Home Science Acid rocks are coloring Alaska’s rivers bright orange – and it’s not good

Acid rocks are coloring Alaska’s rivers bright orange – and it’s not good

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Acid rocks are coloring Alaska's rivers bright orange – and it's not good

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.”

Alaska’s Rusting Rivers: The Alarming Impact of Permafrost Thaw on Arctic Rivers

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
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

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