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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology Bringing Biology Back into Water Quality Assessments G. Wayne Minshall Department of Biological Sciences Idaho State University Pocatello, Idaho SUMMARY For some time now, the quality of the nation's inland waters has been evaluated largely on the basis of chemical and toxicological criteria. However, more recent theories reflect the idea that the native biota, exposed to the full suite of environmental conditions in nature, more accurately reflect the suitability of that environment for survival and long-term persistence. This paper examines the reasons for the resurgence of interest in the biological assessment of water quality and highlights some important considerations in the application of this approach to inland aquatic ecosystems. Biological integrity is a concept central to successful bioassessment because it identifies the essential factors to be measured and provides a reference against which the degree of environmental disturbance or stress, either natural or anthropogenic, can be evaluated. Major anthropogenic stresses on the integrity of inland aquatic ecosystems include livestock grazing; forestry; agriculture; mining and smelting; urban usage; manufacturing; impoundment and diversion; and lake-, marsh-, and stream-bottom alteration. Measurement of the biological health of aquatic ecosystems is a complex issue involving multiple spatial and temporal scales and methodological and logistical considerations. Nevertheless, direct assessment of the status or ecological health of aquatic organisms and communities is essential for proper resource management of inland waters and their sustained diversity and productivity. INTRODUCTION Over the past few decades, water quality has been defined primarily in chemical terms. More recently, however, water management agencies
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology have been increasingly aware of the need to bring biology back into the water quality equation. In some cases, chemical monitoring has actually exceeded the ability to detect biological impacts of chemical contaminants, so that large sums of money have been spent to remove contaminants that do not even affect aquatic organisms. On the other hand, reliance on chemical criteria or laboratory-derived toxicological information taken out of the environmental context has often allowed levels of toxicants or other materials that are harmful to aquatic populations. The return of biology to environmental assessments has brought with it a need for knowledge about whole-organism biology, the study of which has become increasingly neglected in academic institutions over the past several decades. At the same time, many exciting developments, in fields ranging from molecular biology to landscape ecology, have potential application to the study and management of inland aquatic resources. This paper reviews the historical basis for the application of biological methods to water quality assessment and discusses factors that need to be considered in evaluating the biological integrity of inland aquatic ecosystems. HISTORICAL BACKGROUND Modern bioassessment of inland aquatic ecosystems has given rise to several terms and concepts regarding protection or restoration of aquatic environments (Steedman, 1994). Foremost among these are the ideas of integrity, which relates to whether biological systems are intact or restorable, and health, management, and sustainability, which relate to modification of sites by human activity. The idea of biological, and subsequently ecological, integrity is traceable at least as far back as the writings of Aldo Leopold (1949), but its emergence as a formal ecosystem concept did not occur until the mid-1970s (e.g., Cairns, 1977a,b). The Water Quality Act Amendments of 1972 (P.L. 92-500) formalized the term ''biological integrity" under the directive to restore and maintain the "chemical, physical, and biological integrity of the nation's waters." Initially, the primary focus was on chemical and physical aspects of the environment and on toxicity tests performed in the laboratory on both individual contaminants and complex mixtures of waste effluents from industry and other sources. The idea of biological integrity gradually evolved to include naturalness, sustainability, and ecosystem balance, structure, and function (Jackson and Davis, 1994). Karr and Dudley (1981) defined biological integrity as the "ability of an aquatic ecosystem to support and maintain a balanced, adaptive community of organisms having a species composition, diversity, and functional organization comparable to that of natural habitats within a region." Others have refined,
