METAL CYCLING THROUGH AN EPHEMERAL ACID MINE DRAINAGE IMPACTED URBAN RESERVOIR IN OAKLAND, CA

Small urban reservoirs, such as Lake Aliso on the Mills College campus in Oakland, CA, may provide beneficial environmental services by acting as sinks for metal pollution. The damming of Lion Creek in 1888 created Lake Aliso, which is emptied for flood control during the rainy season and filled for irrigation storage in the dry season. The Leona Heights Sulfur Mine (LHSM) began contributing acid mine drainage to Lake Aliso via Lion Creek in the 1920s. Although the tributary draining the LHSM to Lion Creek contributes the least amount of water, it delivers the highest metal load to Lion Creek. The goal of our project is to determine whether Lake Aliso acts as a sink or a source for metals before Lion Creek discharges to San Francisco Bay. Water samples collected regularly from the LHSM site and the inlet and outlet sites of Lake Aliso were analyzed for cadmium (Cd), copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) concentrations by inductively coupled plasma mass spectrometry. When Lake Aliso is full, higher fluxes of Fe and Ni exit the reservoir than enter it (average input fluxes of 13 ± 11 moles Fe per hour and 0.044 ± 0.068 moles Ni per hour vs. average output fluxes of 32 ± 36 moles Fe per hour and 8.7 ± 10. moles Ni per hour), suggesting that Lake Aliso may act as a source for Fe and Ni. In contrast, the flux of Cd is higher at the inlet than at the outlet of Lake Aliso (average input flux of 0.24 ± 0.40 moles Cd per hour vs. average output flux of 0.15 ± 0.22 moles Cd per hour), suggesting that Lake Aliso may act as a sink for Cd. Approximately equal fluxes of Cu and Zn exit and enter the reservoir (average input fluxes of 69 ± 140 moles Cu per hour and 67 ± 140 moles Zn per hour vs. average output fluxes of 69 ± 100 moles Cu per hour and 67 ± 100 moles Zn per hour), suggesting that Lake Aliso is neither a source nor a sink for Cu and Zn. Further research will attempt to quantify how the metal fluxes differ when the reservoir is empty, as well as the effect of other water discharges on the metal fluxes.