Can the NAWQA assessment help to predict total nitrogen concentrations in un-sampled streams?
The results of two linear regression statistical models—one for agriculturally influenced streams (watershed that contain greater than 25 percent agricultural land) and one for nonagricultural streams (watershed that contain less than 25 percent agricultural land)—were aggregated to predict the total nitrogen concentrations in streams across the conterminous U.S. Model results for streams predict that the highest total nitrogen concentrations are in areas with the highest nonpoint source nitrogen inputs, such as agricultural areas in the upper Midwest and selected coastal areas of California. The lowest concentrations are predicted in the mountainous regions of the West, the Appalachians, and the northern parts of New England. Simulated concentration for much of the country is less than 5 mg/L and for major sections is less than 1 mg/L.
