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Vegetation % cover, cover classes, and locations for all mire-wide plots in Stordalen Mire, northern Sweden, sampled in July 2015.  Class = the 5-category classification of Malmer et al., 2005.  Cover type = the 3-category classification of Bäckstrand et al., 2008. Each of the 75 plots had 64 subplots that were each quantified for % cover, such that the total plot-level %cover=Sum(species)/64.  Sum(SUM) is total of all other Sum() columns. Sum(0) and Sum(0 2) are data compilation checks.  FUNDING: National Aeronautics and Space Administration, Interdisciplinary Science program: From Archaea to the Atmosphere (award # NNX17AK10G). National Science Foundation, Biology Integration Institutes Program: EMERGE Biology Integration Institute (award # 2022070). United States Department of Energy Office of Biological and Environmental Research, Genomic Science Program: The IsoGenie Project (grant #s DE-SC0004632, DE-SC0010580, and DE-SC0016440). We thank the Swedish Polar Research Secretariat and SITES for the support of the work done at the Abisko Scientific Research Station. SITES is supported by the Swedish Research Council's grant 4.3-2021-00164. 

Abstract 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 CH₄production in peatlands 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‐CH₄is used in top‐down atmospheric inversion models to partition sources, our ability to model CH₄production pathways and associated δ¹³C‐CH₄values is critical. We sought to characterize the role of environmental conditions, including hydrologic and vegetation patterns associated with permafrost thaw, on δ¹³C‐CH₄values from high‐latitude peatlands. We measured porewater and emitted CH₄stable isotopes, pH, and vegetation composition from five boreal‐Arctic peatlands. Porewater δ¹³C‐CH₄was 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‐CH₄was best explained by sedge cover, CH₄concentration, and the interactive effect of peatland type and pH (r² = 0.50,p < 0.001). Emitted δ¹³C‐CH₄varied greatly but was positively correlated with porewater δ¹³C‐CH₄. We calculated a mixed atmospheric δ¹³C‐CH₄value for northern peatlands of −65.3 ± 7‰ and show that this value is more sensitive to landscape drying than wetting under permafrost thaw scenarios. Our results suggest northern peatland δ¹³C‐CH₄values are likely to shift in the future which has important implications for source partitioning in atmospheric inversion models. 

RGB composite mosaic from over 600 images captured with a Panasonic Lumix-GM1 flown at solar noon aboard a fixed wing Robota Triton unmanned aircraft at approximately 70m above ground. Spatial resolution is 3 cm. For more information on methodology, see related publication. 

RGB composite mosaic from over 600 images captured with a Panasonic Lumix-GM1 flown at solar noon aboard a fixed wing Robota Triton unmanned aircraft at approximately 70m above ground. Spatial resolution is 3 cm. 

RGB composite mosaic from over 600 images captured with a Panasonic Lumix-GM1 flown at solar noon aboard a fixed wing Robota Triton unmanned aircraft at approximately 70m above ground. Spatial resolution is 3 cm. For more information on methodology, see related publication.