How wildfires affect our lakes

Published: August 22, 2018

wildfire-near-lake Photo by Sergey Uryadnikov/Shutterstock

The wildfires tearing through Canadian provinces this summer have left cottagers and cabin owners worried over the state of their properties. Thankfully, many of the wildfires are slowly becoming controlled and curbed away from residences. But even with the assurance of your property being safe, wildfires still affect the quality of the surrounding environment, specifically your lake.

“There are certainly effects, both direct and indirect effects of fire, on the water cycle,” says Lori Daniels, a professor at the University of British Columbia who specializes in wildfires. “You end up with ash and other sediments being washed into streams and then down into lakes.” When a fire is burning hot enough it scorches the soil leaving the mineral surface exposed. It can also cause the soil to become hydrophobic, Daniels says, meaning it repels water. This is due to the melting of organic materials like pine needles that contain fats and liquids. They form a waxy substance near the surface. “So, now when it rains, the water can’t go into the soil. It gets repelled.”

With rain water not able to soak into the soil, the soil remains dry and barren. It also causes the water to wash down over the soil towards streams, resulting in erosion and sweeping materials like ash into lakes. “The ash that is left behind in a fire, it tends to be more of the things that are basics. Not nitrogen. A lot of calcium and magnesium,” Daniels says. The issue with this is that in water, calcium and magnesium form fine, soapy particles that are easily transported via streams and often end up on stream bottoms or impacting the quality of water in lakes, changing it from clear to silty. “That’s a problem for spawning channels for fish like salmon,” Daniels says. It changes their habitat. Instead of smooth pebbles, they’re met with a sandbank. It also makes the water much less pleasant for swimming.

If the surface of a lake is calm enough and a wildfire burns closely, a layer of ash may also form on the surface, eventually settling to the bottom. This could be a problem for cottagers who take their water supply from the lake. “If it’s taken from the surface then there is a risk of having some ash present,” says John Innes, the dean of the Department of Forest Resources Management at the University of British Columbia. But Innes says, once the ash has broken the surface and sufficiently mixed with the water, it shouldn’t prove dangerous.

Unfortunately, once a wildfire has taken root nearby, it’s difficult to mitigate these effects on the lake. The best course of action is to help prevent wildfires in the first place by clearing dead wood and making sure no flames are left untended, especially during dry spells. Otherwise, as Daniels says, you’re left hoping for a change in the weather.

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