Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Climate change and permafrost thaw are unlocking the vast storage of organic carbon held in northern frozen soils. Here we evaluated the effects of thawing ice-rich permafrost on dissolved organic matter (DOM) in freshwaters by optical analysis of 253 ponds across the circumpolar North. For a subset of waters in subarctic Quebec, we also quantified the contribution of terrestrial sources to the DOM pool by stable isotopes. The optical measurements showed a higher proportion of terrestrial carbon and a lower algal contribution to DOM in waters affected by thawing permafrost. DOM composition was largely dominated (mean of 93%) by terrestrial substances at sites influenced by thawing permafrost, while the terrestrial influence was much less in waterbodies located on bedrock (36%) or with tundra soils unaffected by thermokarst processes (42%) in the catchment. Our results demonstrate a strong terrestrial imprint on freshwater ecosystems in degrading ice-rich permafrost catchments, and the likely shift towards increasing dominance of land-derived organic carbon in waters with ongoing permafrost thaw.