Assessing contaminant distributions and sources in Castaic Lake, a mercury-impacted reservoir in Los Angeles County, CA

Castaic Lake, located ~65 km from Los Angeles, is the third-largest water storage facility associated with the California (CA) State Water Project and is regularly utilized for fishing and recreation. It is also one of 71 CA reservoirs listed as impaired due to mercury (Hg) concentrations in fish. Despite the existing fish consumption advisory, no studies investigating water quality in Castaic Lake have been published in the peer-reviewed literature. We, therefore, propose to evaluate potential sources of bioaccumulative organic monomethylmercury (MeHg) within the reservoir?s water column and watershed. Inorganic Hg is transformed into MeHg by anaerobic bacteria that live in low oxygen environments, such as at water column transitions and in the bottom water/sediment of lakes and human-made reservoirs. Castaic Lake anoxic bottom waters may therefore be a key source of biologically available mercury in this system. In addition to Hg-impacts, Castaic Lake is increasingly threatened by wildfires, two of which have already occurred this summer within the Castaic Lake watershed: Lake Fire (127 km2) and Castaic Fire (0.7 km2). We are therefore expanding our Hg study to incorporate analyses for polycyclic aromatic hydrocarbons (PAHs) and heavy metals (e.g., Pb, As, Cd), both of which can be elevated in runoff from wildfire-impacted landscapes. Our results will provide a first step towards developing a contaminant mass balance for Castaic Lake as well as a water quality baseline to assess future change.