplankton abundance, and the concept of trophic state indices are discussed in this section.

4.4.1 Gross Primary Productivity This productivity parameter tells us the total amount of new organic carbon synthesized by the autotrophs per unit time per unit volume/area of the water body. In other words, gross primary productivity (GPP) denotes the rate at which the incoming solar energy is trapped by the ambient autotrophic communities of a water body and transferred to new organic biomass (Huang et al. 2021). GPP depends not only on the phytoplankton abundance but also on the other factors regulating the photosynthetic rate like the solar radiation availability, clarity of the water column, nutrient abundance, etc. (Drylie et al. 2018). Thus, it is one of the crucial parameters that are integral to the overall health of the marine system and governs the ecological food chain. GPP is measured by various tools and approaches. The light bottle dark bottle method has been implemented for a long time to measure GPP. In this method, the researchers usually record the initial dissolved oxygen concentration at a certain time of the day (preferably early morning hours) and incubate the sample under in situ conditions in a transparent bottle and a dark bottle (Selvaraj 2005). Photosynthesis takes place in the light bottle (transparent bottle) and only respiration occurs in the dark bottle (Fig. 4.4). The changes in dissolved oxygen concentrations are used to compute the GPP. In modern days, stable isotopic techniques are used to bio mark the bicarbonate ions and measure the stable isotopic ratio in the newly prepared organic carbon.

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85

Fig. 4.4 The basic principle of light-bottle-dark-bottle method to measure the primary productivity of a water sample

4.4.2 Community Respiration This parameter indicates the amount of CO2 produced via respiration not only by the autotrophs but by all the living entities present in the water column that uses oxygen to carry out life processes and release CO2 as a by-product. Community respiration (CR) is an essential parameter that tells us about the total biogenic load on the available dissolved oxygen (Del Giorgio and Duarte 2002). This parameter is also crucial in understanding the regulators of the air-sea CO2 flux and biological carbon pump. The dissolved oxygen estimation by light bottle dark bottle method and stable isotopic measurements of C-13 in bicarbonate is used to measure CR.

4.4.3 Net Primary Productivity This productivity parameter represents the net production of organic matter via photosynthesis and respiration in the water column (Johnson and Bif 2021). The net primary productivity (NPP) is the result of GPP minus the community respiration (CR). The dissolved oxygen estimation by light bottle dark bottle method and stable isotopic measurements of C-13 in bicarbonate is used to measure this parameter as well. This parameter is crucial in determining whether a marine ecosystem is acting as net heterotrophic (net emitter of CO2 ) or net autotrophic (net sink of CO2 ). When GPP is greater than the CR, NPP becomes positive and it means that the system is acting as a net autotrophic one, and vice-versa (Smith and Mackenzie 1987).

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4.4.4 Phytoplankton Abundance Biological oceanographers often find interest in studying the overall phytoplankton composition of a marine ecosystem. The age-old sample collection and observation under the microscope are still being followed to account for this parameter. Researchers usually sample a substantial amount of water ranging from 10 to 50 L per sample and allow them to settle down to decant the supernatant and save the residual volume for phytoplankton identification. Sometimes phytoplankton nets are also used that facilitate both qualitative and quantitative analysis of phytoplankton abundance. Lugol’s iodine reagent is usually added to the residual volume to stain the existing phytoplankton and the samples are stored in cold conditions (near 4 °C) before analysis. The broad categories of phytoplankton, namely, cyanobacteria, diatoms, dinoflagellates, and coccolithophores (Quere et al. 2005) are identified with the help of the microscope. The species abundance is usually computed with the help of a Sedgwick Rafter (S-R) cell that usually accommodates 1 ml of the residual volume. Repeated measurements are made in the Sedgwick Rafter (S-R) cell and the average values are usually recorded.

4.4.5 Chlorophyll Concentration This parameter is often measured to understand the total strength of the phytoplankton in any water body. Chlorophyll is an essential constituent of any autotrophic organism that is needed to carry out photosynthesis (Yoder et al. 1993). Hence, chlorophyll concentration is unequivocally considered a proxy of the phytoplankton abundance. The higher the chlorophyll concentration, the higher is considered the photosynthetic potential of a marine system. The chlorophyll pigments have various types; chlorophyll-a, chlorophyll-b and chlorophyll-c are the most prominent ones (Marrari et al. 2006). Chlorophyll-a is the most dominant one that remains present in aquatic bodies. Hence, very often, only chlorophyll-a is measured as a proxy of the phytoplankton strength. Chlorophyll concentrations are usually measured with the help of a spectrophotometer or a fluorometer (Roesler et al. 2017). Now-a-days fluorescence sensors are also being deployed to measure real-time chlorophyll concentration in the field.

4.4.6 Zooplankton Abundance Zooplankton are the primary consumers that essentially feed upon the phytoplankton community and play a critical role not only in regulating the phytoplankton abundance but also in shaping the marine ecological food chain (Ward et al. 2012). Zooplankton grazing is one of the key biological processes that often determines

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whether an ecosystem would act as a net autotrophic or a heterotrophic one (Steinberg and Landry 2017). Thus, monitoring zooplankton abundance has become imperative in several types of oceanographic research. Like phytoplankton sampling, zooplankton is also sampled occasionally by the water collection and stagnation procedure. However, zooplankton nets are more commonly used for both qualitative and quantitative analysis of zooplankton abundance. Formalin solution is used to preserve zooplankton samples. Chlorazol black E, lignin pink, rose Bengal, and methylene blue is some of the most used staining agents to count zooplankton density under the microscope. Sedgewick Rafter counting cells are used to quantify zooplankton abundance in the water column.

4.4.7 Trophic State Index (TRIX) Phytoplankton abundance in association with other biogeochemical parameters like dissolved oxygen, available nutrients like nitrogen and phosphorus, and turbidity governs the trophic state of any natural aquatic ecosystem. The marine ecosystems are no exception in this regard. Carlson (1977) formulated the trophic state index (TSI) for lacustrine environments; however, the same concept has been implemented in due course of time for lotic ecosystems like estuaries and open oceanic regions. Vollenweider et al. (1998) formulated a trophic state index for open oceanic waters named TRIX that utilizes the data of chlorophyll-a, dissolved oxygen saturation, inorganic nitrogen, and total phosphorus to characterize the different trophic states based on the TRIX values obtained. This formulation has been modified by several authors to some extent in recent days for several site-specific studies (Andricevic et al. 2021). Usually, TRIX values ranging between 0 and 4 are considered of very good quality and are termed oligotrophic. TRIX ranging from 4 to 6 are considered mesotrophic indicating fair water quality. TRIX values ranging from 6 to 8 and 8 to 10 are classified as eutrophic and hypereutrophic, respectively. These two states are considered poor as these trophic states lead to mass-scale deterioration of the overall water quality of any aquatic system.

4.5 Essential Nutrients Nutrients are crucial parameters that regulate the autotrophic potential of marine ecosystems (Mathew et al. 2021). These nutrients essentially include nitrogen, phosphorus, and silica. Though the inorganic forms of these elements remain most readily available to act as nutrients, the organic counterparts also measured as mineralization of organic nitrogen and phosphorus often enhance the overall nutrient pool of a region (Tian et al. 2020). Usually, in marine ecosystems, these nutrients are found in very low concentrations; however, a plethora of anthropogenic activities often gives rise to the nutrient concentrations to such alarming levels that it triggers

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eutrophication (Douglas et al. 2018). Therefore, to characterize the overall health of a marine ecosystem, nutrient concentrations are often monitored and measured with utmost importance. Nutrient measurements are an integral part of most biogeochemical research undertaken in any marine ecosystem. The various chemical species of nutrients and their ecological significance are discussed in this section.

4.5.1 Nitrate Nitrate (NO3 − ) is one of the most dominant inorganic nitrogenous components found in any marine ecosystem (Henley et al. 2020). Nitrates act as an essential nutrient that facilitates photosynthesis; however, nitrates in excess quantity can lead to serious environmental problems (Wu et al. 2019). Nitrates are often released into marine ecosystems through anthropogenic activities like fertilizer runoff from agricultural plots and aquaculture ponds to the nearshore marine ecosystems. Enhanced levels of nitrates cause not only eutrophication that leads to hypoxia (lowering of dissolved oxygen in water bodies) but can also be toxic to several marine life forms (Torno et al. 2018). Usually, nitrates are found below 1 mg/l in marine ecosystems. Nitrate concentrations are usually measured with the help of spectrophotometers. Sulfanilic Acid and N-(1-Naphthyl) Ethylenediamine Dihydrochloride are generally used as dyes to determine the strength of nitrate in any aquatic samples after passing the samples through a cadmium column that reduces the nitrates to nitrites. The absorbance of the dye is measured at 540 nm wavelength. Using Beer-Lambert’s law, the optical density is measured. Using nitrate solutions of known strengths, a calibration curve is prepared beforehand that enables us to quantify the nitrate concentrations through the above-discussed colorimetric method. Depth profiles of nutrients are studied in various types of oceanographic research to understand the nutrient dynamics throughout the water column of a particular region (Fig. 4.5).

4.5.2 Nitrite Seawater usually remains devoid of nitrite or is found at very low concentrations. However, nitrites in excess can cause several problems to marine organisms (Hashim et al. 2020). Most of the available microorganisms in seawater usually oxidize the organic form of nitrogen to nitrate, and in this biogeochemical transformation, nitrite happens to be an intermediate by-product. However, some bacteria like the Nitrosomonas sp. oxidize ammonia to form nitrites (Kitzinger et al. 2020). In oligohaline environments, nitrites are often found to be potentially toxic to several marine organisms, especially fish. Nitrites also act as a proxy for sewage discharge in the estuarine and nearshore environments. However, some studies showed that nitrite can act as a hypoxic buffer that helps in carrying out mitochondrial respiration and vasodilation for many marine organisms under oxygen-deficient conditions (Jung et al. 2022).

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Fig. 4.5 Typical variation of nitrate concentration observed in the Pacific and Atlantic Ocean (after Webb 2021)

The measurement technique of nitrites is mentioned above in Sect. 4.5.1. In the case of measuring nitrites, cadmium column reduction is not required.

4.5.3 Ammonia Like nitrate and nitrite, ammonia is also another inorganic form of nitrogen that is found in almost all natural aquatic ecosystems of the world and the marine sector is no exception in this regard (Lin et al. 2019). Ammonia can be autochthonously produced in the marine water column by a group of microbial organisms by breaking down organic waste products that end up in the sea. It is also one of the by-products of the natural nitrogen fixation process. However, the excess use of inorganic fertilizers and disposal of domestic untreated sewage materials in the ocean has given rise to excess ammonia generation in some parts of the world (Pang et al. 2021). Several pieces of research have unequivocally indicated that ammonia levels beyond a certain threshold can prove to be toxic to several marine faunas. Under elevated ammonia levels, various biotic organisms cannot excrete properly which leads to the building up of toxicity levels within the body of those organisms. o-phthalaldehyde (OPA) fluorometric methods and indophenol blue (IPB) spectrophotometric methods are some of the most common methods of measuring ammonia concentrations in water (Zhang et al. 2018).

