Sustaining Our Water Resources (1993)

Judy L. Meyer

University of Georgia

Athens, Georgia

Ecological concepts underlying management of water resources have shifted from a deterministic world view based on balance of nature to a recognition that natural systems are inherently variable, patchy, and often require disturbance to persist. Recognition of the interdependency of ecosystem components and the importance of indirect effects also has management implications. Applying these ecological concepts dictates (1) management in the context of the ecosystem rather than managing parts as though they were in isolation and (2) use of an adaptive management scheme that is responsive to changing environmental conditions. Over the past decade committees of the Water Science and Technology Board (WSTB) have reached similar conclusions concerning water resource management. A management challenge to future research in ecology is to provide the conceptual basis for sustaining and restoring the ecological integrity of the earth's aquatic resources.

Approaches to management of water resource systems change because of shifts in societal attitudes and institutions, as described in other papers in this volume. Management approaches also change as a consequence of advances in our scientific understanding, and it is this aspect of changes in system management that is the focus of my paper. Water resource management is grounded in numerous scientific disciplines; I focus on changes in only one of those disciplines, ecology. Inclusion of a paper dealing with ecological issues in this program is in itself an indication of the developments that have taken place in water resource management over the past couple of decades. Technology-based science has always been a strong part of the education of

water resource managers. A recognition of the need for ecological expertise has come about as managers have confronted the environmental consequences of water management decisions and as the nature of water resource problems has changed, for example, from point-source discharges to nonpoint source pollution.

In this paper I focus on two ecological concepts, discuss some recent developments in ecological thought relating to those concepts, consider the management implications of these developments, and end with a discussion of future challenges for ecology.

The first concept is one that is as much philosophical as ecological—''the balance of nature." Over the past 50 years, ecologists have gradually come to recognize that nature is not always in balance. Tansley (1935) defined the ecosystem concept and wrote: "In an ecosystem the organisms and the inorganic factors alike are components which are in relatively stable dynamic equilibrium. Succession and development are instances of the universal processes tending toward the creation of each equilibrated system." Lindeman (1942) introduced the concept of trophic levels to ecology in his study of a Minnesota lake. He wrote: "From the trophic-dynamic viewpoint, succession is the process of development in an ecosystem ... towards a relatively stable condition of equilibrium." These early thinkers in the field of ecology conceived of an ideal system that was at equilibrium, and although natural systems were perhaps imperfect versions of that ideal, their goal as ecologists was to find the mechanisms that worked to keep the system stable. This view has changed as knowledge accumulated from fields such as paleoecology. Studies demonstrated that climate varies over all time scales and that vegetation is continuously responding to these shifts. The view has changed to one that recognizes that natural systems are in a state of flux. An ecosystem is viewed as a dynamic mosaic of patches changing in different temporal patterns.

In his book Discordant Harmonies, Botkin (1990) traces the changes in human perception of nature that underlie our approach to science. He notes that we have moved from perceiving nature as ordered, regular, and stable to a perception of change as a natural and necessary part of the biosphere. He follows the development of scientific thought from a view of a divinely ordered, perfect, and unchanging nature to that of the earth as a complicated machine operating at steady state to today's more "organic" image with a focus

on processes, a recognition that change is inevitable and that ''nature is characterized by chance and randomness" (Botkin, 1990, p. 129). This nonequilibrium paradigm is widely accepted today.

One characteristic of a nonequilibrium paradigm is a recognition of the importance of disturbance in the ecosystem. Stream ecosystems are particularly dependent on natural disturbances such as flooding (e.g., Resh et el., 1988). The biological community is dependent on natural disturbance to shape the channel and create habitat, to provide inputs of resources, and to alter the numbers of predators and competitors. Without natural disturbance, for example, when stream flow is regulated, all aspects of the stream ecosystem change. The removal of floods from an ecosystem is a greater ecological disturbance than the floods.

Other characteristics of a nonequilibrium paradigm include a recognition of priority effects, such as which species happens to arrive first at a site, and a recognition of the importance of time lags. Ecosystem function measured today may be influenced by a policy or fashion in effect a hundred years ago. Consider, for example, beavers.