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology clarified, and extended this concept to specific applications in a series of articles (e.g., Karr, 1991, 1993; Kay, 1991; King, 1993; Steedman and Haider, 1993; Polls, 1994; Steedman, 1994). Still others have addressed the choice of indicators (Keddy et al., 1993), monitoring considerations (Munn, 1993), and descriptions of national programs to measure ecological integrity (EPA, 1990; Marshall et al., 1993; Woodley, 1993; Jackson and Davis, 1994). Because of increasing public awareness of environmental problems, beginning in the mid-1960s and continuing to the present, key ecological issues have been codified as catch phrases, such as ecological or ecosystem health, management, and sustainability. Ecological health generally is regarded as a condition in which natural ecosystem properties are not severely restricted, the ability for progressive self-organization is present, the capacity for self-repair when stressed is preserved, and minimal external support for management is needed (Steedman and Regier, 1990; Karr, 1993). Sites modified by human activity may be considered ecologically healthy "when their management neither degrades the sites for future use, nor results in degradation beyond their borders" (Steedman, 1994). Problems associated with deterioration of ecosystem health must be addressed at a landscape scale of resolution since significant cumulative and interactive effects otherwise might be overlooked. Ecosystem management may be defined as "the skillful, integrated use of ecological knowledge at various scales to produce desired resource values, products, services, and conditions in ways that also sustain the diversity and productivity of ecosystems" over the long term (Avers, 1992). In practice, it means blending the needs of people and environmental values in such a way as to achieve healthy, productive, and sustainable ecosystems. The extent to which these goals are attained can be determined only through biological assessment and monitoring of resource conditions. Ecosystem sustainability is "the ability to sustain diversity, productivity, resilience to stress, health, renewability, and/or yields of desired values, resource uses, products, or services from an ecosystem while maintaining the integrity of the ecosystem over time" (Overbay, 1992). Its return to the resource management equation has come about through the National Environmental Protection Act, the Endangered Species Act, and numerous other federal laws passed during the 1960s and 1970s (e.g., Overbay, 1992) and sustained by federal court decisions. Ecosystem management and sustainability are likely to have a major influence on research and management of many inland aquatic ecosystems in the United States for years to come. These concepts are especially relevant to federal agencies with large land holdings and broad responsibilities for the terrestrial and aquatic resources occupying them, such as
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology the Bureau of Land Management, the National Forest Service, the National Park Service, and the Refuge Management branch of the Fish and Wildlife Service. Both the concepts and the recognition of their responsibility to implement them are new to these agencies; it is still unclear how (and at what rate) they will move toward instituting formal ecosystem management policies. However, it is clear that biological assessments and continued monitoring will be important to ecosystem management in inventorying aquatic biological resources and their status, in assessing the effects of various management practices on them, and in determining suitable management strategies through research and adaptive management practices to ensure ecosystem sustainability. Federal Legislative Initiatives Historically, three major federal legislative actions are responsible for current efforts to increase the use of biological measures and a more meaningful ecological perspective: (1) the Water Quality Act, (2) the National Environmental Policy Act, and (3) the Endangered Species Act. The Water Quality Act of 1965 (P.L. 89-234) and the related Clean Water Act (Federal Water Pollution Control Act Amendments of 1972, Clean Water Act of 1977, Water Quality Act of 1987) were enacted in response to widespread surface water degradation and a growing public environmental awareness and concern. The implications of this legislation for inland aquatic science range from classroom to courtroom, and its implementation provides substantial opportunities for involvement in all aspects of water science. The National Environmental Policy Act of 1969 (NEPA; P.L. 91-190) was responsible for interjecting an ecological perspective into subsequent federal legislation and actions, particularly as they relate to natural resource-oriented projects. NEPA set forth a national policy to protect and improve the national environment by requiring detailed consideration of proposals for federal legislation, construction (e.g., dam construction, channel alteration, draining of wetlands), or resource extraction (e.g., water diversion, logging, or livestock grazing) likely to significantly affect the quality of the air, land, and water environments. Among other things, the law required the identification of (1) any adverse environmental effects that cannot be avoided should the proposal be implemented; (2) alternatives to the proposed action, including total abandonment and mitigation of damages; (3) the relationship between local short-term human uses of the environment and maintenance and enhancement of long-term productivity (i.e., sustainability); and (4) any irreversible and irretrievable commitments of resources that would be involved in the proposed action. This act consistently has been upheld and expanded by federal court decisions. Increasingly, NEPA and its legal interpretations have had far-reaching
