Extensive tidal wetlands and marshes once almost covered South San Francisco Bay below the present-day Dumbarton Bridge. For the last 150 years these wetlands have received mercury-laden drainage from the New Almaden mercury mining district, in the upper reaches of the Guadalupe River watershed. Salt pond construction in the last century buried mercury-contaminated sediments.
But restoration poses challenges for water quality. Redistributing sediment and introducing tidal action can release mercury into the water column and may cause the mercury to methylize, which makes the metal more available to the food web. Methylmercury builds up in the tissues of fish, and has severe toxicological effects on both humans and wildlife that consume local fish. The restoration project is identifying locations of mercury “hotspots” and studying and attempting to reduce the potential for methylation. Learn more about this issue here.
SFEP provides financial management for this important project. Over three years, the Habitat Evolution and Biosentinel Monitoring Project employed a variety of remote sensing and biological techniques to monitor changing habitats. Data from the project is being used to evaluate the progress and consequences of the restoration process and to help develop new tools for implementing wetland restoration projects in tidal marshes throughout the Estuary.
Project partners include the U.S. Fish and Wildlife Service, the National Ocanic and Atmospheric Administration, U.S. Army Corps of Engineers, the U.S. Geological Survey, the California Department of Fish and Game, the State Coastal Conservancy, State of California Wildlife Conservation Board, Santa Clara Water District, Alameda County Flood Control District, the Resources Legacy Fund, and the National Fish and Wildlife Foundation Leopard Shark Account.
Charting Habitat Evolution
Remote sensing technology is used to map and analyze vegetation, mudflat, and channel evolution in sites under restoration. Three years of annual satellite/aerial imagery will provide a visual chronology of mudflats and vegetation communities as they migrate from salt ponds to tidal marsh and managed ponds.
Five species of fish and/or wildlife in Pond A8, located near the mouth of the Guadalupe River, have been identified as “biosentinels” for mercury’s toxic effects, and are being monitored for methylmercury bioaccumulation. Water chemistry is analyzed for a better understanding of the chemical processes that cause changes in mercury bioaccumulation during tidal marsh restoration.
In combination, these two monitoring processes provide essential data relating to baylands restoration approaches and methodologies under changing conditions.