Long before humans began building dams, beavers were major agents for channel modification throughout much of North America. The activities of beavers greatly alter stream ecosystem function, increasing retentiveness, increasing anaerobic processes, and lengthening the turnover time of material in the streams (Naiman et el., 1988). Before the arrival of Europeans in North America, the beaver population was estimated to be 60 million to 400 million individuals, with a geographic range from the arctic to northern Mexico. Extensive removal began in the early seventeenth century largely to serve the whims of fashion. By 1900 beavers were almost extinct, and today their population is somewhere between 1 and 20 percent of their original population. Important attributes of stream ecosystem function were changed by beaver removal long before stream ecologists began any studies, and hence our understanding of stream ecosystems is derived from sites that lack the influence of an ecologically important species. As beaver populations recover, stream ecosystem function will be continuously changing as beavers alter channel morphology and hence organic matter storage. This is a very slow process, and this legacy of beaver removal will continue to alter the pattern of change in both terrestrial and aquatic systems.

A final aspect of the nonequilibrium paradigm that I will discuss is that ecosystems are viewed as dynamic patches that are changing in character of function on different time scales. This leads researchers to study not only processes within patches but also the connectivity between patches and the often accelerated activity at the interface between patches. Taking this approach in a blackwater riverine system, my colleagues and I have studied

food webs and organic matter dynamics in the water column, sandy main channel sites, muddy backwater areas, woody debris that provides a stable attachment site for organisms, the hyporheic zone (deep within the streambed), and the floodplain (Meyer, 1990). Each of these "patches" has characteristic biotic communities with associated rates of organic matter processing, and each operates on a somewhat different time scale. For example, insects of the shifting sandy sediments have very short generation times, whereas many species on the more stable woody debris have only one generation per year. Each of these "patches" is also linked and interdependent; for example, the filter-feeding insects of the woody debris are dependent on organic matter in the water column for food, and sandy sediments are linked with the highly productive floodplains that provide the detritus that fuels their food web. This view of a river as a network of interconnected habitats is at the base of the river continuum concept (Vannote et al., 1980, Minshall et al., 1985), which has stimulated much recent research in lotic ecology. Our management challenge is to create a bureaucracy that is as interdependent as the natural system it manages.

A second development in ecology with management implications is a recognition of the interdependency of system components and the importance of indirect effects. Ecologists have long recognized the importance of direct effects such as the response of lakes to nutrient additions from municipal wastewater. More recently, we have come to recognize that it is not just these direct and "bottom-up" effects that influence aquatic ecosystems. "Top down" and indirect effects are often equally important; as higher trophic levels are altered, there are clearly discernible effects at lower tropic levels and in other aspects of the ecosystem. This phenomenon is called a ''trophic cascade" (e.g. Carpenter and Kitchell, 1988).

A study showing how the nature of the fish population in a lake can alter its thermal structure and heat content provides an example of indirect effects in nature (Mazumder et al., 1990). In either enclosures or small lakes (< 10 ha), the presence of planktivorous fish alters the thermal structure of the water column (Figure 6.1). How can this be? Where planktivorous fish are present, herbivorous zooplankton are less abundant, and algal biomass is higher and dominated by small individuals. Smaller algae have greater light absorption and scattering per unit mass, and hence high biomass of small algae is associated with lower water clarity, shallower mixing depth, and lower heat content (Figure 6.1). Where planktivorous fish are rare, herbivorous

Figure 6.1 Mean Secchi depth (vertical lines on left of panel) and temperature profiles during August for lakes with low (Haynes Lake, open symbol) and high (Lake St. George, solid symbols) abundance of planktivorous fish. Both lakes had nearly identical temperature profiles in May. Heat content of Haynes Lake during August was 12.3 kilocalories/cm² and that of Lake St. George was 8.6 kilocalories/cm². Redrawn from Mazumder et al. (1990).

zooplankton are abundant, algal biomass is lower with proportionally fewer small individuals, water clarity is greater, heat content is higher, and mixing depth is greater. Here is a case where the presence of a higher trophic level (a fish that eats zooplankton) has a direct effect on its prey, and a series of indirect effects on lower trophic levels and on the thermal structure of the

lake. Instead of temperature affecting biology, biology is affecting temperature! Ecologists are coming to realize that indirect effects such as this are the rule rather than the exception in ecosystems.

