Wildfires are increasingly affecting the wet forests of the Pacific Northwest, a trend expected to intensify with climate change. These fires disrupt water quality and streamflow, threatening aquatic ecosystems and drinking water supplies. While the impacts of high-severity wildfires on streams are relatively well-studied, less is known about low- and mixed-severity fires. To address this, researchers studied the mixed-severity 2020 Holiday Farm Fire in two watersheds within the H.J. Andrews Experimental Forest. Watersheds 1 and 9 burned primarily at low to moderate severity, with only small patches of high burn severity. Researchers compared post-fire streamflow and stream chemistry, including samples collected during four post-fire rain events, to long-term pre-fire data from the site. Post-fire measurements of streamflow revealed slight increases in summer low flows, and increased nitrate, phosphate, and sulfate in both watersheds. Stream chemical response was more dynamic in WS1, particularly during the first rains after a prolonged dry summer. This study highlights the importance of monitoring post-fire streamflow and chemistry, even in low- and mixed-severity fires, to understand the transport of sediment, nutrients, and pollutants into streams, which can harm water resources.
Stream chemical response is mediated by hydrologic connectivity and fire severity in a Pacific Northwest forest. Bush, Sidney A.; Johnson, Sherri L.; Bladon, Kevin D.; Sullivan, Pamela L. 2024. Stream chemical response is mediated by hydrologic connectivity and fire severity in a Pacific Northwest forest. Hydrological Processes. 38(7): e15231. doi:https://doi.org/10.1002/hyp.15231