Abstract
<title>Abstract</title> <p>The thaw of ice-rich permafrost is dramatically reshaping Arctic landscapes, driving large-scale mobilization of sediments and solutes from once-frozen repositories into aquatic networks. The ensuing effects on aquatic microorganisms, which drive critical Earth system transformations, remain largely unresolved despite growing implications for climate-sensitive emissions, ecosystem functioning, and environmental resources. Drawing on three years of measurements from thaw slumps in the western Canadian Arctic, we show a reorganization of microbial communities under disturbance. Microbial community richness and diversity contracted immediately downstream of thaw slumps, and communities increasingly reflected thawed inputs as relative disturbance intensified. Concurrently, slump-stream connectivity increased both the potential aerobic and anaerobic microbes, suggesting that the integration of thaw-derived sediments into streams creates a mosaic of redox habitats and therefore metabolic niches. Our findings provide a mechanistic bridge between geochemical change and ecosystem outcomes in slump-affected aquatic systems and point to a systems-level regional reconfiguration of biogeochemical cycling.</p>