Wetlands Ecology: Eco-biological uniqueness of a Ramsar site 303109252X, 9783031092527

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Susanta Kumar Chakraborty Poulomi Sanyal Ratnadeep Ray

Wetlands Ecology Eco-biological Uniqueness of a Ramsar Site (East Kolkata Wetlands, India)

Wetlands Ecology

Susanta Kumar Chakraborty • Poulomi Sanyal Ratnadeep Ray

Wetlands Ecology Eco-biological Uniqueness of a Ramsar Site (East Kolkata Wetlands, India)

Susanta Kumar Chakraborty Department of Zoology Vidyasagar University Midnapore, West Bengal, India

Poulomi Sanyal West Bengal Pollution Control Board Kolkata, West Bengal, India

Ratnadeep Ray JIS University Kolkata, West Bengal, India

ISBN 978-3-031-09252-7    ISBN 978-3-031-09253-4 (eBook) https://doi.org/10.1007/978-3-031-09253-4 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

To all of researchers, environmental planners and activists including common peoples who contributed selflessly for the cause of the ecology of wetlands – the most threatened landscape of the world.

Justification for Writing This Book

Wetland, as “lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water” represents one of the most productive, sensitive and fragile ecosystems of the world. The existence of human civilization is directly connected with the wetlands as this gift of nature provides many ecosystem goods (food, fodders, fuels, medicines and ingredients for building materials) and services (sources of water for human consumption, fresh air loaded with profuse oxygen, accumulation and conversion of wastes into nutrients for the ecosystem, acting as buffer against flood, recharging of ground water, combating of natural disaster by absorbing the initial thrust of the hazards and carbon sequestration for the mitigation of problems due to climate change). In such context, more research-based information is needed on multidimensional aspects of the structure and functions of the wetland ecosystem in order to not only make peoples aware of the necessity of undertaking measures to protect this wonderful gift of nature bur presently the most threatened landscape of the world mainly because of the ignorance and lack of seriousness towards the conservation of this ecosystem along with its resources, both non-living and living ones. Ecology, being an emerging interdisciplinary subject that deals with the study of the interrelationship between species and their environment, involving so many thrust areas such as trophic interactions and flow of energy, microbial decomposition coupled with nutrient cycling, population interaction within the biotic community, resilience and ecological integrity in the functioning of an ecosystem, bio-monitoring and bioremediation as the prerequisite for eco-restoration of eco-­ degraded ecosystem, plant-herbivore interacting systems, evolution of pesticide-­ resistant strains, understanding of the pathways of the eco-toxicological effects of toxic pollutants on biota, and so on, is now being used as an enormously applied scientific field to tackle different environmental issues. In view of the above points, attempt has been made in this book to highlight the eco-­biological uniqueness of a wonderful ecosystems of the world, the East Kolkata Wetlands (EKW), a Ramsar Site in India which earned international recognition because of its potential for natural recycling of both solid and liquid wastes released by the municipal and industrial activities of the Kolkata Metropolitan City in the vii

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state of West Bengal, India. The emphasis throughout this book is on to the practical application of ecology with the prime objective of explaining and interpreting the ongoing ecological processes within wetland ecosystem in general and East Kolkata Wetlands (EKW) ecosystem in particular. The book, alongside emphasizing more on eco-biological uniqueness of the EKW and the scope of applying of GIS and remote sensing methods in the eco-assessment of the same wetland in the backdrop of multidimensional aspects of wetland ecosystem in national and international perspectives, has tried to accommodate as far as possible several pertinent components (basic terminologies and ecological principles relevant to wetland ecosystem, ecosystem services and values, diversity and classificatory schemes of wetlands, ecodynamics of biodiversity, pollution and other environmental stresses, bio-monitoring and bioremediation, sustainable eco-management and conservation strategies) centring around the wetland ecosystem. An integrated and interdisciplinary approach towards unravelling the mysteries of ecosystem dynamics of wetland ecosystem will certainly enable chalking out holistic conservation strategies for wetland ecosystem involving local peoples, stakeholders, environmental planners, administrators and researchers towards sustainable future of wetlands in general and EKW in particular. This book reviews the current scientific developments through several case studies on EKW in order to understand the present ecological status of this Ramsar site along with its ecological past so that all such information can become available and useful for the sustainable management of this wetland ecosystem by ascertaining society to learn more about the evil effects of ongoing perturbation that is going to pave the way for resulting an uncertain future. From this book, readers are expected to get readily available information on the contrasting ecological conditions of wetlands across the world with more emphasis on the Indian scenario with special reference to EKW in the face of ongoing threats from pollution and other human-mediated developments (drastic alteration of land use patterns, intensification of agriculture with more chemical inputs, population explosion coupled with uncontrolled urbanization and industrialization) and also to understand the basic underlying ecological principles for undertaking sustainable eco-management strategies. Midnapore, West Bengal, India Kolkata, West Bengal, India 

Susanta Kumar Chakraborty Poulami Sanyal Ratnadeep Ray

Preface

It should be moral imperative that human society should refrain from ravaging other living organisms along with their habitats. The subject of conservation biology, being the core subject component of environmental science has emerged during the last few decades to deal the maintenance, protection and preservation of the diversity of species along with their habitats, and, therefore must ensure sustainable utilization of natural resources adhering to the basic scientific principles of ecology in such a way so that alongside satisfying the needs of the moment, the natural resource bases should be kept in reserve as not to deprive the future generation from all such gifts of nature. Keeping these two messages in mind, the need of the hour is to devise sustainable conservation strategies for the very productive, sensitive and fragile wetland ecosystem against the changing agro-climatic, cultural and sociopolitical milieu. Wetlands, a transitional eco-zone in between terrestrial and open water systems, include many varied forms of water bodies having some common characteristics, and such unique aquatic ecosystems render valuable ecological services to human beings and offer favourable ecological set up for the growth and proliferation of innumerable biological organisms. However, human intervention in different forms has threatened this landscape to a considerable extent, especially by way of jeopardizing the natural biogeochemical cycles of different categories which operate within the wetlands across the world. Alongside disrupting different beneficial contributions to human beings, the deteriorating ecological conditions of wetlands also ruin the regional, national and global biodiversity. All these have necessitated to undertake proper eco-restoration measures to revive the eco-degraded wetlands environment and also to adopt appropriate conservation strategies to ensure sustainable development by way of judicious understanding of resource availability. The optimum modes of harvest of research information through systematic research and through proper community outreach program emphasizing the eco-potential of wetlands also facilitate the conservation of wetlands. Besides, the prime thrust area in multidimensional aspects of wetlands research during the last few decades revolves around one of the most precious resources of the world, that is, water, and the maintenance, protection and preservation of both ix

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the quantity and quality of water (the main structural component of wetland ecosystem) have become a sharp focus in the present global scenario. In the backdrop of all such conditions, the challenge of global water conversation has taken a new turn relying on increased informational access reaching to a point from where it becomes impossible to ignore the scarcity of the resource. The countries having achieved such successes mainly adhered to four principal guidelines: (i) Water management after being considered as critically significant proposition in any developmental plan is taken care of by different tiers in the administrative managers (from higher to lower level) through adopting proper in science and technology; (ii) development and utilization of appropriate and well-maintained infrastructures; (iii) creation of large pools and water bodies based on ground truth research information derived from right planning, development, operation and maintenance with the prime aim to ensure effective and successful water management at all levels; and (iv) water-use behaviours across the spectrum from household and municipal activities to agricultural and industrial activities should be given more emphasis. Considering water governance being complex and multisectoral, dynamic processes rely on science, technology and socio-ecological system involving generated inputs from continuous learning and building up the capacity to adapt effectively to unpredictable outcomes. Three components can be identified as far as water management and governance are concerned: (i) old and traditional forms of governance in all spheres of human life (public and private sectors) which have become increasingly ineffective; (ii) the newer tactical policy of governance which is likely to be devised involving much broader range of active actors, starting from top environmental administrators to ground level peoples for redesigning and reshaping of conservation strategies over the next few decades; and (iii) instead of only fixing up and vesting permanent allocations of power in the hands of those in senior positions in the environmental management hierarchy, direct involvement and active participation of the stakeholders are needed in order to achieve the desired goals. Biodiversity, being the prime resource base of any wetland ecosystem, has become a buzzword across the world which caters to the basic needs of human beings by supplying food, medicine, clothing and sheltering materials. Biodiversity-­ mediated ecosystem service after assuming renewed momentum during the last century all over the world has prompted the resource managers to attach more importance on the incorporation of socioeconomic aspects in evaluating the roles of biodiversity study in respect of ecosystem services in a given ecosystem. Being such a precious gift of nature, loss of biodiversity has been continuing both at regional and global scales, which has necessitated to connect the goal of sustainable development with the attainment of newly developed concepts and methodologies pertaining to the assessment, monitoring and holistic management of biodiversity. This eco-management venture for conserving biodiversity is only possible by integrating the scientific and socioeconomic components which can safeguard natural habitats for biodiversity such as wetlands and result in sustainable conservation. The true cost on account of the momentum of industrialization during last couple of

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centuries is being paid by the resource bases of the wetlands which has contributed profusly in shaping and structuring contemporary human lifestyle. All of such developments have not only disrupted the balance of cause and effect but also surpassed the assimilation capacity of nature. The buffer against such undesirable and uncontrolled changes in this modern high-tech industrial society is to filter the information of the ongoing state of environmental deterioration, which began in the recent past due human lifestyles. This pace of developments across different developing countries like India has harmed considerably the functioning of so many wetland ecosystems of international significance. The East Kolkata Wetlands (EKW), having a network of more than 100 water bodies, is located in the eastern fringe of Kolkata (erstwhile Calcutta) in the state of West Bengal, and is internationally acclaimed due to its potential for waste water recycling and resource recovery systems. Non-judicious exploitation of the natural resources within EKW during last seven decades has shocked peoples not only of the region but all over the world. The short-sighted environmental planning resulting bleak ecological prospect of this network of wetlands had testified the unprecedented loss of resources for several decades without any doubtely as evident from the verdict of statistics. The green coverage around the wetlands has been considerably reduced by harvesting of plant resources, acidification by rain, accumulation of eroding products and salts, increase in turbidity and hardness, pollution of water by sewage, development of eutrophication; receiving of waste water from industrial and agriculture activities, and deposition and loading of gases and particulates coming out from the exhaust of cars, furnaces and factories etc. However, owing to years of hard work driven by judicious management strategies, new progress can rise up from these ashes. This can be achieved by taking small steps in understanding the problems and finding out appropriate mitigation strategies with the integration of political will coupled with appropriate economic means. In order to successfully realise the goal, one must properly understand the functioning of natural wetland ecosystems and also the scopes of using wetlands to remove wastes through recycling. The first question is to see whether wetland ecosystems powered by sunlight can handle toxicity more efficiently and successfully than any other system running on fossil fuel. Considering all these components, it can be inferred that information pertaining to the potential, utilization, destruction, pollution, eco-degradation and drastic decline of East Kolkata waste-purifying wetland ecosystems resonate ever more strongly with a number of global challenges such as airborne deposition of toxic pollutants, which may not be treated as a regional phenomenon, instead it can become of a national as well as international phenomenon. Sustainable environmental management encompassing “green growth” offers a broad range of social, environmental and economic benefits especially through increased supply of water not only in respect of quantity but also with improved water quality, reduced health risks and water restrictions. All such attributes command ecological reserve requirements and enhance ecosystem service provisioning, by promoting water reuse and recycling, and all of which are supposed to render holistic benefits by reducing the economic losses due to environmental degradation, improved environmental

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accounting, well-timed infrastructure investments and the creation of green jobs in areas such as ecotourism and sustainable fisheries. Conservation constituting the core of environmental science tends to maintain and protect the diversity of species and habitats, for successfully and sustainably using natural resources, with the options of providing future generations optimum resource bases after being driven by moral imperative with the message that humanity should harm the nature by needlessly destroying her wealth of both living and nonliving components. Governance of wetlands are important for eco-management of wetlands which under multiple pressures have become the threatened landscape of the world. It is hoped that the readers will be attracted, persuaded, inspired and enriched by the discussions of the multidimensional issues pertaining to wetlands in general and eco-biological uniqueness of East Kolkata Wetlands (EKW), a Ramsar site in India, in particular. The intention of this book is to pool some salient ideas around the thinking of wetlands, their present ecological status, ongoing perturbation, and related contributing factors, governance, management and conservation by tackling current messages from global arena to a local reality, from within the much studied East Kolkata Wetlands to other numerous wetlands and watersheds that fall under various environmental and managerial categories with the active involvement of end users, the government, private sector, civil society, beneficiaries, stakeholders and local peoples Well-managed water systems can become important drivers for economic growth, particularly in highly populated countries that experience adversity in providing much needed scopes for ensuring sustainable water management of natural water bodies having their own structural components, both biotic and abiotic, maintaining the required ecological health. Different chapters of this book are expected to deepen the holistic understanding of the readers about the functioning of wetland ecosystems which by virtue of resiliency can realign and reorganize to accommodate the burdens associated with different natural and anthropogenic threats. The book’s chapters are based on the existing current knowledge as well as the authors’ experience working on the ecology, GIS and remote sensing, biodiversity, pollution, eco-monitoring and conservation of wetland ecosystems. The target audience of this volume ranges from academics (students, researchers and teachers), technologists and engineers to environmental decision-makers and managers and certainly for policymakers and deep thinkers. The book, with a total of 11 chapters, is robustly conceived and well-organized. Wetlands: Ecology: Eco-biological Uniqueness of a Ramsar Site (East Kolkata Wetlands, India) is divided into 11 chapters including an elaborate introductory 1st chapter and a conclusion as the 11th chapter. The first four chapters (Chapters 1, 2, 3 and 4) explain the basic facts of wetlands including general terminologies, ecology, diversity and classification, values of wetlands in general in the perspective of a tropical country like India. The fifth (5th) chapter explores the uniqueness of East Kolkata Wetlands (EKW) followed by an in-depth analysis on the GIS and remote sensing and their applicability in the eco-assessment of wetland ecosystem with special reference to EKW with several case studies in Chapter 6. The seventh chapter (7) discusses several hypothetical and practical aspects of wetland biodiversity

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with special reference to EKW. Chapter 8 focuses on environmental perturbation and pollution on wetlands across the world in general and EKW in particular. The ninth (9th) chapter attempts to highlight the scopes and methods of applicability of bio-monitoring and bioremediation methods in the eco-management of wetlands citing a number of case studies. Chapter 10 has tried to elaborately explore several dimensions of sustainable management of wetlands ecosystem whereas the last chapter (Chapter 11) as conclusion summarizes the pertinent discussions on multidimensional issues on wetlands which have been elaborated in this book. This book can be a knowledge trove for students, researchers, social workers, politicians, environmental planners and administrators around the globe and is expected to fill up the existing lacunae in the realm of wetlands study and research, venturing to open up a new window for understanding potential, possibilities, prospects and challenges in the understating of eco-potential and ecodynamics of wetlands of India in general and E.K.W. in particular. This book also discusses varied challenges that most countries of the world encounter with regard to governance and conservation issues, highlighting the advantages and disadvantages of various approaches in order to ensure effective and sustainable ecological management of wetlands. It satisfies the need for an interdisciplinary effort by bringing together research communities from different disciplines and practitioners at different levels to exchange and share experiences and research outcomes with an eye to formulate frameworks, policies and perceptions towards successful conservation. Students and researchers having advanced options with the applications of modern methods and techniques to unravel the mysteries of wetland ecosystem in the universities and colleges as part of their course curricula in several basic and applied science subjects such as such ecology, geography, geology, remote sensing and GIS, life sciences, chemistry, agriculture, environmental science, and even civil engineering can develop necessary foundations upon which their knowledge of the relevant subjects can be built up Such developed knowledge bases might certainly trigger their interest for pursuing more complex and detailed study on the topics of their interest. The multidisciplinary nature of the book is supposed also to fulfil the interest of intended audience who may not have any specialist knowledge of any conventional subjects. It is also expected that the readers will be able to work out potential applications of the field, of one’ s own choice in going through not only the text but also following up the references. It is imperative that no single book can cover in depth full range of the multidimensional aspects of science of ecology and practice of conservation, especially in view of rapidly changing perspectives of environmental sciences against specific cultural and policy backgrounds which have been undergoing faster changes. Midnapore, West Bengal, India Kolkata, West Bengal, India 

Susanta Kumar Chakraborty Poulami Sanyal Ratnadeep Ray

Acknowledgement

The challenges for undertaking appropriate conservation strategies for the protection and preservation of wetlands in general and East Kolkata Wetlands in particular, a Ramsar Site in India, have reached a climax due to an unoptimistic future of the precious gift of nature in view of the ongoing environmental perturbation on this very sensitive, fragile, ecologically potent, biologically productive and aesthetically celebrated ecosystem. The competition among users and stakeholders with respect to their narrow interest, coupled with different forms of human-mediated pollution threats including global climate change, has aggravated the problems, pushing so many indigenous and endemic species of aquatic biota to the brink of extinction, resulting in loss of entire wetland ecosystems. In such context, the idea of writing this book was conceived to present the required interpretations of the ongoing ecological changes in the wetland ecosystem, highlighting the basic fabric of ecosystem functioning, representing an acceptable analysis of the classificatory schemes to segregate different categories of wetlands based on their own distinct characteristics and contrasting ecological features with other such habitats, and discussing approaches towards shifting from techno-centric to eco-centric eco-management strategies or hybrid concept to peoplecentric conservation efforts. All chapters of this book are based on the existing knowledge base of the subject from international perspectives which have been blended with the authors’ own research experience in this field citing several case studies and using nontechnical jargon in order to reach a wider audience. The target readers of this book are expected to include students of both undergraduate and post graduate courses of almost all disciplines of physical, chemical, biological, environmental, and social sciences, environmental planners, technicians, administrators and decision-makers, and deep thinkers for the cause of environment in general and wetland ecosystem in particular The tireless efforts of many friends, well-wishers, senior advisers and junior researchers with their commitments have made the publication of this book possible, and the authors extend thanks and gratitude to all of them. The authors are grateful to the authority of Vidyasagar University at Midnapore (West), West Bengal, India, for providing the necessary facilities. Writing of this book would not have been possible

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without the generous support of Springer Publication House, Springer Nature Switzerland AG, Gewerbestrasse 11, 6330 Cham, Switzerland, especially Mr. Aaron Schiller, Ms. Amrita Unnikrishnan, Ms. Michelle Harding and Ms. Sripriya Subramanian who acted as the driving force through their helpful attitude all through the process of writing this book, entitled, Wetlands Ecology: Eco-biological Uniqueness of a Ramsar Site (East Kolkata Wetlands india). This book comprises 11 chapters, including 1 elaborate conclusion. The first four chapters have highlighted some basic facts and operating ecological principles to ensure proper ecosystem functioning and also to maintaining of the ecological integrity of wetland ecosystem along with presenting the pictorial representation of diversified forms of wetlands in India, a transparent classification of schemes and values of wetland ecosystems. The fifth and sixth chapters, apart from projecting the uniqueness of the East Kolkata Wetlands ecosystem, a Ramsar Site in India, have also discussed at length the scope of applicability of remote sensing and GIS methods to understand the eco-dynamics of the East Kolkata Wetlands ecosystem, citing some case studies. The last four chapters have dealt with the biodiversity, pollution and threats to wetlands, biomonitoring and bioremediation with an elaborate analysis of prospective eco-management of wetlands to achieve sustainable conservation. The first author is thankful to a number of research students, Md. Abdullah, Santu, Sankarson, Santanu, Ram, Hirulal, Srinjana, Kishalay, Manjishtha, Sangita, Subhasree, Sujoy, Sayan, Arundhati, Anindita, Jayanti, Joydev and Ashim, for their active support throughout the entire period of this book’s preparation. Also, the authors thank Mr. Jagadish Mahata, supporting staff at Vidyasagar University, for his help in typing and formatting, and the valuable services rendered by the wife of first author, Prof. (Mrs.) Jhuma Chakraborty, and Ms. Tilottoma Chakraborty, student cum cousin of the first author, are thankfully acknowledged. The authors are indebted to a number of their co-authors of several research papers, and many of them happen to be PhD students and co-supervisors of PhD students of the first author  who are Dr. Phanibhusan Ghosh, former scientist at Wetland Research Institute; Dr. (Mrs.) Priyanka Halder Mallick, Associate Professor of Zoology, Vidyasagar University; Dr. Ashish Kumar Paul, Professor of Geography, Vidyasagar University and Dr. Nandan Bhattacharrya, Assistant Director, Academic Staff College, Jadavpur University, Kolkata, West Bengal, India. The authors acknowledge with gratitude the contribution of several natural scientists and well-wishers by providing several photographs of wetlands to make the book more attractive and presentable, and they are Dr. Subrata Beddatta (fishing cat), Scientist, Bombay Natural History Society Mumbai, India; Mr. Santu Paria, Research Scholar, Department of Zoology, Vidyasagar University, Midnapore, West Bengal, India (a number of small mammals, snakes, and landscapes); Md Abdullah-Al Helal (Research Scholar, Department of Zoology, Vidyasagar University, Midnapore, West Bengal (a number of amhibia, wetland plants and landscapes); Mr. Arnab Chatterjee, Research Scholar, Wildlife Research Institute India, Dehradun, Uttarakhand, India (a number of aquatic birds of prey and wetlands of Uttarakhand and Himachal Pradesh); Dr. Sagar Acharya, Assistant Professor of Zoology, Vidyasagar University, Midnapore, West Bengal, India (landscapes of wetlands at Bharatpur, Rajasthan); Dr. Suman

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Pratihar, Associate Professor of Zoology, Sukumer Sengupta Mahavidyalay, Keshpur, Midnapore (West), West Bengal, India (landscapes of wetlands at Arunachal Pradesh, Amarnath, Sikkim and Darjeeling in West Bengal, India); Mr. Nirmalaya Shee, Assistant Professor, Darjeeling Government College, Darjeeling, West Bengal (a number landscapes of wetlands of Darjeeling District, West Bengal, India); Mr. Moulick Sarker, Research Scholar, Wildlife Research Institute of India, Dehradun, Uttarakhand, India (landscape of wetlands of Uttarakhand, India); Dr. Bulganin Mitra, Retired Scientist, Zoological Survey of India (landscapes of Navegao reservoirs of Mumbai, Chilaka of Odisha and one spring from Tamilnadu); Dr. Hariprasad Sarker, Principal of Garbeta College, West Midnapore, India (landscapes of Dal Lake); Mr. Subimal Banerjee, Retired Bank officer, Government of India, (landscapes of Nagarjun Sagar reservoirs in the state of Telangana, India); Dr. Jayanta Kundu, Professor of Zoology, Vidyasagar University (Landscapes of Ladakh, India); Dr. Samaresh Samanta (Research Scholar, Department of Zoology, Vidyasagar University (landscapes of wetlands of Kerala); Mr. Sankarson Roy, Research Scholar, Vidyasagar University (landscape of Sahebband, Purulia, West Bengal, India); Dr. Soumen Bhattacharya, Professor of Zoology, North Bengal University (landscapes of wetlands of Assam, India); Dr. Suniti Mondal, Retired Professor of Botany, Jiagunj College, West Bengal, India (landscapes of wetlands of Nainital, Uttarakhand, India, and Shillong, Meghalaya, India) Dr. Pradip Kar, Professor of Zoology, Panchanan Barma University Coochbihar, West Bengal, India (landscapes of wetlands of Nagaland and Mizoram), Dr. Kajal Narayan Majumder, Associate Professor, Midnapur Autonomous College, West Bengal, India (landscapes of wetlands of Kerala); Dr. Partha Dutta, Scientist, Indian Institute of Science, Education and Research, Mohanpur, Kalyani, Nadia, West Bengal, India (landscapes of wetlands of Assam and Meghalaya) and Shillong, Meghalaya, India); Mr. L.  Joykumar Singh, Indian Forest Service (IFS), Conservator of Forests, Central Circle, Manipur, India (landscapes of Lotak lakes of Manipur, India); Dr. Kisolay Paria, Assisstant Professor, Oriental Institute of Science and Technology (landscapes of Rudrasagar Wetlands, Tripura) and Dr. Rajkumar Kothari, Professor of Political Sciences, Women’s University at Diamond Harbour in the district of South 24 Parganas, West Bengal, India (one photo of spring of Meghalaya). Special thanks are due to Nirmal Dey, Mehtab Uddin Ahmed and Imon Abedin (for the photographs of Tamranga, Doloni beels and Deepali beels). The authors are also thankful to Dr. Debasish Jana, Retired Associate Professor of Botany, Sripat Singh College, Jiagaunj, Murshidabad, West Bengal, India, and Dr. Dulal Kumar De, Associate Professor of Botany, Midnapur Autonomous College, West Bengal, India, for their help identifying aquatic plants. The second author, Dr. (Mrs.) Poulami Sanyal, is grateful to the authority of West Bengal Pollution Control Board Government of West Bengal, India for providing necessary supports, and the third author, Dr. Ratnadeep Ray, is thankful to the authority of GIS, University, Kolkata, West Bengal, India his employer for necessary help and supports. The writing up a research-based textbook is not that easy, as it appears to be, but hazardous as it is really difficult to blend own research information of the relevant subjects with existing knowledge bases already in existence by the research outcomes undertaken by different researchers from different corners of the globe.

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Besides a textbook does not or should not belong as a product of author alone, as so many other research information available in the form of generated research outcomes by others can be accommodated to enrich the subject contents of the book which on reaching to the readers in new forms as presented in every chapter of this book, certainly will refresh their interest and enable them to gain new insights. This approach not only enrich the quality of the book but pay due recognition to the earlier researchers. At the end, the authors are really thankful and indebted to their family members who have withstand all kind of problems because of their inadvertent absence and dissociation from daily affairs without making complains. Midnapore, West Bengal, India Kolkata, West Bengal, India

Susanta Kumar Chakraborty Poulami Sanyal Ratnadeep Ray

Contents

1

 Introductory and Basic Eco-biological Aspects of Wetlands����������������    1 1.1 Definition and Concept of Wetlands: International Perspectives������    1 1.2 Genesis of the Concept of Wetland��������������������������������������������������    3 1.3 Origin of Wetlands����������������������������������������������������������������������������    5 1.4 Criteria for Designating a Wetland as Ramsar Site��������������������������    6 1.5 Types, Classification, Sizes, and Extent of Distribution of Wetland Ecosystems ��������������������������������������������������������������������    6 1.5.1 Wetlands in the Floodplains��������������������������������������������������    9 1.6 Assessment of Wetland Ecosystems of India������������������������������������   10 1.7 Distribution of Wetlands in India������������������������������������������������������   11 1.8 Functional Manifestations of Wetlands Towards Generating Values ����������������������������������������������������������������������������   11 1.9 International Perceptions on the Values and Functions of Wetlands����������������������������������������������������������������������������������������   13 1.10 Biodiversity in the Wetlands of India: Rational Behind the Protection and Conservation of Wetlands ����������������������������������   13 1.10.1 Biodiversity of Wetlands and Determining Attributes����������   14 1.10.2 East Kolkata Wetlands: Potential for Values and Goods������   15 1.10.3 Recreational and Educational Roles of Wetlands ����������������   17 1.10.4 Wetlands and Flood Control ������������������������������������������������   17 1.10.5 Roles of Wetland in Trapping Sediment vis-a-vis Anti-erosion Roles����������������������������������������������������������������   18 1.10.6 Wetlands and Coastal Protection������������������������������������������   18 1.10.7 Roles of Wetlands for Waste Treatment: Phytoremediation������������������������������������������������������������������   18 1.10.8 Physico-chemical Parameters and Biogeochemical Cycle of Wetlands: Contribution to Render Benefits������������   19 1.10.9 Wetland as a “Nursery” and Provider of “Habitats” ������������   20 1.10.10 Recharge and Discharge of Ground Water and Interaction with Surface Water��������������������������������������������������������������   20

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1.10.11 Conservation of Wetlands and Survivability of Aquatic Birds������������������������������������������������������������������������������������   21 1.10.12 Wetlands and Socioeconomic Benefits ������������������������������   21 1.11 Threats on Wetlands and Loss of Biodiversity����������������������������������   22 1.11.1 Assessment of the Causes of Loss of Wetlands��������������������   23 1.11.2 Wetlands, Eutrophication and Carbon Sequestration������������   23 1.12 Functional Assessment of Wetlands��������������������������������������������������   25 1.13 Wetland Management: East Kolkata Wetlands ��������������������������������   26 1.14 Remote Sensing and GIS Methods for Conservation and Management of Wetlands����������������������������������������������������������   27 1.15 Linking Water Crisis: Roles of Governance and Integrity����������������   28 1.16 Conservation of Wetlands: Interdisciplinary and Integrated Approaches ��������������������������������������������������������������������������������������   29 References��������������������������������������������������������������������������������������������������   29 2

 Ecology and History of Wetland Research: Operating Scientific Principles of Eco-­dynamics of Wetland Ecosystem with Special Reference to East Kolkata Wetland, India��������������������������������������������   39 2.1 Ecosystem Ecology: Concept, Origin ����������������������������������������������   39 2.2 Functional Roles of Ecosystems ������������������������������������������������������   39 2.3 Major Structural Components of Wetland Ecosystem����������������������   40 2.3.1 Water and Water Resources: Human Sustenance������������������   40 2.3.2 Sunlight as the Driving Force for all Biological Growth and Interactions��������������������������������������������������������������������   41 2.3.3 Wind as an Important Meteorological Factor ����������������������   41 2.3.4 Soil – Its Texture and Nutrients��������������������������������������������   41 2.4 Interlinkages and Interdependences of Different Freshwater Ecosystems: An Ecological Interpretation����������������������������������������   42 2.5 Hierarchy of Ecological Systems: Population, Community, Biosphere and Ecosystem Ecology��������������������������������������������������   43 2.6 Functioning of Ecosystem as Cybernetic System: Production of Biomass and Flow of Energy��������������������������������������������������������   44 2.7 Hierarchical Organization of Biotic Community: Energy Flows and Productivity��������������������������������������������������������������������������������   46 2.8 Energy and Ecosystem: Driving Force behind all Kinds of Eco-­biological Activities��������������������������������������������������������������   49 2.9 Flows of Energy: Laws of Thermodynamics������������������������������������   50 2.10 Food Chains and Food Web Dynamics Within an Aquatic Ecosystem: Food Web Complexity ��������������������������������������������������   51 2.11 Ecological Efficiency in Plants ��������������������������������������������������������   52 2.12 The Ecological Efficiency of Animals����������������������������������������������   52 2.13 Limnology and Its Different Dimensions ����������������������������������������   52 2.14 Ecological Niche and Habitat: Concept of Resource Partitioning and Metacommunity ������������������������������������������������������������������������   55 2.15 Background Ecology for the Functioning of Wetlands��������������������   60