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology implications for the management of inland aquatic resources at the ecosystem and landscape scales. NEPA has resulted in a more holistic and long-range view of past, present, and future management actions on natural resources in an ecosystem context and has called for a greater and more thorough knowledge of resource states under different management treatments. The Endangered Species Act of 1973 (ESA; P.L. 93-205) protects all species (except pests) of plants and animals in danger of extinction. Twelve percent of all animal species live in inland waters, and many species are restricted to limited geographic ranges. As freshwater habitats have been destroyed, altered, or polluted, biodiversity and ecosystem integrity have declined. The listing of federally recognized threatened or endangered freshwater species is an important means of tracking total biological integrity (Covich, 1993). The Endangered Species Act has served to emphasize the importance of identifying and preserving the diversity of inland aquatic organisms and their habitats, and of assessing long-term trends in their conditions. Several recent developments stemming from these legislative acts have brought the biological aspects of water quality to the forefront: (1) the initiation of several large federal monitoring and assessment programs that emphasize the measurement of water quality in biological rather than solely chemical or physical terms; (2) legal mandates to institute biological criteria into state water quality standards in the next few years; and (3) comprehensive assessment of the status of resources throughout the Columbia River Basin and how to manage these resources. These directives and comprehensive programs at the state and national levels will severely overload existing resource management personnel, a situation that is unlikely to be alleviated at the current rate of qualified graduates entering the work force. Federal Monitoring and Assessment Specific federal programs of monitoring and assessment have been instituted by the Environmental Protection Agency (EPA) and the U.S. Geological Survey (USGS). Presumably, the newly instituted National Biological Service (NBS) also will emphasize biological assessments through wetland surveys, inventories of biological resources, and the like, unless these responsibilities are abrogated by the new Congress. At the moment, the premier U.S. federal program involving bioassessment is the National Water Quality Assessment (NAWQA) Program of the USGS (Gurtz, 1994). This program is designed to integrate chemical, physical, and biological data to assess the status of, and trends in, national water quality. It consists of 60 study units (major river basins and large aquifers) located throughout the country (Gurtz, 1994) that represent
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology major natural and human-impacted conditions that influence water quality. Data collection began in 1991. Biological data include (1) analysis of aquatic organism tissues for a wide array of chemical contaminants; (2) characterizations of algal, macroinvertebrate, and fish communities; and (3) characterizations of vegetation growing in and along streams. Physical data include streamflow and characterizations of in-stream, bank, and floodplain habitats (Meador and Gurtz, 1994). NAWQA has developed nationally consistent biological sampling methods so that results are comparable across different river basins and geographic regions. The Environmental Monitoring and Assessment Program (EMAP) of the EPA has comparable goals, but it uses a more extensive set of sampling sites, including lakes and wetlands (Hunsaker et al., 1990; Paulsen et al., 1991). This program has spent much time developing its philosophical and conceptual underpinnings and has lagged behind NAWQA in making available a standard set of methods and in initiating a full-fledged data collection program. However, a series of pilot studies focusing on lakes was conducted in 1991 (Larsen and Christie, 1993). An Intergovernmental Task Force on Monitoring Water Quality led by representatives of NAWQA and EMAP (Gurtz and Muir, 1994) is working to develop a national water quality survey that would demonstrate effective collaboration among federal agencies. This group has chosen to focus on biological aspects of water quality to better understand the condition of the nation's stream communities and to identify opportunities and barriers to cooperative partnerships (M. Gurtz, USGS, personal communication, 1994). The national survey will initially aim to characterize reference conditions, but the long-term goal is to include all streams regardless of their condition. The Clean Water Act mandates state development of criteria to measure water quality conditions based on biological assessments of natural ecosystems. The general authority for biological criteria comes from Section 101, which establishes as the objective of the act the restoration and maintenance of the chemical, physical, and biological integrity of the nation's waters. This section also includes an interim water quality goal for the protection and propagation of fish, shellfish, and wildlife. Propagation includes the full range of biological conditions necessary to support reproducing populations of all forms of aquatic life and other life that depend on aquatic systems (EPA, 1990). Sections 303 and 304 provide specific directives for the development of biological criteria. Section 303 requires states to adopt protective water quality standards that consist of uses, criteria, and antidegradation measures. Section 303(c)(2)(B), enacted in 1987, requires states to adopt numerical criteria for toxic pollutants specified by EPA. The section further requires that states adopt criteria based on biological assessment and monitoring methods, consistent with information published by EPA under Section 304(a)(B). Section 304 directs
