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Original Article |
1 Department
of Environmental Toxicology, WIGS Laboratory, University of California,
Santa Cruz, CA 95064,
USA
2 Department of Earth
Sciences, University of California, Santa Cruz, CA 95064,
USA
3 United States
Geological Survey, Water Resources Division, Menlo Park, CA
94025, USA
4 California
Regional Water Quality Control Board, 1515 Clay Street, Suite 1400,
Oakland, CA 94612,
USA
The
New Almaden mercury mines in California (USA), which collectively
represent the largest historic producers of mercury in North America,
are a persistent source of mercury contamination to the San Francisco
Bay estuary. An estimate based on total mercury concentration
(HgTOT) and provisional stream flow data measured at a
gauging station in the Guadalupe River during base flow conditions
yields a base flow flux of 30 g of mercury for the month of
October 2000. In contrast to this base flow estimate, one 2-day rain
event in October 2000 resulted in a flux of 22 g of mercury past
this site. An estimate of mercury transport from the entire Guadalupe
River watershed based on a sediment transport model and our measured
suspended particulate HgTOT
(0.5–4 µg g–1)
results in a total of
4–30 kg year–1
transported to the southern reach of the estuary. Sediments in the
southern reach have lower HgTOT (most
0.4 µg g–1 dry wt)
and monomethylmercury (MMHg, c.
1 ng g–1 dry wt)
concentrations than those in the Guadalupe River (HgTOT,
0.41–33 µg g–1
dry wt; MMHg,
1–10 ng g–1 dry
wt). Because the most elevated methylmercury concentrations
(8–12 ng g–1 dry
wt) were found in sediments deposited immediately upstream of hydraulic
structures (e.g. diversion dams and weirs) within the river, it is
proposed that such physical structures may represent important zones of
MMHg production and fluxes to San Francisco
Bay.
Key Words: mercury • methylmercury • water • sediment • Guadalupe River • San Francisco Bay • estuaries
