Freshwater Ecology: Concepts and Environmental Applications of Limnology

By Walter K. Dodds and Matt R. Whiles

Freshwater Ecology, Third Edition, covers everything from the basic chemical and physical properties of water, to the advanced and unifying concepts of community ecology and ecosystem relationships found in continental waters. Giving students a solid foundation for both courses and future fieldwork, and updated to include key issues, including how to balance ecological and human health needs, GMOs, molecular tools, fracking, and a host of other environmental issues, this book is an ideal resource for both students and practitioners in ecology and related fields.

• Winner of a 2020 Textbook Excellence Award (College) (Texty) from the Textbook and Academic Authors Association
• Provides an updated revision of this classic text, covering both basic scientific concepts and environmental applications
• Includes additional biography boxes with greater cultural diversity of the featured scientists
• Covers expanded content on developing nations, ecosystem goods and services, properties of water, global change, impacts of fracking, molecular tools for classification and identification of aquatic organisms, a discussion of emergent diseases and aquatic habitats, and more

• Language: English
• Publisher: Academic Press
• Release date: Apr 3, 2019
• ISBN: 9780128132562

Walter K. Dodds

Walter. K. Dodds received his Ph.D. in Biology in 1986 from the University of Oregon. From 1987 to 1990 he was a post doctoral fellow in the Department of Biology at Montana State University. In 1990 he accepted an Assistant Professor position in the Division of Biology at Kansas State University, in 1995 he was promoted to Associate Professor and in 2002 to full Professor. Over the years, Dodds has taught Limnology, Advanced Aquatic Ecology, Microbial Ecology, Principles of Biology, Conservation Biology, Environmental Problems, Origins of Life, Herbivory, Presentations in Ecology, Aquatic Ecology, Stream Ecology, Algal Identification, Algal Ecology, Bacteriology and Freshwater Biology. He has professional memberships in the American Association for the Advancement of Science, the American Society of Limnology and Oceanography, the American Society of Microbiology, the North American Benthological Society, the Phycological Society of America and Sigma Xi. Dodds has grants from agencies including the National Science Foundation, the United States Environmental Protection Agency, the United States Geological Survey, the Kansas Department of Wildlife and Parks and the Kansas Department of Health and Environment. He has been involved in the Konza Prairie Long-Term Ecological Research (LTER) program and provides leadership for the Konza LTER Aquatic and Hydrological Group and the Konza LTER Research Experience for Undergraduates program. Dodds’ recent research has focused on Aquatic Ecology on Konza Prairie, Nitrogen Uptake Retention and Cycling in Stream Ecosystems, Quality and Quantity of Suspended Solids in Kansas Rivers, and Nutrients and Algae in Streams. Dodds has been invited to present seminars at over 20 US agencies and universities, as well as agencies and universities in Australia, New Zealand and Canada. He has presented at numerous national and international scientific conferences and has produced over 80 peer reviewed publications.

Book preview

Freshwater Ecology

Concepts and Environmental Applications of Limnology

Third Edition

Walter K. Dodds

Kansas State University, Manhattan, KS, United States

Matt R. Whiles

University of Florida, Gainesville, FL, United States

Table of Contents

Cover image

Title page

Copyright

Preface

For the Student

For the Instructor

Why did We Write a Third Edition?

Acknowledgments

Chapter 1. Why Study Continental Aquatic Systems?

Abstract

Human Use of Water: Pressures on a Key Resource

What Is the Value of Water?

Advanced: Methods for Assigning Values to Ecosystem Services

The Anthropocene: Climate Change and Water Resources

Politics, Citizens, Science, and Water

Summary

Questions for Thought

Chapter 2. Properties of Water

Abstract

Chemical and Physical Properties

Advanced: The Nature of Water

Relationships Among Water Viscosity, Inertia, and Physical Parameters

Movement of Water

Advanced: Equations Describing Properties of Moving Water

Forces That Move Water

Summary

Questions for Thought

Chapter 3. Movement of Light, Heat, and Chemicals in Water

Abstract

Diffusion of Chemicals in Water

Movement of Gases Between Atmosphere and Water

Light in Water

Heat Balance in Water

Summary

Questions for Thought

Chapter 4. The Hydrologic Cycle and Physiography of Groundwater Habitats

Abstract

Habitats and the Hydrologic Cycle

Advanced: Prediction of Amount and Variability of Runoff with Global Climate Change

Movement of Water Through Soil and Aquifers

Groundwater Habitats

Interaction of Groundwaters with Surface Waters

Summary

Questions for Thought

Chapter 5. Hydrology and Physiography of Wetland Habitats

Abstract

Definition of Wetlands

Wetland Conservation and Mitigation

Wetland Types

Wetland Hydrology

Restoration Ecology and Wetland Restoration

Wetlands and Global Change

Wetlands as Key Habitat for Wildlife

Summary

Questions for Thought

Chapter 6. Physiography of Flowing Water

Abstract

Characterization of Streams

Streamflow and Geology

Human Influences on Physical Aspects of Rivers

River and Stream Restoration

Transport of Materials by Rivers and Streams

Advanced: Characterizing the Movement of Dissolved Materials in Rivers and Streams

Summary

Questions for Thought

Chapter 7. Lakes and Reservoirs: Physiography

Abstract

Formation: Geological Processes

Lake Habitats and Morphometry

Unique Properties of Reservoirs

Geomorphological Evolution of Lakes and Reservoirs

Stratification

Advanced: Heat Budgets of Lakes

Water Movement and Currents in Lakes

Summary

Questions for Thought

Chapter 8. Types of Aquatic Organisms

Abstract

The Species Concept

Chemical Taxonomic Methods

Molecular Approaches for Assessing Taxonomy and Diversity in Natural Environments

Molecular Methods for General Aquatic Ecology

Major Taxonomic Groups

Classification of Organisms by Function, Habitats, and Interactions

Organisms Found in Freshwaters

Summary

Questions for Thought

Chapter 9. Microbes and Plants

Abstract

Viruses

Archaea

Bacteria

Protoctista

Fungi

Plantae

Summary

Questions for Thought

Chapter 10. Multicellular Animals

Abstract

Invertebrates

Phylum Chordata, Subphylum Vertebrata

Summary

Questions for Thought

Chapter 11. Evolution of Organisms and Biodiversity of Freshwaters

Abstract

Measures of Diversity

Temporal and Spatial Factors Influencing Evolution of Freshwater Organisms

Short-Term Factors Influencing Local Distribution of Species

Genetics and Populations of Species

Global Change and Shifts in Biodiversity

Nonnative Species

Extinction

What Is the Value of Freshwater Species Diversity?