Although the importance of indirect effects is clear, one should not use that to justify the simplistic statement that everything is intimately related to everything else. Some relationships are stronger than others, and it is the role of the ecologist to identify the strong relationships (i.e., to determine the critical features of ecosystem structure) so that the system can be managed more wisely.

What are the management implications of these two shifts in ecological thinking? Put very simply, it means we must manage for change and for complexity (Botkin, 1990).

In ecological research, adoption of a nonequilibrium paradigm has resulted in a shift from a search for an endpoint to a focus on process and trajectory, with a recognition of the openness of ecosystems and the importance of disturbance. Adoption of a nonequilibrium paradigm in management will result in a similar shift as we begin to manage for change, applying management strategies designed to achieve acceptable limits of change.

One example of management for change comes from forestry. For decades forest management agencies prevented fire, seeing it as a disturbance that disrupted the stable climax forest they were trying to preserve. It soon became apparent that this was not an appropriate strategy. In sequoia forests, for example, there were few sequoia seedlings, and the understory was becoming dominated by white fir (Botkin, 1990). Rather than threatening the future of the sequoia forest, fire was necessary for successful sequoia germination and growth. Rather than being evil, fire is a necessary disturbance and an important management tool in many ecosystems.

Many aquatic ecosystems are also dependent on disturbance. A change in the natural disturbance regime is a major cause of alterations in riverine ecosystems after dam construction. For example, when disturbances caused by variable water discharge, high summer temperatures, and massive sediment transport are removed, the system changes. This has happened below Glen Canyon Dam, and it is one of the issues addressed by the WSTB's Glen Canyon Environmental Studies (GCES) (NRC, 1987) committee. Since dam construction, flood flows and sediment transport have been reduced, resulting in depletion of sand stored in the active channel (Andrews, 1991). Because of stabilized flows, a larger riparian area remains moist, and the riparian zone has

expanded and been invaded by several exotic species, including salt cedar or tamarisk (Tamarisk chinensis), camelthorn (Alhagi camelorum ), and Russian olive (Elaeagnus angustifolia) (Johnson, 1991). Release of cool, sediment-poor but nutrient-rich water from Lake Powell leads to high biomass of algae (Cladophora) and invertebrates in the river (Stanford and Ward, 1991). The continued existence of the native fishes is threatened by the altered thermal environment but more critically by the introduction of nonnative species that are able to thrive in the new environment created by the dam (Minckley, 1991). Native fishes are also failing to reproduce because of the absence of large seasonal changes in water level, which synchronized their breeding cycles (Minckley and Deacon, 1991). Clearly, reservoir operations that have altered the natural disturbance regime have had an effect on many components of the downstream ecosystem.

How might one manage for change in this situation? The NRC committee has advocated adaptive management (NRC, 1991a). This includes incorporating environmental dimensions into decisions on dam operation, operating the dam in an experimental mode in which different release schedules are followed to assess their effect on downstream ecosystems as well as on power generation, and ongoing scientific assessment of the downstream ecosystem to provide continued guidance to dam operators. The combination of introducing environmental dimensions at the beginning of the process, using experiments to assess ecological consequences of management activities, and continued dialogue between scientists and managers to evaluate policies in the face of a variable environment are at the core of adaptive management (Holling, 1976). The idea of adaptive management grew from a recognition of basic properties of ecological systems, which include "the unexpected can be expected" and "environmental quality is not achieved by eliminating change" (Holling, 1976). Clearly, this is managing for change.

An additional component of management for change is managing in a probabilistic and risk assessment framework in which one recognizes the inherent unpredictability of nature: in a variable world there is a finite risk of extinction (Botkin, 1990). This is particularly appropriate for managing populations of rare species (e.g., desert pupfishes) but also applies to managing a fisheries resource. Rather than determining a fixed sustainable yield, the manager recognizes that the yield should vary over time as environmental conditions vary. In the long term this produces a more sustainable yield. This type of management requires greater input of scientific understanding and continued monitoring than is currently practiced.

