Abrupt stream acidification and metal mobilization from permafrost degradation

# Abrupt stream acidification and metal mobilization from permafrost degradation *Published: 2026 May 21* 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. DOI: 10.1126/science.aea2898