Fluvial Propagation of Wildfire Disturbances From the Largest Wildfire Recorded in New Mexico

Abstract

Wildfires within the Southwest are expected to increase in frequency and severity, and are known to change terrestrial ecosystems, soil hydrophobicity, and a watershed's runoff response to precipitation. While wildfires' impact on a watershed and its localized effect on nearby stream reaches are well documented, what remains uncertain is how wildfire disturbances on water quality and stream metabolism propagate longitudinally through a fluvial system. To further our understanding of wildfire longitudinal impacts, we utilized five high-frequency in-situ sonde sites downstream of the Hermits Peak Calf Canyon (HPCC) wildfire, the largest wildfire in New Mexico state history, covering 192 km of the Gallinas Creek that included the Las Vegas, NM municipality and Santa Rosa Lake. Our results show a significant increase in turbidity (p-values < 0.05) at monitoring sites upstream of Santa Rosa Lake during periods of high discharge. During these periods, a significant reduction was observed in gross primary production at all monitoring sites upstream of Santa Rosa Lake (p-value < 0.05). Unlike the monitoring sites upstream of Santa Rosa Lake, the site downstream did not experience a significant change in turbidity (p-value = 0.12) and had a significant increase in gross primary production (p-values < 0.05). Stream metabolic fingerprints also indicated increased scouring, DOC, and sediments at sites upstream of Santa Rosa Lake, while the site downstream remained relatively stable. Our novel results demonstrate how a large-scale wildfire can cause localized impacts to water quality and stream metabolism and propagate through a fluvial system spanning multiple stream orders impacting downstream water quality and ecosystem services, and how a large lake was able to buffer those disturbances halting their propagation.