Freshwater Aquatic Biomes GREENWOOD GUIDES TO BIOMES OF THE WORLD Introduction to Biomes Susan L. Woodward Tropical Forest Biomes Barbara A. Holzman Temperate Forest Biomes Bernd H. Kuennecke Grassland Biomes Susan L. Woodward Desert Biomes Joyce A. Quinn Arctic and Alpine Biomes Joyce A. Quinn Freshwater Aquatic Biomes Richard A. Roth Marine Biomes Susan L. Woodward Freshwater Aquatic BIOMES Richard A. Roth Greenwood Guides to Biomes of the World Susan L. Woodward, General Editor GREENWOOD PRESS Westport, Connecticut • London Library of Congress Cataloging-in-Publication Data Roth, Richard A., 1950– Freshwater aquatic biomes / Richard A. Roth. p. cm.—(Greenwood guides to biomes of the world) Includes bibliographical references and index. ISBN 978-0-313-33840-3 (set : alk. paper)—ISBN 978-0-313-34000-0 (vol. : alk. paper) 1. Freshwater ecology. I. Title. QH541.5.F7R68 2009 577.6—dc22 2008027511 British Library Cataloguing in Publication Data is available. Copyright C 2009 by Richard A. Roth All rights reserved. No portion of this book may be reproduced, by any process or technique, without the express written consent of the publisher. Library of Congress Catalog Card Number: 2008027511 ISBN: 978-0-313-34000-0 (vol.) 978-0-313-33840-3 (set) First published in 2009 Greenwood Press, 88 Post Road West, Westport, CT 06881 An imprint of Greenwood Publishing Group, Inc. www.greenwood.com Printed in the United States of America The paper used in this book complies with the Permanent Paper Standard issued by the National Information Standards Organization (Z39.48–1984). 10987654321 Contents Preface vii How to Use This Book ix The Use of Scientific Names xi Chapter 1. Introduction to Freshwater Aquatic Biomes 1 Chapter 2. Rivers 25 Chapter 3. Wetlands 85 Chapter 4. Lakes and Reservoirs 141 Glossary 209 Bibliography 215 Index 225 v This page intentionally left blank Preface This volume describes the freshwater aquatic biome, which consists of lakes, rivers, and wetlands. These life zones are distinguished from terrestrial biomes, such as deserts and tropical forests, and from the marine biome. They thus occupy a unique place in the biosphere. That said, as is the case with other biomes, our conceptual categories are much neater than living nature, which is much more likely to have fluctuating gradients rather than sharp dividing lines. Thus, for example, fresh- water and saltwater tidal marshes exist along a continuum of salinity; riparian wet- lands may be part of the river at times. Nonetheless, our use of concepts and categories helps us to make sense of the world, and in this volume, many concepts applicable to freshwater systems are introduced. Just as this series follows the conventional biogeographic division of Earth’s liv- ing systems into the major biomes, I have followed standard practice in categoriz- ing the freshwater aquatic biome into the three major categories of rivers, lakes, and wetlands. One type of life environment that does not fit easily into any of these three freshwater environments is salt lakes. They are not freshwater environments; nonetheless they are included in this volume, because, one might say, a salt lake is more like a lake than like the ocean. In each of the major freshwater aquatic environments, three examples are pre- sented in some depth. In each case, I describe a low-, a mid-, and a high-latitude system. While this approach is a little different from that followed in the volumes on terrestrial biomes, it offers a broader range of specific manifestations of fresh- water aquatic environments. For example, lakes at very different latitudes are likely vii viii Preface to encompass a greater range of physical conditions than lakes at the same latitude on different continents or in different biogeographic realms. In the chapters on rivers, lakes, and wetlands, I spend considerable time explaining the range of physical conditions within which life has evolved in these environments. I also describe how lifeforms have adapted to the conditions. For example, wetland environments are characterized by low oxygen conditions, par- ticularly in the substrate. What adaptations make it possible for plants to survive in such conditions? Throughout, with an eye toward what I suppose to be the needs and capabilities of the readers of this volume, I have tried to find the right balance between general concepts and specific manifestations. I have attempted to supply enough technical detail to understand a particular environment without unnecessarily burdening the reader. I thank the series editor, Dr. Susan Woodward, for her assistance, collegiality, good humor, encouragement, and many helpful suggestions. How to Use This Book The book is arranged with a general introduction to the freshwater aquatic biome and a chapter on each of the three generally recognized forms of that biome: rivers, wetlands, and lakes. Salt lakes, although not