الأراضي المقدسة الخضراء / GHLands
An international team of researchers has identified the primary causes behind the transformation of many Arctic rivers—once renowned for their pristine waters—into rust-colored waterways contaminated with iron particles and toxic metals. The phenomenon has been directly linked to accelerating climate change and the thawing of permafrost.
The findings, published in the journal Communications Earth & Environment, reveal that the thawing of soils that have remained frozen for thousands of years is triggering new chemical and biological processes that are degrading water quality across large areas, particularly in northern Alaska.
Thawing Permafrost Drives the Phenomenon
Researchers conducted extensive field investigations across Alaska’s Brooks Range, examining environmental changes at multiple scales, from regional patterns and major river basins to detailed analyses of smaller streams and waterways.
The study found that the decisive factor behind the discoloration of rivers is the thawing of permafrost layers that have remained frozen for millennia. As these frozen soils melt, water and oxygen gain access to geological materials that were previously isolated from the environment.
According to Dr. Roman Dial, lead author of the study and Professor Emeritus of Mathematics and Biology at Alaska Pacific University, the mechanisms driving the phenomenon vary depending on elevation. The research identified two distinct processes responsible for turning Arctic waters orange.
Pyrite-Rich Rocks in Mountainous Areas
In high-altitude regions, the problem begins when rocks containing pyrite—commonly known as “fool’s gold”—are exposed to water and air following permafrost thaw.
Researchers explained that this exposure triggers a process known as acid rock drainage, a phenomenon typically associated with mining operations but occurring naturally and on a large scale in Arctic environments.
Tim Lyons, Professor of Geobiology at the University of California, Riverside, and co-author of the study, noted that when pyrite reacts with water, it breaks down and releases iron and sulfur, producing sulfuric acid, sulfates, and other potentially toxic metals.
As iron-rich water mixes with oxygen, the dissolved iron oxidizes and forms rust-like particles. These particles give rivers their characteristic orange color and create layers of reddish sediment along riverbeds.
Wetlands and Bacteria in Lowland Areas
In lower-elevation regions, however, a very different mechanism is at work.
As permafrost thaws, wetlands and marshes expand, creating oxygen-poor soil conditions. Under these circumstances, certain bacteria begin using iron instead of oxygen to carry out their metabolic processes.
This microbial activity converts iron in the soil into a soluble form that can be transported by groundwater into rivers and streams.
Once the dissolved iron reaches oxygen-rich surface waters, it oxidizes and precipitates as rust-colored sediments, producing the distinctive orange coloration observed in affected waterways.
Researchers noted that, unlike the mountain-driven process, this mechanism does not generate sulfuric acid or sulfates, allowing scientists to distinguish between the two sources of contamination.
A Tool for Predicting Future Water Pollution
The study also identified a delayed-response effect that could help scientists forecast areas at risk of future contamination.
Each summer, the active surface layer of permafrost thaws to its deepest extent before refreezing during winter. Iron released during one thaw season may remain trapped underground before eventually being transported into rivers the following year.
By comparing long-term soil temperature records with water chemistry data, researchers successfully linked rising ground temperatures to increasing concentrations of dissolved metals in Arctic waterways.
Scientists believe this relationship could eventually allow temperature data to be used as a predictive tool for assessing future water quality and identifying areas most vulnerable to contamination.
A Direct Threat to Ecosystems
Researchers warn that the ecological consequences of the phenomenon could be severe.
Fine iron-rich particles can remain suspended in water for distances exceeding 100 kilometers, increasing turbidity and reducing light penetration needed by aquatic algae. The sediments can also affect aquatic insects and clog fish gills, disrupting freshwater ecosystems.
In Alaska and northern Canada, researchers believe these changes may already be affecting salmon populations, which depend on clear water and clean gravel beds for successful spawning.
A Global Threat Beyond Alaska
The risks are not confined to the North American Arctic.
The study indicates that similar geological and climatic conditions exist in other regions of the world, including northern Canada, Russia, the Andes Mountains of South America, and parts of the European Alps.
Researchers warn that continued global warming is likely to expand the geographic extent of the phenomenon in the coming years as more permafrost thaws and larger quantities of metals are released into aquatic systems.
“What began as a localized environmental signal in the Brooks Range has now become a growing phenomenon that can be observed in multiple regions around the world,” said Tim Lyons.
No Easy Solutions
The research team emphasized that addressing this form of contamination differs significantly from managing industrial pollution associated with mining activities.
Because the process occurs naturally across vast landscapes, it cannot be easily contained or mitigated using conventional remediation approaches.
Nevertheless, scientists believe that improving the ability to predict high-risk areas could help protect sensitive habitats and safeguard water resources that local communities rely on for food security and fishing livelihoods.
The study concludes that climate change is not only altering temperatures and ice cover in polar regions but is also fundamentally reshaping the chemistry of rivers and aquatic ecosystems—changes that may carry significant environmental and economic consequences for decades to come.
research source :https://www.nature.com/articles/s43247-026-03450-x
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