Retention of sediment and metals by Narragansett Bay subtidal and marsh environments: an update

Abstract

Unlike many estuaries, Narragansett Bay Rhode Island has a sufficient information base regarding sources and sinks to construct mass balances for sediment, Fe, Mn, Cr, Cu, Ni, Pb, Zn, Ag. Decadal differences in subtidal data for Pb, Cr and Cu allowed comparison of retention between the 1970s and 1980s. The role of salt marshes in mass balances is considered for the first time. Calculations suggest that Narragansett Bay retains virtually all incoming sediment, the greater portion of incoming Fe (87%), Cu (102–119%) and Pb (39%–203%), and about one third the input of Zn and Mn. The results for Cr (> 300% retention) suggest an unaccounted source, while results for Ag and Ni (17% and 12% retention) suggest a loss of these metals from the system. The salt marshes are nearly insignificant to retention with the exception of Fe for which they account for one third of total retention. For the metals Pb, Cr, and Cu, comparison of the 1970s and 1980s data suggests reductions in sediment burden reflective of reductions in sewage discharge of metals and limitations on the use of Pb in a gasoline.