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Abstract The West Siberian Lowland (WSL) contains some of the largest wetlands and most extensive peatlands on Earth, storing vast amounts of vulnerable carbon across permafrost‐free to continuous permafrost zones. As temperature and precipitation changes continue to alter the Siberian landscape, carbon transfer to the atmosphere and export to the Arctic Ocean will be impacted. However, the drivers of organic carbon transfer are largely unknown across this region. We characterized seasonal dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition of WSL rivers from the middle reaches of the Ob’ River in the permafrost‐free zone, as well as tributaries of the Taz River in the northern continuous permafrost zone. DOC and aromatic DOM properties increased from spring to autumn in the Ob’ tributaries, reflecting the seasonal transition from groundwater‐sourced to terrestrial DOM. Differences in molecular‐level signatures via ultra‐high resolution mass spectrometry revealed the influence of redox processes on DOM composition in the winter while terrestrial DOM sourcing shifted from surface litter aliphatics and highly unsaturated and phenolic high‐O/C (HUPHigh O/C) compounds in the spring to subsurface soils and HUPLow O/Ccompounds by autumn. Furthermore, aromaticity and organic N were related to landscape properties including peatlands, forest cover, and the ratio of needleleaf:broadleaf forests. Finally, the Taz River tributaries were similar to summer and autumn Ob’ tributaries, but more enriched in N and S‐containing compounds. These signatures were likely derived from thawing permafrost, which we expect to increase in northern rivers due to active layer expansion in a warming Arctic.
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Signatures of Arctic Change: Molecular‐Level Composition and Bioavailability of Shifting Dissolved Organic Matter Sources
The Arctic is experiencing unprecedented rates of climate change, leading to numerous disturbances on the terrestrial landscape, including shrubification, increased frequency of wildfires, and permafrost thaw. These changes may impact the mobilization of terrestrial organic carbon into Arctic rivers and are hypothesized to lead to distinct alterations to the molecular composition and thus the reactivity of riverine dissolved organic matter (DOM). To understand how these three major perturbations may impact DOM dynamics in Arctic fluvial and coastal systems, we examined the concentration and bioavailability of dissolved organic carbon (DOC) together with the molecular‐level DOM composition of different source endmember leachates from the Yukon River watershed using biodegradation incubation experiments and Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). Simulated climate‐related landscape perturbations generally led to increased leachate DOC concentrations. Incubations demonstrated that the biodegradability of leachate DOC was lowest for vegetation endmembers, particularly for shrubs (12.3% DOC loss), and highest for thawing Yedoma permafrost (64.9% loss) and organic‐rich tundra soil (70.9% loss). FT‐ICR MS highlighted that aliphatic and high‐H/C molecular formulas were preferentially biodegraded, whereas condensed aromatic and polyphenolic compounds were relatively enriched post‐biodegradation in all endmember leachates. Together these findings suggest that with continued climate change and landscape perturbation, larger amounts of less bioavailable DOC will be mobilized into Arctic rivers leading to higher relative amounts of highly aromatic, biologically stable DOM being exported into receiving ecosystems and the Arctic Ocean, potentially altering the rates and mechanisms of carbon turnover in the coastal zone.
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- Award ID(s):
- 2300039
- PAR ID:
- 10681465
- Publisher / Repository:
- Journal of Geophysical Research: Biogeosciences
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 130
- Issue:
- 7
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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