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2.16 Biogeochemistry and Biogeochemical Cycling��������������������������������   60 2.17 Nutrients Loads and Ecological Alternations: An Example of East Kolkata Wetlands, a Ramsar Site������������������������������������������   63 2.18 Spatial Heterogeneity of Nutrient Controls��������������������������������������   63 2.19 Ecological Processes and Parameters vs Biota in Wetland Ecosystem ����������������������������������������������������������������������������������������   64 2.20 Regulating Nutrient Cycles and Water Quality: Roles of Macrophytes��������������������������������������������������������������������������������������   64 2.21 Adaptive Strategies of Aquatic Organisms: Role of Limiting Factors����������������������������������������������������������������������������������������������   65 2.22 Ecosystem and Environment Interrelationships: Perspectives of Wetland Ecosystem����������������������������������������������������������������������   66 2.23 Ecological Significance of Soil Organic Matter ������������������������������   67 2.24 Historical Account of Wetlands Research����������������������������������������   68 2.24.1 Historical Background on the Ecological Concept and Definition of Wetland ����������������������������������������������������   68 2.25 Information of Distribution of Wetlands in India�����������������������������   70 2.26 Ecosystem Functioning of Wetlands and Ecological Variables��������   71 2.27 Wetland Hydrology ��������������������������������������������������������������������������   71 2.28 The Relationship among Water Quality Parameters (Abiotic Factors and Biotic Factors): An Ecological Perspective����������������������������������������������������������������   72 2.28.1 Temperature��������������������������������������������������������������������������   72 2.28.2 Hydrogen Ion Concentration (pH)����������������������������������������   73 2.28.3 Dissolved Oxygen����������������������������������������������������������������   73 2.28.4 Turbidity and Transparency��������������������������������������������������   74 2.28.5 Specific Conductivity������������������������������������������������������������   74 2.28.6 Total Solids [Total Suspended Solids (TSS) and Total Dissolved Solids (TDS)] ��������������������������������������   75 2.28.7 Transparency������������������������������������������������������������������������   75 2.28.8 Alkalinity������������������������������������������������������������������������������   75 2.28.9 Total Hardness of Water (Calcium Hardness and Magnesium Hardness)����������������������������������������������������   76 2.28.10 Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD)������������������������������   76 2.28.11 Ecological Characteristics of Soil: Determinant of Other Structure Components of Wetlands����������������������   76 2.28.12 Ecological Significance of Soil Organic Carbon and Bulk Density����������������������������������������������������������������   77 2.28.13 Soil Bulk Density (BD)������������������������������������������������������   77 2.29 Historical Review of the Studies of Physico-chemical Parameters in Freshwater Wetlands ��������������������������������������������������������������������   77 2.30 Decomposition and Consumption: Cycling of Chemical Elements and Nutrient Availability������������������������������������������������������������������   80

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2.31 Functional Roles of Different Components of Detritus in Wetland Ecosystem ����������������������������������������������������������������������   81 2.31.1 Cellulosic Substances�����������������������������������������������������������   81 2.31.2 Phenolic Substances��������������������������������������������������������������   82 2.31.3 Humic Substances����������������������������������������������������������������   82 2.32 Case Study on the Seasonal Fluctuation of Physico-­chemical Parameters from Four Ecologically Contrasting Wetlands of East Kolkata Wetlands, India��������������������������������������������������������   83 2.32.1 Selection of Suitable Study Sites������������������������������������������   83 2.33 Wetland’s Functioning in the Historical Perspectives����������������������  119 2.34 Wetlands in the Landscape: Their History and Evolution����������������  119 2.35 Ecological Uniqueness of Aquatic Systems��������������������������������������  153 References��������������������������������������������������������������������������������������������������  154 3

Diversity and Classification of Wetlands in International and National Perspectives ����������������������������������������������������������������������  167 3.1 Classificatory Scheme: Categorization of Global Wetlands ������������  167 3.2 Relevant Information of Different Research Studies on Wetland Classification������������������������������������������������������������������������������������  168 3.3 Broad Categories of Wetlands����������������������������������������������������������  169 3.4 Coastal Wetlands: Ecological Characteristics����������������������������������  169 3.4.1 Types and Structural Components of Coastal Wetlands ������  170 3.5 Inland Wetlands��������������������������������������������������������������������������������  171 3.5.1 Freshwater Swamps��������������������������������������������������������������  171 3.5.2 Riparian Wetlands ����������������������������������������������������������������  172 3.5.3 Bogs��������������������������������������������������������������������������������������  172 3.5.4 Peatlands ������������������������������������������������������������������������������  172 3.5.5 Constructed Wetlands�����������������������������������������������������������  173 3.5.6 Mires and Spring������������������������������������������������������������������  173 3.5.7 Depressional Wetlands����������������������������������������������������������  174 3.5.8 Terminal Wetlands����������������������������������������������������������������  174 3.5.9 Floodplains����������������������������������������������������������������������������  174 3.6 Human-Made Wetlands��������������������������������������������������������������������  176 3.7 Categorization of Wetlands as per the Observations of Mitsch and Gosselink (2007)������������������������������������������������������������������������  176 3.7.1 Peatlands: Organic Soil Wetlands ����������������������������������������  176 3.7.2 Bog: Acidic Ecological Condition����������������������������������������  176 3.7.3 Fens – A Unique Wetland with Natural Supply of Water��������������������������������������������������������������������������������  177 3.7.4 Marsh������������������������������������������������������������������������������������  178 3.8 Changing Wetlands: Development vs. Succession ��������������������������  183 3.8.1 Diversity and Ecological characteristics of wetlands in India����������������������������������������������������������������������������������  183 3.8.2 Wetlands in India in Different Biogeographic Zones ����������  185 3.9 Classification of Wetlands in Indian Perspectives����������������������������  188

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3.10 Major Determining Factors Structuring Wetland Ecosystem ����������  191 3.10.1 Salinity as Hydrological Parameter��������������������������������������  191 3.10.2 Morphometric and Morphoedaphic Factors��������������������������  192 3.10.3 Sources of Water for Wetlands����������������������������������������������  192 3.10.4 Species Composition������������������������������������������������������������  192 3.10.5 Depth of the Wetlands: Influence on Biotic Community������  193 3.11 Classification and Ramsar Sites: Indian Perspectives����������������������  194 3.12 Classified Categories of Wetlands in Indian Perspectives����������������  195 3.13 Drainage and Flooding of Water to Wetlands: Ecological Implications��������������������������������������������������������������������������������������  214 References��������������������������������������������������������������������������������������������������  222 4

Ecosystem Services and Values of Wetlands with Special Reference with East Kolkata Wetlands��������������������������������������������������  227 4.1 Concept on Ecosystem Services in Relation to Biodiversity������������  227 4.2 Ecosystem Services: Concept and Types������������������������������������������  228 4.3 Wetlands and Their Ecosystem Services������������������������������������������  229 4.3.1 Types of Ecosystem Services������������������������������������������������  229 4.3.2 Detailed Account of Different Ecosystem Services of Wetlands���������������������������������������������������������������������������  232 4.4 Ecosystem Functioning vs Biodiversity: Avenues for Ecosystem Services ��������������������������������������������������������������������������������������������  243 4.5 Wetlands and Recreation������������������������������������������������������������������  246 4.6 Socioeconomic Benefits from Wetlands ������������������������������������������  247 4.7 The Economic Context: Economics of Wetlands������������������������������  248 4.8 Valuation of the Ecosystem Services of Wetlands����������������������������  248 References��������������������������������������������������������������������������������������������������  249

5

Eco-biological Uniqueness of East Kolkata Wetland, a Ramsar Site in India����������������������������������������������������������������������������������������������  257 5.1 Locational and Climatic Information of EKW ��������������������������������  257 5.2 Ecological and Geomorphological Evolution of East Kolkata Wetlands��������������������������������������������������������������������������������������������  258 5.3 Geo-Hydrological Condition of East Kolkata Wetlands ������������������  260 5.4 Historical Background of East Kolkata Wetlands (EKW)����������������  261 5.5 Historical Account of Ecological Transformation of East Kolkata Wetlands��������������������������������������������������������������������������������������������  265 5.6 Historical Account of the Location and Climate of East Kolkata Wetlands (EKW) ������������������������������������������������������������������������������  266 5.7 Eco-geo-transformation from Marsh to Megacity����������������������������  267 5.8 East Kolkata Wetlands – International Recognition ������������������������  268 5.8.1 Extent and Earlier Records of Physiography������������������������  268 5.9 East Kolkata Wetlands and Sundarbans Mangrove Ecosystem��������  270 5.10 East Kolkata Wetlands – Basin: Geomorphological Alteration��������  271

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5.11 Ecological History of the Conservation Strategies for East Kolkata Wetlands��������������������������������������������������������������������������������������������  272 5.11.1 Early History of Expanse and Climate of EKW ������������������  273 5.11.2 Historical Account of the Conversion of Bidyadhari Interfluves ����������������������������������������������������������������������������  273 5.12 Scientific Principles Behind Fishery Development��������������������������  274 5.13 Threats on the Traditional Waste Recycling Wetlands����������������������  274 5.14 The Major Changes Regarding the Management of City’s Sewage ������������������������������������������������������������������������������  275 5.14.1 Chronological Summarization of Major Threats to the EKW ��������������������������������������������������������������������������  276 5.15 Significance of East Kolkata Wetlands ��������������������������������������������  276 5.15.1 Outcomes from the Resource Recovery from EKW������������  277 5.15.2 Agricultural Activities����������������������������������������������������������  280 5.15.3 Scopes of Navigability����������������������������������������������������������  282 5.15.4 Socio-Economic Values of East Kolkata Wetlands ��������������  283 5.16 Reclamation of ErstWhile Salt Lake������������������������������������������������  284 5.17 Urbanization, History of Kolkata City and EKW ����������������������������  285 5.17.1 Historical Background of East Kolkata Wetland������������������  286 5.17.2 Establishment, Growth, Urbanization of City of Kolkata����  286 5.18 Expansion Drive for the City of Kolkata������������������������������������������  288 5.19 Uniqueness of Ecosystem Functioning of EKW: Eco-­potential, Problems and Prospect����������������������������������������������������������������������  289 5.19.1 Constrains and ShortComings in the Restoration and Conservation of EKW����������������������������������������������������  290 5.20 Eco-management in Tune with the Need of the Hour: Traditional Use of Wetlands for the Resource Recovery������������������  291 5.20.1 Mudiali Fishermen Cooperative Society (MFCS): A Cooperative Approach for Successful Fisheries Through Wastewater Recycling��������������������������������������������  292 5.20.2 Salient Points of the Natural Waste Recycling System��������  294 5.20.3 Recycling of Urban Wastes of Kolkata Within EKW ����������  296 References��������������������������������������������������������������������������������������������������  297 6

 Basics of Remote Sensing Techniques Applicable in Wetlands Ecosystems������������������������������������������������������������������������������������������������  303 6.1 Basic Facts About GIS and Remote Sensing with the Scope of Their Applicability in Environmental Assessment ����������������������  303 6.2 Application of Remote Sensing Techniques in the Ecological Assessment of Wetland Ecosystems ������������������������������������������������  304 6.3 Application of Satellite Sensors for Identification of Wetlands����������������������������������������������������������������������������������������  307 6.3.1 Landsat MSS������������������������������������������������������������������������  307 6.3.2 Landsat TM��������������������������������������������������������������������������  308 6.3.3 Landsat 8/OLI ����������������������������������������������������������������������  308

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6.3.4 SPOT as First Earth Resource Satellite��������������������������������  309 6.3.5 AVHRR ��������������������������������������������������������������������������������  309 6.3.6 IRS Satellites������������������������������������������������������������������������  310 6.3.7 RADAR Images��������������������������������������������������������������������  310 6.4 Case Study: A Remote Sensing-Based Assessment of Inland Wetland Dynamics������������������������������������������������������������  312 6.4.1 Ecological Information of the Study Area (EKW) ��������������  312 6.4.2 Material and Methods of the Study��������������������������������������  313 6.4.3 Case Study 1: Decadal Changes in the Land Use Patterns in the East Kolkata Wetland��������������������������������������������������  319 6.5 Case Study 2: A Remote Sensing-Based Assessment of Inland Wetland Dynamics (East Kolkata Wetlands)��������������������  332 6.5.1 Spectral Response of Water Bodies��������������������������������������  334 6.5.2 Methodology: Spectra for Different Water Quality��������������  335 6.5.3 Major Outcomes of the Remote Sensing-Based Assessment on the Water Quality and Vater Levels in East Kolkata Wetlands��������������������������������������������������������������������������������  336 6.6 Case Study 3: Ecosystem Service Valuation of EKW Using Geoinformatics����������������������������������������������������������������������������������  337 6.6.1 Reasons behind the Roles of Wetlands as Important Providers of Ecosystem Services������������������������������������������  340 6.6.2 Different Ecosystem Services of Wetlands ��������������������������  340 6.6.3 Assessment of Ecosystem Service Value (ESV)������������������  342 6.6.4 Determination of Importance of the Ecosystem Functions������������������������������������������������������������������������������  344 6.6.5 Spatio-temporal Changing Pattern of Ecosystem Service Values������������������������������������������������������������������������������������  345 6.6.6 Changing Trend in Ecosystem Function������������������������������  346 6.7 Analysis of Criteria Importance��������������������������������������������������������  349 6.8 Interpretation on the Findings on ESVs in EKWs����������������������������  352 6.9 Characterization of Wetland Ecosystem by Assessing the Water Quality Parameters by GIS and Remote Sensing Methods: A Case Studies from East Kolkata Wetland Ecosystems����������������������������������������������������������������������������������������  358 6.9.1 Seasonal Dynamics of Physicochemical Parameters of Water��������������������������������������������������������������������������������  360 6.9.2 Remote Sensing Technique: Image Pre-processing: Atmospheric Correction��������������������������������������������������������  360 6.9.3 Characterizing the Wetlands with the Help Landsat Associated Tools ������������������������������������������������������������������  361 6.10 Application of GIS and Remote Sensing for the Classification on Delimitation of the Territory of Wetland��������������������������������������  363

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6.11 Ecological Status and Threats: Increment of Surface Imperviousness Due to Urban Sprawling������������������������  364 6.11.1 Urbanization in Kolkata: Impact on East Kolkata Wetlands ����������������������������������������������������  365 6.12 Concluding Remarks on the Efficacy of Remote Sensing and GIS ��������������������������������������������������������������������������������������������  366 References��������������������������������������������������������������������������������������������������  367 7

Biodiversity and Its Functional Significance: Case Studies from East Kolkata Wetlands��������������������������������������������  379 7.1 Definition and Concept of Biodiversity��������������������������������������������  379 7.2 Biodiversity and Ecosystem Functioning ����������������������������������������  382 7.3 Biotic Community, Biodiversity and Ecosystem Functioning����������  382 7.4 Aquatic Ecosystems and Their Biodiversity in Asia������������������������  384 7.5 Biodiversity of Wetlands: Indian Scenario����������������������������������������  385 7.5.1 Detailed Account of Biodiversity: Flora and Fauna��������������  388 7.5.2 Diversity of Habitats: Zonations Within an Wetland and Associated Biodiversity��������������������������������������������������  389 7.5.3 Some Primitive Group of Organisms in Freshwater Ecosystems����������������������������������������������������������������������������  390 7.5.4 Wetlands Plants��������������������������������������������������������������������  391 7.5.5 Studies on Aquatic Invertebrates: Strategies for Survival of Aquatic Organisms ����������������������������������������������������������  403 7.5.6 Faunal Diversity of EKW�����������������������������������������������������  407 7.5.7 Plankton��������������������������������������������������������������������������������  409 7.5.8 Zooplankton as the Secondary Producers in the Wetland Ecosystems����������������������������������������������������������������������������  412 7.5.9 Statistical Evaluation������������������������������������������������������������  430 7.5.10 Organic Phosphorus Dynamics in EKW������������������������������  457 7.5.11 Functions of the Benthic Fauna: P and N Loading and Cycling ��������������������������������������������������������������������������  458 7.5.12 Eutrophication and Causative Biota: Management Strategies in EKW����������������������������������������������������������������  458 7.5.13 Diversity of Benthos as Important Functional Biotic Component����������������������������������������������������������������������������  461 7.5.14 Studies on Aquatic Vertebrates ��������������������������������������������  472 7.5.15 Diversity of Flora and Fauna from Four Selected Study Sites of East Kolkata Wetlands (EKW)��������������������������������  472 7.5.16 Microbial Communities��������������������������������������������������������  491 7.6 Importance of Detritus����������������������������������������������������������������������  493 7.7 Behavior and Interactions Among Microorganisms and Invertebrates ������������������������������������������������������������������������������  493 7.8 East Kolkata Wetlands: Nutrient Dynamics as Root Cause of Biodiversity Development������������������������������������������������������������  494

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7.9 Piscicultural Practices with Prospective Constrains in EKW ����������  496 7.10 Wetland Ecology in the Perspective of Biodiversity������������������������  497 7.11 Values of Biodiversity: Interlinkages of Biodiversity and Ecosystem Services��������������������������������������������������������������������  498 7.12 Summary of Biodiversity Potential of East Kolkata Wetlands ��������  499 References��������������������������������������������������������������������������������������������������  504 8

Pollution, Environmental Perturbation and Consequent Loss of Wetlands ����������������������������������������������������������������������������������������������  521 8.1 Ecological Potential and Ecological Health of Wetlands������������������  521 8.1.1 Ecological Health of Wetland: An Indicator for Eco-­assessment of River Ecosystem ������������������������������  521 8.2 Loss of Wetlands: Different Threats ������������������������������������������������  522 8.2.1 Eco-degradation Leading to the Loss of Wetlands ��������������  525 8.3 Threats to East Kolkata Wetlands: Some Relevant Facts������������������  525 8.4 Loss Wetlands in India: Threats to Ecological Balance on Wetlands��������������������������������������������������������������������������������������  527 8.5 Chronic Losses of Wetlands: Alteration of Upper Watersheds ��������  528 8.6 Bioinvasion and Introduced Species ������������������������������������������������  528 8.7 Ecological Problems Faced by Wetlands with Special Reference to Pollution����������������������������������������������������������������������������������������  529 8.7.1 Pollution of Wetland: Multidimensional Perspectives����������  529 8.7.2 Point and Non-point Sources of Pollution: Entry Path and Roles of Environmental Variables����������������������������������  530 8.8 Roles of Geo-Hydrological Factors on Pollutant’s Behaviour����������  531 8.9 Differential Biological Responses against Pollution Pressures��������  533 8.10 Environmental Perturbations Vis-a-Vis Anthropogenic Activities on the Habitats of Wetland Ecosystem����������������������������������������������  534 8.10.1 Deforestation and Contribution to the Ecosystem Functioning ��������������������������������������������������������������������������  534 8.10.2 Pollution from Agriculture as Non-point Sources����������������  535 8.10.3 Environmental Impacts of Different Pollutions��������������������  535 8.11 Relevance of Input of Chemicals into Wetland Ecosystems������������  536 8.12 Surface–Water Pollution ������������������������������������������������������������������  536 8.13 Pollution of Wetlands with Nutrients: Eutrophication����������������������  537 8.14 Acidification of Wetlands and Consequences ����������������������������������  539 8.15 Pollution of Wetlands by Organic Compounds��������������������������������  540 8.16 Climate Change on Wetland Ecosystems������������������������������������������  541 8.16.1 Global Climate Change and Its Impact on Ecosystem Functioning of Wetlands ������������������������������������������������������  542 8.16.2 Impact of Climate Change: Alteration from Molecules to Wetland Ecosystem ����������������������������������������������������������  543 8.16.3 Bioecological Impacts of Thermal Regimes on Fauna of Wetlands���������������������������������������������������������������������������  544

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8.16.4 Impact of Temperature: Experimental Evidences on Fresh Water Major Carp Species (Order Teleost: Class Pisces), India ��������������������������������������������������������������  544 8.16.5 Carbon Sequestration: An Option for the Mitigation of the Global Warming����������������������������������������������������������  546 8.17 Fish Diseases Leading to Ecological Disturbance Within Aquatic Ecosystems��������������������������������������������������������������������������  547 8.18 Toxic and Persistent Pollutants in Wetlands Ecosystem ������������������  548 8.19 Toxic Organic Chemicals (TOCs): Sources and Background����������  549 8.20 Effect of Pesticides on Wetland Ecosystem: Ecosystem Stability and Resilience ����������������������������������������������������������������������������������  550 8.21 Synthetic Detergents as Potential Water Pollutants in Wetland Ecosystem ����������������������������������������������������������������������������������������  552 8.22 Oil Spills: Impact on the Ecology of Wetlands��������������������������������  552 8.23 Plastics and Microplastics: Pollution Threats on Wetlands��������������  553 8.24 Eco-physiological Adjustment of Aquatic Biota in Wetlands����������  553 8.25 Environmental Problems as Observed in the East Kolkata Wetlands (EKW), West Bengal, India����������������������������������������������  554 8.25.1 Natural and Anthropogenic Threats on East Kolkata Wetlands��������������������������������������������������������������������������������  554 8.26 Metals as Toxic Pollutants in the Wetland Ecosystem����������������������  555 8.27 Seasonal Dynamics of Heavy Metals (Pb, Cr, Cd and Hg): A Case Study from East Kolkata Wetland����������������������������������������  557 8.27.1 Seasons and Climate ������������������������������������������������������������  558 8.27.2 Selection of Study Sites for Detailed Ecological Study�������  558 8.27.3 Bio-Concentration Factor (BCF): An Indicator of the of Heavy Metals Pollution������������������������������������������  567 8.28 Hydrogeological Assessment of Water Pollution: Surface Water vs. Groundwater Interaction ��������������������������������������������������  569 8.29 Pollution and Wetlands: Prospective Mitigation Strategies��������������  573 References��������������������������������������������������������������������������������������������������  574 9

Bio-monitoring and Bio-remediation of the Ecological Changes in Wetlands: Case Studies from East Kolkata Wetlands����������������������  583 9.1 Bio-indicator – The Most Essential Component of Bio-monitoring ����������������������������������������������������������������������������  583 9.2 Relationships Between Bio-indicator and Bio-monitoring��������������  584 9.3 Concept and Scope of Applicability: An Introductory Analysis������  584 9.4 Relevance of Bio-monitoring as an Environmental Monitoring Tool��������������������������������������������������������������������������������  585 9.5 Bio-remediation: Definition, Concept, Types and Application��������  587 9.6 Phytoremediation a New Option: Competitive and Sustainable Solution for Heavy Metal Contamination����������������������������������������  587 9.7 Biological Assessment on the Ecological Changes of Wetland Ecosystem: Roles of Bio-indicator Species��������������������������������������  588

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9.8 Acceptable Methods for Bio-monitoring������������������������������������������  590 9.9 Biological Monitoring Programme (B.M.P.): New Approach in the Environmental Management ��������������������������������������������������  590 9.10 Biotic Indices and Their Applicability in the Assessment of Ecological Changes����������������������������������������������������������������������  591 9.10.1 The Saprobic Index of Pantle and Buck�������������������������������  592 9.10.2 Chandler Biotic Score (CBS)������������������������������������������������  592 9.11 Comparison of Physico-chemical Monitoring with Biological Monitoring����������������������������������������������������������������������������������������  592 9.12 Advantages of Biological Assessment as the Part of Bio-monitoring in Wetland Ecosystem����������������������������������������  593 9.13 Eco- and Bio-monitoring: Emerging Tools for Eco-assessment of Ecosystem Health ������������������������������������������������������������������������  594 9.14 Criteria to Become a Successful Bio-indicator��������������������������������  595 9.15 Case Studies of Bio-monitoring of Four Ecologically Contrasting Wetlands of Kolkata, West Bengal, India Based on Zooplankton Eco-dynamics and Biotic Indices (CPV and SPV) ��������������������������  596 9.15.1 Selection of Study Sites��������������������������������������������������������  596 9.15.2 Deduction and Application of Biotic Indices: Species Pollution Value (SPV) and Community Pollution Value (CPV)������������������������������������������������������������������������������������  597 9.15.3 Calculation of Similarity Index��������������������������������������������  598 9.15.4 Seasonal Dynamics of Physico-chemical Parameters of Water��������������������������������������������������������������������������������  599 9.15.5 Relationship Between Physico-chemical Parameters of Water with CPV����������������������������������������������������������������  599 9.15.6 Relationship Among Physico-chemical Parameters of Soil with CPV������������������������������������������������������������������  604 9.15.7 Zooplankton as Bio-indicators at EKW��������������������������������  605 9.16 Rotifers, the Tiniest Zooplanktonic Fauna as Bio-indicator Organisms: A Case Study from the Riverine Networks of South West Bengal, India��������������������������������������������������������������  609 9.17 Bio-monitoring of Aquatic Habitats with the Help of Aquatic Insects ����������������������������������������������������������������������������������������������  612 9.18 Eco-Bio-monitoring of a Transboundary River, India by Molluscan Community Indices: A Case Study from the Riverine System from the South West Bengal, India������������������  613 9.19 Molecular Biology and Physiology of Living Organisms for Bio-­monitoring����������������������������������������������������������������������������  614 9.20 Bio-monitoring of Aquatic Ecosystems with Molecular Markers: A Case Study from the South West Bengal, India����������������������������  614 9.21 Deduction of WQI: As the Eco-monitoring Tool for the Eco-assessment of East Kolkata Wetlands����������������������������  616 9.21.1 Pollution Load Index (PLI)��������������������������������������������������  617 9.21.2 Bio-concentration Factor (BCF) ������������������������������������������  617

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9.22 Seasonal Variation of Different Water Quality Indices Relating to Ecology of East Kolkata Wetland ������������������������������������������������  617 9.22.1 Seasonal Variation of WQI����������������������������������������������������  617 9.23 Bio-adjustment of Aquatic Organisms Against Heavy Metals ��������  619 9.24 Eco-potential of Phytoremediation Along with Its Subgroups ��������  620 9.24.1 Phytoextraction ��������������������������������������������������������������������  621 9.24.2 Phytofiltration ����������������������������������������������������������������������  621 9.24.3 Phytostabilization������������������������������������������������������������������  621 9.24.4 Phytovolatilization����������������������������������������������������������������  622 9.25 Bio-remediation and Roles of Macrophytes: A Case Study ������������  622 9.26 Bio-remediation: Roles of Aspergillus (Fungi (F-12), a Fungus for the Removal of Metals)������������������������������������������������  623 9.26.1 Fourier Transforms Infrared Spectroscopy (FTIR Analysis): A Tool for the Assessment of Metal Removal Efficiency of Functional Groups������������������������������������������������������������  624 9.26.2 Soil-Inhabiting Bacteria of EKW as Bio-remediator������������  625 9.26.3 Chemical Partitioning and Risk Assessment Code: Assessment of Heavy Metal Pollution at East Kolkata Wetland ��������������������������������������������������������������������������������  626 9.27 Eco-restoration via Bio-monitoring and Bio-remediation: A Case Study on the Roles of Benthic Fauna from the Estuarine Wetlands��������������������������������������������������������������������������������������������  628 9.28 Phytoremediation: A Case Study from the East Kolkata Wetlands��  629 9.29 Need for Bio-monitoring and Bio-remediation as Prerequisite for Wetlands Eco-management ��������������������������������������������������������  637 References��������������������������������������������������������������������������������������������������  638 10 Sustainable  Management and Conservation Strategies of Wetlands with Special Reference to East Kolkata Wetland, India����������������������  649 10.1 Global Environmental Issues, Crisis and Conservation������������������  649 10.2 Perspectives and Distinctions of Conservation Biology: Historical and Social Requirements������������������������������������������������  650 10.2.1 The Origins of Conservation: Conservation in Historical Context ��������������������������������������������������������������������������  650 10.3 Forums for International Conservation: The United Nations and the International Union for the Conservation of Nature����������  650 10.4 Management and Legislation for Wetland Conservation: Challenges in Habitat Conservation������������������������������������������������  651 10.5 Legal Frameworks on Jurisdiction and Management of Wetlands: Perspectives of Developing Countries ����������������������  653 10.6 Ecosystem Management: A Prerequisite to Wetland Management and Conservation������������������������������������������������������  655 10.7 Management of Biodiversity of Wetlands��������������������������������������  657 10.8 Biomanipulation: An Option Towards Eco-friendly Conservation ����������������������������������������������������������������������������������  659

