Isotopic insights into methane production, oxidation, and emissions in Arctic polygon tundra

• Published in: Global Change Biology
• Main Authors: Vaughn, Lydia J. S., Conrad, Mark E., Bill, Markus, Torn, Margaret S.
• Other Authors: Biological and Environmental Research
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Arctic; Climate change; permafrost; Tundra
• Online Access: http://dx.doi.org/10.1111/gcb.13281; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fgcb.13281; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.13281; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/gcb.13281; https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/gcb.13281

Abstract Arctic wetlands are currently net sources of atmospheric CH 4 . Due to their complex biogeochemical controls and high spatial and temporal variability, current net CH 4 emissions and gross CH 4 processes have been difficult to quantify, and their predicted responses to climate change remain uncertain. We investigated CH 4 production, oxidation, and surface emissions in Arctic polygon tundra, across a wet‐to‐dry permafrost degradation gradient from low‐centered (intact) to flat‐ and high‐centered (degraded) polygons. From 3 microtopographic positions (polygon centers, rims, and troughs) along the permafrost degradation gradient, we measured surface CH 4 and CO 2 fluxes, concentrations and stable isotope compositions of CH 4 and DIC at three depths in the soil, and soil moisture and temperature. More degraded sites had lower CH 4 emissions, a different primary methanogenic pathway, and greater CH 4 oxidation than did intact permafrost sites, to a greater degree than soil moisture or temperature could explain. Surface CH 4 flux decreased from 64 nmol m −2 s −1 in intact polygons to 7 nmol m −2 s −1 in degraded polygons, and stable isotope signatures of CH 4 and DIC showed that acetate cleavage dominated CH 4 production in low‐centered polygons, while CO 2 reduction was the primary pathway in degraded polygons. We see evidence that differences in water flow and vegetation between intact and degraded polygons contributed to these observations. In contrast to many previous studies, these findings document a mechanism whereby permafrost degradation can lead to local decreases in tundra CH 4 emissions.