Metal-Complexing Ligands and Metal Speciation in Sediment Pore Waters: Implications for Sediment/Water Exchange and Water Column Speciation.

Fluxes of TDCu and Cu ligands have been determined at two sites in the Chesapeake Bay for June and October 95, and in March 96. TDCu appears to flux out of the sediments at both sites in both spring and summer. In March 95, the TDCu flux out of site M mid-Bay sediments 41 or - 10 nmolsq md exceeded that at site S southern Bay 7 or - 3 nmolsq md. However, in June 95, the TDCu flux out at site S 52 or - 25 nmolsq md exceeded that at site M 13 or - 15 nmolsq md. There is a significant out-flux 200 to 800 nmolsq md of total Cu-binding ligands TLcu from the sediments at both sites in both spring and summer, but the TLcu flux at site M exceeded that at site S. The TLcu is 3-60x greater than the TDCu flux, and the ligands fluxing out are comparable in strength log K15 to that of the very strong L1 class that controls the speciation of TDCu in most marine surface waters, and previously only observed in these surface waters. Sediment fluxes of this very strong ligand in June 95 ranged from 200 to 600 nmolsq md, representing up to 50 of the sediment TLcu flux, and exceeded the TDCu by up to 20x. Thus, sediments may be a significant, but previously-unrecognized, source of Cu-complexing ligands to overlying waters.