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4.5.4 Total Nitrogen Several groups of researchers are often interested to characterize the total nitrogen load in the water column. Total nitrogen is an essential parameter for biological oceanographers, especially those who study phytoplankton dynamics with respect to nutrient variability. Total nitrogen is often used to compute the N:P ratio in the water column to study nutrient limitations and it is often compared with the ideal Redfield ratio (N:P = 16:1) (Hofmann et al. 2021). Nitrate, nitrite, and ammonia together comprise the dissolved inorganic nitrogen (DIN), whereas a substantial amount of nitrogen remains in the water column in organic form (Zheng et al. 2021). Technically, the sum of inorganic and organic forms of nitrogen in the particulate as well as dissolved forms gives us the total nitrogen load. To measure total nitrogen, often a UV-thermal digestion technique is deployed to convert all organic forms of nitrogen to nitrate, which is then further reduced to nitrite and measured spectrophotometrically. Most commonly the Total Kjeldahl Nitrogen (TKN) which is the sum total of ammonia and all organic nitrogen is measured by the digestion method (Adamski 1976), and the nitrates and nitrites are measured separately by spectrophotometric methods. The sum of TKN, nitrates, and nitrites fetch us the total nitrogen.

4.5.5 Soluble Reactive Phosphorus Apart from nitrogen, phosphorus (P) is another crucial micronutrient without which any autotrophic activity is not possible. It is also used by a plethora of marine organisms for their growth and proper metabolism (Karl and Björkman 2001). In the marine water column, phosphorus usually remains at very low concentrations. The intrinsic low concentrations of phosphorus act as a limiting factor for excessive phytoplankton growth (Hao et al. 2020). Like nitrogen, phosphorus also exists in dissolved inorganic and organic forms. The inorganic forms of phosphorus principally consist of HPO4 2− ions and a small proportion of PO4 3− ions known as soluble reactive phosphorus or orthophosphates. Spectrophotometric determination of soluble reactive phosphorus using potassium antimony tartrate and acidified molybdate reagent is most practiced (Boltz and Mellon 1948). Phosphomolybdic acid produced in this method is reduced with the help of ascorbic acid to molybdenum blue forming a blue-coloured solution. The optical density of this solution is measured at 880 nm wavelength using a spectrophotometer.

4.5.6 Total Phosphorus Like total nitrogen, total phosphorus is also an essential nutrient parameter that considers the sum of inorganic phosphorus and all the phosphorus that exists in

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the organic form. This parameter is of immense significance in tracing unnatural bloom formation or red tides (Zohdi and Abbaspour 2019). Total phosphorus acts as a proxy of anthropogenic effluents in coastal waters and is considered an active promoter of eutrophication (Zhou et al. 2020). This parameter also plays a crucial role in regulating the phytoplankton dynamics of a particular region in the marine sector (Bargu et al. 2019). The measurement protocol involves the conversion of organic phosphorus to inorganic phosphate by oxidization and the inorganic phosphate is measured spectrophotometrically as discussed in Sect. 4.5.5.

4.5.7 Reactive Silicate Besides nitrate and phosphate, reactive silicate (also known as reactive silica/ filterable reactive silicon) is a crucial micronutrient, especially for the silicifying microorganisms that constitute the lion’s share of the entire marine phytoplankton community. Out of the various types of phytoplankton, diatoms are known to make use of substantial quantities of silica, which in turn links the nutrient stoichiometry with the biological carbon pump in the ocean (Tréguer and Pondaven 2000). In contrast to nitrogen and phosphorus, substantial concentrations of reactive silica remain in the marine water column, as this chemical constituent is geochemically produced through erosion and weathering of silica-rich rocks (Tréguer et al. 2021). However, recent pieces of research indicate that silica concentrations vary depending on the hydrodynamics of the nearshore waters and riverine discharge through estuaries, which can further proliferate the chances of eutrophication (Tréguer and De La Rocha 2013; Chen et al. 2014; Zhang et al. 2020). Like inorganic nitrogen and phosphorus, reactive silica is also measured with the help of spectrophotometric procedures. Ammonium molybdate reacts with marine water samples to form silicomolybdate, which is reduced to a blue-coloured solution of silicomolybdous acid with the help of oxalic acid. The absorbance of this solution is measured with the help of a spectrophotometer. However, at the present date, several automated analyzers are being innovated to measure these nutrients in real-time in the field (Fang et al. 2022).

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Sharqawy, M.H., Lienhard, J.H., and Zubair, S.M. (2010). Thermophysical properties of seawater: A review of existing correlations and data. Desalination and Water Treatment, 16(1–3): 354–380. Shi, W. and Wang, M. (2010). Characterisation of global ocean turbidity from Moderate Resolution Imaging Spectroradiometer ocean colour observations. Journal of Geophysical Research: Oceans, 115(C11). Smith, S.V. and Mackenzie, F.T. (1987). The ocean as a net heterotrophic system: implications from the carbon biogeochemical cycle. Global Biogeochemical Cycles, 1(3): 187–198. Steinberg, D.K. and Landry, M.R. (2017). Zooplankton and the ocean carbon cycle. Annual Review of Marine Science, 9(1): 413–444. Sulpis, O., Agrawal, P., Wolthers, M., Munhoven, G., Walker, M. and Middelburg, J.J. (2022). Aragonite dissolution protects calcite at the seafloor. Nature Communications, 13(1): 1–8. Takahashi, T., Sutherland, S.C. and Kozyr, A. (2018). Global Ocean Surface Water Partial Pressure of CO2 Database: Measurements Performed During 1957–2017 (Version 2017). ORNL/CDIAC160, NDP-088 (V2017), (NCEI Access. 0160492), Version, 4. Takvam, M., Wood, C.M., Kryvi, H. and Nilsen, T.O. (2021). Ion transporters and osmoregulation in the kidney of teleost fishes as a function of salinity. Frontiers in Physiology, 12: 664588. Telesh, I.V. and Khlebovich, V.V. (2010). Principal processes within the estuarine salinity gradient: A review. Marine Pollution Bulletin, 61(4–6): 149–155. Tian, D., Wang, Y., Xing, J., Sun, Q., Song, J. and Li, X. (2020). Nitrogen loss process in hypoxic seawater based on the culture experiment. Marine Pollution Bulletin, 152: 110912. Torno, J., Einwächter, V., Schroeder, J.P. and Schulz, C. (2018). Nitrate has a low impact on performance parameters and health status of on-growing European sea bass (Dicentrarchus labrax) reared in RAS. Aquaculture, 489: 21–27. Tréguer, P. and Pondaven, P. (2000). Silica control of carbon dioxide. Nature, 406(6794): 358–359. Tréguer, P.J. and De La Rocha, C.L. (2013). The world ocean silica cycle. Annual Review of Marine Science, 5: 477–501. Tréguer, P.J., Sutton, J.N., Brzezinski, M., Charette, M.A., Devries, T., Dutkiewicz, S., ... and Rouxel, O. (2021). Reviews and syntheses: The biogeochemical cycle of silicon in the modern ocean. Biogeosciences, 18(4): 1269–1289. Velasco, J., Gutiérrez-Cánovas, C., Botella-Cruz, M., Sánchez-Fernández, D., Arribas, P., Carbonell, J.A., ... and Pallarés, S. (2019). Effects of salinity changes on aquatic organisms in a multiple stressor context. Philosophical Transactions of the Royal Society B, 374(1764): 20180011. Vollenweider, R.A., Giovanardi, F., Montanari, G. and Rinaldi, A. (1998). Characterisation of the trophic conditions of marine coastal waters with special reference to the NW Adriatic Sea: proposal for a trophic scale, turbidity and generalised water quality index. Environmetrics: The official Journal of the International Environmetrics Society, 9(3): 329–357. Wang, H., Wei, H., Tang, L., Lu, J., Mu, C. and Wang, C. (2018). Identification and characterization of miRNAs in the gills of the mud crab (Scylla paramamosain) in response to a sudden drop in salinity. BMC Genomics, 19(1): 1–12. Wang, K. and Yin, K. (2021). Barrier Effect of the Pearl River Estuarine Plume on Wind-Induced Coastal Upwelling of Nutrients. Journal of Geophysical Research: Biogeosciences, 126(11): e2020JG006067. Wang, N., Luo, Y.W., Polimene, L., Zhang, R., Zheng, Q., Cai, R. and Jiao, N. (2018). Contribution of structural recalcitrance to the formation of the deep oceanic dissolved organic carbon reservoir. Environmental Microbiology Reports, 10(6): 711–717. Ward, B.A., Dutkiewicz, S., Jahn, O. and Follows, M.J. (2012). A size-structured food-web model for the global ocean. Limnology and Oceanography, 57(6): 1877–1891. Watson, A.J., Schuster, U., Shutler, J.D., Holding, T., Ashton, I.G., Landschützer, P., ... and GoddijnMurphy, L. (2020). Revised estimates of ocean-atmosphere CO2 flux are consistent with ocean carbon inventory. Nature Communications, 11(1): 1–6. Webb, P. (2021). Introduction to Oceanography. Roger Williams University. Willis, J.K., Chambers, D.P., Kuo, C.Y. and Shum, C.K. (2010). Global sea-level rise: Recent progress and challenges for the decade to come. Oceanography, 23(4): 26–35.

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Chapter 5

Coastal Pollution—An Overview

5.1 What is Marine Pollution? The term “marine pollution” has several definitions. The ocean-scientific community universally accepts the one framed by a joint panel of experts formed by the United Nations in 1982 on the Scientific Issues of Marine Pollution (Pinet 2019). According to them, marine pollution is the act of human-activity-driven introduction of any matter or energy into the oceanic realm, including the coastal water bodies, that directly or indirectly leads to harmful effects on the marine organisms and habitat, which further can lead to human health hazard, and hamper ocean-based activities like fishing, and eventually compromise the seawater quality and reduces its potential to offer ecosystem services to humankind. Table 5.1 lists potential pollutants recognized unanimously worldwide. Marine pollutants usually spread out in various layers of the oceanic depth. Many significant contaminants chemically bind to suspended particles with high settling velocity and directly accumulate in the benthic substratum. Bottom-dwelling marine fauna homogenizes these contaminants into the ocean floor. Some contaminants can concentrate along the pycnocline that separates water masses of different densities. In some instances, the dissolved and solid wastes can remain afloat at the air-sea interface. This critical junction, called the neuston layer, comprises a very thin laminar microlayer. Here, pollutants in gaseous and particulate forms tend to aggregate and may affect plankton of all types, including all sorts of fish and invertebrates, during their embryogenesis that transiently remains at this interface. Marine contaminants can harm the biotic community from the cellular to the community levels (Table 5.2).

