Limnology Lake and River Ecosystems Third Edition ROBERT G. WETZEL f jp\ ACADEMIC PRESS An Imprint of Elsevier San Diego San Francisco New York Boston London Sydney Tokyo This book is printed on acid-free paper, w Copyright© 2001, 1983, 1975, Elsevier. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permissions may be sought directly from Elsevier's Science and Technology Rights Department in Oxford, UK. Phone: (44) 1865 843830, Fax: (44) 1865 853333, e-mail: [email protected]. You may also complete your request on-line via the Elsevier homepage: http://www.elsevier.com by selecting "Customer Support" and then "Obtaining Permissions". Academic Press An Imprint of Elsevier 525 B Street, Suite 1900, San Diego, California 92101-4495, USA http://www.academicpress.com Academic Press 32 Jamestown Road, London NW1 7BY, UK http://www.academicpress.com Library of Congress Catalog Card Number: 00-110178 ISBN-13: 978-0-12-744760-5 ISBN-10: 0-12-744760-1 PRINTED IN THE UNITED STATES OF AMERICA 11 EB 14 To Theodore Jones, who took the time to inspire a fledgling at an early, critical time, and to Carol Ann (né Andrée) Wetzel for her unending understanding and support Preface to the Third Edition Limnology is currently experiencing a period of in­ foundation or relevance for modern interpretations. trospection. Such criticism is healthy if done construc­ Additional nonsense arguments emerge that too much tively and the causes of underlying deficiencies are rec­ information exists to integrate. With modern search ognized and addressed. Many problems have arisen, and organization capabilities, such ignorance of past however, in part because of the purported necessity to research is much more than laziness; it represents a de­ respond rapidly to governmental and societal demands ficiency in the teaching of how science is properly con­ without an in-depth scientific underpinning. A root ducted. Bibliographic negligence is more than a lack of cause is our continuing inability to properly educate responsible scholarship because it leads to increasing and train students and the public. Society must recog­ scientific redundancy and inefficient use of intellectual nize that intellectual creativity is essential to excellence and financial resources. A result is an increasing ten­ in science and that excellence in science is essential to dency to promote old ideas and interpretations under the most effective and cost-efficient management of our the guise of new and invariably ambiguous "buzz resources. word" terms. These redundant ideas are actively pro­ Improvements in science education and training moted as inspiration among noncritical peers, science are critically needed. A fundamental requirement of sci­ writers, and even granting agency administrators who entific education is to obtain comprehensive back­ are unfamiliar with the background development of the ground information prior to interpretation and synthe­ subdiscipline. Many contemporary topical reviews are sis. One observes an increasing erroneous reliance upon incredibly naive, biased, and incomplete, and parts are uninformed excuses that old perceptions have little simply wrong. Such deficiencies in scholarship must be xui Xiv Preface severely condemned and can be countered by more rig­ was well received; it has been widely cited as a source orous preparatory study. work (e.g., ISI Citation Classic) and has been translated There is an increasing tendency, particularly in the into several other languages. United States, to capitulate to the masses of informa­ Since the appearance of these editions, a number of tion on any subject and accept, even promote, superfi­ other general treatments of limnology have appeared in cial understanding of ecological subjects. That level of English, French, German, Spanish, Portuguese, and inquiry may be acceptable for the lay public but is not other languages. Essentially all of these works are di­ acceptable for professional limnologists, aquatic ecolo- rected at providing general overviews of the subject, gists, and water resource managers. A superficial level and some accomplish this objective very well. Some of of understanding is unacceptable in all rigorous disci­ these books are simple but interesting overviews of the plines that contemplate systems of equal complexity to subject that can be assimilated in a long evening of natural ecosystems. For example, the great strides reading, whereas others are more involved and clearly made in human medicine are the direct result of con­ are intended to accompany instructional programs in certed, systematic evaluation and rigorous experimen­ initial introductory courses in limnology. tal investigations of the mechanisms controlling human Such general books introduce students at college and pathogen physiology. and university levels to the fascinating subject of inland In ecology, as in many other disciplines, the "cop aquatic ecology. These accomplishments assist in ful­ out" deference strategy to the information glut is filling an enormously important responsibility of edu­ increasingly to specialize in a small area and to then cators: the general public, particularly those obtaining aggregate teams of specialists to attempt to understand higher education, should be aware of the magnitude, how all of the pieces fit and operate together. The general operation, and management problems of inland present emphasis on interdisciplinary studies is little waters upon which so much of their well-being de­ more than an expansion of the identical process that pends. The information presented in