DID DROUGHT INTENSIFY THE GEOCHEMICAL IMPACTS OF ACID MINE DRAINAGE ON AN URBAN SAN FRANCISCO BAY WATERSHED?

Due to the recent California drought, spanning from 2011 to 2019, the San Francisco Bay (SFB) watersheds have undergone severe stress. The approximately 200 urban reservoirs/watershed pairs in the SFB provide a variety of services that include flood control and water storage. We examined the Lion Creek/Lake Aliso system in Alameda County SFB to assess how the recent drought may intensify contaminant discharge to urban environments that are impacted from acid mine drainage (AMD), freeways, and development. The sulfur mine impacting the system had undergone a remediation process in 2015 and continued in 2016. Lake Aliso is ephemeral due to a dam that opens/closes during wet/dry seasons. We compared water quality data collected from the reservoir inlet, outlet, and a tributary to the inlet before, after, and during the drought. We measured standard geochemical parameters (conductivity, temperature, and dissolved oxygen (DO)), nutrients, and metals. Lake Aliso has a significant depth gradient in temperature and low DO, whenever it is full. DO for the inlet is higher than the outlet during the summer months, but DO for the outlet is higher than the inlet during winter months. Conductivity in the inlet and the outlet have shown an upward trend from WY11 to WY16 and a downward trend from WY16 to present. The reversal of the trend in conductance could be the water’s slow recovery during the later years of the drought. The AMD tributary seemed to temporarily recover in conductance after the remediation.