ATMOSPHERIC INPUT OF INORGANIC NITROGEN TO DELAWARE BAY

The coastal waters of the mid-Atlantic region of the United States rec eive inputs of atmospheric pollutants as a consequence of being locate d downwind from major industrial and urban emissions. These inputs are potentially the largest received by any marine area of the country. O f current interest is the atmospheric input of dissolved inorganic nit rogen (DIN = NO3- + NH4+). We have conducted a first-order examination of the magnitude of atmospheric DIN deposition relative to other larg e-scale inputs for Delaware Bay, a partially urbanized mid-Atlantic co astal plain estuary. The following loading terms: direct atmospheric d eposition, indirect atmospheric loading, urban point discharges, fluvi al input, benthic flux, and salt marsh export were evaluated. On an an nual basis, municipal-industrial effluent provide a dominant source (c a. 40%) of the DIN input to the estuary. Total (wet plus dry) atmosphe ric deposition accounts for about 15% of the total annual DIN inputs. However, during summer, which is characterized by low river-flow and s easonally maximum atmospheric loading, this figure increases to around 25%. Although atmospheric input can satisfy only a fraction of the pr imary production demands, this summer flux may represent an ecological ly important source Of external DIN, half of which is directly deposit ed to surface photic zones where it is readily available for biologica l uptake.