Over the past decade, a network of usually pristine blue rivers and lakes that winds through Alaska’s breathtaking Brooks Range mountains has been starting to look a little… rusty.
Scientists first noticed the unusual orange plumes flowing into the water back in 2018. They began to investigate, collecting water samples from various sites so remote they can only be accessed by helicopter – but at the time, they were only able to get a snapshot of what was going on.
“The more we flew around, we started noticing more and more orange rivers and streams,” said ecologist Jon O’Donnell, of the US National Park Service. “There are certain sites that look almost like a milky orange juice.”
Environmental toxicologist Brett Poulin (of UC Davis) was intrigued at how similar the orange staining looked to the acidic pollution he had seen draining from metal mines.
There are no mines nearby – but a new study led by environmental chemist Taylor Evinger, a member of Poulin’s lab at UC Davis, confirms that the orange stuff flowing into these rivers may be an even bigger cause for concern.
The new study is published in AGU Advances.
The rust, Evinger and colleagues say, can be attributed to thawing Arctic permafrost. As water seeps through once-frozen soils, it encounters bedrock minerals that have been locked away for potentially thousands of years.
When these minerals are oxidized, they release metals – iron, aluminum, manganese, zinc, nickel, cadmium, and rare earth elements – that can then seep into waterways, hence the rivers’ rusty appearances.
From 2022 to 2024, Evinger and team collected water samples from six different watersheds across the Brooks Range, to track how the river chemistry was changing over time.
Some of those samples revealed water more acidic, and loaded with more metals, than those used for drainage from metal mines.
On the Salmon River, one of these seepages bumped metal levels up to 70 times higher than usual, even 60 miles downstream from the source.
The team were able to trace a major release of metals back to Alaska’s warmest summer on record, 2019, which was followed by an abnormally snowy winter.
“When you have more snow, it insulates the soil, preventing refreezing,” says Evinger.
“We think water went deeper into the soil because of soil thaw, interacted with these minerals, and all of these watersheds were triggered around the same time.”
In the wake of that warm summer, the rivers experienced a sudden, steep rise in sulfate and zinc concentrations, which then steadily fell in the years that followed.
Questions remain about how this sudden influx of acidic metals impacts communities that rely on the rivers.
Since 2018, more reports have come in from across thousands of seepages in North America’s permafrost zone, documenting acid rock drainage into more than 200 rivers and streams.
“This was a process that was not forecast, predicted or included in any assessment of how the Arctic will change under a warmer climate, but we’re seeing it in rivers across the Arctic,” says Poulin.
“‘Rusting rivers’ have been documented in Boreal and Arctic Canada, and other parts of the world that have permafrost.”
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Earth scientist Elliott Skierszkan, of Carleton University in Canada, says “this widespread outcome of global warming presents a major risk to water resources and aquatic ecosystems,” in a related article also published in AGU Advances.
The toxic metals entering these waters – and the low pH affected rivers can sometimes reach – can be detrimental to ecosystems. So far, scientists have seen extensive areas of plants die back near acidified rivers, as well as a loss of important fish like salmon and whitefish, along with other aquatic creatures.
The rural Arctic communities – many of whom are Alaska Native peoples – that live in these regions would be especially affected, since they rely on the rivers and their fish to survive.
But for the Brooks Range region, those impacts are yet to be seen – at least for now.
“While we are not seeing massive fish die-offs, and we’re not aware of drinking water quality issues currently harming villages, the numbers of observations are still concerning,” Evinger says.
“Many watersheds – hundreds of them – have acid rock drainage inputs. These rivers are pretty much untouched, and yet this is happening here. It’s a new reality of climate change.”
The research has been published in AGU Advances.
This article was fact-checked by Rachel Garner and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