How do we manage for complexity? The obvious answer, given by numerous WSTB committees (e.g., NRC, 1991a), is to manage in an ecosystem context. Rather than managing for a single resource (board feet of lumber or acre feet of water), we should manage to sustain the diversity of services provided by the ecosystem with a recognition of the complex interactions and numerous indirect effects that characterize ecological systems.

An example of an attempt at this type of management is offered by the U.S. Forest Service's (USFS) New Perspectives program, now called the Ecosystem Management program (Kessler et al., 1992). This program "involves a shift in management focus from sustaining yields of competing resource outputs to sustaining ecosystems" (Kessler et al., 1992). Earlier practices of multiple use implied that different pieces of the landscape could be set aside for different uses, which ignores the fact that the landscape is interconnected and cannot be managed as individual pieces. One of the documents stimulating this change is Forestry Research: A Mandate for Change (NRC, 1990). It proposes a research and management paradigm using an ecosystem approach that views the landscape as a living system with "importance beyond traditional commodity and amenity uses" (Kessler et al., 1992). Ecosystem management recognizes that: "If it is the entire system and its continued productivity for a wide array of uses and values that we desire, then production goals for individual resources ... might not point a path toward sustainability. We need instead objectives that relate to ecological and aesthetic conditions of the land ... and that sustain land uses and resources yields compatible with those conditions" (Kessler et al., 1992). As expressed by Salwasser (1990 in Swanson and Franklin, 1992), forestry practice has evolved from regulating uses (i.e., avoiding undesirable activities), to sustained yield management that focuses on a few desired products, to sustainable ecosystem management, which considers the well-being of the ecosystem that provides numerous goods and services.

I have been involved in the planning for an ecosystem management project in a national forest in North Carolina. I offer the following partial list of desired future conditions that are guiding watershed management as an example of how this new perspective could alter management of lands that in decades past have been managed primarily to meet a specified timber yield:

• populations of native fish species that equal or exceed current levels,

• maintenance of a diversity of stream productivity levels to maintain diverse gene pools of aquatic species, and

• stream sedimentation rates that maintain and/or enhance baseline fish reproduction and growth rates.

Ecosystem management is a very young program, and we do not know how well it will be implemented by land managers. It is a program with considerable promise. Clearly, the tasks of future WSTB committees would be very different if other federal agencies truly adopted a "new perspective" for land and water management.

The need for a new perspective in a larger landscape context on federal lands becomes particularly apparent when one considers declining biodiversity. Federal lands offer a rare opportunity to include maintenance of biodiversity as a management objective; 26 threatened or endangered invertebrate species live on USFS lands, and 69 percent of the fish species listed as threatened or endangered occur on USFS or Bureau of Land Management lands, which include 453,000 kilometers of permanent streams and 2.6 million hectares of lakes and reservoirs (Williams and Rinne, 1992). Ecosystem management in a landscape context will be necessary to maintain this national trust of biodiversity.

Another example of ecosystem management comes from the Pacific Northwest and involves management of the riparian zone. In past decades, riparian management objectives in the West have focused on controlling stream temperatures and limiting sediment input to meet water quality goals while still harvesting timber. Ecological research has shown that the riparian zone provides habitat and food resources for fish and other wildlife, provides channel structures (most important, woody debris) that modify the retentiveness of stream channels, and modifies light and nutrient availability in streams (e.g., Gregory et al., 1991). The interaction between forest and stream varies depending on the geomorphic setting of the channel; for example, wide unconstrained valleys offer more habitat and food resources for fish than do constrained valleys, but their channels also show greater lateral movement (Swanson and Franklin, 1992). This ecological understanding has been used to develop a riparian management plan based on an ecological definition of the riparian zone that permits management to achieve specific objectives (Gregory and Ashkenas, 1990). For example, to ensure sustainable salmonid populations, wider forested zones are recommended in unconstrained reaches in wide valley floors where lateral movement of the channel is more likely. The goals of basin planning are "to minimize the potential for cumulative effects, maintain potential inputs of woody debris, maintain continuous riparian corridors with structurally complex plant communities throughout the basin, and rehabilitate degraded riparian resources within the basin" (Gregory and Ashkenas, 1990). This is ecosystem management in a landscape context.

