In the Northwest Arctic, runoff from permafrost thaw is turning rivers and streams a rusty orange color, releasing extremely acidic water, and creating dead zones for plants and animals. The phenomenon, which researchers call “rusting rivers” is baffling - and worrying - scientists.
“It's really apocalyptic to see,” said Patrick Sullivan, an ecologist and director of the Environment and Natural Resources Institute with the University of Alaska.
Sullivan has spent the last two decades studying vegetation in the Northwest Arctic. In that time, he’s witnessed many ecological changes. But none of it compared to a scene Sullivan first encountered back in 2019.
“It was like somebody poured gasoline all over the tundra, lit a fire, burned off all the vegetation, and then released some sort of like, orange goo to kind of trickle down through,” Sullivan said.
The landscape that Sullivan described is from acid seeps, mostly along remote tundra hillsides. The caustic chemical flows into the surrounding land and bodies of water, and in the process can kill much of the vegetation in its path. Sullivan said acid seeps make the water cloudy and in some cases, distinctively orange-colored. He believes the orange color is caused by a reaction to the water with limestone-rich rocks from the Brooks Range.
What surprised him more was what his research team found after analyzing
the water itself.
“It has a pH of two and an electrical conductivity of, like, 5000,” Sullivan said. “It's completely loaded with metals.”
That combination of highly acidic, highly conductive, metal-laden water
poses a direct risk to fish.
"The greatest concern for human health and subsistence resources is really
the impact that this might be having on salmon, Dolly Varden, grayling —
the fish that are in the stream," Sullivan said. "Many of those metals have
known toxic effects on fish."
Sullivan says acidic water has now been documented in at least 30 rivers
and streams across the Alaskan tundra. This summer, he worked with a crew of scientists to study its effects on the Salmon, Alatna, and Kobuk
rivers — all three designated Wild and Scenic Rivers — sampling acid seeps
along tributaries including the Tukpahlearik and Annaktok creeks.
Reaching the sites was its own challenge. The crew took a chartered
bush plane roughly an hour and a half from the nearest airstrip, then
hiked more than 30 miles from the drop-off point to reach the sampling
locations.
"It's definitely one of the most remote wilderness areas in North
America," Sullivan said.
Sullivan and other researchers studying what he calls "rusting rivers"
believe the cause lies in sulfur-rich minerals buried in the bedrock of
these watersheds.
"What we think is happening is that as that permafrost thaws, these
sulfide minerals are being exposed to oxygen for the first time in a
very, very long time... like, geologic time scales," Sullivan said. "And
when the sulfide minerals are exposed to oxygen and water, they produce
sulfuric acid."
Scientists estimate that 75% of the Earth's near-surface permafrost will
be gone by the end of the century. Sullivan said the phenomenon has taken
much of the scientific community by surprise.
"We had been anticipating that there would be the proliferation of
shrubs, the northward advance of the tree line, the thawing of permafrost
and the release of CO2 and methane associated with that," Sullivan said.
"But I don't think that anyone anticipated that this would happen."
It's possible, he said, that acid seeps emerged from thawing permafrost
before, perhaps thousands of years ago, prior to the last ice age. He doubts it ever happened at today's pace.
"The rate of warming that we're basically imposing on these landscapes is
far greater than anything they've experienced historically," Sullivan
said.
Sullivan said there's still a lot of research ahead. He hopes to return to
the Brooks Range next summer with a team of scientists to look for
archaeological evidence and continue documenting the region's acidic
drainage.
