Environment

Alaska's technicolor rivers are rapidly spreading – and we now know why

View 3 Images
An aerial view of the rust-colored Kutuk River in Gates of the Arctic National Park in Alaska. Thawing permafrost is exposing minerals to weathering, increasing the acidity of the water, which releases metals like iron, zinc and copper
Ken Hill/National Park Service
An aerial view of the rust-colored Kutuk River in Gates of the Arctic National Park in Alaska. Thawing permafrost is exposing minerals to weathering, increasing the acidity of the water, which releases metals like iron, zinc and copper
Ken Hill/National Park Service
An aerial view of the Kutuk River in Alaska's Gates of the Arctic National Park that looks like orange paint spilling into the clear blue water
Ken Hill/National Park Service
An aerial view of the Kutuk River in Alaska’s Gates of the Arctic National Park, where a portion of the water is rust-stained
Ken Hill/National Park Service
View gallery - 3 images

For the first time, a large team of scientists from across North America has formed a clear picture of Alaska's 'rusting' rivers and streams, closely tracking 75 areas in the remote Brooks Range that are flushed with the bizarre hue so bright it's even visible from space.

Researchers from the National Park Service (NPS), US Geological Survey, the University of California, Davis (UC Davis) and other institutions have published the findings, the result of nearly two years of sampling and studying water in this wilderness area the size of Texas.

“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 a milky orange juice."

O'Donnell first observed this phenomenon in 2018, in a river that had been crystal clear a year earlier. But satellite images have since revealed there was evidence of these waterways, far from any sizeable human populations or industrial and mining activities, beginning to 'rust' back in 2008. But what was once an oddity on aerial imaging has now ballooned to cover a great expanse of this remote wilderness.

“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.”

Late last year, there was growing consensus among the science community that thawing permafrost was the most likely culprit. With a warming climate, this arctic region is experiencing more rapid melting of this frozen ground. Metal ores that have been locked up in the ice for hundreds to thousands of years react when exposed to oxygen and water, which in turn releases acid and metals directly into the adjacent river or stream.

Like the 'Gateway to Hell', Siberia's permafrost melt that's resulting in whole landscapes collapse around a giant crater-like slump, the problem is accelerating as more of the long-frozen surface areas are exposed to warming air. While streams can clean themselves naturally and permafrost can freeze, climate change is making it harder for this to occur.

“Chemistry tells us minerals are weathering,” said Brett Poulin, an assistant professor of environmental toxicology at UC Davis, a principal investigator in the study. “Understanding what’s in the water is a fingerprint as to what occurred.”

An aerial view of the Kutuk River in Alaska's Gates of the Arctic National Park that looks like orange paint spilling into the clear blue water
Ken Hill/National Park Service

Poulin and researcher Taylor Evinger analyzed samples taken across a period of time, and found that the orange rivers are becoming increasingly acidic, as a result of the cocktail of minerals flowing into them. Some samples returned a pH reading of 2.3, when the average 'healthy' river for the region should be at pH 8.

They found that the weathering of sulfide minerals was creating an acidic and corrosive environment for even more metals to be released. As such, high levels of iron, zinc, nickel, copper and cadmium have been found in the team's samples.

“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 color change.”

An aerial view of the Kutuk River in Alaska’s Gates of the Arctic National Park, where a portion of the water is rust-stained
Ken Hill/National Park Service

So what does this mean for the diverse wildlife that rely on these rivers and streams, and for rural Alaskan communities that access them for drinking water and fish? The scientists are still unsure. They hope to be at this point when they wrap up this three-year study.

“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."

"Those orange streams can be problematic both in terms of being toxic but might also prevent migration of fish to spawning areas," he added.

"This study is the first to report acid rock drainage in response to permafrost thaw in an Arctic region unimpacted by land-use effects," the researchers noted in the study, adding that they predict it's likely to result in reduced numbers of invertebrates and fish species.

“The stained rivers are so big we can see them from space,” added Poulin. “These have to be stained a lot to pick them up from space.”

The study was published in Nature journal Communications Earth & Environment.

Source: UC Davis

View gallery - 3 images
  • Facebook
  • Twitter
  • Flipboard
  • LinkedIn
2 comments
Karmudjun
Thanks for the write up Bronwyn, I knew the acidification played into it somehow, but I thought it was due to acid rain. It looks like there are issues with the Alaskan & near Arctic wildlife ranges if the waterways are becoming that acidic. If we can't come up with a solution to allow our former permafrost ecosystem to maintain an inhabitable pH, we may see our food chain collapse leaving hunters, fishery, and climate scientists off in the wilds without potable water or local wildlife - other than predators like Polar Bears. Have you heard that joke - What do Polar Bears Eat? The answer is Whatever they want to Eat!
cgroh
It might help if the scientists compare what happened to rivers in the southern hemisfere, where orange-like color is rule.
In the region where I live there was not been much extinction of natural species, despite of the color of the water been orange since I can remember.
Intensive fishing, hunting and deforestation - all man-made interventions - are to blame.
But we can notice a deep increase in landsliding due to excessive rain provoked by the global warming, though.