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Mallard Island

By Nicole David Lester J. Mckee and Jon E. Leatherbarrow


Mercury is a potent neurotoxin of concern to humans and wildlife. Historic gold and mercury mining districts in the Sierra Nevada and Coast Range Mountains (California, USA), in addition to expanding urbanization in the Central Valley, are ongoing sources of mercury to San Francisco Bay. The large magnitude of runoff and associated sediment entering the Bay through the Sacramento-San Joaquin River Delta makes Delta outflow an important transport pathway for mercury and other particle-associated contaminants. From WY 2002 to WY 2006, water sampling and continuous monitoring of suspended sediment concentrations were performed at the landward boundary of the Bay to quantify mercury concentrations and loads associated with storm events. Mercury concentrations ranged from 3.2 to 25 ng/L and showed a strong correlation (r2 = 0.8) to suspended sediment concentrations. The collection of continuous turbidity measurements allowed for extrapolation of the suspended sediment record to estimate daily average total mercury loads. Daily mercury loads ranged from 3 to 13,530 g, while annual mercury loads varied from a minimum of 61 ± 21 kg in WY 2002 to a maximum of 131 ± 45 kg in WY 2004. In January of 2006, a series of large storms, with a return frequency of about eight years for the biggest storm, caused high flows and widespread flooding. This high flow year will result in an annual load much larger than previously estimated. Samples collected during these high flows make this one of the most valuable datasets on loads to the Bay. Combined with information on other significant transport pathways, the data collected will assist in understanding the long-term recovery of San Francisco Bay from mercury contamination and will influence implementation of the Bay mercury TMDL. Woodland Y o l o B y p a s

Topics: The Sacramento Rive
Year: 2011
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