A Slimy Mystery

It’s fitting that Lienne Sethna grew up near the Cuyahoga River, a northeast Ohio waterway that was once so choked with oil that it frequently caught on fire. The river, which helped spur the creation of the Clean Water Act in the 1970s, is healthier today due in part to the efforts of environmental scientists with a passion for dirty water. Count Sethna as a member of this camp. Through her work with the St. Croix Watershed Research Station, the scientist is studying toxic blue-green algae in lakes in Superior National Forest. Also known as cyanobacteria, the algae typically blooms near urban areas and farmland, the result of warming waters and chemical pollution. So what’s up with algal blooms occurring in our most pristine lakes? Sethna and her fellow researchers hope to answer that question with $1.3 million in research funds awarded during Minnesota’s last legislative session.

Q | How did you come to study water?
I’ve always liked science, and I started out as a geology major at Ohio State. But when I graduated, I became more interested in how people are influencing the environment. People have had a profound impact on water, so I kind of moved in that direction and got my Ph.D. in environmental science from Indiana University–Bloomington.

Q | How long have you been with the Science Museum of Minnesota’s St. Croix Watershed Research Station?
I joined them in 2022—specifically to study harmful algae blooms that were appearing in the Boundary Waters.

Q | Describe your algae research.
Well, initially we thought that dust from agricultural land was blowing into the Boundary Waters and causing the blooms. Ag dust contains lots of nutrients, like nitrogen, that feed these blooms. So that was one theory. But when we tried to collect this dust, we couldn’t get enough material to do a proper analysis. This told us that maybe there was some other reason for the blooms. That led us to think more about how climate change might be affecting these northern lakes. Our latest theory is that waters are warming, causing lakebeds to release naturally occurring phosphorus that rises to the top of the water column, where algae have a field day because there’s now plenty of nutrients available for them to grow. We call this recycling process “internal phosphorus loading.”

Q | How are you gathering data for this research?
We deploy buoys in wilderness lakes that have oxygen and temperature monitors to determine if this mixing is happening and to what extent. We also collect mud samples—sediment cores—from lakes, which can show us what the nutrient conditions of a lake have been over decades, dating all the way back to the 1850s.

Q | That’s amazing. What would this historic data tell you?
We want to understand whether these lakes have been blooming since the 1800s or if we’re just noticing more blooms now that we’re studying them. We’re also working with the Red Lake Department of Natural Resources and the 1854 Treaty Authority to study lakes outside of the Boundary Waters. So we’re really expanding our geographic reach to look at lake mixing trends.

Q | If your mixing theory is correct, what can we do about algal blooms in the wilderness?
That’s a good question. It’s not like urban lakes, where you could potentially manage blooms with fertilizer bans or shoreline management, or even water treatment. It would be very expensive to try to manage cyanobacteria in the wilderness. For now, we’re just hoping to understand these blooms better.

Q | How can visitors to the Boundary Waters and other wilderness areas stay safe if they encounter a toxic algae bloom?
I think the first step is recognizing a bloom. Cyanobacterial blooms tend to be blue-green, hence the cyano name. Avoid swimming in or drinking water that looks thick and paint-slicked. I’m big into open-water swimming and so I try to be aware of the quality of the water I’m in. And it’s good to know that peak season for algae blooms seems to be in the warmer months of late summer and early fall.

Q | A lighter question to end our chat: What’s your favorite lake for open water swimming?
I love Square Lake! I do most of my swimming there.

For more information on the St. Croix Watershed Research Station’s algae research, visit smm.org/scwrs.