Global warming increases human health risk due to toxic algae in Canadian Prairie lakes

New research by scientists at the University of Regina’s Institute of Environmental Change and Society shows that global warming is increasing levels of toxic algae detrimental to human health. The studywaspublished online, in the journal Limnology and Oceanography Letters

“Our decade-long project establishes that global warming is increasing toxin levels in Prairie lakes,” says Dr. Peter Leavitt, a Canada Research Chair in Environmental Change and Society and a co-author of the study. “What is particularly worrying is that the chance of exceeding toxin levels that cause acute human health effects has increased to one in four in several lakes in southern Saskatchewan.”

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Among the lakes affected are Pasqua and Crooked lakes which border on Pasqua and Cowessess First Nations, respectively, while Buffalo Pound is the drinking water source for the City of Regina.

Leavitt explains that urban growth and intensive agricultural activities increases pollution of freshwaters with nutrients from fertilizers, which increases growth of harmful algae known to produce potent water-borne toxins.

“Warming temperatures due to climate change have caused earlier and larger outbreaks of toxic algae, leading to growing toxicity levels that can pose a high risk of acute health effects according the United States Environmental Protection Agency guidelines,” says Leavitt, who is also a fellow of the Royal Society of Canada. 

The team’s research shows that nearly half of the surveyed Prairie lakes had elevated levels of microcystin, a toxin from blue-green algae that appears as green scum in water. Late summer toxin levels were high in both the drinking water reservoir for Regina, Saskatchewan, and in downstream lakes bordering First Nations territories. 

The study’s authors, led by University of Regina research fellow Dr. Nicole Hayes, measured historical changes in climate, lake conditions, and toxins from blue-green algae over 11 years in six lakes of the Qu’Appelle River drainage basin. This area covers nearly 40 per cent of southern Saskatchewan, including most of Treat 4 territory, and drains directly into the Assiniboine River and Lake Winnipeg. 

“While toxic algae are known to prefer warm waters, ours is the first study to demonstrate increased human health risk due to a longer growing season for algal blooms,” explains Hayes, now a faculty member at University of Wisconsin Stout. 

Leavett adds that “the fact that global warming both increases growing season and average water temperatures provides the direct link of climate change to human health.”

Leavitt says that in addition to the Qu’Appelle long-term study, the scientists also conducted a mid-summer survey over 100 lakes in southern Saskatchewan. They found that 59 per cent of lakes exceeded drinking water guidelines for infants, while 42 per cent exceeded adult guidelines, and two lakes were nearly twice the levels known to cause acute human health effects.

Despite these findings, Leavitt notes there is some good news.

“Toxin levels in the Prairies were actually quite a bit lower than in the US Great Plains, where warmer summers promote more intense blooms of harmful cyanobacteria. As well, many Canadian water treatment plants have effective protocols for removing toxins from domestic water supplies.” 

Rather than be complacent, Leavitt says that society needs to address the underlying problems. 

“Global warming will increase temperatures in southern Saskatchewan by three to five degrees. By studying the Qu’Appelle lakes for nearly 30 years, we have been able to show that a three degree warming will nearly double the amount of toxin-producing cyanobacteria. The warmer it gets, the worse the problem will become,” says Leavitt.

Although the report focused mainly on lakes of southern Saskatchewan, the findings could be relevant to a region of nearly 15 million square kilometers; with similar findings expected for both Manitoba and Alberta.

A copy of the Paper and its Supplementary information is available at https:/doi.org/10.1002/lol2.10164

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