PREVIEW

Alaska's once-pristine arctic rivers are undergoing a dramatic transformation, turning a rusty bright orange colour that scientists call "alarming."

Dozens of Alaska’s most remote streams and rivers are changing from a crystal-clear blue to a cloudy orange, potentially due to minerals exposed by thawing permafrost, according to new research published in the journal Nature Communications: Earth and Environment.

For the first time, researchers from the National Park Service, U.S. Geological Survey, University of California, Davis, and other institutions have documented and sampled some of these impaired waters, identifying 75 locations across a Texas-sized area of northern Alaska’s Brooks Range.

The degraded rivers and streams could have significant implications for drinking water and fisheries in Arctic watersheds as the climate changes, the researchers noted.

“The more we flew around, we started noticing more and more orange rivers and streams,” said lead author Jon O’Donnell, an ecologist for the NPS’ Arctic Inventory and Monitoring Network. “There are certain sites that look almost like milky orange juice."

Those orange streams can be problematic both in terms of being toxic and potentially preventing fish migration to spawning areas, O'Donnell added.

O’Donnell first noticed the issue in 2018 when he visited a river that appeared rusty despite being clear the previous year. He began gathering information and water samples whenever possible in the remote region, where access to the rivers and streams typically requires helicopters.

“The stained rivers are so big we can see them from space,” said Brett Poulin, an assistant professor of environmental toxicology at UC Davis and a principal investigator in the research. “These have to be stained a lot to pick them up from space.”

Poulin, an expert in water chemistry, observed that the staining resembled acid mine drainage, although no mines are near the impaired rivers, including along the famed Salmon River and other federally protected waters.

One hypothesis is that thawing permafrost, essentially frozen ground, releases minerals that, when exposed to water and oxygen, result in the release of acid and metals.

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

The impacted rivers are on federal lands managed by the Bureau of Land Management, Fish and Wildlife Service, and NPS, including Gates of the Arctic and Kobuk Valley National Parks.

Poulin and PhD candidate Taylor Evinger analysed initial samples and collected more during a trip last August, while others took samples in June and July. This year, they plan three additional trips during the summer to collect more samples.

Some samples from the impaired waters have a pH of 2.3, compared to the average pH of 8 for these rivers. This indicates that sulfide minerals are weathering, leading to highly acidic and corrosive conditions that release additional metals. Elevated levels of iron, zinc, nickel, copper, and cadmium have been measured.

“We see a lot of different types of metals in these waters,” Evinger said. “One of the most dominant metals is iron. That’s what is causing the colour change.”

Although O’Donnell first noticed the change in 2018, satellite images have revealed stained waters dating back to 2008.

“The issue is slowly propagating from small headwaters into bigger rivers over time,” he said. “When emergent issues or threats come about, we need to be able to understand them.”

The researchers are in the second year of a three-year grant aimed at understanding what is happening in the water, modelling other areas at risk, and assessing implications for drinking water and fishing stocks.

The problem is growing, affecting habitat, water quality, and other ecological systems, turning healthy areas into degraded habitats with fewer fish and invertebrates. If rural communities rely on these rivers for drinking water, treatment may eventually be necessary, and the fishing stocks that feed local residents could be impacted.

“There’s a lot of implications,” O’Donnell said. “As the climate continues to warm, we would expect permafrost to continue to thaw, and so wherever there are these types of minerals, there’s potential for streams to be turning orange and becoming degraded in terms of water quality.”

More research is needed to understand the problem better and determine whether rivers and streams can rebound, possibly after cold weather promotes permafrost recovery.

“I think there will be a lot more detailed work to follow up to address some of the uncertainties that we currently have,” O’Donnell said.

Scientists from Alaska Pacific University, Colorado State University, University of Alaska Anchorage, and UC Riverside also contributed to the research.

The research was funded by the U.S. Geological Survey–NPS Water Quality Partnership program, the U.S. Geological Survey Changing Arctic Ecosystem Initiative, and the NPS Arctic Inventory and Monitoring Program.