Summary

Questions for Thought

Chapter 12. Aquatic Chemistry and Factors Controlling Nutrient Cycling: Redox and O2

Abstract

Chemicals in Freshwaters

Redox Potential, Potential Energy, and Chemical Transformations

Oxygen: Forms and Transformations

Photosynthesis

Respiration

Metabolic Balance of Photosynthesis and Respiration, and Temperature Effects

Controls of Distribution of Dissolved Oxygen in the Environment

Summary

Questions for Thought

Chapter 13. Carbon

Abstract

Forms of Carbon

Transformations of Carbon

Global Emission of Methane and Carbon Dioxide Related to Inland Aquatic Habitats and Climate Change

A Conceptual Introduction to Nutrient Cycling

The Carbon Cycle

Summary

Questions for Thought

Chapter 14. Nitrogen, Sulfur, Phosphorus, and Other Nutrients

Abstract

Nitrogen

Sulfur

Phosphorus

Silicon and Iron

Cycling of Other Elements

Gradients of Redox and Nutrient Cycles and Interactions Among the Cycles

Summary

Questions for Thought

Chapter 15. Adaptations to Extreme and Unusual Habitats

Abstract

Adaptations to Extremes

Saline Lakes

Hot Springs

Cold Habitats

Temporary Waters and Small Pools

Ultraoligotrophic Habitats

Hypertrophic Habitats

Deep Subsurface Habitats

The Water Surface Layer

Summary

Questions for Thought

Chapter 16. Responses to Stress, Toxic Chemicals, and Other Pollutants in Aquatic Ecosystems

Abstract

Basic Toxicology

Bioassessment

Organic Pollutants

Acid Precipitation

Metals and Radioactive Pollutants

Nanomaterials

Salt Pollution

Suspended Solids

Thermal Pollution

Anthropogenic Increases in UV Radiation

Urbanization

Summary

Questions for Thought

Chapter 17. Nutrient Use and Remineralization

Abstract

Use of Nutrients

Nutrient Limitation and Relative Availability

Resource Ratios and Stoichiometry of Primary Producers

Nutrient Remineralization

Stoichiometry of Heterotrophs, Their Food, and Nutrient Remineralization

Summary

Questions for Thought

Chapter 18. Trophic State and Eutrophication

Abstract

Definition of Trophic State

Advanced: Determining Reference Nutrient Conditions in Freshwater Environments

Why does Alteration of Trophic State by Nutrient Pollution Matter in Lakes?

Natural and Cultural Processes of Eutrophication

Relationships among Nutrients, Water Clarity, and Phytoplankton: Managing Eutrophication in Lakes

Advanced: Empirical Relationships Used to Predict Control of Eutrophication

Mitigating Lake Eutrophication

Managing Eutrophication in Streams and Rivers

Case Studies of Eutrophication in Lakes and Lotic Systems

Managing Eutrophication in Wetlands

Summary

Questions for Thought

Chapter 19. Behavior and Interactions Among Microorganisms and Invertebrates

Abstract

Behavior of Microorganisms

Interaction Types in Communities

Predation and Parasitism, Including the Microbial Loop

Competition

Mutualism: Facilitation and Syntrophy

Chemical Mediation of Microbial Interactions

Summary

Questions for Thought

Chapter 20. Predation and Food Webs

Abstract

Herbivory

Detritivory

Omnivory

Adaptation to Predation Pressure

Adaptations of Predators

Nonlethal Effects of Predation

Trophic Levels, Food Webs, and Food Chains

The Trophic Cascade

Summary

Questions for Thought

Chapter 21. Nonpredatory Interspecific Interactions Among Plants and Animals in Freshwater Communities

Abstract

Competition

Mutualism and Facilitation

Other Species Interactions

Summary

Questions for Thought

Chapter 22. Complex Community Interactions

Abstract

Disturbance

Succession

Indirect Interactions

Strong Interactors

Theoretical Community Ecology and Aquatic Food Webs

Thresholds and Alternative Stable States

Invasion and Extinction Revisited

Summary

Questions for Thought

Chapter 23. Fish Ecology, Fisheries, and Aquaculture

Abstract

Biogeographical and Environmental Determinants of Fish Assemblage Diversity

Physiological Aspects Influencing Growth, Survival, and Reproduction

Population Dynamics of Fishes

Regulating Exploitation of Fish Stocks

Stocking for Fisheries

Aquaculture

Summary

Questions for Thought

Chapter 24. Freshwater Ecosystems

Abstract

General Approaches to Ecosystems

Secondary Production

Energy Fluxes and Nutrient Cycling

Nutrient Budgets

Biodiversity and Ecosystem Function

Groundwater Ecosystems

Streams and Rivers

Lakes and Reservoirs

Advanced: Reservoirs as Unique Ecosystems

Wetlands

Whole-Ecosystem Experiments

Comparison of Freshwater Ecosystems

Summary

Questions for Thought

Chapter 25. Scaling, Landscapes, Macroecology, and Macrosystems in Freshwaters

Abstract

Scaling

Landscape Ecology

Macroecology

Macrosystems

Summary

Questions For Thought

Chapter 26. Conclusions

Abstract

Appendix. Experimental Design in Aquatic Ecology

Natural Observations and Experiments

Multivariate Methods

Simulation Modeling

Manipulative Experiments

Whole-System Manipulations

Summary

Glossary

References

Taxonomic Index

Geographic Index

Subject Index

Copyright

Academic Press is an imprint of Elsevier

125 London Wall, London EC2Y 5AS, United Kingdom

525 B Street, Suite 1650, San Diego, CA 92101, United States

50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States

The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom

Copyright © 2020 Elsevier Inc. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: http://www.elsevier.com/permissions.

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein).

Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library

Library of Congress Cataloging-in-Publication Data

A catalog record for this book is available from the Library of Congress

ISBN: 978-0-12-813255-5

For Information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals

Publisher: Candice Janco

Acquisition Editor: Louisa Hutchins

Editorial Project Manager: Hilary Carr

Production Project Manager: Denny Mansingh

Cover Designer: Matthew Limbert

Typeset by MPS Limited, Chennai, India

Preface

For the Student

This book was written for you. We obtained as much student input as possible by having student reviewers assess the text and the approach used in it. The idea for the text was based on teaching students who were not satisfied with the existing texts. Teaching aquatic ecology and limnology have made it clear to us that most students enter ecological sciences for practical reasons. They often are concerned about conservation of resources from a classical (e.g., fisheries program) or from environmental issue perspectives. Most existing texts limit the applied aspects of aquatic ecology to a section at the end.

The aim of this text was to incorporate discussion of the issues as they arise when we cover the basic materials. This allows you to see the applications of difficult topics immediately and, we hope, provides additional impetus for doing the work required to gain an understanding. We also attempted to use the broadest possible approach to freshwater ecosystems; scale and linkages among systems are important in ecology. Most students in ecological courses had some interest in the natural world as children. They spent time exploring under rocks in streams, fishing, camping, hiking, or swimming, which stimulated a love of nature. This book is an attempt to translate this basic affinity for aquatic ecosystems into an appreciation of the scientific aspects of the same world. It is not always easy to write a text for students. Instructors usually choose a text, giving the students little choice. Thus, some authors write for their colleagues, not for students. We tried to avoid such pressures and attempted to tailor the approach to you. We hope you will learn from the materials presented here and that they will adequately supplement your instructor’s approach. When you find errors, please let us know. This will improve any future editions. Above all, please appreciate the tremendous luxury of being a student and learning. You are truly fortunate to have this opportunity and we are grateful for the time you take with this text.

