ATMOSPHERIC DEPOSITION TO THE CHESAPEAKE BAY WATERSHED - REGIONAL ANDLOCAL-SOURCES

Atmospheric deposition is an important source of mercury to the Chesap eake Bay and its watershed. Estimates from our collections at four sit es around the Chesapeake Bay and in western Maryland show that the reg ional wet flux is between 10 and 20 mu g m(-2) yr(-1) with higher conc entrations being found close to local sources. The Hart-Miller Island site, in close proximity to Baltimore, had a wet flux of 25 mu g m(-2) yr(-1). Amount of rainfall is also important. At Frostburg, in wester n Maryland, the Aux estimate of 23 mu g m(-2) yr(-1) is largely a resu lt of the higher than average rainfall during the study period. Our me asurements of total throughfall deposition in western Maryland and our measurements of particulate mercury at the Chesapeake Biological Labo ratory indicate that dry deposition is not a dominant source of mercur y at either site. Direct deposition to the Chesapeake Bay contributes more than half the mercury entering the Bay and our preliminary estima tes for watershed retention suggest that most of the mercury deposited to the watershed (90% or greater) is retained in the terrestrial doma in. For methylmercury, atmospheric deposition is not the most importan t flux to the Bay. Additionally, our results suggest that methylmercur y is being generated within the watershed and transported to the Bay i n river runoff. Where comparisons can be made, our results confirm tha t deposition to the Chesapeake Bay is elevated compared to that of oth er regions of the U.S.A. except perhaps Florida. (C) 1997 Elsevier Sci ence Ltd.