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A plan to fight toxic algae in one of North America’s Great Lakes has the potential to backfire, scientists warn, and make the lake even more toxic.
Lake Erie, located along the border between Canada and the US, has been battling blooms of cyanobacteria, also known as “blue-green algae”, for decades as a result of increased concentrations of nutrients like nitrogen and phosphorus, mainly from agriculture and lawn care.
Over the past few years, the US and Canadian governments have agreed to limit phosphorus runoff into the lake to try to prevent these stinky, toxic blooms.
However a new study warns that while that may reduce the total amount of the algae, what remains might be more toxic than before.
The study is a forecast based off a model - and not a measurement of actual conditions in the lake. But researchers say that their findings raise new questions about how to predict and reduce toxicity in one of the continent’s largest bodies of freshwater.
“There are organisms in nature that make compounds that are not good for the environment, or even good for us,” Steven Wilhelm, a study author and microbiologist at the University of Tennessee, tells The Independent.
“And one thing we found, surprisingly, is that in efforts to try to reduce those organisms, we may help them make these compounds.”
Lake Erie has had cyanobacteria blooms for decades, with scientists pinning these phenomena on excess phosphorus and nitrogen from sources like agricultural fertilizer.
It’s never pleasant — the blooms can wash up on shore, bringing a putrid smell with them, and prevent people and pets from enjoying the water. In some years the impacts have been especially bad, such as in 2014, when residents of Toledo, Ohio were warned off their tap water after some algae made it into the drinking water system.
While Lake Erie has had the most consistent algal blooms, it is a problem across the Great Lakes – which combined provide drinking water to around 40 million people. There’s also some indication that blooms could become more frequent as the climate crisis raises water temperatures.
To stem these outbreaks, efforts are being focused on reducing the amount of phosphorus in the lake, long considered the limiting factor for cyanobacteria growth. Measures include monitoring water quality, land management to prevent nutrient runoff and creating buffer zones between fertilizer and waters.
But these cyanobacteria aren’t always toxic, Dr Wilhelm says, and scientists still don’t understand entirely what controls how toxic a bloom might become.
The new study, published on Thursday in Science, used a model of cyanobacteria growth based on hundreds of different experiments to see how the algae might respond to different conditions, like varying concentrations of nitrogen and phosphorus.
The results don’t dispute the theory that limiting phosphorus will reduce the total amount of algae. But the study also finds that by reducing phosphorus and not nitrogen, you could end up with conditions more favourable to toxin production.
Dr Wilhelm says that he was not expecting the study to yield this result. The dogma of the field for the past 25- 30 years has been that by reducing phosphorus you can reduce the total amount of algae, he added, and if you reduce the total amount of algae, you’d get less toxin.
However the new study suggests this may not be entirely true — because the few algae that remain could make up some lost toxicity.
“This paper, actually, for the first time, has put together a model that explains why the toxin is produced and the environmental factors that cause the cells to produce toxin,” Richard Stumpf, an oceanographer at the National Oceanic and Atmospheric Administration who has studied algal blooms but was not involved with the new paper, tells The Independent.
Dr Stumpf called the conclusion that reducing phosphorus in the lake could increase toxicity “a bit of an overreach.”
He pointed out that the model is based on cellular biology but conditions in real life have a lot more permutations. He also noted that when blooms start, and toxicity is the most concerning, there’s already “far more nitrogen” than the cells could possibly use. Even if the algae remaining is more toxic, less overall algae could still mean less toxicity, he added.
Dr Stumpf said that he’d like to use the model to forecast toxicity in the lake and then compare it to actual observed toxicity levels to see how the forecast pans out.
Dr Wilhelm also notes that the model may not represent every important factor determining algal growth and toxicity in the lake. Adding factors like temperature and pH level could improve the model over time, he added.
In addition, the takeaway here isn’t to leave the phosphorus in the lake, he notes — it’s that reducing both nitrogen and phosphorus may be the best strategy.
While more research is needed, the study is a warning that efforts to clean up Lake Erie may not yield the expected results, Dr Wilhelm says.
“This is sort of a warning that this could be happening, and we need to keep an eye on it,” he says.