EVALUATING THE ROLE OF SOILS IN THE TRACE METAL BUDGET OF THE PATAPSCO RIVER WATERSHED

Enhanced erosion rates in the Chesapeake Bay due to urbanization and constant agricultural development have increased contaminant loading to the Bay’s tributaries over the last 150 years. The sources of the contaminants carried by the suspended load are derived from both natural and anthropogenic sources. Based on samples collected from the Patapsco River watershed, we propose that trace metal concentrations in soils, suspended sediments and bay sediments are comparable indicating that soil-derived trace metals are the major component of the trace metal budget for the Chesapeake Bay. Natural sources for trace metal concentrations and the flux of trace metals were determined from sampling locations across the rural to urban gradient capturing the maximum number of potential sources of trace metals to the bay.

Suspended sediment samples from three separate storm events were analyzed and compared to integrated soil samples from the same locations as well as three locations with in the Baltimore Harbor and the Chesapeake Bay. Of the eight transition metals analyzed, the highest concentrations were seen in Mn and Zn. Values as high as 3000 ppm were recorded in suspended sediment samples collected with in the Piedmont province and as high as 1500 ppm within the Coastal Plain province. All metals from analyzed soil samples exhibited higher concentrations at sites within the Piedmont as compared to those sampled within the Coastal Plain. Metal concentrations from integrated soil samples, suspended sediments and Bay sediments, with the exception of one Bay sample collected near a known point source, show a similar range in concentrations in all analyzed metals.

These results illustrate the role suspended sediments play in the trace metal budget of the Chesapeake Bay. It is expected that enhanced erosion rates due to urbanization and constant agricultural development have increased contaminant loading to the Bay’s tributaries over the last 150 years. From these results it is likely that soil derived suspended sediments are of great importance to the trace metal budget of the Chesapeake Bay and should be considered when determining acceptable maximum contaminant values for the estuary.