Trends in water quality at Bryce Canyon National Park, water years 2006–2021

The National Park Service collects water-quality samples on a rotating basis at three fixed water-quality stations in Bryce Canyon National Park (NP): Sheep Creek, Yellow Creek, and Mossy Cave Spring. Data collection began at Sheep Creek and Yellow Creek in November 2005 and at Mossy Cave in July 2008. Data on in-situ parameters, fecal-coliform samples, major ions, and nutrients are collected monthly, while trace elements are sampled quarterly. This report analyzes data from the beginning of the period of record for each station through water year 2021 to test for trends over time. Concentrations are also compared to relevant water-quality standards for the State of Utah. Overall, water quality at the park’s monitoring stations continues to be excellent, and park managers have been successful in their goal of maintaining these systems in unimpaired condition. Infrequent but continued Escherichia coli exceedances from trespass livestock at Sheep and Yellow creeks support the need for regular fence maintenance along the park boundary. High-quality conditions may qualify all three sites as Category 1 waters, the highest level of anti-degradation protection provided by the State of Utah. Minimum and maximum air temperatures at the park have increased, while precipitation remains highly variable. Increasing air temperatures have led to increasing water temperatures in Sheep and Yellow creeks. Sheep Creek also had a decrease in flow across several quantiles from 2006 to 2021, while higher flows decreased at Yellow Creek in the same period. Surface flows in these two creeks are likely to be increasingly affected by higher evapotranspiration due to warming air temperatures and possibly decreasing snowmelt runoff as the climate changes. The influx of ancient groundwater in both creek drainages helps sustain base flows at the sites. Mossy Cave Spring, which is sampled close to the spring emergence point, showed less of a climate signal than Sheep and Yellow creeks. In our record, the spring shows a modest increase in discharge, including higher flows at higher air temperatures. An uptick in visitation to Water Canyon and the Mossy Cave Trail has so far not been reflected by changes in water quality. There are additional statistical trends in water-quality parameters at all three sites. However, most of these trends are quite small and are likely ecologically negligible. Some statistical trends may be the result of instrument changes and improvements in quality assurance and quality control over time in both the field sampling effort and the laboratory analyses. Long-term monitoring of water-quality stations at Bryce Canyon NP suggests relatively stable aquatic systems that benefit from protection within the park. To maintain these unimpaired conditions into the future, park managers could consider: Regular fence checks and maintenance along active grazing allotments at the park boundary to protect riparian areas and aquatic systems from trespass livestock. Developing a springs-monitoring program to track changes in springflow at spring emergences to better understand bedrock-aquifer water supplies. These data would also help quantify springflow for use in water-rights hearings. Supporting hydrogeologic investigations to map the extent and flow paths of groundwater aquifers. Working with the State of Utah to develop groundwater-protection zones to protect groundwater aquifers from developments that would affect springs in the park. Prioritizing watershed management with proactive fire risk-reduction practices. Explicitly including watershed protection as a goal in plans for fire management and suppression. Using additional data and analyses to better understand the drivers of trends in water quality and their ecological significance. These could include higher-frequency data to better understand relationships between groundwater, precipitation, and surface flows at the sites. These could also include watershed metrics...