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology EPA to develop and publish water quality criteria and information on methods for measuring water quality, including biological monitoring and assessment methods to determine (1) the effects of pollutants on aquatic community components (e.g., plants, plankton, fish) and community attributes (e.g., diversity, productivity, stability) in any body of water, and (2) the factors necessary to restore and maintain the ecological integrity of all navigable waters (EPA, 1990). Development and use of biological criteria also will help states to meet the intent of several other legislative acts that require an assessment of risk to the environment (including resident aquatic communities) to determine the need for regulatory action (EPA, 1990). Some examples of the latter are the Comprehensive Environmental Response, Compensation, and Liability Act of 1980; the Federal Land Policy and Management Act of 1976; the Fish and Wildlife Conservation Act of 1980; NEPA; the Resource Conservation and Recovery Act first enacted in 1976; and the Wild and Scenic Rivers Act passed in 1968. Under the Clean Water Act, states were required to begin instituting narrative biological criteria into state water quality standards during 1991-1993; numeric criteria and full implementation are scheduled to occur within a few years (EPA, 1990). These requirements also apply to federal agencies responsible for the management of large tracts of public land (e.g., the U.S. Forest Service and Bureau of Land Management), especially in the western United States. Narrative biological criteria are general definable statements of conditions or attainable goals of biological integrity and water quality for a given use designation; numeric criteria establish specific values based on measures such as species richness, presence or absence of indicator taxa (taxonomically related groups), and trophic composition. Need for Cooperation Among Federal Agencies A good example of cooperation among federal agencies in addressing these aspects using biological assessment is the cooperative survey of the Apalachicola-Chattachoochee-Flint River Basin recently initiated by NAWQA and the NBS (NAWQA Information Sheet, April 6, 1994). This river basin, one of the largest in the eastern Gulf Coast Plain, was known for its rich diversity of at least 45 species of unionid mussels, but these populations have either declined or died out. Mussels are sensitive indicators because they are sessile and are dependent on good water quality, physical habitat conditions, and populations of host fish. The life cycle of unionid mussels is closely linked to fish because mussel larvae are obligate parasites on fish before becoming free-living adults. Conservation efforts to protect or restore declining mussel populations require information on both mussel and fish populations in watersheds with differing
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology land uses and water quality conditions. The NAWQA program, with its interest in monitoring water quality, and the NBS program, with its interest in identifying and protecting populations of aquatic organisms, both require information on the distribution and abundance of aquatic organisms in different environmental settings. Recent awareness of the rapidly declining status of 76 anadromous fish stocks in the Columbia River Basin (Nehlsen et al., 1992), together with documentation of declining freshwater habitat conditions (Sedell and Everest, 1991), has resulted in intensive efforts by several federal agencies to head off potential extensive curtailment of their resource extraction activities throughout the entire river catchment. Of immediate concern is the fact that protections offered for threatened and endangered fish under the ESA could result in severe curtailment or alteration of U.S. Forest Service and Bureau of Land Management activities. Ideally, improved management of aquatic and riparian ecosystems on lands administered by these two agencies, combined with improvements in hydropower operations, hatchery practices, and fish harvest management, can prevent additional stocks from becoming extinct and preclude the need to extend the protections of the Endangered Species Act to other at-risk anadromous fish stocks (U.S. Forest Service-U.S. Bureau of Land Management, 1994). In addition, both agencies are required by the Clean Water Act of 1976 (33 USC 1251, 1329) to ensure that activities occurring on lands they administer comply with requirements concerning the discharge or runoff of pollutants. A reasoned response to this new information on serious declines in anadromous fish stocks and aquatic habitat conditions is crucial to the two agencies' success in meeting the "continuing compliance" obligations of NEPA, ESA, the