Rivers across Alaska’s Arctic are turning orange and acidic as permafrost thaws, threatening subsistence resources that thousands of people rely on.
The phenomenon known as “rusting rivers” happens when once-clear streams release highly acidic and metal-laden water, which pose a direct threat to fish and vegetation. It’s happening throughout Alaska’s Brooks Range, but scientists have documented it in cold climates around the world, including Northwest Canada, alpine regions of Peru, and the Pyrenees and Alps.
Now researchers say they've built a model that could predict where it will happen next. Patrick Sullivan directs the Environment and Natural Resources Institute at the University of Alaska Anchorage. He’s spent decades studying Northwest Alaska’s most remote areas by snowmachine, pack raft and on foot.
“Our packs tend to be like close to 45 pounds after you account for the pack raft, and then our tents and sleeping bags, and our food for a week, and then on top of that we're carrying sampling kits,” Sullivan said.
His boots-on-the-ground research focuses on the complex ways the Arctic is changing rapidly. He said the question driving his research into rusting rivers is, Which of the Arctic rivers that support the most fish are the most at risk?
In the 1980s, the Alaska Department of Fish and Game created an inventory of Dolly Varden spawning watersheds in Northwest Alaska. Sullivan’s team used that inventory to decide where to make predictions of rusting risk.
“Once we had a good model, we made the predictions for all 18 of these Dolly Varden spawning habitats, spawning watersheds, and basically ranked them in terms of their risk for rusting,” Sullivan said.
Centering on fish was important, he said. Tens of thousands of Dolly Varden — regionally referred to simply as “trout” — are harvested for subsistence in the area his team studied in the Noatak watershed and along the Kivalina and Wulik Rivers. Many of the same watersheds that support trout also support chum salmon, which are similarly important.
Sullivan said the model predicts where the acid seeps are likely to emerge as the climate warms. It factors in geology, including shale bedrock and proximity to faults, vegetation, and thermal conditions of permafrost. It also identifies which rivers fish could migrate to for refuge.
Sullivan said his modeling shows that some rivers that are already experiencing heavy impacts are expected to see fewer new seeps emerge in the future.
“Permafrost thaw is like a wave that's like moving north,” Sullivan said. “The warmest watersheds that we looked at were like the Kivalina and the Wulik. Those are watersheds that are going to see reduced risk of new seeps emerging in 10 years.”
But Sullivan said colder watersheds further north, like the Nimiuktuk and the Anisak Rivers, are expected to see increased risk of new acid seeps in the future.
His research also found that many of the seeps are linked to fault lines, and the metals being released can be traced back 350 million years. At the time, a low-oxygen equatorial ocean covered this part of Alaska. Sulfide minerals formed on the ancient seafloor and were locked into rock before eventually getting thrust upward into the mountains of the Brooks Range. Sullivan’s team found that the mineral seeps that cause rusting rivers cluster around these fault lines.
Sullivan said he and his colleagues are learning new details all the time.
“Every few weeks I feel like we add a new nugget of information that we didn't have before,” he said.
Once his team’s findings are published, Sullivan said the model will be made public. He said it could be applied to watersheds anywhere permafrost is thawing, not just in Alaska.