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Table 5.1 A list of well-recognized marine pollutants and their natural and anthropogenic sources Pollutants

Natural sources

Human sources

Hydrocarbons

Oil, gas, or tar seeps, rivers, runoff, aquatic bacterial communities, gas hydrates, volcanic eruptions, atmospheric phenomena

Urban effluents, transportation, production of aerosols

Heavy or trace metals

Volcanism, riverine erosion, catchment discharge, geological features that introduce mantle materials to the crust

Industrial and municipal effluents

Particulates

Rivers, runoffs, suspended matter, nepheloid layers, currents, biotic productivity, bottom churning, aeolian dust

Farming, fisheries (i.e., trawling), industrial and municipal effluents, drilling mud

Radioactive materials

Riverine discharge, denudation, Industrial wastewater and weathering, volcanism, fumes, nuclear power plants, geological features that mining activities introduce mantle materials to the crust, air-borne transport

Nutrients

Watershed-driven runoff, upwelling, detrital cycle, air-borne dust

Municipal effluents, agricultural fertilizers, and slurry mixtures

Thermal effects

Volcanism, hydrothermal vents

Cooling tower discharges, ocean thermal energy conversion

Biological oxygen demand (BOD)

Natural decay, aquatic detritus, primary production

Municipal and industrial discharge, cannery wastes

Source Modified from Geyer (1980) Table 5.2 Responses to chemical constituents of pollutants at different organism levels Organism level

Responses

Cells

Metabolic disorders, toxification (poisoning), cellular deformity, detoxification

Organisms

Behavioural and physiological alterations, susceptibility to disease, declined reproductive efficiency, abnormalities in the larval stage

Population

Alterations in mortality ratio, recruitment, size, age group variability, trophic level biomass, and degree of reproductive efficiency

Community

Alterations in species composition, biotic interactions between different trophic levels, species distribution, and species competition

Source McDowell (1993)

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5.2 Coastal Geography The coastal zone denotes the critical junction where the terrestrial and marine sectors converge. The influence of marine hydrodynamic processes is prominent in this region. It is the zone between marine and terrestrial ecosystems and witnesses several human activities. The continental shelf break acts as the offshore limit of this sector. The first noticeable topographical change beyond the extent of significant storm waves marks the onshore extent. The coastal zone has four broad sub-divisions: . . . .

Coast Shore Shore face Continental shelf.

The coastal zone includes flood plains, deltaic regions, bays, estuaries, wetlands, lagoons, mangroves, seagrasses, salt marshes, and corals, offering diverse and rich water resources. Compared to the global continental land mass, the coastal periphery in the past century has witnessed a dramatic change owing to the massive increase in population, proliferation of trade and commerce, and urban sprawl spread in the coastal periphery. Myriads of anthropogenic activities like aquafarming, agriculture at the cost of coastal vegetation, infrastructural changes in human settlements, residential areas, and tourism-related affairs have altered the coastal topography and geomorphology to a great extent.

5.3 Sources of Marine Pollution Terrestrial sources: About 80% of the substances that pollute the marine domain originates deep inland because of several anthropogenic activities that eventually drain through the continental catchments and watersheds and meet the nearby rivers and streams, which meet the ocean Occasionally, direct untreated discharges from the industrial belt in coastal regions lead to severe pollution. Air-borne sources: Aeolian dust and emission-based atmospheric inputs to the sea can also substantially pollute the marine environment. Figure 5.1 shows a snapshot of all the principal factors contributing to coastal pollution.

5.4 Types of Inputs for Marine Pollution . . . .

Untreated dumping of waste materials into the marine domain Drainage that alters the energy environment in seas (light and thermal regime) Ship pollution Radioactive wastes, harmful chemicals, and trace metals

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Fig. 5.1 A glimpse of factors that contribute to coastal pollution

. . . .

Grease and oily products Atmospheric pollution Deep sea mining Plastics (macro and micro).

5.4.1 Direct Discharge Humans discard several substances, including natural (sewage) and artificial (plastics) materials, into the ocean. Through domestic sewage and industrial effluents, several harmful contaminants reach the coastal waters and eventually end up in the open ocean. Leachates from mining activities in the continental landmass drain into the marine sector. Weathering and erosion often play a crucial role in mixing sediments rich in pollutants with the river water that flows into the ocean. For example, onshore copper mining often introduces enhanced copper levels in coastal waters, which is fundamentally responsible for the development of coral polyps.

5.4.2 Sewage Municipal sewage contains various substances, including solids, semi-solids, and liquids of inorganic and organic nature, leading to forming a thick sludge-like heterogeneous mixture.

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5.4.3 Surface Runoff Surface runoff from agricultural fields, aquaculture ponds, and urban effluents from domestic sector and construction activities can erode sediment layers rich in essential nutrients and minerals. This nutrient enrichment in the oceanic realm accelerates primary production to such an extent that it leads to algal mat formations, commonly known as blooms. These blooms can cut off gaseous exchange between the hydrosphere and the atmosphere leading to severe oxygen deficiency in the marine water column.

5.4.4 Hydrocarbon in the Sea Carbon, hydrogen, and small amounts of nitrogen and some bound metals through metamorphosis led to the formation of complex hydrocarbons, i.e., petroleum, in various proportions and different molecular structures. Products of hydrocarbon, especially oils, have a detrimental effect on marine organisms that thrive near the air–water interface (hyponeuston) and several other marine organisms (Table 5.3). Hydrocarbon pollution significantly alters the trophic structure of the marine ecological food chain and reduces productivity. An increment in sea-based transport and ocean vessels causing oil spills, oil drilling in the continental shelf zones, and an utter lack of proper law enforcement to combat this evil in the open seas (internationally) have increased the degree of hydrocarbon pollution in the oceans. Oil pollution leads to the mortality of thousands of marine birds.

5.4.5 Shipping Pollution Accidental oil spillage and continued oil introduction from the marine transport sector severely impact the oceans. Many constituents of oil and petroleum products, like polycyclic aromatic hydrocarbons (PAHs), have a long residence time in nature and persists for a long time in water column and sediments, and easily bioaccumulates and biomagnifies in marine organisms The higher residence time of these pollutants in the marine environment facilitates their bioaccumulation in smaller life forms and biomagnification to higher life forms across the ecological food chain.

5.4.6 Deep Sea Mining Ocean miners concentrate in sea-bottom regions rich in polymetallic modules and defunct hydrothermal vents at varying depths from the air–water interface. The

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Table 5.3 The impact of oil spillage on different types of ecosystem Ecosystem

Initial impact

Recovery

Wetlands, salt marshes, and mangroves

Heavy, widespread mortality of plants and animals leads to decreased population densities and a change in species abundance and diversity. Significant impact on biological productivity

Slow to moderate, toxicity prolongs with residence time, and biological succession occurs at a moderate rate once oil dilutes

Estuaries, bays, and harbours Moderate to heavy, depending on the season (spawning, migration) and oil’s persistence. Depresses populations and alters the species’ composition and abundance

Fast to slow, dependent on current flow, shoreline characteristics, and community stability

Outer continental shelf

Planktonic organisms and larvae remain the most affected. Oil subsiding to the ocean bottom affects the benthic organismsm

Planktonic organisms quickly recover as they generate and reproduce at an elevated rate. Benthic organisms take a much longer time to recover

Open ocean

Light. Many organisms avoid spills. Impact ton plankton is local and depends on a chance encounter with the spill Usually, water is too deep for a significant impact on benthos

Oil degradation and dispersion take place at a fast rate

Source Hyland and Schneider (1976)

miners often deploy bucket-pulley manifold assembly and hydraulic pumps to extract the minerals. These activities irrevocably jeopardize the benthic environment and significantly alter the seascape. Deep sea mining generates plumes at the benthic regions by perturbing the sea bottom. Plume formation near the air–water interface significantly compromises the autotrophic potential of the water column. These plumes exhibit wide spatiotemporal variability governed by the characteristics of the particulate matter. Mining-associated corrosion, spillage, and leakage often add to the problem.

5.5 Impacts of Marine Pollution Marine pollution degrades marine habitats, affects biotic health, compromises recreational features, deteriorates the water quality, and reduces ecosystem services in the following ways:

5.6 Human Impacts on Marine Environments

. . . . .

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Mechanical measures like marine dumping Nutrient-enrichment-induced hypoxia or anoxia Saprogenic processes and phenomena Toxicological attributes Carcinogenic and mutagenic alterations.

5.6 Human Impacts on Marine Environments Eutrophication: Rivers act as the bridging link between the terrestrial and marine sectors, and through these waterways, essential nutrients end up in the coastal periphery. Enhanced fertilizer use for agricultural purposes and aquafarming have increased the nutrient load in the rivers and coastal oceans. These nutrients, which are otherwise of utmost necessity for photosynthesis by phytoplankton, in excess amounts, increase primary productivity and lead to harmful algal blooms. These blooms display toxic effects on the adjacent marine biotic communities and lead to a severe depletion in oxygen levels and mortality. Ocean acidification: The oceans have been absorbing a substantial part of the anthropogenically emitted CO2 , thus relieving the atmospheric burden of greenhouse gases. However, excess incorporation of CO2 in the marine sector decreases the sea pH levels, which makes it difficult for calcareous marine organisms to thrive properly. Plastic Pollution: Since humankind started manufacturing plastics to meet various demands, the oceans have become a dump yard of the same. The absence of a proper recycling mechanism and lack of regulatory enforcement leaves plastic wastes of macro to nanomolecular structures in the oceans that severely impacts marine life forms. Plastic debris potentially entangles, suffocates, and is often ingested by higher life forms of the marine trophic chain. Discarded fishing nets made of plastics pose a severe threat to many oceanic organisms. Toxic pollutants: An array of intentionally produced and unintentionally manufactured industrial byproducts end up in the oceans that exhibit toxic effects on several marine life forms. i. Organochlorine pesticides, polychlorinated biphenyls, dioxins, furans, phenols, and radioactive wastes persist in the maritime domain for a long time. ii. Higher atomic number trace metals, also known as heavy metals, often pose toxic effects at an elevated concentration beyond a certain threshold. iii. Heavy metals like chromium, copper, arsenic, mercury, cadmium, nickel, and lead, enter living organisms through water and food ingestion and bioaccumulate in the organs and tissues. These metals often leave the water column and precipitate in the adjoining sediments, which is a signature of anthropogenic activities.