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10.9 Different Thrust Areas in the Eco-Management of Wetlands ��������  660 10.10 Societal Perspectives: Social Potentials of Wetlands����������������������  661 10.11 Ecological Management of Wetland Ecosystem����������������������������  662 10.12 Natural Water Management as a Prerequisite for Fishery Production in Wetlands������������������������������������������������  663 10.13 Remote Sensing and GIS Methods for Wetland Conservation and Management����������������������������������������������������������������������������  664 10.14 Ongoing Programmes on Wetland Conservation: Action Plan of the Government of India������������������������������������������������������������  665 10.15 Awareness Building Programme for the Conservation of Wetlands��������������������������������������������������������������������������������������  666 10.16 Sustainable Conservation Proposition for Wetland Ecosystems������������������������������������������������������������������  667 10.17 The Integrated Approach Towards the Conservation of Wetlands: Special Reference to East Kolkata Wetlands ������������  667 10.18 Ramsar Convention and Sustainability in Respect of Wetland Conservation ����������������������������������������������������������������������������������  669 10.18.1 Criteria for Designating a Wetland as Ramsar Site��������  669 10.19 Wetland Management: Current Status��������������������������������������������  672 10.20 Sustainable Conservation Strategy: An Integrated Approach for EKW������������������������������������������������������������������������������������������  673 References��������������������������������������������������������������������������������������������������  674 11 Conclusion  on Eco-biological Uniqueness of Wetland Ecosystem with Special Reference with East Kolkata Wetlands, India ����������������  679 11.1 Wetlands as a Unique Landscape of the World������������������������������  679 11.2 Wetland Functions and Values��������������������������������������������������������  680 11.3 Wetlands and Biodiversity��������������������������������������������������������������  681 11.4 Present Threats and Pollution ��������������������������������������������������������  682 11.5 Ramsar Convention: An Expedient for Conservation of Wetlands��������������������������������������������������������������������������������������  683 11.6 Ramsar Convention and Wetlands in India ������������������������������������  683 11.7 East Kolkata Wetlands and Eco-potentiality as Natural Waste Recycling System����������������������������������������������������������������������������  685 11.8 Urbanization and East Kolkata Wetlands����������������������������������������  686 11.9 Wastewater Aquaculture: Roles of Traditional Know-­How of Local Peoples����������������������������������������������������������  687 11.10 Summary of the Case Studies on EKW (July, 2008–June, 2011)������������������������������������������������������������������  688 11.10.1 Selection of Study Sites Based on Contrasting Ecological Characteristics����������������������������������������������  689 11.10.2 Geomorphological Evolution of East Kolkata Wetlands ����������������������������������������������  689 11.10.3 Seasonal Variation of Ecological Parameters of the Studied Wetlands��������������������������������������������������  690

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11.10.4 Statistical Interpretation of Research Information ��������  690 11.10.5 Application of GIS and Remote Sensing as a Tool to Assess Environmental Change ����������������������������������  691 11.10.6 Biodiversity and Zooplankton: Seasonal Dynamics������  692 11.10.7 Seasonal Dynamics of Zooplankton������������������������������  693 11.10.8 Arrangement of the Status of Bio-indicator Species of Zooplankton ��������������������������������������������������������������  693 11.10.9 Ecological Relationship Among Selected Study Sites ��  694 11.10.10 Ecological Dynamics Made of Phytoremediation����������  694 11.10.11 Seasonal Dynamics of Heavy Metals����������������������������  695 11.10.12 Seasonal Variation of Water Quality Indices������������������  695 11.10.13 Pollution Load Index and Seasonal Dynamics��������������  695 11.10.14 Seasonal Variation of Bio-concentration Factors ����������  696 11.10.15 Seasonal Variation of Biotic Indices (SPV and CPV)����  696 11.10.16 Status of Biodiversity and Trend of Temporal and Spatial Changes ������������������������������������������������������  697 11.10.17 Diversity and Distribution of Zooplankton��������������������  697 11.10.18 Eco-dynamics of Zooplankton and Relevance in Eco-­­management of Wetlands������������������������������������  698 11.11 The Cause of Wetland Degradation������������������������������������������������  698 11.12 Eco-management Strategies for the Sustainability of East Kolkata Wetlands����������������������������������������������������������������  699 11.13 Hypothesis Pertaining to Ground Water–Surface Water Interaction: Functional Determinant of Wetland Ecosystem����������  701 References��������������������������������������������������������������������������������������������������  702 Index������������������������������������������������������������������������������������������������������������������  707

About the Authors

Susanta Kumar Chakraborty  Professor of Zoology, Vidyasagar University, born on 31st, July, 1960, has been in active research since 1982 after completion of his M.Sc. in Zoology from the Calcutta University. He did his M.Phil. in Environmental Science and Ph.D. in Marine Science from the Calcutta University in the years 1984 and 1992 respectively. His subject preferences on research centered around on Ecology and Environmental management. He has been imparting teaching spanning a period of more than three decades mostly in the postgraduate level covering different aspects of Zoology in general and Ecology/ Environmental Science in particular. So far, he has successfully supervised the Ph.D. thesis of 40 researchers, published around 190 research papers in different reputed International and National Journals, written a number of books including the text book, Riverine Ecology (Volume I and II) published by Springer Nature, U.S.A., completed fifteen (15) research projects including Consultancy projects on Environmental Impact assessment earned two international patents, visited several countries such as Australia, U.S.A., Hong Kong, Belgium, France, and Bangladesh in connection with his academic commitments. Delivered more than hundred of lectures in different Seminars/ Symposia/Conferences/Workshops/Refreshers Courses etc. in different parts of India and abroad highlighting his scientific thoughts and research achievements. Besides, he has shouldered a number of administrative responsibilities in his own Universities such as, Dean,

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About the Authors

Faculty of Sciences, Head of the Department, Member of the Executive Council, Member of the Finance Committee, Chairman of College Governing bodies etc. and also in other Universities as an Expert member of Selection Committees, Academic Bodies, etc. alongside contributing as an Expert Member for several Government Departments like U.G.C., I.C.A.R. etc. He has been associated with a number Scientific Bodies in India as Life Members, and Reputed Journals (Elsevier, Springer, Taylor and Francis, Willis etc.) as a member of editorial bodies. He has received a number of awards in recognition of his research commitments. Poulami  Sanyal  Born on 26th September 1980, Dr (Mrs) Poulami Sanyal passed her M.Sc in Environmental Sciences from Vidyasagar University in the year 2004. She was awarded with her Ph.D. degree from the same University in the year 2015 in the topic, entitled, “Hydrobiological and geomorphological study of the wetlands of Kolkata.” She has so far published a number of research papers on ecomonitoring and phytoremediation in reputed scientific journals. She has presently been associated with the West Bengal Pollution Control Board, Department of Environment, Government of West Bengal, India as Junior Laboratory Assistant. She is having working experiences in the Research and Development wings of a number of industries and analytical research laboratories. Ratnadeep  Ray  Born on 08.01.1983, Dr. Ratnadeep Ray is presently acting as the Assistant Professor (Department of Remote Sensing and GIS) of JIS University, Kolkata, In the previous years, he has acted as Co-ordinator (Remote Sensing and GIS), Opsis Academy, Kolkata and Academic advisor (Remote Sensing and GIS), KIRS, Kolkata Amity University AUUP Noida, Uttar Pradesh, Environmental Education & Research of Bharati Vidyapeeth, Pune, Maharastra and Besides, he has served as Visiting Faculty for the Department of Remote Sensing and GIS, Vidyasagar University, Midnapore, West Bengal, India and the Department of Geography along with a number ungraduate colleges ok Kolkata, West Bengal, India. He received his Ph.D. from Vidyasagar University, West

About the Authors

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Bengal, India. His main research interests are Remote Sensing and Digital Image Processing, Application of Remote Sensing and GIS techniques in Urban Planning, Resource management, Statistical simulation modeling, Photogrammetry etc. and published more than twenty (20) international and national research articles in various renowned journals and edited books.

Chapter 1

Introductory and Basic Eco-biological Aspects of Wetlands

1.1 Definition and Concept of Wetlands: International Perspectives The recent Directory of Important Wetlands (Usback & James, 1993) has included the definition of a wetland put forward by the Ramsar International Wetland Convention (1971) as “Wetlands are marked as areas designated by different terminologies such as fen, marsh, swamp, peat land, or any other water body whether natural or artificial, permanent or temporary, with water that is static or flowing, freshwater, brackish water or saline water, including areas within marine ecosystem where the water depth should not exceed six meters during low tide.” It is really a challenging task to bring the wider dimensions of diversity of disparate ecological habitats in the defined framework of single term, and thereby it poses real difficulty in defining wetlands incorporating all the facets of this unique landscape of the world. As different wetlands exhibit varied properties, combination of which makes a given wetland unique, and therefore, some proposed definitions have been found to be very restrictive. Different countries have proposed and adopted different terminologies for different purposes where the old, local and common terms have been continuously in use inviting more confusion. However, currently more than 140 contracting parties, including the European Commission, Ramsar Convention, had tried to propose a comprehensive definition on wetlands which has been facing criticism mostly because of inconsistency in the scientific temperament in the realm of this definition, where a range of several ecosystems not only overlap but also lump together with small ranged focus on the rationale other than a general reference to “wetness.” Such dissension is magnified more by the recent inclusion of coral reefs and cave ecosystems under the purview of the term wetlands.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 S. K. Chakraborty et al., Wetlands Ecology, https://doi.org/10.1007/978-3-031-09253-4_1

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All these debates and contradictions have posed difficulties in the development and implementation of wetland-specific legislations and policies because of the large extent of wetlands ‘habitats and changing perception and dependence of different groups of stakeholders. Paijmans et al. (1985) undertook a rational overview of wetlands and used the definition as: “Land temporarily or permanently under the water or in waterlogged habitats.” Wetlands representing one of the sensitive, vulnerable and productive ecosystems of the globe comprise around 6% of the world’s surface contribute profusely ecological and economic benefits to the human beings and other natural components of this mother earth (Hines, 1972; Gosselink & Maltby, 1990; Mitsch, Lewis, 1995, 1994; Mitsch et al., 2013). Although many such definitions for wetlands have so far been proposed and used in the literatures over the years, the most acceptable definition of wetland across the world was put forward by Cowardin et al. (1979), which was subsequently adopted by the U.S. Fish and Wildlife Service, as “Land having an excess of water which plays dominant roles in determining the patterns of soil development and the floristic and faunistic inhabitants at the soil surface within the span of a continuum of environments where terrestrial and aquatic ecosystems are integrated in order to exchange required life supporting substances between the two ecosystems. This definition accommodates three different aspects, water, soil, and organisms, which have been taken into consideration for discussion by the researchers of the ecology of wetlands with the objective of eco-assessment of wetland environments. Wetlands are also defined as “lands which are transitional in between aquatic and terrestrial ecosystems and where the water table generally remains at or near the surface or the land is covered by shallow water” (Mitsch & Gosselink, 2007; Gosselink, 2015). Wetlands tend to remain sandwiched in between the terrestrial and open water system and ensure exchange of materials in between them in order to make both the ecosystems productive. Owing to the varied form of contradictions and conflicts with regard to the appropriate definition of a wetland and the problems of interpreting, this term has been the subject of considerable debate. Cowardin et al. (1979) also acknowledged that there is no single, non-controversial and correct definition for wetlands, mainly because of the large scale diversity of wetlands in respect of their structure and function and the prevailing demarcating factors that tend to exist along a continuum of dry and wet environments. In the definition of Cowardin et al. (1979), more stress was put to delimit the extent of the variety of areas of wetlands that fall into one of five different categories: 1.  Any area which is endowed with hydric soils along with hydrophytes, such as those commonly known as fens, bogs, marshes and swamps. 2.  Any area possessing hydric soils but without hydrophytes, for example, flats of sediments where drastic fluctuation occurs in respect of water volume and level, wave action, turbidity or high concentration of salts and all those factors may prevent the growth of hydrophytes. 3.  An area characterized by the presence of hydrophytes but without hydric soils, such as margins of impoundments or excavations where hydrophytes are seen to grow but hydric soils do not exist.

1.2  Genesis of the Concept of Wetland

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4. An area without any natural sediments but with the presence of hydrophytes, such as the sea weeds which can even grow and cover some parts of rocky shores. 5.  An wetland without any hydric soil and hydrophytes, such as beaches with gravels or rocky shores which hardly support the vivid presence of vegetation. According to Charman (2002), wetlands must have four basic morphogeological features: 1. Wetlands are associated and connected with ground water which represents the water table or zone of saturation. 2.  Wetlands must possess hydric soil (wet soils). 3.  Wetlands are endowed with specialized hydrophilic vegetation which are commonly referred to as hydrophytes with the potential to grow up as aquatic or semi-aquatic vegetations (moss, sedges, grasses, reeds, cattail, woody halophytes, cypress, etc.). 4. The substrate of wetlands should be saturated with water or covered by shallow water at least for a continuous some period during the rainy season of each year.

1.2 Genesis of the Concept of Wetland Representing the transitional zone in between aquatic and terrestrial ecosystems, there have been long-standing debates among the experts and non-experts across the world during last several decades pertaining to the concept of wetlands in the changing ecological conditions. The Convention of Wetlands of International Importance (UNESCO, 1971, http://www.ramsar.org/key_conv_e.htm) had included both lotic (estuaries, rivers, etc.) and lentic (lakes, shallow water bodies, including natural reservoirs) water bodies within the purview of the concept of wetlands. Shaw and Fredine (1956) referred “The term wetlands” as “lowlands covered with shallow or sometimes temporary or intermittent waters.” They are named as marshes, swamps, bogs, wet meadows, potholes, sloughs and river-overflow lands. These categories also include some commonly occurred shallow water small water bodies (ponds and lakes) having emergent macrophytes as the main characteristic properties, whereas the permanent water bodies, like deep lakes, reservoirs and streams, are not included. Besides, very temporary water areas without that much effect on the development of moist-soil vegetation can be considered as wetlands. Ramsar Convention in the year of 1971 on wetlands had attempted to discern any water-covered landscape areas whether natural or artificial, temporary or permanent, running (lotic) or without water movement (lentic), fresh water, brackish water or saline water, even in the realms of marine ecosystem but the depth of the water in any case should not be more than six metres during the low tide (fen, bog, peat land or marsh). For regulatory purposes, the meaning of the term wetlands include “those areas which experience in normal state of inundation or saturation by surface or ground water at a frequency and duration sufficient to support the growth and propagation of aquatic vegetation naturally adapted for their

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survivility in saturated soil conditions which generally include swamps, marshes, bogs, and similar areas” in accordance with the Clean Water ACT, USA, which became the laws in the year 1972. In Sweden, “wetlands” are considered to have two under-mentioned key ecological features as advocated by Swedish Environmental Protection Agency (2005): 1. They hardly possess permanent surface waters but are flooded by surface waters or ground water for large parts of the year (Leonardson et al., 1994). 2. They have vegetation but at least 50% of which should be hydrophytes (SEPA, 2005). This category of wetlands include all varied types of mires, wet forests, shore pastures, shallow water bodies of different sizes and also shallow saline water impoundments along the shores (SEPA, 2005). However, all these criteria would not be appropriate with the inclusion of the extensive lake and river systems which are often considered as wetlands in some countries, especially which are located around the Mediterranean region. US Army Corps Engineers, 1987, considered the term “wetland” to represent that part of the landscape which remains water saturated or inundated by surface water or ground water with the required intensity, frequency and duration of water stagnation which are sufficient to support the prevalence of aquatic vegetation suited to lead an aquatic life in saturated conditions. Wetlands generally are represented by marshes, swamps, bogs, fens and similar areas. Mitsch & Gosselink, 2000, explained that “Wetlands must have many distinguishing features, the most notable of which are the presence of standing water, unique wetland soils, and vegetation adapted to or tolerant of saturated soils.” Clymo et al. (1995) highlighted three common features in order to justify a wetland systems which are mentioned below: 1. Porous solid matrices partially or completely filled with water that may be moving or stagnant. 2. Water present near or above the surface of the matrix for at least some parts of the year, thus emphasizing the transitional state of the water rather than its permanence. 3. Microbiological activity on the bottom substrates within the wetland ecosystem in the absence of sufficient oxygen and sunlight often creates anoxic ecological conditions in at least part of the matrix. Lewis et al. (1999), expounded that the generic term “wetland” is now used worldwide and includes specific ecosystems known regionally as fens, bogs, bottomlands, floodplains, marshes, swamps, mangroves, peat lands, potholes, reed swamps, sloughs, meadows and prairies. A plethora of wetlands are delimited due to varied ecological characteristics generated within this transitional landscape. In order to overcome all these controversies and conflicts, certain characteristic features and criteria as mentioned below are being highlighted to designate a landscape as wetland. 1. Wetlands are distinguished predominantly by the presence of some specific ecological properties of water, either at the surface or within the root zone.

1.3  Origin of Wetlands

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2. Wetlands must possess characteristic soil or sediment conditions that differ from adjacent non-wetland areas. 3. Wetlands support vegetation and also animals which are specifically adapted to permanently or seasonally wet conditions. Different facets of this definition have further been clarified by setting the boundary of wetlands within both the terrestrial and deepwater habitats which are appeared to assume more importance in the context of Ramsar’s definition and also in the perspectives of the management of wetlands. Wetlands are broadly grouped into two under mentioned categories: 1. Fresh water (inland) occurring above the mean sea level which includes those water bodies which are either developed in the terrestrial environment (fresh water) and in the saline waterbodies (salt lakes) experiencing estuarine or brackish water conditions (lagoons and backwaters). 2. Marine (coastal) wetlands occurring in the junction of terrestrial and marine ecosystems which include estuaries, lagoons and mangroves.

1.3 Origin of Wetlands The shapes, sizes, water retaining capacity, depth and volume of water, geomorphology, vegetation, water chemistry, sediments profiles and biodiversity wealth of wetlands vary according to their origin and geographical location. For example, marshes, one of the productive wetland ecosystems among all other ecosystems in the world are dominated by herbaceous plants and sustained by different water sources other than direct rainfall where ground water, surface springs or streams cause frequent flooding. Wetlands are found to have developed naturally or they may have been constructed or modified by the direct human activities which are locally designated in India as fish ponds, dighi, bheries, paddy fields, etc., or partly natural after being developed as indirect human activities, such as bills, lakes, jheels and shallow reservoirs. It must be emphasized that all kinds of wetlands (all inland aquatic ecosystems) are integrated into different river basins, from where they may remain separated by some physical barriers but are linked together by the hydrological cycle. However, mangroves or salt marshes have their uniqueness in respect of their developments, existence and connections with other wetlands. The interactions between wetlands and adjacent systems involve the exchange of organic matter through different structural components, like water, soil, flora and fauna (Odum, 1971; David Moreno-Mateos et al., 2012). As stated by Naiman et al. (1989), wetlands have also been described as ecotones, providing a transition between dry land and water bodies. Wetlands being the most productive ecosystems on the Earth among all other ecosystems (Ghermandi et al., 2008), provide many important services to human society (Brink et al., 2012). In addition, different categories of the wetland ecosystems demonstrate specific ecological sensitivity and required

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adaptability (Turner et al., 2000). The term “wetland” refers to an assemblage of various forms of habitats which share a number of common features, the most important of which is the presence of continuous, seasonal or periodic standing water along with saturated hydric soil endowed with distinct vegetational composition (Finlayson & Von Oertzen, 1996; Finalayson et al., 1997; Mitsch & Gosselink, 1986, 1993, 2007, 2015; Mitsch et al., 1989, 2010, 2012; Hansel et al., 1991; Maltby & Baker, 2009; Marti-Ortega, 2015).

1.4 Criteria for Designating a Wetland as Ramsar Site With an aim at ensuring proper protection and conservation of wetlands, the Ramsar Convention states in the Article 2.1. that “riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water not deeper than six meters at low tide should be included within the umbrella of wetlands” (Ramsar Convention Secretariat, 2013). Ramsar Convention (1971) also adopted definition stressing upon the importance of macrophytes in structuring as well as driving the ecological functioning of wetlands and included bogs, fen, swamp and marsh, all of which were characterized by specific plant communities. Since then a lot of research works have been undertaken but a universally acceptable definition of wetlands could not be agreed upon (Maltby, 2009). In order to substantiate that claim in the practical perspective, Ramsar Convention also took into consideration different forms of water bodies, such as lakes and rivers, as to be the parts of “wetlands in their entirety, regardless of their depth”. Pittock et al. (2015) used the term wetlands interchangeably with freshwater ecosystems with that of different inland water bodies and define them as areas within landscape where water is considered as the prime factor controlling the diversity and distribution of flora and fauna where the water table lies at or near the land surface as standing water mass covering the land.

1.5 Types, Classification, Sizes, and Extent of Distribution of Wetland Ecosystems However, wetlands serve so many ecological and economic goods and services for peoples of the globe, occupying only 6% of the land surface of the world. However, detailed information pertaining to the types, location, functions, values and ecological status of wetlands across the world are still remained substantially incomplete and extremely limited because of the lack of proper inventory. However, the wetlands of the tropical regions represent collectively some of the most ecologically significant areas of the world which are poorly understood in comparison to the wetlands of temperate regions (Gopal & Mitsch, 1995).

1.5  Types, Classification, Sizes, and Extent of Distribution of Wetland Ecosystems

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There exists a striking contrast in between the developed, mostly located in temperate regions, and developing world having tropical climatic conditions in terms of the ecology and management priorities of their wetland resources. It has made it imperative to recognize this distinction in any assessment in tune with the current demands of the researchers involved to take care of the burning environmental issues related to wetlands. The research and development on the diverse networks of wetlands ecosystems, including fresh, brackish and saltwater marshes, inland and coastal swamps, floodplains, peat lands and shallow water bodies in respect of their resource bases, and optimum utilization strategies on the tropical wetlands are still found in the negligible state of affairs. Thus, wetlands have turned into waters without the role of “land” in them. A wetland classification approach was initiated where wetlands are arranged along the hydrological gradients which play primary roles in determining the interactions among different gradients of nutrients and salinity (Maltby & Turner, 1983; Gopal et al., 1990; Keddy, 2010). Recognizing of wetlands as ecotones has necessitated to elaborate the ecological concept of ecotones in respect of wetlands as being a transitory zone in between land and water and such proposition also may help understand the significance and conservation strategies of wetlands (Patten et al., 1985). In such respect, alongside considering the wetlands as ecotone, it is important to note that wetlands are also considered as ecosystems because of their own structural and functional merits (Naiman & Decamps, 1990). Over the past five decades, the resolutions adopted in the Ramsar Convention have been expanded the flexibility and scope of wetlands to include all kinds of aquatic ecosystems except oceans (Ramsar Convention Secretariat, 2013). Thus, all rivers, dams, large lakes, coral reefs, karst and subterranean systems can also be recognized as wetlands, putting greater emphasis only one unifying character that is the continuous presence of water at least for some period of the year. In addition to macrophytes, next living components which demand more attention in characterizing the wetlands are “waterfowl”. In view of the rapidly deteriorating ecological conditions, sound management policy coupled with the scientific understanding in respect of the functioning of wetlands through the interactions of their several structural components is very much needed in order to ensure the supply of various forms of ecosystem goods and services for both the ecological and economic benefits of human beings in a sustainable manner (Chamberlain, 1960; Keddy & Lauchlan, 2000; Sipauba-Tavares et al., 2002). Among so many initial attempts to highlight classificatory schemes of wetlands, classifications systems, devised by Cowardin et al. (1979), emphasized mostly on the ecological, hydrological and geological properties of different types of wetlands, such as Marine (coastal wetlands including rock shores and coral reefs), Estuarine (deltas, tidal marshes and mangrove swamps), Lacustrine (lakes), Riverine (rivers and streams) and Palustrine (marshes, swamps and bogs). Wetlands occur extensively all over the World from the cold Arctic and Alpine regions to the moist and warm tropical rainforests and hot and dry subtropical deserts. The diverse eco-climatic regimes of India have contributed for the development of a diversified forms of wetland systems ranging from cold desert wetlands of

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high altitude to hot and humid wetlands in the marine-estuarine-coastal environment supported by different forms of plants and animals (Prasad et  al., 2002). According to Deepa and Ramachandra (1999) the freshwater wetlands alone account for the 20% of the familiar and common range of biodiversity components of India. Besides, an estimate has revealed the presence of 58.2 million hectares of wetlands, including areas under direct agricultural activities (Prasad et al., 2002). Another estimate has shown the occurrence and extent of coastal ecosystems (including mangroves) in India as to be around 43,000  km2 (Kathiresan & Thakur, 2008). The areal extent of wetland ecosystems was found to range from 917  million hectares (Lehner & Doll, 2004) to more than 1275 million hectares (Finlayson & Spiers, 1999) in the global perspective. Panigrahi et al. (2012) recorded an extent of wetlands in India nearly to be around 15.26 million hectares of which inland wetlands occupy an area of 69.22% (10.564 million hectares) in contrast to the coastal wetlands accounting for 27.13% (4.14 million hectares), whereas high altitude wetlands (situated >3000  m asl) across the Himalayan mountains account for about 126,249 hectares. According to Cowardin et al. (1979), the boundary between wetland and deepwater habitats within the marine and estuarine ecosystems coincides with the elevation of the extreme low water of spring tide where permanently flooded areas are considered deep-water habitats in these systems. The boundary between shallow wetlands (small streams of Riverine, Lacustrine and Palustrine) and deepwater aquatic ecosystems (the marine and estuarine ecosystems, the depth of all should remain within 2 m) enables for the growing up of emergent shrubs, or hydrophilic trees beyond this depth at certain period of time. Cowardin et al. (1979) also pointed out the ecological status of wetlands as an ecotone representing the transitional systems because of their location between deepwater and terrestrial habitats. In such context, the floodplains, lakes, littoral lagoons and intertidal zones experiencing water inundation of not more than 6 metres receive fresh water from the surrounding uplands and also remain connected with the adjoining sea during the tides. Temporary wetlands which possess surface water or water logging of sufficient frequency and duration pose adaptive challenges to aquatic biota (Storrs & Finlayson, 1997). In order to device goal oriented objectives, it is imperative to understand the distinction between the natural and artificial wetlands towards formulating strategies for proper conservation but making such distinction has appeared to be very much blurred. Similarly, determination of morphometric and ecological differences in between floodplains and reservoirs (irrigation channels, dams for hydropower, etc.); marshes and swamps; fish ponds and lakes; paddy fields and shrimp farms; etc., is also required to be done. Each category of wetland is having its own distinct ecological characteristics. Marshes, swamps, bogs, fens, etc. constituting broad categories of wetlands tend to exhibit distinct differences with respect to hydrology, vegetative communities and soil types. All these types of wetlands are mainly dominated by as follows: (i) Marshes (tidal and non-tidal) which are periodically saturated, flooded or with

1.5  Types, Classification, Sizes, and Extent of Distribution of Wetland Ecosystems

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water in depressed land and characterized by herbaceous (non-woody) vegetation grown up on fertile bottom soils loaded with minerals or organic matter; (ii) Swamps which are primarily fed by surface inputs and supply of mineral or organic matter enriched soils which prompt the growth and propagation of woody halophytic trees and shrubs as mangroves; (iii) The main source of water for bogs is rainwater and these unique freshwater wetlands are characterized by spongy peat deposits; (iv) Fens, being the peat-forming wetlands, are groundwater fed and grasses, sedges, reeds and other such kinds of plants dominate its biotic community. Forty two (42) types of wetlands are grouped into three categories through the discussions in the Ramsar Convention which include Marine and Coastal Wetlands, Inland Wetlands and Human-made Wetlands (IUCN, UNEP, WWP, 1985; Ramsar Convention Secretariat, 2013). Moreover, based on the water and soil qualities, sizes and shapes, volume and depth of water and morphometric and morphoedaphic factors, following five categories of wetlands, can be distinguished: 1. Marine and coastal wetlands (coastal lagoons, rocky shores and coral reefs). 2. Estuarine (deltas, tidal marshes and mangrove swamps). 3. Lacustrine (wetlands associated with lakes). 4. Riverine (wetlands along the rivers and streams). 5. Palustrine (small water bodies, “marshy” marshes, swamps and bogs). Moreover, some artificial wetlands may be cited as other categories, such as ponds or small water bodies of various types (ponds for fish and shrimp culture, irrigation channels, wet agricultural land, salt pans, dams and reservoirs, gravel pits and sewage canals, etc.). Besides, other man-made wetlands, such as reservoirs, ponds, lagoons, extraction pits, waterways tend to mimic the established mitigation strategies against wetland losses and these have become an increasing scenario of both the developed and developing world. The concept pertaining to the mitigation efforts is now recognized as an important avenue to conserve the wetland resources, but its acceptability depends on the intensity and extent of functioning of artificial wetlands in order to mimic the functions as well as appearance of natural wetlands.

1.5.1 Wetlands in the Floodplains Wetlands in the floodplains with the assemblages of vegetation must have the following criteria: 1. The habitat is inundated or saturated by surface or ground water periodically during the season with higher precipitation. 2. The soils within the root zone become saturated periodically during the monsoon season.

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3. The growth, maturity, reproduction and survivability of woody plant species take place within wetlands because of their morphological and physiological adaptabilities for ensuring survivability in restricted eco-zones of wetlands with anaerobic soils for varying periods during the growing season.

1.6 Assessment of Wetland Ecosystems of India Wetlands, which are important providers of various types of services to the humans, are defined as “areas of marsh, fen, peatland or open water bodies, either natural or artificial, temporary or permanent, lentic (static) or lotic (flowing), freshwater, brackish water or saline, including areas of marine water, the depth of which does not exceed six meters at low tide” (Article 1.1, Ramsar, 1971). Wetlands constituting around 9% of the total land area have been under the process of ecodegradation during last one century and more than 50% of the existing wetlands have been degraded on the verge of permanent loss because of so many anthropogenic activities, including industrial and agricultural activities, urbanization, water pollution and climate change (Zedler & Kercher, 2005; U.S. Fish and Wildlife Service and U.S. Census Bureau, 2002; Arimoro et al., 2015). Assessment of the extent of different forms of wetlands (natural to man-made) in India, in contrast to global scenario, is fraught with dealing the difficult issues in respect of definition and methodologies. Consistent baseline data and research information with regard to the hydro morphometrical constituents (maximum depth, length and breadth, total surface area and habitats suitable for flora and fauna) are only available for specific types of wetland, for example, mangroves, which have been studied by multiple group of researchers on getting supports from international, national and regional environmental agencies (Chaudhuri & Chaudhury, 1994; Chakraborty, 2011, 2017) during the last five decades. Moreover, since the initial situation, rapid changes have resulted in respect of identifying the thrust areas of research, changing state in the assessment methodologies for recording and interpolating of the research information in order to assess and ascertain the trend of changes in the perception and conservation of wet lands in the country. In order to overcome the problems pertaining to the inconsistent national database of inland wetlands, the first major attempt was made to map the wetlands of India using remote sensing techniques in the year 1998. When using the satellite data of the years 1992–93, wetlands were mapped mostly on scales of 1:250000 and also for some areas at a scale of 1:50000 (Garg et al., 1992, 1998; Panigrahy et al., 2012; Pattanaik et al., 2015; Garg, 2015).