For the Instructor

We hope this book will make your job a little easier. The chapters are short, mostly self-contained units to allow the text to conform to a wide variety of organizational schemes that may be used to teach about freshwaters. This will also allow you to avoid sections that are outside the scope of the course you are teaching. However, we integrated environmental applications into the text because we view basic science and applications as integrated issues. We attempt to create instructional synergism by combining these aspects of aquatic ecology. Describing applications stimulates student interest in mastering difficult scientific concepts. We employ a variety of pedagogical approaches in an attempt to engage student interest and facilitate learning. These include highlights, biography boxes, and method boxes. We have advanced sections for areas where you might want the students to get a little more in-depth, but in areas that we often skip in our own lectures for a first class in freshwater ecology. We also include an appendix on experimental design in ecological science and a glossary because we have found many advanced undergraduates have little exposure to the practical side of doing science. These sections help when we ask students to read and report on primary literature. It is always difficult to know what to include and where to go into detail. We supply some detailed examples to enforce general ideas. The choice of example is probably not always the best one, just the best one we could find while preparing the text. Suggestions for improvements in this and any other areas of the text are encouraged and appreciated. Thanks to the instructors using the first two editions that did just that. We apologize for any errors.

Why did we write this? In our experience, teaching limnology/freshwater ecology is more work than teaching other courses because of the breadth of subject, differential preparation of students, and associated laboratories, but always seems to be the most fun. Of course it is fun, it is the best subject! We hope this book facilitates your efforts to transmit what is so great about the study of freshwater ecology.

Why did We Write a Third Edition?

Given the money savings of used texts for students, there needs to be a good reason for a new edition. In the near decade since writing of the second edition, many new advances have occurred, and new topics have gained prominence with respect to environmental effects and hot areas of research interest. In our attempt to cover these new areas we have added over 800 new and updated references, 46 new figures, 67 figures updated to color, 1 new chapter, and expanded the length of the text. Particularly, we included more emphasis on toxins, pollution, and large-scale approaches than in the previous edition. Dedicated students in WKD’s classes found numerous errors in previous editions (with a potential award of test points for each unique error), as did instructors across the country. We hopefully corrected these without introducing too many new ones. We hope you find this new edition even more useful than the last one.

Acknowledgments

We thank Dolly Gudder, who was involved in all aspects of the writing and compilation of the first two editions of this book, including proofing the entire text, drafting and correcting all the figures from the first edition, library research, writing the first draft of the index, and obtaining permissions. Alan Covich provided extensive conceptual guidance and proofread the first edition of text; his input was essential to producing this work. Eileen Schofield-Barkley provided excellent editorial comments on all chapters of the second edition. The fall of 1998 Kansas State University limnology class proofed Chapters 1–8 and 11–18 of the second edition. The Kansas State University limnology (freshwater ecology) classes proofread all chapters (especially Michelle Let, Katie Bertrand, and Andrea Severson.). The L.A.B. Aquatic Journal Club, Chuck Crumly, Susan Hendricks, Stuart Findlay, Steve Hamilton, Nancy Hinman, Jim Garvey, Chris Guy, and Al Steinman provided suggestions on the first edition. Early helpful reviews on book concepts were provided by James Cotner, David Culver, Jeremey Jones, Peter Morin, Steven Mossberg, Stuart Fisher, Robert Wetzel, and F. M. Williams. The anonymous reviews (obtained by the publisher) are also greatly appreciated, including those who completed a detailed survey on the prospect of a second edition. Many of the good bits and none of the mistakes are attributable to these reviewers. We appreciate the support of the Kansas State University Division of Biology, the Kansas Agricultural Experiment Station, and Southern Illinois University Carbondale. This is publication # 19-234-B from the Kansas Agricultural Experiment Station.

For the second edition, thanks to Lydia Zeglin for help on describing molecular methods. Excellent suggestions for corrections also came from Robert Humston, David Rogowski, John Havel, Sergi Thomas, Daniel Welsh, Erika Iyengar, Matt McTammany, Jack Webster, and Robert Humston. Kabita Ghimire produced the global distribution maps of freshwater habitats. Keith Gido, James Whitney, and Joe Gerken helped clarify Chapter 23. Thanks to Erika Martin, Joshua Perkin, and Kyle Winders for detailed review of the entire draft manuscript from the second edition. Thanks to Andy Richford who assisted in the development of the ideas for the second edition while he was editor at Elsevier.

For the third edition, we thank Priscilla Molley, Anne Schechner, Elizabeth Renner, and Lindsey Bruckerhoff for proofing and suggestions. Suggestions for corrections came from several freshwater ecology classes, Charles Booth, Kristen Bouska, Jessica Fulgoni, Justin Murdock, Ishi Buffam, Becky Bixby, and David Locky. Kevin Wilson provided comments on Devils Hole Pupfish. Alex Shepack provided valuable assistance with the declining amphibians box, and Frank Anderson updated the invertebrate phylogeny section.

MRW thanks F.E. Anderson, L.L. Battaglia, J.E. Garvey, J.W. Grubaugh, R.O. Hall, A.D. Huryn, K.R. Lips, R. Lira, and S.D. Peterson for valuable input and advice on this work. His early mentors, M.E. Gurtz, C.M. Tate, G.R. Marzolf, and J.B. Wallace provided guidance at critical points of his life and helped him realize that he could actually make a career out of his interests in ecology. His parents, Jim and Jane, and his sister, Wendy, tolerated and even supported his somewhat odd boyhood interests and laid the foundation for all these. S.G. Baer provided support, encouragement, and advice. For the third edition, his recent and current graduate students (Sophia, Jessica, Kelley, Lucas, Jared Katie, Kelsey, Kasey, and Adam) and L. Hsieh were sources of inspiration who tolerated his preoccupation and absent mindedness. N. Baccus helped the Whiles’ laboratory running smoothly, and B. Comer and T. Sherk kept the Cooperative Wildlife Research Laboratory humming along. As always, he is particularly grateful for the ongoing, lifelong support of his parents, Jane Whiles and the late James Whiles.

MRW and WKD’s children, Hannah, Joey, Sadie, and Rowland, and grandchildren (Jaxon and Samuel) put it all in perspective; the next generations are the reason this text includes environmental applications. We both deeply appreciate the support and love of our families.

Chapter 1

Why Study Continental Aquatic Systems?

Abstract

All life depends on water for existence. Although 71% of our planet is covered by water, only a very small proportion is associated with the continental areas to which humans are primarily confined. Over 99% of the water associated with continents is in the form of groundwater or ice and is therefore difficult for humans to use. Humans mostly depend on freshwater streams, rivers, marshes, lakes, and shallow groundwaters; we rely heavily on a rare commodity. In this chapter we introduce the reasons to study freshwaters and broadly discuss its importance and value.