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5.7 Coastal Zone Management The Coastal Zone Management (CZM) comprises a holistic governance procedure involving the legal and institutional framework required to warrant that development plans for coastal regions essentially fulfill the environmental and social goals and that the development activities must involve the participation of the local inhabitants who are affected. The management principles and issues consider the following issues: . The dynamism of coastal set-up should be at the forefront while zoning problematic areas. The management endeavours should help maintain the natural dynamic forces. . CZM should resolve an issue or dispute using laws and enforcement, and where conflicts do not resolve, planning and legislation need strict implementation. . The management strategies should be flexible enough to cope with changing scenarios and altered scales of human development over time. . Public awareness and consultation are essential steps for controlling pollution. . Many conventional acts are being introduced to curb pollution. . The Oslo Convention (1972) regulates the dumping activities from ocean vessels and flights into the maritime realm. . The Marpol Convention (1973) regulates shipping and transport-based polluting activities. . The OSPAR Convention (1992) strives to protect the marine environment of the north Atlantic ocean. The administrative control in coastal regions often remains poorly defined in many regions. It is poorly fragmented between and within several government levels in many nations. Hence, integrated management of the coast is required. Integrated Coastal Zone Management (ICZM) is a device that considers many aspects related to the coast, and various laws, regulations, and jurisdictions. Thus, to ensure the sustainability of the future coastal peripheries, which is the main motto of ICZM, the physical, chemical, geological, and biological attributes should receive equal attention in addition to the socio-economic spheres of development and services.

5.8 Conclusion This chapter discusses the various causes of marine and coastal pollution owing to the different sources due to hydrocarbon exploration, oil spills, heavy metals, and chemical constituents discharged from municipalities and industries. All countries’ governments have adopted different legal policies to prevent coastal pollution and protect the environment. An integrated coastal zone management method has been undertaken to sustain and preserve natural coastal bodies and organisms.

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References Geyer, R.A. (ed.) (1980). Marine environmental pollution, 1: Hydrocarbons. Elsevier Oceanography Series, 27(A). Elsevier Scientific Publishing Company: Amsterdam/London/New York. Hyland, J.L. and Schneider, E.D. (1976). Petroleum hydrocarbons and their effect on marine organisms, populations communities, and ecosystems. In: Sources, effects, and sinks of hydrocarbons in the aquatic environment. American Institute of Biological Sciences, Washington, D.C., pp. 463–506. McDowell, J.E. (1993). How marine animals respond to toxic chemicals in coastal ecosystems. Oceanus, 36(2): 56–62. Pinet, P.R. (2019). Invitation to oceanography. Jones & Bartlett Learning.

Chapter 6

Nutrient Pollution

6.1 Introduction Excessive addition of nutrients causes nutrient over-enrichment, while nutrient bleaching creates a nutrient deficit in the aquatic ecosystems leading to the degradation of the natural ecology. The input of some elements into the system in excessive amounts creates an ecological imbalance affecting the entire environment of that area. National and international bodies and non-profit organizations adopted numerous measures to combat marine pollution. Antipollution laws have been executed at several levels of society in the past years to limit the unmonitored discharge of toxic elements. But these have been principally emphasized to control the effluents of pollutants from industrial and municipal use. However, significant endeavours to check the ingress from agricultural and urban runoff types of non-point sources into the waterways are scarce. The input of nutrients in excess leads to most environmental issues faced in coastal regions as they cause ecological imbalances.

6.1.1 Nutrient Pollution The introduction of excess nutrients into the coastal systems from various sources leads to nutrient enrichment. Excessive nutrient enrichment causes nutrient pollution. This type of contamination has several impacts. Acceleration of eutrophication, i.e., the increase in the organic enrichment of an ecosystem, is one of the most observed phenomena. This material generates in the ecosystem due to primary productivity (i.e., photosynthetic activity). When anthropogenic activities cause nutrient overenrichment due to the introduction of high nitrogen and phosphorus concentrations, it may stimulate harmful effects like algal blooms and consequent hypoxia in the water column.

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Table 6.1 Cause and effect of nutrient over-enrichment Phenomena

Causes

Eutrophication Over-enrichment of nutrients like N, P

Effects Algal bloom and reduced gaseous exchange between hydrosphere and atmosphere

Hypoxia

Heavy seawater mixes with the less dense Fish kills leading to the estuarine freshwater, it causes stratification of the depletion of fish stocks and water column and reducing oxygen concentration damage to the ecosystem

Anoxia

Excessive nutrient-induced high rates of productivity enhance water column heterotrophy, which extinguishes all the dissolved oxygen

Mass mortality of all sorts of aerobic life forms below the water

6.1.2 Problems of Nutrient Imbalance The coastal environment is one of the most productive ecosystems on Earth as it houses diverse flora and fauna and provides significant resources for sustaining terrestrial lives. The nutrient imbalance may lead to an ecological imbalance, thereby destroying the entire ecosystem. These natural resources are in grave danger from majorly two factors. These are: i. Over-enrichment of nutrients, causing eutrophication: Various other problems occur due to excess input of nutrients, especially nitrogen and phosphorus. The coastal environment often experiences the mixing of fresh and saltwater as all rivers flow to seas and oceans. When the river discharges water into the sea, they transport vast amounts of nutrients. Hence estuaries have a higher concentration of land-borne nutrients. Nutrient over-enrichment causes numerous problems ranging from economic to non-economic levels. It includes eutrophication associated with hypoxia and anoxia, seagrass bed loss, coral loss, loss of fishery resources, biodiversity loss, structural changes in ecology, and many others (Table 6.1). ii. Lack of nutrients in the coastal regions: This happens when wastewater from industries or the vast amount of municipal sewage from nearby urban areas undergoes chemical treatment to eliminate harmful chemicals. This activity, in turn, renders the water sterile and unfit for supporting any life form.

6.1.3 Ecological Impact Due to Nutrient Over-Enrichment Problems due to nutrient over-enrichment in water have multi-layered effects on the ecosystem affecting life on both land and water. Nitrogen and phosphorus are the major inimical factors that harm the environment. Various anthropogenic activities like municipal sewage wastes, agricultural fertilizers, livestock wastes, aquaculture

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or coastal pisciculture, burning of fossil fuels, and effluents from ports are most pollutants responsible for the ecological hazards in the aquatic environments. Overdose of nutrients has numerous effects on the coastal ecosystem as it adversely changes the biological diversity of the aquatic environment. This impact includes alarming biogeochemical phenomena in lentic and lotic ecosystems like eutrophication, algal bloom, hypoxia, and anoxia. Hypoxia and anoxia extirpate the sensitive and less mobile organisms, and reduce suitable habitats for other organisms, causing permanent alterations in the prey-predator relationships in that ecological niche, thereby changing the community structure. Dead zones (hypoxia or anoxia) create low oxygen zones with concomitant fish kills, leading to the mass death of fish, thus adversely impacting the economy (in the fisheries sector). Algal blooms can also adversely affect human health. Certain algae produce toxins that get incorporated into the ecological food chain when clams and other organisms consume such algae. When humans consume such affected seafood, they get sick. Coming in direct contact with toxins can cause various skin problems and may even lead to death in certain instances.

6.1.4 Role of Seagrass Habitat and Their Impact on the Ecosystem The benthic plant community contributes to primary production only in presence of adequate light, passing through the water column down to the seafloor in coastal regions. Under suitable conditions, a dense population of seagrass and perennial macroalgae grow and attain high net primary production similar to a prolific terrestrial ecosystem (Charpy–Roubaud and Sournia 1990). Seagrasses and other benthic organisms support species like finfish and shellfish by providing them with crucial habitats and stabilizing estuarine floor sediments. The presence of seagrass indicates a healthy ecosystem and helps to preserve the estuarine and coastal ecosystems. The perennial macrophytes depend less on the nutrient levels of the water column compared to that phytoplankton and ephemeral macroalgae, and photo availability is crucial for their growth control (Sand-Jensen and Borum 1991; Dennison et al. 1993; Duarte 1995). Perennial seagrasses of the temperate regions obtain their food nutrients from sediment-stored nitrogen pools, internal recycling, and nutrient sources (Pedersen and Borum 1996) as a result of which, excess nutrients do not stimulate their populations. However, excess nutrient input leads to a shift in undesirable phytoplankton bloom of benthic macroalgae. In tropical waters, seagrass growth is limited as nutrient (phosphorus) uptake is more rapid for fast-growing phytoplankton and macroalgae, which takes place of the dominant primary producer replacing seagrass in an enriched ecosystem (Fig. 6.1) (McComb 1995). These fast-growing unwanted macroalgae are filamentous forms such as Ulva, Cladophora, and Chaetomorpha that accumulate as thick mats over the seagrasses or sediment surface causing macroalgal

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Fig. 6.1 Replacement of seagrass beds with macroalgae due to increased nutrients in shallow marine systems stimulates the phytoplankton growth in the water column and attached epiphytes (algae) on the seagrass (McComb 1995)

bloom. This macroalgal bloom causes a loss of habitat for bottom-dwelling or near-bottom-dwelling organisms.

6.2 Eutrophication Eutrophication, as defined by Nixon (1995, 1998), is the process of organic material enrichment in water bodies. Naturally, this process takes about centuries. It can occur in both freshwater lakes and coastal marine ecosystems but occurs mostly in the continental shelf region where nutrient inputs are high. Eutrophication is an important effect caused due to over-enrichment of nutrients. For example, a change in the relative abundance of certain nutrients may cause nutrient imbalance Nutrient imbalance. This results in unfavourable changes concerning some species’ relative abundance without contributing to an overall net primary productivity increase. Moreover, a surge in primary production leads to eutrophication along with secondary sets of problems like dissolved oxygen deficiency, reduction in sunlight in the water column, and ocean acidification among others. These in turn affect the entire ecosystem of that region. The changing concentrations of chlorophyll-a lead to changes in the trophic status of the aquatic systems (Fig. 6.2). The oligotrophic to mesotrophic state is considered healthy and optimum for any natural aquatic ecosystem. However, the shift from trophic states to eutrophic and hypereutrophic states poses problems, as mentioned above.

6.2 Eutrophication

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Fig. 6.2 Classification of waters based on average algal density (OECD 1982)

6.2.1 Cultural Eutrophication When excess nutrients are introduced into the system due to various anthropogenic activities, eutrophication occurs at a much faster rate. This process is called cultural eutrophication (Fig. 6.3). The introduction of elements like Nitrogen and Phosphorous into the system is the most detrimental as these are the major accelerating factors toward cultural eutrophication.

