While excess nitrogen (N) and phosphorus (P) from anthropogenic activities are known to contribute to the eutrophication of aquatic ecosystems, curbing their inputs poses a management challenge due to poorly understood interactions between land cover, nutrient inputs, and climate. In chapter 1 we examined nutrient inputs, losses, and retention in Minnesota watersheds, across a gradient of environmental variables. Fertilizer inputs were dominant sources of N and P inputs to agricultural watersheds, driving hydrologic losses. Greater runoff decreased retention, suggesting the interactive effects of climate, hydrological modifications, and high nutrient inputs contribute to sustained high hydrologic exports. In chapter 2 we examined the factors controlling concentration-discharge relationships describing P and sediment mobilization in agricultural watersheds in Minnesota. P and sediment were concentrated with greater discharge at most sites. Mean concentrations were elevated by anthropogenic land uses, and bluffs were positively related to particulate concentrations. The mobilization of P is highly sensitive to discharge and its different forms deserve explicit consideration in management strategies.