Alaska’s Colorful Rivers are Rapidly Growing, and We’ve Discovered Why
For the first time, a large team of North American scientists has mapped Alaska’s ‘rusting’ rivers and streams, tracking 75 areas in the remote Brooks Range. These rivers have a bright, unusual hue visible even from space.
Researchers from the National Park Service (NPS), US Geological Survey, University of California, Davis (UC Davis), and other institutions have published their findings after nearly two years of sampling and studying water in this vast wilderness area, comparable in size to Texas.
Increasing Observations of Orange Rivers and Streams in Alaska
“The more we flew around, the more orange rivers and streams we noticed,” said lead author Jon O’Donnell, an ecologist with the NPS Arctic Inventory and Monitoring Network. “Some sites even resemble a milky orange juice.”
O’Donnell first noticed this phenomenon in 2018, in a river that had been crystal clear the previous year. Satellite images have since shown evidence of these waterways starting to ‘rust’ as far back as 2008, in areas far from significant human activity or industrial and mining operations. What began as an anomaly in aerial images has now spread extensively across this remote wilderness.
“The issue is gradually spreading from small headwaters into larger rivers over time,” he said. “We need to understand emerging issues or threats as they arise.”
Late last year, the scientific community increasingly agreed that thawing permafrost was likely to blame. With the warming climate, this Arctic region is experiencing rapid melting of the frozen ground. Metal ores locked in the ice for centuries react when exposed to oxygen and water, releasing acid and metals into nearby rivers and streams.
Similar to Siberia’s Permafrost Melt, Exposing Long-Frozen Surfaces to Warming Air Worsens the Problem
Similar to the permafrost thaw in Siberia, which results in significant landscape collapses around crater-like depressions, the situation is worsening as more frozen surfaces are exposed to warmer air. While streams can naturally clean themselves and permafrost can refreeze, climate change is making this process more difficult.
“Chemistry indicates minerals are weathering,” said Brett Poulin, an assistant professor of environmental toxicology at UC Davis and a principal investigator in the study. “Understanding what’s in the water provides clues about what has happened.”
Poulin and researcher Taylor Evinger analyzed samples collected over time and discovered that the orange rivers are becoming increasingly acidic due to the mix of minerals flowing into them. Some samples showed a pH reading of 2.3, while the average ‘healthy‘ river in the region should have a pH of 8.
Weathering of Sulfide Minerals Creates an Acidic Environment, Releasing High Levels of Iron, Zinc, Nickel, Copper, and Cadmium
They found that the weathering of sulfide minerals was creating an acidic and corrosive environment, releasing even more metals. Their samples revealed high levels of iron, zinc, nickel, copper, and cadmium.
“We see a lot of different types of metals in these waters,” Evinger said. “One of the most dominant metals is iron, which is causing the color change.”
Ken Hill/National Park Service
Uncertainty Remains for Wildlife and Rural Alaskan Communities Relying on Affected Rivers; Scientists Aim for Clarity by Study’s End
So what does this mean for the diverse wildlife that rely on these rivers and streams, and for rural Alaskan communities that use them for drinking water and fishing? The scientists are still uncertain. They hope to have more answers by the end of this three-year study.
“There are a lot of implications,” O’Donnell said. “As the climate continues to warm, we expect permafrost to keep thawing, so wherever these types of minerals are present, there’s potential for streams to turn orange and degrade in water quality.”
“These orange streams can be problematic, not only because they might be toxic but also because they could prevent fish from migrating to spawning areas,” he added.
“This study is the first to report acid rock drainage due to permafrost thaw in an Arctic region unaffected by land-use impacts,” the researchers noted, predicting it could lead to reduced numbers of invertebrates and fish species.
“The stained rivers are so large we can see them from space,” added Poulin. “They have to be significantly stained to be detectable from space.”
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