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11h ago

PNAS Study Confirms Permafrost Thaw Is Turning Alaska’s Salmon River Orange

Researchers report metal levels exceeding EPA toxicity thresholds for aquatic life.

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“This is what acid mine drainage looks like,” Tim Lyons, a biogeochemist at UC Riverside, told the university in a September 2025 article. “But here, there’s no mine.”
The scientists’ observations at the watershed suggest the potential for “for widespread future stream degradation with permafrost thaw further north and elsewhere at high latitudes,” they wrote. 

Overview

  • Thawing permafrost is exposing sulfide-rich rock, driving oxidation that produces sulfuric acid and mobilizes iron, cadmium, and aluminum into the river.
  • Nine of ten tributaries in the watershed exceeded federal thresholds for at least one metal, signaling widespread degradation beyond the main channel.
  • Cadmium is accumulating in fish organs and iron-rich water is smothering insect larvae, threatening salmon and other species vital to local food webs.
  • The chemical signature matches acid mine drainage even though no mining is present in the area.
  • Authors warn similar transformations could emerge across Arctic watersheds with suitable geology, and they describe conventional remediation as impractical in these remote settings.