National Forest Management Act of 1976 (NFMA), the Federal Land Policy and Management Act of 1976 (FLPMA), and other environmental laws. By using the latest scientific information on chemical, physical, and biological integrity, the agencies will be better able to ensure the long-term viability of anadromous fish species and the continuing production of goods and services from public lands. Interim and longer-term management strategies are being examined in several geographically specific environmental impact statements as required under NEPA; also under development is a comprehensive ecosystem management plan for the interior Columbia River Basin (Science Integration Team, 1994). STRESSES ON BIOLOGICAL HEALTH OF INLAND WATERS The biological integrity of inland aquatic ecosystems is being assaulted in many ways (Power et al., 1988; Resh et al., 1988; Covich, 1993). Numerous
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology anthropogenic disturbances affect inland waters and their associated riparian ecosystems: Livestock grazing contributes to increased inorganic sediments, nutrients, and organic matter; breakdown of stream banks; and removal of riparian vegetation. Forestry and logging practices, including extensive road building, introduce sediments and logging slash; remove large woody debris; increase runoff and streambed scour; and erode stream banks. Agricultural practices add sediments, nutrients, and toxicants; deplete streams through irrigation withdrawal; channelize streams; drain wetlands; and destroy riparian habitats. Pesticides applied to forest and agriculture lands often reach waterways. Mining and smelting operations release heavy metals and other poisonous substances to water bodies via surface, subsurface, and aerial pathways. Urban usage removes water for domestic consumption; adds sewage and many complex household and other chemicals; converts stream channels into concrete-lined gutters; and contributes fertilizers, herbicides, and pesticides. Manufacturing and processing operations release chemicals and heated water and, along with motorized vehicles, contribute airborne pollutants that reach waterways. Fish management practices use poisons to remove unwanted species and introduce exotic species. Impoundment for flood control, electric power generation, navigation, and recreation drowns rivers, changes flow patterns, alters nutrient and sediment loads and temperatures, and thereby destroys the habitat and impedes or blocks the movement of native aquatic fauna. Diking, channelization, and removal of woody debris for navigation, flow "enhancement," flood control, or fish passage all speed up the flow of water; destroy habitat; disrupt in-stream processing of organic matter and nutrients; and prevent interchange of nutrients, organic matter, and sediments within the riparian environment. Production of electricity by coal-fired or nuclear reactor steam plants depletes water by evaporation and by diversion from natural water bodies and may increase temperature, trace elements, and other chemicals. Nutrients from many of the above activities, particularly nitrogen and phosphorus, cause the accelerated enrichment (cultural eutrophication) of lakes and streams. This can result in large-scale fish kills and the elimination of desirable fish species, production of foul odors, uncontrolled growth of algae and toxic bacteria, and obnoxious accumulations of filamentous algae and vascular plants. Not only do these activities affect the ecological integrity of inland
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology aquatic ecosystems, but the effects of each type of disturbance may be synergistic among types and cumulative in space and/or time (Sidle, 1990). Although viewed as relatively local, they often have large-scale, far-reaching effects. Some large-scale stresses affecting aquatic ecosystems, whether natural or human induced, are rapid and dramatic. Examples include certain recent cases of massive deforestation, urbanization, development of crop- and pasturelands, forest fires, plant disease outbreaks, and insect infestations. Other disturbances occur over extended periods of time and, hence, often are not recognized as such until the situation becomes extremely difficult or impossible to reverse. These include acidification, some types of logging and mining, livestock grazing, fire suppression, irrigation, and potentially, global climate change (Minshall, 1992, 1993; Covich, 1993). Global climate change could profoundly alter riparian ecosystems through its effect on terrestrial vegetation, thermal and hydrologic regimes, nutrient cycles, and so on (Firth and Fisher, 1992). Fast or slow, disturbances of riparian ecosystems may result in changes in water temperature or runoff, channel straightening, scouring or sedimentation, loss of physical habitat, alteration of food base, and waterlogging or drying of riparian soils. Challenges of Assessing Biological Integrity Although legislation calls for maintaining biological integrity, measuring the biological health of inland waters is extremely complex; this complexity results not only from the need to account for natural variations in time and space, but also from the need to consider individual species as well as interactions among organisms in a particular aquatic community. Importance of Scale (Space and Time) There is