Atmospheric Deposition of Nitrogen Oxides onto the Landscape Contributes to Coastal Eutrophication in the Northeast United States

Recently compiled data document a 3−8-fold increase in nitrate fluxes from 10 watersheds in the Northeast United States since the early 1900s. During this period, nitrogen oxide emissions from combustion sources have increased about 5-fold. For 17 large watersheds with relatively minor agricultural or urban influences, riverine nitrogen fluxes from 1990 to 1993 were highly correlated with atmospheric deposition onto their landscapes and also with nitrogen oxide emissions into their airsheds. These relationships provided two methods of estimating riverine nitrogen export directly from either deposition or emission fluxes. For 10 benchmark watersheds with good historical data, about 36−80% of the riverine total nitrogen export, with an average of 64%, was derived directly or indirectly from nitrogen oxide emissions. Atmospheric deposition of nitrogen represented only about 25% of the airshed emissions with the remaining 75% transported out of the airshed. Nitrogen is the element most responsible for eutrophication in coastal waters of this region. Our analysis suggests a strong linkage between the increase in cultural eutrophication of the coastal waters of the Northeast United States and the increase in nitrogen oxide emissions from fossil fuel combustion.