Utilizing Benthic Macroinvertebrates to Assess the Impacts of the Hermits Peak/Calf Canyon Fire on Water Quality in Regional Watersheds

Abstract

Wildfires can have short-and long-term impacts on the health of a watershed. The loss of vegetation, abundance of charred materials, and destabilization of hillsides can increase stream sedimentation and impact water quality. This project assessed the 2022 Hermits Peak/Calf Canyon Wildfire’s impact on water health in regional streams using macroinvertebrate numbers and populations as proxies for water quality. Approximately 115,542 acres burned in the Headwaters Gallinas River Watershed, 21% of which were classified USFS Burned Area Emergency Response (BAER) team as high burn severity while approximately 34% of the 40,150 acres burned in the UPW were classified as high burn severity. Such classification raised concerns for post-fire impacts to water quality from increased river discharge, hillside erosion, and fire sedimentation. We followed the NM Water Quality Bureau’s SOP for Benthic Macroinvertebrate Sampling; Section 6.1 Wadeable Streams/Rivers and collected samples from two sites along both the Upper Pecos River and Gallinas River over a 6-week period following August 2022 fire containment. The Upper Gallinas Canyon site was at Canovas Canyon (35°41’51’’N; 105°25’00’’W) and Lower Gallinas Canyon site was at the National Avenue Bridge (35°35’41’’N; 105°13’28’’W). The Upper Pecos River site was at 35°35’00’’N; 105°40’20’’W and Lower Pecos River site was at the Village Bridge (35°34’35’’N; 105°40’10’’W). The Gallinas River was more degraded post-fire than the Upper Pecos River. Macroinvertebrate species observed in the Gallinas River (worms, black flies, scuds, dragon flies, and riffle beetles) were more pollution tolerant, indicating poor to moderate water quality, while those observed in the Upper Pecos River (stoneflies, nymphs-adults, caddis flies, mayflies) were more pollution sensitive, indicating good water quality. Both systems showed decreasing numbers and diversity in macroinvertebrate species from upper to lower sites, indicating diminishing downstream water quality. These observations suggest that (1) the Headwaters Gallinas Watershed shows poorer aquatic ecosystem health relative to the Upper Pecos River Watershed; (2) both systems remain vulnerable to post-fire floods and water quality impairments; and (3) downstream sites in particular should be monitored for water quality health and targeted for stream bank restoration.