USGS Western Ecological Research Center

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Mercury Contamination and The South Bay Salt Pond Restoration Project

Forster's Tern with fish. --Photographer: Ken Phenicie

The San Francisco Bay Estuary has a long history of mercury contamination from past mercury and gold mining in its tributaries. The South Bay Salt Pond Restoration Project is the largest tidal wetland restoration project on the West Coast, and plans to convert 50-90% of the 25,000 acres of former salt evaporation ponds into tidal marsh and other enhanced wetland habitats. However, this large-scale wetland restoration project may also result in changes to the distribution, availability, and bioaccumulation of methylmercury within the San Francisco Bay Estuary. Methylmercury is the most bioavailable and toxic form of mercury, and it is known that methylmercury levels within the Estuary currently exceed several wildlife toxicity thresholds. Rates of methylmercury production, export, and bioaccumulation are higher in wetlands than in other types of water bodies. Thus, the potential exists to unintentionally increase mercury bioavailability in the South San Francisco Bay as former salt ponds are restored to tidal marsh. This is a particularly important concern because current mercury concentrations in waterbirds breeding in the Estuary are high and are known to impair avian reproduction. Thus, any increase in methylmercury production and subsequent bioaccumulation may negatively affect local wildlife and fish populations.

USGS WERC has implemented a long-term mercury monitoring program within the South Bay Salt Pond Restoration Project area to help guide the wetland restoration process. Our research provides managers with long-term datasets on mercury concentrations in birds and fish that improves the ability to assess the risk of mercury contamination to wildlife and fish and how this risk has changed over time. Our research and monitoring program is designed to provide this information for individual wetland restoration projects as well as in down-stream Estuary habitats. Thus, we are providing both a local and regional perspective on the impact that the South Bay Salt Pond Restoration Project will have on mercury contamination within the Estuary.

USGS Contact For This Project
Josh Ackerman
(530) 669-5087
Dixon Field Station
800 Business Park Drive, Suite D
Dixon, CA 95620
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