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Controls on stable methane isotope signatures in northern peatlands and potential shifts in signatures under permafrost thaw scenarios

July 8, 2024

Northern peatlands are a globally significant source of methane (CH4), and emissions are projected to increase due to warming and permafrost loss. Understanding the microbial mechanisms behind patterns in CH4 production in these systems will be key to predicting annual emissions changes, with stable carbon isotopes (δ13C-CH4) being a powerful tool for characterizing these drivers. Given that δ13C signatures of CH4 are used in top-down atmospheric inversion models to partition sources, our ability to model CH4 production pathways and associated δ13C-CH4 signatures in peatland types impacted by a changing climate is critical. We sought to characterize the role of environmental conditions, including both hydrologic and vegetation patterns associated with permafrost thaw, on δ13C-CH4 signatures from a diverse set of high-latitude peatlands. We measured porewater and emitted CH4 stable isotopes, pH, and vegetation composition from five boreal-Arctic peatlands. Porewater δ13C-CH4 was strongly associated with peatland type, with δ13C enriched values obtained from more minerotrophic fens (-61.2 ± 9.1‰) compared to permafrost-free bogs (-74.1 ± 9.4‰) and raised permafrost bogs (-81.6 ± 11.5‰). Variation in porewater δ13C-CH4 was best explained by sedge cover, CH4 concentration, and the interactive effect of peatland type and pH (r2 = 0.50, p < 0.001). Emitted δ13C-CH4 varied greatly but was positively correlated with porewater δ13C-CH4, suggesting that porewater data can be used to predict changing emissions signatures from these systems. We calculated a weighted mean mixed atmospheric CH4 signature for northern peatlands of -65.3 ± 7‰ and show that this signature is more sensitive to landscape drying (4 to 10 % depletion in δ13C) than wetting (1.5 to 5% enrichment in δ13C) under permafrost thaw scenarios. Our results suggest northern peatland δ13C-CH4 signatures are likely to shift in the future which has important implications for source partitioning in atmospheric inversion models.

Publication Year 2024
Title Controls on stable methane isotope signatures in northern peatlands and potential shifts in signatures under permafrost thaw scenarios
DOI 10.1029/2023JG007837
Authors McKenzie A. Kuhn, Ruth K. Varner, Carmody K. McCalley, Clarice R. Perryman, Mika Aurela, Sophia A. Burke, Jeffrey Chanton, Patrick Crill, Jessica DelGreco, Jia Deng, Liam Heffernan, Christina Herrick, Suzanne B. Hodgkins, Cheristy P. Jones, Sari Juutinen, Evan S. Kane, Louis J. Lamit, Tuula Larmola, Erik Lilleskov, David Olefeldt, Michael W. Palace, Virginia I. Rich, Christopher Schulze, Joanne H. Shorter, Franklin Sullivan, Oliver Sonnentag, Merritt R. Turetsky, Mark Waldrop
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research: Biogeosciences
Index ID 70261225
Record Source USGS Publications Warehouse
USGS Organization Geology, Minerals, Energy, and Geophysics Science Center
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