SOURCES OF NITROGEN IN WET DEPOSITION TO THE CHESAPEAKE BAY-REGION

Nitrogen-containing compounds in wet deposition can provide significan t sources of nutrients to phytoplankton and potentially contribute to eutrophication in estuaries and coastal waters. Quantifying both inorg anic and organic forms of nitrogen in wet deposition as well as.determ ining their sources is important for understanding how to control eutr ophication. Stable nitrogen isotope data can provide information regar ding what source processes produced nitrogen in precipitation and air mass trajectories can predict where the air mass which produced the pr ecipitation was geographically located before the event occurred. In t his study, the wet deposition concentrations, fluxes, and delta(15)N v alues of ammonium, nitrate, and dissolved organic nitrogen were determ ined for 60 precipitation events collected from May, 1993 to December 1994 at a site near the Chesapezke Bay, an estuary currently experienc ing eutrophication. Grouping;the concentration data according to seaso n showed a peak in ammonium coupled with depleted delta(15)N values in the spring which were indicative of agricultural emissions. A peak in nitrate in the spring seemed to indicate greater soil emissions at th at time, but concentrations were also high at other times of the year. No trend was observed for the dissolved organic nitrogen with season. Back trajectories were calculated for each precipitation event and gr ouped into five major transport patterns. Combining the flux and isoto pic composition data with the air flow history revealed that dominant sources of ammonium in precipitation to the region are probably fertil izers, soil, and animal excreta emissions which have the highest fluxe s in air masses originating from the southwest and west. The dominant source of nitrate to the region is probably fossil-fuel combustion and the highest fluxes originate From the northwest and west. Speculation on the dissolved organic nitrogen sources is probably premature, but its flux pattern is similar to the nitrate pattern, suggesting that th eir sources may be similar. (C) 1988 Elsevier Science Ltd. All rights reserved.