Presence of rising algae | Our lakes are hot

(Quebec) Have you noticed more and more algae in the lake where you like to go fishing, make the paddle board or in front of which is your chalet? You are not the only ones and the phenomenon may gain momentum with climate change.

A new study by Quebec researchers analyzed 80 lakes in Canada. Their observation is clear: almost all of them have seen the seaweed increase and much faster in the last 50 years.

These results are disturbing because the presence of cyanobacteria or blue-green algae in our bodies of water can affect swimming, the presence of fish or even make water unfit for consumption.

The researchers even made a surprising discovery. “We see that algae also increases in lakes far from all human activity. Algae increases in all regions of Canada, ”notes Hamid Ghanbari, principal of the study and postdoctoral researcher at Laval University.

This discovery disconcerted the authors. “Generally, when you see an increase in algae in the lakes, it comes from an excess of nutrient, phosphorus, etc. »Note Yannick Huot, professor at the University of Sherbrooke in applied geomatics and co -author of the study.

How to explain then that the analysis results show an increase in algae even in distant lakes little affected by humans?

“This is a bit of the index that brought us to climate change, because it took an effect that was everywhere in Canada even in lakes where the quantity of nutrients did not increase because of humans. This is where we looked at the climate change a little climate, ”explains Professor Huot.

Researchers notably found that:

• The average increase in chlorophyll – an indicator of the presence of algae – was seven times faster between 1966 to today than from 1850 to 1966 in Canadian lakes;
• Between 1850 and 1966 the presence of algae increased significantly in 58 % of the lakes studied, against 84 % of the lakes after 1966;
• Between 1850 and 1966, only 28 % of the sites studied saw the room temperature increase, but after 1966, the 80 sites studied, except one, saw their average temperature increase.

The researchers therefore conclude that a “very strong association” between the temperature of the ambient air and the presence of algae in the lakes.

How to explain it? Probably the ice.

“We don’t have the final answer. But what we think is that because it has been warmer, the period without ice has lengthened and that is what allowed to have a longer period to push, having nutrients that enter the lakes, explains Yannick Huot. It remains a hypothesis, but it seems the most logical. »»

“Do not be discouraged”

Climate change is therefore added to the long list of factors that harm Quebec lakes and participate in their accelerated aging (eutrophization). Is it discouraging for experts in the field?

“It is not discouraging. But it’s worrying. I think we have to adapt, we have no choice. We have to work at the source to better protect our watersheds, so our lakes, “launched Mélissa Laniel, coordinator of the reminder of the Limnology team, a water protection cooperative.

“You shouldn’t be discouraged,” she said. Things can be implemented to protect our lakes in a context of climate change. »»

Experts observe other climate effects on lakes. The larger and abundant rains can create more erosion and runoff. The rise in temperatures on the melting of ice can also harm the brewing of lakes and therefore limit the supply of oxygen, which harms fish.

At the same time, Quebec lakes are more colonized by invasive exotic aquatic species.

On the ground, Mélissa Laniel notes that citizens and municipal elected officials are increasingly aware of good practices.

“This is not good news. At the same time it does not mean that you have to stop other efforts. It is a more stress that we impose on our lakes, ”says Yannick Huot. “We have to reduce other stressers so that our lakes make up better with climate change. »»

Read the study (in English) published in Communications Earth & Environment

Practices to make the difference

Here are some recommended practices to improve the health of lakes:

• Vegetalize the riparian strips from 10 to 15 meters on the edge of the lakes, to reduce runoff and erosion;
• Avoid using fertilizers, fertilizers or even compost in the riparian strip, so as not to fertilize the lakes;
• Ensure the conformity and good maintenance of septic installations, a large source of pollutants;
• Clean your boat at the entrance and exit of a body of water and limit its speed, especially in shallow water, to reduce waves and erosion.