6.2.2 Factors Affecting Eutrophication Excess addition of nutrients to the marine system triggers a set of chain reactions in the ecosystem that are detrimental to the entire biotic community. Elements such as nitrogen and phosphorous are the major contributing factors that cause eutrophication and its ensuing problems. The primary sources of excess nitrogen and phosphorus are: • Agriculture: Animal manure and chemical fertilizers, which are necessary to help crops grow faster and efficiently have two basic and important ingredients i.e., nitrogen and phosphorus. The problem arises when these fertilizers are applied in excess and the plants cannot fully utilize them. These fertilizers then leach into water bodies, adversely impacting the quality of the water body, and ultimately flowing into the adjacent water shades. • Atmospheric: Losses of nitrogen in gaseous form in nitrogen-based compounds like ammonia and nitrogen oxides can be harmful to aquatic life if large amounts

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Fig. 6.3 a Natural eutrophication is referred to as the lake’s response to nutrient enrichment naturally. Eutrophication increases primary productivity, leading to greater biomass and sedimentation, b Cultural eutrophication induced by human activities, generates rapid changes in nutrient enrichment and ecosystem characteristics (Gold and Sims 2005)

of these compounds get dissolved into freshwater or marine water from the atmosphere. • Stormwater: As urban and suburban areas have the highest amounts of paved and hard surfaces; it creates more stormwater runoff. As the precipitated water flows over hard surfaces, the dissolved pollutants get very little chance to get filtered into the grounds. This polluted and untreated sewage water, enriched in nitrogen

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and phosphorus pollutants flows directly into the local water bodies and nearby streams or rivers. • Wastewater: Wastewater produced from human waste, soaps, and detergents is often enriched in pollutants like nitrogen and phosphorus. Though treatments of this wastewater are in operation in many developed urban and suburban areas, a significant amount of unfiltered and untreated wastewater escapes to the streams due to the improper operation of treatment plants. • Fossil Fuels: Excessive amounts of artificial nitrogen oxides are being introduced to the atmosphere, due to the burning of fossil fuels at an alarming rate. The formation of acid rains and smog are contributed by this toxic oxide. The principal causes of nitrogen oxide emissions are being fossil fuel utility cars, coal-fired power plants, and larger industrial operations due to the increasing population. Ammonia is also produced from fossil fuels. Fossil fuel caused nitrogen oxides to get deposited back to the land which washes into the nearby aquatic body, contributing to the harmful ecological effects of algal bloom and an oxygendeficient aquatic environment.

6.2.3 Harmful Algal Bloom (HAB) Algae are aquatic microscopic organisms that can photosynthesize like plants from sunlight. In water bodies when toxin-producing algae start growing excessively, it is known as a harmful algal bloom (HAB), or algal bloom. When these are visible to the naked eye, they can be classified depending on the algae type into green, blue-green, brown, red, etc., depending on the type of algae. When these are visible to the naked eye, those events are also known as red or brown tides. Depending on the algal type, HABs can cause adverse health effects and are even fatal. For example, consumption of toxin-contaminated seafood from algae Alexandrium can cause paralytic shellfish poisoning, leading to paralysis or death. The algae Pseudonitzschia produces a toxin called domoic acid that causes vomiting, seizures, confusion, diarrhoea, short-term memory loss, or death when taken in high quantities. Freshwater-occurring HABs, like the Great Lakes and other potable water sources, are dominated by the cyanobacteria Microcystis. They produce a liver toxin responsible for gastrointestinal illness and hepatic damage.

6.3 Limiting Nutrients and Their Biological Role Nutrients are elements or compounds that are taken up by marine organisms for their survival. Nutrients can be classified into, macronutrients, which are required in large amounts, and micronutrients, which are required in minor amounts. Of these, certain elements control the growth of plants. These elements, though necessary in minor quantities, control the growth of plants. These are called limiting nutrients. The six

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essential components constituting over 95% of organic matter (by mass) are carbon, nitrogen, phosphorus, oxygen, silicon, and hydrogen. Other than these, inorganic ions such as calcium, potassium, sodium, and trace elements like manganese, cobalt, iron, etc., are also taken up by organisms. Nitrogen and phosphorus act as limiting nutrients for plants. Nitrogen is the building block for amino acids while phosphorus is present in DNAs and required in the oxidative phosphorylation of ATP in all aerobic eukaryotes. Sometimes when these two elements are present in excess, scarcity of carbon can also limit primary productivity. The low availability of silica may limit primary productivity in some instances as silica is essential for diatoms.

6.3.1 Redfield Ratio Nitrogen and phosphorus are the limiting nutrients in most cases, but it was found that carbon, nitrogen, and phosphorus when present in a certain ratio, the primary productivity of a certain area is optimally stimulated. In 1934, Alfred Redfield discovered this ratio of carbon to nitrogen to phosphorus to be 106:16:1 and this ratio was approximately constant throughout the world’s oceans, in both phytoplankton biomass and dissolved nutrient pools. Over the years this insight has proved invaluable in understanding marine biogeochemical cycles (Moore et al. 2013). However, gradually it was discovered that this ratio has variations, although minor, from taxa to taxa and from place to place.

6.3.2 High Nutrient-Low Chlorophyll (HNLC) Regions Sometimes it is seen that although the level of macronutrients, nitrogen and phosphorous, are never really depleted, the amount of phytoplankton biomass remains constant all year long (Fig. 6.4). Phytoplankton requires small amounts of the trace elements like iron for photosynthesis and to grow. Iron is necessary for the synthesis of chlorophyll; they are a component of cytochromes which are electron transport chains. Iron is necessary for nitrate utilization and most importantly, it is essential for N2 fixation. However, iron is highly insoluble in oxygenated seawater and tends to precipitate easily. In regions far away from continental shelves, primary iron input occurs via atmospheric deposition and upwelling. In many HNLC regions, upper ocean concentrations of Fe are < 0.1 nM. For proper growth, phytoplankton biomass is measured to be 106C: 16N: 1P:0.005Fe. However, in certain areas of the oceans, the waters are deficient in these metals, rendering the growth of phytoplanktons impossible. Thus, in these areas, although the macronutrients may be present, iron acts as the limiting nutrient (Pitchford and Brindley 1999). These areas have phosphorus and nitrogen in sufficient amounts but due to the lack of iron, primary productivity remains limited. These HNLC regions are found in the North Pacific, East-central

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Fig. 6.4 Map of high nutrient-low chlorophyll (HNLC) regions around the world. Measurement in the map is of nitrate, with the scale as a gradient of colour pictured on the bottom (Hopes et al. 2017)

Pacific, and Southern Oceans. Presently all over the world, HNLC regions cover about 20% of the world’s oceans.

6.4 Dead Zone Dissolved oxygen content in the water varies depending on the seasons and also due to other factors. Patches of low oxygen areas in water bodies where organisms cannot survive are called dead zones (Fig. 6.5). Oxygen gets dissolved primarily by diffusion from the atmosphere due to air-sea interaction and from oxygen released as a by-product from aquatic plants. When dissolved oxygen content is less than 2–3 mg l−1 , it is critical for the survival of aquatic organisms and is called hypoxia. When the dissolved oxygen level further drops, to about 0 mg l−1 , it becomes fatal for organisms, and it is called anoxia. Over-enrichment of nutrients in the water bodies is the major contributing factor to eutrophication, which leads to the formation of dead zones. These are areas in water that have little or no dissolved oxygen, and thus, aquatic flora and fauna cannot survive in these areas. This condition is known as hypoxia and these areas are the result of algal bloom, which consumes oxygen as they die and decay. The Gulf of Mexico and the Black Sea are two of the well-known hypoxia-affected areas. Every year in late summer, a seasonal hypoxic zone forms over The Gulf of Mexico.

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Fig. 6.5 Global distribution of dead zones in the coastal and global ocean. In the coastal areas, more than 500 low-oxygen-conditioned sites have been identified. In the open ocean, the extent of low-oxygen waters amounts to several million km2 (Breitburg et al. 2018)

6.4.1 Causes Dead zones are complex ecological phenomena that have consistently increased due to human activities. Due to a balance between the input of O2 from both atmospheric as well as biochemical procedures, variation in aquatic O2 concentrations is observed both seasonally and temporally. A. One of the major contributing factors to the creation of dead zones is Climate Change. The oxygen retention capacity of water reduces with increasing temperature because the warmer the water, the lesser the oxygen it can dissolve. Warmer ocean water is more buoyant than cooler water and tends to hold less oxygen thereby leading to reduced mixing of oxygenated surface water with oxygen-poor deep waters. Hence, lesser oxygen is available for bottom-dwelling organisms. Warming also alters the patterns of global ocean water circulation, thus affecting the mixing of deeper waters with oxygenated surface waters. B. When freshwater with higher dissolved oxygen levels from estuaries mixes with seawater having lower dissolved oxygen levels it leads to stratification of the water column. Stratification may be horizontal with oxygen levels reducing from inland to oceanward, or it may be vertical with the more oxygenated freshwater staying afloat on the less oxygenated saline seawater. Stratification of the water column is dependent on temperature, density, and dissolved substances like oxygen and salts. Stratification causes low oxygen levels or hypoxic conditions naturally. Due to limited vertical mixing between the water layers, there is a restriction of oxygen supply from the freshwater to the saline water creating a hypoxic condition for sea-bottom dwelling organisms. C. Eutrophication is another major contributing factor to the reduction of oxygen levels in the water column. An increase in nutrient content leads to excessive algal growth, called algal bloom which when dead settles to the bottom waters

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and gets decomposed by the bacteria. During this decomposition process, the bacteria use up the dissolved oxygen, thus rendering the water column devoid of oxygen. Nutrient-rich, slow-moving and poorly mixed water is more likely to become hypoxic.

6.4.2 Effects of Hypoxia Hypoxia affects directly by killing fish, depleting valuable fish stocks, and damaging the ecosystem. Fish kills also result in a foul smell from the decomposing marine life, which is unpleasant and harms the health of the residents and tourists. Oxygenated water is essential for breathing by aquatic animals. Adult fishes and other mobile organisms, survive hypoxia by escaping into more oxygenated waters. However, young fish cannot escape such conditions easily. Hence, they are forced to stay in that hypoxic area, which results in reduced physiological growth of fish or sometimes mortality too. Non-mobile bottom-dwelling organisms such as clams caught by hypoxic episodes are often killed as they cannot move into healthier waters. This causes a severe or complete loss of animal biodiversity in hypoxic and near-anoxic zones. Nursery habitat for fish and shellfish is often affected by hypoxia since it occurs in regions of poor water mixing, like estuaries or near-shore areas. In absence of proper nursery grounds, the young animals are unable devoid of food or habitat and often do not attain adulthood. This causes years of weak recruitment to adult populations resulting in an overall reduction or destabilization of important stocks. Birds and animals having fish-dependent nutrition are also affected due to the lack of fish availability. Hypoxic areas are more susceptible to various stresses like pest outbreaks, overfishing, storm damage, etc. Chemical reactions between bottom sediments and hypoxic water release pollutants trapped in sediments, which further fuels the hypoxic conditions or otherwise pollutes the ecosystem.

