RESULTS FROM 18 MONTH WATER QUALITY MONITORING OF THE UPPER PECOS RIVER, NEW MEXICO

Our team collected water quality data for the Upper Pecos River to establish baseline conditions and determine if waters are meeting water quality standards (WQS) for the Upper Pecos River’s high-quality cold-water designation (NMAC 20.6.4). We established five monitoring sites along a 25 km stretch to capture conditions above an historic mine site, at the confluence of a tributary downslope of a proposed exploratory hard rock drilling site, and at several high-use recreation areas. The team collected bi-weekly in-the-field physical-chemical parameters (electrical conductivity, temperature, dissolved oxygen, and pH) using a USI 556 Multi Probe and collected grab water samples for turbidity analysis using a Hach TL2300 turbidimeter. Electrical conductivity increased downstream along the study stretch but remained within the 300 µS/cm threshold. Temperature increased downstream and throughout the summer months, but remained below the 23°C (73°F) segment-specific criterion. Dissolved oxygen values were ≥ 6.00 mg/L in accordance with WQS for most sites throughout the sampling period. The Pecos Village site had < 6.00 mg/L dissolved oxygen on 5 days between June and September corresponding to high stream temperature days. The pH values varied greatly between sites and throughout the study period with average pH ranging between 6.4-6.8. The pH generally decreased downstream possibly reflecting input from natural sulfide-bearing bedrock and historic mine workings. Turbidity values varied widely with most (96%) values below the 10 NTU threshold. We calculated Pearson’s correlation coefficients (r-values) for pH and turbidity versus discharge. For pH, r-values ranged between -0.3434 to -0.4931 indicating a weak negative correlation with streamflow. For turbidity, r-values ranged between 0.5074 to 0.7677 indicating a moderate to moderately strong positive correlation with streamflow. We report that the Upper Pecos River is in good health for its domestic water supply, fish culture, high quality cold-water aquatic life, and other designated uses. Minimizing recreation, reducing trampling, and increasing streamside vegetation along the river banks at the Pecos Village site could decrease turbidity, decrease temperature, increase dissolved oxygen and overall maintain and improve the health of the river.