Alaska’s Rivers Are Turning Orange as Thawing Permafrost Releases Metals Into Waterways

A new study identifies at least 75 Arctic streams where minerals, especially iron, are staining water with a rusty hue

An orange tributary of the Kugororuk River.
An orange tributary of the Kugororuk River. Josh Koch, USGS

In recent years, the typical purples, blues and greens that color Alaska’s tundra ecosystems have been cut through with an unexpected hue as rivers run orange.

The phenomenon was first widely noted by scientists in 2018, and satellite imagery confirmed that as far back as 2008, certain waterways in the state have been changing from clear to rusted.

“The more we flew around, we started noticing more and more orange rivers and streams,” Jon O’Donnell, an ecologist for the National Park Service who has sampled the affected waters, says in a statement. “There are certain sites that look almost like a milky orange juice.”

In research published this week in the journal Communications: Earth & Environment, O’Donnell and a team of other scientists suggest they have pinpointed the cause of this color shift—and it’s linked to climate change.

As the Arctic warms, its permafrost is thawing. When this occurs, acid and metals—including zinc, nickel, copper, cadmium, iron and aluminum—are released from the loosening soil and exposed to water and oxygen through weathering. This process causes the metals—especially iron—to essentially rust, staining the rivers a muddy orange-brown.

Orange tributary waters mix with clearer waters of the Anaktok River.
Orange tributary waters mix with clearer waters of the Anaktok River. Josh Koch, USGS

Across about 600 miles of waterways in northern Alaska’s Brooks Range, the researchers identified 75 rivers and streams that have turned orange. Many are stained so deeply that their new rusted hue is visible in imagery taken from space.

Study lead author Brett Poulin, an organic geochemist at the University of California, Davis, used to teach a class in Colorado’s Rocky Mountains, where acid mine drainage discolored waterways near abandoned mines. “We’re seeing the same sequences of changes in water chemistry in these rivers, but far from mine sources,” he says in a video about the research.

Water samples registered pH levels of 2.6, significantly more acidic than the typical river water pH range of 6.5 to 8.

How these changes may impact fisheries and wildlife is another area of research the team would like to explore.

“When the river turned orange, we saw a significant decrease in macroinvertebrates and biofilm on the bottom of the stream, which is essentially the base of the food web,” Poulin tells the Guardian’s Aliya Uteuova. “It could be changing where fish are going to be able to live.”

With more metals in the rivers, scientists are concerned the phenomenon could impact rural drinking water—and at the very least affect the water’s taste, reports CBS News’ Aliza Chasan.

“It’s an area that’s warming at least two to three times faster than the rest of the planet,” Scott Zolkos, an Arctic scientist at Woodwell Climate Research Center who was not involved in the study, tells the Guardian. “So, we can expect these types of effects to continue.”

An orange tributary of the Kugororuk River
An orange tributary of the Kugororuk River. Josh Koch, USGS

Many rivers throughout Alaska have already experienced significant declines in salmon runs due to rising water temperatures and other factors, intimately affecting Alaska Native communities and subsistence users. Researchers have also observed chum salmon increasing their populations in cooler, northern latitudes.

Permafrost thaw across the Arctic has been linked to the release of a variety of other substances, including long-frozen viruses and massive amounts of stored carbon. This melting has also destabilized the ground in some areas, creating housing crises in the tundra as the shifting land affects infrastructure.

More work is needed to better understand the effects of permafrost thaw on water quality, the researchers say, and to determine how to prevent further damage.

“Chemistry tells us minerals are weathering,” Poulin says in the statement. “Understanding what’s in the water is a fingerprint as to what occurred.”

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