| Summary: | The vast reservoir of organic matter (OM) locked up in Arctic permafrost may become vulnerable to degradation with increased thawing. In recent years, higher than average Arctic temperatures have increased the frequency of abrupt permafrost thawing events. On sloped terrain, deeper seasonal thawing of permafrost soils can initiate landslide-like events called active layer detachments (ALDs) which can release large amounts of previously unavailable carbon into the surrounding environment. Once exposed, more easily degraded permafrost-derived OM may be transported and mineralized through hydrological networks, altering biogeochemical cycles both locally and globally. It is therefore important to investigate the environmental fate of permafrost-derived OM following release by ALDs. Several complementary methods were used to investigate soil and sedimentary OM composition from an ALD-impacted High Arctic watershed, including: biomarker analyses via gas chromatography-mass spectrometry (solvent extractable compounds, base hydrolysable products, CuO oxidation products, phospholipid fatty acids), solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, and radiocarbon analysis using accelerator mass spectrometry. Samples collected from the watershed represented three distinct environments: soils, fluvial sediments, and lacustrine sediments. Soil OM composition of depth profiles from upslope and downslope regions of the disturbance were compared. Lower amounts of labile OM upslope, suggesting increased erosion, contrasted with higher amounts downslope indicative of the accumulation of OM. Additionally, labile OM observed in subterranean soil downslope indicates storage of more easily degraded material in deep permafrost. Fluvial sedimentary OM composition downstream of the disturbance was investigated to characterize potential shifts in OM composition resulting from ALD inputs. In addition, downstream translocation of ALD inputs over time was determined when comparing samples from 2011, 2013, and 2014. OM composition in areas along the river receiving ALD inputs also shifted from permafrost-derived biomarkers toward more contemporary aquatic-derived inputs over time. OM composition from recent lacustrine sediments contained older, more persistent compounds suggesting that the labile OM released by ALDs likely undergoes degradation before reaching the lake. Overall, this thesis reveals the ongoing shifts in the OM composition of ALD-impacted Arctic landscapes and contributes to the growing body of evidence suggesting enhanced losses of labile permafrost-derived carbon with future warming and climate change. Ph.D.
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