Agriculture in the U.S. Midwest is a major source of nutrients to streams and a significant contributor to the “Dead Zone” in the Gulf of Mexico. Nutrient reduction exchange (NRE) is a conceptual, voluntary framework to improve water quality in which point sources could invest in upstream conservation measures to meet regulated water quality standards at a lower cost. This research develops the scientific framework for a NRE program in Iowa by evaluating agricultural conservation practices for nutrient and flow reduction under variable hydrologic conditions using a physically-based modeling approach.