Intergrated Aquatic Ecosystem Restoration
The goal of this chapter is to explain the need to consider proposed restoration projects in their landscape and watershed contexts on a scale appropriate to the needs of affected plant and animal species. Concepts of landscape ecology are useful in this endeavor. In landscape ecology, one studies the influences of the landscape on biotic and abiotic processes. The focus of landscape ecology is on the effects of the landscape's spatial heterogeneity, geometry, and areal extent on ecological processes. Although still a new field, landscape ecology has demonstrated persuasively that both the temporal and the spatial scales of many ecological studies are too small (Karr, 1991). Principles of landscape ecology help to provide theoretical and empirical underpinnings for resource management and other applied sciences (Risser et al., 1984).
Integrated resource management is the term this committee uses to indicate resource management that seeks to restore the structure and function of whole ecosystems by striving to understand and respond holistically to cumulative ecological impacts. The integrated approach to aquatic restoration tries to consider the major ecological interactions in a watershed and seeks to nurture the watershed's restoration to a functioning system, rather than to manage for a single species or for a resource commodity such as game fish.
Lakes, streams, rivers, ponds, ground water, estuaries, and wetlands are interconnected parts of larger landscapes. Stabilization of
lake levels or stream flows may hamper wetland restoration, which depends on variable water levels. Conversely, wetland restoration may increase bird or fish populations in ways that affect stream or lake restoration efforts. In addition to taking such ecosystem interconnections into consideration, aquatic ecosystem restoration also requires that cumulative impacts to ecosystems be considered. Regulating the input of each chemical pollutant to the Great Lakes independently, for example, without considering the chemicals' synergistic and cumulative impacts, is an example of fragmentary management. By contrast, the Great Lakes Water Quality Agreement of 1978 requires signatories to consider the cumulative influence of each chemical, a more integrated approach (NRC/RSC, 1985). However, aquatic ecosystem restoration requires more than water quality management.
Restoration of an aquatic ecosystem requires that the management of all significant ecological elements be coordinated in a comprehensive approach, often on a watershed or other landscape scale. This is a practical approach to resource management. Many state agencies have model watershed programs, and many states have excellent regional planning programs organized by watershed basin, such as the Interstate Commission on the Potomac River Basin and the Tahoe Regional Planning Agency. The U.S. Geological Survey and many state or regional water resource agencies have organized water data by watersheds for years. The Soil Conservation Service's Watershed Program is also concerned with landscape-level processes.
Renewed attention to ecological questions posed on large spatial scales is evident in the science of landscape ecology (Turner, 1987; Dale et al., 1989) and in approaches to population dynamics on continental scales (Brown and Maurer, 1989). More attention to ecological research on large spatial scales is arising from new technological developments in remote sensing and geographic information systems that have expanded research opportunities. Most of this research has dealt with terrestrial systems. However, applications to large, complex freshwater systems include studies of archipelagoes of lakes connected by streams and ground water (Tonn and Magnuson, 1982; Magnuson et al., 1990) and studies of the effects of beaver on extensive lake, stream, and wetland complexes (Naiman et al., 1988). In Europe, where landscape ecology was developed, geographic areas on the scale of 10 to 10,000 km2 were used in studies of water movement patterns and changes in water quality (e.g., Naveh and Lieberman, 1984; Forman and Godron, 1986).
INSTITUTIONAL BARRIERS TO INTEGRATED AQUATIC RESTORATION
Fragmentation of ecosystem management is common in U.S. governmental organizations and in industry. Watershed and political boundaries often overlap. Furthermore, different components of a watershed are usually administered by different agencies. As an example, the International Joint Commission established joint U.S. and Canadian goals for the Great Lakes. However, at the national level in the United States, responsibilities are divided among the U.S. Environmental Protection Agency (EPA; water quality and contaminants) and the Fish and Wildlife Service (animal communities and habitats). Independent water quality managers and fishery managers exist in each of six states (Minnesota, Ohio, New York, Pennsylvania, Michigan, and Wisconsin) bordering the Great Lakes. Important constituencies, such as anglers, environmentalists, and industry, are frequently at odds over basinwide issues such as the effects of organochlorine contaminants. The politics and consensus building required for integrated management of the resource are often as complex as the ecosystem itself.
