Mercury deposition in a tidal marsh downstream of the historic New Almaden mining district, CA Christopher H. Conaway a, Elizabeth B. Watson b, John R. Flanders a, and A. Russell Flegal a a WIGS Laboratory, Department of Environmental Toxicology, University of California at Santa Cruz b Department of Geography, University of California at Berkeley

Overview San Francisco Estuary contaminated by historic mining –Hydraulic gold mining in Sierra Nevada 1852–1884 –Mercury mining in Santa Clara Valley 1845–1975

Introduction Background data Mining history at New Almaden Current study

Background Sediment Data 20 –200 ng/g worldwide average in uncontaminated soils (Adriano 2001; Faure 1998) 50 –100 ng/g Northern Coast Range streams (Domagalski 2001) 1 –20 ng/g Pacific Coast Ranges (Kerin 2002) 200 ng/g upstream of New Almaden (Thomas et al., 2002) Surface sediments of estuary 200–600 ng/g (Hornberger et al., 1999; Conaway et al., 2003, Marvin- Dipasquale et al., 2003)

Mining History at New Almaden Pre-mining –Native Americans mined cinnabar for vermilion (D’Itri and D’Itri, 1977) Mining era –Large scale development began 1845 –Produced 37 million kg of mercury (Cargill et al., 1980) Remediation by DTSC –Contaminated soils 10–1000 ppm on mine site (Dames and Moore, 1989) –Downstream concentrations 1–5 ppm (Thomas et al., 2002)

Current Study Mercury concentrations exceed regulatory criteria (Davis, 1999; Thompson et al., 2000) –Water, sediment, fish Effect on biota –Humans (Davis 1999) –Birds (Lonzarich et al., 1992; Hothem et al., 1995, 1998; Hoffman et al., 1998; Hui, 1998) What is the natural background? –i.e., what is the contribution of natural weathering of mercury- rich rocks?

Methods Sampling Lab analysis Dating methods

Sampling San Francisco Bay –Gravity coring –3 cores in South Bay Triangle Marsh –Piston coring –Tidal marsh where Coyote Creek and Guadalupe River enter estuary

Analysis Subsamples sieved to <63 microns to account for grain-size effects Digested in hot HNO 3 /H 2 SO 4 SnCl 2 reduction, Au-amalgamation, CVAFS (Bloom and Crecelius, 1987)

Dating Methods AMS 14 C dating of shell and organic material Appearance of non-native pollen –Eucalyptus –Plantago lanceolata Abundance of Cyperaceae (sedge family) pollen related to ENSO events

Results and Discussion Description of core trends Assessment of pre-mining mercury concentrations Interpretation of core profile –Impact of mining –Other factors

Description of Core Trends

Assessment of Pre-mining Concentrations Hornberger et al ± 10 ng/g Triangle Marsh 80 ± 30 ng/g Southern reach 70 ± 10 ng/g

Interpretation of Core Profile Impact of Hg mining –Dominant contributor Other factors –Hydraulic mining debris –Wastewater –Hydrography –Subsidence

Impact of Hg Mining Production from New Almaden reaches 100 million kg in 1880 Little production from 1910 to 1940 Brief renaissance of production in 1940s –surface ore dumps –open cuts Mines close in 1975

Other Factors Hydraulic Mining –Contemporaneous –Little sediment transported to from northern to southern reach (Krone, 1979; Ritson et al., 1999) Industrialization –Hydrography Increased erosion Changing sediment sources –Wastewater Santa Clara Water Pollution Control Plant –Subsidence

Conclusion Pre-mining mercury concentration in estuary is about 70 ng/g Clear anthropogenic influence in Hg-deposition history Complex history beneath profile Contribution of natural weathering of Hg-rich rocks to contamination in SFB is relatively small

Acknowledgements UCSC –Liz Kerin, Miranda Spang, Allison, Luengen, Andy Fisher, Glen Spinelli UCB –Roger Byrne, Liam Reidy, Brenda Hamilton Others –Clyde Morris, Gordon Smith, Richard Looker, Khalil Abu-Saba, Roberto Anima, John Callaway, and Tom Grieb Funding by the San Francisco Bay Regional Water Quality Control Board, SFEI, UCTSR&TP, and the W. M. Keck Foundation