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Rivers in Alaska turn orange. The reason even surprised scientists

(CNN) — According to a new study, rivers and streams in Alaska change color — from clear, bright blue to rusty orange — because of the toxic metals released when permafrost thaws.

The finding surprised researchers from the National Park Service, the University of California at Davis and the US Geological Survey, who conducted tests at 75 sites in the waterways of Alaska’s Brooks Range. According to the study published in the journal Communications: Earth & Environment, the area’s rivers and streams appeared to be rusting and turning cloudy and orange over the past five to 10 years.

The discoloration and cloudiness are caused by metals such as iron, zinc, copper, nickel and lead, the researchers found — some of which are toxic to river and stream ecosystems — as permafrost thaws, exposing waterways to minerals trapped underground. thousands of years.

“We’re used to seeing this in parts of California, parts of Appalachia where we have a mining history. This is a classic process happening in rivers here in the continental US that have been affected for more than 100 years since some mining in the 1850s,” said Brett Poulin, co-author of the study and professor of environmental toxicology. at UC Davis.

“But it is very surprising to see it when you are in some of the most remote wilderness and far from a mining source.”

Arctic soils naturally contain organic carbon, nutrients and metals, such as mercury, in their permafrost, the study said. High temperatures have caused these minerals and the water sources around them to meet as the permafrost melts.

Research has shown that the Arctic is warming four times faster than the rest of the world.

“What we think we’re seeing is the thawing of the soil, which is happening faster there than elsewhere,” says Poulin. “It really is an unexpected consequence of climate change.”

Researchers used satellite images to determine when the color change occurred at different rivers and streams.

“This happened in several locations, with the most drastic increases occurring between 2017 and 2018, coinciding with the warmest years on record,” Poulin said.

This discoloration has been linked to a “dramatic decline” in aquatic life, raising concerns about the impact of continued permafrost melt on communities that rely on these waterways for drinking and fishing.

Alaska’s Arctic rivers alone are home to a variety of fish that are “critical to subsistence, sport and commercial fishing,” researchers wrote. Poulin said local communities have expressed their concerns and observations to researchers starting seven years ago.

Alaska isn’t the only state experiencing this phenomenon. Another study, published just a month before researchers in Alaska made their findings public, describes how Colorado’s Rocky Mountains are experiencing similar effects from, among other things, a warming climate.

The study, published by Water Resources Research, finds an increase in metal concentrations – namely sulfate, zinc and copper – in 22 mountain streams in Colorado over the past 30 years. Researchers found that reduced streamflow was responsible for half of the increase, while the other half, they say, is due to thawing of frozen ground that allows minerals to leach from the bedrock.

These studies have also expanded beyond the US in the past. Similar research on the increase in concentrations of metals and rare earth elements in mountain rivers and streams has been done in the Chilean Andes, the European Alps and the Pyrenees in northern Spain.

While some of these areas are exposed to mining sites and have thus seen metal concentrations in rivers and streams over the years, the observed increases raise questions about how climate change will continue to impact mountain water sources.

Researchers in Alaska will continue their research in the coming years to determine the location of the metal and mineral resources, and how aquatic life and humans will be affected.

The CNN Wire
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