Keywords

Climate change; value; hydrologic cycle; citizen science

Contents

Human Use of Water: Pressures on a Key Resource 5

What is the Value of Water? 9

Advanced: Methods for Assigning Values to Ecosystem Services 14

The Anthropocene: Climate Change and Water Resources 15

Politics, Citizens, Science, and Water 17

Summary 19

Questions for Thought 20

Figure 1.1 Crater Lake, Oregon.

All life depends on water for existence. Although 71% of our planet is covered by water, only a very small proportion is associated with the continental areas to which humans are primarily confined (Table 1.1 and Fig. 1.2). Over 99% of the water associated with continents is in the form of groundwater or ice and is therefore difficult for humans to use. Humans mostly depend on freshwater streams, rivers, marshes, lakes, and shallow groundwaters; we rely heavily on a rare commodity.

Table 1.1

Source: Data from Todd (1970); Wetzel (2001); Pidwirny (2006).

Figure 1.2 An image illustrating the relative amounts of water on Earth. The largest blue sphere represents all the water in groundwater, ice caps, oceans, lakes, and rivers. The medium-size blue sphere is the volume of water in groundwater, and the smallest sphere is the global freshwater in lakes and rivers. Image courtesy: Howard Perlman, United States Geological Survey.

Why study the ecology of continental waters? To the academic, the answer is easy: because it is fascinating and we enjoy learning for its own sake. Thus the field of limnology¹ (the scientific study of continental waters) has developed. Limnology has a long history of academic rigor and broad interdisciplinary synthesis (e.g., Hutchinson, 1957, 1967, 1975, 1993; Wetzel, 2001). One of the truly exciting aspects of limnology is the synthetic integration of geological, chemical, physical, and biological interactions that define aquatic systems. No limnologist exemplifies the use of such academic synthesis better than G. E. Hutchinson (Biography 1.1); he did more to define modern limnology than any other individual. Numerous other exciting scientific advances have been made by aquatic ecologists, including refining the concept of an ecosystem, developing ecological methods for approaching control of disease, devising methods to assess and remediate water pollution, understanding how effects of large predators can cascade to primary producers, establishing ways to manage fisheries, restoring freshwater habitats, understanding the deadly lakes of Africa, and conserving unique organisms. Each of these advances will be covered in this book.

Biography 1.1

George Evelyn Hutchinson

George Evelyn Hutchinson (Fig. 1.3) was one of the top limnologists and ecologists of the 1900s, and likely the most influential of the century. His career spanned an era when ecology moved from a discipline that was mainly the province of natural historians to a modern experimental science. In large part, he and his students were responsible for these developments. Born in 1903 in Cambridge, England, Hutchinson was interested in aquatic entomology as a youth and authored his first publication at age 15. He obtained an MA from Emmanuel College at Cambridge University and worked in Naples, Italy, and South Africa before securing a position at Yale University. He remained at Yale until the end of his career and died in 1991.

Figure 1.3 G. Evelyn Hutchinson. Courtesy: The Yale Image Library.

Hutchinson’s range of knowledge was immense. He was well versed in literature, art, and the social sciences. He published on religious art, psychoanalysis, and history. His broad and innovative view of the world enriched his scientific endeavors. Hutchinson published some of the most widely read and cited ecological works of the century. His four volumes of the Treatise of Limnology are the most extensive treatment of limnological work ever published. His writings on diversity, complexity, and biogeochemistry inspired numerous investigations. Hutchinson organized a research team to study the Italian Lake Ianula in the 1960s; this multidisciplinary approach has since become a predominant mode of ecological research (Hutchinson and Cowgill, 1970). He reportedly was always able to find positive aspects of his students’ ideas and encouraged them to develop creative thoughts into important scientific insights. As a consequence, many of Hutchinson’s students and their students are among the most renowned ecologists today.

Hutchinson earned many major scientific awards in his career, including the National Medal of Science. He wrote popular scientific articles and books that were widely distributed. He was a staunch defender of intellectual activities and their importance in the modern world. Hutchinson’s mastery of facts, skillful synthesis, evolutionary viewpoint, cross-disciplinary approach, encouragement of students and collaborators, and knack for asking interesting and important questions make him an admirable role model for students of aquatic ecology.

We hope to transmit our excitement and appreciation of nature that comes from studying aquatic ecology. Further justification for study may be necessary for those who insist on more concrete benefits from an academic discipline or for those interested in preserving water quality and aquatic ecosystems in the broader political context. There is a need to place a value on water resources and the ecosystems that maintain their integrity, and to understand how the ecology of aquatic ecosystems affects this value. Water is unique and has no substitute. A possible first step toward placing a value on a resource is documenting human dependence on it and how much is available for human use.

Humankind would rapidly use all the water on the continents were it not replenished by precipitation. Understanding hydrologic fluxes, or movements of water through the global hydrologic cycle, is central to understanding water availability but much uncertainty surrounds some aspects of these fluxes. Given the difficulty that forecasters have predicting the weather over even a short-time period, it is easy to understand why estimates of global change and local and global effects on water budgets are beset with major uncertainties (Mearns et al., 1990; Mulholland and Sale, 1998; Junk et al., 2013). Scientists can account moderately well for evaporation of water into the atmosphere, precipitation, and runoff from land to oceans. This accounting is accomplished with networks of precipitation gauges and measurements of river discharge. Recently, sophisticated methods for estimating groundwater flow and recharge, including those based on remote sensing, have improved our ability to account for global hydrology.

The global water budget is the estimated amount of water movement (fluxes) among compartments (the amount of water that occurs in each area or form) throughout the globe (Fig. 1.3). This hydrologic cycle will be discussed in more detail in Chapter 4, but is presented here briefly to inform our discussion of how much water is available for human use (Fig. 1.4). Total runoff from land to oceans via rivers has been reported as 22,000, 30,000, and 35,000 km³/year by Leopold (1994), Todd (1970), and Berner and Berner (1987), respectively. These estimates vary because of uncertainty in gauging large rivers in remote regions. So, what are the demands on this potential upper limit of sustainable water supply?

Figure 1.4 Fluxes (movements among different compartments) in the global hydrologic budget (in thousands of km³ per year). Data from Berner and Berner (1987).

Human Use of Water: Pressures on a Key Resource

People in developed countries generally are not aware of the quantity of water that is necessary to sustain their standard of living. In North America particularly, high-quality water is often used for such luxuries as filling swimming pools and watering lawns. Perhaps people notice that their water bills increase in the summer months. Publicized concern over conservation may translate, at best, into people turning off the tap while brushing their teeth or using low-flow showerheads or low-flush toilets. Few people in developed countries understand the massive demands for water from industry, agriculture, and power generation that their lifestyle requires (Fig. 1.5).

