Toxic Metals Are Turning Alaskan Rivers Orange, Highly Acidic

Toxic Metals Are Turning Alaskan Rivers Orange, Highly Acidic

“The stained rivers are so big we can see them from space,” said Brett Poulin, an assistant professor of environmental toxicology at UC Davis who was a principal investigator in the research. “These have to be stained a lot to pick them up from space.” Poulin is an expert in water chemistry and thought the staining looked similar to acid mine drainage. However, there are no mines near any of the impacted rivers. One hypothesis is permafrost. This is essentially frozen ground that stores minerals. When it’s warmed, the metal ores are exposed to water and oxygen, releasing acid and metals.

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

Acidic Water and the Risks

Part of the Kutuk River runs alongside an unspoiled section of the same river; Ken Hill/National Park Service

When researchers gathered water samples, the pH levels were lower than normal. Instead of the average pH of 8 for these rivers, the impacted rivers showed a pH of 2.3. Researchers say this indicates sulfide minerals weathering, resulting in “highly acidic and corrosive conditions that release additional metals.” Elevated or high levels of iron, zinc, nickel, copper, and cadmium are present. “We see a lot of different types of metals in these waters,” Ph.D. candidate Taylor Evinger said. “One of the most dominant metals is iron. That’s what is causing the color change.”

O’Donnell noticed the stained water in 2018; however, satellite images show staining 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 assessing the implications for drinking water and fishing stocks. According to the researchers, the problem is turning healthy areas into degraded habitats with fewer fish and invertebrates. If rural communities rely on these rivers for drinking water, they may eventually require treatment. In addition, the fish that feed rural communities could be affected.

More work is needed to understand the problem and if these toxic waterways can rebound, perhaps after cold weather promoted permafrost recovery.

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

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