these works need has been carried on for decades by competent ecosys­ not include details underlying certain basics of the tem scientists. Emphasis, particularly by nonscientist operation and should be presented in an interesting, administrators, on forced collaboration, regardless of scientifically correct manner. expertise, either directly or by fiscal coercion is an There are different levels of training in any subject. increasing problem. Such realities of collaborations The gap is large between general texts suitable for the reinforce the need for participants to be versed on general public and nonspecialist students and detailed some comprehensive introductory understanding of the research-level treatments, such as G. E. Hutchinson's whole. four-volume A Treatise on Limnology. Somewhere in I argue that one cannot manage aquatic ecosystems between is the need for a more detailed introductory effectively without understanding how they operate in instructional text for students interested in becoming response to interactions of physical, chemical, and biotic professionals in this discipline and desiring greater environmental variables. This insistence is analogous to depth of inquiry and understanding. For nearly a the statement that one cannot effectively manage human decade, among other responsibilities, I have been revis­ health without understanding human physiological and ing this general limnology text for a third edition for biochemical interactions with environmental variables. this introductory instructional objective. Superficial or biased training in limnology can only lead Those persons familiar with the past editions of to superficial and biased understanding. There is a need Limnology will recognize marked differences in the for rigorous limnological training, even at the introduc­ present Limnology: Lake and River Ecosystems. The tory level. The U.S. National Academy of Sciences basic format of previous editions is maintained, al­ (1996) also emphasized that need in the recent thorough though the parts are completely reorganized, modified, evaluation of limnological education. and updated with recent advances in understanding. A The first edition of this book, initiated in the early number of introductory texts have taken the tack of 1970s, resulted from my frustration with the available presenting an ecosystem overview initially, in some texts at the time, which, at best, offered interesting but cases constituting half the text, and then presenting superficial analyses of inland aquatic ecosystems. The a somewhat hackneyed discussion of the parts initial edition, issued in 1975, was well received as of the ecosystems thereafter that may influence the an alternative. The second edition, published in 1983, biota within the ecosystem. In Limnology: Lake and represented an extensive updating with new findings, River Ecosystems I opine first that, apart from the appreciable reorganization, and clarifications based on structure of water and a few physical properties, experience in my own classes and constructive inputs aquatic ecosystem structure, energy flow, and produc­ from many students and colleagues. Again the book tivity are regulated by biogeochemical cycling. One Preface XV cannot talk effectively about chemical cycles, for exam­ involved, I argue that regulatory generality prevails ple, without treating microbial mediation of those across the individual species and diversity of processes. cycles. Thus, it is essential to comprehend these ecosys­ Regulation of metabolic rates among different com­ tem components before discussing the integration of munities is where generality emerges. From both the­ the entire ecosystem. Nonetheless, a very general dis­ oretical relationships and management methods of cussion of aquatic ecosystem structure and productivity controlling the effects of disturbances, integration of appears early in the text, largely in order to introduce quantitative process rates of metabolism, energy fluxes, the terms used throughout the subsequent topical treat­ and material fluxes is where commonality emerges ments. True ecosystem integration follows in the indi­ among highly disparate and complex interacting para­ vidual community treatments and then finally in the meters within ecosystems. important synthesis chapter on organic carbon. Combining lacustrine, reservoir, and running water Second, I make major attempts to present data limnology in one integrated synthesis volume on this dis­ supporting conceptual relationships among biota and cipline immediately causes manifold increases in the the environment in a realistic and unbiased manner. I published literature to be evaluated. Indeed, the litera­ have been accused of being biased against the roles that ture on certain subjects, such as stream invertebrate animals play in aquatic ecosystem structure and ener­ ecology, is both formidable and intimidating. Yet, amid getic transfer. Nothing could be further from the truth. the maze of individual detail, commonality of processes Evaluation of the data, however, simply does not sup­ and regulatory mechanisms emerges. I make no pretense port some of the entrenched dogma that prevails in to being comprehensive in coverage, and among the contemporary limnological writings, including many stream and river literature in particular I relied heavily textbooks. I do present historical developments of on many thorough reviews of topical subjects. some of those ideas even if new findings demonstrate Saline lakes constitute approximately half of inland them to be erroneous. Alternative