Figure 1.5 Estimated uses of water (A) and total population and per capita water use (B) in the United States from 1950 to 2010. Note that industrial and irrigation uses of water are dominant. Off-stream withdrawals used in these estimates do not include hydroelectric uses. Data courtesy: The United States Geological Survey.

Some of these demands, such as domestic use, require high-quality water. Other uses, such as hydroelectric power generation and industrial cooling, can be accomplished with lower quality water. Some uses are consumptive and preclude further use of the water; for instance, a significant portion of water used for agriculture is lost to evaporation. The most extreme example of nonrenewable water resource consumption may be water mined (withdrawal rates in excess of rates of renewal from the surface) from aquifers (large stores of groundwater) that have extremely long regeneration times. Such withdrawal is practiced globally (Postel, 1996; Gleeson et al., 2012) and accounts for a significant portion of the United States’ water use, particularly for agriculture (Fig. 1.6). In many cases use rates exceed the rate at which the aquifer is replenished, and the groundwater is overexploited. Other uses are less consumptive. For example, hydroelectric power consumes relatively less water than agriculture (i.e., evaporation from reservoirs increases water loss, but much of the water moves downstream).

Figure 1.6 Amounts of surface and groundwater used in the United States from 1950 to 2010. These estimates include only withdrawals and not hydroelectric uses. Data courtesy: The United States Geological Survey.

How much water does humankind need? A wide disparity occurs between per capita water use in and among countries, particularly in semiarid countries in which surface water is scarce (Table 1.2). Israel is one of the most water-efficient developed countries, with per capita water use of 500 m³/year (Falkenmark, 1992), about four times more efficient than in the United States. Increases in standard of living lead to greater water demands (per capita water use) if not accompanied by increases in efficiency of use.

Table 1.2

Source: After la Rivière (1989); Falkenmark (1992); Gleick et al. (2004).

The maximum total water available for human use is the amount that falls as precipitation on land each year minus the amount lost to evaporation. As mentioned earlier, the maximum amount of water available in rivers is 22,000–35,000 km³/year. However, a large amount of water is lost to floods in populated areas (temporal inaccessibility) or flows occurring in areas far removed from human population centers (spatial inaccessibility), leaving approximately 9,000 km³/year for all human uses (la Rivière, 1989). Thus only about one-third of the water that flows through the hydrologic cycle is available spatially or temporally. Humans cannot sustain water use rates that exceed this supply rate without withdrawing groundwater more quickly than aquifers can renew their stores, collecting from melting ice caps, transporting from remote areas, or reclaiming (desalinizing) water from oceans. These processes are expensive or impossible to sustain in many continental regions without tremendous energy input, as we discuss later in this chapter.

Predicting future water use is difficult but instructive for exploring possible future patterns and consequences of this use. Total annual off-stream withdrawals (uses that require removal of water from the river or aquifer, not including hydroelectric power generation) in the United States in 1980 were 2,766 m³/person and have decreased slightly since that time, mostly due to a decrease in total industrial use (Fig. 1.5). If all of the people on Earth used water at the current United States rate (i.e., if global standard of living and water use efficiency were the same as in the United States), over half of every bit of water produced by the hydrologic cycle would be used. Globally, humans currently withdraw about 54% of geographically and spatially accessible runoff (Postel et al., 1996); if all people in the world used water at the per capita rates used in the United States, all the water available (spatially and temporally accessible) would be used.

On a local scale, water scarcity can be severe. Political instability in Africa is predicted based on local population growth rates and limited water supply (Falkenmark, 1992). Similar instabilities are likely to arise from conflicts over water use in many parts of the world (Postel, 1996). Large urban areas have tremendous water demands, and very strong effects on local and regional hydrology, generally decreasing water availability (Fitzhugh and Richter, 2004). For example, in some large cities in arid regions, major river flows are almost completely composed of sewage effluent, and some small streams that were ephemeral have become permanent because of runoff from lawn watering. In the arid southwestern United States, human water uses can account for more than 40% of the total supply (Waggoner and Schefter, 1990). In such cases, degradation of water quality has substantial economic consequences. Cape Town South Africa turned off their taps serving 4 million people in 2018, and this scenario is likely to become more common in cities around the world.

The population of Earth was estimated at 7.4 billion people in 2014 and is predicted to exceed 11 billion people by the end of the century (United Nations, 2015). The global population will have increased more than 10% between the second and third editions of this book. Given the increase in human population and resource use (Brown, 1995a,b), demand for water will only intensify (Postel, 1996). As the total population on Earth expands, the value of clean water will increase as demands escalate for this finite resource (Dodds, 2008). Population growth will increase demand for water supplies, even in the face of uncertainty over future climate (Vörösmarty et al., 2000) with particularly acute effects in rapidly urbanizing areas (McDonald et al., 2011). Increased efficiency has led to decreases in per capita water use in the United States since the early 1980s (Fig. 1.5). Efforts to boost conservation of water will become essential as water becomes more valuable (Brown, 2000).

Despite the existence of technology to make water use more efficient and maintain water quality, the ongoing negative human impact on aquatic environments is widespread. Most uses of water compromise water quality and aquatic ecosystem integrity, and future human impact on water quality and biodiversity is inevitable. An understanding of aquatic ecology will assist humankind in making decisions to minimize adverse impacts on our aquatic resources, and will ultimately be required for the development of policies that lead to sustainable water use practices (Gleick, 1998). Accounting for the true value of water will help policy makers decide how important its use is, and students reading this book understand how water is a vital resource to learn about.

What Is the Value of Water?

Accurate accounting for the economic value of water includes determining both the immediate benefit and how obtaining a particular benefit alters future use. This accounting can be essential to planning sustainable development (Garrick et al., 2017). Availability of water is essential, but the quality of water must also be considered. Consumption and contamination associated with each type of use dictate what steps are crucial to maintaining aquatic ecosystems and water quality and quantity. Establishing the direct benefits of water use, including patterns and types of uses, is also necessary. Elucidation of benefits allows determination of economic value of water and how its use should be managed.

Aquatic ecosystems provide us with numerous benefits in addition to direct use. Estimates of the global value of freshwater wetlands ($1.5 trillion/year in 2007) and rivers and lakes ($2.4 trillion/year) indicate the key importance of freshwaters to humans (Costanza et al., 2014, Fig. 1.7). These estimates will increase as researchers are able to assign values to more ecosystem goods and services (Dodds et al., 2008). Freshwater ecosystems have the greatest value per unit area of all habitats. Estimates suggest that the greatest values of natural continental aquatic systems are derived from flood control, water supply, and waste treatment. The value per hectare is greater for wetlands, streams, and rivers than for any terrestrial habitats. The next section details how these values are actually assigned.

Figure 1.7 Relative values per unit area (A) and global values (B) by service for wetlands and lakes and rivers. Data from Costanza et al. (2014).

