Study: Harmful algae blooms like it hot, but can occur in cold water

18 02 2023

A neon blue algae bloom is seen on Burnt Lake in the Boundary Waters Canoe Area Wilderness on Sept. 28. Photo: Courtesy of Lienne Sethna

By Dan Kraker from Minnesota Public Radio News • Reposted: February 17, 2023

Harmful algae blooms, those thick, blue-green, oily layers of scum that have become more common on Minnesota lakes in recent years, are typically seen when water temperatures warm. 

But a new paper challenges assumptions of what causes these sometimes toxic blooms. It documents more than three dozen cases of harmful algae in relatively cold water, including when there’s snow on the ground, and even, under ice. 

“It’s really counterintuitive to what we’ve understood about blooms in the past,” said Kaitlin Reinl, Research Coordinator at the Lake Superior National Estuarine Research Reserve in Superior, Wis. She collaborated with 27 other scientists through the Global Lake Ecological Observatory Network to author the paper published in the journal Limnology and Oceanography Letters.

New discoveries

In recent years, cyanobacteria, the stuff that forms harmful algae blooms, has been blamed for the deaths of several dogs in Minnesota. In 2014 it temporarily forced the shutdown of the public water supply in Toledo, Ohio. 

The algae is most commonly seen on lakes surrounded by homes and agricultural land, because the blooms are fueled by nutrients that run off into the lakes from lawns and farm fields. They often occur in calm conditions in mid-to-late summer when water temperatures spike. 

Lately, scientists have been shocked to find them in lakes with very cold, very clean water: Lake Superior, and in the Boundary Waters Canoe Area Wilderness

This new paper, called “Blooms also like it cold,” collected reports of 37 blooms in scientific journals, media articles, and personal accounts that occurred when water temperatures were below 15 degrees Celsius, which is about 60 degrees Fahrenheit. 

A few of the blooms were in the Upper Midwest, including one in Minnesota, in Lake Itasca. Others were documented across North America and Europe. 

Likely undercount

Reinl said researchers didn’t try to count every single instance of a reported cold-water bloom. And she said there’s definitely an “observer bias” in where the blooms were recorded, based on where researchers are located. 

Scientists, for the most part, also aren’t actively looking for algae blooms in cold-water conditions. Most monitoring programs occur when it’s warmer and easier to gather data. So there’s likely a significant undercount of cold water cyanobacteria. 

The point of the article, Reinl said, isn’t to challenge the fact that algae blooms “like it hot,” which is the name of an oft-cited study published over a decade ago. 

Rather, it’s to challenge researchers to consider that some blooms also don’t seem to mind it when it’s cold. 

“We don’t want to create a blind spot with bloom ecology and our ability to manage blooms and steward our lakes, just because we have these preset assumptions that blooms only happen when you have high temperatures,” Reinl said. 


In the paper, researchers propose several ways in which algae blooms can form even when the water is relatively frigid. 

For example, cyanobacteria has developed adaptations in which they can form even in conditions with very low light, temperatures and nutrient levels. This is helpful in the winter, when there’s not a consistent influx of nutrients, the water is colder and ice cover can block sunlight. 

Blooms can also form when nutrients deep in lakes are brought to the surface when the water is mixed by big storms or underwater currents such as upwelling. 

And some algae may form when the water is warm, and then persist in the lake after the water cools. 

“Those are the things we hypothesize,” said Reinl. “And so some of the next steps are to test those hypotheses in the lab and by collecting monitoring data.” 

Bob Sterner, director of the Large Lakes Observatory at the University of Minnesota Duluth, says recent blooms in Lake Superior have been clearly linked to warmer temperatures. 

“When it’s a warmer year we’re much more likely to see a bloom happen in Lake Superior,” Sterner said. “We tend to think that it’s a climate change driven problem that we’re just beginning to experience.”

Still, Sterner said the more scientists learn about cyanobacteria, it’s clear there are many different conditions in which harmful algae blooms can thrive, including when lakes are cool. 

“So it’s really good to have this paper come out and help us appreciate the diversity of organisms out there.”

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Feds slap 20-year mining ban on land near Boundary Waters

27 01 2023

The Kawishiwi River (right) flows Wednesday, in June 2019 near Ely, Minn. Twin Metals planned to setup its mining operations to the left of the river, but a 20-year ban Thursday on new mining projects in the area deals a huge blow to the proposal. Photo: Derek Montgomery for MPR News 2019

By Dan Kraker from Minnesota Public Radio News • Posted: January 27, 2023

The U.S. Department of the Interior issued a 20-year mining moratorium Thursday on 225,000 acres of federal land near the Boundary Waters, dealing a further blow to the proposed Twin Metals mine near Ely, Minn. and other potential mines for copper, nickel and precious metals within the watershed of the canoe wilderness area.

The decision is the latest milestone in a long and contentious tug of war over mining near the popular wilderness area that has spanned more than six years and three presidential administrations.

President Obama first proposed withdrawing federal land from future mineral exploration and leasing within the watershed of the Boundary Waters near the end of his second term in 2016. The Trump administration then stopped the environmental review of that proposal, before it was restarted under the Biden administration in 2021.

The decision announced Monday followed more than a year of analysis by the Bureau of Land Management and U.S. Forest Service of the potential environmental and cultural impacts of mining in the region upstream from the Boundary Waters, and the review of 225,000 public comments.

“Protecting a place like Boundary Waters is key to supporting the health of the watershed and its surrounding wildlife, upholding our Tribal trust and treaty responsibilities, and boosting the local recreation economy,” said Secretary of the Interior Deb Haaland in announcing her decision.

“With an eye toward protecting this special place for future generations, I have made this decision using the best-available science and extensive public input.”

Duluth Complex

The decision limits the mining of a significant portion of the Duluth Complex, one of the largest undeveloped deposits of copper, nickel, cobalt and other platinum-group metals in the world.

Those metals are critical for the manufacturing of electric vehicle batteries, solar panels, wind turbines and other technologies crucial to the transition to a carbon-free economy.

Industry proponents argue that modern mining in Minnesota would be conducted with stronger environmental and human rights protections than in many other parts of the world. They further contend the projects would bring major economic benefits and high-paying jobs to the northeastern corner of the state.

Proponents further argue mining companies should be allowed to submit their specific mining plans to state and federal officials for review — they say that’s the only way to predict whether they can protect the environment.

“This action begs the question: why doesn’t the government have confidence in its own agencies’ ability to review proposed specific projects?” asked David Chura, chair of the business and labor group Jobs for Minnesotans. 

Julie Lucas, executive director of the industry group Mining Minnesota, said the decision will make it more difficult to achieve President Biden’s climate goals. She said it will also limit the role the state can play in powering a transition to 100 percent carbon-free energy — something the state legislature is considering requiring by 2040. 

“We should be prioritizing the safe and responsible development of these minerals, not putting them in a lockbox to ensure they can’t be used,” Lucas said. 

An Interior Department official speaking on background said the Biden administration is committed to developing a strong domestic mineral supply chain, and supports responsible mining to develop those critical minerals.

“But we have to do so in a responsible manner,” the official said. “That includes balancing our commitment to ensure we protect some of our country’s most spectacular outdoor places for future generations. The Boundary Waters and its surrounding watersheds are one of those places.”

Mining impacts

While iron ore mining has a rich history in the state, mining for copper, nickel and precious metals has never been done before in Minnesota, and carries with it the risk for acid mine drainage and other severe water pollution.

Environmental groups have argued that risk is incompatible with the Boundary Waters — a fragile, million acre wilderness of interconnected lakes and rivers that hosts more than 150,000 visitors a year from around the world, and supports a thriving tourism and recreation-based economy.

As part of its analysis of the mineral withdrawal, the U.S. Forest Service looked at 20 other copper-nickel mines across the U.S. and Canada, and found all resulted in some level of environmental degradation, and that the environmental reviews of those projects frequently underestimated their eventual impacts.

“Our request for this withdrawal was based on concern for irreparable harm to this watershed,” said a Department of Agriculture official speaking on background.

“During the last decade or more numerous examples of environmental harm resulting from mining and sulfide mineral deposits have occurred. Although contamination containment strategies exist, the prospect of their failure as evidenced by harmful releases elsewhere, demonstrates the risk of irreparable harm to the Rainy River watershed, tribal treaty rights and the wilderness values in the Boundary Waters Canoe Area wilderness.”

Becky Rom, National Chair of the Campaign to Save the Boundary Waters, called the withdrawal the most significant land conservation measure in Minnesota in 45 years, since Congress passed a law in 1978 that expanded the Boundary Waters Canoe Area and banned mining within it. 

“Today Secretary Haaland completed the protection of the Boundary Waters adding to the mining ban area federal lands and minerals in the headwaters of the Boundary Wates, where all waters flow downstream into the Boundary Waters.” 

That area within the Rainy River watershed covers a swath of about 350 square miles where any rain or snow that falls flows north and west into the Boundary Waters, Quetico Provincial Park, Voyageurs National Park and beyond. 

“You don’t let the most polluting industry in America operate next to a pristine wilderness that contains an abundant supply of the cleanest water in the country,” said Chris Knopf, executive director of Friends of the Boundary Waters Wilderness. 

“This is commonsense, and it’s supported by the rigorous findings of an exhaustive, two-year scientific study.”

Twin Metals

Thursday’s decision places another roadblock in front of the proposed $1.7 billion dollar Twin Metals project, an underground copper-nickel mine near Ely, just south of the Boundary Waters and within the mineral withdrawal area. 

Last year the Biden administration canceled two federal mineral leases held by Twin Metals along Birch Lake in the Superior National Forest. Those leases are required to mine the valuable metals underground.

The company has sued to have those leases reinstated. But even if it prevails, the mineral withdrawal puts additional federal leases that Twin Metals had hoped to obtain off limits.

“Twin Metals Minnesota is deeply disappointed and stunned,” Twin Metals spokesperson Kathy Graul said about the withdrawal, adding the company remains “committed to enforcing Twin Metals’ rights.”

The withdrawal does not have an impact the proposed PolyMet mine, which lies within the Lake Superior watershed, south of the withdrawal area.

That project has been approved by state regulators, but has been tied up in legal and regulatory proceedings for the past three years.

Permanent protection? 

There have been about 90 mineral withdrawals enacted across the U.S. in the last roughly 50 years, said Save the Boundary Waters’ Rom. 

Over the years both Democrats and Republicans have supported withdrawals, including the protection of about 30,000 acres in Montana known as Paradise Valley, in 2018 under the Trump administration, from potential mining federal lands north of Yellowstone National Park. 

The withdrawal could be reversed by future administrations, or modified. That’s why DFL. Rep. Betty McCollum said she plans to reintroduce a bill to permanently ban mining within the watershed of the Boundary Waters. 

But that proposal would likely not pass out of the House with its newly elected Republican majority. 

“Today is an attack on our way of life,” said GOP Rep. Pete Stauber, who represents the area where the mineral withdrawal was imposed. “I can assure you that this Administration, from the President to the Forest Service, to the Interior Department, will answer for the pain they elected to cause my constituents.” 

Bills have also been introduced in the Minnesota legislature to ban mining on state lands within the watershed of the Boundary Waters.

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