Can the NAWQA assessment help to predict nitrate concentrations in un-sampled groundwater?
A statistical model was developed to predict nitrate concentrations in shallow groundwater (less than 10 meters, or 33 feet) based on concentrations measured at 97 studies across the conterminous U.S. along with selected explanatory factors. The model predicts moderate to severe nitrate contamination in the High Plains, northern Midwest, and other areas of intensive agriculture in both the East (eastern Pennsylvania and the Delmarva Peninsula) and the West (the Columbia Plateau in Washington, the San Joaquin Valley in California, and the Snake River Plain in Idaho). The highest nitrate concentrations are predicted in areas with large nitrogen inputs, factors that promote rapid transport of nitrogen in groundwater, and a lack of attenuation processes. The model for shallow groundwater explained about 80 percent of the variation in nitrate concentrations. Factors that represent nitrogen sources include farm fertilizer, manure from confined livestock, and population density, as well as th