We explore values of aquatic ecosystems because monetary figures can influence perceived value to society. Assigning values to ecosystems can provide evidence for advocates of minimizing anthropogenic impacts on the environment. Ignoring ecosystem values can be particularly problematic because perceived short-term gain often outweighs poorly quantified long-term harm when political and bureaucratic decisions are made about resource use. For example, restored wetlands may not be as valuable as conserved wetlands (Dodds et al., 2008), so policy decisions should be made accordingly. The concept of no net loss, when a constructed wetland can be substituted for a wetland that is removed for development, may not capture all the values a natural wetland provides to society.

Management of freshwater resources can lead to conflicting values and trade-offs. For example, increased water supply through reservoirs may not protect biodiversity. Thus valuation of ecosystem services can be used to scale economic consequences of varied management approaches (Dodds et al., 2013). Such approaches can be applied from local to global scales. It can also be used to account for multiple effects of environmental change in specific cases, such as occurs when lakes shift from phytoplankton to macrophyte dominated states (Hilt et al., 2017).

Quantification of some values of water is straightforward, including determining the cost of drinking water, the value of irrigated crops, some costs of pollution, and direct values of fisheries. Others may be more difficult to quantify. What is the value of a canoe ride on a clean lake at sunset or of fishing for catfish on a lazy river? What is the worth of all the species that inhabit continental waters including nongame species?

What is the actual value of water? The local price of clean water will be higher in regions in which it is scarce. Bottled water costs vary by region, but people are willing to pay roughly $0.50 to $1.00 L−1 of water, or over $500 m−3. Thus clean drinkable water is very valuable to most people. Highly subsidized irrigation water sold for about $0.01 m−3 in Arizona, but clean drinking water costs $0.37 m−3 in the same area (Rogers, 1986). In the same time period, drinking water costs were between $0.08 and $0.16 m−3 in other areas of the United States (Postel, 1996). In 2013, average rates for the 50 largest cities in the United States were $0.13 m−3 (retrieved from https://www.saws.org/who_we_are/community/RAC/docs/2014/50-largest-cities-brochure-water-wastewater-rate-survey.pdf, 2 February 2018). At the rate of $0.01 m−3, and assuming that people on Earth use 2,664 km³/year for irrigation (according to the Food and Agriculture Organization for 2001), the global value of water for irrigation can be estimated as $26 billion/year. Global agricultural production was worth $3.1 trillion in 2015 (retrieved from http://data.worldbank.org/indicator/NV.AGR.TOTL.CD, 26 December 2016). The Food and Agriculture Organization estimates that 20% of crop area is irrigated but 40% of production is from irrigated areas [FAO, 2016. AQUASTAT website. Food and Agriculture Organization of the United Nations (FAO). Website accessed on 26 December 2015].

Use of freshwater for irrigation does not come without a cost. Agricultural pesticide contamination of groundwater in the United States led to total estimated costs of $1.8 billion annually for monitoring and cleanup (Pimentel et al., 1992). Erosion related to agriculture caused losses of $5.1 billion/year directly related to water quality impairment in the United States (Pimentel et al., 1995). This estimate includes costs for dredging sediments from navigation channels and recreation impacts, but it excludes biological impacts. These estimates illustrate some of the economic impetus to preserve clean water.

The economic value of freshwater fisheries, including aquaculture, worldwide is over $112 billion/year (Table 1.3), and has almost doubled between 2007 and 2014. This economic estimate includes only the actual cash or trade value of the fish and crustaceans. In many countries, sport fishing generates considerable economic activity. For example, in the United States, $41.8 billion was spent on goods and services related to freshwater angling in 2011 (U.S. Department of the Interior and Bureau of the Census, 2011). Similarly, 20 million freshwater anglers were estimated to have spent a collective 10 billion Euros in 2006 (Brainerd, 2010). In addition, 63% of nonconsumptive outdoor recreation visits in the United States included lake or streamside destinations, presumably to view wildlife and partake in activities associated with water (U.S. Department of the Interior and Bureau of the Census, 1993). Many of these visits result in economic benefits to the visited areas. Maintaining water quality is vital to healthy fisheries and healthy economies. Pesticide-related fish kills in the United States were estimated to cause $10–24 million/year in losses (Pimentel et al., 1992). Finally, maintaining fish production may be essential to ensuring adequate nutrition in developing countries (Kent, 1987). Managing fisheries clearly requires knowledge of aquatic ecology. These fisheries and other water uses face multiple threats from human activities.

Table 1.3

Sediment, pesticide and herbicide residues, fertilizer runoff, other nonpoint runoff, sewage with pathogens and nutrients, chemical spills, garbage dumping, thermal pollution, acid precipitation, mine drainage, hydraulic fracturing for oil extraction, urbanization, damming, and habitat destruction are some of the threats to our water resources. Understanding the implications of each of these threats requires detailed understanding of the ecology of aquatic ecosystems. The effects of such human activities on ecosystems are linked across landscapes and encompass wetlands, streams, groundwater, and lakes (Covich, 1993). Management and policy decisions can be ineffective if the linkages among systems and across spatial and temporal scales are not considered (Highlight 1.1). Effective action at the international, national, and local governmental levels, as well as in the private sector, is necessary to protect water and the organisms in it. Success requires whole-system approaches grounded with sound scientific information (Vogt et al., 1997). Productive application of science requires explicit recognition of the role of temporal and spatial scale in the problems being considered and the role of the human observer (Allen and Hoekstra, 1992). We therefore consider scale throughout the book. We give numerous examples in this book that illustrate that the understanding of the mechanisms behind problems such as nutrient pollution, flow alteration in rivers, sewage disposal, and trophic interactions has led to successful mitigation strategies. Many rivers in developed countries are cleaner than they were a half century ago, so there is hope. Future efforts at protection are more likely to be successful if guided by informed aquatic ecologists interested in safeguarding our water resources.

Highlight 1.1

Valuation of Ecosystem Services: Contrasts of Two Desired Outcomes

Ecosystem services refer to the properties of ecosystems that confer benefits to humans. Here, we contrast two types of watershed management and some economic considerations of each. The first case involves the effects of logging on water quality and salmon survival on the northern portion of the Pacific coast of North America and the second involves water supply in some South African watersheds. The preferred management strategies are different, but both rely on understanding ecosystem processes related to vegetation and hydrologic properties of watersheds. When watersheds have more vegetation, particularly closer to streams, runoff can be less and have less sediment. Removal of streamside vegetation is a major concern for those trying to conserve salmon.

Several species of salmon are considered endangered, but they have direct effects on the biology of the streams in which they spawn (Willson et al., 1998). Sport and commercial salmon fisheries have considerable value on the northwest coast of North America. Dams that prevent the passage of adult fish and habitat degradation of streams are the two main threats to salmon survival in the Pacific coastal areas. Logging (Fig. 1.8), agriculture, and urbanization lead to degradation of spawning habitat. The main effects of logging include increased sedimentation and removal of habitat structure (logs in the streams). These factors both decrease survival of eggs and fry. Even moderate decreases in survival of young can have large impacts on potential salmon extinction (Kareiva et al., 2000)

Figure 1.8 A clear cut across a small stream. Courtesy: The United States Forest Service.

