Alaskan rivers turning orange

In the north of Alaska, rivers that were once clear have turned orange, sometimes within a single season. This change is linked to the thawing of permafrost, which releases minerals that affect water quality.

Acidity levels in the rivers

According to Jon O'Donnell's team from the National Park Service, 75 rivers in the Brooks Range have changed color, with a pH dropping as low as 2.3. This level of acidity is harmful to fish and can be compared to the acidity of vinegar.

Chemical process behind the change

The thawing of permafrost releases mineral sulfides, which when oxidized generate sulfuric acid and dissolve metals such as iron, zinc, nickel, and copper in the rivers. This chemical reaction alters the water and leads to the orange coloration.

Historical role of permafrost

For millennia, permafrost has acted as a natural barrier, trapping minerals and heavy metals and preventing them from interacting with water and air. This frozen layer has been a natural safe deposit box for these substances.

Accelerated Arctic warming

The Arctic is warming approximately four times faster than the rest of the planet. This rapid warming is causing the permafrost to melt, releasing the trapped minerals and altering the environment.

Scientific documentation of the phenomenon

Jon O'Donnell's study, published in May 2024 in the journal Communications Earth & Environment, documents this phenomenon. It highlights how the thawing of permafrost leads to the release of acidic and metal-rich waters.

Scale of the issue

A USGS and National Park Service team, mobilized since 2019, has already identified more than 70 affected sites just in the Brooks Range. The scale of this issue has increased significantly compared to previous, more sporadic occurrences.

Extreme acidity levels

A pH of 2.3 is extremely acidic, comparable to the acidity of a car battery. This level is found in some of the rivers, with metal concentrations up to 70 times higher than normal.

Toxic impact on aquatic life

A study published in AGU Advances found that the Salmon River has sulfate, iron, and zinc levels up to 70 times higher than normal. These high concentrations are toxic to aquatic organisms, including fish and invertebrates.

Impact on specific fish species

In the Akillik River, which turned orange within a year, juvenile Dolly Varden trout and slimy sculpins have completely disappeared. This change has had a significant impact on the local ecosystem.

Speed of the environmental change

The Akillik River turned orange in just one year, from 2017 to 2018. The biological consequences followed almost immediately, with two fish species disappearing from this section of the river.

Broader ecological consequences

Abagael Pruitt from UC Davis confirmed a complete loss of these species in a tributary of the Akillik. She estimated that more than 200 rivers in Alaska have turned orange in recent years, affecting the local ecosystem.

Role of sensitive fish species

Dolly Varden trout and Pacific salmon are among the species most sensitive to these dissolved metals. Their local disappearance affects the ecosystem of several national parks and reserves in Alaska.

Rapid ecosystem transformation

What is striking about this case is the speed at which an ecosystem can shift, in just a few seasons. The transformation of rivers highlights the rapid changes occurring in the Arctic.

Ongoing research and monitoring

Researchers continue to monitor these rivers, aware that they tell, in their own way, the story of an Arctic changing before our eyes. The ongoing study aims to understand and document the environmental impact of permafrost thaw.