The objective of our research is to estimate the effect of agro-environmental policies aimed at mitigating nutrient pollution on the value of freshwater ecosystem services. The specific research activities (RAs) for this project are: (1) link changes in P-related management practices on farm fields to changes in freshwater ecosystem services including fish species composition, fish biomass, and beach quality, (2) link changes in freshwater ecosystem services to changes in the value of these ecosystem services, and (3) use the linked models to simulate the effect of agro-environmental policies and changes in farmer behavior on the value of the modeled freshwater ecosystem services. The policies and farmer behaviors to examine include extrapolating trends in farmer P-use; posited changes in farmer P-use due to other reasons (e.g. changing norms, changing attitudes or changing technologies); the effect of existing conservation programs such as P fertilizer use, cover crops, and conservation tillage; and the effects of soil tests adoption combined with (a) a tax on soil P beyond the recommended level or (b) a watershed-level cap-and-trade program for P beyond the recommended level. Results will help USDA and policy makers better allocate conservation dollars to improve water quality and enhance ecosystem services.