1.8  Functional Manifestations of Wetlands Towards Generating Values

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1.7 Distribution of Wetlands in India Wetlands in India expand over 58.2  million hectares, including areas under wet paddy cultivation (40.9  million hectares) (Directory of Asian Wetlands, IUCN, 1989). Maltby and Turner (1983) had reported the extent of wetlands area of the World which was around 6.4% of the total land area. Wetlands covering around 6% of the total World’s land surface, are found to exist in all types of climate and on all the continents in the World (Hillel, 1992). The Ministry of Environment and Forests, Government of India (1990) has estimated that India has about 67,429 wetlands with an area coverage of about 4.1 million hectares (excluding paddy fields and mangroves). Out of these, about 2175 wetlands are natural wetlands occupying an area of 1.5 million hectares and about 65,254 wetlands were man-made with 2.6  million hectares area. Out of the total area covered by the wetlands in India, 0.45 million hectares have been occupied by mangroves, about 80% of which are distributed in the Sundarbans of West Bengal and Andaman and Nicobar Islands, while the 20% are found in the coastal states of Odissa, Andhra Pradesh, Tamil Nadu, Karnataka, Kerala, Goa, Maharashtra and Gujrat (IUCN, 1989; Garg et al., 1998; Chakraborty, 2011). The nationwide wetland inventory carried out by Garg et al. (1998) reveals that there are 7.6 million hectares of wetlands in the India of which 4.0 million hectares are coastal wetlands and 3.6 million hectares are inland wetlands. Most of the freshwater inland wetlands remain associated with the major rivers of India, like Ganges, Brahmaputra,Godavari, Narmada, Krishna, Kaveri and Tapti (Prasad et al., 2002). All of these inland wetlands occur in the hot arid climatic eco-regions of Gujarat and Rajasthan, the deltaic regions of the east and west coasts, islands of Andaman and Nicobar and Lakshadweep, highlands of central India and wet humid zones of south peninsular India.

1.8 Functional Manifestations of Wetlands Towards Generating Values Wetlands of the world are formed from the interactions of several physical forces determined by hydrological, geomorphological and biological parameters which in turn provide energy and nutrient subsidy to the associated environmental set-ups. The ecological functions of the wetlands are regulated by interactions within biotic community, physico-chemical processes, water availability and budgeting (surfacewater storage and groundwater storage), thereby contributing valuable ecological services to human beings in respect of biomass production, sustenance of food chains and food-webs, development of habitats for fish and wildlife, control of erosion, maintenance of water quality, storage of water and control of floods, augmentation of environmental flows, and recharging of aquifer (Mitsch et al., 1989, 2010).

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Any eco-zone designated as wetland must have hydric soils soaked or filled up with water at least for a certain duration of a year, and therefore, many of the wetlands are found to be completely without any water at certain times of the year, especially during hot dry seasons. However, all categories of wetlands always render some very common valuable ecosystem services that directly benefit people and wildlife and are technically described as the values out of wise use of wetlands. In the 1970s, scientists, ecologists and conversationalists began to emphasize upon the values and functions of wetlands which constitute an important driving force for global hydrologic cycle (Helfgott et al., 1973; Bertulli, 1981; Michael & Sharma, 1988; Naiman et al., 1988; Arimoro et al., 2015). The functioning of the wetlands due to the physical, chemical and biological processes involving so many eco-biological attributes is found to play vital roles in ensuring the ecological integrity of the wetland ecosystem. Values, on the other hand, are wetland attributes that are perceived as being valuable to society (Adamus et  al., 1991). According to the opinion of some scientists, such as Mitsch & Gosselink, 1993; Mitsch & Wu, 1995; Keddy, 2000; Fairbairn & Dinsmore, 2001, the functions of wetland depend on (i) wetland characteristics (size and morphometry); (ii) adjoining environment; (iii) watershed characteristics; (iv) position of the wetland in the watershed and (v) greater landscape condition. Forman and Godron (1986) put forward the view on the determining roles of hydrologic regime, plant species composition and soil type in shaping structure and function of wetland ecosystem. In this connection, Bruce et al. (2006) advocated with regard to the variable capacity of a given wetland to perform a given function under variable ecological conditions. All of these values of wetlands are mentioned below: 1. Act as shelter for a wide variety and number of wildlife and plants by providing them proper habitats. 2. Filter, recycle, clean and accommodate water so that wetlands can serve as kidneys of nature. 3. Resist the thrust of flood water by acting as buffer and on receiving water hold it and recharge the ground water by accelerating the percolation process. 4. Resist natural disasters storms and cyclone by combating the wind and tidal pressures. 5. Provide aesthetic and recreational avenues. 6. Accumulated water within the wetlands acts for filtering and purifying water flowing over the wetland system during flood and thereby maintains the level of water at normal state. 7. A variety of plants within the wetlands help control water erosion.

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1.9 International Perceptions on the Values and Functions of Wetlands Wetlands possessing unique ecological features provide numerous products and services to humanity. The values rendered by wetlands through ecosystem functioning have been acknowledged and accepted by the international community and have been increasingly receiving due attention as such contribution not only sustains the natural ecosystem but also enables sustainable human development. All these values in the form of ecological services and production of essential commodities (food, medicines, shelter and clothing materials, etc.) act for the survivability of human beings (Mitchell & Gopal, 1990; Mitsch & Gosselink, 2015). Ecosystem goods and services provided by the wetlands by virtue of ecosystem functioning include water for direct human consumption and also for other domestic activities, irrigation and draining of water of water for agriculture and fisheries, nutrients cycling, generation of biomass for supplying fodders, fuels and building materials, purification of water, attenuation of floods, prevention of soil erosion, maintenance of streamflow, recharging of ground water and development of avenues for recreational purposes (Turner et al., 2000). The ongoing interaction of man with wetlands during the last few decades has been increased considerably due to the higher rate of population growth, rapid pace of urbanization coupled with industrial developments, etc. And all these incidents have contributed for the ecodegradation of wetlands mostly by the impact of both point and non-point sources of pollutants, such as domestic and industrial sewage, agricultural run-offs loaded with chemical fertilizers, insecticides and feedlot wastes (Gopal, 1990; Conley et al., 2009).

1.10 Biodiversity in the Wetlands of India: Rational Behind the Protection and Conservation of Wetlands The total water resources of the earth equal to 326 million cubic mile; only 2–5% of water is fresh water and 97.5% is salt water. Water resources being the most precious gift of nature support the lives of galaxy of flora and fauna in aquatic ecosystems. Aquatic biodiversity is one of the most essential characteristics of the aquatic ecosystem for maintaining its stability and means of coping with any environmental changes. Almost 69% of freshwater resources are locked up in the glaciers and ice caps, whereas about 30% remains as ground water and only about 0.27% is seen as surface water, inland aquatic ecosystems and their biodiversity (Bassi et al., 2014; Chakraborty, 2021b).

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1.10.1 Biodiversity of Wetlands and Determining Attributes The diversity of wetlands are determined by their genesis, geographical location, water regime and chemistry, dominant species and soil and sediment characteristics (Space Applications Centre, 2011). In Asia, the biodiversity of wetlands is determined by a spectrum of complex interacting ecological, economic, socio-cultural and political factors which operate in the continuum of environmental gradients which determine their present and future of biodiversity wealth. The diversity of biophysical environments ensures the growth of rich biodiversity components of inland aquatic bodies and their present status has been greatly determined by human societies that have depended on them for millennia. The aquatic biodiversity and future prospect for sustenance in Asian countries are expected to be determined by the national policies on water, based on prevailing research information. India, being one of the 18 “megadiverse” countries, is endowed with a diversity of ecological habitats, like forests, grasslands, wetlands, deserts and coastal and marine ecosystems. From the biodiversity point of view, India is regarded as a mega diversity country. Out of the total estimated species of the world, about 8.5 million species are reported from India. Wetlands, one of the most productive ecosystems in the world, bridge the gap between land and water and ensure the interlinkages and interdependences of so many structural components of both the ecosystems by virtue of continuous exchange of materials among different biotic components (trees, grasses, shrubs or moss) and are named swamp, marsh and bog. Deepa and Ramachandra (1999) proposed that freshwater wetlands alone support 20% of the known range of biodiversity in India. According to Prasad et al. (2002), natural wetlands in India include high altitude Himalayan water bodies, flood plains of the major river systems, saline and temporary wetlands of the arid and semi-arid regions, mangroves, swamps, estuaries, lagoons and corals as coastal wetlands. In fact almost all types of wetlands of the world are found in India excepting the bogs, fens and temperate salt marshes. Moreover, a variety of man-made wetlands also contribute to the faunal and floral diversity of Indian wetlands. A sizeable portion of large wetlands remain away inaccessible to large mammals, including man, and thereby enable a diversity of ecologically important and aesthetically celebrated wildlife to flourish. Besides, putting additional emphasis on palaeolimnological studies in generating information of ontogeny of wetland ecosystems facilitated towards preservation of a stratified record of past succession of different biogeochemical processes (importance of dissolved and particulate detritus as the overall stabilizer in the metabolism of ecosystems), trend of exploitation and conversion of wetlands to paddy fields, etc. Fishes being the most visibly dominant living components of both lotic and lentic systems constitute almost half of the total number of vertebrates in the world (Day, 1889). From ecological point of view, the diversity of flora and fauna in wetland ecosystems species indicates the relative importance of the aquatic biodiversity having environmental, social and economic value (Prasad et al., 2002). Wetlands permit

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to grow different kinds of aquatic plants and animals, therefore, known as “Diversity of Life in A Vessel” (Greenway & Woolley, 1999; Kar et al., 2000; Kusler, 2003; Ghatak, 2010). Wetlands are also home to many threatened and endangered species. Freshwater and marine life, including sunfish, trout, pike, striped bass, crappie, crab and shrimp, rely on wetlands for food, cover, spawning and nursery grounds. 131 species of different freshwater fishes belonging to 67 genera, 28 families and 10 orders from Indian Wetland have been reported (Kar et al., 2000). The fish population as nektonic communities plays in significant role in energy flow of system (Kennish, 2002). More than 40% of all the world’s recorded species and 12% of all animal species have been estimated to be present in the wetlands (Schuyt & Brander, 2004). Individual wetlands are also important for their roles in supporting high numbers of endemic species, as, for example, Lake Tanganyika in Central Africa harbours 632 endemic animal species (Schuyt & Brander, 2004). Currently, wetlands are located as the home to 22% of native birds and 30% of total inland fish production in the state of West Bengal, India (Paul et al., 2011). Zooplankton constituting one of the important faunal components of wetland ecosystem is the principal herbivorous consumers, converting from plant to animal matter, provide food for numerous benthic and nektonic fauna (Kennish, 2002). The species diversity of zooplankton has gained importance in recent decades because of their applicability for the bio-monitoring of wetlands in the face of ongoing ecological perturbations and pollution (Khan, 2003; Pradhan et al., 2003). The dominance of zooplankton in shallow water bodies by rotifers, cladocera or copepods varies according to the degree of organic pollution (Rao & Durve, 1989; Walsh et al., 2005; Arimoro & Oganah, 2010). More than 600 species of different zooplankton have been found to inhabit in the freshwater wetlands of India (Willams, 1993; Shukla et al., 2012).

1.10.2 East Kolkata Wetlands: Potential for Values and Goods The city of Kolkata, the state capital of West Bengal, is sustained by a unique and friendly water regime and the city was grown along the levee of the river Hooghly which flows in the west of the city and the river Kulti-Bidyadhari flows around 30 km eastwards that carries the drainage to the Bay of Bengal. A copious reserve of ground water is present underneath the city. However, the main ecological pride of the city is the vast wetland area beyond its eastern edge of the city where the sewage-based wastewater is transformed into the wealth of fisheries, vegetable gardens and paddy fields in successive tracts of land, thereby converting the entire area as the ‘waste recycling region’ (Ghosh, 1985). This entire network of wetlands within the East Kolkata Wetland with the tremendous power of waste recycling covers about 12,500 hectares which represents the largest natural “waste recycling

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region” in the world. The underlying scientific principles operating behind such remarkable way of transformation of wastes into valuable products have been applied by the local peoples, especially fish farmers in an innovative as well as upgraded manner, towards the wise use of wetlands. Economic values of wetlands are directly linked up with the ecological services towards production of wetland’s goods, such as food, fodders, fuels, building materials, and aesthetic appeal along with supplying of water for drinking, cooking and washing (Turner et al., 2000). Kundu (2010) highlighted the role the wetland system in securing ecological and economic security of the Kolkata city along with most of the parts of the entire Gangetic Delta. Considering all the available research facts, East Kolkata Wetlands can be recognized as the backbone of food security of Kolkata city. Dhapa produces around 150 MT of vegetables daily (Kundu, 2010). According to Ghatak (2010), around 60,000 working population directly depend on the East Kolkata Wetlands for their livelihoods. Considering the eco-potential of wetlands for recycling the wastes, these fragile, sensitive but biologically productive ecosystems are assigned with the status of “kidneys of the landscape” (Mitsch & Gosselink, 2007) which can trap wastes and filter out the pollutants and thereby enhance the quality of water in one hand and enable the biological components to survive on the other (Abbasi, 1987, 1991; Abbasi & Nipaney, 1991; Abbasi et al., 1992). As a part of phytoremediation process by using macrophytes as biofilters for waste water, wetlands tend to improve the production and consequently decrease the harmful impact of the toxic substances (Tavares & Favero, 2002; Sanyal et al., 2015a, b; Chakraborty et al., 2021). In addition, aquatic plants play vital roles in the removal of nutrients and retention of the same within floral biomass and help in preventing the eutrophication of wetlands. According to Williams (1990), toxic residues from water products, such as heavy metals, pesticides and herbicides, can be removed from the water by ion exchange and absorption processes from the organic and clay sediments through the uptake by aquatic plants, like bull rush (Schoenoplectus lacustris), common reed (Phragmites australis) and water hyacinth (Eichhornia crassipes) (as the aggressive colonizers of water bodies) (Liao & Chang, 2004). As the common floating aquatic plants, both water hyacinth (Eichhornia crassipes) and duckweed (Lemna sp.) have shown their ability to reduce concentrations of BOD, TSS, Total Phosphorus (P) and Total Nitrogen (N) (Ajibade et al., 2013). The experimental study of water hyacinth by Norman et al. (1998a) demonstrated the potential of water hyacinth to reduce chromium from the water and soils of wetland. This plant displays great ability to absorb high nutrient concentrations from the medium, and absorption levels are related to plant growth conditions (Gopal, 1999). Landscape characteristics control wetland hydrochemistry and hydrobiology (Chapman, 1996). The hydrological properties of water bodies are directly related with the modification or changes of chemical and physical properties, such as nutrient availability, soil salinity, texture and nutrients of sediments and pH.

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These alterations in the non-biological environment in turn have a direct impact on the biotic response in the wetlands (Gosselink & Turner, 1978). The biota responds with the changing ecological hydrological conditions in wetlands by altering the species composition and richness of the biotic community and biological productivity in the ecosystem (Gopal, 1995). Wetlands retain water and maintain the water table high and relatively stable during dry periods by soaking up surfacewater run-off and releasing it gradually which often results in an increase in the production of agriculture and fishery sectors of the surrounding areas. During periods of flooding, wetlands tend to attenuate floods (to soak up water like a sponge) and reduce downstream erosion through trapping suspended solids and nutrients. Wetlands also act as a sink for contaminants in many agricultural and urban landscapes (Bassi et al., 2014). Tidal and inter-tidal wetland systems having mangroves or corals through their ecosystem functioning help protect and stabilize coastal zones by resisting natural disaster, like storms or cyclones, and also maintain shorelines (Chakraborty et al., 2014; Chakraborty, 2017).

1.10.3 Recreational and Educational Roles of Wetlands Countless avenues and scopes are provided by the wetlands for environmental education, research and public awareness programmes because the diversity of living organisms offers opportunities for sightseeing, fishing, hunting, hiking, boating, bird watching and photography (Ramchandra & Solanki, 2007).

1.10.4 Wetlands and Flood Control Several works related to flood flows desynchronization as one of the wetland ­functions have been highlighted by Young and Klawitter (1968), Johnson and Senter (1977), Carter et  al. (1979), Clark and Clark (1979), Novitzki (1979), Chamberlain (1982) and Schwan (1985). The flood control function of a wetland is partly dependent on wetland–watershed ratio, size, depth and live storage (Reinfield, 1998). Wetlands by virtue of their efficient functional roles against natural disasters, including flood, can become an effective natural capital for conventional flood control investments, such as dams, dykes and embankments (Boyd & Banzhaf, 2007).

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1.10.5 Roles of Wetland in Trapping Sediment vis-a-vis Anti-erosion Roles Wetlands improve water quality by acting as sediment sinks (Houlahan & Findlay, 2003). Vymazal (1995) gave an idea on absorption of toxicants, nutrients and other mobile chemicals by vegetation in water body. Wetlands and Atmospheric Equilibrium: Several other researches have pointed out about the atmospheric maintenance as one of the wetland functions (Vymazal, 2007, 2014). Therefore, he wetlands all over the world help combat and reduce global warming mediated climatic changes by storing carbon within live and preserved (peat) plant biomass instead of releasing it to the atmosphere as carbon dioxide, a major greenhouse gas [Intergovernmental Panel On Climate Change (Sengupta et  al., 2002; Ray et  al., 2011; IPCC, 2013)].

1.10.6 Wetlands and Coastal Protection Coastal marshes absorb wave energy and reduce erosion on estuarine shorelines and so buffer the land from storms. More than 50% of wave energy is dissipated within the first 2.5 metres of the marsh. The coastal subsidence due to global sea level rise can be survived by the coastal wetlands. (Williams, 1993). Coastal wetlands particularly mangroves help in shoreline stabilization and storm protection by dissipating the force by reducing the damage of wind and wave action (Badola & Hussain, 2005). In India, coastal wetlands (including mangroves) covering an area of around 43,000 km2 play substantial roles in carbon sequestration (Mitra, 1998; Kathiresan & Thakur, 2008).

1.10.7 Roles of Wetlands for Waste Treatment: Phytoremediation Wetlands act as filters and sponges (Voss, 1997). Water that enters a wetland is filtered through the substrate and wetland plants, removing nutrients, i.e. nitrogen and phosphorous and toxins. Mitsch and Gosselink (2007) proposed that wetlands were described as “Kidneys of the Landscape.” According to Maltby (1986), the city’s huge waste water was utilized for fish farming and that process could help the natural recovery of nutrients. Phytoremediation being a bio-ecological process of removing toxic substances along with cleaning up the environment mostly with the help of plants, and rhizosphere microflora by eliminating, degrading or stabilizing the complex environmental contaminants. Several works were carried out regarding phytoremediation of wastewater with varied approaches, including those of Dinges (1976), Reddy and

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Sutton (1984), Abbasi (1987), Abbasi and Nipaney (1991), Mitra (1996), Shova (2000) and Chattopadhyay et al. (2014). The very common macrophyte (Eichhornia crassipes) as encountered in many ecologically degrading and eutrophicated wetlands possess the tremendous power of bioaccumulating ability coupled with higher bio-concentration of the trace elements. In an experimental study, these flowering plants are grown up in an aquatic ecosystem utilizing only low concentrations of five major heavy metallic elements, such as cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and nickel (Ni), where they exhibited higher tolerability (Liao & Chang, 2004). The Water Hyacinth (Eichhornia crassipes) and also Duckweed (Lemna) as very common floating aquatic plants in the wetlands of the tropics have displayed their abilities to reduce concentrations of BOD, TSS and total phosphorus (P) and total nitrogen (N). Eichhornia crassipes and Salvinia sp. are involved to take up the toxic chemicals from sewage and accumulate them in their own system and are also known to hasten the decomposition of biodegradable constituents of sewage due to their hardiness and fast growth rate. Tavares and Favero (2002) suggested that the use of biofilter can ensure sustainable development of aquaculture activity. Based on the base line research information, control and management of macrophytes of wetlands are performed after removing species of macrophytes and also digging of the bottom soils having higher litter contents and other obnoxious chemical substances in anaerobic condition for their removal (Beharrel et al., 2002). Out of so many, the macrophytes, such as Typha, Phragmites, Eichhornia, Azolla and Lemna, have been identified as phytoremediators for the removal of heavy metals (Ray, 2008).

1.10.8 Physico-chemical Parameters and Biogeochemical Cycle of Wetlands: Contribution to Render Benefits The physico-chemical parameters of water, referred to as a major feature, not only make a difference between the habitats of wetland from other terrestrial habitats but also influence biological response by the their physical chemical properties in tune with the depth and movement of water. The basins of the water bodies with their landform act as the water container which determines size, shape and depth of a wetland. Landforms are also categorized on the basis of cross-sectional geometry and geomorphology of the wetlands. In addition, water within wetlands can be categorized on the basis of its quality, persistence or longevity, constancy of water quality and the ecological dynamics for the existence of the wetland. Brinson (1993) also suggested that biogeochemical and other wetland functions changed along environmental gradients. The ecosystem functioning of wetlands depends on their biogeochemical processes and hydrological conditions to make them capable as net sequesters or producers of greenhouse gases (Bassi, 2014). Biogeochemical cycling involves the physical, chemical and biological transformations of various nutrients within the biota, soils, water and air.

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1.10.9 Wetland as a “Nursery” and Provider of “Habitats” Wetlands are considered as “nature’s nurseries” providing critical habitat for fish and wildlife (U.S. Fish and Wildlife Service, 2012). The Fish and Wildlife Service of USA had estimated that around 43% of the threatened and endangered species of wetlands depend directly or indirectly on the habitats and foods available in the respective wetlands for their survival (the wood stork, Florida panther, whooping crane, swamp pink and Canby’s dropwort). Ecosystem goods and services provided by the wetlands include water for direct human consumption, domestic uses, irrigation, fisheries, and water supply, for industries and recreation. Others services include carbon sequestration, flood control, groundwater recharge, nutrient removal, retention and cycling of toxic wastes and biodiversity maintenance (Turner et al., 2000).

1.10.10 Recharge and Discharge of Ground Water and Interaction with Surface Water Wetlands play an important role in ground water, thereby making the wetlands as common important groundwater discharge areas (Schwartz & Milne-Home, 1982; Carter & Novitzki, 1988; Siegel, 1988). Recharge of ground water by wetlands had also been documented with proper explanations of their functional contribution towards the sustainability of wetlands (by Wood & Osterkamp, 1984; Mills & Zwarich, 1986; Siegel, 1988). The structure and function of wetlands are regulated by an array of complex interactions in between ground water and surface water, but the presence as well as roles of ground water cannot be directly observed. Proper understanding of the modes of interactions of ground water with surface water help in chalking out plans for environmental monitoring and land management in order to evaluate impacts of different developmental projects on wetlands. Surface water after being supplied to wetlands through continuous rainfall, streamflow, flooding from adjoining landscapes, discharge from ground water, tidal influence, etc., may be present perennially or seasonally within a wetland (Mitsch & Gosselink, 1993). The rate and intensity of percolation process of surface water in the process of generating ground water are strengthened with the higher intensity of precipitation and downward seepage within the surface water bodies through unsaturated soils and rocks until it reaches the saturated zone. This process of development of groundwater table is known as groundwater recharge and the flows of ground water in the saturated zone form confined or unconfined aquifer systems. The quantity and quality of groundwater discharge tend to influence the physical and chemical properties of surface water and the volume, movement and expanse of surface water in turn regulate the patterns of ground water recharging. So many attributes connected with the hydrological processes (precipitation, evaporation, surfacewater flow, groundwater flow and evapotranspiration) are supposed to control the trend of formation,

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persistence, size and function of wetlands. The vegetative composition and soil types of soils among different types of wetlands are caused primarily by geology, topography, climate, flow paths of water movement, water quality and the degree of natural or human-mediated disturbances on wetlands. Groundwater discharge occurs through wells, seepage or springs, and directly through the process of evapotranspiration where the water table is near the land surface or plant roots reach the water table. Groundwater discharge influences the physico-chemical properties of water of the receiving wetland along with influencing water quality parameters of the adjacent aquifer. The groundwater discharge areas of wetlands and also groundwater recharge processes are affected by topographic position, vegetational coverage and seasonality of hydrogeology (transmissivity, permeability, hydraulic conductivity, textural composition of soils, etc.) (Siegel, 1983; Golet & Lowry, 1987; Novitzki, 1989).

1.10.11 Conservation of Wetlands and Survivability of Aquatic Birds Wetlands are also a necessary habitat for all waterfowl. According to certain estimates, the approximate number of species of migratory birds recorded from India is between 1200 and 1300, which is about 24% of India’s total bird species (Agarwal, 2011; Bassi et al., 2014). The present trend of ecodegradation of wetlands accounting for about 50% during the last century (Mitsch & Gosselink, 2007) has resulted in considerable decline of wetland-dependent species, especially the avifauna as they represent sensitive indicators of wetland conditions (Sievers et al., 2018). One of the major causes of the decline of the diversity of birds is the unprecedented urbanization coupled with industrialization which has necessitated to provide enhanced habitat and increase resource availability for the birds through the protection of the existing wetlands along with their expansion with the provision of more resource availability. In such context, prior information of the habitat requirements of birds (transparent water with less density in water plants, and free from human disturbance) make wetland habitats suitable for the birds for breeding, stopover and wintering site (Chamberlain, 1960; Bertulli, 1981; Young and Karkoski, 2000; Ma et al., 2010; Terörde & Turpie, 2013; Murray & Fuller, 2015).

1.10.12 Wetlands and Socioeconomic Benefits Goklany (2007) has focused on socioeconomic benefits as food, commercial animal populations, fuel, timber or fibre production, recreation, aesthetics and education. In addition, opening up new avenues of employment based on the harvesting, processing and marketing of resources from wetlands boosts up not only the moral for new

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hope for survivability but also uplifts the socioeconomic condition of the area profusely. Turpie et al. (2010) has discussed about the socioeconomic values and sustainability studies of wetland.

1.11 Threats on Wetlands and Loss of Biodiversity Wetlands as one of the most productive ecosystems of the world contribute a number of benefits to the human society (Paul et al., 2011). In addition to that, wetlands are being considered as one of the most threatened environmental landscapes of the world (William, 1990; Prasad et al., 2002). The current rates of wetland in India can lead to serious consequences in respect of economy and ecology as 74% of the human population in this country resides in the rural areas depending very much on the supply of goods and services from wetlands (Anon, 1994). More than 50,000 freshwater bodies have been polluted to that level of being considered as “Dead” by continuous accumulation of sewage, industrial effluents and agricultural run-off (Chopra, 1985). Wetlands in India, as elsewhere, are increasingly facing several anthropogenic pressures. Moreover, the number and area of wetlands in India have been dwindling with the passage of time because of ongoing pace of increase in population and urbanization. Most of such wetlands under threats have been eco-degraded due to the inflow of polluted urban, agricultural and industrial wastewaters and also filling up of water bodies for other land use purposes. In such respect, the burgeoning developmental activities, increasing human population, drastic alteration in the land use changes and non-judicious usages of watersheds have all together caused hydrological perturbations and different other forms of aquatic pollution leading to a considerable depletion of wetlands and their resources of India (Phukan & Saikia, 2014). Innovative methods of constructing roads and bridges can reduce the impacts associated with the urbanization on wetlands (Azous & Horner, 1997). Overfishing and overhunting in very unsustainable manners hamper the functioning of wetlands with the development of ultimate threats on the wildlife habitat, aquatic food chains and recreational scopes for human beings (Shaw and Shebbeare, 1937; Paul et al., 2011; Witte and Giani, 2016). Therefore, the need of the hour is to protect thousands of wetlands that are, ecologically and economically important but do not have any legal status (Prasad et al., 2002). Losses in habitat have threatened the species diversity of birds of wetland (Mitchell & Gopal, 1990). Thailand has lost up to 20% of its mangroves in recent decades (McIntosh, 1983). During mining operation, the acidity and the heavy metal concentrations have altered the biotic community composition and resulted in mortality (Mitsch & Gosselink, 2007; Wuana & Okieimen, 2011). Although natural wetlands have the capacity to buffer some of the acidity and absorb a certain amount of the pollutants, over time, the assimilative capacity will be saturated (Bentrup, 2008). The functioning of wetlands contributes significantly

1.11  Threats on Wetlands and Loss of Biodiversity

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towards conservation of almost whole environment and that prompted several researchers to estimate the values of wetlands so that people also should pay attention for the preservation of wetlands (Ghatak, 2010). Despite all these value and cost-benefit analysis, wetlands are being threatened worldwide. Therefore, ecologically sound management is the only way to protect wetland (Gopal, 1995; EKWMA, 2011).

1.11.1 Assessment of the Causes of Loss of Wetlands During the past few decades, lot of concerns have been cropped up over the rapid loss of biodiversity in general and the causes and consequences of such loss in the inland aquatic ecosystems focusing on the factors responsible for such decline particular (Groombridge & Jenkins, 2002; Revenga et al., 2000). The accounting of loss of wetland ecosystems contributes sizeable loss in the natural economic wealth and ecological health. In India, accounting measures in order to determine the monetary values of such kind of loss is treated as a “floor value” and this—moving economy of the nation but—ecosystems services which serve as crucial means to constitute the economic foundation of the country. Designing of an appropriate indicator, such as Net National Product (NNP), has proved to be helpful for the policymakers with such effective and efficient policies in respect of resource allocation in the economy as a part of poverty alleviation goal (UNEP, 2011). The trend of wetland loss is assumed to follow a linear path and the drivers of such change in the wetland area have been mostly anthropocentric involving two major contributing forces for such changes, such as agricultural expansion and urbanization (Kumar, 2009).

