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).