Status and trends in water quality at Curecanti National Recreation Area and Black Canyon of the Gunnison National Park, 2001–2014

Weissinger, Rebecca; Gibney, Nicole

From 2001 to 2014, the National Park Service supported monthly water-quality sampling in May–October at 23 fixed water-quality sites in Curecanti National Recreation Area (CURE) and Black Canyon of the Gunnison National Park (BLCA) (Figure i). Sites included streams and reservoirs protected within or upstream of the parks. This report analyzes the data to look for trends over time (Figure i, Tables i–iv) prior to re-evaluating the parks’ water-quality monitoring program. Concentrations are also compared to water-quality standards for aquatic life and recreation established by the State of Colorado. Trends in concentrations mostly indicated improving water quality, including decreases in nutrients, chloride, and metals at several sites. Improvements in water quality in Red Rock Canyon included decreases in total phosphorus, nitrite plus nitrate, and copper concentrations (see Tables iii, iv). These changes may be linked to a change in irrigation practices from 2006 to 2008, from flood irrigation to a sprinkler system that reduced overland flow. However, these improvements were not sufficient to bring water quality in Red Rock Canyon within state standards. The interim value for total phosphorus and the standard for fecal indicator bacteria (Escherichia coli) were still regularly exceeded at the upstream site in Red Rock Canyon. Selenium concentrations still exceeded the state aquatic-life standard at both the upstream and downstream sites on almost all visits. Continued management action is needed to bring irrigation return flows in Red Rock Canyon into compliance with state water-quality standards. A state plan for reducing selenium loading, the recent purchase of private land inholdings upstream of the canyon by the National Park Service, and a phase-out of livestock grazing upstream of the canyon may assist in bringing these waters into compliance. In Pine Creek, water-quality changes were a mixture of improving and degrading trends. Decreases in flow-adjusted concentrations of several ions and specific conductance may be linked to better targeting of dust suppressants on roads over time, with less spillover of suppressants into the creek. Increases in nitrite plus nitrate and selenium (see Tables iii, iv) were concerning but still at low concentrations. Residential septic systems or park pit toilets could contribute to increases in nitrite plus nitrate concentrations and could be checked for leaks to rule out these point sources. Total phosphorus regularly exceeded the state’s interim water-quality standard at many tributary sites (see Figure i). While human activities that increase erosion, such as live-stock grazing, roads, and agricultural activity, can contribute phosphorus to water bodies, volcanic rock common in the region can also be high in phosphorus. High phosphorus concentrations in tributaries have not caused algal blooms or other indicators of eutrophication at CURE or BLCA. Historically, Rocky Mountain streams have been more sensitive to increases in nitrogen species than to phosphorus concentrations. Evidence of eutrophication has been noted in Blue Mesa Reservoir in low water years, even when phosphorus concentrations have remained acceptable. Several localized fish kills were observed in the middle of the reservoir in 2013, and the most upstream site in the reservoir occasionally exceeded the interim chlorophyll-a standard for cold-water reservoirs. Park monitoring has been updated to include sampling dissolved oxygen and water temperature at multiple depths for better comparison with state water-quality standards. NPS personnel are also coordinating with the state to increase nutrient sampling in the reservoir. Investigations into sources of nutrients in watersheds in this area, particularly nitrogen species, may help land managers to develop a plan for improving water quality in Blue Mesa Reservoir.

Status and trends in water quality at Curecanti National Recreation Area and Black Canyon of the Gunnison National Park, 2001–2014

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