Economic analysis of efforts to preserve salmon populations includes calculation of the costs of modifying logging, agriculture, and dam construction and operation as opposed to the benefits of maintaining salmon runs. The economic benefits of salmon fisheries were estimated at $1 billion/year (Gillis, 1995). Costs of modifying logging, agriculture, and dam construction and operation probably exceed the direct economic value of the fishery.

The second case involves shrubland watersheds (fynbos) in South Africa that provide water to large agricultural areas downstream and considerable populations of people in urban centers and around their periphery (van Wilgen et al., 1996). Introduced weed species have invaded many of these shrubland drainage basins (watersheds or catchments). The weeds grow more densely than the native vegetation and reduce runoff to streams. Also, about 20% of the native plants in the region are endemic and endangered by the weedy invaders.

Costs of weed management are balanced against benefits from increased water runoff. Costs associated with weed removal are offset by a 29% increase in water yield from the managed watersheds. Given that the costs of operating a water supply system in the watershed do not vary significantly with the amount of water yield, the projected costs of water are $0.12 m−3 with weed management and $0.14 m−3 without it. Other sources of water (recycled sewage and desalinated water) are between 1.8 and 6.7 times more expensive to use. An added benefit to watershed weed control is protection of native plant species. Weed removal is therefore economically viable.

These two cases illustrate how ecosystem management requires understanding of hydrology and biology. In the case of the salmon, vegetation removal (logging) is undesirable because it lowers water quality and reduces reproductive success. In the South African shrublands, the removal of introduced weeds is desirable because it increases water yield. Knowledge of the ecology of systems is essential to making good decisions.

Advanced: Methods for Assigning Values to Ecosystem Services

An entire field of defining ecosystem services has arisen as a branch of ecological economics. In this section, we discuss how values are actually assigned, and how this relates to freshwaters. A simple calculation can illustrate how valuable water is. About 9,000 km³ of water are available each year to humans through the global hydrologic cycle when and where we need that water. It takes 2,443 J of energy to evaporate each gram of water. This means that 2.19×10²² J of energy are required each year to move water from the ocean into the atmosphere. Humans currently use about 5×10²⁰ J of energy each year, mostly from fossil fuels. Thus, it would take about 40 times our global energy use to evaporate all the water available, or 16 times to evaporate all the water we actually use. The average elevation on Earth is roughly 800 m, and lifting the 9,000 km³ of water to that elevation would require about 10% of human energy use (this does not account for frictional loss in pipes or inefficiencies of pumps) that would be required if humans needed to pump the water from sea-level to the areas they inhabit.

Several schemes have been constructed to value ecosystem services. Probably the most widely agreed upon scheme was developed in conjunction with the Millennium Ecosystem Assessment (MEA, 2003). This scheme recognizes utilitarian (provisioning, regulating, and supporting aspects) and nonutilitarian values (ethical, religious, cultural, and philosophical aspects). Utilitarian values can be broken down into direct use values, indirect use values, and option values. Direct use values include consumptive (harvesting fish or aquatic plants) and nonconsumptive (water sports and recreation) use values. Indirect use values include water purification, water supply, and other ecosystem processes that benefit humanity. Option values are values that are not used currently, but may be used in the future (e.g., maintaining a fishery so your offspring can use it). For direct uses, consumptive values can be directly estimated by the market value of the item of interest.

Nonconsumptive values can be determined on the basis of the amount of money people spend to partake in particular activities and surveys to gauge how much they would be willing to pay to maintain that activity (Wilson and Carpenter, 1999). In the previous section, we discussed surveys documenting how much people spend for freshwater angling. One can calculate how much property value would increase if a lake was cleaner, or how many more recreation days would be spent on a clean lake compared to a polluted lake coupled with the average amount of money spent per recreational visit. In an example of determining a relationship between an economic benefit and an ecosystem attribute, Michael et al. (1996) demonstrated that a single meter increase in lake clarity translated into increased property values of $32–656 m−1 of frontage. This general approach was taken to assess decreases in value of freshwater ecosystem services caused by nutrient pollution (eutrophication). These analyses for the United States indicated that the largest losses of value were related to declining property values and decreased recreational use (Dodds et al., 2009). Thus, it can be established how much people are willing to pay for some esthetic values.

Indirect uses can also be quantified. For example, if water pollution is of concern, one could calculate the cost required to bring water up to usable quality. Another example would be wetlands, where we rely on flood regulation as an ecosystem service allowing water to spread out and cause less damage downstream. The cost of protecting downstream areas from floods if the wetlands were removed can be used to assign values for wetland flood protection.

The idea of quantifying ecosystem services is controversial in the field of economics (e.g., Bockstael et al., 2000). Critics argue that discounting (the lost cost of investment opportunity) is ignored. The argument is fundamentally philosophical, with proponents for conserving economic values of ecosystem services arguing that benefits are accrued to society rather than individuals, so benefits are worth as much if they are used immediately or withheld as option values for future generations.

The second critique of valuation of ecosystem services is that they do not have exact or directly accounted value (e.g., using willingness to pay survey methods, Keeler et al., 2012). Economists who argue this are more comfortable assuming that values of ecosystem services are externalities, meaning they are economic values that are not readily assigned a monetary value. This critique is based on the argument that a poorly constrained estimate of value is worse than no estimate at all.

Nonutilitarian values are more difficult to quantify. Still, people are willing to pay to protect aspects of the environment that are important to them for ethical, religious, cultural, or philosophical reasons. For example, many people are willing to allot tax dollars to help protect parks and natural areas even if they are unlikely to ever visit those areas. Díaz et al. (2018) suggest that the way that all ecosystem services (utilitarian and nonutilitarian) influence human society and culture should be taken into account. This approach would be less focused on economic benefit and more directly on human wellbeing.

The fact remains that humanity values many aspects of freshwater. Rivers and lakes are some of the most desirable places to live and recreate, and we have multiple dependencies on them as a source of water. As the field of ecological economics matures, we will be able to assign more concrete values to freshwater ecosystem services.

The Anthropocene: Climate Change and Water Resources

The influence of humans is now global and is causing geological changes radical enough that we are in a new geological era, the Anthropocene (Crutzen, 2006; Zalasiewicz et al., 2011). There is now consensus among scientists that human-induced climate change is warming the planet (Intergovernmental Panel on Climate Change (IPCC), 2013), though some of the details remain uncertain. Knowledge of the basics of freshwater ecology will be essential if future scientists, such as the students reading this book, hope to be able to deal with the consequences of global climate change.

