In 2018, the Task Force measured among the highest summer nitrogen levels in the West Fork 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.
Average nitrate levels from 2000 to 2016 were between 0.01 mg/L and 0.07 mg/L 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 the recommended level (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.
Average total phosphorous levels (summer only) ranged from 0.0048 mg/L to 0.022 mg/L on the Gallatin River and between 0.0063 mg/L to 0.013 mg/L in the West Fork Watershed. On average, all sites were below 0.03 mg/L critical value used by the Montana Department of Environmental Quality (MT DEQ).
Average total nitrogen levels (summer only) fell between 0.08 mg/L and 0.10 mg/L on the Gallatin River and between 0.09 mg/L and 0.25 mg/L in the West Fork Watershed. On average, all sites were below the 0.3 mg/L critical value used by the Montana Department of Environmental Quality (MT DEQ).
For more information, check out this review of our community water quality monitoring data from 2016.