MICROBIAL ASSEMBLAGES IN A SMALL, URBAN RESERVOIR IMPACTED BY ACID MINE DRAINAGE, OAKLAND, CA

Lake Aliso is a small, urban reservoir located on the Mills College campus in Oakland, CA. The dam that created Lake Aliso was built in 1888 to provide a reliable water supply to Mills College during dry summer months. Lion Creek, which discharges into Lake Aliso, is an acid mine drainage impacted stream that contributes large metal fluxes during some times of the year. The goal of this research is to determine the relationship between the microbial assemblages present and the physicochemical conditions of the reservoir. During the summer months, we measured the temperature, conductivity, dissolved oxygen, and pH in the reservoir, the inlet, and the outlet and collected water samples for microbial analysis. Biological activity reaction tests were used to determine the type of bacteria present at each site. Results indicate that heterotrophic bacteria, iron related bacteria, sulfate reducing bacteria, and enteric bacteria exist in all sites. Pseudomonads (organic matter decomposing bacteria), are present in the lake surface waters and at the reservoir outlet. There are no nitrifying bacteria and denitrifying bacteria present at any of the sites. Heterotrophic and enteric bacteria are commonly observed microbes in urban runoff, which can contribute significant discharge to Lake Aliso. Interestingly, the iron related bacteria and sulfate reducing bacteria present in Lake Aliso are not usually found in healthy natural freshwater systems or at the near neutral pH measured in the reservoir, although they are generally found together in low pH acid mine drainage waters. We speculate that the presence of these unusual bacteria is related to the metal content of the reservoir. Future research will explore this possibility.