New Mexico Geological Society Annual Spring Meeting — Abstracts

The Upper Pecos Watershed (UPW), part of the Rio Grande Basin, extends from the headwaters of the Pecos River in the Sangre de Cristo Mountains (elevation > 12,000 ft) to its confluences with Cow Creek and El Rito (elevation ~ 6,000 ft). The Upper Pecos River supports recreation, agriculture, cattle grazing, tourism, and other uses. It is one of the most ecologically diverse and culturally significant waters of New Mexico. The UPW, along with nearby regional watersheds, was impacted by the 2022 Hermits Peak/Calf Canyon Fire, the largest wildfire in New Mexico’s history (>340,000 acres). Approximately 40,150 acres burned in the UPW, 34% of which were classified by the USFS Burned Area Emergency Response (BAER) team 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 collected weekly in-the-field physical-chemical parameters (conductivity, temperature, dissolved oxygen, and pH) using a YSI 556 Multi Probe and grab water samples for turbidity analysis using a Hach TL2300 turbidimeter throughout Summer 2022 to assess the after-effects of the wildfire. These data were compared to water quality data collected by our team in Summer 2020 and 2021 to determine if and how much the water quality departed from baseline values. From the onset of the monsoon rains (mid-June), ash and floating debris were observed in the stream, along with high turbidity and low dissolved oxygen values both in exceedance of the NMAC 20.6.4.900 water quality threshold (> 10.00 NTU and 6 mg/L respectively). Values of pH ranged between 3.79-7.69 with the lowest values corresponding roughly to high discharge events. Temperature and electrical conductivity met water quality standards for the Upper Pecos River’s high-quality cold-water designation (NMAC 20.6.2). We continue to monitor the river, as water quality in the system sets the basis for the rest of ecosystem health.