Background/Question/Methods: Wildfires alter the lateral transfer and in-stream export of carbon, thus impacting river biogeochemistry at the watershed scale. The frequency and intensity of both wildfire and storm events are increasing as a result of our changing climate, but the biogeochemical links between precipitation, runoff, and material export is still poorly understood in fire-affected systems. Given known wildfire effects on landscape hydrology and geomorphology, we expected the first major post-fire storm event to mobilize a disproportionately large amount of dissolved organic carbon (DOC) and pyrogenic carbon (PyC). However, capturing the “first flush” of carbon after a burn is particularly elusive, due to the logistical challenges inherent to sampling coincident wildfire and rainfall events. In August 2020, an experimental watershed located at the Blue Oak Ranch Reserve (Diablo Range, CA, USA) was burned during the Santa Clara Unit Lightning Complex Fire. Our ongoing fieldwork in the area allowed us to quickly mobilize and collect stream samples during the first post-fire storm events in the following winter. Watershed hydrology and in-stream export of DOC and PyC were assessed from a combination of in situ sensors, automatic samplers, and grab samples. Results/Conclusions: Our preliminary data suggest the export of dissolved PyC may be completely decoupled from bulk DOC during the first flush in fire-affected headwater streams – A novel finding since these two carbon forms are typically correlated in river systems studied to date. Overall, we expect in-stream DOC and PyC export to be primarily controlled by the hydrologic routing of water through the system (e.g., surface runoff versus groundwater inputs). By establishing direct linkages between hydrologic flow paths and material export, we will produce an integrated view of how watershed biogeochemistry is altered by wildfire and rainfall on short timescales.
