In 2014, massive wildfires swept across the southern Northwest Territories, incinerating forests and destroying wildlife habitat across 5,000 square kilometres of landscape, forcing the closure of the Yellowknife Highway and polluting the air as far away as southern Saskatchewan and Manitoba. These events, which reflect a worldwide trend that’s seeing wildfires increasing in frequency and size, gave University of Alberta biologist Suzanne Tank and her colleagues an exceptional opportunity to start investigating some of the least understood consequences of northern wildfires: their effect on the ecosystems of streams and lakes.
“The water in aquatic environments is derived from the landscape,” says Tank, whose research is supported in part by Polar Knowledge Canada. “Precipitation runs off over the land into streams and lakes, carrying with it the characteristics of the landscape it’s flowing over.”
Fire changes soils, and burns away the layer of vegetation that insulates permafrost, the barrier of ice that keeps runoff water on the surface of the ground. With vegetation gone, permafrost thaws and runoff penetrates the ground, where it picks up material from deeper soils and carries it into streams.
Tank and her colleagues compared large burned areas to unburned areas, looking at the minute details of the water in the soils and the soil chemistry. They found the greatest changes — increases in nutrients and ions, changes in organic carbon and hydrology (how water flows across the landscape) — in areas that had been burned.
At a wildfire site, you get phenomenal growth of wildflowers and other flora because fire releases nutrients. But by the time you get to a stream outlet you see less striking effects in the water.
“At a wildfire site, you get phenomenal growth of wildflowers [and other flora] because fire releases nutrients,” says Tank. “But by the time you get to a stream outlet you see less striking effects in the water. We did see differences in the water during the spring snow melt, but those effects seemed short-lived.” Tank has noted that there is less difference between burned and unburned drainage basins over time, which indicates that as it flows from burnt landscape to creek mouth, something (still to be identified) is happening in the runoff water that may be tempering the effects of fire.
While wildfires can be disastrous for human communities and the terrestrial wildlife and plants in their path, Tank’s research is showing that they are far less disruptive for northern streams and lakes. The reasons for this lie hidden within the complexity of northern aquatic ecosystems and their response to new conditions. Decoding that puzzle will be essential as we try to predict the effects on the landscape of more frequent wildfires in the North.