6.4.3 Impact on Coral Reef Coral reefs are known to be highly productive and diversified ecosystems in the world. They grow as a thin column of living coral tissue on the outside of the hermatypic (reef-forming) coral skeleton. Most important coral reefs are distributed around the tropics and subtropics, in the nutrient-poor surface waters. The high rates of productivity by coral reefs are dependent upon the abundant sunlight, a characteristic feature of the equatorial zones of the earth, along with the nutrient recycling within the coralzooxanthellae symbiosis (Muscatine and Porter 1977). Thus, the decline in coral reefs worldwide is extremely disturbing. One direct impact associated with elevated nutrients is decreased calcification, which results in dramatic decreases in the growth of reefs (Kinsey and Davies 1979;

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Marubini and Davies 1996). Indirect effects of nutrient over-enrichment include an increase of phytoplankton biomass (Caperon et al. 1971), which alters the particulate matter quality and quantity along with water column optical properties in a predictable fashion, with subsequent effects on reefs (Yentsch and Phinney 1989). The cause and control of eutrophication in coastal marine ecosystems are highly dependent on nitrogen. Silicon and iron are also important in regulating HAB occurrences in coastal waters and help to determine the consequences of eutrophication. However, coastal water nutrient over-enrichment is primarily due to nitrogen, while the importance of silicon and iron comes secondary to it. Nitrogen and phosphorus have different chemical properties, thereby possessing different physiochemical properties while reacting with certain other compounds and their derivative also exhibit differences in their physicochemical properties. The overall biogeochemical cycle of these elements’ changes drastically with the change in the distribution or relative abundance of the various compounds containing these element forms, caused by anthropogenic activities. Alterations in these important cycles are mainly due to anthropogenic causes, especially the use of inorganic fertilizers (Fourney and Figueiredo 2017).

6.5 Strategies to Combat Nutrient Over-Enrichment Governments in various parts of the world systematically monitor and report various coastal issues and draw out plans to curb the issue of nutrient pollution. Coastal ecosystems include estuaries, bays, shelf systems, etc., and each of these systems reacts to nutrient enrichment in different ways. By understanding the various factors which lead to nutrient over-enrichment and how the different systems react to such problems, then we can mitigate the effects. Estuaries are shallow marine regions mixing freshwater with marine water and are one of the most biologically diverse ecosystems. Major communities like mangroves, swamps, macrophytes coral reefs, rocky intertidal zones, and plankton systems thrive here. Factors affecting nutrient over-enrichment in estuaries are as follows: i. The geomorphology of the estuarine setting plays an important role that determines its base for primary production (various primary producers respond differently to nutrient loading due to differences in their unique temporal and nutrient requirements). ii. Hypsography refers to the relative areal extent of land surface elevation and can be a crucial indicator for measuring the susceptibility of estuarine systems to eutrophication induced through nutrients present in the system. iii. Coastal systems are some of the most nutrient-loaded regions of the earth as runoff from various sources carrying various nutrients flows into the oceans. iv. Dilution of the nutrients that flow into the coastal regions also affects the per unit area availability of nutrients in the ecosystems.

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v. Water residence time also affects the nutrient concentration at a certain area at a particular time. Steady-state conditions in a waterbody have intermediate episodes of fluxes into and out of the system. Hence residence time of water, and thus the nutrients present in a particular area determines the occurrences of ecological phenomena dependent on nutrient loading (Howarth et al. 2000). For example, algal blooms only occur if the phytoplankton turnover time exceeds the water residence time. vi. Stratification of waters, both horizontally and vertically also impacts eutrophication and other ecological effects caused by nutrient overloading in coastal regions. vii. By studying the estuaries in depth, a clear idea regarding the significant presence of marsh, submerged vegetation, phytoplanktons, etc., can be obtained. viii. Cloern et al. (1985) have pointed out the limitations in the accumulation of algae due to grazing by benthic filter feeders. Denitrification involves the conversion of nitrates to biologically unavailable gaseous nitrogen and N2 O. It helps in providing a nitrogen sink in estuaries. It also reduces the responses to eutrophication by counteracting the input of allochthonous nutrients. Denitrification is proportional to the organic nitrogen remineralization rate in sediments (Seitzinger 1988), which is coupled with the magnitude of primary production that is oxidized by the benthos (Nixon 1981, 1992; Seitzinger and Giblin 1996). Denitrification and eutrophication share a non-linear relation. ix. Factors like anoxia in the bottom water, high sulfide concentrations, etc., can limit nitrification thereby impacting the process of denitrifying in the bottom waters of estuaries also. Based on physical parameters and geomorphic characteristics estuaries are classified into the following three categories: geomorphic, hydrodynamic, and habitat enumeration approaches. USA’s NOAA and its National Ocean Service have developed procedures for estimating the susceptibility of estuaries to nutrient over-enrichment. The “dissolved concentration potential” (DCP) is an index developed to compare the integrated nutrient loads with an estimate of estuarine dilution and flushing. The dilution parameter is proportional to the estuarine volume and the flushing parameter is calculated with the Ketchum (1951) fractional freshwater method, which is derived from the replacement of the freshwater component of the total system volume by river flow.   DCP = Q f /V f (1/ Vt )N Qf = Vf = Vt = N=

discharge of freshwater estuarine freshwater volume total volume in estuaries mean nutrient load for all estuaries.

DCP provides a quantitative measure of estuarine susceptibility to nutrient loading and is based on the physical parameter of estuarine volume, freshwater volume, and

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freshwater input. The DCP estimates the average nutrient concentration throughout an estuary with the assumption of the absence of any biological processing. Systems with a high DCP tend to concentrate nutrient inputs, while dilution of flushing of nutrients occurs in systems with a low DCP. NOAA categorizes estuaries based on DCP concentration, low (< 0.1 mg l–1 ), medium (0.1 to 1.0 mg l–1 ) and high (> 1.0 mg l–1 ) susceptibility to nutrient loading, respectively. Some frameworks that can help to curb these problems are: • Implementing management practices like fertilizer management practices, livestock manuring, run-offs, pisciculture drainage, avoiding the use of chemical fertilizers, and promoting the usage of biological nitrogen fixers (integrated plant nutrient management), etc., for implementation of pollution abatement at the source. • Optimization of nutrients used in agriculture by implementing advanced agricultural practices, treatment of municipal waste and sewage water, and better control of urban runoff can be effective in controlling nutrient pollution in the water bodies. • Estimation of natural availability of nutrients in a certain area before application of fertilizers, crop requirements, and crop rotation and post-fertilizer application management needs to be implemented. • Creating frameworks and indicators to analyze nutrient load, helping to better analyze the factors contributing to nutrient pollution and assessing the impact of such nutrient pollution regularly. • Spatial modeling assessment of nutrient load for the development of a better understanding of the sources. Moreover, as data collection on nutrients is arduous since pollution is diffuse, numerical modeling of the affected areas may be developed for definitive determination of the sources and affected regions and further provide solutions to such problems. • Active measures need to be taken by the governments and international regulatory bodies in the forms of policies and regulation framing. • International cooperation, data sharing, and actions through regional frameworks of dialogue and actions. • The Harmful Algal Bloom and Hypoxia Research and Control Act of 1998 (HABHRCA 1998, reauthorized in 2004, 2014, and 2019, Public Law 113–124) reaffirmed and expanded NOAA’s mandate for advancing scientific understanding of hypoxia. It also focused on helping scientists to detect, monitor, predict and mitigate the occurrences of hypoxia and harmful algal blooms.

6.6 Case Studies A. The Chesapeake Bay, the United States’ largest estuary, holds a significant proportion of nutrients. Each year, the Susquehanna River contributes loads of nitrogen (41%) and phosphorous (25%) to the Chesapeake Bay. Three large reservoirs present at the lower end of the river have been protecting this area

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from nutrient leakage, for decades. In 2012, the misfunctioning of the reservoir behind the Conowingo Dam resulted in a nutrient overload followed by the creation of a Dead zone that ultimately suffocates the marine life, reported by the U.S. Geological Survey (USGS). Given the current overloading of the waterways, the situation is expected to get worse in the coming days. However, measures like lowering the sediment as well as nutrient pollution upstream of the Dam, green roof, rain barrel, or rain garden installation for capturing and absorbing rainfall, etc., can benefit the health of the bay. B. Water near the bottom of the northern Gulf of Mexico, an area stretching around the Louisiana-Texas coast contains less than two ppm of dissolved oxygen that contributes to hypoxia, which was first documented in 1972. The size of the hypoxic zone (measured each summer) is an important indicator of the approaches taken to reduce nutrient inputs into the Gulf. The 2021 measurement shows that The Gulf of Mexico dead zone is approximately 6,334 square miles decreasing around 2,442 from the maximum recorded value of 8,776 square miles in 2017 (EPA, Northern Gulf of Mexico Hypoxic Zone). This condition damages important commercial fisheries in the region over the long term by disrupting the food webs and impacting organisms at all trophic levels. Over the last years, the discharge of the Mississippi River system (a major source of freshwater and nutrients into the region) is controlled so that 30% of flow can be directed seaward through the Atchafalaya River delta and the rest 70% through the Mississippi River birdsfoot delta. This along with additional measures is expected to combat the problem of spreading dead zones across the Gulf of Mexico.

6.7 Conclusion The coastal system of the hydrosphere plays an important role in maintaining world biodiversity. The coastal environment is very sensitive and complex. Global warming, increasing population, and human interference in the ecosystem disturb the balance of the ecosystem. One such issue is nutrient over-enrichment which leads to eutrophication, algal bloom, hypoxic and anoxic conditions, and a set of problems that affect various life forms. Eutrophication caused by nutrient over-enrichment leads to problems of high complexity and extreme variability at different levels. Due to the presence of various issues like the complexity of sources rapid nutrient increase, etc., intertwined with different socio-political and socio-economic issues, making the problem is more acute. Hence the requirement of a multifaceted solution is of utmost importance involving coordinated efforts from the local, state, regional, and national bodies along with the participation of a diversified group of stakeholders. The involvement of people at various levels can be the only way to combat such a complex all-pervading problem (Fig. 6.6).

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Fig. 6.6 Major points to develop and put into the strategies to manage specific nutrients

1. Research scientists—(within academia, industry, and government) are responsible for conducting thorough studies and research, to give us a greater understanding of the problems and provide suitable solutions to those issues as seen in the modern-day environment. 2. Administrative bodies and various organizations—government implements certain rules and regulations to combat certain problems. Various government

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and non-profit organizations also help to monitor such situations and circulate advanced scientific understanding in simpler terms to create awareness among common people. Often, they act in support or oversight roles as the government works to ensure that local and state entities have the information needed to address environmental problems effectively. They also represent national priorities where they might conflict with local perspectives. They set policy and delegate specific legal and administrative powers to federal agencies. They also control the fiscal and human resources required to implement programs. 3. Coastal and watershed management—this directly or indirectly influences how coastal areas and watersheds are managed, by formulating strategies to deal with local or regional problems or through various permitting responsibilities. Their decisions significantly affect local and state economies.

