MINOR AND TRACE METAL CONCENTRATIONS IN SURFACE SEDIMENTS OF THREE SAN FRANCISCO BAY REGION RESERVOIRS

The San Francisco Bay is a diverse ecosystem, which is home to a variety of species. Urbanization and legacy mining have created threats to the health of the bay by increasing metal concentrations within the watersheds that drain into the bay. The concentrations of arsenic (As), nickel (Ni), cadmium (Cd), and lead (Pb) were measured in the surface sediment of three East Bay urban stream/reservoir pairs: Wildcat Creek/Lake Anza (Berkeley, CA, dammed in 1938), Lion Creek/Lake Aliso (Oakland, CA, dammed in 1871), and San Lorenzo Creek/Don Castro Reservoir (Hayward, CA, dammed in 1964). Lake Anza serves as the study control as its watershed is completely contained in parklands. Don Castro Reservoir is impacted by freeway runoff. Lake Aliso’s watershed includes an abandoned sulfur mine in addition to freeways, so the reservoir is subject to acid mine drainage (AMD) as well as freeway runoff. Prepared sediment samples, collected from the reservoir inlets and outlets, were digested using concentrated nitric acid and analyzed on an inductively coupled plasma optical emission spectrophotometer (ICP-OES). Percent relative standard deviation values, based on analysis of replicate samples, for As, Pb, Cd, and Ni are, respectively: 0.65%, 0.06%, 1.57%, and 0.01%. Lake Aliso has higher metal concentrations (5.03 ppm for As, 2.66 ppm for Pb, 133 ppb for Cd, and 2.18 ppm for Ni) than both Lake Anza and Don Castro, as expected due to AMD. Don Castro’s concentrations of Ni and Cd, typical metals in freeway runoff, are notably lower than expected considering the proximity of the freeway. Lake Anza and Don Castro showed similarly low concentrations for most metals. Lake Anza has a greater concentration of As than Don Castro, probably due to natural source rocks in the watershed. Based on these samples, Lake Aliso is a source (outlet > inlet) for As, Ni and Pb, and a sink (inlet > outlet) for Cd, Lake Anza is a source for Pb, and is sink for As, Ni, and Cd, and Don Castro is a sink for all metals. Future work includes analysis on down core sediments from all three reservoirs, which will facilitate a reconstruction of the historical evolution of the sites.