Since 2000, the Gallatin River Task Force has monitored water quality in the upper Gallatin watershed. Staffers and volunteers have routinely sampled several locations throughout the watershed to determine how land-use practices impact our streams, creeks, and rivers. This data plays a key role in tracking the long-term health of the river system, planning and evaluating of restoration projects and management actions, while also helping to identify and monitor unforeseen events. In 2018, one such unforeseen event occurred—a late-summer algae bloom far beyond historic norms.
Naturally, as an organization grounded in science, we asked why. To find out, in partnership with Montana DEQ, we launched a 3-year study focused on algae growth and the conditions that lead to widespread, detrimental algae bloom. While algae occurs naturally in the upper Gallatin, too much algae is harmful to aquatic wildlife like trout and insects, and large blooms negatively affect recreation, like boating and fishing, making this condition undesirable environmentally and socially.
Factors that can exacerbate algae growth include phosphorus and nitrogen levels, water temperature, hardness, pH, water velocity, sunlight, and water clarity. Task Force data collected in 2018 provided some insight into the conditions that might have caused the algal bloom. Nitrogen levels were some of the highest ever recorded in the West Fork of the Gallatin River. Potential sources of anthropogenic nitrogen include fertilizer, stormwater runoff, land application of treated wastewater effluent on the Big Sky golf course and Big Sky Community Park, pet and horse waste, and septic system effluent.
In addition to elevated nitrogen concentrations, average weekly water temperature during the last week of July at the West Fork streamflow station was the highest ever recorded. Anecdotal evidence from local river users documented more sunny days over July and fewer afternoon thunderstorms that reduce water clarity than in years past. The elevated nitrogen levels combined with warm water temperature, clear water and abundant sunshine might have contributed to increased algae growth in 2018.
So, what does the 2019 data show and what conclusions can we draw, if any, from the two data sets?
For one, last summer was cooler and wetter, meaning water temperatures were generally lower and water quantity was generally higher. While algae growth was possible and was indeed observed at all of the study sites, conditions for a large-scale event weren’t ideal, and no large-scale event was observed. We found algae production above state recommended levels at some testing sites, and nitrogen and phosphorus levels were also above state standards at certain sites at certain times.
These findings are only part of the story. Combined with the 2018 data, they’re chapters in a book that will take years to write, with many revisions along the way. What we do know, and have known for some time, is that nitrogen levels in the upper Gallatin watershed are too high. There are steps that individuals can take to lower their nitrogen footprint, like regularly maintaining septic systems, conserving water, and landscaping with native plants.
For the greatest improvement, we also need to implement large-scale restoration and conservation projects, and better regulate land-use practices to account for stormwater runoff and excess nitrogen loading. An upgraded wastewater treatment plant will go a long way toward reducing nitrogen in the West Fork, and streamside restoration projects can filter runoff before it reaches surface waters, improving in-stream water quality. The Task Force-led Headwaters Alliance is updating and expanding a plan to prioritize nutrient-reduction strategies, and will have a draft produced later this summer.
As we head into summer, forecasters are not optimistic about precipitation or temperatures, and on June 10, the snowpack measured 74% of normal. (By June 24, the snowpack was at 15% of normal.) Low snow levels, less rain, and higher temperatures could mean significant algae growth this summer, as water levels will likely be low and water temperatures will likely be high.
Once runoff subsides, we’ll be back in the river, gathering data, forming an outline and, hopefully, getting one step closer to understanding nuisance algae growth, an understanding that will inform future actions toward mitigation.