How atmospheric pollution affects Flathead Lake

A cattle feed lot in Spokane. A wildfire in Colorado. Dust from the Sahara desert.

They are all vastly different, but they all can affect water quality in Flathead Lake. Researchers at Flathead Lake Biological Station are studying how smoke, dust and atmospheric particulate contribute to algae growth in the lake. Smoke from wildfires, pollen from crops and road dust contribute to increased nitrogen and phosphorous in Flathead Lake, and have the potential to increase algae growth. For the last 30 years the biological station in Yellow Bay has compiled data on atmospheric nutrients in the lake and they are continuing their work this fall to see how nitrogen and phosphorus work independently or together to increase nutrient loads in Flathead Lake. Researchers in November will set out dozens of containers in Flathead Lake to measure the independent effects of nitrogen and phosphorus on algae growth.

Scientists at the biological station are correlating data to measurements taken from around the world, and are seeing there is a very real connection between increasing nitrogen content in the atmosphere and amount of nitrogen collecting in Flathead Lake.

This time of year, the amount of nitrogen at certain areas in the lake is at very low, almost undetectable levels after algae have pulled out the nitrogen from the water column. If a wildfire or controlled burning begins to kick in high amounts of smoke, algae in Flathead Lake welcome the additional nutrients and there’s an increased opportunity for rapid production of algae. “Any additional nitrates from the atmosphere has the potential to really stimulate further production, we believe,” Dr. Bonnie Ellis said.

In some years, the amount of ammonium measured in Flathead Lake surpasses the amount contributed to the lake from Flathead River and its tributaries, Ellis said. “When you consider how big the mainstem Flathead Fiver is, that’s pretty phenomenal,” she said. While ammonium in Flathead Lake tends to arrive from local sources, nitrates come from more distant sources. Researchers are able to correlate data from nitrate sources around the world — such as the EPA emission reports or meteorological data— with increased nutrients in Flathead Lake.

Air inversions are one of the main contributors to increased nutrient load in Flathead Lake. The colder air trapped in the valley helps keep atmospheric nutrients trapped.

Combined with temperature inversions, even smaller, localized sources, such as field burning or road dust, can have an effect on Flathead Lake, Ellis said. “If there’s a local source and you have an inversion, those local sources can have quite an impact,” she said.

But, what’s found in Flathead Lake is not all local. “We are not alone,” Ellis said.