explanations and waters. Again, chemical and biological characteristics hypotheses are then presented. I recognize that some of saline lakes are not treated separately but rather are colleagues will have difficulty with these conclusions, integrated within topical discussions with fresh waters. although I believe my conclusions accurately represent The chemistry and biota of saline lakes are fascinating reality. and of great evolutionary significance. The mineral and Throughout the development of our understanding biotic values of contemporary saline lakes, however, of limnology, emphasis has been on differences among are dwarfed by the collective values of freshwater sur­ lakes and rivers, differences among the physical and face and groundwater repositories to humankind. As a chemical characteristics of waters of various geomor- result, treatment here has been subordinate to freshwa­ phological regions, and the diversity of different biota ter ecosystems. Hammer (1986) and Williams (1988, and their growth characteristics. That differentiation 1996) have summarized well selective characteristics of among lakes and rivers and their physical, chemical, saline lakes. and biological properties was the impetus behind a half Many persons have been generous and helpful with century of lake and river classification studies. A major suggestions for improving this edition. In addition to evolution of my syntheses in Limnology: Lake and persons cited in the preface to the second edition, River Ecosystems is the comparative treatment of top­ numerous colleagues and friends offered constructive ics across lake, reservoir, and river ecosystems. These criticism on portions of this book: Vernon Ahmadjian, analyses do indeed indicate differences among the Hartmut Arndt, Michael T. Arts, Arthur C. Benke, properties of lakes, land-water interface regions, reser­ Riccardo de Bernardi, J. Marie Boavida, Nina Caraco, voirs, and rivers. Importantly, these analyses also indi­ Robert Carlson, Perry Churchill, Daniel Conley, cate marked commonality in function. G. D. Cooke, Clifford Dahm, Anthony Davis, Stanley It is essential that we search for commonality, in Dodson, Eric Espeland, Steven Francoeur, Walter addition to differences, among these aquatic ecosys­ Geller, Chris E. Gibson, Alex Huryn, Frank M. D'ltri, tems (Wetzel, 2000). Because of the dynamic properties Eileen Jokinen, Klaus Jürgens, Mark Johnson, Susan S. of metabolism, growth, and reproductive capacities of Kilham, Joachim Kleiner, Reiner Koschel, Winfried organisms as they respond to the bewildering array of Lampert, Richard C. Lathrop, Gene E. Likens, S. Mac- dynamic environmental factors influencing growth and Intyre, Robert P. Mclntosh, Jürgen Marxsen, William J. development, variability is enormous and often difficult Matthews, R. Michael McKay, J. Melack, Robert E. to fathom. Modeling at the present level of understand­ Moeller, Walter T. Momot, Roland Psenner, Peter H. ing is unable to cope with so many nonlinear variables Rich, Eric E. Roden, Philippe Ross, Mark R. D. Sea­ that are changing rapidly. Although reductionism is ward, Arthur J. Stewart, Ruben Sommaruga, Eugene essential to provide information on the properties Stoermer, Raymond G. Stross, Keller Suberkropp, XVi Preface Nancy C. Tuchman, A. Vähätalo, Jack R. Vallentyne, to exude unending patience and understanding of the Anthony E. Walsby, Amelia K. Ward, G. Milton Ward, siren call of my limnological mistress. Portions of un­ William D. Williams, and Edward O. Wilson. Deborah published results cited in the text were supported by Cook has patiently sustained my constant barrage of subventions of the National Science Foundation. Re­ manuscript drafts, tabular materials, endless organiza­ gardless of the assistance of the persons mentioned and tion of thousands of references, and requests for help many unnamed, the responsibility for the synthesis and with figure preparations. Her uncompromising atten­ interpretations rests with me. tion to detail has assisted me enormously in the prepa­ ration of this work. Mark Dedmon also assisted with preparation of many figures. My wife, Carol, continues Robert G. Wetzel PROLOGUE I. Our Freshwater Resources V. Scientific Approaches II. Demotechnic Growth VI. Search for Commonality, III. Human Impact on Freshwater Not Only Differences Ecosystems VII. Altered Perspectives IV. The Study of Limnology VIII. Summary A basic feature of the earth is an abundance of supply is constantly expanded in response to growing water, which extends over 71% of its surface to an demands. The unfortunate effect of essentially uncon­ average depth of 3800 m. Over 99% of this im­ trolled growth is that consumption increases in response mense hydrosphere is deposited in ocean depressions to rising supply. Every increase in supply is met by a (Table 1-1). The relatively small amounts of water that corresponding increase in consumption, because in con­ occur in freshwater lakes and rivers belie their funda­ temporary society, voluntary control of consumption is mental importance in the maintenance and survival of ineffective unless economically advantageous. terrestrial life. II. DEMOTECHNIC GROWTH I. OUR FRESHWATER RESOURCES The impending environmental problems are not Any analysis of inland water resources must address only the result of population growth (Vallentyne, 1972, the preeminence of exponential human growth and uti­ 1988). They result also from technological growth, lization of fresh water. Humans must be recognized for both directly in the sense of increased per capita what they are: