The accelerating pace of landscape and climate modification makes predicting watershed vulnerability an important challenge facing 21rst century river conservationists.  River ecosystems are directly dependent on the interaction of climate with landscape physiography and land cover for their characteristic water and material budgets; these in turn shape and constrain biological communities and populations. The Muskegon River Ecological Modeling System (MREMS) links a Land Transformation Model (LTM2) to a series of hydrologic, loading, and biological models via a GIS-based valley segment classification framework.  The result is an open, multi- modeling system capable of exploring alternate land use and climate scenarios, and their resulting impact on hydrology, chemistry, and biological integrity/productivity in a spatially explicit framework.  The system is being used to both better understand and complex stressor-response relationships, and to help regional stakeholders visualize management options and set sub-basin priorities.