Airborne dust may spur toxic algae blooms on remote Minnesota lakes

Two miles deep into the woods of  Isle Royale National Park, Mark Edlund smelled something foul. He was stunned when, a quarter-mile down the trail, he reached a small lake and saw that his nose was right.

In one of the most remote and protected places in the Upper Midwest, far out from the Lake Superior shore, an intense outbreak of toxic blue-green algae had taken control of the little island lake.

That lake and others on Isle Royale have turned thick with noxious algae blooms every other year or so since that 2007 visit, said Edlund, senior scientist of the Science Museum of Minnesota's St. Croix Watershed Research Station. So have lakes in Voyageurs National Park and in federally protected forests along the North Shore and near the headwaters of the Mississippi River.

The toxic blooms are sadly expected now in ponds and lakes of cities, suburbs and rural towns where heavy runoff from fertilized fields and lawns fuels the growth, turning lakes a sickly, oily green. The blue-green algae can kill pet dogs and can be poisonous to people when ingested. It has shut down beaches, fisheries and, in some cases, drinking water supplies.

Now scientists are racing to find out why the outbreaks are reaching some of Minnesota's most pristine, faraway lakes.

"What's happening in these wilderness lakes is giving us a real gut check," Edlund said. "We need to tease apart why this is happening, because our tool box for managing lakes is fairly limited."

A warming climate is certainly one of the culprits, Edlund said. With less ice cover and longer growing seasons, the conditions are better for growth of the bacteria that causes the blooms.

There is also mounting evidence that winds pick up pollution and nutrients from even the smallest fragments of dust and soil and drop them onto every part of the region, even the inland waters of Isle Royale.

Those nutrients, which could be coming from across the continent, are changing the very makeup of life within the waters.

Cyanobacteria, the organisms that cause the harmful blooms, are among the most ancient living species on Earth and are found everywhere. But in a natural environment, it's rare for one species of bacteria to dominate a lake or a water body in the way cyanobacteria does during these blooms, said Janice Brahney, a Utah State University scientist.

As lakes become warmer and more filled with nutrients, cyanobacteria outcompete other organisms and algae to the point their population grows out of control, releasing higher concentrations of the toxins they produce.

Scientists have only recently started looking to the air, and the dust collected and deposited by the wind, as a potential cause for changing lakes around the globe.

Brahney has been tracking changes to aquatic life in remote parts of the Rocky Mountains. Lakes far from any known source of pollution are building up enough nutrients to disrupt ecosystems and shift which species dominate, she said.

The nutrients are most likely getting into the lakes by the wind.

"We've seen that this dust carried up in the atmosphere can bring a significant amount of nutrients to remote and pristine water bodies," Brahney said. "Now we're trying to study and understand just how much dust is contributing to ecosystems across space and time."

In a first of its kind project, researchers at the Science Museum plan to work with the Minnesota Pollution Control Agency and National Park Service to set up a series of monitors across 16 lakes that will measure the dust-fall. Edlund then plans to take samples of the sediment's core deep under each lake to measure how the climate and dust-borne nutrients have changed over time.

Brahney authored a paper last month in the journal Science that found wind has been carrying tiny shards of microplastics everywhere around the globe. There is already some evidence that it's picking up minerals from soil and dust and raining them into Minnesota lakes as well, Edlund said.

"We're finding these fairly large mineral inputs in small lakes surrounded by peatlands where it would be impossible to come from erosion," he said. "So if these minerals can't come from the land, they have to be coming from the air."

Funding for the algae research is uncertain. Edlund and the Science Museum requested about $800,000 from the state's environmental legacy trust fund for the study. Lawmakers, however, couldn't reach a deal on how to spend this year's trust fund dollars.

Little research has been done into how much more prevalent the outbreaks have become over time.

In 2010, the national nonprofit Environmental Working Group began recording and mapping public reports of outbreaks and closed lakes or beaches. The group was able to find 79 reports of the toxic blooms nationwide in 2010. Last year, there were reports of more than 530 outbreaks.

"It's not an exact science, but we know these are getting way more frequent," said Anne Schechinger, senior economic analyst for the Environmental Working Group. "Part of the problem is once this phosphorus gets into the water, it's extremely hard to remove it. So it keeps building up in these water bodies."

Minnesota lakes have typically seen algae blooms between midsummer and early fall, when water temperatures are at their highest. But already early this spring, three lakes in Minneapolis closed because of toxic blooms. KSTP reported the closures came shortly after a dog died after drinking infested water in Cedar Lake.

Extra nutrients work in concert with warmer temperatures to make the algae blooms more likely, Edlund said.

Minnesota has been steadily seeing warmer winters with fewer days of ice coverage on its lakes. Ice coverage varies annually, but Edlund estimated that Lake of the Woods, on Minnesota's northern border, gets about 30 more days of open water each year than it did a generation ago.

That's an extra month of sunlight for algae and bacteria, Edlund said.

The key to controlling the outbreaks is understanding where they are coming from, Edlund said.

Existing efforts to manage the blooms focus on the cabins, homes, farms and logging immediately around a water body, he said. But if the nutrients are coming in on the wind from across the continent, it is going to take much more comprehensive action to solve.

"The causes of these changes seem multifaceted, but we need to learn what they are," he said. "That is the only way we are going to be able to figure out how to protect our lakes."

Greg Stanley • 612-673-4882