How much nitrogen and phosphorus is transported to streams?
Nitrogen and phosphorus inputs that are not taken up by plants, immobilized in soil, or lost to the atmosphere through volatilization can be transported to streams. The amount of nitrogen and phosphorus lost per square mile from watersheds to streams—referred to as yields—increases with increasing nutrient inputs regardless of land use, with 5 to 50 percent of nutrient inputs lost from watersheds to streams. Variability in the amount lost can be explained in part by differences in agricultural practices, soils, geology, and hydrology. For example, agricultural lands with 5 percent or more of the watershed in tile drains are 3 times more likely to export more than 25 percent of nitrogen to streams than agricultural lands with less than 5 percent of the watershed in tile drains. Less nitrogen is lost to streams in the Southeast because of greater amounts of denitrification in the soils and shallow groundwater that ultimately discharges to streams. Similarly, less nitrogen is lost to west
