U.S.
GEOLOGICAL SURVEY
Open-File
Report 02-453
NEAR FIELD RECEIVING WATER MONITORING OF TRACE METALS IN CLAMS (MACOMA BALTHICA) AND SEDIMENTS NEAR THE PALO ALTO WATER QUALITY CONTROL PLANT IN SOUTH SAN FRANCISCO BAY, CALIFORNIA: 1999-2001
ABSTRACT
This
report presents trace element concentrations analyzed on samples of fine-grained
sediments and clams (Macoma balthica) collected from 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 was started in
1994. The data for 1999-2001 are interpreted within that context. Generally,
metal concentrations in both sediments and clam tissue samples have been
within the range of values produced by seasonal variability. Copper and
zinc, however, display a continued decrease, recording the lowest winter
maxima concentrations in both sediment and tissue samples in 2001. Yearly
average of bioavailable copper, zinc and silver concentrations in 1999-2001
are some of the lowest recorded since monitoring began in 1975. A slight
increase in mercury in sediments and selenium in tissue in early 2001 are
also observed. These enrichments are believed to be mainly caused by hydrogeologic
processes affecting the area although only continued sampling will confirm
whether anthropogenic sources influence the concentrations of these elements.
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Send questions or comments about this report to Stacey Andrews (sandrews@usgs.gov) (650) 329-4468
For more information about USGS activities concerning Ecology and Contaminants in San Francisco Bay, visit the USGS Ecology and Contaminants Website.
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