Atmospheric nitrogen deposition and the Chesapeake Bay estuary

In this report we examine anthropogenic sources of nitrogen to the Chesapeake Bay to determine the relative contribution of atmospheric deposition. Previous analyses have generally failed to account for dry deposition and have also ignored the portion of riverine nitrogen loadings attributable to atmospheric sources. Two methods, based on different assumptions about ecosystem retention of nitrogen, are used to calculate loadings to the Bay. Our base case estimate indicates that approximately 25% of the anthropogenic nitrogen loading to the Bay originates as atmospheric nitrate deposition, which arises almost entirely from anthropogenic emissions of nitrogen oxides. A sensitivity analysis was also performed indicating a range of 20% to 30% for the contribution of atmospheric nitrate. Atmospheric ammonium deposition contributes another 14% of the total. We conclude that atmospheric sources of nitrogen, particularly nitrogen oxides emissions, should be considered in management strategies aimed at reducing nitrogen loading of coastal waters.