Atmospheric wet deposition of trace elements to Chesapeake and Delaware Bays

The atmospheric wet depositional fluxes of selected trace elements (Al, Fe, Mn, Pb, Cd, Zn, Cu, Ni and Cr) were examined at two mid-Atlantic sites, which were located on the shore of the Delaware (Lewes) and Chesapeake (Stillpond) Bays from September 1995 to August 1996. Sampling was carried out on a weekly integrated basis, using “clean” techniques developed especially for trace elements. Monthly integrated depositional fluxes showed large variability in space and time for most of the measured elements, with similar ranges of variation for both sites. A good correlation (r2=0.80, Fe/Al=0.59) between Al and Fe fluxes at both sites suggests their major origin from the earthʹs crust (resuspended regional soils). Based on the enrichment factor calculation, it is suggested that at least half of the Cr and Mn and more than 90% of the Cd, Zn, Pb, Cu, and Ni are from non-crustal (presumably anthropogenic) sources. Seasonal variations of Al, Fe and Mn appear to be mainly controlled by local/regional agricultural activities, whereas Pb and Cd fluxes are largely dictated by precipitation amounts. Factors controlling fluxes of other elements (Zn, Cu, Ni and Cr) are not clearly distinguished due to large episodic inputs of local/regional contamination sources. A comparison of annual trace element fluxes during 1991–1996 reveals a factor of 2–4 higher fluxes of Zn, Cu and Ni during 1995–1996 at both sites, indicating regional (i.e., mid-Atlantic region) increase of the fluxes during the sampling period. The similar annual fluxes and trends at both sites suggest that these data can be employed to estimate atmospheric wet flux of trace elements to mid-Atlantic coastal waters (including Chesapeake/Delaware Bays and mid-Atlantic Bight).