An emerging phenomenon in Northern Alaska has perplexed scientists. Mountain streams, once the spawning grounds for several fish species, are becoming too acidic for most life and turning orange. Researchers believe the phenomena could be caused by thawing permafrost.
Jon O’Donnell is an Anchorage-based ecologist with the National Parks Service. For decades, he’s been studying the same rivers and streams with the Arctic Inventory and Monitoring Network, flying into remote areas along the Brooks Range that are only accessible by helicopter.
Back in 2018, he noticed something strange on a tributary of the Akillik River, which flows into the larger Hunt and Kobuk Rivers. O’Donnell said the water, once full of fish like juvenile Dolly Varden and sculpin, had drastically changed from the previous year.
“We noticed that the stream had changed color from this pristine, clear water to a bright orange,” O’Donnell said. “There were no fish — all the fish had left.”
O’Donnell and his team also noticed a decline in the population and diversity of macroinvertebrates, the small, aquatic bugs the fish eat.
Then, a year later, they noticed more orange streams.
“So then we started to think that this might be a bigger story than just a one-off stream in the Kobuk,” O’Donnell said.
O’Donnell published a paper with a team of researchers in May documenting the orange streams, calling them “rusting rivers.” They often originate from tiny streams or seeps on tundra hillsides, releasing highly acidic water inhospitable to most marine and plant life. O’Donnell says the rusting rivers could pose threats to subsistence food sources and affect drinking water in rural, Arctic communities.
Over the last decade or so, the researchers have found 75 of these streams in northern Alaska.
O’Donnell said the cause is most likely permafrost thaw. In recent years, warmer and snowier Arctic winters have accelerated the thaw in Northern Alaska.
“There are places where these rusting rivers have been going on for decades, and I think the difference in what we're seeing now is the sheer spatial scale of the problem.” O’Donnell said. “It's also the timing implied. This is a climate-induced problem.”
O’Donnell said the effects of the rusting rivers are similar to acid mine drainage which, according to the United States Geological Survey, can disrupt the lives of aquatic plants and animals, contaminate drinking water, and corrode infrastructure.
In the case of rusting rivers, newly exposed mineral deposits from permafrost thaw react with oxygen. This reaction releases iron, which changes the water’s color. He said the reaction also releases trace amounts of toxic metals, like copper, cadmium, and nickel into the water.
“Under cooler climates, in the past, all of these mineral deposits
were basically inert, and they were frozen in frozen ground,” O’Donnell said. “Now that the climate has warmed up and thaws deeper, it exposes these mineral deposits.”
O’Donnell said his team’s research focused on the geochemistry — essentially, how the thawing permafrost is reacting to the rocks and minerals of the region. The next step for researchers is to look more closely at the ecological effects; for example, how this could affect fish spawning areas.
He said his team is planning on floating down the Noatak River to study how the orange streams react as they flow into the headwaters of larger rivers.
“There's still a lot of research to be done,” O’Donnell said. “We're trying to understand how these rivers change from year to year, and how they change from season to season.”
O’Donnell’s team will be in several national parks in the Northwest Arctic in June to take water samples and install equipment for a long-term monitoring program, as well as to study recent surges in Arctic beaver populations.
