The writer John McPhee once described Alaska’s Salmon River as having “the clearest, purest water” he’d ever seen. Today, that same river runs orange with toxic metals unleashed by thawing permafrost. “During the summer of 2019, the clear waters of the Salmon turned distinctly orange and have remained discolored and turbid since,” according to a new study published in the Proceedings of the National Academy of Sciences. The Salmon River’s transformation represents a much larger crisis. In Alaska’s Brooks Range,75 streams have “recently turned orange and turbid,” the study found. “This is what acid mine drainage looks like,” said Tim Lyons, a biogeochemist at the University of California, Riverside, and co-author of the study. “But here, there’s no mine. The permafrost is thawing and changing the chemistry of the landscape.” The cause lies underground in permanently frozen soil, known as permafrost. As global temperatures rise, this ancient layer is thawing. When water and oxygen reach the newly exposed soil, they trigger chemical reactions that break down sulfide-rich rocks, creating sulfuric acid that leaches naturally occurring metals like iron, cadmium and aluminum from rocks into the river, the research shows. Researchers tested 10 major tributaries of the Salmon River and found that nine had toxic concentrations of at least one metal on at least one of three sampling dates. The study shows that levels of metals in the river’s waters exceed U.S. Environmental Protection Agency (EPA) toxicity thresholds for aquatic life. Metal levels in the Salmon River mainstem were dangerously high…This article was originally published on Mongabay

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