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yesterday

Study Ties Alaska’s Orange Rivers to Permafrost Thaw and Toxic Metal Leaching

Researchers identify sulfide mineral weathering as the trigger for persistent contamination in the Brooks Range.

In Alaska verfärben sich immer mehr Gewässer orange. © Ray Koleser
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Overview

  • In a new PNAS analysis, nine of ten main Salmon River tributaries showed at least one metal above U.S. EPA thresholds, including cadmium measured at 74.1 ppb in the Savilhaq River.
  • Field campaigns in 2022–2023 reached remote sites by foot and inflatable boats and found sulfate-rich chemistry consistent with oxidation of sulfide minerals that mobilizes iron, aluminum, cadmium, copper and zinc.
  • Observed impacts include severe drops in algal biomass and invertebrates and the disappearance of juvenile fish in affected streams, with regional salmon catches plunging from about 700,000 in 2018 to roughly 5,000 in 2024.
  • Researchers have documented at least 75 additional Brooks Range waters with similar orange discoloration and warn the process can be long-lasting or effectively irreversible once underway.
  • The study did not measure mercury, and separate research has reported permafrost-derived mercury in Arctic river sediments, underscoring the need for expanded monitoring.