DISSOLVED SULFIDES IN THE OXIC WATER COLUMN OF SAN-FRANCISCO BAY, CALIFORNIA

Trace contaminants enter major estuaries such as San Francisco Bay fro m a variety of point and nonpoint sources and may then be repartitione d between solid and aqueous phases or altered in chemical speciation. Chemical speciation affects the bioavailability of metals as well as o rganic ligands to planktonic and benthic organisms, and the partitioni ng of these solutes between phases. Our previous work in south San Fra ncisco Bay indicated that sulfide complexation with metals may be of p articular importance because of the thermodynamic stability of these c omplexes. Although the water column of the bay is consistently well-ox ygenated and typically unstratified with respect to dissolved oxygen, the kinetics of sulfide oxidation could exert at least transient contr ols on metal speciation. Our initial data on dissolved sulfides in the main channel of both the northern and southern components of the bay consistently indicate submicromolar concentrations (from <1 nM to 162 nM), as one would expect in an oxidizing environment. However, chemica l speciation calculations over the range of observed sulfide concentra tions indicate that these trace concentrations in the bay water column can markedly affect chemical speciation of ecologically significant t race metals such as cadmium, copper, and zinc.