Researchers study water quality impacts following 2021 Greenwood Fire
The 2021 Greenwood Fire, which burned nearly 27,000 acres in northeastern Minnesota following a summer of heat and drought, has become a desirable place for scientists across the Midwest and regions of Canada to study the aftermath of a large-scale wildfire in a remote boreal landscape.
Immediately following the fire, researchers began planning studies to conduct moose habitat surveys, tree planting, and, more recently, the intricate relationship between wildfires and lake water quality.
According to Chris Filstrup, an applied limnologist at the Natural Resources Research Institute (NRRI) at the University of Minnesota Duluth and co-author of a recently published study, there is minimal knowledge of how direct wildfire burns within watersheds affect lake water quality, including which lakes are most sensitive to wildfires and what wildfire characteristics lead to the most significant water quality impacts.
While some research has been conducted in the western U.S. following large-scale wildfire events, the relationship between northern forested regions of Minnesota and inland lakes has yet to be explored. “It’s something we really don’t know a lot about,” Filstrup said.
The researchers at NRRI quickly secured funding following the Greenwood Fire and, within six months, deployed into the thick remote landscape with a team of 10 researchers.
“The fun part of this research was we had colleagues from Michigan State University and colleagues from Canada in Montreal that joined our research team,” Filstrup said. “It got a little cumbersome because we had so many field research teams out there. But it was really enjoyable to all be out there at the same time.”
After months in the field, including a buggy June, collecting water samples and additional data on 30 inland lakes, Filstrup said the research results were “surprising.”
Lakes directly impacted by wildfires had substantially more nutrients, including nitrogen and phosphorus, than other nearby streams or lakes. Filstrup said that increased nitrogen and phosphorus levels typically lead to algae growth, which contributes to reduced dissolved oxygen and hypoxia. However, even though the lakes impacted by the fire had increased levels of nutrients, algae growth has yet to be apparent.
“We didn’t see that in any of these lakes,” Filstrup said. “What that leads us to believe is although we had more nutrients, we also had more sediment in the water. Less light was able to penetrate because of that.”
Due to increased sediment from wildfire debris, the limited light conditions created tea-stained, murky water in many directly impacted wildfire lakes, limiting algae growth.
Filstrup said it will be interesting to see, long-term as the sediments fall out of the system, “how that may persist going forward in these lakes.”
While the research showed that the directly impacted wildfire lakes had increased levels of sediment and nutrients, Filstrup said the most significant ecological impact may be disruptions to ecosystem services. “If we do start seeing increased algae growth that could be fueling hypoxia in these lakes, it will start affecting the fish population.”
“Low oxygen can be really stressful to fish,” he said. If algae growth does begin to develop in the near future, Filstrup is concerned about potential fish kills in many of the directly impacted lakes. Another area of concern is mercury and the changes in mercury cycling in the lakes.
While the research team is on a temporary hiatus, Filstrup said they plan to head back into the field to continue water sampling later this fall. “We got a little bit of short-term funding to continue monitoring.” Funding for long-term research in 2024-2026 is currently pending.
As the limnologists prepare to head back into the field, Filstrup said this research is incredibly valuable to understand how wildfires and climate change’s potential implications impact inland lakes. “I think this is a really good start for looking at wildfire impacts in the midwest.”
WTIP’s Kalli Hawkins spoke with Chris Filstrup, an applied limnologist and co-author of the recently published research from NRRI. The audio from the interview is below.