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Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy
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