Scorched Legacy: Wildfire Impacts on Water Quality in a Montane Valley Creek

Abstract

Wildfires can impact watershed catchments and streams in a variety of ways. In 2021 the Dixie Fire burned 963,309 acres of Northern California including part of Red Clover Valley (RCV), a montane meadow with active stream restoration projects, located in the Sierra Nevada. Two creeks flow through RCV; Dixie Creek, whose watershed was heavily burned, and Red Clover Creek, whose watershed was largely unburned. Water quality was measured in the RCV creeks before and after the fire, to compare water quality parameters pre-fire and post-fire. Of the parameters assessed, stream temperature, dissolved oxygen, and nitrate were significantly different pre-fire compared with post-fire (p-value <0.05). Stream temperature was significantly lower during the post-fire period, for both watersheds; this may be attributed to higher precipitation during the 2023 water year. The sampling period with the lowest stream temperature was during the intra-fire period (August 2021), likely due to smoke and particulate matter from the fire. Dissolved oxygen decreased during the post-fire low-flow period compared to pre-fire, with all the measurements in the burned area, or Dixie Creek Watershed, below the suggested level for salmonid mortality. The in-situ nitrate concentrations increased significantly two-years post fire (p-value <0.05). for both watersheds, possibly due to delayed nitrification. The results of this study show that while wildfire can have a significant impact on water quality, the Red Clover Valley restoration efforts may have mitigated the impacts making the area more resilient to disturbance.