1.11.2 Wetlands, Eutrophication and Carbon Sequestration On realizing the eco-potential of wetlands for improving the quality of water by absorbing and recycling pollutants, the wetland ecosystems command all-round recognition. Researches on these issues have mostly been done in the temperate climates (Mitsch & Gossenlink, 2007), whereas paucity of information prevails the effectiveness of wetlands, particularly natural wetlands, in tropical regions. The filtering power of wetlands to improve the quality of water by retaining or removing sediment and nutrients has long been used for the waste water removal or treatment process (Greenway & Woolley, 1999; Toet et al., 2005). The recognition of these filtering processes and the success derived from such activities have prompted the environmental planners to construct artificial wetlands in order to treat the pollutants present in the sewage or waste water as either diffuse (non-point) or

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immediate (point) sources of pollutants from a range of human activities, such as agricultural, industrial and urban land uses (Cooke, 1994; Garcia-Linares et  al., 2003; Jordan et al., 2003). Several ecological factors and processes play their roles to materialize wetland filtering, which include nutrient loading (Nichols, 1983; Dørge, 1994), water level fluctuations (Tanner et  al., 1999), wetland soil oxygen status (Baker & Maltby, 1995; Flynn et al., 1999), presence of aquatic plants having the power nutrient bioaccumulation (Brix, 1997; Greenway, 1997) or other types aquatic vegetation having rhizomes to store nutrients (Sorrell & Orr, 1993), carbon availability (Hogan et al., 2004), hydraulic loading (amount of water entering per unit area of wetland), residence times (Blahnik & Day, 2000; Holland et al., 2004) and biological production and biomass generation (Kim & Geary, 2001; Browning & Greenway, 2003). The removal of sediment and nutrients by natural wetlands in some eco-zones of the wetland alters water quality in such a way so that resulted changes influence the other parts of the same water body (Johnston, 1991; Fisher & Acreman, 2004). Such filtering effects of wetlands also reveal that phosphorus retention capacity of the soil is lessened over time with the diminishing capacity of the wetland soils to absorb the phosphorus. Similarly, there exists a tendency during high flow events for lowering the nitrogen reduction rates, which indicates higher rates of denitrification (Johnston, 1991). Although wetlands act as natural buffers against wastes derived nutrients, nutrients generated through N2 cycle in the surrounding watersheds, forests and other modes of anthropogenic activities and thereby resist significantly the process of eutrophication caused by the steady over enrichment of N, P, C etc. Denitrification process has been observed as the fastest biogeochemical process in the soils of wetlands (Ullah & Faulkner, 2006). Moreover, steady and continuous supply of nutrients into wetlands substantially increases the possibility of eutrophication, especially in coastal systems (Shaw et al., 2003). Coastal eutrophication is mainly caused by industrial release of nitrogen, which is used mostly as fertilizer in agricultural practices as well as within septic waste run-off (Howarth, 2008). Wetlands remove nutrients from surface and ground water by filtering and by converting nutrients to unavailable forms (Gopal, 1995). In India, coastal wetlands are playing a major role in carbon sequestration by playing an important role in global biogeochemical fluxes (William, 1990; Chakraborty et al., 2014; Kar, 2014). The roles of geo-chemical and carbon sequestration have emerged as the growing concern for global implications of changes in the atmospheric carbon balance, especially in view of escalating increase of carbon burning anthropogenic activities (Maltby, 1986; Winkler & De Witt, 1985). The periodic flooding of wetlands in the river valleys has become a common feature of producing a complex variety of wetlands depending on climate, water regime and form of the floodplain. The wetland complexes as fringing floodplains have now been in the process of rapid disappearance due to the ongoing deepening of river channels, levee construction and other changes in the land use patterns. The most of the seasonal floodplains of the world

1.12  Functional Assessment of Wetlands

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are now distributed to the tropics and subtropics, but they have been under various forms of anthropogenic threats (Greenway & Woolley, 1999).

1.12 Functional Assessment of Wetlands The assessment of true value of wetlands, considering both ecological and economical perspectives, has appeared to pose real challenges to the environmental planners and decision-makers because of difficulty in identifying overriding factors contributing to wetland loss and degradation (Maltby et al., 1994). Besides, in taking into consideration of the relative merits of preserving a wetland emphasizing on the imbalance of cost and benefits in terms the perception and interest of the peoples towards achieving urbanization, industrialization and other such short term direct benefits. For example, costs may involve the manifestation of increased sedimentation or deterioration in water quality in another part of the catchment, while the benefits of wetland degradation (e.g.) may be apparent locally through the improvement of drainage. In general, decision-making bodies lack adequate integration of different facets of management practices starting from developing of appropriate institutional infrastructures with flows of funds and competent staff through which appropriate land and water management strategies, such as recreational avenues, agricultural support, facilities for fishing, bird watching and even permitted hunting, can be enforced. Five factors have so far been highlighted which can strengthen the ongoing inadequacy of a traditional conservation practices as the only approach to the wise use of wetland resources. These factors are as follows: 1. Limited finance can do justice only on undertaking protection of a small proportion of the remaining wetland resource to make them a part of a formal protected area network. 2. The beneficial contributions of wetlands can have wider socioeconomic impacts with the values arisen out of their functioning but such emerging views are rarely taken into consideration in the decisions-making process. 3. Although many wetlands have appeared to remain unaltered and unaffected, several circumstantial evidences, such as declining bird populations and fisheries, have confirmed the impairment of ecosystem functioning. 4. In the decision-making process the major portions of the wetland resource bases do not get due attention with regard to their functional roles for the sustenance of these ecosystems. 5. Virtual absence of effective conservation policy or legislation categorically can address the importance of linkages of wetland ecosystem functioning to environmental protection. However, Water Framework Directive (WFD) has emphasized the functional roles of wetlands in meeting the needs of water quality maintenance and revival of “good ecological condition” (EC, 2000). In addition, Common Implementation Strategy Working Group (CISWG) has been formed by the WFD to identify the values of wetlands in biodiversity

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enhancement, driving of food chains, water quality improvement, flood control, and governing of greenhouse gas emissions, which are to be integrated in the political or environmental decision-making process towards framing holistic conservation strategies of wetlands.

1.13 Wetland Management: East Kolkata Wetlands Wetlands are crucial in maintaining the water cycle. Wetlands can be hardly delineated under any specific administrative jurisdiction. The primary responsibility for the management and conservation of these ecosystems remains under the control of the Ministry of Environment and Forests. Although some wetlands could draw the attention of the international and national pro-environmental organizations mainly due to the compulsion of formulating of the Wildlife Protection Act (2006), others without such wildlife emphasis are in grave danger of extinction. Effective coordination and integrative management efforts among different Government departments, like water resources, energy, fisheries, agriculture, transport and revenue, are required for the protection of these ecosystems (Paul et  al., 2011). According to a report of East Kolkata Wetland Management Authority (EKWMA, 2004), the wetland has been under constant pressures for conversion for settlements and agriculture. Changes in land use, alteration of the hydrological regimes due to rapid siltation, pollution and conflicts among stakeholders have greatly hampered wetland functioning. Realization of the values of wetlands to human society has led to measure as well as to control losses in some developed countries, but wetlands conversion and destruction have been continuing in some Third World countries at an accelerating pace (Gosselink & Maltby, 1990). The West Bengal Town and Country Planning and Development Act, 1979 and Fisheries Act, 1984 (as amended in 1993) banned conversion and filling up of the wetland 9 sites as a token initiative for the protection and conservation of EKW. The Conservation and management Ordinance, 2005, for the East Kolkata Wetlands came into force on 16th November 2005, which subsequently passed an Act on 31 March 2006, in the West Bengal Legislature assembly with the name as East Kolkata Wetlands Conservation and Management Act, 2006, and that Act helped the State Government of West Bengal to form an authority, called East Kolkata Wetland Management Authority (EKWMA) (as a nodal agency for systematic implementation of wise use principles for the management of Ramsar Site), under the Chairmanship of Chief Secretary to the Government of West Bengal, India. Water-related ecosystem services provided by wetlands at different scales, such as clean water provision, waste water treatment and groundwater replenishment, offer significant scopes for addressing water management problems and also to achieve sustainable goals in most instances in a very cost effective manners with the involvement and participation of local peoples. These services can be substantiated by man-made infrastructure in order to facilitate the delivery of water supply, sewage treatment and energy.

1.14  Remote Sensing and GIS Methods for Conservation and Management of Wetlands

27

1.14 Remote Sensing and GIS Methods for Conservation and Management of Wetlands Wetlands are the first among the victims of modern development and degrading with time. Conservation and wise use of wetlands have been given priority world over. India harbours different categories of wetlands and the first step for undertaking appropriate planning and management strategies for the conservation of wetland resources in a sustainable manner only utilizing necessary, accurate and updated database (Panigrahi et al., 2012). Geographic Information System (GIS) and satellite remote sensing are the best available technologies for such a purpose. A striking seasonal variation in respect of aerial expanse and extent of water bodies, mode of occurrence of macrophytes, and turbidity of the open water have been noted with the help of remote sensing data and GIS methods (Panigrahi et  al., 2012). As the effective method for the ecological assessment of wetlands remote sensing data in combination with Geographic Information System (GIS) hydrological modelling have proved its utility which in turn help flood management, generation of data on the capacity of reservoir and also for eco-monitoring of the environmental changes using water quality mapping and recording (Kar, 2014; Ray and Mandal, 2015; Sanyal et al., 2021). In addition, satellite data can also be used for the interpretation and delineation of flood – inundated regions, flood – risk zones. Remote sensing data are used for the analysis of water quality parameters and modelling and as well as characterization of wetlands (Ray & Mandal, 2015). Water quality studies have been carried out using the relationship between reflectance, suspended solid concentration and chlorophyll–a concentration. In the near-infrared wavelength range, the amount of suspended solids content is directly proportional to the reflectance. Owing to variable resolution in the temporal and spatial scales, generated information pertaining to both point and non-point sources of pollution and intensity of their flow pattern for mixing with the wetlands are required to be regularly monitored. Besides, widespread and consistent use of satellite-based remote sensors in a cost effective manner is also needed for the purpose of frequent monitoring and also for the reason of holistic management because of the eco-­ dynamics in the functioning of the wetland ecosystem. (Winter and Woo, 1990; Prasad et al., 2002; Ravenga et al, 2005; Townsend and Walsh, 2011). Regular and upgradation of applied tools are important in view of the increasing demand for the harvesting of resources of wetlands keeping pace with the rapid developmental activities and population pressure. Under the above pretext, the present study is an effort of wise and sustainable use of wetland along with innumerable values and classification of wetlands. Limitation of the present study is Kolkata wetlands, being a very unique landscape of international significance because of its role as model for natural waste recycling systems, remain unattended by the researchers, planners, administrators and environmental conversationalists up to 1950s. Afterwards although some notable conservation efforts (Ghosh, 1999) were made to unearth information pertaining to the uniqueness of the functional system of this network of waterbodies which appeared to provide an alternative approach towards solid and liquid waste management of urbanized sectors of the World, in

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general, and Kolkata Metropolitan of the state West Bengal, India, in particular. The global importance of these wetlands was later confirmed by the declaration of this landscape as to be the Ramsar Site in the year 1971 and later as “Wetland of International importance” in the year 2002. Alongside undertaking research efforts to highlight some relevant research information relating to eco-dynamics of water bodies giving due importance of the ongoing temporal and spatial changes of the biotic components, especially zooplanktonic faunal components, in relation to prevailing ecological parameters and also changing patterns of some other determining attributes, such as urbanization, biodiversity and geomorphology in historical perspective, historical perspectives , such research studies should take into consideration different other environmental management plans, like Aquaculture Management Plan (AMP), Waste Water Management Plan (WWMP), Waste Recycle Management Plan (WCMP), Livelihood Generation Plan (LGM), etc. which are supposed to ensure overall environmental improvement of the wetland in general and sustainable management of this ecosystem in particular. Instead of covering entire wetland systems through ground truth verification, the present study has identified some suitable water bodies having contrasting ecological characteristics for long-term studies relating to biodiversity, seasonal dynamics of biotic and abiotic factors, identification of eco-toxicological stresses (heavy metals load) and mode of phytoremediation. An attempt has also been made for blending the application of both ground truth survey with that of Remote sensing and GIS method in order to fulfil the prime objectives of the eco-monitoring of the wetlands.

1.15 Linking Water Crisis: Roles of Governance and Integrity Although the major reason for water crisis is due to the scarcity of water resources, but inefficient governance because of not properly dealing with the overall effectiveness and efficiency of the water sector (lack of infrastructure, institutional inefficiency, limited staff capacities, scarce financial resources, inappropriate planning priorities and political instability) is also considered as contributing prime factor. Integrity, defined as the adherence of water stakeholders and institutions to apply appropriate governance principles with much clarity, transparency, accountability and overall participation of the stakeholders relying and emphasizing the core values of honesty, equity and professionalism. This mode of perception towards overall water resource management has emerged as a new and critical conceptual component in order to improve water governance and achieve more sustainable water management and development. The linking up of integrity with different components of water resource governance, keeping aside all the negative roots, magnitude and consequences of the lack of integrity in water governance mainly enunciated due to evil effects of human corruption, can only bring about successful, sustainable and equitable water use, access and allocation overcoming all negative consequences.

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1.16 Conservation of Wetlands: Interdisciplinary and Integrated Approaches Wetland ecosystems by virtue of ecosystem functioning maintain water quality, create habitat for a variety of fish and wildlife, act as buffer against flood, recharge groundwater, provisioning for drinking water, creating recreational and fishery avenues, etc., and thereby contribute significantly to maintain regional ecological balances (Norman et al., 1998a, 1998b; Shaw, 2005). Therefore, any disruption in the functioning of wetlands because of draining and modern agricultural activities, serious loss of values are resulted causing harm to the human society in particular and overall environment in general. The philosophy and objective of conservation have been explained and interpreted by different peoples in different manners but the main essence of the conservation strategy is to ensure the interest of future generations by reserving the diminishing resources for their uses. In order to achieve the targeted goal of conservation, interdisciplinary approach integrating the diverse fields of conservation science, such as biology, philosophy, economics, chemistry, welfare and human rights towards understanding natural functioning wetland ecosystem, is required to successfully achieve the prime objective of wetland conservation ((IUCN,1987;  The Ministry of Environment and Forests, Government of India, 1990; IPCC, 2002; WWF, 2011). In view of the above, the entire book with ten (10) chapters have been divided into three board aspects: (i) the first part explains the definition, concept, classification, historical research perspectives and basic ecological principles applicable in the research studies of wetlands; (ii) the second part has dealt with the uniqueness of East Kolkata Wetlands in the backdrop of national and international research perspectives on wetlands, mostly highlighting the physico-chemical parameters, different modern GIS methods for the eco-assessment of wetlands and identification of different threats on wetlands with special emphasis with pollution and biodiversity; (iii) the third part mostly takes into consideration of the conservation strategies and scopes for livelihood generation involving the participation of indigenous peoples.

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Townsend, P. A., & Walsh, S. J. (2001). Remote sensing of forested wetlands: Application of multitemporal and multispectral satellite imagery to determine plant community composition and structure in southeastern USA. Plant Ecology, 157(2), 129–149. Turner, R. K., Bergh, J. C. J. M. V. D., Soderqvist, T., Barendregt, A., Straaten, J. V. D., Maltby, M., & Ierland, E. C. V. (2000). The values of wetlands: Landscape and institutional perspectives – Ecological-economic analysis of wetlands: Scientific integration for management and policy. Ecological Economics (Elsevier), 35, 7–23. Turpie, J., Lannas, K., Scovronick, N., & Louw, A. (2010). Wetland valuation Volume I Wetland ecosystem services and their valuation: A review of current understanding and practice. In H.  Malan (Ed.), Wetland health and important research programme (Wetland Research Commission Report No. TT 440/09) (pp. 1–132). U.S. Fish and Wildlife Service. (2012). Wetland as a ‘Nursery’ and provided ‘Habitat’ Wetlands are considered as “nature’s nurseries” providing. U.S. Fish and Wildlife Service (USFWS) and U.S. Census Bureau. (2002). 2001 National survey of Fishing, hunting, and wildlife-associated recreation – Quick facts. Ullah, S., & Faulkner, S. P. (2006). Use of cotton gin trash to enhance denitrification in restored forested wetlands. Forest Ecology and Management, 237(1–3), 557–563. US Army Corps of Engineers (Waterways Experiment Station). (1987). Wetlands delineation manual (Prepared by Environmental Laboratory) as wetlands research program. Washington, DC, 20314-1000. Usbank, S., & James, R. (1993). A directory of important wetlands in Australia (pp.  1–687). Australian Nature Conservation Agency. Voss, H. (1997). The importance of wetlands Great Lakes Bulletin News Service. Vymazal, J. (2007). Removal of nutrients in various types of constructed wetlands. Science of the Total Environment, 380, 48–65. Vymazal, J. (Ed.). (2014). The role of natural and constructed wetlands in nutrient cycling and retention on the landscape (p. 326). Springer. Walsh, C. J., Roy, A. H., Feminella, J. W., et al. (2005). The urban stream syndrome: Current knowledge and the search for a cure. Journal of the North American Benthological Society, 24, 706–723. Williams, M. (1990). Wetlands: A threatened landscape. Blackwell, Oxford. Wilson, E. O. (1992). The diversity of life. The Belknap Press of Harvard University Press. Winkler, M. G., & De Witt, C. B. (1985). Environmental impacts of peat mining in the United States: Documentation for wetland conservation. Environmental Conservation, 12(4), 317–330. Winter, T. C., & Woo, M.-K. (1990). Hydrology of lakes and wetlands: Surface water hydrology (pp. 159–187). The Geological Society of America. Witte, S., & Giani, L. (2016). Green house gas emission and balance of Marshes at the Southern North Sea. Coast, 36, 121–132. Wood, W. W., & Osterkamp, W. R. (1984). Recharge to the Ogallala aquifer from Playa Lake Basins on the Liano Estacado. In G.  A. Wetstone (Ed.), Ogallala Aquifer Symposium II.  Lubbock, Texas, Proceedings (pp. 337–349). Wuana, R. A., & Okieimen, F. E. (2011). Heavy metals in contaminated soils: A review of sources, chemistry, risks and best available strategies for remediation. ISRN Ecology, 1–20. WWF (World Wildlife Fund). (2011). The value of wetlands. http://wwf.panda.org/about_our_earth/ about_freshwater/intro/value/ Young, C.  E., & Klawitter, R.  A. (1968). Hydrology of wetland forest watersheds (Council on Hydrology Clemson University Water Resources Research Institute, Report No. 4) (pp. 29–38). Young, T. F., & Karkoski, J. (2000). Green evolution: Are economic incentives the next step in nonpoint source pollution control? Water Policy, 2, 151–173. Zedler, J.  B., & Kercher, S. (2005). Wetland resources: Status, trends, ecosystem services, and restorability. Annual Review of Environment and Resources, 30, 39–74.

Chapter 2

Ecology and History of Wetland Research: Operating Scientific Principles of Eco-­dynamics of Wetland Ecosystem with Special Reference to East Kolkata Wetland, India

2.1 Ecosystem Ecology: Concept, Origin In the realm of the subject ecology, ecosystem constitutes the main foundation on which other aspects of ecology stand, and thereby, a new phrase, “ecosystem ecology,” has emerged in the arena of environmental sciences dealing with the fluxes and cycling of materials (carbon, phosphorus, etc.), flows of energy, generation and cyclical movements of nutrients, production of biomass, interactional pathways of biotic and biotic components, maintenance of water quality, formation and organic enrichment of soils, etc. Ecosystem ecologists are mainly concerned with finding the causative factors determining all these ecological processes and incidents. Living organisms within an ecosystem remain interlinked and interconnected with each other mainly through the food chain and food web dynamics and also with the physical and chemical structural components through their adaptive adjustments. Ecosystems being complex adaptive systems are broadly categorized as aquatic, terrestrial and atmospheric because of the different forms of interactions among a multitude of life processes that form self-organizing patterns which are characterized by the unique constituents of biotic and abiotic factors (Preston,1948; Pimm, 1982; Adoni, 1985; Dutta, 2001, 2003; Mitsch et al, 2012; Chakraborty, 2021b).

2.2 Functional Roles of Ecosystems The functional contribution of ecosystems ultimately sustains life-supporting systems and is reflected by the generation of several natural capitals through biomass production (food, fiber, fuel and medicine), regulation of climate and driving of biogeochemical cycles in regional and global perspectives, water filtration, © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 S. K. Chakraborty et al., Wetlands Ecology, https://doi.org/10.1007/978-3-031-09253-4_2

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formation of soil and control of erosion, flood protection and similar other naturally occurring materials, substances and ecological processes having scientific, historical and economic values.

2.3 Major Structural Components of Wetland Ecosystem 2.3.1 Water and Water Resources: Human Sustenance Water being a universal solvent sustain the functioning of ecosystem by facilitating the cycling of various essential constituents, including nutrients, and also promoting vital biological processes, like photosynthesis, which play key roles in determining the diversity, distribution and density of aquatic organisms. Since the inception of human civilization, water has been serving continuously for the causes of agriculture, industries, navigation, hydroelectric production and also various other purposes of human beings. Out of the total amount of available water in the world (326 million mile3), around 97% remains as salt water and the rest 3% is as freshwater, of which about 69% are tied in glaciers and ice caps, 30% as groundwater and a very negligible amount as 0.27% as surface water. Water resources ensure the survivability of the planet by supporting the lives of aquatic biodiversity as one of the most essential characteristics of the aquatic ecosystem and also providing means for enabling them to cope with any environmental change. Alongside acting as energy “sinks,” water can absorb a large amount of solar energy without increasing the temperature of the water bodies in comparison to a similar area of land. In order to use water as maximum as possible extent, all living organisms, including the aquatic ones, have developed their own adaptability and as such so many animals (insects, mammals, etc.) have experienced adaptive convergence, even by adopting secondary adaptations. Water as the major ingredient of wetlands distinguishes this habitat from other terrestrial habitats and triggers a lot of biological responses by their availability, volume, depth, currents and physico-chemical properties. The landform acts as the water container and by virtue of its geometry determines the cross-sectional geometry along with the shape, volume, depth and also extent of a wetland. The functional constancy of water quality and the mechanism for its maintenance within the wetland ecosystem are determined in accordance with the persistence, duration of presence, physical and chemical properties. Water within wetlands can be categorized on the basis of its persistence or longevity, its quality and the mechanism for maintaining the constancy of water quality (Dunson & Travis, 1991; Das, 2004; Dutta et al., 2005; Garg et al., 2006; Hutchinson, 1957; Goldman & Horne, 1983; Wetzel, 2001; Klaff, 2002; Chakraborty, 2021a).

2.3  Major Structural Components of Wetland Ecosystem

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2.3.2 Sunlight as the Driving Force for all Biological Growth and Interactions Being the prime source of energy, sunlight enables the green plants to perform photosynthesis through which kinetic energy is converted to static energy forming the green biomass, which in turn regulates the global ecology by trophic interactions and food chain–food web dynamics. The biological world becomes associated with several ecological phenomenon, such as seasonal fluctuation of ecological parameters, photoperiodicity and circadian rhythms, synchronization of plant–animal requirements and dependence on each other, etc. All of such eco-biological activities are meant for getting sunlight as maximum as possible (Rao and Govind, 1964; Rao, 1975; Priban & Ondok, 1985; Krishnamoorthy, 1990; Handoo & Kaul, 1997; Goher et al., 2014).

2.3.3 Wind as an Important Meteorological Factor Wind and wind flows regulate both water and terrestrial ecosystems in varied manners, such as by accelerating the mixing of atmospheric oxygen with surface water, triggering soil erosion, facilitating the processes of evaporation and convection, enabling biological organisms overcoming the problems of desiccation, promoting the growth of plants by controlling the rate of photosynthesis, etc.

2.3.4 Soil – Its Texture and Nutrients The texture of soils formed mainly by three major soil components, such as sand, silt and clay, determines the power of permeability, hydraulic conductivity, transmissivity and several other soil-dependent physical processes which contribute to the maintenance of the structure and function of the wetlands. Besides, soils containing several other minor constituents in the form of macro- and micronutrients provide inputs for several other metabolic activities of both aquatic and terrestrial organisms. The chemical constituents of soil are derived from both organic (primarily as decomposition products and backbones of such substances are formed by carbon and hydrogen) and inorganic sources (mainly generated as eroded products from rocks or other terrestrial landforms). Different water quality parameters, such as pH, turbidity, conductivity, alkalinity and hardness, are also dependent on the texture and chemical composition of soils.

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2.4 Interlinkages and Interdependences of Different Freshwater Ecosystems: An Ecological Interpretation Various eco-biological parameters such as external material inputs, vegetative communities, different physico-chemical parameters of water and soils along with various ecological processes pertaining to interactions among biotic components, biological productivity, energy flows and all of which together control the biogeochemical cycles. Like many open ecosystems, freshwater wetlands are also considered as open systems which receive inputs (flows of water loaded with organic matters and nutrients) from the adjoining brackish water estuaries, forest, agricultural and urban areas. Supply, deposition and loading of nutrients (such as nitrogen and phosphorus) for a long period lead to cause the development of distinct gradients in the water and soil of the wetlands. Continuity of such processes in the wetlands results in the higher accumulation of organic matters and nutrients along with different other pollutants which all together lead to developing eutrophic conditions. Very few wetlands in the world are oligotrophic. Although, considerable volume of information is available on the productivity and above-ground nutrient cycling within freshwater wetlands (Batzer & Sharitz, 2006), not that much is known about the roles of nutrients ecology of microbial decomposers, planktonic, benthic and periphytonic communities associated with biogeochemical cycling, bioaccumulation and bioavailability of nutrients. In oligotrophic wetlands, a gradient exists in respect of quality and quantity of organic matters, accumulation of nutrients, biogeochemical cycles, composition and function of microbial communities and diversity of other living organisms due to differential availability of nutrients near and furthest points of the input. In contrast, oligotrophic wetlands representing relatively closed, efficient elemental cycling are influenced by low external loading of nutrients (Odum, 1969, 1985). Primary productivity coupled with microbial activity being the nutrient-­ limited manifestations efficiently utilize and conserve nutrients uptake and reallocate nutrients at very low nutrient concentrations. Detritus, in this category of wetlands mostly derived from the decomposition of plants’ biomass, possesses nutrients with higher C:N:P ratios which remain held in tight and closed cycles having the efficiency to maintain energy flow where microbial and periphytic communities outcompete vascular plants for nutrients. The total turnover rate of organic matters having high C:N and N: P ratios within the long-term but slow decomposition processes is seen to become both carbon and nutrient limited (Davis, 1991; DeBusk & Reddy, 1998, 2003, 2005). Environmental factors, such as water table fluctuations, sudden fires and flooding, can result in pulsed release of nutrients which may provide a significant source of plant-available nutrients in low-nutrient systems (Lodge et al., 1994). The wetland systems provided with higher nutrients experience fast turnover of carbon and nutrients by the process of open elemental cycling due to over inputs of nutrients against the optimum requirements. Several ecological conditions such as the fluctuations of water tables and flooding have found to enhance the nutrients’

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availability in the oligotrophic wetlands which as low-stress systems, experience varying degrees of internal cycling by microbes and plants which bear direct connection between higher net mineralization or release of nutrients during decomposition as compared with nutrient loading from external sources. Increased loading of phosphorus, a limiting nutrient in oligotrophic wetlands results to develop gradients among different eco-zones (different strata of water column, littoral, pelagic, benthic, etc.) both in terms of quality and quantity of organic matter, nutrient accumulation, microbial communities, biogeochemical cycles, which in turn trigger to develop the diversity of microbial consortia and associated processes. In addition, functional contribution of several biogeochemical processes involving the cycling of carbon, nitrogen, phosphorus, sulphur and other such elements in many of the freshwater wetlands is directly or indirectly related to the turnover of organic matter, denitrification, methanogenesis, phosphate sorption, sulphate reduction, metal precipitation and similar other reactions in most of the tropical wetlands. Enhanced input of nutrients brings about the growth and changes in the species composition of primary producers, both phytoplankton and macrophytes which in turn results in the increase of turbidity, shifts in the mode of dominance of macrophytes over phytoplankton, decrease in the biomass of large-bodied zooplankton, increase in the diversity of both planktivorous and benthivorous fish and losses of piscivorous fish in the water bodies (Jeppesen, 1998; Jeppesen et al., 1998, Whillans, 1996; Chow-Fraser et al., 1998; Alvarez-Cobelas et al., 2005).