freshwater, are also included in the chapter on lakes, as are manmade lakes (reservoirs). The biome chapters begin with a general overview, proceed to describe the distinctive physical and biological char- acteristics of each form, and then focus on three examples of each in some detail. Each chapter and each example can more or less stand on its own, but the reader will find it instructive to investigate the introductory chapter and the introductory sections in the later chapters. More in-depth coverage of topics perhaps not so thor- oughly developed in the examples usually appears in the introductions. The use of Latin or scientific names for species has been kept to a minimum in the text. However, the scientific name of each plant or animal for which a common name is given in a chapter appears in an appendix to that chapter. A glossary at the end of the book gives definitions of selected terms used throughout the volume. The bibliography lists the works consulted by the author and is arranged by biome and the regional expressions of that biome. All biomes overlap to some degree with others, so you may wish to refer to other books among Greenwood Guides to the Biomes of the World. The volume entitled Introduction to Biomes presents simplified descriptions of all the major bio- mes. It also discusses the major concepts that inform scientists in their study and understanding of biomes and describes and explains, at a global scale, the environ- mental factors and processes that serve to differentiate the world’s biomes. ix This page intentionally left blank The Use of Scientific Names Good reasons exist for knowing the scientific or Latin names of organisms, even if at first they seem strange and cumbersome. Scientific names are agreed on by inter- national committees and, with few exceptions, are used throughout the world. So everyone knows exactly which species or group of species everyone else is talking about. This is not true for common names, which vary from place to place and lan- guage to language. Another problem with common names is that in many instan- ces European colonists saw resemblances between new species they encountered in the Americas or elsewhere and those familiar to them at home. So they gave the foreign plant or animal the same name as the Old World species. The common American Robin is a ‘‘robin’’ because it has a red breast like the English or Euro- pean Robin and not because the two are closely related. In fact, if one checks the scientific names, one finds that the American Robin is Turdus migratorius and the English Robin is Erithacus rubecula. And they have not merely been put into differ- ent genera (Turdus versus Erithacus) by taxonomists, but into different families. The American Robin is a thrush (family Turdidae) and the English Robin is an Old World flycatcher (family Muscicapidae). Sometimes that matters. Comparing the two birds is really comparing apples to oranges. They are different creatures, a fact masked by their common names. Scientific names can be secret treasures when it comes to unraveling the puzzles of species distributions. The more different two species are in their taxonomic rela- tionships, the farther apart in time they are from a common ancestor. So two spe- cies placed in the same genus are somewhat like two brothers having the same father—they are closely related and of the same generation. Two genera in the xi xii The Use of Scientific Names same family might be thought of as two cousins—they have the same grandfather, but different fathers. Their common ancestral roots are separated farther by time. The important thing in the study of biomes is that distance measured by time often means distance measured by separation in space as well. It is widely held that new species come about when a population becomes isolated in one way or another from the rest of its kind and adapts to a different environment. The scientific classi- fication into genera, families, orders, and so forth reflects how long ago a popula- tion went its separate way in an evolutionary sense and usually points to some past environmental changes that created barriers to the exchange of genes among all members of a species. It hints at the movements of species and both ancient and recent connections or barriers. So if you find two species in the same genus or two genera in the same family that occur on different continents today, this tells you that their ‘‘fathers’’ or ‘‘grandfathers’’ not so long ago lived in close contact, either because the continents were connected by suitable habitat or because some mem- bers of the ancestral group were able to overcome a barrier and settle in a new loca- tion. The greater the degree of taxonomic separation (for example, different families existing in different geographic areas), the longer the time back to a com- mon ancestor and the longer ago the physical separation of the species.