Dissolved nickel and benthic flux in South San Francisco Bay: a potential for natural sources to dominate.

Aqueous concentrations of nickel in the southern component of San Francisco Bay (South Bay) have periodically exceeded the water-quality criteria (8.2 ppb Ni) established in accordance with the EPA’s Clean Water Act. Nickel-rich serpentinite formations around the San Francisco Bay-estuary, particularly South Bay, are eroded, transported and accumulated in estuarine sediments, providing a natural source of nickel (Fig. 1). Although the areal coverage of these formations is not pronounced, their potential importance is suggested by the spatial distribution of serpentinite throughout nearly all watersheds surrounding South Bay. This non-anthropogenic source, as well as the intermittent exceedances in South Bay nickel concentrations, has motivated a reexamination of potential nickel-transport processes and regulatory strategies.