References Breitburg, D., Levin, L.A., Oschlies, A., Grégoire, M., Chavez, F.P., Conley, D.J., et al. (2018). Declining oxygen in the global ocean and coastal waters. Science, 359(6371): 7240. Caperon, J., Cattell, S.A. and Krasnick, G. (1971). Phytoplankton kinetics in a subtropical estuary: Eutrophication. Limnology and Oceanography, 16(4): 599–607. Charpy-Roubaud, C. and Sournia, A. (1990). The comparative estimation of phytoplanktonic, microphytobenthic, and macrophytobenthic primary production in the oceans. Marine Microbial Food Webs, 4(1): 31–57. Cloern, J.E., Cole, B.E., Wong, R.L. and Alpine, A.E. (1985). Temporal dynamics of estuarine phytoplankton: a case study of San Francisco Bay. In: Temporal dynamics of an estuary: San Francisco Bay (pp. 153–176). Springer, Dordrecht. Dennison, W.C., Orth, R.J., Moore, K.A., Stevenson, J.C., Carter, V., Kollar, S. et al. (1993). Assessing water quality with submersed aquatic vegetation. Bioscience, 43(2): 86–94. Duarte, C.M. (1995). Submerged aquatic vegetation in relation to different nutrient regimes. Ophelia, 41(1): 87–112. EPA (1987). Quality Criteria for Water. Office of Water Regulations and Standards, Washington, Environmental Protection Agency. (n.d.). Northern Gulf of Mexico Hypoxic Zone. EPA. Retrieved October 25, 2021, from https://www.epa.gov/ms-htf/northern-gulf-mexico-hypoxiczone. Fourney, F. and Figueiredo, J. (2017). Additive negative effects of anthropogenic sedimentation and warming on the survival of coral recruits. Scientific Reports, 7(1): 1–8. Gold, A.J. and Sims, J.T. (2005). Eutrophication. Elsevier Inc., pp. 486–494. Hopes, A., Thomas, D.N. and Mock, T. (2017). Polar microalgae: Functional genomics, physiology, and the environment. In: Psychrophiles: From Biodiversity to Biotechnology (pp. 305–344). Springer, Cham. Howarth, R.W. Anderson, D.B., Cloern, J.E., Elfring, C., Hopkinson, C.S., Lapointe, B., et al. (2000). Nutrient pollution of coastal rivers, bays, and seas. Issues in Ecology, 7: 1–16. Ketchem, B.H. (1951). The exchanges of fresh and salt waters in tidal estuaries. Journal of Marine Research, 10: 18–38. Kinsey, D.W. and Davies, P.J. (1979). Effects of elevated nitrogen and phosphorus on coral reef growth 1. Limnology and Oceanography, 24(5): 935–940. Marubini, F. and Davies, P.S. (1996). Nitrate increases zooxanthellae population density and reduces skeletogenesis in corals. Marine Biology, 127(2): 319–328.

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McComb, A.J. (1995). Eutrophic shallow estuaries and lagoons. CRC press. Moore, C.M., Mills, M.M., Arrigo, K.R., Berman-Frank, I., Bopp, L., Boyd, P.W., et al. (2013). Processes and patterns of oceanic nutrient limitation. Nature Geoscience, 6(9): 701–710. Muscatine, L. and Porter, J.W. (1977). Reef corals: mutualistic symbioses adapted to nutrient-poor environments. Bioscience, 27(7): 454–460. Nixon, S.W. (1981). Remineralization and nutrient cycling in coastal marine ecosystems. In: Estuaries and nutrients (pp. 111–138). Humana Press. Nixon, S.W. (1992). Quantifying the relationship between nitrogen input and the productivity of marine ecosystems. Proceedings Advances in Marine Technology Conference, 5: 57–83. Nixon, S.W. (1995). Coastal marine eutrophication: a definition, social causes, and future concerns. Ophelia, 41: 199–219. Nixon, S.W. (1998). Physical energy inputs and the comparative ecology of lake and marine ecosystems. Limnology and Oceanography, 33(4): 1005–1025. OECD (1982). Eutrophication of Waters. Monitoring, Assessment, and Control, Paris: Organisation for Economic Co-Operation and Development 1982, pp. 154. Pedersen, M.F. and Borum, J. (1996). Nutrient control of algal growth in estuarine waters. Nutrient limitation and the importance of nitrogen requirements and nitrogen storage among phytoplankton and species of macroalgae. Marine Ecology Progress Series, 142: 261–272. Pitchford, J.W. and Brindley, J. (1999). Iron limitation, grazing pressure, and oceanic high nutrientlow chlorophyll (HNLC) regions. Journal of Plankton Research, 21(3): 525–547. Sand-Jensen, K. and Borum, J. (1991). Interactions among phytoplankton, periphyton, and macrophytes in temperate freshwaters and estuaries. Aquatic Botany: 41(1-3): 137–175. Seitzinger, S.P. (1988). Denitrification in freshwater and coastal marine ecosystems: ecological and geochemical significance. Limnology and Oceanography, 33(4 part not2): 702–724. Seitzinger, S.P. and Giblin, A.E. (1996). Estimating denitrification in North Atlantic continental shelf sediments. In Nitrogen cycling in the North Atlantic Ocean and its watersheds (pp. 235–260). Springer, Dordrecht. Yentsch, C.S. and Phinney, D.A. (1989). A bridge between ocean optics and microbial ecology. Limnology and Oceanography, 34(8): 1694–1705.

Chapter 7

Organic Pollution

7.1 Introduction From the use of fertilizers to the burning of oil and petroleum, various sources contribute to waste in the form of effluents. These effluents contain a large portion of organic compounds like nutrients from fertilizers, persistent organic pollutants (POPs), suspended biogenic substances, etc. The presence of such compounds is detrimental to the environment including all flora and faunal ecosystem health.

7.2 Biochemical Oxygen Demand (BOD) 7.2.1 Background All natural water bodies contain a certain amount of organic matter which is dissolved or in suspended form in the water. The organic matter in water can be classified predominantly into four types based on their form and origin, such as bio-organic matter, dissolved organic matter, colloid organic matter, and aggregate organic matter. The bio-organic matters derived from organisms and plants act as a source for other organic compounds in the water. The dissolved organic matter (DOM) found within oceans, lakes, or streams is considered to be predominantly derived products of the decomposition of organic matter (coming from plants or animals) by microorganisms present in the water. Colloid organic matter and DOM are very important for aquatic ecosystems because of their high chemical activity. They may coalesce with each other or any inorganic matter to produce the fourth type of organic matter i.e., aggregate organic matter. Now, it is clear that the microorganisms (e.g., bacteria, fungi, etc.) that reside within the water help in decomposing the organic matter which they eventually use as supplements. In marine ecosystems, the solubility of dissolved oxygen happens to © Capital Publishing Company, New Delhi, India 2023 S. Mukherjee et al., Environmental Oceanography and Coastal Dynamics, https://doi.org/10.1007/978-3-031-34422-0_7

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Table 7.1 The solubility of oxygen (in mg l−1 ) across varying water temperatures and salinity in marine ecosystems (after Adams and Bealing 1994) Salinity

Temperature 0 °C

5 °C

10 °C

15 °C

20 °C

25 °C

30 °C

0

14.6

12.8

11.3

10.1

9.1

8.3

7.6

5

14.2

12.4

11.0

9.8

8.9

8.0

7.4

10

13.7

12.0

10.7

9.5

8.6

7.8

7.2

15

13.3

11.7

10.3

9.3

8.4

7.6

7.0

20

12.9

11.3

10.0

9.0

8.1

7.4

6.8

25

12.4

10.9

9.7

8.7

7.9

7.2

6.6

30

12.0

10.5

9.4

8.4

7.6

7.0

6.4

35

11.5

10.2

9.0

8.2

7.4

6.8

6.2

be a function of both water temperature and salinity (Table 7.1). The microorganisms use up the oxygen dissolved in the marine ecosystems to oxidize certain organic compounds and degrade them. In this very process, a certain amount of energy is released which is used by the particular microorganism for its growth, development, and reproduction. The amount of dissolved oxygen (DO) required by a population of aerobic microorganisms of a particular water sample in a specific temperature and time for the decomposition of organic matter is known as biochemical oxygen demand (BOD). It is proportional to the demand for the microbial metabolism of a certain population of a specific water system. Hence, an increase in the microbial population inevitably increases the BOD of a certain water body. Thus, the BOD value of a selected water sample can provide us with the measure of the organic pollution for that sample. The BOD test conceptualizes first as the measuring test of organic pollution for river water in 1908 after the formation of the Royal Commission on Sewage Disposal. Though the basic principle and the ideal temperature for carrying out the test were first proposed by the Commission in 1912, it is still relevant and practiced in a wide manner for testing organic pollution in water. The basic principle of BOD is to incubate the sample water in a closed system in absence of light for 5 days at constant 20 °C and the consumption of oxygen in the process is measured, which is the value of BOD for the given water sample. This test is known as the 5-days BOD test (expressed as BOD5 ). Similarly, the BOD value for a much longer incubation time is known as the Ultimate or Limiting BOD (expressed as BODL ).

7.2.2 Wastewater Quality Indicators Several laboratory tests are used as the standardized parameters to detect the quality of the disposed wastewater. These are known as wastewater quality indicators. These parameters work as a benchmark to determine whether wastewater is suitable for

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129

disposal or treatment or reuse. The type of wastewater and its origin determines which quality indicator test will be suitable for the waste. These laboratory tests measure different entities of sample wastewater: such as physical, chemical, or biological entities. Table 7.2 depicts the major types of wastewater. Table 7.2 A list of wastewater quality indicators Indicator type

Indicators

Remarks

Physical indicators

Temperature

Microbial growth requires a specific temperature range. Industry-generated waste may elevate the temperature. Thus, the temperature of the waste is measured, mostly in cases of waste originating from power stations or irrigation runoff. It is measured with a thermometer

Solids

Solids in water may either be in dissolved form or settled or suspended. The dissolved solids are termed Total Dissolved Solids (TDS). Settleable solids are measured by the volume of solids settled in the sample water. Total Suspended Solids (TSS) are the solids that cannot be filtered

pH values

The measure of the Hydrogen ion concentration in the wastewater Indian permissible limit for Inland surface, water Public Sewers, Land for irrigation, and Marine coastal areas is 5.5 to 9.0

BOD

The quantity of dissolved oxygen (DO) needed by a population of aerobic microorganisms of a particular water sample in a specific temperature and time for the decomposition of organic matter is known as BOD BOD5 : It is the BOD for 5 days incubated water, at 20 °C BODL : Ultimate or Limiting Biochemical Oxygen Demand

COD

The quantity of oxygen needs to process a chemical reaction in a sample fluid (e.g., Wastewater). It is also measured by mg l−1 unit, the same as BOD

Nitrogen (N)

It is a measure of total dissolved nitrogen in the form of nitrates and ammonia. Ammoniacal nitrogen (as N) in Indian standards for inland surface water, public sewers, and marine coastal areas is 50 mg l−1 The standard value of Nitrate Nitrogen for inland surface water is 10 mg l−1 and for marine coastal areas is 20 mg l−1

Phosphorus (P)

It is a measure of total dissolved phosphorus and phosphate in each sample of wastewater. Dissolved Phosphates (as P) in Indian standards for Inland surface water is 5 mg l−1

Chemical indicators

Biological indicators

There are different measures like the Bioassay test, Coliform index, Aquatic toxicology, and Whole Effluent Toxicity (WET) tests to measure the biological entities of a wastewater sample

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7.2.3 BOD as Wastewater Quality Indicators As discussed before, the BOD value is a measure of oxygen consumption for a specific water sample. Generally, the unit of this oxygen consumption is mg l−1 . It is used to assess the quality of wastewater and thus can be called a wastewater quality indicator. Royal Commission on Sewage Disposal in 1908, first used BOD as the definitive indicator of wastewater quality index. BOD is still the most effective yet simple method parameter to assess the degree of organic pollution. The global standard of BOD for municipal sewage (which has been treated with wastewater treatment processes) is 20 mg l−1 . Whereas untreated sewage would have a value of about 200 mg l−1 in the United States and about 600 mg l−1 in Europe.

