Climate change is turning Alaska's rivers orange

SAN FRANCISCO (KCBS RADIO) – In 1975 – the year that Jaws topped the box office – streams in Alaska’s Brooks Range were known as some of the purest in the world. Today, the formerly clear water is stained orange.

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New research indicates that the drastic shift in color and quality is due to climate change in the Arctic. It may not be filled with killer sharks, but the new color does have some concerning implications.

“Here, we present an emergent threat to Arctic watersheds based on observations from 75 streams in Alaska’s Brooks Range that recently turned orange, reflecting increased loading of iron and toxic metals,” said a study published May 20 in the Communications Earth & Environment journal .

Back in the mid-70s, author John McPhee visited the Salmon River and said it had “the clearest, purest water I have ever seen flowing over rocks,” in his work Coming into the Country . According to an opinion piece in the Anchorage Daily News , the Salmon was running clear as recently as fall 2018. Then, its renowned waters turned orange-green by summer 2019.

“Three summers have now passed and, sadly, the Salmon remains severely discolored, with orange stains on the banks and its once outstanding fish habitat degraded,” said the Daily News in November 2022. This January, Scientific American reported that the beautiful waters are “quite literally rusting.”

As he looked at the gasoline-like rainbow sheen on the waterway, Patrick Sullivan, an ecologist at the University of Alaska Anchorage said: “This is bad stuff,” per that outlet.

Sullivan was part of the team who worked on the recent study, and they did find bad stuff lurking in the ochre waters.

“Stream discoloration was associated with dramatic declines in macroinvertebrate diversity and fish abundance,” said the study. “These findings have considerable implications for drinking water supplies and subsistence fisheries in rural Alaska.”

Researchers used remote sensing to constrain the timing of stream discoloration to the last 10 years. Since there was also rapid warming and snowfall during that same period, a link between permafrost thaw and the orange hue is suggested.

“Thawing permafrost can foster chemical weathering of minerals, microbial reduction of soil iron, and groundwater transport of metals to streams,” the study authors explained.

They also found that, compared to clear streams, orange-stained waterways had lower pH, higher turbidity, and higher sulfate, iron, and trace metal concentrations. That finding indicates sulfide mineral weathering contributed to the color. In particular, it seems that water containing iron is associated with the phenomenon. The release of iron from thawing permafrost and subsequent detection of particulates in surface waters has been documented in a small watershed on the North Slope of Alaska.

“Arctic rivers provide habitat for a broad array of resident and diadromous fish (i.e., fish that migrate between salt and fresh water), many of which are critical for subsistence, sport, and commercial fisheries. Climate change is already impacting high-latitude fish species, including Pacific salmon ( Oncorhynchus spp.), due to effects of warming on marine and freshwater ecosystems,” said the study of potential hazards the orange waters signal. “Adding to those concerns, mobilization of [iron] and toxic metals to Arctic streams in northern Alaska may both degrade water quality and reduce habitat.”

According to the researchers, this is the first study to report acid rock drainage in response to permafrost thaw in an Arctic region unimpacted by land-use effects.

“Ultimately, a complete water quality assessment could ascertain if trace metal concentrations exceeded acute and chronic exposure levels for a range of aquatic biota based on water pH, hardness,” and more, they said.

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