2.5 Hierarchy of Ecological Systems: Population, Community, Biosphere and Ecosystem Ecology The different structural components in the ecosystem, both living and non-living, interact with each other and ensure ecological integrity, stability and biological productivity. Such interacting processes following a hierarchy of gradation ranging from the bio-molecules (genes) to ecosystems via individuals, populations and biotic communities can ensure interrelationships and interdependence among all the compartments of the natural environment and thereby develop the main essence of two overlapping subjects (community ecology and ecosystem ecology) under the umbrella of parent subject, ecology. A population constituted by a group of individuals belonging to the same species occupying a unit area cannot function independently in an ecosystem but plays important roles by interacting through mutual coexistence or competition with other such populations for sharing limited resources (food, water, space, etc.). Several interacting populations within an ecosystem are referred collectively as a community or an assemblage of several species (Boate, 1962; MayNard Smith & Slatkin, 1973; Lodge and Lorman, 1987; Lodge and Hill, 1994; Dutta, 2003; Chakraborty, 2021b). An example is the coexistence of herbivores that consume plants, and predators that eat prey, whereas other individuals belonging either to the same or different

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species tend to compete for basic required resource bases in order to maintain life. Different constituent populations of a biotic community interact either as prey or predator and thereby sustain the eco-dynamics of ecosystems. Decomposition cycle maintains the reservoir of resources by breaking down of dead biomass through the exo-enzymatic activities of an array of microorganisms which recycle the nutrients contained in their dead tissues back into the soil. In such context, it has become peremptory for the increasing detachment of the perspectives of two major subdisciplines under the subject ecology, community ecology and ecosystem ecology, each one of which undergoes independent growth after being endowed with own concepts, theories and significance towards explaining the complexity of ecological interaction in the functioning of ecosystems. The ecological exercises at population and community levels are mainly taken into consideration the diversity, species-to-­ species interactions and relationships, eco-dynamics and evolutionary pathways of eco-development, after being initiated from the population levels. The main concern of ecosystem ecology is to highlight the overall functioning of the entire ecosystem because of the continuous interactions among all its structural components, both biotic and abiotic, with the initiation point having unidirectional flow of energy and cyclical movement of matters through the active roles of decomposers and thereby trigger the functioning of all compartments within the ecosystem. Although these two newly emerged subdisciplines of ecology have been flourishing separately not having that much of communication between them, proper understanding of the relationship between biodiversity and ecosystem processes has appeared to play an important role for the development of higher integration which in course of time will certainly enable to explain ecological processes more fruitfully by developing new area at the interface of community, ecosystem and evolutionary ecology (Jones & Lawton, 1995; Jones et al., 1997).

2.6 Functioning of Ecosystem as Cybernetic System: Production of Biomass and Flow of Energy Ecosystem being a self-sustaining system through self-regulation is considered as Cybernetic System through which energy flows and materials circulate (Wiener, 1948). This kind of functioning of ecosystem has had both + (positive) and – (negative) feedback. The negative feedback refers to a type of response that halts or reverses the movement away from and returns it to the set point. The positive feedback involves continued movement away from the set point. The measure of the feedback is inversely proportional to input in the case of negative feedback which is in contrast to positive feedback where direct relationships exist in between feedback and input. In such context, the positive feedback embodies deviation which facilitates accelerating the functioning of system which is counteracted by the deviation derived from the negative feedback.

2.6  Functioning of Ecosystem as Cybernetic System: Production of Biomass and Flow…

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Homeostasis, an adaptive mechanism to maintain the stability of ecosystem. The diversity, distribution and population dynamics of species either independently or in conjunction with the prevailing community interactions in the changing ecological conditions due to the impacts of diurnal, monthly, seasonal and annual variations of the environmental parameters are determined through depiction of morphological adaptabilities and eco-physiological adjustments. In order to achieve a fruitful existence by maintaining adaptive success, the living organisms always strive to maintain steady-state condition by counteracting the fluctuating internal environmental condition by withstanding any change of the external environment. Homeostasis, a kind of physiological adaptive manifestation in order to preserve and carry on the stability of internal environment at the organismic level, can be achieved by mobilization of all the physiological functioning in accordance with the biological requirements of the concerned species. Such stability at the ecosystem level can only be possible by the combined adaptive activities at the molecular, physiological, behavioural and ecological levels and is maintained by the followings: 1. Through feedback control. 2. Through redundancy of components. Redundancy takes into account the functional abilities of several components of the ecosystem for enhancing stability and includes two categories: 1. Resilience stability: It represents the ability of an ecosystem under the ongoing stress of perturbation to return to its normal state with all of its structural components on recovering from the displaced and deviated functional ecological state to the normal functional condition. 2. Resistance stability: It shows the ability of a biotic community to initially resist any effect of perturbation and thereby avoid displacement by maintaining its own structure and function. The destruction due to the total redundancies of components of an ecosystem takes place on the massive curtailment and supply of inputs of matters and energy. The ecosystem tends to exhibit zero equilibrium state at the time of normal stability through effective adaptation but experience non-equilibrium dynamics after being perturbed by the disruption of ecological functioning. In such context, it is concluded that balanced interactions of all the structural components can ensure right order of functioning of an ecosystem even under environmental stressed conditions (Odum, 1971; Krebs, 1994; Smith, 1996; Chakraborty, 2021a).

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2.7 Hierarchical Organization of Biotic Community: Energy Flows and Productivity The hierarchically organized populations within biotic communities representing different trophic levels (producers, consumers and decomposers) along with other abiotic factors influence species growth, reproduction and dispersal through several ecological processes, such as the flow of energy and the circulation of materials which in turn facilitate geological, hydrological and atmospheric forces to play their roles in determining habitat quality, species distributions and species abundances (Fig. 2.1).

Fig. 2.1  Schematic representation of the structure and function of a wetland ecosystem

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Energy flows through many species within the ecosystems are influenced by precipitation, land use changes, soil erosion and other physical constraints, such as geomorphology and habitat fragmentation. The flows of energy involve three prime steps, which are (i) accumulation of energy; (ii) transformation of energy and (iii) transfer of energy. The flows of energy through successive stages within the trophic interactions are represented by several other eco-biological attributes, like biomass (the total mass of the body of a species and is expressed as g/unit area); biomass yield (the product of all harvested biomass as expressed as grams of organic matter per square meter (g/m2); the standing crop (the biomass present in a population at the time of its measurement) and productivity (the rate of biological production). The biological productivity being the fixing up of energy by green plants and consequent transfer of the same to the higher trophic levels is manifested by growth patterns, shapes, sizes and weight of the organisms forming different trophic levels. The term production indicates the amount of accumulated organic matter during specific time frame through the continuous production process (Odum & Barrett, 2005). The rate at which solar energy in the form of kinetic energy is converted to static energy by the process of photosynthesis by green plants (primary producers) is known as primary productivity. The primary productivity is also represented as the rate of production of new organic substances by the primary producers (autotrophs) which subsequently results in developing biomass on being bioaccumulated within the living body. The two different forms of primary productivity are as follows: 1. Gross productivity (G.P.P.): It denotes the rate of conversion of total amount of solar (radiant or kinetic) energy into a plant’s biomass as chemical (static) energy by all the autotrophs of an ecosystem and thereby can also be represented as the rate of production of biomass by the autotrophic organisms of an ecosystem. 2. Net primary productivity (N.P.P.): It refers to the rate of utilization of the total amount of biomass by the autotrophs for their own needs of energy and nutrients, whereas the leftover residual portions are manifested as new biomass. In view of the above, this relationship can be expressed by the following: Net primary productivity  Gross productivity  Energy lost in respiration. Primary productivity denotes the rate at which green plants (autotrophs) can produce and accumulate biomass in an ecosystem. Gross primary productivity (G.P.P.) is the total amount of energy used by the green plants for the building up of the biomass of living bodies and also for undertaking different physiological functions, such as digestion and respiration. Net primary productivity (N.P.P.) refers to the residual amount of energy left within the bodies of the plants after the utilization of energy for the purpose of various physiological activities, especially respiration. In the process of energy flows, primary producers serve as the food for the herbivores which are subsequently consumed by the carnivores facilitating the predator–prey interactions within the complex trophic relationships of food web through which only organic carbon can be assimilated instead of fixing CO2 (Fig. 2.2).

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Fig. 2.2  Flow of energy through different tropic levels within wetland ecosystem

Therefore, all the organic carbon moving through different biotic compartments within the biosphere can only be returned through such trophic interactions starting from the autotrophs (primary producers) and ending to top carnivores via several other heterotrophs (Chakraborty, 2021a).

2.8  Energy and Ecosystem: Driving Force behind all Kinds of Eco-biological Activities

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Fig. 2.3  Schematic representation of conceptual analysis of the functioning of a wetland ecosystem

2.8 Energy and Ecosystem: Driving Force behind all Kinds of Eco-biological Activities Energy as the capacity to do work acts as the driving force behind all functional activities of an ecosystem. The sun being the ultimate source of energy for all ecosystems of the biosphere promotes so many important eco-biological processes of the earth, like photosynthesis of green plants where radiant energy after being received and processed by the autotrophs is subsequently transformed into chemical

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(static) energy through different metabolic activities of the consumers, the heterotrophic organisms (herbivores, omnivores, carnivores and detritivores) and is manifested as biomass, biological productivity, standing crop, etc., within the ecosystems (Fig. 2.3). The consumers as per their choices and requirements for foods are categorized within an aquatic ecosystem as herbivores (plant feeder insects, zooplankton, fish, etc.) and carnivores (animal eater zooplankton, insects, reptiles, fish, birds, etc.). Another important category of heterotrophic organism is represented by decomposers which harvest energy in the process of decomposition of dead or decaying biomass of other living organisms (microorganisms, bacteria, fungi, actinomycetes, etc.) (Odum, 1971; Chakraborty, 2021a).

2.9 Flows of Energy: Laws of Thermodynamics The basic laws of thermodynamics can explain all the naturally occurring biogeochemical processes in the biosphere. Thermo (heat) indicates “energy in transit”, whereas dynamics refers to “movement”. Therefore, studies on thermodynamics focus on the movement of energy and the reasons behind the mechanisms to lend support to all eco-biological processes through such movement. The laws of thermodynamics advocate the possibility of the exchange of energy between physical systems as heat or work in terms of quantity, named as entropy. Two important laws of thermodynamics can explain the unidirectional pathway of energy flows in an ecosystem, which is as follows: 1. The first law of thermodynamics: The first law of thermodynamics deals mostly with the conservation of energy by postulating that energy can neither be created nor destroyed and the total fixed amount of energy within the universe may only be transformed from one form to another. 2. The second law of thermodynamics: The second law of thermodynamics embodying the concept of entropy highlights that the spontaneous reactions process always proceeds in the direction of increasing order and releases energy on reaching towards equilibrium. Entropy being a measure of the randomness within the disorder of reactants and products can harness to work. This law also affirms that non-random energy (chemical, mechanical or radiant) cannot be altered without any degradation into heat energy. The processes of such transformation of the energy can only happen spontaneously when the flows of energy tend to decrease at each step of trophic interactions due to the loss of heat occurring with each stage of transferring of energy from higher to lower trophic levels. Such reduction of energy can be explained with the concept of entropy which tends to increase when a part of energy encounters dispersion or absorption in the surroundings instead of undergoing transformation. For example, at the time of transfer of energy from one organism to another in the form of bioaccumulated organic matters, a portion is stored in the living tissue as stored

2.10  Food Chains and Food Web Dynamics Within an Aquatic Ecosystem: Food Web…

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energy, which allows the dissipation of a large part of the energy as heat resulting in an increase of energy (Smith, 1996; Chakraborty, 2021a).

2.10 Food Chains and Food Web Dynamics Within an Aquatic Ecosystem: Food Web Complexity The transfer of energy from one trophic level to another through repeated eating and being eaten phenomenon is known as food chain. The food chains within an aquatic ecosystem in the form of chain of sequences of energy transfer take place from phytoplankton to zooplankton to small fishes to large fishes and then to carnivorous birds and like other animals representing the higher trophic levels. The food webs are formed by the interlocking and interconnection of so many food chains which serve to maintain the ecological stability and integrity of the aquatic ecosystem. Three types of food chains are as follows; (i) Grazing food chain (initiated from the autotrophs and ending to top carnivores via herbivores, omnivores, etc.); (ii) Parasitic food chain (moving from the larger organisms in order to reach to smaller ones deviating from the normal rules of prey–predator relationships without outright killing the weaker and smaller ones as observed within host–parasites interactions) and (iii) Detritus or Saprophytic food chain [the semi-decomposed dead organic remains on their derivation from the decomposition of dead and decomposing organisms by the decomposers as detritus forms the major source of energy for a group of organisms, called detritivores which extract their life supporting ingredients (food, shelter, etc.) from detritus and thereby belong to that food chain named as detritus food chain]. In the estuarine mangrove ecosystem, greater movement and transfer of energy take place in the detritus food chain in comparison to the energy flows as practised in the grazing food chain. In the ecosystem, shorter food chains not exceeding four links result in higher biological productivity (Pimm, 1982). Food webs developed due to the interconnections and inter-linkages among several food chains tend to involve more species providing the required life support materials and experiencing more complexity in the processes of exchanges. However with the increase in complexity in the food web with the involvement of increased number of species, the connectedness among different trophic levels decreases. The average number of links among different trophic levels (autotrophs, herbivores and carnivores) indicates about the relative complexity of food web (Chakraborty, 2017, 2021a).

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2.11 Ecological Efficiency in Plants Ecological efficiency is defined as the amount of energy that is transferred from one trophic level to the next. This follows the rule of 10% where around 10% of the energy at one level will be available to the next level for the purpose of utilization. Photosynthetic efficiency is the amount of light energy used by the green plants to convert radiant energy into chemical energy by the process of photosynthesis. In other words, the photosynthetic efficiency is directly linked up with the ability of green plants to convert the atmospheric CO2 in the form of simple carbohydrates. The photosynthetic efficiency can be calculated with the help of two scientific propositions as “Energy equivalent of carbon compounds produced per unit area per unit time” and “ Energy input per unit area per unit time” (Krebs, 1994; Smith, 1996).

2.12 The Ecological Efficiency of Animals The herbivorous animals feeding on green plants (herbivores) occupy the second trophic level, whereas predators or carnivores enjoy their positions at the third trophic level and so on in the food chain which ultimately ends up with top carnivores. Owing to the active habits and proficient mobilities of animals in search of food, shelter and also for reproductive mate, they as the constituents of food chains are more energy efficient. The Lindeman’s Law of trophic efficiency from one trophic level to another is 10% of the net primary productivity for the producers which ends up as herbivores and during such transfer 10% of the transferred energy is stored within the biomass of each trophic level. This law emphasized that the amount of transferred energy from one trophic level to the next as a percentage of the total amount available in the lower level is equivalent to the ecological efficiency of animals. The Lindeman efficiency takes also into account the total utilization of energy for the respiration of the species representing both the lower and higher trophic levels (Smith, 1985; Chakraborty, 2021a).

2.13 Limnology and Its Different Dimensions The subject limnology deals with the study of the structural and functional uniqueness of the inland water bodies with special emphasis on the interrelationships of aquatic organisms governed by the eco-dynamics of the total ecosystems, involving physical, chemical and biological parameters. The freshwater biology refers to the study of interrelationships and interactions of biological components of the freshwater ecosystem. Among the different trophic interactions, predator–prey interactions have appeared to play most decisive roles not only to structure biotic

2.13  Limnology and Its Different Dimensions

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Fig. 2.4  Linkage in between wetlands and upland terrestrial system

communities but enable to provide insight with regard to the mode of coexistence of prey with predators in the light of coevolution. Freshwater as one of the most important natural resources plays a crucial role in ensuring the survivability of all living beings. Alongside providing drinking water, fresh water bodies also help in growing up so many essential food ingredients and promote industrial growth, hydropower generation and waste disposal process. Limnology is that science which deals with the physico-chemical characteristics, biodiversity and the ecosystem processes of freshwater ecosystems (Wetzel & Likens, 2004; Chakraborty, 2021a). After emerging as a scientific discipline first in Europe, it became matured and flourished both in Europe and North America, from where several limnologists explored and collected research information of the freshwater ecosystems of Asia, Africa and South America. In due course, continued interest in this subject attracted so many researchers from tropical countries, including India, to venture in this field of science under the auspices of a number of international organizations, like the UNESCO, International Society of Limnology, Limnological Society of America, Australia, etc. Limnology, primarily, as an offshoot of the parent subject ecology includes some of the research components that go well beyond the limits of biology on relying on certain principles and methodologies mainly derived from the ingredients of physics, chemistry, hydrogeology, geography, meteorology, etc. Such interdisciplinary approach for the solution of problems pertaining to the inland aquatic systems is undertaken with the prime objective of analysing the mode of functioning of the complex web of climatic, physical, chemical and biological factors in all natural aquatic systems and also to find out the reasons behind of those

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Fig. 2.5  Interactive relationships between ecological variables, processes, development and structuring of wetland ecosystem

problems of freshwater ecosystem management (Goldman & Horne, 1983, Wetzel, 2001). Therefore, to overcome the ongoing environmental problems created mostly due to the overpopulation, unplanned urbanization coupled with industrialization, intensification in aquaculture, etc., development and standardization of several environmental management tools have been undertaken for the treatment of sewage, to combat the problems of pollution of natural waters and to undertake eco-restoration of eco-degraded aquatic ecosystem on properly adhering to the basic operating

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scientific principles of limnology. In such context, the generated research information based on limnological studies are being used by environmental planners and administrators mainly to understand the natural ongoing ecological processes of the freshwater ecosystem with an aim to identify and evaluate the influences of ecological variables on the functioning of freshwater ecosystems so that the biological productivity as well as ecological integrity of the ecosystem may be enhanced (Figs. 2.4 and 2.5) (Goldman & Horne, 1983; Wetzel, 2001; Wetzel & Likens, 2004; Chakraborty, 2021a).

2.14 Ecological Niche and Habitat: Concept of Resource Partitioning and Metacommunity In the study of biotic community, the prime division of the biocoenosis is dealt with associations which are characterized by dominant or at least characteristic species. The concept of association points out the assemblages of plants, animals and also microbes which recur and coexist under comparable ecological conditions in different places. In the process of such analytical study on biotic assemblages or association, the concept of ecological niche and habitats has been emerged. The niche of a species is defined by Grinnell (1917) as the functional role and position of an organism in its community. Subsequently, ecological niche was recognized as the fundamental unit of an organism or a species population in a community by Elton (1927) who emphasized more on its place in the biotic environment and its relations to food and enemies. The acceptable definition of ecological niche was given by Odum (1971) as “the position or status of an organism within the biotic community and ecosystem because of the structural adaptations, physiological responses, and specific behavior (inherited and learned) of the conserved organism”. MacFayden (1957) considered niche as the indicator of the environmental quality and defined as “A niche is a set of ecological conditions which are exploited by a species in order to harvest the required resources and energy effectively for the purpose of growth, reproduction and colonization”. Huchinson (1958) put forward his views about the niche as “the totality of abiotic and biotic factors to which a species is exposed and uniquely adapted”. The concept of multidimensionality in the niche was advocated by Hutchinson (1965) where a population is exposed to a range of ecological variables, such as temperature, intensity of light, humidity and food particles. The multidimensional aspects of ecological niche are discussed by different ecologists in different periods to analyse and interpret the behavioural manifestations of living organisms among themselves in relation to the non-living surroundings (Grinnell, 1917; Elton, 1927; Huchinson, 1958; Odum, 1971; Krebs, 1994; Smith, 1996; Ricklefs & Miller, 1999) and some of these attributes are mentioned below:

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1. Niche space: The niche is determined by the prevailing ecological parameters and the flux of resources which are required for the survivability of the individuals within the biotic community. 2. Ecotope: It is the term used for highlighting niche or niche space as a function of habitat and it combines habitat with the other axes of a niche. 3. Niche packing: A community-building process through intense interspecific competition in order to determine maximum number of species within the community. 4. Niche breadth: It refers to that habitable extent (width) of niche in order to utilize a broad spectrum of the environment. The niche breadth, speaking for the width of distribution of each species, indicates the extent of use of the different categories of resources or the range of ecological conditions tolerated by the individuals constituting the population. 5. Niche overlap: It is a measure of the association of two or more species due to their occurrence in a habitat indicating their similar habitat requirements in search of food and other life-supporting resources. The extent of sharing of resources or similarity in the patterns of tolerance of ecological conditions is known as the niche overlap. The niche breadth and niche overlap exhibit inverse relationship. In the absence of niche overlap between species, niche breadth will be wider in the biotic community with fewer number of species. 6. Niche complementarity: Almost all coexisting species using more than a single niche axis differ considerably in respect of their utilization of other resources and this condition is named as niche complementarity. 7. Ecological equivalents: Ecological equivalents refer to those taxonomically different species which occupy similar ecological niches performing similar functions but in different geographical regions. Therefore, ecological niche should not be treated only as the space occupied by a species but should recognize the functions or roles played by a species. Therefore, on summarizing the above concept, it can be hypothesized that the term ecological niche is used as an abstract but in purely intensive sense tends to highlight the requirements of an organism abstracted from the specially extended habitat. The relationship of species in respect of niche has appeared to be a determining limiting factor or resource resulting in competition of two species for a limited resource which has prompted them to evolve mechanism to reduce competition and thereby to ultimately result in higher population density and less possibility of extinction. The concept of the niches seems to be closely related with the concept of competitive relationships and thereby competitive exclusion among species which stresses on the non-existence of two species on a single niche at a time in particular ecological set-up where one must be driven out and diverge into different niches through natural selection. The multidimensional niche concept rests upon four important ecological perspectives (Howe & Westley, 1988) as mentioned below: 1. Availability of life-supporting resources varies with time and space.

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2. The diversity, abundance and distribution of species constituting a biotic community are determined by resource availability and physico-chemical parameters. 3. The preference and power of tolerance of some species differ from some other species belonging to the same biotic community. 4. Competition only occurs within the biotic community when one species limits the supply of resources to other species. Resource partitioning is resulted because of intense competition of two or more species to acquire and divide a particular resource, like food or space for their feeding, breeding and other life-supporting requirements. Sharing of a particular habitat by several species leads to cause habitat shrinkage, which is ecologically designated as ecological compression and this ecological condition subsequently invites competition among the constituting species within the biotic community. In other words, resource partitioning within the habitats limits the occurrence and distribution of two or more species who tend to divide a limited resource and thereby by avoiding competition help in finding out ways and means for coexistence. A number of hypotheses have been proposed to explain the intricate relationship among niche, resource partitioning and distribution of animals which are as follows: 1. The random-niche hypothesis (MacArthur, 1960): The resembling process by playing important roles in determining the abundance of each species within a biotic community ensure random partitioning of distributed resources along a continnum of resource types (MacArthur, 1960). 2. The niche-preemption hypothesis: This hypothesis postulates that the maximum space within ecological niche is being preempted by the most successful or dominant species followed by the successful claims the next largest share of the space by the second one and the least successful species is left with the option to share little leftover space. This hypothesis supposes that the most successful or dominant species preempts the most space. The next successful claims the next largest share of space, and the least successful occupies what little space is left. After the initial colonization, each new species tends to preempts more than 50% of the smallest remaining niche, where the empty niche space declines with the increasing species richness in a community (MacArthur, 1968). The niche preemption concept also enables geometric series model to explain species abundance where an ecological succession prompts a species to colonize an area in and thereafter to preempt a constant fraction of the remaining resources (Whittaker, 1975; Wilson, 1991). 3. The log-normal hypothesis (Preston, 1962): The log-normal hypothesis highlights the importance of ecological attributes, such as food, space, microclimate and other parameters which determine the success of a species to occupy a niche space. Moreover, the relative importance of each species is also determined by the mode of influence imparted by the ecological variables on the concerned species (May, 1981). 4. Niche-diversification hypothesis (Anderson et al., 1981): This hypothesis states that in an ecosystem having equilibrium, each species has evolved a very specific

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niche in search for food and microhabitat avoiding competition by maintaining niche segregation and niche differences. 5. Intermediate disturbance hypothesis (Connel, 1978): The biodiversity is slated to be higher in habitats having moderate level of disturbances rather than at habitats under low or high level of disturbances. In the state of existence of equilibrium and spatial uniformity within the ecosystem, the community is represented by a few dominant species (best competitors) following the principles of competitive exclusion. However, in the non-equilibrium state of the community due to the presence of severe predation, herbivory, fluctuating ecological conditions, natural disasters and such modes of disturbances, competitive equilibrium is prevented resulting in driving out of the constituent species and even the extinction (Krebs, 1994). However, in between these two extreme cases, an intermediate level of disturbance prevails which maximizes the biodiversity and this conceptual development is highlighted by intermediate disturbance hypothesis (Connel, 1978; Ricklefs & Miller, 2000). The development of the concept of metacommunity has led to the emergence of a number of conceptual models in respect of patch dynamics, species sorting, species traits, mass effect, environmental heterogeneity and geographical distance causing dispersal constraints (Leibold et al., 2004; Hubbell, 2001). Metacommunity in contrast to a biotic community (assemblages of several interacting populations along with their constituent individuals residing a single patch or habitat), refers to a set of local communities that are interlinked because of dispersal and migration (emigration and emigration) of several interacting species (Wilson, 1992; Halder Mallick & Chakraborty, 2015). The relationships among different constituent populations within metacommunities are seen to experience reorganizations at various scales in tune with the changing environmental context (Leibold & Miller, 2004). The metacommunity dynamics in wetlands confront with several ecological problems because of habitat fragmentation causing hindrance to dispersals among communities mainly due to the increasing isolation and loss of patches. Freshwater wetlands as isolated and closed systems embedding within the terrestrial matrix hardly encounter absolute isolation as the inhabitant individuals can move between neighbouring water bodies through both direct connections e.g. water channels or flooding (Michels et al., 2001) and overland dispersal (Cáceres & Soluk, 2002; Cohen & Shurin, 2003), thereby bridging the gap among fragmented habitats with subpopulations for their mixing within the metacommunity (Halder Mallick & Chakraborty, 2015). Wetlands encountering such type of problems have been facing excessive destruction and fragmentation as evidenced by several studies (Perrow & Day, 2002; Halder Mallick & Chakraborty, 2015). Biotic community within the local area (specific type of freshwater wetland) can be developed by several ecological interaction processes fluctuating ecological parameters, competition, predation, dispersal, immigration, emigration, spatial configuration along with connectedness of the habitats, etc. (Cottenie et al., 2003). The ecological perspective of metacommunity determines the regulatory process of the

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community and modifies the same in accordance with the changing ecological condition. This proposition can be substantiated by the functional roles of aquatic vegetation which provide nutritional support to the aquatic ecosystem and also scopes for getting protection against predation and shelter for both the larvae and adults of the aquatic fauna alongside constituting proper habitats for the growth and survivability of epiphytic and other littoral organisms (Joniak et  al., 2007; Declerck et al., 2011). The local ecological constraints can become the prime determining factor in determining species composition and trophic interactions biotic communities even enjoying the high interconnectedness among adjoining water bodies (Cottenie et al., 2003). Fontaneto et al. (2008) based on their studies on molecular ecology of planktonic zooplankton (rotifera) had hypothesized that bdelloid rotifers could exhibit low species diversity but high habitat selectivity, limiting the ability of colonists to become established due to the occurrence of rare scopes for dispersal coupled with higher availability of habitats. The success of dispersals among habitat patches by potential individuals within the metacommunity is supposed to be determined by the distance and ecological nature of connectedness among separated habitat patches (Shurin, 2000). The movement of population in the metacommunity matrix invites interactions among several populations of different habitat patches which in turn affect the genetic reshuffling within the individuals of concerned populations, promoting habitat patch occupancy and leading to cause recolonization of patches after extinction at local levels (Meffe et  al., 1997). The temporally and spatially heterogeneous areas are found to be more superior than the homogeneous areas as the former can accommodate biotic and abiotic disturbance better than the latter one and thereby can offer a species a diversity of habitats at a certain time. The internal dynamics of habitat patches as regulated by the presence or absence of a species in a specific habitat patch helps in maintaining the overall diversity (Pickett & Thompson, 1978). The metapopulation dynamics is considered to play a more critical role for small biota, for example, zooplankton in the freshwater ecosystems because of their small body sizes, short duration in life cycles, high rates of population turnover, higher selectivity for habitats and more vulnerability to localized density-independent ecological factors (Murphy et al., 1990; Fontaneto et al., 2008; Declerck et al., 2011; Halder Mallick & Chakraborty, 2015). In contrast to the metacommunity concepts and related models, niche-based theories emphasized more on differences among the individuals in respect of their ability to perform under different environmental conditions and also to predict those environmental dissimilarities which are expected to be resulted because of the decrease of community similarity among sites (Gilbert & Lechowicz, 2004). A number of studies have tried to address the questions of metapopulation and metacommunity dynamics based on the ecological assessment of zooplankton community in small freshwater bodies where it was observed that although both zooplankton and phytoplankton are tightly coupled via food web interactions sharing similar environmental gradients, but zooplankton tend to display dissimilar responses and spatial structuring to major ecological determinants than phytoplankton because of the differences in body size, dispersal capacity, trophic position and rate of

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population dynamics (Rothhaupt, 2000, Cottenie & De Meester, 2003, Cottenie et al., 2003, Soininen et al., 2007). The zooplanktonic community residing in the intermediate and also in the higher trophic levels, enjoying suitable ecological niche, imposes top-down effects to regulate food web dynamics by grazing phytoplankton (McQueen et al., 1989; Soininen et al., 2007).

2.15 Background Ecology for the Functioning of Wetlands Although all wetlands of the world share some common criteria, but based on several other ecological criteria, especially on the vegetational types and categories, wetlands are of different categories (marshes, swamps, fens, etc.), but all of the wetlands serve as “sink,” “source” and also “transformer” for pollutants. Sink  This facilitates biological transformation from the biologically unavailable forms within the ecosystem, like the conversion of nitrate (NO3) to N2 gas through a biological reaction, called denitrification. Source  In natural systems so many forms of substances both toxic and non-toxic ones are transported from one ecosystem to another. In the process of inter-­ ecosystem exchanges facilitated by several eco-biological processes, such as flood, decomposition in the floors of forests, soil erosion, bioaccumulation, bio-­ transformation, and bio-magnification of persistent chemical pollutants, a good amount of allochthonous nutrients loaded with suspended solids and other pollutants move from the upland ecosystems to the low-land wetlands. Nutrients also move from the eutrophic wetlands which act as the “source” of nutrients and other toxic substances and gases to adjacent aquatic systems, such as streams, rivers, lakes and estuaries. Transformer  Continuous releasing and transformation of several persistent pollutants as complex compounds with new physico-chemical properties to wetland ecosystems over time trigger the soils of the wetlands to act as sinks and transformers of different accumulated substances imposing considerable impact on the eco-­ dynamics of the wetlands.

