Hannah Riedl and Ryan Koeblein from the Watershed Protection Section of the Montana Department of Environmental Quality were in the Bitterroot last week collecting algae samples which will undergo laboratory analysis as part of the agency’s 20-year plan for monitoring nutrient trends in the Bitterroot River.
All freshwater streams and rivers contain varying amounts of nutrients. In fact, nitrogen and phosphorous are essential to the growth of aquatic plants that become a food source to other organisms. However, high levels of nitrogen and phosphorous, can be a problem when they cause rampant algae growth.
According to Reidl, besides coating the riverbeds in brownish to greenish slime, mats of algae create shade and block sunlight from reaching more beneficial organisms below the river’s surface. Algae also makes it hard to wade and fish and can clog irrigation intakes and canals, creating problems for both agricultural and recreational activities. Then, as the algae dies, the decomposition process sucks oxygen out of the water, and has a suffocating effect on trout and bugs.
Long-term nutrient trend monitoring began in earnest in the Clark Fork Basin Watershed, of which the Bitterroot is a part, in the late 1990s as part of a tri-state effort to address the enormous nutrient pollution problems showing up in Lake Pend Oreille.
In the Clark Fork Basin, a 10-year cooperative agreement (1998 to 2008), called the Clark Fork Voluntary Nutrient Reduction Program (VNRP), was initiated that included the basin’s four
largest point-source dischargers—the municipal wastewater treatment plants in Butte, Deer Lodge, and Missoula, and the (former) Smurfit-Stone Mill. The VNRP was created and implemented by the Tri-State Water Quality Council based in Sandpoint, Idaho, as a collaborative effort involving state governments, municipalities, private industries such as Avista, and citizen groups like the Clark Fork Coalition.
Long-term trend monitoring has continued since then but mostly along the mainstem of the Clark Fork River, only being renewed along the Bitterroot River in 2019.
The latest study, the Clark Fork River Nutrient Water Quality Status and Trends Report, 1998-2017, published by Montana DEQ and Avista, contains some good news in relation to algae and some of the nutrients that contribute to the problem.
It appears that through a combination of education, regulations, and innovative partnerships, the nutrient pollution status of the Clark Fork River is mostly improving, especially in the middle section, which includes Missoula.
A lot of work has been done in the Clark Fork River basin to reduce and control nutrient impacts to water quality. Point source and non-point source nutrient reduction activities have occurred across the basin, more are planned and some are already in progress. Nutrient reduction activities in Missoula have resulted in highly significant decreasing trends for all nutrients at the monitoring station below Missoula. Decreasing trends in total phosphorous concentrations were found throughout the river. Despite these gains, summer concentrations of total nitrogen and total phosphorous continue to exceed numeric water quality standard thresholds, especially in the upper river.
As for algae growth, time trends analysis found benthic algal levels to be holding steady or decreasing at the seven stations monitored for algae. No increasing trends in chlorophyll-a were found. In regard to numeric nutrient standard thresholds for chlorophyll-a, this work found a decreasing percentage of samples that exceeded the mean and maximum summer chlorophyll-a standard for most monitoring stations when comparing the two time periods.
Reidl said that a trend analysis requires at least five years’ worth of data, but the first three years of data show a pretty health system.
“I call the Bitterroot River the unicorn of Montana,” said Reidl. “In a river of this size serving a large population, it is surprising to find such low levels of nutrients.” According to Reidl, it is important to track the nutrient trends because after reaching a certain tipping point nutrient pollution is very difficult to reverse.