no single correct scale for the study, assessment, or management of aquatic-riparian ecosystems (O'Neill et al., 1986; Levin, 1992; Johnson et al., 1993); rather, the appropriate scale depends on the scientific question or management problem being addressed. The importance of various environmental factors and the interpretation of measurements taken on aquatic ecosystems vary with scale (O'Neill et al., 1986; Minshall, 1988). Further, since ecosystem boundaries vary with scale, the spatial boundaries also must be correlated with the temporal framework appropriate for a particular disturbance (O'Neill et al., 1986). Most ecosystems extend over comparatively large areas and persist for long periods of time. It is thus difficult to devise large-scale, single-value measurements of ecosystem integrity. However, the hierarchical structure of ecosystems results in a series of scaled interactions that can act as natural integrators of local processes. For example, measurement of community metabolism of a river segment or lake can serve to integrate the status of
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology conditions from a myriad of spatial patches and compartments within these ecosystems. This natural integration is especially evident at the scale of entire water catchments (King, 1993) where, for example, the ecological health of an entire forest may be reflected in the condition of the stream flowing through it. Use of scales of assessment close to the scale of the entire ecosystem will increase the likelihood that observed changes will be of consequence for the entire ecosystem. These larger-scale integrated measures are invaluable for detecting changes in loss of ecosystem integrity, but they may have to be supplemented with finer-scale measurements to determine cause and effect (King, 1993). For example, measurements of primary production at the level of patches or compartments within river segments or lakes are necessary to determine the relative importance of each and to isolate the specific factors responsible for any differences. In lakes, measurements performed on the plankton are better for lakewide assessments of phosphorus availability, whereas measurements utilizing attached algae such as Cladophora permit more localized assessments (Cairns et al., 1993). As noted above, there is a range of biological information that can be used to evaluate water quality. Studies at the population and community levels of organization emphasize species populations and interactions within and among them, such as competition. In this approach, the physical environment is seen as external to the system of organisms and biotic interactions (King, 1993). Population and community studies emphasize biotic interactions, whereas ecosystem studies focus on the processing and transfer of matter and energy in which the environment is an integral (as opposed to external) part of the system (O'Neill et al., 1986; King, 1993). Study of landscapes commonly addresses patterns of distribution within and among ecosystems, thus generally implying spatial scales of relatively broad extent. Geology, topography, and climate all influence the characteristics of a river basin or watershed ecosystem (e.g., Minshall et al., 1985) and thus act at the scale of the landscape (Omernik, 1987; Hughes and Larsen, 1988). Landscape patterns (such as regional or river basin) influence many ecological phenomena in inland aquatic ecosystems (Hughes et al., 1986; Karr, 1991). For example, streamflow characteristics vary with the type of soils and underlying geology; the topographic relief; and the form, amount, and timing of precipitation. The resulting flow regime in turn influences a variety of ecologically relevant features, including channel form, substratum size composition and stability, woody debris, and the nature of the food base. Patterns of stream discharge and disturbance regimes show a strong geographic separation (Minshall, 1988; Poff and Ward, 1989), implying the operation of landscape-level phenomena. Differences in flow regimes, coupled with climatically mediated thermal characteristics and geologically determined substratum characteristics,
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology In addition to measures of ecosystem processes such as energy flow and nutrient cycling, measurement of functional integrity should include genetic and evolutionary aspects of the biota (Regier, 1993). Biological systems are in continual states of adjustment (adaptation) to their environment and evolve over time. Thus, the scale of their response and the patterns subsequently produced can be expected to be the product of selection by long-term evolution. Failure to address evolutionary aspects adequately has led to major misconceptions regarding ecosystem properties and processes such as succession (Hagen, 1992; Colinvaux, 1993). The dilution, isolation, and extinction of genetic pools are bound to be major problems in inland waters both now and in the future (Noss and Cooper-rider, 1994). Awareness of this problem is just becoming widespread and is restricted mainly to fish and mollusks (Williams and Miller, 1990; Nehlsen et al., 1992; Bogan, 1993), but effects on other aquatic groups are expected to be equally severe (e.g., Zwick, 1992). Methods for measuring these long-term fitness features of ecosystem functional