Atmospheric nitrogen deposition to estuares in the mid-Atlantic and northeastern United States.
The purpose of this work was to determine the contribution made by atmospheric nitrogen (N) deposition to the total N input to 10 estuaries on the east coast of the United States. We estimated the amount of N fixed by human activities in the watersheds (N fertilization, biotic N2fixation by legumes and pastures, atmospheric N deposition, and net food and feed import of N) of these 10 estuaries and used a land-use specific approach to estimate the N available for transport to the estuary from different watershed N sources (runoff from agriculture, urban areas and upland forests, point sources, and atmospheric deposition). Total atmospheric N inputs (watershed runoff plus direct deposition to the surface of estuary) accounted for 15-42% of the total N inputs to these 10 estuaries. Direct deposition to the surface of the estuary was an important atmospheric N source for four estuaries, accounting for 35-50% of the total atmospheric N inputs. Simulated reductions of atmospheric N deposition by 25% and 50% of current deposition rates reduced the contribution made by atmospheric N deposition to the total N loads by 1-6% and 2-11%, respectively. Largest reductions occurred in estuaries with direct atmospheric N deposition contributions >35% of the total atmospheric N input. Results from our simulated reductions suggest that considerable reductions (>25%) in atmospheric N deposition will be needed to significantly reduce the contribution made by atmospheric N deposition to the total N loads to our study estuaries. In addition, reductions in atmospheric N deposition will first be detected in estuaries with relatively high direct deposition inputs of atmospheric N deposition.
Castro
Mark S
MS
Appalachian Laboratory, University of Maryland Center for Environmental Science, Frostburg, Maryland 21532, USA. castro@al.umces.edu
Driscoll
Charles T
CT
D000383:Agriculture; D000392:Air Movements; D000393:Air Pollutants / Q000032:analysis*; D017753:Ecosystem; D004784:Environmental Monitoring; D005068:Eutrophication; D005308:Fertilizers; D009584:Nitrogen / Q000032:analysis*; D014481:United States; D014873:Water Pollutants / Q000032:analysis*
D000393:Air Pollutants; D005308:Fertilizers; D014873:Water Pollutants; D009584:Nitrogen