RAPID: Investigation of Immediate Post-fire Hydro-geochemical Coupling and Contaminant Flux in an Urban-fringe Watershed in Southern California

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The Station fire is currently noted as the largest fire in Los Angeles County history as well as the 10th largest fire in California history. The burned region is located immediately adjacent to dense urban areas on the east side of the Los Angeles basin. These urban-wildland regions, located in the San Gabriel Mountains, will now be impacted by increased flooding, debris and sediment-laden flows, and significant water quality issues. The San Gabriel Mountains are known to receive high loads of atmospheric pollutants (dry and wet)originating from the Los Angeles metropolitan region. Runoff from these mountains normally supplies significant runoff into downstream urban water ways, which is then directed to infiltration ponds or zones for aquifer recharge, or into conveyance channels that route water through dense urban areas to coastal bays. Postfire runoff in these urban-fringe watersheds may now contribute significant, and potentially toxic, chemical loads into downstream urban systems, affecting regional water supplies, biota and ecosystem function. Funds from this RAPID grant will allow an immediate and extensive investigation of storm-driven contaminant flux (including nutrients, metals, PAHs, sediments, and other ancillary parameters) in an urban fringe watershed affected by significant atmospheric deposition and that was burned in its entirety. Previously collected pre-fire data on the study watershed will allow a unique and comprehensive comparison to pre-burn behavior,advance knowledge on post-burn hydro-geochemical coupling and alterations in basin mass loading, and provide critical data to improve geochemical and hydrologic modeling in post-burn systems. The overarching goal of the proposed research is to better understand the mechanisms controlling alterations in the chemical and physical response of urban fringe watersheds after a catastrophic wildfire. Specifically, we propose to address the following science questions: 1) How does post-fire hydro-geochemical coupling (behavior) alter from pre-fire conditions? 2) How does storm variability influence post-fire runoff behavior and coupled contaminant flux? 3) What is the effect of burn on riparian nitrate soil storage and streamwater export? and 4) What is the impact of a catastrophic burn on seasonal pollutant loading to downstream urban systems?