Water temperature plays a minor role in the development of blue-green algae, even though cyanobacterial explosions occur mostly during the hottest periods of summer, concludes a new international study in which a researcher from Laval University.
It is mainly the concentration in the water of nutrients such as phosphorus and nitrogen that is to blame, write the authors in the journal Harmful Algae. Without these nutrients, no matter how hot, there will be no cyanobacterial blooms, they point out.
Conversely, blue-green algae can thrive in very cold weather if they have the right nutrients. The researchers thus documented the case of a lake in Resolute, on the island of Cornwallis, one of the coldest inhabited places in the world, which had experienced blooms in the past, because the wastewater from a the airport and a military base provided nutrients.
“Cyanobacteria, and especially the potentially toxic forms, are a threat to water quality and drinking water almost everywhere in the world,” said Professor Dermot Antoniades, of the Department of Geography and the Center for Nordiques from Laval University, who discussed the findings of the study first with The Canadian Press.
“If we want to protect sources of drinking water and lakes, this is a topic of great importance. »
Blue-green algae can also pose a risk to human health. Contact with these algae can cause digestive symptoms, headaches, fever, and skin and throat irritation.
Researchers from eight countries studied data from 464 lakes in North and South America.
While previous blue-green algae studies often focused on a single body of water, the new research’s water bodies were distributed along a 14,000 kilometer north-south gradient, from Tierra del Fuego in Argentina to Ellesmere Island in Nunavut. They are located in areas where the climate ranges from equatorial to polar.
The researchers attempted to establish correlations between the biomass of cyanobacteria in these lakes and various environmental factors. They thus concluded that the temperature in itself does not influence the biomass of cyanobacteria, but that the main factor responsible for the variations in this biomass in the Americas is the concentration of nutrients in the waters of the lake.
Phosphorus plays a major role; the abundance of nitrogen also has an effect, but it is most apparent in lakes that are less than three meters deep, it was said.
“There has been a long debate about the importance of phosphorus and nitrogen,” said Professor Antoniades. Others say that climate change explains why we have more and more blooms of cyanobacteria. But what we’ve seen is that it’s not the temperature per se that’s the problem. »
Rather, global warming has a side effect, he added, such as more pronounced stratification of lakes that can amplify the problem. But ultimately, without an overabundance of nutrients, even with higher temperatures, there won’t be a problem, the researcher said.
In Quebec and at comparable latitudes, cyanobacterial blooms occur in summer not because it is particularly hot, but rather because it is the time of year when nutrient inputs from natural runoff, Lake sediments and human activities are the most important, explained the authors.
So that’s what we have to tackle if we hope to solve the problem.
“If we control the sources of nutrients and the concentrations of nutrients in the lakes, that will reduce the problems of flowering and overabundance of cyanobacteria, even if there are side effects of warming, concluded Professor Antoniades. If there are no nutrients, the problem will not appear. »