Ecosystem modeling for evaluation of adaptive management policies in the Grand Canyon

An Adaptive Environmental Assessment and Management workshop process was us ed to assist Grand Canyon scientists and managers in developing conceptual and simulation models for the Colorado ecosystem affected by Glen Canyon Da m. This model examines ecosystem variables and processes at multiple scales in space and time, ranging from feet and hours for benthic algal response to diurnal flow changes, to reaches and decades for sediment storage and dy namics of long-lived native fish species. Its aim is to help screen policy options ranging from changes in hourly variation in flow allowed from Glen Canyon Dam, to major structural changes for restoration of more natural tem perature regimes. It appears that we can make fairly accurate predictions a bout some components of ecosystem response to policy change (e.g., autochth onous primary production, insect communities, riparian vegetation, rainbow trout population), but we are moderately or grossly uncertain about others (e.g., long-term sediment storage, response of native and non-native fishes to physical habitat restoration). Further, we do not believe that existing monitoring programs are adequate to detect responses of native fishes or v egetation to anything short of gross habitat changes. Some experimental man ipulations (such as controlled floods for beach/habitat-building) should pr oceed, but most should await development of better monitoring programs and sound temporal baseline information from those programs.