7.2.4 Standard Values The permissible limiting value of BOD for all effluent discharges in India is 30 mg l−1 (Table 7.3). To describe the standard BOD value for India, Environmental Act 1986 says: All effluents discharge including from the industries such as cotton textile, composite woolen mills, synthetic rubber, small pulp and paper, natural rubber, petro-chemicals, tanneries, paint dyes, slaughterhouses, food and fruit processing, and dairy industries into surface waters shall conform to be BOD limit specified above, namely 30 mg l−1 . For discharge an effluent having a BOD more than 30 mg./l, the standards shall conform to those given, above for other receiving bodies, namely, sewers, coastal waters, and land for irrigation.

For river waters, the unpolluted river would have a BOD of about 1 mg l−1 (Table 7.4). When the BOD value ranges between 2 and 8 mg l−1 , the river is moderately polluted. If the value exceeds 8 mg l−1 , it is unanimously a severe condition of river pollution. The limiting BOD for Harbour waters (for 3 days incubation at 27 °C) is 5 mg l−1 (EPA 1986). Table 7.3 The permissible limit of BOD in India

Water type All effluent discharges Inland surface water

Permissible limit# (mg l−1 ) 30 30

Public Sewers

350

Land for irrigation

100

Marine coastal areas

100

# All

BOD values are obtained from 3 days incubation method at 27 °C Source EPA (1986)

7.3 Chemical Oxygen Demand (COD)

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Table 7.4 A list of global BOD permissible limits for different types of water bodies Water source

Typical BOD values* or permissible limit (mg l−1 )

Clean natural waters

8

Run-off water

10–15

Municipal sewage water (treated)

20,000 tons) for controlling locust outbreaks by the locals. This qualifies as a major source for POPs

Poland

• Agriculture sector (commonly used pesticides are HCB, Aldrin, dieldrin, toxaphene, etc.) • Manufacturing • Fuel and wood combustion

Great Lakes of • According to the USEPA, PCB is excessively present in these areas America • Population pressure and rapid industrial growth are also reasons for the excess amount of POPs Mediterranean • This area also experiences extreme population pressure sea • Other crucial reasons for such presence are: 1. Urbanization 2. Industry 3. Energy generation and.consumption 4. Transportation systems 5. Tourism and recreation 6. Agriculture, fisheries 7. Forestry and mining Atlantic ocean • Like the above-mentioned places, heavy population pressure along with rapid industrial and agricultural expansion is the reason for POPs to be present here • Commonly found chemicals are PCB, HCB, Taxaphene, Aldrin, etc. Polar regions

• In the cold climate of the Arctic and Antarctic, low evaporation rates trap POPs resulting in their entry into the food chain

8.12 Conclusion

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8.9 Environmental Impacts of POPs The POPs leave disastrous signatures in several strata of the ecological food chain including human beings. The endocrine and reproductive systems are severely impacted by these compounds (Damstra 2002). It even leads to several types of abnormalities among newborns (Dewan et al. 2013). Several types of embryogenic defects are observed among the wildlife faunas due to the POPs (Table 8.6). Overall, the ecological balance of the environment can be severely jeopardized due to the presence of these lethal compounds beyond a certain threshold.

8.10 Silent Spring—The Book Silent Spring is the book that spread the seed of the global grassroots of the environmental movement. Released in 1962, the book deals with the aftermath of the use of harmful chemical pesticides like DDT in the then US agriculture. Marine biologist by profession, Rachel Carson and her work began initiating a shift in global environmental consciousness. Her work is said to be the reason behind the establishment of the UP Environmental Protection Agency. Silent Spring carries an important message which is still relevant in today’s era. We, humans, are an integral part of the environment and are highly dependent on the ecosystem around us. Thus, disregarding the protection of the environment is sheer stupidity. Her approach to shedding the light on the naked truth through her book still inspires youth and activists around the world today.

8.11 Remedies To control the extensive usage of pesticides, several remedies have been adopted following the instructions of several international conventions. A general list of such remedies is listed in Table 8.7.

8.12 Conclusion Pesticides, for a prolonged time, have played a significant role in various sectors like agriculture, manufacturing, etc. though in the initial years their negative impacts were not identified, due to clear pieces of evidence and an advanced analytical approach they were identified as toxic. Rachel Carson in her book Silent Spring talked about the negative impacts DDT has on birds that are eventually responsible for their mortality resulting in decreased abundance of birds in natural environments. Not only the avian

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Table 8.6 Impact of POPs on human health, wildlife, and the overall environment On human health Effect

Mechanism

Endocrine disruption

• Teratogenic effects due to exposure during critical developmental periods impair their organ development • Along with these POPs inhibit endocrine disruption in human bodies

Reproductive system

• For male reproductive systems: reduction in quantity and quality of sperm, sex ratio alteration, early onset of puberty • For female reproductive systems: endometriosis, reproductive tissue alteration, disruptive pregnancy outcomes

Gestational weight gain and newborn head circumference

• Exposure to PCBs is found to lead to birth weight, gestational age, and head circumference in infants • Impaired fetal growth, reduced birth weight as well as head and chest circumference upon exposure to HCH, DDT, and DDE

On wildlife • • • • • • • • • •

Behavioral abnormalities in wildlife species Physiological damage like Crossed beaks, clubfoot, tumors, etc. Disruption of the immune system of faunal species Impairment of reproductive system among birds: Reduced or slow egg production, increased embryo mortality, thinner eggshells, embryonic defects, slow egg growth and hatching POPs tend to get accumulated in the lipid tissues of aquatic animals and hence enter into the food chain

On overall environment • Ecological imbalance • Disruption of natural habitats of Amphibian, Pacific Salmons, Sea Turtles, American Eagle, etc. • Bioaccumulation and biomagnification, on one hand, increase the levels of toxicity among organisms and on the other hand disrupt their abundance in the natural environment

species but others like amphibians, mammals, and plants are also equally susceptible to their negative impacts. Over time several international organizations have also identified these harmful chemicals and how can countries take appropriate measures for their mitigation. For this, though a significant amount of restrictions were implied for their controlled usage, in the future more strict measures are to be taken for a better result.

References

149

Table 8.7 A list of international conventions concerning the remediation of POP’s impact on the environment Name of the convention

Year Aims

The Vienna convention

1989 • Banning production and use of the ozone-depleting substance and protecting the ozone layer • POPs are identified to be in this category

Basel convention

1992 • Protect human health and the environment against hazardous and other wastes • POPs are identified to be in this category

Convention on Long-Range Transboundary Air Pollutants (LRTAP)

2003 • To reduce POPs. And to control and eliminate its discharges and emissions

Globally Harmonized System (GHS) 2003 • Promoting classification of chemicals based on for classification and labelling of health, physical and environmental hazards chemicals Stockholm convention

2004 • Reduce the release of POPs chemicals on a global basis

Rotterdam convention

2004 • Promote shared responsibilities concerning the importation of hazardous chemicals and contribute to safe use

International convention on the control of harmful Anti-fouling systems on ships

2008 • Prohibition of usage of organotin in anti-fouling paints

References Damstra, T. (2002). Potential effects of certain persistent organic pollutants and endocrine-disrupting chemicals on the health of children. Journal of Toxicology: Clinical Toxicology, 40(4): 457–465. Dewan, P., Jain, V., Gupta, P. and Banerjee, B.D. (2013). Organochlorine pesticide residues in maternal blood, cord blood, placenta, and breastmilk and their relation to birth size. Chemosphere, 90(5): 1704–1710. El-Shahawi, M.S., Hamza, A., Bashammakh, A.S. and Al-Saggaf, W.T. (2010). An overview on the accumulation, distribution, transformations, toxicity, and analytical methods for the monitoring of persistent organic pollutants. Talanta, 80(5): 1587–1597. Fernández, P. and Grimalt, J.O. (2003). On the global distribution of persistent organic pollutants. CHIMIA International Journal for Chemistry, 57(9): 514–521. Jiménez, J.C., Dachs, J. and Eisenreich, S.J. (2015). Atmospheric deposition of POPs: Implications for the chemical pollution of aquatic environments. Comprehensive Analytical Chemistry, 67: 295–322, Elsevier. Nieder, R., Benbi, D.K. and Reichl, F.X. (2018). Health risks associated with organic pollutants in soils. Soil Ccomponents and Human Health, pp. 575–657, Springer, Dordrecht. O’Sullivan, G. and Megson, D. (2014). Brief overview: Discovery, regulation, properties, and fate of POPs. Environmental Forensics for Persistent Organic Pollutants, pp. 1–20. Elsevier. Safe, S.H. (2000). Toxicology of persistent organic pollutants. European Journal of Lipid Science and Technology (Germany), 102(1): 52–53.

Chapter 9

Heavy Metals

9.1 Introduction Heavy metals are found naturally in the earth’s crust; however, humankind has put these metals into use ever since the industrial revolution for multifarious purposes. Mining activities unearthed these metals and introduced them into the open environment. Presently, almost all the nooks and corners of the world exhibit heavy metal contamination of some sorts. . Heavy metals can be defined as a group of metals and semimetals (metalloids) associated with contamination and potential toxicity or ecotoxicity (Tchounwou et al. 2012). . Several metallic components if introduced to organisms may cause significant deterioration of body functions and hence qualify as toxic metals distributed through different pathways. . Metals are being used widely in various industries and in daily usage products (Alves et al. 2016). Though they have wide spectrum utilities without proper recycling metal wastes add to a serious level of toxicity in the environment (Fig. 9.1).

9.2 General Principles of Metal Toxicity Many heavy metals are toxic and exhibit toxicological effects on floras and faunas. These heavy metals easily bio-accumulate in several species through the ecological food chain and bio-magnify in higher life forms. . The toxicity of metal increases with the increase in atomic number and electropositivity (Enache et al. 2000). . Among metal salts the toxicity rises as the following sequence:

© Capital Publishing Company, New Delhi, India 2023 S. Mukherjee et al., Environmental Oceanography and Coastal Dynamics, https://doi.org/10.1007/978-3-031-34422-0_9

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Fig. 9.1 A schematic diagram showing the pathways through which heavy metals are introduced into the open environment

Nitrates