It exemplifies the type of management needed in a greater array of ecosystem types.

The need for ecosystem management that recognizes the complexity and patchy nature of the landscape is particularly apparent in the current controversy over wetlands (e.g., Alper, 1992). A functioning wetland consists of interconnected habitats with different inundation frequencies; some patches may not be wet every year. It is a patchy and dynamic landscape that will require a level of complexity in regulation that has not been characteristic of U.S. wetlands policy to date. This is a problem that the WSTB will be tackling in its second decade.

The current challenge for ecology is "to integrate and synthesize the ecological information available from all levels of inquiry into an understanding that is meaningful and useful to managers and decision makers" (Likens, 1992). The extent to which we take an interdisciplinary approach to ecology will dictate the extent to which we will be able to meet that challenge. Ecology is sometimes viewed as a biological science that studies the distribution and abundance of organisms. This is an outmoded view of ecology and one that does not serve the needs of our time.

Ecology is an integrative science that investigates the linkages among and between biotic and abiotic components of the environment. The Sustainable Biosphere Initiative, a recent visionary document produced by the Ecological Society of America (Lubchenco et al., 1991) is based on this view of ecology as an integrative science and recognizes the need for an integrated multidisciplinary approach to solving environmental problems. This offers a challenge to educators as well as researchers and managers. The recent WSTB volume Opportunities in Hydrologic Sciences (NRC, 1991b) provides suggestions on ways to achieve an integrated approach. Studies currently being contemplated by the WSTB on the science of inland aquatic ecosystems could provide further guidance in this area.

Current problems in water resource management offer numerous challenges to the ecologist. With the concern over salmon stocks and similar issues in the news, water managers recognize that water is not simply a commodity to be managed to meet established quantity and quality criteria. Water is a living resource. One challenge for ecologists is to use that fact to develop better ecological indicators of water quality that rely on the living communities of water to provide information on the ecological integrity of the aquatic ecosystem. One such index based on fish communities in running

waters has been successfully used in North America (Karr, 1991). More such indices are needed based on different taxa and different ecological attributes of the system. The water manager needs a palette of available ecological indices from which to choose. This offers a direct research challenge to the community of ecologists.

A final research challenge for ecologists is provided by the need to restore aquatic ecosystems, so well documented by the recent WSTB report Restoration of Aquatic Ecosystems (NRC, 1992). As human assaults on natural systems have accelerated over the past decade, so has the need for a more holistic concept of system management that has the goal of maintaining and restoring the ecological integrity of the resource rather than simply preserving water quantity or quality. Restoration offers exciting challenges to ecologists by providing a real-world testing of ecological theories on how ecosystems are structured. Restoration of damaged ecosystems based on sound ecological principles is really one part of a larger discipline, ecological engineering. Its practitioners seek to use insight from applied and theoretical ecological studies to develop self-designing and self-sustaining ecosystems to solve environmental problems (Mitch and Jorgensen, 1989). These ecosystems are supported by solar energy and require lower inputs of nonrenewable resources. Understanding gained from this work should stimulate further developments in the fundamental ecological sciences. Examples of this approach include use of wetlands to treat acid mine drainage or wastewater and use of water hyacinth beds or a Phragmites-filled lagoon to treat wastewater (case studies in Mitch and Jorgensen, 1989). In several of these examples a useful product (e.g., water hyacinth for forage) is harvested from the engineered ecosystem, making it economically more appealing. Fundamental ecological research is needed for optimal construction, biotic composition, and operation of such engineered ecosystems. A greater emphasis needs to be placed on the use of native species instead of relying on imported exotics that pose a threat if they escape.

In this paper I have discussed some management implications of advances in ecological thinking with respect to the balance of nature and the importance of indirect effects. A third development that bears mentioning in conclusion is recognition of the global nature of ecological science. The human species currently uses, coopts, or destroys nearly 40 percent of the terrestrial net primary productivity of the planet (Vitousek et al., 1986). We have altered the hydrologic cycle as well as cycles of most elements; human activities seem to be affecting climate; biodiversity is declining rapidly. Events such as these require scientists and managers alike to think on a global scale. In one sense or another, we all live downstream.

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