Canadians are proud of the Great Lakes, and for good reason—they supply two large countries with a lot of fresh drinking water, support irrigation and other agricultural activities, and are crucial in shipping and transportation in the area. Plus, they’re great for sailing, swimming and watching the sunset.
“Lakes are great indicators of what’s going on in the watershed,” says Sapna Sharma, an associate aquatic ecology and limnology professor at York University. “They give a good idea of what environmental degradation may be happening on land.”
A new study published in Bioscience looks at decades of lake research to understand how climate change is affecting lakes around the world, like Canada’s Great Lakes, which hold more than 20 per cent of the planet’s freshwater. Sharma, a key author in the study, explains what it all means.
Shorter ice seasons
“What we’re seeing in recent decades,” Sharma says, “is the decrease in the extent of ice cover.” Northern Hemisphere lakes are experiencing shorter winters and shortened frozen lake periods. Researchers estimate that nearly 15,000 lakes in the north that traditionally froze yearly, including the Great Lakes, are now going ice-free.
Since 1997, there have been four or five ice-free years. “When we go back to our records from 1857, this has never happened before,” says Sharma.
A 2015 study on lake temperature shows that almost 90 per cent of lakes are warming. And the 10 per cent that are not warming are cooling because of glacial ice melt or water clarity change.
“Ice acts like a lid on the lake in the winter,” Sharma explains. “When you remove that lid, there’s more freshwater evaporating.”
By the end of this century, the study reports the average annual lake evaporation is expected to increase by 16 per cent globally. Changes in ice cover, ice thickness, and snow cover are amplified in the Canadian Arctic where there are 24-hour-daylight summers.
Winter evaporation directly decreases freshwater supply and warms water temperatures. This impacts food chains and helps invasive species spread. Warmer lakes favour nonnative, predator fish like the smallmouth bass, squeezing native fish out of the water.
Warm water also supports increased algae production. Eutrophication—a bloom of plant growth due to an excess of nutrients caused by sunlight, fertilizer, or even intense rainfall—becomes more common too. In Ontario’s Grand River Watershed, a historic rainfall increased the presence of fertilizing phosphorus and catapulted an unseasonably early bloom season.
There are reports of more common and later blooms happening throughout Ontario. Algonquin Provincial Park’s Dickson Lake experienced a toxic bloom that led the park to pause overnight camping permits in 2015. These blooms are a top cause of poor water quality affecting fish and birds on a wide scale and pose serious threats to livestock, pets, and humans.
A lot of the changes can’t be seen by the eye, says Sharma. “You can’t tell that the water temperatures are warmer. You can’t tell that fish populations are stressed as you’re walking along the shoreline,” she says. “Things are bad when you can start observing water quality degradation by eye.”
Look for murky or green water and algal scum. Or, take a whiff. Degraded water quality definitely has a smell.
Water access for all
“There’s a huge inequity issue,” Sharma says. “There are boiling water advisories on Indigenous reserves, right next to other towns that don’t [have advisories]…it’s just going to get worse with climate change as water quality is expected to degrade further.”
There is a ton of work happening in Africa, Asia, and South America that Canada can look to when it comes to the future of our lakes. “We need to start bridging those gaps. We need to recognize how their lakes are changing,” Sharma says, calling the science community to approach freshwater research more inclusively.
“Our field, and accessibility to water, will only improve,” she says.