WATER QUALITY DEGRADATION AND ALGAL BLOOMS CONTINUE TO CREATE CONCERNS IN THE GREAT LAKES REGION. FEDERALLY-SPONSORED CONSERVATION POLICIES HAVE INCENTIVIZED FARMERS TO ADOPT BEST MANAGEMENT PRACTICES FOR DECADES, BUT THEIR IMPACT REMAINS LIMITED. CHANGES IN PHOSPHORUS (P)- RELATED MANAGEMENT PRACTICES ON FARMS AFFECT FRESHWATER ECOSYSTEM SERVICES, HOWEVER THERE HAS BEEN LIMITED SYSTEMS-BASED SCIENCE TO QUANTIFY FEEDBACKS BETWEEN POLICY EFFECTS ON ECOSYSTEM SERVICES AND ECONOMICS.THE OVERALL OBJECTIVE OF OUR RESEARCH IS TO INTEGRATE ECONOMIC AND BIOPHYSICAL MODELS TO EVALUATE THE EFFECT THAT AGRI-ENVIRONMENTAL POLICIES HAVE ON THE VALUE OF FRESHWATER ECOSYSTEM SERVICES. THE SPECIFIC RESEARCH ACTIVITIES FOR THIS PROJECT ARE: (1) LINK CHANGES IN P-RELATED MANAGEMENT PRACTICES ON FARM FIELDS TO CHANGES IN THE VALUE OF FRESHWATER KEY ECOSYSTEM SERVICES INCLUDING FISH SPECIES COMPOSITION, FISH BIOMASS, AND BEACH QUALITY, AND (2) USE THE LINKED MODELS TO EVALUATE THE EFFECT OF AGRI-ENVIRONMENTAL POLICIES AND CHANGES IN FARMER BEHAVIOR ON THE VALUE OF THESE FRESHWATER ECOSYSTEM SERVICES.WE WILL EXAMINE THE EFFECTS OF HISTORICAL AND NEW CONSERVATION PROGRAMS ON ECOSYSTEM SERVICES AND VALUATION. HISTORICAL PROGRAMS INCLUDE P FERTILIZER USE, COVER CROPS, AND CONSERVATION TILLAGE; WHILE NEW POLICIES INCLUDE EFFECTS OF SOIL TEST ADOPTION WITH (A) RESTRICTIONS ON P APPLICATION BEYOND RECOMMENDED LEVELS OR (B) A TAX ON SOIL P BEYOND RECOMMENDED LEVELS. RESULTS WILL HELP THE USDA AND POLICY MAKERS BETTER ALLOCATE CONSERVATION DOLLARS TO IMPROVE WATER QUALITY, ENHANCE ECOSYSTEM SERVICES, AND PROMOTE MORE-SUSTAINABLE AGRICULTURAL PRODUCTION.??