New study reveals Greenwood fire’s impact on nearby lakes

DULUTH, MN. (Northern News Now) - More than two years ago, the Greenwood fire raged through 26,000 acres in Northern Minnesota destroying the land and homes.

Researchers at the University of Minnesota Duluth’s Natural Resources Research Institute wanted to know how the nearby lakes were affected.

“The real motivation for this study was seeing all the images in the media from the Greenwood fire,” said Chris Filstrup, one of the lake and stream scientists at the NRRI involved in the study.

In collaboration with Michigan State University and the University of Montreal, the study is the largest study of lakes in response to a single wildfire in the country’s history.

“We studied 15 lakes that were in the impacted zone or the Greenwood fire burned zone across gradients of wildfire severity and also the extent of the burn area within watersheds,” said Filstrup.

The group of 20 field scientists took four-liter samples from each of these lakes from May to October of 2022.

Filstrup and crew compared those samples to ones taken from 15 lakes outside of the burn zone to determine the wildfire’s impact on the lakes’ water quality.

“What we were looking at primarily are nutrients such as nitrogen and phosphorus and we saw that the most severe wildfires could increase phosphorus concentrations in these lakes by twofold,” said Filstrup.

These levels of phosphorus typically lead to algae blooms harmful to humans and animals, but Filstrup said because of the murkier water from excessive mineral deposits, the scientists found no blooms in this study.

However, the high phosphorus levels can still classify the lakes as “impaired” which means they should not be used for any recreational activities like fishing or swimming.

Although Minnesota is seeing an above-average year for the number of wildfires, the Minnesota Department of Natural Resources leaders said not all of them will be devastating to the land.

“Most of our wildfires are relatively small in size, and that limits their impact or their effect,” said Travis Verdegan, Predictive Services Coordinator for the DNR. “Even if we have a half-acre fire that burned very intensely, just because it’s small, it’s less likely to have some of those larger impacts that you might see with a fire like the Greenwood fire from 2021.”

Even with small fires, Filstrup is looking for answers to the big questions.

“We know there are these short-term impacts the year after the fire, but we don’t know, if we extend this out two, three, four, five years, if we’re going to see those same impacts,” said Filstrup.

Filstrup’s research team has already been selected for funding for a follow-up study.

They plan to return to the same lakes in 2024, 2025, and 2026 to test for any possible long-term effects.

Even the short-term findings can have a lasting impact.

“The lakes that we know now may look very different in the future,” said Filstrup. “What we’re trying to do is generate the foundational information that can be used to help manage these lakes and a changing landscape going forward.”

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