Modeling Atmospheric Nitrogen Deposition and Transport in the Chesapeake Bay Watershed: A GIS Approach GIS/EM4 No. 37

The atmospheric deposition of nitrate and ammonia species has been identified as a major factor in the decline of water quality in the Chesapeake Bay. Recent reports have indicated that atmospheric deposition may account for 25 to 80% of the total nitrogen load entering the Bay. However, many uncertainties exist regarding the accuracy of these estimates including the accuracy of the atmospheric deposition inputs, nitrogen retention coefficients, and in-stream nutrient uptake rates that were used in these reports. This project is designed to reassess the impact of atmospheric nitrogen deposition through the use of a high-resolution wet deposition model, improved dry deposition and nutrient retention estimates, existing soils and land use data, and Arc View and ARC/ INFO software. Preliminary results indicate that the method describe below is a relatively simple way to arrive at accurate seasonal estimates of the contribution of atmospherically deposited nutrients on the Chesapeake Bay watershed and perhaps other watershed / estuary systems.