integrity have only recently begun to be developed for freshwater organisms. They are often more difficult to apply to field conditions and require larger numbers of samples than other types of processes because of the sensitive, tedious, and specialized laboratory analyses involved (Funk and Sweeney, 1990; Robinson et al., 1992) or the detailed life history, functional, and behavioral information required (e.g., Resh et al., 1994; Usseglio-Polatera, 1994). Nonetheless, it is important to address genetic and evolutionary components in the assessment of the ecological integrity of inland waters. Two general types of tools are available to do this: (1) those that permit determination of the genetic makeup, particularly the extent of allelic heterozygosity and gene polymorphism, of populations within the ecosystem; and (2) those that assess the occurrence of various measurable traits expected to evolve in particular environments or be selected for under different types and frequencies of environmental stress. Most natural environments are predominantly nonequilibrium, populated by organisms whose populations have relatively high levels of heterozygosity (Hedrick, 1986). Genetic diversity will decline as populations near extinction. Species traits that are likely to contribute to fitness, and hence are likely to be selected for or against under particular environmental conditions, include (1) physiological adaptations to generally unfavorable physical conditions, (2) adaptations for defense, (3) food harvesting and somatic development, (4) reproduction, and (5) tactics for escape in space or time (Southwood, 1988). These traits are postulated to vary in a predictable manner in relation to the degree of stress (adversity) in the environment and the frequency of disturbance or extent of temporal heterogeneity (Southwood, 1977, 1988; Hildrew and Townsend, 1987). Environmental disturbances to which a population has not adapted over evolutionary
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology time may adversely affect its genetic diversity and threaten its long-term survival. Tools that permit determination of the degree of genetic heterozygosity rely on biochemical measures of gene frequencies and polymorphisms. One common biochemical approach is to use gel electrophoresis to identify loci associated with various enzymes (Shaw and Prasad, 1970; Harris and Hopkinson, 1976). The loci are then scored, based on relative distance of the bands from the origin and determinations of allelic frequencies and heterozygosities. Finally, population polymorphisms and population heterozygosities are calculated from the scored loci (Ayala, 1982). Measurement of species traits important to long-term fitness uses relevant morphological, physiological, and behavioral features of a population (e.g., size, body form, reproductive capacity, mode of respiration, dispersal ability, feeding method). This procedure involves the selection of traits, quantification of the extent to which the different life history stages of individual populations possess those traits, derivation of species-trait and species-habitat-type matrices, and evaluation of relationships between the two matrices using appropriate statistical analyses (Doledec and Statzner, 1994; Usseglio-Polatera, 1994). Bioassessment procedures that incorporate multiple measures (metrics) of the responses of population aggregates ("communities") are recommended because different measures are sensitive to different types of water quality impairment. Often individual metric scores are summed in the belief that a collective "signal" is easier to discern than individual ones (Plafkin et al., 1989; Karr, 1991, 1993). However, some of the metrics respond in opposite ways, many are biased toward a particular type of pollution (e.g., organic wastes), and not all types of pollution are represented or adequately determined. Therefore, the common practice of summing the results of individual metrics to obtain a single total score tends to conceal valuable information and to produce equivocal results. Additional work is needed to remove uninformative redundancy and develop metrics specific to different types of degradation. IMPLICATIONS FOR THE FUTURE Modern water science encompasses a broad array of skills and areas of expertise. Future scientists, teachers, and resource managers will need to be broadly trained in these areas. The complexity and magnitude of the questions facing researchers and resource managers will increasingly require an interdisciplinary approach and the ability to work cooperatively. The ecological integrity of inland waters is being assailed on many fronts. Direct assessment of the biota is crucial for the protection and management of aquatic resources. Sound understanding of basic biological
