Near-field receiving water monitoring of trace metals and a benthic community near the Palo Alto regional water quality control plant in south San Francisco Bay, California: 2004

Abstract

Abstract : Trace elements in sediments and clams, clam reproductive activity and benthic community structure are reported for a mudflat one kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant in South San Francisco Bay. This report serves as a continuation of the Near-Field Receiving Water Monitoring Study, which began in 1974. Prior to this report, trace metal and reproductive activity/community structure data were reported separately. The data for 2004, herein, are interpreted within that context and are consistent with those previously reported. Metal concentrations in both sediments and clam tissue samples are within the range of values previously observed due to seasonal variability. Copper and zinc concentrations in sediment and bivalve tissue display continued decreases over the last decade. In 2004, copper in sediment was observed to drop below the ERL (Effects Range-Low) concentration for the fourth consecutive year. The concentration of zinc in sediment never exceeded the ERL. Yearly average concentrations of copper, zinc and silver for 2004 are some of the lowest recorded since monitoring for metals began in 1975. The concentrations of mercury and selenium, during April and January 2004, respectively, were the highest values observed for these elements during this study. However, the concentrations of these elements in sediments and clams at Palo Alto were similar to concentrations observed elsewhere in the San Francisco Bay.