In Alaska’s Brooks Range, rivers once clear enough to drink from now run orange and hazy with toxic metals. As warming thaws formerly frozen ground, it sets off a chemical chain reaction that is poisoning fish and wreaking havoc on ecosystems.
Researcher testing murky waters in Alaska's Brooks Range. (Photo: Taylor Rhoades)
As the planet warms, a layer of permafrost — permanently frozen Arctic soil that locked away minerals for millennia — is beginning to thaw. Water and oxygen creep into the newly exposed soil, triggering the breakdown of sulfide-rich rocks, and creating sulfuric acid that leaches naturally occurring metals like iron, cadmium, and aluminum from rocks into the river.
Often times, geochemical reactions like these are triggered by mining operations. But that is not the case this time.
“This is what acid mine drainage looks like,” said Tim Lyons, a biogeochemist at the University of California, Riverside. “But here, there’s no mine. The permafrost is thawing and changing the chemistry of the landscape.”
How the Salmon River looked prior to the permafrost thawing. (Patrick Sullivan/University of Alaska)
A new paper detailing the severity of the contamination has been published in the Proceedings of the National Academy of Sciences. Though the study focuses on the Salmon River, researchers warn that similar transformations are already underway across dozens of other Arctic watersheds.
“I have worked and traveled in the Brooks Range since 1976, and the recent changes in landforms and water chemistry are truly astounding,” said David Cooper, Colorado State University research scientist and study co-author.
Ecologist Paddy Sullivan of the University of Alaska first noticed the dramatic changes in 2019 while conducting fieldwork on Arctic forests shifting northward — another consequence of climate change. A pilot flying Sullivan into the field warned him the Salmon River hadn’t cleared up after the snowmelt and looked “like sewage.” Alarmed by what he saw, Sullivan joined forces with Lyons, Roman Dial from Alaska Pacific University, and others to investigate the causes and ecological consequences.
The research team on site in the Alaska wilderness. (Photo: Taylor Rhoades)
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