an animal whose population growth is in production and consumption and indirectly in that an exponential phase. In spite of its absurdity, a belief technology has furthered the growth of population and prevails that the earth's supply of finite water resources urbanization. This demotechnic concept of growth can be increased constantly to meet exponential de­ encompasses the combined effects of population in a mands. Fresh waters are a finite resource that can be biological sense as well as of production-consumption increased only slightly. For example, desalinization of in a technological sense. The importance of the concept ocean water requires tremendous energy expenditures of demotechnic growth lies in its emphasis on both for the treatment process and distribution of the prod­ production and consumption. It describes the cycle in uct once obtained. That distribution is energetically which degradation of the biosphere occurs as a result prohibitive within only short distances from marine of utilization of the environment for production and sources. Society as a whole, and many freshwater ecolo- consumption of technological products. Both processes gists, have tended to ignore humans, and their use and lead to pollution of water resources. In demotechnic misuse of fresh waters, as influential factors in the main­ growth, attention is correctly focused on all aspects of tenance of lake and river ecosystems. Freshwater utiliza­ technological growth, that is, the technological metab­ tion is governed by the spiraling relationships in which olism of humans. 1 1. Prologue TABLE 1-1 Water in the Biosphere Volume (thousands of km3) Percentage of total Renewal time Oceans 1,370,000 97.61 3100yearst Polar ice, glaciers 29,000 2.08 16,000 years Ground water (actively exchanged)^ 4067 0.295 300 years Freshwater lakes 126 0.009 1-100 years)§ Saline lakes 104 0.008 10-1000 years)§ Soil and subsoil moisture 67 0.005 280 days Rivers 1.2 0.00009 12-20 days)! Atmospheric water vapor 14 0.0009 9 days "''Modified from Vallentyne (1972), after Kalinin and Bykov. In: The Environmental Future, London, Macmillan Publishers, Ltd. Reprinted by permission of Macmillan London and Basingstoke. Slightly different values are given by Shiklomanov (1990), but ratios are similar. f Based on net evaporation from the oceans, φ Kalinin and Bykov (1969) estimated that the total ground water to a depth of 5 km in the Earth's crust amounts to 60 X 106 km3. This is much greater than the estimate by the U.S. Geological Survey of 8.3 X 106 km3 to a depth of 4 km. Only the volume of the upper, actively exchanged ground water is included here. § Renewal times for lakes vary directly with volume and mean depth and inversely with rate of discharge. The absolute range for saline lakes is from days to thousands of years. f Twelve days for rivers with relatively small catchment areas of less than 100,000 km2; 20 days for major rivers that drain directly to the sea. The demands that demotechnic growth have successfully with environmental resource limitations imposed upon freshwater resources are monumental. Al­ and disastrous situations of overexploitation decreases though about 105,000 km3 of precipitation, the ultimate continually. Stability becomes increasingly tenuous. source of the freshwater supply, fall on the land surface Vagaries in climate (e.g., Bryson and Murray, per year, only about one-third of it (ca. 37,500 km3 1977) are superimposed upon the immediate de­ year-1) reaches the oceans as river discharge (Vallentyne, motechnic pressures of resource utilization. Fluctua­ 1972). About two-thirds of the annual water supply is tions in climate have resulted in catastrophic crises returned to the atmosphere by evaporation and plant both in the availability of resources and effective transpiration. If the potential water supply of 37,500 resource utilization. Rapid climatic changes affect not km3 year-1 were divided evenly among some 5.5 billion only the availability of adequate food resources but humans now existing on Earth (2000), each person availability of fresh water as well; the two are inex­ would have potentially 6800 m3 year-1 or 18,680 liters orably coupled. Although major climatic changes are day-1. These values would be halved at a projected pop­ difficult to predict, such changes are certain and, on the ulation level of 10 billion humans by approximately the year 2050. Even though these quantities seem large in comparison to the human physiological requirement of 2 liters person-1 day-1, they are insufficient in view of FRESH WATER „ modern technological demands. Domestic consumption averages 250 liters person-1 day-1, the average indus­ trial consumption is 1500 liters person-1 day-1 in devel­ oped countries, and agriculture uses up to several thou­ sand liters person-1 day-1 in countries with hot, dry climates (Vallentyne, 1972). Historical patterns of environmental resource uti­ lization have resulted in a series of crises, particularly among populations of developed countries (Fig. 1-1). As the human population increases, the severity of the crises increases. Particular resource-related problems are confronted with various actions by humans (Francko and Wetzel, 1983). Most of these actions are therapeutic adaptations and adjustments rather than 1900 1950 2000 FIGURE 1-1 Stresses of increasing severity imposed upon human true corrective, prophylactic measures. As a result, populations of developed countries resulting largely from excessive stress levels increase. The margin between coping demotechnic growth. (Modified from Wetzel, 1978.)