Mercury in estuarine systems: Downcore trends of Hg in San Francisco and Tomales Bay, CA
- Geological Survey, Menlo Park, CA (United States)
Mining, both historic and current, is a source of concern with regard to inputs of Hg into the environment. Active Hg mine sites exist primarily in the Circumpacific and Mediterranean-Himalayan belts and Hg releases are associated with gold mining in the same areas. Sediment cores collected in San Francisco Bay (SFB) and Tomales Bay (TB) show contaminant profiles of Hg and provide a historical perspective on Hg contamination where both Hg mining and gold mining occurred in the watershed. Three sources of input of Hg contamination to SFB can be identified: hydraulic gold mining in the late 1800`s in the Sierra Nevada mountains; Hg mined in the watershed of the South Bay; and industry. Historical sources into TB are limited to inputs from local Hg mining. Pre-anthropogenic concentrations of Hg in both Bays were 0.05 ug/g. Maximum concentrations in TB reached 0.4 {micro}g/g in the upper 40 cm. Maximum concentrations in SFB were {approximately}0.5--1.0 {micro}g/g. The highest concentrations of Hg are buried at 1 m depth in the North Bay cores, suggesting inputs of Hg from mining in the Sierra Nevada mountains during the late 1800`s to early 1900`s. This suggests that modern industrial sources are small compared to the mass of Hg employed by mining. Enriched concentrations of Hg near the mouth of the estuary average about 0.5 {micro}g/g. The difference from upstream is consistent with dilution of contaminated riverine sediment, with clean, marine sediment, as indicated by geologic tracers (Cr and Al) in sediments from the Sierra Nevada Mountain ranges.
- OSTI ID:
- 203605
- Report Number(s):
- CONF-9511137--; ISBN 1-880611-03-1
- Country of Publication:
- United States
- Language:
- English
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