Wildfires impact river corridors by altering both the availability of organic matter (OM) and nutrients within the landscape and the hydrological mechanisms responsible for OM delivery to aquatic systems. A shift in post-fire inputs to aquatic systems can have cascading impacts on OM content and composition that may impact stream metabolism. In fire-impacted systems across North America, we found no significant differences in dissolved organic carbon (DOC) compared to non-fire impacted systems across climates and percent of watershed area burned. Rather, DOC shifts in burned catchments exhibited high spatial variability and were best explained by catchment characteristics. In companion research across a stream network in the Pacific Northwest (PNW), we found that wildfire impacts on DOC were masked by variability of site-level landscape characteristics. During dry periods, burn severity was not a major influencing factor. As the basin rewet seasonally, we observed an inverse relationship between catchment burn severity and DOC concentrations. In streams with drainage areas entirely within the burn perimeter, burn severity was a major spatial driver of OM chemistries during the first storm post-fire, but was partially modulated by localized hydrological processes. Together, our results suggest that spatiotemporal controls on the transport of fire-altered OM to the stream network influence in-stream OM quantity and composition, highlighting complexity in upscaling localized watershed scale processes across systems and scales.

Authors:

Allison Myers-Pigg, Pacific Northwest National Laboratory  (allison.myers-pigg@pnnl.gov)

J Alan Roebuck Jr., Pacific Northwest National Laboratory  (alan.roebuck@pnnl.gov)

Vanessa Garayburu-Caruso, Pacific Northwest National Laboratory  (vanessa.garayburu-caruso@pnnl.gov)

Katie Wampler, Oregon State University  (wampleka@oregonstate.edu)

Jake Cavaiani, Pacific Northwest National Laboratory  (jake.cavaiani@pnnl.gov)

Peter Regier, Pacific Northwest National Laboratory  (peter.regier@pnnl.gov)

Kevin Bladon, Oregon State University  (Kevin.Bladon@oregonstate.edu)

River Corridor SFA Team, Pacific Northwest National Laboratory  (burning.issues.community@pnnl.gov)