The USGS has developed spatially referenced regression (SPARROW) models of nitrogen transport in streams in 2002 for the U.S. These models provide information about the spatial distribution of nitrogen loads and concentrations in streams and loads delivered to receiving water bodies. The models are developed by statistically relating measured stream nitrogen loads with datasets of nitrogen inputs to the watershed in 2002, including National Atmospheric Deposition Program (NADP) wet deposition of total inorganic nitrogen. Export coefficients that relate input quantity to total (inorganic plus organic) nitrogen load in streams are empirically estimated for each nitrogen source. The NADP wet deposition data are used in these models as proxy for the contributions of total (wet plus dry) nitrogen deposition. The export coefficient estimated for atmospheric deposition varies by about 5-fold by region and according to physical watershed properties such as soil permeability and temperature. For the Southeast and Midwest the average export coefficient is 0.5, meaning that for a watershed with wet deposition rate of 400 kilograms per square kilometer per year, 200 kilograms per square kilometer per year is estimated to reach the channel of the nearest stream. The relative contribution of atmospheric deposition to the total mass of nitrogen delivered to the stream varies with the importance of other sources, such as wastewater discharge, agricultural fertilizer and livestock, and urban land, in the stream’s watershed.  The relative contribution is greatest (more than 60 percent for some river basins) in areas such as New England, the northernmost part of the Midwest, and much of the Southeast, where other sources contribute smaller amounts to loading. Using the NADP wet deposition data in these models as proxy for total deposition assumes that the regional patterns of wet and dry deposition are generally correlated over large areas of the U.S.   The USGS recently developed a nitrogen SPARROW model for the eastern U.S. that uses modeled total deposition (wet plus dry) from an air quality model (Community Multi-scale Air Quality Model, or CMAQ) in place of the NADP wet deposition data. The NADP wet deposition data are used, however, to calibrate the CMAQ model.  The coupled CMAQ-SPAROW model can account for contributions from the individual source categories of atmospheric nitrogen: emissions to the atmosphere from power plants, other industry, vehicles, livestock, and fertilizer, and background sources.  Accounting for individual components of atmospheric nitrogen increases usefulness of the model for management applications.