The warming climate is causing permafrost to melt, releasing trapped metal ores into rivers and streams, resulting in their rust-colored appearance.
A team of scientists from the National Park Service (NPS), the United States Geological Survey (USGS), the University of California, Davis (UC Davis), and other organizations have announced new findings on the “rusty” rivers and streams of Alaska after nearly two years of sampling and research. These findings were published in the journal Nature Communications Earth & Environment on May 20.
Rust-colored Kutuk River in Gates of the Arctic National Park, Alaska, viewed from above. (Photo: Ken Hill/National Park Service).
Ecologist Jon O’Donnell from the NPS, the lead author of the study, first observed this strange phenomenon in Alaska in 2018. The river he watched turned orange, although it had been very clear just a year before. The number of rivers and streams changing color has been increasing, and they can now even be observed from space.
By the end of last year, the scientific community suggested that the melting of permafrost is likely the culprit. With the warming climate, this situation in Alaska is accelerating. Metal ores trapped in the ice for hundreds to thousands of years react when exposed to oxygen and water, releasing acid and metals directly into nearby rivers and streams. While rivers and streams can naturally self-clean, the ongoing climate change is making this process more challenging.
Brett Poulin, an associate professor of environmental toxicology at UC Davis, along with researcher Taylor Evinger, analyzed collected samples and found that the orange rivers are increasingly acidic due to the influx of mineral mixtures. Some samples had a pH of 2.3, while the “healthy” rivers in the area had an average pH of 8.
The researchers discovered that the weathering of sulfide minerals is creating an acidic and corrosive environment, resulting in the release of more metals. Consequently, they obtained samples with high levels of iron, zinc, nickel, copper, and cadmium. “One of the most common metals is iron. That is what leads to the discoloration,” Evinger stated.
“As the climate continues to warm, we anticipate that permafrost will continue to melt. Therefore, anywhere with these types of minerals, rivers and streams are likely to turn orange and experience a decline in water quality. These orange waters can cause many issues, not only being toxic but also hindering fish migration to spawning areas,” O’Donnell remarked.
The team of scientists is still uncertain about the impact of the orange rivers on the wildlife that depend on them, as well as on rural Alaskan communities that rely on them for drinking water and fishing. They hope to gain a better understanding of this when their three-year study concludes.
