Three-dimensional modeling of Cu and Pb distributions in Boston Harbor, Massachusetts and Cape Cod Bays

Abstract

The transport and distribution of dissolved Cu (Cu diss) and Pb (Pb diss) in Boston Harbor (BH), Massachusetts Bay (MB) and Cape Cod Bay (CCB) were simulated using an existing three-dimensional hydrodynamic model. Treatment of Cu diss as a conservative tracer produced model results in good agreement with observational data in MB and CCB. Pb diss was modeled as a non-conservative tracer using particulate organic carbon (POC) extracted from a water quality model as the sorption and scavenging matrix for particulate Pb. Despite cessation of discharge from a major treatment plant in 2000 and concurrent reduction in metal loading, Cu diss and Pb diss concentrations in the Harbor remained relatively unchanged between 1998 and 2002. In contrast model results produced water column concentrations in Boston Harbor that were about 10% of the observed current standing stock of Cu diss and only about 20% of Pb diss in 2002. Both field observations and model results incorporating Cu and Pb benthic fluxes suggest that release of these metals from the previously contaminated sediments of the Harbor is now the major source of these metals to the Harbor.