2.16 Biogeochemistry and Biogeochemical Cycling The prime driver of most of the ecological processes of a wetland ecosystem is the biogeochemistry of the same ecosystem embodying the flux and cycling of different structural constituents of global environment which facilitate the exchange of materials between living and non-living components of the biosphere. Wetland biogeochemical cycles have blended the chemical transformations and chemical transport

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processes which are appeared to be very unique for wetland ecosystems. However, as biogeochemistry encompasses interactions from the smallest scale to the global scale in the biosphere, wetland, as an ecosystem with small-scale activities render significant impact on other landscapes of the world. Wetland biogeochemistry focuses on surface or near-surface processes in wetlands that govern biogeochemical cycles, growth and production of macrophytes, nutrient availability and microbial transformations, removal of pollutants, atmospheric exchange and sediment transport. Biogeochemical cycle being a part of wetland biogeochemistry refers to circulation of different chemical elements, such as carbon, oxygen, nitrogen, phosphorus, calcium and water through exchange of materials between living and living components by way of different ecological, biological, geological and chemical processes at various hierarchal stages of ecospheres. In this cyclical process, the concerned substance is found to get back in the initiation phase after a specific amount of time and the set of pathways is then repeated. The time required for a chemical to remain detained in one place is called its residence time. These cyclical phenomena of the biogeochemical cycles of relevant elements, such as water, oxygen, carbon, nitrogen, phosphorus and sulphur, are determined by the prevailing environmental conditions where various elements show characteristic cycling periods. In the process of movement and cycling of elements through biogeochemical cycling, an element gets accumulated in specific area, called reservoirs which tend to hold substances for longer times than the actual period required for cycling. Both the cycling time and storage time have appeared to be critical factors determining the behaviour and role of a particular substance or element throughout its biogeochemical cycle. In addition, all biogeochemical processes operating in wetland ecosystems with the involvement of a host of complex biotic communities (microbes, planktons, benthos, periphytons, fish, etc.) have been observed to contribute significantly towards global biogeochemical cycles and influence considerably on several burning global environmental issues, such as global warming, eutrophication, carbon sequestration, turnover of organic matters and maintenance of water quality, mostly by rendering help wetlands act as both sources and sinks of carbon dioxide, methane, oxides of nitrogen (NOx), etc. Moreover, the impacts of biogeochemical cycles on the structure and function of the wetland ecosystems may have a number of positive or negative impacts and result in several ecological consequences which can be summed up with the following headings: 1. The oligotrophic wetlands are converted to eutrophic ones with gradual but steady enrichment of nutrients which subsequently result in a series of ecological changes starting from the changes in the species composition of the natural biotic community, decrease in the species diversity, acidification of water, depletion of dissolved oxygen (DO), appearance of tolerant but undesirable species having the ability to produce toxic substances, changes of decomposition patterns from the aerobic to anaerobic states, etc. 2. Higher primary productivity due to the receiving of nutrients from both the allochthonous and autochthonous sources results in increased rates of organic

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matter accumulation and also in the development of sink for increased CO2 sequestration. 3. Increased rates of carbon accumulation trigger more microbial activities in soil and within the water column. 4. Enhanced microbial activities in the eutrophicated water bodies with anaerobic conditions in the bottom soils produce a good amount of ammonia (NH3) and oxides of nitrogen (NOx) as greenhouse gases. 5. The research information derived from the biogeochemical cycles can be useful for predicting the environmental fate of the naturally occurring elements and compounds of the wetlands. 6. The excess water and soil oxidation–reduction processes also play important roles in the cycling of several elements of nutritional significance, responses of wetland vegetation and transformation of toxic organic substances. 7. The physical–chemical properties of water of wetlands are regulated by two prime ecological attributes: (i) the amount and intensity of precipitation of rainwater having mild acidity and poor nutrient contents and (ii) rocks or soils through which the rainwater flows. The rainwater in the nearby zones of seas or oceans contains a good amount of cation in elements, such as calcium, sodium and magnesium, whereas the water moving over the acid rocks, such as granite or sandstone, before reaching and mixing with the water of wetlands is generally poor in calcium but while passing through the limestone, the water is endowed with more calcium. The contents of nitrates and phosphates in wetland‘s water are mainly due to the different types of human activities (agro farming, disposal of sewage and wastes from industries). 8. The bottom sediments of wetlands act as the reservoir of both inorganic and organic substances. At the initial phase of the formation and development of wetlands, bottom sediments mainly contained inorganic materials but a lot of organic materials are produced and deposited in the course of succession over time. The recording of several fossils artefacts within the sediments can indicate the course of development of a wetland so that the direction of successional changes in respect of bio-chemical entities can be reconstructed. The sediments of wetlands therefore act as archival historical information which on proper interpretation through accurate dating (radiocarbon dating) of sediment horizons help in achieving the target of fulfilling the understanding about past developmental phases of wetlands. 9. The storage of energy within the organic remains of some ancient wetlands, mostly as peat lands, provide information about the evolution and development of living organisms and ecosystems because of their profound effect on the development of human culture and other socio-economic conditions forming the basis for the industrial revolution.

2.18  Spatial Heterogeneity of Nutrient Controls

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2.17 Nutrients Loads and Ecological Alternations: An Example of East Kolkata Wetlands, a Ramsar Site Historically, the major source of nutrients to the EKW has been from the nutrients-­ loaded sewage from the adjoining Kolkata Metropolitan and industrial complexes, deposition of particulates from the atmosphere and secondary inputs of some nutrients through infrequent sheet flooding. Considerable amount of both N-based and P-based allochthonous nutrients load from sewage water has not only altered aquatic algal and plant communities but also enhanced nutrient accumulation (Davis, 1991; DeBusk et al., 1994; Newman et al., 1997). In addition, traditional pisciculture practices have enhanced the inputs of autochthonous nutrients which also lead to cause significant alterations in the structure of indigenous biotic community and rates of nutrient accumulation. The maximum accumulation rates are noted in areas closer to the source of nutrient inputs, and the minimum accumulation rates occur in areas furthest from the input points. Continual nutrient loading to the erstwhile oligotrophic EKW wetlands around several centuries back resulted in a zone of high nutrient availability near the input and low nutrient availability in the zones away from the zone of inputs. Out of major elemental forms of nutrients, some noted ones, such as N, P, C and S, exhibit more susceptibility to accumulation within the wetland ecosystems as minimum loss of this vital nutritional element through the gaseous conversion takes place in the P cycle. In the EKW, several cyclical processes involving C, N, P, S and other related chemical elements tend to govern so many biogeochemical processes within the soil and water which mostly mediated by microbial, benthic, periphytonic and macrophyte communities. Different nutrients-mediated biogeochemical processes respond rapidly to physico-chemical properties of soil, detritus and water column and baseline scientific information act as indicators to determine impacts of nutrients in the recovery and restoration processes (Ghosh & Furedy, 1984; Chatterjee et al., 2002).

2.18 Spatial Heterogeneity of Nutrient Controls Different ecological parameters of wetlands display both positive and negative relationships among one another and thereby determine the availability of both biotic and abiotic components of the wetlands. The nutrient contents of the wetlands not only vary among distantly located wetlands but also among different eco-zones of the same wetland. The conductivity and total organic carbon although display a close relationship but are inversely related with total nitrogen and nitrate, whereas chlorophyll-a is found to exhibit positive relationships with ammonia and dissolved organic carbon. The total phosphorus demonstrates dependence not only on soluble reactive phosphorus but also with ammonia. The total nitrogen shows direct relations with ammonia and nitrate. Besides, flooding has been observed to inversely control the conductivity and total organic carbon, nitrate and ammonia concentration of the water of the affected wetlands.

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2.19 Ecological Processes and Parameters vs Biota in Wetland Ecosystem Wetlands with the help of water, energy and nutritional inputs enhance the primary production which in turn triggers a series of ecological changes through the continuous interactions among different structural components of the ecosystem. Enhanced availability of nutrients, increased turbidity, decreased pH and DO causing a shift in the primary producer community with phytoplankton dominance instead of submerged macrophyte dominance, decrease of biomass of large-bodied zooplankton, increase of biomass of planktivorous and benthivorous fish and drastic decline in the population of piscivores animals in the eco-degraded wetlands (Whillans, 1996; Chow-Fraser et al., 1998; Alvarez-Cobelas et al., 2005). Increase of organic production due to the least entry larger macrophytes having higher biomass, mostly the floating and emergent ones into the food chains directly which causes the removal and decrease atmospheric carbon pool, most of which are accumulated (sequestered) in the plant biomass, animal biomass or also in the dead organic matter. Moreover, the decomposition process within the wetland ecosystems in anaerobic conditions returns less amount of CO2 in the atmosphere instead of enhancing the production and releasing of more greenhouse gases. (Sahrawat, 2003). The wetland ecosystem also plays a significant role in regulating the microclimate of the region through the process of évapotranspiration which registers its higher rates relative to open water surfaces in the wetlands (Otis, 1914; Mower & Nace, 1957; Acreman et al., 2003; Xu et al., 2011). Wetlands also act as an energy sink by facilitating latent heat flux process and generate an “air conditioning effect” by regulating the temperature of not only the territory but also the adjoining areas of the wetlands (Priban & Ondok, 1985; Wessel & Rouse, 1994; Pokorný et al., 2010; Rejskova et al., 2012).

2.20 Regulating Nutrient Cycles and Water Quality: Roles of Macrophytes In the functioning of the wetland ecosystem, cyclical movement of nutrients occurs within and also outside the concerned wetlands through complicated interactional pathways among different biotic and abiotic components of the ecosystem. The nutrients of soil and water of wetlands contribute important regulatory services through the linkages with water quality of wetlands where macrophytes serve as a sink or source of nutrients towards regulating water quality (Maltby & Barker, 2009). Nutrient cycling for the function of ecosystems with the active participation

2.21  Adaptive Strategies of Aquatic Organisms: Role of Limiting Factors

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of microorganisms results in primary and secondary production by plants and animals, respectively, which in turn lend supporting service. The ability of macrophytes to uptake and accumulate higher amount of nutrients may also be considered as a provisioning service because human beings directly consume and utilize these nutrient-rich plants as foods and for other purposes (medicine, biofertilizers, biochemicals etc.), respectively. Macrophytes by absorbing and bioaccumulating nutrients along with other toxic substances maintain and improve water quality by lowering the nutrient content, enhancing the oxygenation of the water column and keeping the water clean and transparent even in the face of ongoing negative human intervention (Carpenter & Lodge, 1986; Carrick et al., 1993; Madsen et al., 2001; Cronin et al., 2006).

2.21 Adaptive Strategies of Aquatic Organisms: Role of Limiting Factors The fluctuating ecological parameters after being influenced by oscillating meteorological conditions of the tropical regions pose real threats and challenges for the survivability of all living organisms of wetlands and compel them to adopt their own survival strategies by responding, interacting and adapting for the adjustment with the changing environmental conditions by modifying their morphology, anatomy and physiology which have been designed and selected in the course of evolution by the combined activities of natural selection and heredity. In order to fulfil the primary objective of an aquatic species to survive and reproduce successfully alongside ensuring the perpetuation of races, the adaptation strategies can become only stable after being selected and transmitted from one generation to others in the evolutionary process. The organisms inhabiting in the aquatic ecosystems having fluctuating ecological parameters through different seasons and years face the problems of unstable environmental conditions caused not only by a single factor but also by the cumulative influences of multiple factors, such as temperature, pH, dissolved oxygen content, wind flow, atmospheric pressure density of both air and water, and turbidity (MacArther, 1957; Dhanapathi, 1975, 2000; Khan and Siddiqui, 1976; Chakraborty, 2021a). The concept of limiting factors have been emerged with the assumption that exceeding the limits of tolerance of the organisms against the prevailing ecological parameters due to the differential ability of living organisms to cope up with and the tolerance against varied environmental conditions caused by oscillating ecological parameters can be considered as a limiting condition or a limiting factor (Odum & Barrett, 2005).

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2.22 Ecosystem and Environment Interrelationships: Perspectives of Wetland Ecosystem The water entering a wetland directly or indirectly from the surrounding landscapes and moving over the vegetation, soils and rocks accumulates a good amount eroded particles and also some other materials derived from the rocks or decomposition of dead biomass. In contrast, water reaching directly from precipitation may have only some dissolved solutes but almost no particulate matter apart from particulates (carbon particles, pollens, etc.) and those are collected during downpour through the atmosphere. Out of two different types of wetlands based on the sources of water, very little particulate matter is brought to the ecosystem from outside in an ombrotrophic wetland (fed solely by rain), whereas in the other one, the rheotrophic wetland (fed both by rain and drainage water), different categories of eroded materials are brought from the catchment into the wetland ecosystem. The environment being the sum total of all constituents of the earth acts as the protective umbrella under which life vibrates and the interplay of all living organisms (plants and animals) takes place. All the biota constituting important structural entities depend on an array of life-­ supporting ingredients, such as soils, water, air, sunlight, temperature, rain and snow, in order to find secured shelters for settlement, growth, proliferation, feeding, breeding and propagation as the prerequisites for their fruitful survivability and continuance of the life. The environment of human beings embodies inter alia historical and regional elements in terms of faiths, beliefs, social and cultural heritages, educational, morals and ethical components etc., which direct the lifestyle and control the quality of life. In such context, the environment encompassing the physical and social worlds of human relations help in building up a world of human creation (Kulshreshtha & Gopal, 1981; Kulshreshtha & Johri, 1991; Chakrapani & Krishna, 1994; Chakrapani & Ramkrishna, 1996; Maity et al. 2014). Understanding the cause and effect on the effectiveness of environmental components on life leads to develop the concept of linking up all the constituting components operating in an ecosystem together as an integrated whole or holocoenotic system which depicts the dialectical approach of ecology integrating the organisms and the environment into a dynamic whole. The undesirable deviation of any such ecological or environmental factor will become instrumental to result in an alteration in the dynamic state of the entire ecosystem. In the normal functioning of an ecosystem, the sunlight is utilized by the green plants after converting the kinetic energy into static (chemical) energy through the process of photosynthesis which following the pathways of the food chains and food webs supply energy to all other living organisms for their growth, proliferation and propagation. All biological communities depend exclusively on the organic matter produced either within the ecosystem by photosynthetic production as autochthonous nutrients (production) or as allochthonous nutrients (derived from an

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external source) and thereby help all other animals sustaining by living on plants (herbivory, omnivory and carnivory) and also by transporting to microbial community dead or decomposing materials for utilization through heterotrophy (Carrick et al., 1993) (Figs. 2.4 and 2.5).

2.23 Ecological Significance of Soil Organic Matter Soil organic matters not only promote the growth of vegetation within a wetland ecosystem but also serve for various other ecological functions, such as (i) a major contributor of the global carbon budget; (ii) as a source of CO2 and NH3 emissions into the atmosphere; (iii) as a source of mineralizable nutrients for the growth of plants and other microorganisms; (iv) as a source of energy for heterotrophic microorganisms; (v) as a source of Dissolved Organic Matter (DOC); (vi) promote the exchange capacity for cations in soils; (vii) ensure long-term storage of nutrients in soils; (viii) help in formation of metallic complexes in soils and (ix) act as strong adsorbing agent for toxic organic compounds in soils. It is being hypothesized that as many strategies for survival exist as there are species because particular species may adopt different strategies in different places or at different times. The planktonic and benthic organisms utilize the opportunities and overcome constraints associated with life in water very clearly by virtue of their interactions and interrelationships with other structural components of wetland ecosystems. These are manifested by the eco-biological attributes of an organism such as body size, colour, behaviour, food, reproductive activities and habitat preferences and all these multitudinous facets of life supporting systems assume selective importance towards strategies for survival. The finding out of positive relationships in between past and future environmental conditions indicate the positive impact of past selection pressures to the present and also for the near future. The common eco-biological properties of life history strategies (foraging, dispersal, migration, parental care, reproductive fitness, etc.) denote the trade-off between competitive ability, predator defence and productivity which tend to detract from each other mainly because of limited time or energy available to an organism (Harpes, 1978; Krebs & Davies, 1978; Maynard Smith, 1978; Pianka, 1978). The physiological mechanism of achieving greater adaptive fitness and higher survivability for an individual consists of either getting and utilizing more food, greater survival rates supported by specialized morphological structures and efficient behavioural manifestations. However, organisms hardly achieve the maximum possible adaptive fitness in nature and thereby optimization of adaptive fitness through development of required genotype and phenotype mainly because of sudden changes of interpopulation gene flow followed by mutations which are subsequently screened and accepted by natural selection to ensure fruitful survivability (Chakraborty, 2021a).

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2.24 Historical Account of Wetlands Research 2.24.1 Historical Background on the Ecological Concept and Definition of Wetland From the surveys of literature, different perceptions on the definition of wetlands are encountered in various countries in varied ways. Prior to the 1960s, wetlands were largely neglected and unappreciated and considered probably the most poorly understood landscape and ecosystem, attaching no significance either to land or water (Boate, 1632; William, 1990). The Ramsar Convention on Wetlands (Ramsar, 1971) through an international and intergovernmental treaty, broadly defined wetlands citing some criteria applicable to this landscape. Among the most widely accepted definitions across the world is that of Cowardin et al. (1979), which was adopted by the U. S. Fish and Wildlife Service and defined “Land where an excess of water is the dominant factor determining the nature of soil development and the types of animals and plant communities living at the soil surface”. It traverses a continuum of environments where aquatic intergrade with terrestrial ones. This definition emphasized on three major structural components of wetlands (water, soil and living biota) which have so far been accepted by wetland scientists as the basis for recognizing and describing wetland environments. Maltby (1986) quantitatively illustrated the landscape, wetland as to be a water-logged wealth. Wetlands are defined as areas that are saturated with water at least for that period which enables the aquatic plants and animals to grow and flourish in that area (Hillel, 1992). Wetland was defined differently by World Wildlife Fund (WWF) in the year 1987, Anon (1994) and many others depending on the objectives of the wetland research studies. Anon (1994) defined wetland as all submerged or water saturated lands, natural or man-made, inland or coastal, permanent or temporary, static or dynamic and vegetated or non-vegetated, which necessarily possesses a land–water interface. Both Schot (1999) and Charman (2002) summarized the uniqueness of wetlands based on three basic components (characteristic vegetation, groundwater and hydric soil) which determine the properties of wetlands. However, the common, overlapping and overriding components of most of the definitions embodies some of the ecological features pertaining to hydrologic conditions (Zedler & Kercher, 2005; Moore, 2008). Despite these, controversies prevail by wetland researchers with regard to the degree and extent of variability of ecological conditions of a wetland (Gopal & Masing, 1990, Zedler & Kercher, 2005; Ramsar, 2011). This was exemplified with a definition put forward by Niering and Lowe (1985), in which he described a wetland as an area which on accumulation of water controls the diversity and distribution biota in relation to the prevailing ecological conditions of the water bodies. The National Research Council (NRC, 1992) simply identified wetlands as transitional areas between terrestrial and open water systems, whereas in 1995, the NRC defined the wetland as “an ecosystem that depends on constant or

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recurrent, shallow inundation or saturation at or near the surface of the substrate”. A number of environmental scientists postulated different hypothesis in order to justify the evolution of wetland landscapes in different parts of the world during different time scales of last century (Mayer, 1935; Hewes, 1951; Hewes & Frandson, 1952; Kaatz, 1955). The physical characteristics of wetlands began to attract serious scientific attention in the seventeenth century which gained momentum by adopting different classification schemes of wetlands by different researchers confronting with a lot of complications in depicting the ecology of wetlands due to a wide range of variations in the water, soil and biodiversity assemblages for ensuring those attempts acceptable to the utmost satisfaction of all. Since the 1950s, a plethora of literatures on the holistic and integrative analysis of the ecology of wetlands became available mostly produced by several noted ecologists, like Teal (1962); Odum (1971) Baird and Ulanowicz (1989), Pomeroy (1991), Jones & Lawton, 1995; Mitsch & Gosselink, 2007; etc., which stimulated intellectual curiosity about wetlands throughout the world. To meet up this curiosity and also to address the problems in categorizing wetlands, Cowarding et  al. (1979) had classified five main wetland systems as Marine, Estuarine, Riverine, Lacustrine and Palustrine. The hydrogeomorphic approach was a system developed by the U.S. Army Corps of Engineers to classify all wetlands based on three major factors influencing the ecosystem functioning of the wetlands which are (i) positioned in the landscape (geomorphic setting); (ii) sources of water and mode of maintenance of water quality (hydrology); and (iii) hydrodynamics in the wetland with special reference to flow and fluctuation of water. Mitsch and Gosselink (2007) had proposed a classificatory scheme highlighting several wetlands with unique and contrasting ecological features, such as Bog, Fen, Mire, Marsh, Playa, Slough, Swamp, Wet meadow and Open water. Two different approaches towards classification of aquatic resources include one with geographical orientation and another based on the contributions of other disciplines of environmental sciences independent of geography, but both the approaches rely on environmental characteristics that determine ecological status of aquatic ecosystem status and also contribute towards vulnerability of ecosystem (Detenbeck et  al., 2000). According to Prasad et al. (2002), Indian wetlands can also be grouped as Himalayan wetlands, Indo-Gangetic wetlands, Coastal wetlands and Deccan wetlands. Specific bog variety (sphagnum-dominated peat lands) and fens represent rare and unique wetland types that were formed in closed depressional systems created by glaciation (Kulzer et al., 2001; Bell, 2007). The South African wetland classification system as proposed by Ewart-Smith et al. (2006) initially splits wetlands into three different groups according to their connectivities to the sea, namely, marine systems (part of the open ocean), estuarine systems (partially enclosed systems connected to the open ocean) and inland systems (no existing connection to the open ocean).

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2.25 Information of Distribution of Wetlands in India Wetlands in India occupy 58.2 million hectares, including areas under wet paddy cultivation (40.9  million hectares) (Directory of Asian Wetlands, IUCN, 1989). Maltby and Turner (1983) while reporting the status of wetlands of the World mentioned about an estimated 6.4% of the total land area come under the purview of wetland area. Wetlands cover approximately 6% of the World’s land surface and are found in all types of climate and on all the continents in the World (Hillel, 1992). The Ministry of Environment and Forests, Government of India (1990) had estimated that India has about 67,429 wetlands, covering an area of about 4.1 million hectares area (excluding paddy fields and mangroves). Out of these, about 2175 are natural wetlands occupying an area of 1.5 million hectares and about 65,254 man-­ made wetlands with 2.6 million hectares area. Out of the total area, 0.45 million hectares are covered by mangroves and associated water bodies. About 80% of the total mangroves in India occur jointly in the Sundarbans of West Bengal and Andaman and Nicobar Islands, while the rest are present in the states of Odisha, Andhra Pradesh, Kerala, Tamil Nadu, Karnataka, Goa, Maharashtra and Gujarat in India. The nationwide wetland inventory carried out by Garg (1998) reveals that there are 7.6 million hectares of wetlands in India of which 4.0 million hectares are coastal wetlands and 3.6  million hectares are inland wetlands. The major rivers of India, like Ganges, Brahmaputra, Godavari, Narmada, Kaveri, Krishna and Tapti, support the viability of so many inland wetlands, including floodplains by directly or the indirectly influencing them through the exchange of water, nutrients and even living organisms (Prasad et al., 2002). All of these wetlands are governed by the agroclimatic conditions of the different regions of the country, like the hot arid climate of Gujarat and Rajasthan, highlands of central India, the deltaic environments of the east and west coasts, wet humid zones of south peninsular India, the Andaman and Nicobar and Lakshadweep islands. Deepa and Ramachandra (1999) mentioned that freshwater wetlands alone support around 20% of the recorded biodiversity in India. According to Prasad et al. (2002), the occurrence of natural wetlands as lakes is observed in high altitude Himalayan regions of India followed by innumerable wetlands belonging to different categories (freshwater or brackish water, temporary or permanent, oligotrophic or eutrophic) in the river basins of hundred of rivers as well as lagoons, backwaters, estuaries, mangrove swamps, coral reefs and marine wetlands. In contrast with the exception of bogs, fens and typical salt marshes, Indian wetlands cover the whole range of the wetland ecosystem types as found in other parts of the world. Besides, in addition to the various types of natural wetlands, a large number of man-made wetlands also contribute to the wealth of aquatic biodiversity.

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2.26 Ecosystem Functioning of Wetlands and Ecological Variables In the functioning of the ecosystem, dynamic interactions among biotic and abiotic components are constantly taking place and thereby bring forth structural and functional changes. The water quality denotes the overall presence of different ecological variables and their cumulative impact in determining the properties of water which reflect the intended use of the water. Physical characteristics of the concerned wetlands, such as size, depth, volume and density of water and intensity of available sunlight, interact with other water quality parameters, like the temperature, pH, alkalinity, DO, etc., and thereby determine water quality in respect of colour, taste, temperature, odour, solid particles, nutrients and living biota. In the aquatic ecosystem, water constitutes the prime structural component within which all other aquatic organisms (bacteria, fungi, phytoplankton, zooplankton, fish, etc.) interact in order to get shelter and also to derive nutrients (nitrogen and phosphorus) from the overlying water along with other abiotic factors (temperature, pH, dissolved oxygen etc.). The continuous interactions among aquatic plants, animals and microbes result in different ecological processes, such as decomposition and nutrient cycling, and thereby bring about changes in the water quality. The ecological health of freshwater ecosystem is maintained and determined by a chain wise interactions of all of its physical, chemical and biological parameters, and proper understanding of all those ecological changes through proper ecological assessment has appeared to become prerequisite for undertaking restoration strategies for the management and sustainable conservation of the targeted wetland ecosystem along with their natural resources (Smith, 1965; Smith and Adams, 1986; IUCN, 1987; Wallace et al., 1999; Zedler & Keraher, 2004).

2.27 Wetland Hydrology Proper identification, assessment and understanding of the hydrological processes are important to understand the eco-dynamics of the wetland ecosystem. The direct infiltration from rainfall and discharged through evapotranspiration from the open system help in internal balance of water input and output. Although there has been a general assumption by various workers that groundwater recharged by meteoric infiltration being the underlying hydrological mechanism sustain the wetlands which demonstrate a balance between rainfall and groundwater rise and fall. However, the general hypothesis of vertical pathways of rainfall recharge and evapotranspiration discharge is not sufficient to explain the variability of water regime in wetland water levels and annual hydroperiod. The role and significance of lateral flow in this regard should also be given emphasis. Long-term water level behaviour is required to be examined in order to identify trends, and also to assess the significance of short-term water level variability in wetlands. Besides, consideration of hydrological parameters (seasonality in the volume of rainfall, intensity and

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frequency of evaporation and regional gradients of through flow at the basin and bedding scale in tune with the long-term climatic cycles) are required to be considered along with assessing the mode of development of wetland vegetation and small-scale hydrological processes. These in turn govern the seasonal fluctuation of water availability in the water table and soil water content in response to the intensity and amount of precipitation. All of these information help in determining the role of hydrological processes in the evolution of the wetlands and also in delineating some of the site-specific small-scale hydrological processes which tend to facilitate selective abilities of plants within wetland plant and sustainability of the entire wetland ecosystem.

2.28 The Relationship among Water Quality Parameters (Abiotic Factors and Biotic Factors): An Ecological Perspective A number of abiotic factors play their roles in the wetland ecosystem in determining the diversity and distribution of different biodiversity components and also they exhibit relationships among themselves in both positive and negative manners.

2.28.1 Temperature The temperature of soils, water and atmosphere not only imposes considerable impacts on the distribution of flora and fauna of wetlands ecosystem but also is related to the pH, dissolved oxygen DO, salinity, conductivity, etc. Water temperature is considered as the most important ecological parameter which influences so many other parameters, such as pH, DO, salinity and conductivity. In addition, temperature being one of the key regulators regulates so many biogeochemical processes in wetlands and influences the growth, activity and survival of organisms. Temperature plays an important role in the functioning of a number biochemical entities, like hormones and enzymes, and regulates the rate of decomposition of organic matters. Increased temperature enhances the microbial activity and decomposition of organic matters depending on the prevailing environmental conditions and composition of microbial communities. Several bio-molecules of living organisms, such as proteins, nucleic acids and other cellular components, like the plasma membrane, undergo denaturation and collapse due to the higher temperature above the permissible levels. Decomposition of labile soil carbon is influenced by temperature as revealed from the fact that low temperatures promote the occurrence of high levels of labile organic carbon in soils, whereas high levels of more recalcitrant organic matter are maintained relatively at higher temperatures (Dalias et al., 2001). Seasonal changes

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in temperature impose considerable impacts in controlling the rates of different biogeochemical processes, production and decomposition of organic matter, including enzyme activities, emissions of CO2 and NH3.

2.28.2 Hydrogen Ion Concentration (pH) pH being the negative logarithm of hydrogen ion concentration displays a range of 4.0–9.0. in most of the freshwater bodies where water bodies for becoming biologically productive require a pH above 7, which is to be considered as slightly basic because of the presence of carbonates and bicarbonates. A deviation from the desired level of pH in the aquatic ecosystems may be due to the influx of acidic or alkaline wastes derived from both natural (anaerobic decomposition) and anthropogenic activities. The acidity and alkalinity are measured as of the total resistance to pH change or buffering capacity of the water pH representing the free hydrogen ion activity not bound by carbonate or other bases. The pH being the negative logarithm of hydrogen ion concentration of both in the water and soils of wetland ecosystem influences not only the abundance of living organisms by regulating their metabolic activities but also helps in mobilization of different toxic substances, like heavy metals within the wetland ecosystem. The pH of natural waters ranges from 4.0 to 9.0, where the water of the wetlands having preferred ecological health remains slightly basic because of the presence of carbonates and bicarbonates. The solubility of water and also bioavailability of nutrients (Nitrogen, phosphorus, carbon, etc.) as well as heavy metals (iron, copper, cadmium, etc.) from water are determined by the pH of the water. The degree of solubility of heavy metals indicates the intensity of their toxicity which tends to be more toxic at lower pH of water because solubility of heavy metals increases in acidic water.

