Abstract
AbstractClimate 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 toward increasing dominance of land‐derived organic carbon in waters with ongoing permafrost thaw.
Highlights
Climate change and permafrost thaw are unlocking the vast storage of organic carbon held in northern frozen soils
specific ultraviolet absorbance at 254 nm (SUVA254) was higher in thaw ponds, suggesting a larger proportion of terrestrial dissolved organic matter (DOM) in these ponds as compared to bedrock and tundra ponds
Consistent with this interpretation, S289, slope ratio (SR), and fluorescence index (FI) values were lowest in thaw ponds, suggesting smaller amounts of carbon derived from aquatic primary production, higher DOM molecular weights, and a terrestrial origin for fulvic acids, respectively
Summary
Climate change and permafrost thaw are unlocking the vast storage of organic carbon held in northern frozen soils. 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 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 Author Contribution Statement: MW and MR co-led the study, which was based on a research question formulated by MR. MW and MR designed the approach and all authors contributed data. MW conducted the statistical analyses and interpretation. MW led the manuscript preparation and all authors contributed to the text
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