IMPORTANCE OF INTEGRATED AQUATIC ECOSYSTEM RESTORATION TO WILDLIFE
The amount and timing of water fluctuations and changes in water quality constitute the most important variables limiting the viability of many species of plants and animal populations. For such species, the rate and distribution of environmental change are essential determinants of their survival. Natural succession must be allowed to operate to continue providing diverse landscapes with heterogeneous niches for wildlife, but the tendency of humans is to build static structures (e.g., geographically fixed wildlife refuges and wetlands with immovable borders) that inhibit species' survival.
Some animals exist as subpopulations on patches of aquatic habitat scattered across a watershed. The animals move or migrate to the most favorable sites as the habitat becomes less suitable for them. Subpopulations may become reduced on other patches as the resources there become less usable. This is analogous to ducks moving south to open water as the last pond in their vicinity freezes over. These patches of exploitable habitat, whatever their character, are often the result of natural changes. Changes in landscape should be anticipated to maximize the effectiveness of restoration programs, by recognizing
that restoration or management of one part of a watershed will affect other parts of the aquatic ecosystem.
Natural ecosystems are spatially and temporally dynamic, expanding and shrinking with the prevailing rainfall, stream flow, or tidal regimes. For example, wetlands around the Great Salt Lake are widespread during years of heavy rainfall and runoff; marshes along the Colorado River expand after months of river flooding; prairie potholes expand in size and number during wet years; adjacent lakes that are separate in dry years may merge in wet ones; stagnant waters become flowing with increased runoff. A site designed as a marsh might eventually become a pond or a lake, or vice versa.
Watersheds contain arrays of habitats and sites particularly suitable for certain species. In theory, each site may at some time provide a refuge for a species during a period of stress. The importance of a single site to regional biodiversity is variable-ranging from highly critical during years of restricted habitat to redundant during years of expanded habitat. Marginal (redundant) sites during one set of conditions may be the best or the only sites when conditions change. These sites have often been converted to another habitat and are not available when needed. For many species, opportunistic site use allows them to exist in regions not generally adequate for them. Restoration plans thus must be developed with a landscape perspective-an understanding of how specific sites are related to the remaining resources in the watershed or region.
Restoration of aquatic ecosystems to sustain mobile, migratory, or opportunistic species can be immensely complex. Many of these species select what is the best available habitat at a particular time. Individual plants or animals invade or retreat from sites as a result of changes in their range over time. A site may contain few individuals for long periods of time but may provide an essential refuge for the population during periods of stress.
Migration is a seasonal effort to find optimal habitat. Many desert aquatic species, such as spadefoot toads (Scaphiopus couchi, S. hammondi), appear after rain in normally dry streambeds, where they feed and reproduce. These streams carry water irregularly, and each of the streams in the toads' population range may vary its flood regime independently. The toads have adapted to this scattered multiwatershed system. An effort to provide habitat for this species might require coordination of restoration activities over more than one watershed.
Like the toad, many opportunistic plants exploit ephemeral niches that occur periodically. These plants have multiple reproductive and dispersal adaptations that allow them to spread through the landscape and find appropriate places to exist. Many herbivorous insects
survive by playing a kind of hide-and-seek game within a landscape; they must feed on ephemeral plants before some other herbivores eat the plants and must also try to stay one jump ahead of their predators.
Many declining species-such as the California least tern, the mangrove cuckoo, many frogs and salamanders, and some puddle ducks-are broadly distributed but are rare or threatened at individual sites. These species have evolved to find and use specialized habitat that appears at regionally scattered sites. Regional long-term climate trends and human conversion of these sites have significantly reduced the animals' opportunities to find suitable habitats. A minimum number of sites is needed to maintain a viable population. Most resource management agencies, however, focus on individual sites, rather than on the regional distribution of aquatic types and their summed functions. Future restoration projects would benefit from a large-scale integrated management approach that seeks to help managers understand what attracts and supports mobile species within a target area.
APPROPRIATE SCALE FOR AQUATIC ECOSYSTEM RESTORATION
Gosselink and Lee (1989) discuss the question of the appropriate scale for managing aquatic ecosystems for specific species, focusing on the problem of understanding and evaluating cumulative losses to the ecosystems. They suggest that the area of concern for any given species should be its range. For example, they propose the term duckshed as analogous to watershed for the unit of management for a local population of ducks. A duckshed would include any area where individuals of the population might have to go to survive under the worst conditions, as well as the ecosystem that supports the population. The range may have within its boundaries considerable space that is used regularly by the particular species. Other areas may serve as occasional habitat and still others as refuges in which the species can survive during periods of natural stress. These ''stress shelters" may be of marginal use to the species most of the time, but because these refuge areas appear marginal, they are often not properly protected and are lost. Much of the nation's waterfowl habitat has been lost in this way.
