New Mexico Geological Society Annual Spring Meeting — Abstracts

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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 degrade water quality. The 2022 Hermits Peak/Calf Canyon (HP/CC) Fire, the largest wildfire in New Mexico’s history (>340,000 acres), impacted the Gallinas Watershed – the source water for the City of Las Vegas’s drinking water supply, as well as a designated water resource for high-quality cold-water aquatic life, irrigation, livestock watering, and wildlife habitat (NMAC 20.6.4.215). Approximately 115,542 acres burned in the Gallinas River headwaters with 21% classified as high burn severity. This study assessed the HP/CC's bearing on water quality using data from USGS real time surface water gaging station 08380500 (Gallinas Creek at Montezuma). Amounts and trends in daily average values for dissolved oxygen, pH, specific conductance, temperature, and turbidity were assessed relative to discharge from September 01, 2022-August 31, 2025, to understand the fire’s impact on potable supplies and ecosystem services. Dissolved oxygen, pH, and specific conductance remained within the NMAC’s water quality standard ranges throughout the post-fire period. Dissolved oxygen ranged between 6.5-12.0 mg/L and stayed above the 6.0 mg/L threshold. Values of pH fluctuated between 7.4-9.0 and persisted above the 6.6 pH minimum. Specific conductance had a high of 309 μS/cm @ 25°C, low of 73 and an average of 221.64. Daily average values exceeded the 300 μS/cm maximum only 3 out of the 598 days of record (<1.0 %). Water temperature reached a high of 26.8°C intermittently during summer months, though daily average temperature values exceeded the NMAC 20°C threshold only 11 of 722 days of record (<2%). Turbidity values ranged from negligible to >3500 NTU. More than 25% of the 712 days of record exceeded 20 NTU, the City of Las Vegas’ current water treatment plant limit and more than 50% exceeded the high-quality cold-water tolerance of 10 NTU (NMAC 20.6.4.900). Calculations showed that the average yearly turbidity values decreased from Y1 to Y3 with the yearly averages dropping from 61.80 (SD = 153.85) to 24.84 (SD = 66.45). A one-way ANOVA was performed to examine the differences in average turbidity across the three post-HP/CC years. Results showed that the average yearly data differences were statistically significant across time, F (2, 710) = 5.941, p =.003. We interpret the decreased turbidity averages and narrowed fluctuations in high and low turbidity values as indicating that the negative effects of the wildfire on turbidity are decreasing over time. Turbidity in the City of Las Vegas’ current water system persists as a significant water quality issue, at times leading to mandatory boil water advisories and water supply challenges. Monitoring water quality remains imperative to manage fire sedimentation, protect water supplies, and inform adaptation strategies.