The Task Force published a review of our community water quality monitoring data in 2016. The report identified strong spatial and seasonal trends in nitrate levels, but no conclusive long-term trends.
Nitrate is a form of nitrogen readily available to plants and animals. If nitrate exceeds 0.1 mg/L during the growing season, elevated nitrate may accelerate algae growth, which impacts recreation and aquatic insect habitat.
Average nitrate levels from 2000 to 2016 were between 0.01 mg/L and 0.07 mg/ on the mainstem Gallatin and between 0.02 mg/L and 0.18 mg/L in the West Fork Watershed. The average nitrate levels exceeded recommended levels (0.1 mg/L) at the two West Fork sites (“Community Park” and “West Fork above South Fork”) downstream of the golf course and upstream of the South Fork confluence.
Across the watershed, nitrate was highest in the fall and winter when water levels were low. Sixteen years of nitrate data demonstrated no conclusive long-term trends. This may be due in part to limited data and the variety of factors influencing nitrate levels, including streamflow and human influence. Our results from 2017 supported the trends observed between 2000 and 2016.
In 2018, the Task Force measured among the highest summer nitrogen levels in the West Fork downstream of the golf course and upstream of the South Fork confluence: 0.42 mg/L for total nitrogen and 0.31 mg/L for nitrate. In contrast, the state standard for total nitrogen is 0.3 mg/L. The state standard for nitrate was removed by the Montana Department of Environmental Quality in 2013; however, the Task Force still uses the previous standard of 0.1 mg/L as a trigger value for elevated nitrate in local streams. The only historical nitrate measurements similar to the summer 2018 values were collected at two sites on the West Fork downstream of the Big Sky Community Park in August 2008.