A method that may be useful for planning aquatic ecosystem restoration programs is the Adaptive Environmental Assessment (AEA) approach of Holling (1978) (Walters, 1986). The AEA is a process for involving scientists, resource managers, policy analysts, and decision makers interactively in designing resource management programs.
The focus of AEA workshops is shared responsibility for the development of a simulation model of the system to be managed (e.g., restored). However, the benefits of AEA usually derive from the interactions among participants during the process of model building and not from the model itself (Walters, 1986). The process attempts to take into account, at the earliest stages of the assessment, all relevant social, economic, and environmental considerations, addressing conflicts directly and developing a framework for evaluating trade-offs. The variability and uncertainty common to all environmental systems are explicitly recognized. The key to AEA's success may be its flexibility and lack of prescriptions for problem solving (Holling, 1978).
USE OF HISTORICAL RECORDS IN RECONSTRUCTING WATERSHEDS
To obtain a broad historical perspective on a watershed prior to planning its restoration, one must gather its ecological history, often through the use of old maps, old newspaper articles, and interviews with area residents. Studying available ecological information and correlating it with available historical information suggest how people have changed a watershed over time and what management tools might best accomplish the restorative changes desired.
Geography provides a unifying focus for such studies. By examining original land survey data, early U.S. Geological Survey maps, and early soils maps, experts can develop maps of a watershed's stream flow and land use patterns at various times. Aerial photographs of most watersheds have been available since about 1940, and in some places, aerial photos are available at relatively frequent intervals from 1940 to the present. In the 1970s, remotely sensed satellite photography also became available for many watersheds, to add to the geographic record. Careful study of existing conditions and of the photographic record over time demonstrates changes in land use in watersheds. In general, not enough research support has been available for comprehensive assessments of ecological change in watersheds combined with evaluation of resource policy options there. One exception was the study by Gosselink et al. (1990) concerning the assessment and management of cumulative effects on wetland resources in the Tensas Basin of Arkansas and Louisiana.
The authors examined a wide variety of existing environmental data about the Tensas watershed and then mapped those that had geographic elements, such as land use, drainage, habitat value, and the distribution of plant communities. Bears are the largest animal
species in the area and require a large home range to survive. The study chose this home range as the minimum useful unit of the landscape to acquire. Gosselink et al. (1990) scanned the watershed for areas of restorable and available "bearshed"-sized property to acquire. They also looked for bearsheds that connected larger already protected habitat units. Their recommendations, if followed, will greatly increase the habitat value of the entire watershed. This EPA sponsored study did bridge the gap between assessing ecological conditions and making policy recommendations, by setting priorities for land acquisition.
Interpretation of Historical Data for Restoration Purposes
Resource maps for various time periods show the geographical array of resources and suggest patterns of change. Existing hydrological and ecological models then can be used to describe the processes that link resources dynamically in the landscape. By understanding these processes well enough, scientists can show the general outcomes of various potential management policies so that decision makers are able to compare these outcomes critically.
Many states and water basins have resource maps and historical records currently available. These records can serve as inputs to a geographical information system (GIS) data base so that a wide variety of parameters can be examined simultaneously. Sets of related data when superimposed on a GIS map often reveal opportunities for restoring aquatic ecosystem so as to maximize a number of functions, such as reduction of flood damage, erosion control, habitat for species of concern, and water quality improvement. In some areas, sufficient data have been accumulated to approach landscape-scale watershed restoration planning. Other areas may lack even organized inventories of resources or planning capabilities. The EPA has attempted to develop advanced identification systems in some regions to establish wetland restoration priorities. However, the committee knows of no region, watershed, or state that has used its full resource planning capabilities to designate restoration priorities.
Wherever possible, decisions about the management and restoration of aquatic resources throughout the United States should not be made on a small-scale, short-term, site-by-site basis, but should instead be made to promote the long-term sustainability of all aquatic
resources in the landscape. Whereas restoration on the large landscape scale is therefore definitely preferable to piecemeal restoration, small restoration efforts are not necessarily worthless or ineffective. Success in recreating a self-sustaining ecosystem is more likely, however, when the restoration is planned within the context of the target ecosystem's larger landscape. Nonetheless, any shift of a damaged ecosystem to a superior ecological condition is preferable to allowing the system to remain damaged or to suffer further degradation. Restoration efforts should not be postponed by those using the complexity of a landscape-scale restoration as a rationale for inaction.
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