THE URBANIZATION HISTORY OF AN ACID MINE DRAINAGE IMPACTED RESERVOIR IN THE SAN FRANCISCO BAY AREA, AS DETERMINED BY SEDIMENTARY TRACE METAL, PHOSPHORUS, NITROGEN, AND CARBON RECORDS
Fe and Mn concentrations within the core are an order of magnitude higher than in sediments of other local reservoirs with less anthropogenic impact (e.g., Lake Anza, Berkeley, CA). Since Fe is released during the oxidation of pyrite, it is likely that acid mine drainage is the Fe source. Typically, Cd, Cu, Zn, Pb, Ni, and As are present in both acid mine drainage and in freeway runoff. We see highly correlated increases in Cu, Zn, Cd, and As concentrations from the bottom to the top of the core, indicating greater delivery of these metals to the lake over time. The concentrations of Pb and Ni do not fit this pattern. Nutrient and C data indicate eutrophication of the lake through time. Organic P deposition increases from the bottom to the top of the core, indicating increased nutrient delivery. An increase in C/N ratio from the bottom (10) to the top (15) of the core may indicate a shift in source from algae within the lake (typical values of <10) to terrestrial organic matter being delivered to the lake (typical values > 20). The sedimentary δ13C values decrease and the δ15N values increase towards the top of the core, consistent with increasing eutrophication. The watershed history of urbanization and acid mine drainage is recorded in the sediments of Lake Aliso.