MP12 Organic, Metallic, Organometallic Pollutants
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(DAV-1117-748925) Mercury Transport to San Francisco Bay through the Sacramento-San Joaquin River Delta.

David, N¹, Leatherbarrow, J¹, McKee, L¹, ¹ San Francisco Estuary Institute, Oakland, CA, United States

ABSTRACT- San Francisco Bay is currently listed as impaired on the Clean Water Act 303(d) list for mercury due primarily to elevated concentrations in sport fish and the issuance of current fish consumption advisories. The large magnitude of sediment and runoff entering San Francisco Bay through the Sacramento-San Joaquin River Delta makes these major rivers important transport pathways for mercury and other particle-associated contaminants. Historic gold and mercury mining in the Sierra Nevada and Coast Range Mountains as well as expanding urbanization in the Central Valley of California are ongoing sources of mercury to the Bay. Between January 2002 and January 2005, water samples were collected at a downstream location of the Sacramento River to quantify mercury concentrations and loads in surface runoff associated with large storm events and re-suspension of river sediments. Mercury concentrations ranged from 3.2 to 14 ng/L and showed a strong correlation (r2 = 0.8) to suspended sediment concentrations. The collection of continuous turbidity measurements by U.S. Geological Survey at the study location allowed for extrapolation of the suspended sediment record to estimate daily average total mercury loads. For the first two years of monitoring in water years (WYs) 2002 and 2003, daily mercury loads ranged from 3 to 1,800 g, while annual mercury loads were approximately 58 ± 20 kg in WY 2002 and 97 ± 20 kg in WY 2003. Preliminary load estimates for WYs 2004 and 2005 reflect annual mercury loads of similar magnitudes. Results from this study have helped refine current estimates of mercury loads to the Bay from the Sacramento-San Joaquin River system. In the context of other significant transport pathways and numerical models, these refined estimates will further assist in understanding the long-term fate of mercury and recovery of impaired waters of the Bay.

Key words: mercury, loading, transport, Sacramento River