2.28.3 Dissolved Oxygen Dissolved oxygen (DO) denotes the amount of oxygen which remains dissolved in water, occupying the space in between two water molecules, is referred to as dissolved oxygen (DO) This very important ecological parameter serves so many ecological functions in the aquatic ecosystem, especially towards the very existence and survivability of aquatic biota, and thereby facilitates the eco-dynamics of the same ecosystem. Dissolved oxygen (DO) remains dissolved in water and profusely determines the eco-dynamics of the wetland ecosystem especially by producing O2 to the aquatic organisms for respiration and also by maintaining the aerobic conditions for the microbial decomposition process. The main sources of DO content in water include three sources: (i) photosynthetic activity of the green plants; (ii) diffusion of atmospheric air from the air–water interface and (iii) wind-driven mixing of atmospheric O2.

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2.28.4 Turbidity and Transparency The turbidity of water bodies is developed because of the suspension of particulate matter which interferes with the penetration and passage of light causing hindrance to its straight transmission by making the light scattered or absorbed. It is an optical characteristic of water which denotes a measure of relative clarity of water and acts effectively as a significant parameter in determining the opaqueness of water that reflects the intensity of scattering of light. The size, shape and refractive index of suspended particulate matters rather than their total concentration within the water bodies are responsible for resulting turbidity. The turbidity of water reflecting the opaqueness of water retard the photosynthetic activities of primary producers, especially the phytoplankton, and thereby the overall diversity of other aquatic fauna, including fishes. Moreover, limiting photosynthesis consequently leads to depleting the oxygen content of water. Overloading of suspended particulate matters, both of organic and inorganic natures (blooming of microscopic organisms, clay, silts, etc.), in water impart interfering effects on the passage of light, which refer to as the “turbidity”. The transparency of water varies inversely with turbidity. From the aesthetic viewpoint, turbid water becomes highly undesirable for bathing and other water usage, including industrial application. Turbidity affects considerably the photosynthetic processes of plants and thereby reduces the primary productivity of an aquatic system. The amount of dissolved and suspended particles mostly determines turbidity. Turbid water is not suitable for the purpose of drinking and also for other direct human uses. The turbidity of water is directly related to the transparency of water and inversely varies with the latter. Higher transparency of water means more scopes for the penetration of sunlight in the water column to a greater depth which by triggering photosynthetic activities enhances the diversity and biomass of different biodiversity components of the aquatic ecosystem.

2.28.5 Specific Conductivity Conductivity refers to the ability of water to conduct electric current which varies both in respect of the number and types of ions present in the solution. Most of the dissolved inorganic chemicals remain in an ionized form within water and thereby contribute to develop conductance. Therefore, estimated data on water conductivity can indicate also the quantum of dissolved mineral contents of water. Conductivity (mhos/cm) in turn is influenced by the diurnal and seasonal variation of temperature of any perennial water body.

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2.28.6 Total Solids [Total Suspended Solids (TSS) and Total Dissolved Solids (TDS)] Solid substances remain in the water either as dissolved or suspended state and influence a number of water quality parameters, like salinity, turbidity, transparency, conductivity and hardness of the same water body. Water bodies with a higher amount of dissolved solids result in unpalatable taste, whereas water containing more suspended solids develop aesthetically unpleasant condition. Estimation of total solids along with the fractional components (TSS and TDS) has appeared to be very important in the wastewater treatment processes. Total solids (mg/L) refers to the materials that are deposited after being left over in the bottom of boiling glass-­ made flasks after the evaporation of the water sample followed by complete drying in the oven at a defined temperature.

2.28.7 Transparency Transparency is resulted because of the cumulative effect of colour and turbidity on water and acts as a measure of the light penetrating ability through the water body. The clean and clear water allows more light to penetrate deeply into the water than does turbid water. Transparency values as expressed in cm or mm indicate the pollution load and also sometimes the nutrient status of the water bodies (eutrophic or oligotrophic).

2.28.8 Alkalinity The alkalinity of water being a measure of its capacity to neutralize acid is developed due to the presence of various salts, like carbonates, bicarbonates, silicates, phosphates, etc., along with the hydroxyl ions in free state. Alkalinity of water in contrast to the acidic pH exhibits the capacity to neutralize the effects of strong acid. The quantity and chemical properties of the compounds responsible for the development of alkalinity collectively cause a shift of the pH to the alkaline side of neutrality. The alkalinity of natural waters is caused by the presence of bicarbonates (CaCO3). The total alkalinity involving three kinds of alkalinity is developed because of the contribution of three kind of salts in the wetland ecosystems: (i) alkalinity due to hydroxide radicles (OH); (ii) alkalinity due to carbonate (CO3) and (iii) alkalinity due to bicarbonate (HCO3). The estimated values of alkalinity, expressed in mg/L, help in developing proper guidance in standardization and application of proper doses of chemicals in the wastewater treatment processes, particularly in dealing with coagulation, softening and operational control of anaerobic digestion.

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2.28.9 Total Hardness of Water (Calcium Hardness and Magnesium Hardness) Water hardness, expressed as mg/L, reflects the ability of water to produce lather on reacting with soap and is caused mostly by the calcium and magnesium ions (bivalent cations) present in water which occur in far higher amount over other hardness-­ producing ions.

2.28.10 Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) Both BOD and COD, as expressed by mg/L, are very important water quality parameters which indicate multidimensional aspects of the ecology of water bodies, like pollution load, presence of inorganic and organic matters, microbial activities, status of dissolved oxygen concentration, etc. BOD is a measure of total amount of dissolved oxygen taken up by the microbes for the decomposition of organic waste matter within unit volume of water and thereby indicates the intensity of pollution by the organic matter. The COD is also a measure of the oxygen-consuming capacity of both the inorganic and organic matter present within wastewater. In other words, COD in water refers to the total amount of oxygen required by the organic substances to oxidize them by a strong chemical oxidant. Water pollution by sewage releases a good amount of oxygen demanding organic nutrients that stimulate growth of phytoplankton and promote enhancing of other living biomass, all of which causes a decrease in the average concentrations of dissolved oxygen. The death and simultaneous decomposition of dead organic biomass ultimately result in depletion of DO by microbial activities as manifested by BOD, whereas oxidation of both inorganic and organic pollutants leads to cause depletion of DO by COD.

2.28.11 Ecological Characteristics of Soil: Determinant of Other Structure Components of Wetlands Same as water, different soil-based ecological parameters (texture, soil bulk density, nutrients, minerals, organic matter, etc.) of wetland soils, technically designated “hydric soils” (soils formed under water saturation condition) play important roles for the growth of different species of macrophytes which in turn contribute to the maintenance of water and other biodiversity components. Both the water and soils in wetland systems always exist in dynamic states which experience periodic import, retention, and export through various processes of transformations at the sediment– water interface as a part of their functional roles in these ecosystems. On getting the supply of both organic and inorganic suspended solids, nutrients and other materials

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from the adjoining ecosystems by periodic flooding, the collected materials get accumulated onto sediment particles of the wetlands.

2.28.12 Ecological Significance of Soil Organic Carbon and Bulk Density Soil organic matters not only promote the growth of vegetations within an wetland ecosystem but serve for various other ecological functions, such as (i) a major contributor of the global carbon budget; (ii) as a source of CO2 and NH3 emissions into the atmosphere; (iii) as a source of mineralizable nutrients for the growth of plants and other microorganisms; (iv) as a source of energy for heterotrophic microorganisms; (v) as a source of Dissolved Organic Matter (DOC); (vi) promote the exchange capacity for cations in soils; (vii) ensure long-term storage of nutrients in soils; (viii) help in formation of metallic complexes in soils and (ix) act as strong adsorbing agent for toxic organic compounds in soils.

2.28.13 Soil Bulk Density (BD) The bulk density, often referred to as volumetric mass of the soil, is expressed as the weight of the oven dry soil per unit volume (gm/cm2). It encompasses both the weight of the solid soil particles and the pore space within the soil. This is in contrast to the dry mass which refers only to the mass of the dry soil devoid of any pore space. It is found to increase with the depth and with the occurrence of more compact soil because of the pressure exerted by the top layer of the soil and also due to the presence of low organic matter content. Bulk density of soil varies with the changing compactness of soil, abundance of mineral particles, availability of organic matter and bioturbating activities of the benthic animals. This important soil attribute also helps in determining the degree of compaction of specific soil along with focusing soil aeration status.

2.29 Historical Review of the Studies of Physico-chemical Parameters in Freshwater Wetlands A number of studies on various physico-chemical and biological aspects of wetlands have been done in India. Important contributions were made by Hutchinson (1937), Gonzalves and Joshi (1946), Sarup (1961), George (1964), Khan et  al. (1970), Ghosh et al. (1974), Singh et al. (1982), Mahajan (1980), Handoo and Kaul (1982), Kulshreshtha and Gopal (1982), Seshavathararn and Chandramohan (1982), Adoni and Saini (1984), Vyas (1984), Khatri (1984) and Ramalingam and Jayaraman

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(1985). Gosselink and Turner (1978) had postulated the idea that the modifications of the physico-chemical environment, in turn, would have a direct impact on the biotic response within the wetland towards bringing about changes in hydrological condition. The productivity is related to abiotic as well as biotic factors of any water body and therefore study of phytoplankton, zooplankton, macrophytes as well as periphyton and nekton have drawn the attention of a number of ecological researchers (Govind, 1963; Sreenivasan, 1972; Mathew, 1972; Haniffa & Pandian, 1980; Sing et al., 1980; Sarangi, 1983; Battish, 1992; Chakraborty et al., 1995; Chakraborty, 2021a). The variability in the diversity, distribution and population dynamics of zooplankton have been found to exhibit significant positive and negative relationships with different abiotic parameters (climatic or hydrological parameters, like temperature, salinity, stratification, advection) and also with biotic parameters (food limitation, predation, competition) or to a combination of both (Roff et al., 1988; Christou, 1998; Escribano & Hidalgo, 2000; Beyst et  al., 2001; Pradhan & Chakraborty, 2006; Pradhan et al., 2006, 2008; Halder et al., 2013; Chakraborty, 2021a). Maruthanayagam et al. (1997) studied the zooplankton diversity along with the physico-chemical parameters in Thirukkulam pond, Mayiladuthurai, Tamilnadu. Higher abundance of zooplankton was recorded during the monsoon period with copepods as the dominant group of fuanal components followed by other categories of zooplankta, such as cladocera, rotifera and ostracoda. Pandey et al. (2009) from a study on the seasonal fluctuation of zooplankton community in relation to physico-­ chemical parameters in river of Ramjan of Kishanganj, Bihar advocated in favour of the seasonal preferences of different zooplanktonic taxa. Dhanapathi (1995) pointed on the disappearance of rotifers at the high alkalinity, low pH and in the higher temperature (>29 °C). Chandrasekhar (1996) showed that the water temperature, turbidity transparency and dissolved oxygen favoured the flourishing of rotifer population. The lower abundance of rotifers during monsoon was supposed to be due to neutral pH. The higher dominance of rotifers was recorded during the period of winter (Kulshreshtra & Joshi, 1999). The higher density of rotifer as found in a studied pond during summer followed by winter might be due to the hyper tropical condition of the water body at high temperature coupled with lower level of water (Singh et al., 2002). The differences in respect of seasonal density of zooplankton during different seasons were explained as because of varied loads of nutrition and biotic interactions (Pawar & Pulle, 2005). Rajagopal et  al. (2010) from another study reported that the rotiferan population represented 51% of total population of zooplankton of freshwater bodies. Rao and Kumar (1982) studied the physico-chemical parameters and zooplankton diversity of perennial tank, at Hutchammankere in Bangalore district, of the state of Karnataka, India for a period of 2 years. Chakrapani (1989) compared the zooplankton diversity and physico-chemical analysis of both urban (19) and non-­ urban (24) freshwater lakes. Water temperature plays an important role in determining different limnological properties of an aquatic ecosystem, such as stratification, solubility of gases, pH, conductivity and planktonic distribution (Singh, 1990). The nutrient status and other physico-chemical parameters of water body play decisive roles in regulating the growth and proliferation of zooplankton. Owing to their short

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span of life cycle, zooplanktonic fauna respond promptly with the changes in the aquatic environment (water quality, such as pH, colour, taste, etc.) and thereby are established as important bio-indicator and help in assessment of overall ecological health or condition of their habitat (Thorp & Covich, 1991; Carrick & Schelske, 1997). Sukumaran and Das (2002) had studied the seasonal changes of the distribution and density of zooplankton in relation to physico-chemical parameters of Mancharibele reservoir, located in the outskirt of Bangalore city, the state capital of Karnataka, India. Garg (2002) studied the fluctuations on physico-chemical parameters of river Mandakini in Madhya Pradesh. Hydrobiological studies conducted in a lake of the Himalayan mountain, named Mirik in the district of Darjeeling, West Bengal, India, had showed that the pH of the lake was found to be acidic in nature and other physico-chemical parameters also tended to deviate from the permissible limit mainly because of the negative impacts of tourisms and plankton analysis also confirmed the deteriorating water qualities of that aquatic ecosystem due to contaminants let into the lake, but conditions improved modestly due to dilution of the contaminants by the heavy rainfall during monsoons (Jha & Barat, 2003). Patil et  al. (2013) observed that cladocera and meroplanktonic larva reached peak abundance in saline water mass. A study on the physico-chemical limnology and productivity of Jaisamand lake, Udaipur was conducted by Sharma and Sarang (2004). Sunkad and Patil (2004) had assessed the water quality of Fort lake, Belgaum, Karnataka. Zooplanktons are found to be very sensitive to ecological changes in habitats because of various pollutions, especially organic pollution (Ramachandra et al., 2005). Seasonal fluctuation of cladocerans (crustacean zooplankton) showed positive correlation with the temperature and salinity of water as the overall population of cladocerans reached its peak in the month of February coinciding with cold temperature and modest salinity (Mahar et  al., 2016). The investigations on the effect of seasonal variations in the physico-chemical variables have revealed direct impacts on the diversity and density of abundance of zooplankton (Davies et al., 2009) and also on their biomass dynamics (Zuykov et al., 2009). Mulani et al. (2009) had advocated for the direct roles of water quality parameters on the zooplankton community based on their long-term studies of the Panchganga river, Kolhapur city in the state of Maharashtra, India. Sharma et al. (2010) worked on water quality status of historical Gundolav Lake at Kishangarh, India in order to generate primary data which are to be used for sustainable aquatic ecosystem management. They established that the zooplankton could indicate the eutrophic condition of the lake as pollution indicators which included different groups and species of zooplankton, such as protozoans, rotifers (Brachionus calyciflorus, Brachionus forficula, Keratella tropica and Keratella procurva) and copepods (Neodiaptomus schmackari, Mesocyclops leuckarti and Mesocyclops hyalinus). Badsi et al. (2010) based on their investigation on the structure of the zooplankton community had highlighted the roles of water quality parameters in determining the distribution of zooplankton of Massa Lagoon in Southern Morocco. Johnson and Host (2010) have discussed the use of classificatory approach to predict biotic assemblages and also to assess the impacts of human disturbance, especially urbanization on the structure and function of the ecosystem of freshwater stream. Patra et al. (2011) observed the

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seasonal abundance and population dynamics of zooplankton community and its relationship with physico-chemical factors of the water bodies of Santragachi Jheel in the district Howrah, West Bengal. Sharma and Sharma (2010) opined based on their findings from hydrobiological research on monthly population of total copepod zooplanktons and their correlation coefficient with some physico-chemical factors of Lony dam at Teonthar of Rewa in the state of Madhya Pradesh, India. Halder Mallick et al. (2013) reported the determining roles of low pH values on the mortality of three freshwater zooplankton that inhabit the freshwater ponds of Midnapore district of West Bengal, India. This study helped in understanding negative impact of toxicity of anthropogenic chemicals that could induce changes in the aquatic ecosystems by altering the physico-chemical parameters of water and ultimately posing a threat to aquatic organisms. Bohra et al. (2014) conducted the study of the relationship between inorganic matter and distribution of genera of rotifers and population of bacteria in various types of sewage waters.

2.30 Decomposition and Consumption: Cycling of Chemical Elements and Nutrient Availability In nature, continuous supply of chemical elements, being the essential constituents of protoplasm is required to ensure the growth, reproduction, multiplication and overall survivability along with maintaining of the biomass of living organisms. Depletion in the supply of even a single essential chemical element may limit the growth of a population, which in turn bring about changes in the species composition of the entire community. Most of those essential elements are supplied to the populations and members of the biotic communities of wetland ecosystem through the terrestrial runoff into from the outside. However, maximum flow of energy and materials take place through the detritus food web. In addition, supply of elements through recycling tends to determine the fate of detritus. In view of such observations, the cycling of chemical elements within wetland ecosystems differ from those of terrestrial habitats as the input of water loaded with various form of substances, including nutrients, is more and all such inputs of particulate and dissolved materials lead to the modification of decomposition and recycling processes (Figs. 2.10 and 2.11). The decomposition rate within the wetland ecosystem is directly related to nutrient availability by limiting the growth rate of microbial decomposers. The nutrient loading has been observed to be more in wetlands than in uplands due to different ecology of both of these landscapes. The microorganisms obtain the growth-­limiting nutrients (nitrogen and phosphorus) from the organic materials accumulated in the bottom sediments and from the organic remains that remain dispersed in the water column. Therefore, the ratios of carbon to nitrogen (C:N) and carbon to phosphorus (C:P) in organic matters often play the determining roles to facilitate the decomposition process (DeAngelis, 1992; Bouillon et al., 2000).

2.31  Functional Roles of Different Components of Detritus in Wetland Ecosystem

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2.31 Functional Roles of Different Components of Detritus in Wetland Ecosystem Detritus, a semi-decomposed organic substance formed by the decomposition and decaying of dead biomass of both plants and animals. Out of so many feeding categories of animals (herbivory, carnivory, detritivory and parasitic), detritivores occur mostly in the shallower parts of the freshwater ecosystem and consume detritus endowed with a lot of organic substances, like celluloses and lignins. The celluloses occur in much higher quantity than lignin in nature. The complexity in the chemical composition of the dead biomass determines the pathways of decomposition which after mixing with water and interacting with the microbes undergo decomposition where non-nitrogenous compounds with free inorganic nitrogen are found to be more rapid relative to certain very stable organic nitrogen compounds. Odum et al. (1979) had suggested that the stable compounds are represented by the aminosugar polymers, such as chitin, complexes proteins with lignin and terpenoids, phenols Other essential chemical ingredients of detritus in addition to cellulose and lignin include sugars, fatty acids, amino acids, hemicelluloses, fats, waxes, resins and minerals. The physical–chemical properties as well as proportionate distribution of all the components in detritus vary with the sources of organic substances, the rate and intensity of decomposition process and the stage of maturity of the decomposing materials. Based on the chemical composition of organic matters, the decomposing substances belong to different categories, such as non-humic substances (carbohydrates, proteins and fats), humic substances (high-­ molecular-­weight aromatic compounds having heterogeneous constituents) and phenolic substances (lignin and tannins) (Stevenson, 1994; Moore et al., 2004).

2.31.1 Cellulosic Substances Cellulose being a major constituent in vascular plants is water insoluble and fibrous substance and constitutes major portion of woody plant tissue (>80%) and some portion of herbaceous plant tissue up to 30%). This important structural component of plant biomass is formed by linear and unbranched polysaccharide constituted by more than 10,000 glucose units connected by ß(1, 4) linkages. Hemicellulose another category of polysaccharides with diverse groups of polymers are comprised of monomeric units (carbon sugars, uronic acids, and sugars) which remain connected via ß(1, 4) or β(1, 3) linkages and are found to occur in cell walls of higher plants with virtual absence occur in algae and microbes (Boulton & Boon, 1991; DeAngelis, 1992; Moore et al., 2004).

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2.31.2 Phenolic Substances Lignin and tannins as the representatives of common phenolic substances and organic matter in detritus of wetland ecosystem constitute important structural components of the secondary cell walls of plants and are found to occur with the amount of 15–30% in the woody plant tissue and near about 10% in the herbaceous plants. Lignin as a very complex polymer includes highly branched random polymer of phenyl propanoid unit composed of a basic unit of an aromatic ring, a phenyl group, with a three-carbon side chain and phenyl propanoid subunit, all of which are connected by C–C and C–O linkages with methoxy or hydroxy groups. Tannins are composed of a group of phenolic compounds developing as a compound with heterogeneous properties. Both lignins and tannins help in the decomposition of labile plant constituents through the formation of complex with proteins and formation of bondages between cellulose and hemicellulose (Boulton & Boon, 1991; Moore et al., 2004).

2.31.3 Humic Substances Humic substances are present in nature as heterogeneous mixtures of compounds and formed by dynamic alterations of resistant tannins and lignins by abiotic and biotic reactions, resulting in accumulation of humic substances of different physical–chemical properties: (i) Fulvic acid (soluble only in acid and base); (ii) Humic acid (insoluble in acids but soluble in base) and (iii) Humin (insoluble both in acid and base). These very important components of detritus contain aromatic organic compounds, acid functional groups of acids and high amounts of carboxyl, phenolic, hydroxyl and carbonyl structures as oxygen-containing functional groups. The humic substances after being derived from the residual lignin undergo microbial interactions involving demethylation, oxidation and condensation of amino compounds. The series of reactions also involves transformation of residual lignin, cellulose and other non-humic substances into humic substances by activities of different enzymes released from the microbial assemblages. The newly produced compounds, such as phenolics, aldehydes and amino acids released undergo further enzymatic reactions to be converted into quinone (Stevenson, 1994). The continuous supply of organic matters to the wetland ecosystem acts as the driving force behind the eco-dynamics of the system and such supply is ensured from both external and internal sources. The point and non-point sources as external sources add particulates and also organic matter added from sewage effluents and industrial discharges. The biodegradability of this material depending on the complexity of their chemical structure range from easily decomposable to highly resistant.

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Fig. 2.6  Map showing the location of study sites

Internal sources of detritus include plant litter and also dead floral and faunal biomass, algal and microbial mats. The largest share towards formation of detritus in wetlands is contributed by the emergent macrophytes in marshes and trees in forested wetlands. Moreover, the belowground portion of macrophytes (roots and rhizomes) also contributes to the reservoir of detritus in a wetland. The dead biomass derived from the benthic invertebrates and fish also contributes good amounts of organic substances to wetland soils through the microbial decomposition (Figs. 2.11 and 2.12) (Boulton & Boon, 1991; Stevenson, 1994; Moore et al., 2004).

2.32 Case Study on the Seasonal Fluctuation of Physico-­chemical Parameters from Four Ecologically Contrasting Wetlands of East Kolkata Wetlands, India 2.32.1 Selection of Suitable Study Sites Four wetlands were selected as for study (sampling) sites (S-I, S-II, S-III and S-IV) based on their contrasting ecological characteristics among the hundreds of wetlands having different sizes, shapes and ecological variables within the web of water bodies in the East Kolkata Wetland (EKW) and detailed studies were undertaken with regard to the estimation of different physical–chemical parameters

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Fig. 2.7  Ecological characters of Study site I. (a) Well-managed clean and open water body for sampling in the year 2012. (b) Highly eutrophicated condition of the same water body after 10 years in the year 2021. (c) Efforts to clean macrophytes from the eutrophicated water body during 2021. (d) Open water sampling site in the year 2012. (e) Highly eutrophicated same water body during 2021. (f) Cleaning and eco-reclamation efforts by removing macrophyte during 2021. (g) A part of eco-reclaimed and eco-restored open water body during 2021

through nine (9) different seasons each with four (4) months duration of three consecutive years (July, 2008 to June, 2011) (Fig. 2.6). 2.32.1.1 Ecological Background of Study Sites The study site-I (S-I), locally named as Banabitan, is located at almost central position of Bidhannagar, Salt Lake city of the state of West Bengal, India. The marshy swamp of Salt Lake city of today reminds the existence of one of the Salt Water Lakes. The Salt Lake was formed by the tidal action of the streams flowing through the district of North-24 Paraganas (the tributaries, distributaries and re-distributaries of the River Hugli, Bidyadhari and Kulti), West Bengal, India (Chattopadhyaya, 1990). Presently known as “Central Park”, this study site-I was originally a Bheri named as “Rammahan” (Pramanik, 2000). This park has been rehabilitated and ornamented with new plantation of trees, shrubs and climbers plants in a decorative

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Fig. 2.8  Ecological uniqueness of Study site II. (a) Water body by the side of the E M Bypass and behind Landmark Hotel during 2012. (b) Other side of the same water body. (c) Sampling of the zooplanktons from Study Site II. (d) Sampling of the zooplanktons from the other side of the same wetland. (e) Blooming of macrophytes at one corner of this wetland filtering a good amount of wastewater. (f) Activities of washermen utilizing the water from this water body

manner in and around the water body where migratory birds used to pay visit in large numbers in search of their ecological niche and habitats both in the water body and also on the surrounding vegetations. As a part of recreation activities, boating facility is also available and all such rehabilitating efforts make this park as an eco-­ friendly area with lot of availability of fresh air for breathing. The study site-II, located by the side of the Eastern Metropolitan Bypass (EM Bypass), a major recently developed metallic road passing through the East Kolkata Wetland and connecting the extreme south with the extreme north of the greater Kolkata city, the state capital of West Bengal, India. The other two study sites (S-III and S-IV) are located within the Nature Park, recently under the possession of Mudiali Fish Cooperatives Society (MFCS). The S-III is a wetland receiving wastewater mostly derived from the city’s sewage generated and released from the municipal and industrial activities where phytoremediation activities take place with the help of macrophytes. The S-IV is a wetland with clear and nutrient-enriched water received

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Fig. 2.9  Ecological features of Study site III. (a) Draining of water at MFCs ‘s water bodies. (b) Filtering and phytoremediation process. (c) Mechanical screening of molluscs prior to releasing of the phytoremediated water to the pisciculture ponds. (d) Water body with clean water for fish culture

from the S-III after phytoremediation (Figs. 2.6, 2.7, 2.8, 2.9, 2.10, 2.11, 2.12 and 2.13). 2.32.1.2 Seasonal Dynamics of Physico-chemical Parameters of Water Seasonal variations in ecological parameters exert a profound effect on the distribution and population density of both animal and plant species (Odum, 1971). Water pollution has now reached a crisis point specifically in developing World. Considering the importance of every water body, it is extremely important for undertaking eco-monitoring by continuous long-term assessment of the pollutants with the routine estimation of ecological parameters (Warhate et  al., 2006). The seasonal variation of water quality parameters of four study sites having contrasting ecological features through nine seasons of three continuous years (July, 2008– June, 2011) have been depicted in Figs. 2.14, 2.15, 2.16, 2.17, 2.18, 2.19 and 2.20.

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Fig. 2.10  Eco-biological potentials of Study site IV. (a) Premises of Mudiali Fish Cooperative Society’s integrated fish farming site. (b) Fishing gears and craft used by Mudiali Fish Cooperative Society’s members. (c) Members of MFSC in action for fishing. (d) Development of vegetable garden utilizing the phytoremediated water

2.32.1.2.1  Water Temperature Temperature represents the prime ecological variable in the aquatic ecosystem since it regulates various physico-chemical as well as biological activities (Radhika et al., 2004; Maity et al., 2014; Chakraborty, 2021a, 2021b). As most of the ecological processes, such as food chain–food web dynamics and decomposition are temperature dependent in aquatic ecosystems, a general warming of the water column will change trophic interactions and ecosystem functioning considerably (Beaugrand & Reid, 2003; Alheit et al., 2005). It varied from 18.8 °C (December, 2010) to 31.0 °C (May, 2010) for study site-I; 18.6  °C (December, 2009) to 30.5  °C (June, 2010) for study site-II, 21.8  °C (January, 2010) to 32.5  °C (July, 2008) for study site-III and 19.5  °C (January, 2011) to 31.2 °C (May, 2009) for study site-IV. The fluctuation of water temperature showed distinct seasonal trend being maximum in pre-monsoon followed by monsoon and post-monsoon in each study site. Water temperature exhibited positive correlation with turbidity, total dissolved solids (TDSs), chloride (Cl) and conductivity at both the study site-I and study site-III, while it expressed significant negative correlation with Mg and total hardness at study site-IV. It also demonstrated a

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Fig. 2.11  Schematic representation of microbial decomposition process of organic matter in wetland ecosystem: Production pathways of nutrients having different fractional components of biochemical entities with the regulators

significant negative correlation with heavy metals (Cr and Hg at study site-I; Pb and Cd at study site-II; Cr, Cd and Hg at study site-III and Cd and Hg at study site-IV) (Tables 2.1 and 2.3). 2.32.1.2.2 Turbidity Turbidity, by way of allowing or inhibiting sunlight penetration within the aquatic ecosystem, plays a vital role in determining biological productivity. High turbidity value can protect microorganisms from the effects of disinfection thereby can

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Fig. 2.12  Organic carbons and other chemical elements: Driving force for the nutrient cycling with wetland ecosystem

stimulate bacterial growth (Haloi & Sarma, 2012). Turbidity of the study site-I ranged from 3.0 NTU (November, 2008) to 13.0 NTU (July, 2010). It varied from 6.7 NTU (May, 2011) to 35.1 NTU (November, 2008) at study site-II. For study site-III and study site-IV, maximum turbidities were estimated to be as 7.0 NTU (March, 2009) to 37.8 NTU (October, 2009) and 3.0 NTU (February, 2009) to 11.9 NTU (September, 2009), respectively (Fig. 2.14). Turbidity was observed to depict higher values at study site-III and study site-II than the other two sites. It exhibited positive correlation with TDS, Mg, Cl, total hardness, conductivity, Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD), while it displayed negative correlation with only DO at study site-I. Turbidity showed significant

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Fig. 2.13  Interaction and interconnection of wetland ecosystem with other adjoining ecosystems

Fig. 2.14  Monthly variation of turbidity values of water of four study sites during 2008–2011

positive correlation (p