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology (ecological) relationships is prerequisite to sound management (Jumars, 1990; Edmondson, 1993). Several large federal monitoring and assessment programs under development emphasize the measurement of water quality in biological, rather than solely chemical-physical, terms. Consequently, the need for training in systematics, basic biology, and ecology of key groups of inland aquatic flora and fauna (e.g., diatom algae, macroinvertebrates, fish) will increase in the future. Considerations of scale are increasingly a part of the process by which aquatic ecologists approach a variety of ecological issues and problems (King, 1993). The effects of natural and human-caused factors on inland aquatic ecosystems require consideration at multiple spatiotemporal scales that include adequate heterogeneity across landscapes (Covich, 1993). Hierarchy theory commonly is used to address these questions of scale (Allen and Hoekstra, 1992). Thus, ecological integrity will have to address questions of scale and hierarchy; the approach will vary with the particular research question or management problem. However, for the immediate future, the ecosystem and landscape perspectives will be especially important if sustainable biological aquatic resources are to be protected adequately in the face of pressures from the burgeoning human population. Numerous pressing challenges face the future of inland waters, their study, and their management for sustained benefits and uses. Ecosystem, landscape, and global perspectives will be necessary to provide adequate quantity and high-quality water for human use and natural habitats (Covich, 1993). The remaining natural freshwater habitats that have high biodiversity or endemic species should be protected (e.g., Boon, 1992), and degraded waterways should be restored and their natural linkages reestablished. Basinwide planning and management are needed to protect and restore riverine ecosystems and avoid cumulative effects. Agency personnel and the public must be educated on the new strategies and techniques in aquatic ecosystem management and restoration at the catchment and basin levels. Improved funding is necessary for research and education to enhance information, improve skills, and increase the number of personnel to ensure proper management of sustainable inland aquatic ecosystems. Most of the methods being applied to the evaluation of structural and functional attributes of inland aquatic ecosystems have been around for a long time. Although there is much to be said for the use of widely accepted, time-tested approaches, there is also the danger that complacency will lead to lack of needed improvement and innovation. Continued refinement of existing methods is necessary. At the same time, many exciting new developments in biology—including genetic markers; molecular, morphological, and behavioral indicators of exposure to toxic substances; and molecular measures of function—are emerging as fertile
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Freshwater Ecosystems: Revitalizing Educational Programs in Limnology fields for additional research and for application to the understanding and management of inland aquatic ecosystems (e.g., Petersen and Petersen, 1983; Alvarez et al., 1993; O'Brien, 1994). Computer-based geographical information systems, satellite imagery, and remote sensing are providing valuable techniques for addressing both research and management questions at various levels of resolution in the landscape (Osborne and Wiley, 1988; Johnston et al., 1990; Paris, 1992; Richards and Host, 1994). Rapid technological advances in these and other areas such as data logging and wireless transmission, radiotelemetry, geographical positioning systems, acoustical sounding, electronic surveying and distance measurers, and pressure transducers for remote water-level sensing will increasingly provide powerful tools for addressing important questions relating to inland aquatic resources. ACKNOWLEDGMENTS W. T. Edmondson and several committee members (P. Brezonik, E. Gorham, T. Frost, and R. Wetzel) contributed a number of helpful ideas, comments, and references to an early draft of this paper. J. MacDonald is responsible for major improvements in the organization and presentation of the material. J. N. Minshall provided editorial suggestions that improved the presentation. Special recognition is due my colleague C. T. Robinson and graduate students, especially K. N. Myler, T. V. Royer, and E. B. Snyder, for their comments and advice. REFERENCES Allard, M., and G. Moreau. 1986. Leaf decomposition in an experimentally acidified stream channel. Hydrobiologia 139:109–117. Allen, T. F. H., and T. W. Hoekstra. 1992. Toward a Unified Ecology. New York: Columbia University Press. Alvarez, A. J., E. A. Hernandez-Delgado, and G. A. Toranzos. 1993. Advantages and disadvantages of traditional and molecular techniques applied to the detection of pathogens in waters. Water Sci. Technol. 27:253–256. American Public Health Association (APHA). 1989. Standard Methods for the Examination of Water and Wastewater. New York: APHA. Anderson, N. J. 1994. Comparative planktonic diatom biomass responses to lake and catchment disturbance. J. Plankton Res. 16:133–150. Avers, P. E. 1992. Introduction in Taking an Ecological Approach to Management: Proceedings of the National Workshop. Washington, D.C.: U.S. Forest Service, Watershed and Air Management. Ayala, F. J. 1982. Population and Evolutionary Genetics: A Primer. Menlo Park, Calif.: Benjamin/Cummings Publishing Company. Bahls, L. L. 1993. Periphyton Bioassessment Methods for Montana Streams. Helena, Mont.: Department of Health and Environmental Sciences, Water Quality Bureau. Barbour, M. T., J. L. Plafkin, B. P. Bradley, C. G. Graves, and R. W. Wisseman. 1992.
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Representative terms from entire chapter: