Alum a useful tool to combat toxic algae

The chemical has been used in the U.S. to clear lakes of algal blooms but hasn’t seen widespread acceptance in Canada

It’s no magic bullet, but aluminum sulphate can significantly reduce toxic algal blooms in lakes, American scientist John Holz told conservationists at a Winnipeg conference on December 3.

John Holz
photo: Geralyn Wichers

“It is a common tool,” said Holz, whose company HAB Aquatic Solutions, has done 104 applications of the product, also called ‘alum,’ in the U.S.

Holz spoke at the 2019 Manitoba Conservation Districts Association conference alongside aquatic scientist Dorte Koster.

In Canada, however, aluminum sulphate has rarely — if ever — been applied to natural lakes to treat nutrient overloads, which lead to algal blooms, and experts say this may not be without good reason.

Why it matters: Prairie lakes are prone to blooms of toxic algae, which can kill animals and scare off swimmers? aluminum sulphate has been shown to starve off these blooms, but hasn’t seen widespread use in Canada.

What’s in a bloom?

Over the past few years, the stain of toxic blue-green algal blooms has become an unfortunate fixture of summer, and the living representation of campaigns to “save Lake Winnipeg.”

The algal blooms are caused by eutrophication, which is a condition caused by an overabundance of nutrients, like phosphorus, according to the Lake Winnipeg Foundation website.

While “it’s normal for a lake to have some algae,” the website says, some types of blue-green algae can be toxic to humans and animals, and can alter the chemical composition of lakes.

Dorte Koster.
photo: Geralyn Wichers

Lake Winnipeg might be the biggest, stinkiest example, but Koster told the conference audience that Prairie lakes tend to have a “perfect storm” of conditions for eutrophication.

Koster, a senior aquatic scientist with Associated Environmental Consultants, has been studying Stephenfield Lake in southwestern Manitoba. The lake, which Koster said is a reservoir built in the 1960s, is prone to algal blooms.

The lake’s watershed feeds it with phosphorus, said Koster. However, she found that while the greatest load of the nutrient entered the lake in April, the blooms occurred in late summer.

She suggested this may be due to internal loading — nutrients accumulated in the sediment on the lake bottom, and then reincorporated into the water.

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Holz’s alum targets exactly this kind of phosphorus. Holz showed the audience how his company uses barges to spread alum in precise doses.

The alum turns into flaky “floc,” which sinks to coat the lake bottom, not unlike a couple of inches of snow. The floc binds phosphorus, deactivating it, and barring it from re-entering the water.

The alum doesn’t kill algae, but starves it by taking away the phosphorus. Holz said he’d seen lakes where 90 per cent of the phosphorus came from the lake bottom and efforts to clean up the watershed weren’t helpful for controlling blooms.

He showed before and after photos of lakes, first green, then clear after alum application. The effect can last for decades, he said (a report from the International Institute for Sustainable Development says an application typically doesn’t last more than 15 years).

Aluminum sulphate is already used in waste water and water purification processes, including in Canada, said Holz.

It was applied to lakes in the U.S. as early as the 1970s, according to a 1979 report to the U.S. Environmental Protection Agency. The same report says the first lake-wide application of alum was in Sweden in 1968.

What’s the catch?

So why not dump alum in every green lake? As a reporter asked Holz, what’s the catch?

Koster and Holz said alum has never been applied to natural lakes in Canada, though, to their knowledge, it isn’t illegal.

Aluminum sulphate appears for sale on Home Depot’s website, for instance.

Koster and Holz said the lack of alum use is likely due to caution. In Canada, said Koster, there’s a regulatory vacuum and lack of precedent. As a result, it’s hard to get people in government to agree it’s a risk worth taking.

“They’re not allowing for widespread, unregulated use, and that’s good,” Holz said.

Holz added that there needs to be more Canadian studies, like Koster’s at Stephenfield Lake, to show where nutrients are entering the lake, and if alum will be helpful.

Scott Higgins told the Co-operator there’s also a lack of followup on lakes after alum is applied.

“They just do it once and then they walk away,” said Higgins, a research scientist at the International Institute for Sustainable Development, based in Winnipeg.

He said there’s not much short-term evidence of alum being toxic if properly applied. However, the “slow, chronic effects” of alum haven’t received much study.

Alum is also a bit of a band-aid fix.

“It’s not really treating the problem. It’s treating the symptoms,” said Higgins. “If there aren’t efforts to address phosphorus loads, you have to keep applying alum.”

For instance, Lake Winnipeg has been shown to have high internal loads of phosphorus, said Higgins.

However, the lake’s watershed pumps phosphorus into it at a rate of 5,500 tonnes per year, according to the Lake Winnipeg Foundation. While alum might treat settled nutrients, those would quickly be replaced. Without turning off that tap, alum application wouldn’t be too effective.

Alum can also be toxic in lakes if the water pH drops too low or becomes too high, Higgins said.

Lake Winnipeg is also shallow. In shallow lakes, wave action can stir up sediment, dislodging the phosphorus-binding floc from the bottom and reincorporating phosphorus buried beneath.

And it’s big. Based on Higgins’ quick math, it would cost billions to apply alum to the entirety of Lake Winnipeg. Spot treatment would be an option, but would reduce effectiveness, Higgins said.

“It takes a long time to create the problem,” said Higgins. “It can take a long time to solve the problem.”

About the author

Reporter

Geralyn Wichers grew up on a hobby farm near Anola, Manitoba, where her family raised cattle, pigs and chickens. Geralyn graduated from Red River College’s Creative Communications program in 2019 and was previously a reporter for The Carillon in Steinbach. Geralyn is also a published author of science fiction and fantasy novels.

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