Algae and cyanobacteria in Lake Erie, a tireless struggle

This year, harmful algal blooms in Lake Erie have been less than predicted by US authorities. Nothing to do with the summer of 2014, when the city of Toledo, located at the extreme west of the lake, had been deprived of drinking water because of cyanobacteria. But the war against these sometimes toxic blue-green algae is far from being won.

For 40 years, Didier Marotte has crossed Lake Erie to practice his favorite pastime: fishing. The lake is a Mecca for walleye fishing.

“Everyone is asking me if I’m eating fish … Of course!” He exclaims. “Because in 40 years, the situation has changed. It’s much less polluted. Industrial and wastewater discharges have decreased. Nothing to do with the time when he was fishing for deformed fish with ulcers. “Six out of ten walleyes had ulcers,” he explains.

Today, what worries him is the proliferation of algae, caused inter alia by agricultural waste.

It dirties the reel to the point where it can no longer be turned. It affects sport fishing.

Didier Marotte

The growth of algae and aquatic plants is stimulated by the phosphorus contained in agricultural waste. During heavy rains, fertilizers spread in the fields run down to the water. And in water as on land, phosphorus is a fertilizer.

Fertilizers go into the lake; Algae are plants … So they grow!

Anique Gauvin, student at the University of Windsor

The quest for samples

Throughout the summer, Anique Gauvin travels Lake Erie and her tributary, the Detroit River, in search of water samples. The bachelor’s student in biology and environmental science at the University of Windsor is part of a massive surveillance campaign that is monopolizing efforts on both sides of the border. “It’s important for me because I like fishing on the lake,” exclaims the young woman, wearing a cap where she displays her passion.

The temperature and turbidity of the water are among the parameters measured from the time of picking on the boat. Then, the samples take the path of the laboratory.

Toxic or not?

In the laboratory, researchers measure chlorophyll, a good indicator of plant biomass. And they observe the samples under the microscope to identify the organisms present. In their line of sight: cyanobacteria, also called blue-green algae. Often toxic, but not always, which complicates the work of scientists.

One of the most common cyanobacteria in Lake Erie belongs to the genus Microcystis, which has several species. “For the same species, we have toxic lineages that compete with others that are not. Environmental factors will favor a winner, “says Arthur Zastepa of the Harmful Algae Lab at the Canada Center for Inland Waters. Together with his colleagues, he monitors the progression of cyanobacteria in Lake Erie.

It is clear that phosphorus stimulates biomass production. But we do not know exactly what influences toxicity.

Arthur Zastepa, researcher at the Harmful Algae Laboratory of the Canada Center for Inland Waters
The challenge for researchers is to understand what triggers the production of toxins in cyanobacteria. Among the tracks studied: the heat waves approaching the autumn and the excesses in nitrogen inputs.

Cyanobacteria: both algae and bacteria

Because they live in water and sometimes produce green filaments, cyanobacteria are often considered as algae. But these organisms are both algae and bacteria. Like algae, cyanobacteria live in water and are capable of photosynthesis. Like bacteria, they are among the oldest living organisms on Earth. They therefore had ample time to adapt to their environment.

In the presence of high levels of phosphorus, cyanobacteria proliferate. Over time, they have become champions in the art of moving in the water column, which benefits them when phosphorus abounds. Some species are even able to go back to the surface of the water to take nitrogen from the atmosphere.

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