PNNL

Abstract

Wildfires generate watershed-scale disturbances initiated by post-fire rainfall-runoff events. These disturbances affect water quality and ecosystem processes, driving sustained aquatic impairment. While the impacts of wildfires on associated streams and rivers have received increased attention in the last decades, wildfire disturbance propagation along fluvial networks is poorly understood. To address this deficiency, we deployed water quality sondes co-located with flow gages along streams and rivers draining areas burned in the 2022 Hermit’s Peak-Calf Canyon wildfire, the largest in New Mexico state history. Our monitoring began two weeks after fire ignition but before the first post-fire flush, continued for several months, and included sites located within the burned area and up to 170 km downstream. Data collected before and after the mobilization of burned material during the regional rainy season provide evidence of how large wildfires impact water quality and ecosystem processes along fluvial networks. The wildfire resulted in the near total removal of vegetation from large portions of the burn scar in affected forested areas, causing significant increases in runoff (up to 10-year recurrence interval) from modest post-fire rainfall events (2-year recurrence interval). The clear separation of magnitudes and trends in water quality parameters and ecosystem metabolism before and after rainfall connected terrestrial and aquatic ecosystems suggests persistent impacts extending over hundreds of kilometers. However, the potential of the wildfire to generate and export runoff and wildfire disturbances was weakened by the co-occurrence of historically average rainfall events on the burn perimeter and net-losing conditions prevailing along the fluvial networks draining the mostly arid lands downstream of the burn scar.