Fluctuations of Copper, Zinc, and Silver in Tellenid Clams as Related to Freshwater Discharge--South San Francisco Bay
Samuel N. Luoma, U.S. Geological Survey
Daniel J. Cain, U.S. Geological Survey

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ABSTRACT:

Significant contamination of the tellenid clam Macoma balthica with Cu and Ag was observed at stations in southern San Francisco Bay. The degree of contamination appeared to be greatly influenced by the discharge of fresh water into South Bay. Local runoff appeared to provide an important source of the contaminants, especially in the summer and fall. Fresh-water discharge, either from local sources or from the Sacramento-San Joaquin Delta, also provided the force that flushed biologically available Cu and Ag from South Bay, and the degree of this flushing force appeared to determine the magnitude of the annual peak in Cu and Ag concentrations of the clam. A metal discharge index, combining an indirect estimate of annual metal loading (derived from cumulative rainfall) with the inverse of fresh-water discharge at the Delta, was found to explain 60-80% of the temporal variance in the Ag and Cu concentrations of M. balthica. The index represents a first step toward quantitatively predicting the effect of any reduction in fresh-water discharge into the Bay on Ag and Cu contamination in South Bay. Significant differences between temporal variations in Zn concentrations in the clams and the variations in Cu and Ag concentrations suggest all contaminants do not behave similarly in South Bay.

 

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