Physical and chemical speciation of trace metals in estuarine and shelf water systems: San Francisco Bay, Gulf of the Farallones, and the Bering Sea

The bioavailability of nutrient and contaminant trace metals in estuarine and coastal marine environments is dependent upon the physical and chemical speciation of a particular trace metal. Trace metal speciation measurements were performed using two newly developed analytical methods: (1) differential pulse anodic stripping voltammetry (DPASV) with a Nafion-coated thin mercury film electrode (NCTMFE) for the determination of dissolved copper speciation in the San Francisco Bay estuary, and (2) mass sector-inductively coupled plasma-mass spectrometry (MS-ICP-MS) for the determination of the physico-chemical speciation of different size-fractions consisting of operationally-defined total and leachable (25% acetic acid leach) particulate (> 10 mum and 0.4--10 mum size-fractions), dissolved (< 0.4 or < 0.2 mum pore-size filtrate), colloidal (0.03--0.4 mum or 0.03--0.2 mum), and soluble (< 0.03 mum). Fractionation studies were performed to determine the distribution of trace metals within the San Francisco Bay plume and Gulf of the Farallones and within a shipboard incubation experiment performed in the shelf waters of the Bering Sea, where low-abundance isotopes of Fe and Zn were used as amendments.; The results from the three separate studies demonstrate the importance of trace metal speciation in the overall bioavailability to marine phytoplankton. First, the DPASV-NCTMFE method proved to be an effective tool in distinguishing between electrochemically inert and labile copper species, even in the presence of high concentrations of dissolved organic matter. The dissolved copper speciation results indicated that > 99.9% of all copper was bound to strong copper-binding ligands and lowered the ambient [Cu2+] to levels that were not toxic to marine phytoplankton in San Francisco Bay. Second, the particulate elements (Al, P, Mn, Fe, Co, Cu, Zn, Cd, Pb) and dissolved trace metals (Mn, Fe, Co, Cu, Zn, Cd, Pb) data from the Gulf of the Farallones suggest that the anthropogenic inputs of macronutrients and trace metals in the San Francisco Bay plume contribute substantially to the concentrations found in the Gulf of the Farallones. However, this input may not greatly disrupt the stoichiometric balance of macronutrients and trace metal macronutrients within coastal waters given the similarities to sources in upwelled water. Dissolved Cu and Co, along with particulate Pb, served as excellent tracers of the plume. Lastly, the incubation experiment in the Bering Sea successfully demonstrated the use of low-abundance isotopes in observing the exchange of Fe and Zn between the different physico-chemical fractions. The data from this incubation experiment led to the following conclusions: (1) there is a distinct dissolution mechanism for colloidal Fe and this fraction is bioavailable to marine phytoplankton, (2) regeneration of refractory particulate Fe contributes to the bioavailable Fe pool, and (3) Zn regeneration does not play a significant role in Zn cycling within this system.