Metal-Complexing Ligands and Metal Speciation in Sediment Porewaters: Implications for Sediment/Water Exchange and Water Column Speciation

摘要

In this project, we determined: concentrations and benthic fluxes of total dissolved Cu (TDCu), Zn (TDZn) and Cu- and Zn-complexing ligands (L sub Cu and L sub Zn) Cu and Zn complexation and speciation in the sediment porewaters and water column of two sites in the Chesapeake Bay, at mid-Atlantic continental shelf Site WC7, and at one site in the Elizabeth River, during 2-3 seasons per year. We also studied the persistence and photodegradation of porewater-derived L sub Cu in the water column. Although porewater and bottom water TDCu and TDZn are similar, porewaters contain very high concentrations (up to micromolar) of very strong Cu ligands and moderately-strong Zn ligands. The large ligand excess relative to ambient metal concentrations results in porewaters having high levels of organic complexation (Cu: 87-99%; Zn: 80-90%), and very low concentrations of bicavailable inorganic Cu and Zn. Our measurements indicate that porewater Cu and Zn ligands flux out into the overlying water column. This porewater ligand source can supply significant amounts of the Cu and Zn ligand standing stocks in the water column. Cu-ligands appear to persist in bottom waters for significant time periods (>/= 30 days)-long enough to escape the estuary, thus potentially influencing Cu complexation and speciation in coastal (and perhaps open ocean) waters.