There have been large alterations in the Earth’s surface waters globally between 1984 and 2015 as verified by remote sensing at high resolution (Pekel et al., 2016). Overall, the amount of surface water has increased because of reservoir construction, with 184,000 km² new surface water formed; about twice the surface area of Lake Superior. However, in some regions of the Earth a total decrease in about 90,000 km² has occurred due to diversion and withdrawal. This loss is mostly concentrated in the Middle East and Central Asia related to human activities, but long-term drought in Australia and the United States have also led to losses.

The Earth’s warming climate is expected to negatively affect the quality and quantity of freshwater resources. Along with direct effects of warming temperatures, climate models forecast changes in regional precipitation patterns and overall higher variability in precipitation that will lead to increased frequency, magnitude, and unpredictability of flooding and droughts in many regions. Reductions in snow pack in mountain regions, which are already shrinking at an alarming rate, will cause reduced stream flows (Giersch et al., 2017). Warming will also result in earlier melting of snow pack causing changes in the seasonal hydrology of receiving streams (Barnett et al., 2008). Climate change will decrease freshwater availability in many areas because of increased losses to evaporation and human use, and warming water temperatures are expected to have both additive and synergistic effects with other stressors such as nutrient pollution and the spread of exotic species. Smaller bodies of water will likely be affected first by climate change because they have less thermal and hydrologic buffering capacity and are more highly influenced by local precipitation patterns (Heino et al., 2009).

Warming temperatures will exacerbate current water pollution problems because increased water loss will reduce the volumes of water in lakes, streams, and wetlands, effectively concentrating pollutants and reducing the flushing of these materials (Whitehead et al., 2009). Along with the obvious ecological consequences, increasing levels of pollutants will increase water treatment costs accordingly. Freshwater habitats in many regions are already stressed from increasing nutrient inputs from human activities; this coupled with reduced water volumes and warming water temperatures will fuel growth of undesirable algae (Wrona et al., 2006). Algal growths will lead to changes in community structure and reduced dissolved oxygen availability, further harming freshwater organisms.

Predicting exact responses of different freshwater habitats to the combined effects of warming and other human impacts is difficult. For example, increased nutrient levels and water temperatures might initially increase biodiversity in a cold, nutrient-poor lake, whereas similar changes to a nutrient-rich lake would likely result in a decrease in biological diversity because of reduced oxygen storage capacity (Heino et al., 2009). Warming may also directly influence the availability of nutrients and other materials. For example, in arctic regions, predicted melting of upper layers of permafrost will liberate phosphorus, which can lead to cascading effects on the productivity of regional streams and lakes (Hobbie et al., 1999).

Climate change will alter biotic conditions for many organisms. For example, seasonal patterns in lakes will change with extended ice-free seasons and periods of summer stratification of lakes in higher latitudes. As temperatures warm, lake mixing patterns will change, with extended periods of summer stratification. Extended stratification will increase the probability of anoxia in cooler, deep water habitats that cold-water species need to survive. In streams, climate change will alter flow regimes globally, altering the conditions which aquatic species need to survive (Pyne and Poff, 2017). These changes will leave aquatic biota vulnerable to climate change. Markovic et al. (2017) document many vulnerable species across Europe, and such vulnerability certainly exists in many other parts of the Earth.

Freshwater habitats are expected to face some of the greatest losses in biodiversity, and thus ecosystem function and stability, as a result of climate change and other human impacts (Xenopoulos et al., 2005). Growth rate, adult size, and ultimately fecundity of most aquatic organisms are all influenced by temperature. Even subtle changes in average or maximum water temperatures can have measurable effects on the biota; in some cases, these effects are sublethal, but can still be serious. For aquatic insects such as many mayflies, warming water temperatures just 2°C–3°C above optimal can greatly reduce the number of eggs produced by females (Vannote and Sweeney, 1980; Firth and Fisher, 1992), which has important implications for future mayfly populations, predatory fish production, and overall ecosystem health. Warming can also desynchronize life cycles and seasonal phenologies of consumers and their resources, a pattern that has been documented in flowers and pollinators (Memmott et al., 2007), as well as in freshwater and marine food webs (Thackeray et al., 2010).

Global climate change has led us into a no-analog world, where predicting hydrology on the basis of past patterns is difficult or impossible (Milly et al., 2008). A mechanistic understanding of hydrologic process coupled with downscaled global circulation models is therefore necessary to predicting the future availability of water in various regions as well as patterns of drought and flooding that will influence human society.

Politics, Citizens, Science, and Water

Given the undeniable importance of water to human affairs, the fact that water issues are political is scarcely surprising. Globally, water could well become the first limiting resource for humanity (Dodds, 2008). More than two billion people on earth live in areas where water is scarce (Oki and Kanae, 2006) and more than a billion lack adequate safe drinking water (Pimentel et al., 2007). Locally, many communities are limited by water. Most major cities on Earth are located near water because people need an adequate supply, and rivers and lakes served as primary transportation avenues before road, rail, and air travel were available. Wetlands also have historic importance; the ancient Chinese fueled one of the world’s great civilizations for centuries with rice harvested from wetlands.

Now, particularly in arid regions, politics and water are deeply intertwined. In the arid western United States, water law is convoluted and water rights transcend most other property rights. Communities appropriate water from far away, and subsidize its use to encourage development. However, water is not just limiting in the United States, and conflicts over water have occurred throughout recorded history (Gleick, 2008). Rates of conflicts involving water are increasing globally (Fig. 1.9). Most of these conflicts revolve around controlling or harming water supplies as a military target or in border disputes. Cut-off of water was used as a military tool as early as 2,500 BC, and is still used to this day. Violent clashes have repeatedly occurred over water, including between Ethiopia and Kenya in 2006, between villagers in Kashmir India in 2002, between Chinese farmers in 1999 (with riot damages reaching $1 million), and even between a government and its people, as in 1993 when the Iraqi government started draining the Mesopotamian marshes to punish people living in the area. Political conflict over water occurs across borders including India–Pakistan, Israel–Jordan, and Mexico–United States. The degree of conflict will only increase with a growing population vying for a finite amount of water and water pollution and exploitation decreasing the availability of that which is clean and accessible.

Figure 1.9 Number of human conflicts over water per year. Data from http://www2.worldwater.org/conflict/list/, downloaded December 2016.

As we harm the quality of water, less is suitable to support native biota and for human uses. When water is a more limited commodity, its market value swells, even more so as the economic values associated with ecosystem goods and services provided by water are increasingly recognized. The United States’ Clean Water Act, the European Union’s Water Framework Directive, India’s system of Water Quality Standards, and the Law of the People’s Republic of China on Prevention and Control of Water Pollution are just a few examples of how governments are attempting to protect water quality. Such protection requires sound scientific understanding of how aquatic ecosystems function and how humans influence that function.

So far, the history of water resources for wealthier countries has been to impair and then repair (Vörösmarty et al., 2015). In this model, countries develop by impairing their water, then follow with costly remediation and restoration of their water resources. Less developed countries are able to impair, but often not able to repair damage done to their water resources given the costs. In the best possible outcome, the causes of impairment are