Algal blooms in boundary waters raise questions and concerns

Algal blooms in boundary waters raise questions and concerns

Adam Heathcote has been studying blue-green algal blooms for more than 15 years, including extensive work in lakes in Iowa and southern Minnesota surrounded by farms and other developments, where it is common to see severe algal blooms.

But that didn’t prepare him for what he saw last month in the Boundary Waters Canoe Area Wilderness, when he paddled Burnt and Smoke Lakes – two small lakes off Sawbill Lake, a hot spot. popular BWCA entrance north of Tofte, Minnesota.

Brilliant seaweed blooms along a lake shore

A neon blue algal bloom was seen on Burnt Lake in the Boundary Waters Canoe Wilderness Area last month.

Courtesy of Lienne Sethna

“It was the worst bloom I’ve seen in Iowa in my entire PhD, in a lake that was two portages into boundary waters,” said Heathcote, who leads the Department of Water and Change. Climate at St. Croix Watershed Research. Station, part of the Science Museum of Minnesota.

“I had never seen a flower so much that it was like thick paint, neon blue, neon green, lake-wide, not just [in] a small secluded bay,” Heathcote described. “Two of the three lakes we sampled in boundary waters had this over most of their surface.”

Heathcote was surprised because these lakes are protected; they are surrounded by wild nature.

Algae exist in all lakes. They are an integral part of the ecosystem. This becomes problematic when the algae become dominated by cyanobacteria, which can produce toxins that are harmful to people and pets.

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Not all algal blooms are toxic. But Lienne Sethna, a postdoctoral fellow working with Heathcote, said they examined algae found in the boundary waters under a microscope. And they spotted three species of cyanobacteria that produce different types of toxins.

“It’s something that really concerns us, and something that we really hope to address through this study,” Sethna said.

Minnesota’s Most Pristine Lakes

Researchers are studying some of the cleanest and most pristine lakes in the state, inside and just outside the Wild Area. They are trying to figure out why the algae situation is changing unexpectedly. They also documented cyanobacteria in Elbow and Finger Lakes, which are part of the Timber-Frear Canoe Route in the Upper National Forest, and on Sawbill Lake.

A paddle sits in lake water next to neon blue seaweed

A neon blue algal bloom was seen on Burnt Lake in the Boundary Waters Canoe Wilderness Area last month.

Courtesy of Adam Heathcote

Scientists measure nutrients and algae, water temperature and oxygen levels. They focused in part on Burnt and Smoke lakes due to previous reports of algal blooms.

Clare Shirley owns Sawbill Canoe Outfitters with her husband Dan. She said her family remembered seeing algae on these lakes since her grandparents started the business in 1957.

Shirley said these lakes are shallow, with muddy bottoms and historically good walleye fishing that doesn’t appear to have been affected by algae.

“No one has ever gotten sick or reported any issues that way either,” Shirley said. “So it’s something we’ve lived with for a very long time and have always been aware of. But we’re excited and grateful that someone is investigating it. And we’ll be really curious to hear what they find out. “

History in the sediments

Heathcote said there is evidence of algal blooms in shallow northern Minnesota lakes as far back as 18th century travellers’ accounts. But he suspects blooms in the region are getting larger, more persistent and more toxic.

To verify this, scientists extract cores from sediments that gradually accumulate at the bottom of the lakes. Cyanobacteria create pigments that are stored in sediments.

A person on a boat extracts a sample of sediment from a lake

Adam Heathcote extracts a sediment core from East Twin Lake in the Upper National Forest.

Courtesy of Lienne Sethna

“And we can look back through those layers, almost like reading the pages of a book,” Sethna explained.

“We use these layers to understand how nutrients and algae have changed over time. And so we use that to understand how cyanobacteria or harmful algal blooms have happened in the past and what kinds of factors have changed from historical conditions to the present day to help us understand why they’re happening now.

Two possible causes

Scientists have two hypotheses about what triggers the blooms in these wild lakes.

First, climate change. The lakes are warmer. This allows nutrients that have accumulated in the sediment to be more readily available to algae at the top of the lake.

The second theory: dust. Researchers suspect that nutrients are falling into the lakes from the atmosphere and helping to fuel these algal blooms.

“We kind of had to take the laugh test on that one first because of course you’re thinking, ‘What could the dust do to those huge lakes? ‘” Heathcote admitted.

But he said several influential studies have documented the impact of dust in remote alpine lakes in the foothills of the Rocky Mountains in Colorado.

A seaweed blooms along the shore of a lake

A bright green algal bloom is observed along the shoreline of Smoke Lake in the boundary waters.

Courtesy of Lienne Sethna

For the first time in Minnesota, Heathcote and colleagues have set up a network of dry deposition monitors to capture and measure nutrients falling from the sky.

Heathcote thinks it’s likely that global warming and atmospheric deposition are contributing to the increased trend of toxic cyanobacterial blooms in northern Minnesota. This project seeks to confirm this.

Although much research has been done on algal blooms in areas where human impact is evident, scientists are still struggling to understand the more global drivers that power them.

“We don’t really know what we’re going to find out,” Heathcote said. “It’s really cutting-edge research. This is a first-of-its-kind study in Minnesota and one of the first of its kind in the world.

Anyone who sees what they suspect is a harmful algal bloom on a remote northern Minnesota lake is asked to contact researchers at ResearchStation@smm.org or on twitter @scwrs_mn


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