https://doi.org/10.1126/science.aea2898

Skierszkan, E.K., Szeitz, A.J., Lindsay, M.B.J., and Carey, S.K. (2026). Abrupt stream acidification and metal mobilization from permafrost degradation. Science, 392(6800), 863–867. https://doi.org/10.1126/science.aea2898

Stream chemistry and ecosystem function are being transformed by abrupt acceleration of sulfide-mineral oxidation in permafrost-underlain headwater catchments of the Yukon and Mackenzie river basins—the two largest (sub)Arctic rivers in North America. Over the past decade, dozens of acidic (pH ~3) seepages have emerged in these headwaters, causing vegetation dieback and mobilizing metals at acutely toxic concentrations in receiving streams. Acid generated during sulfide-mineral oxidation also accelerates carbon dioxide emissions by driving carbonate-mineral dissolution. Downstream (sub)Arctic rivers show statistically significant multidecadal increases in sulfate concentrations, yet their metal concentrations remain stable because of attenuation and dilution processes. Headwater stream acidification signals a major perturbation in metal, carbon, and sulfur cycling linked to permafrost thaw with far-reaching consequences for water resources, northern communities, ecosystem health, and Earth’s biogeochemical future.

Permafrost in high northern latitudes is thawing at an accelerating rate due to climate warming. This has serious consequences for streams that originate in those areas and for areas beyond. Skierszkan et al. documented changes in stream chemistry and ecology in three headwater catchments in the Yukon-Mackenzie watershed of Canada. They showed how the oxidation of sulfide minerals found in thawing permafrost causes stream water acidification, acid-rock drainage, elevated metal and metalloid concentrations, and toxicity for most of the exposed terrestrial and aquatic organisms. These effects are worsening as permafrost thawing increases. —Jesse Smith

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