Adding stable carbon isotopes improves model representation of the role of microbial communities in peatland methane cycling

• Published in: Journal of Advances in Modeling Earth Systems
• Main Authors: Deng, Jia, McCalley, Carmody K., Frolking, Steve, Chanton, Jeff, Crill, Patrick, Varner, Ruth, Tyson, Gene, Rich, Virginia, Hines, Mark, Saleska, Scott R., Li, Changsheng
• Language: unknown
• Published: 2021
• Subjects: 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; permafrost; Subarctic
• Online Access: http://www.osti.gov/servlets/purl/1393576; https://www.osti.gov/biblio/1393576; https://doi.org/10.1002/2016MS000817

Climate change is expected to have significant and uncertain impacts on methane (CH 4 ) emissions from northern peatlands. Biogeochemical models can extrapolate site-specific CH 4 measurements to larger scales and predict responses of CH 4 emissions to environmental changes. However, these models include considerable uncertainties and limitations in representing CH4 production, consumption, and transport processes. To improve predictions of CH 4 transformations, we incorporated acetate and stable carbon (C) isotopic dynamics associated with CH 4 cycling into a biogeochemistry model, DNDC. By including these new features, DNDC explicitly simulates acetate dynamics and the relative contribution of acetotrophic and hydrogenotrophic methanogenesis (AM and HM) to CH 4 production, and predicts the C isotopic signature (δ 13 C) in soil C pools and emitted gases. When tested against biogeochemical and microbial community observations at two sites in a zone of thawing permafrost in a subarctic peatland in Sweden, the new formulation substantially improved agreement with CH 4 production pathways and δ 13 C in emitted CH 4 (δ 13 C-CH 4 ), a measure of the integrated effects of microbial production and consumption, and of physical transport. We also investigated the sensitivity of simulated δ 13 C-CH 4 to C isotopic composition of substrates and, to fractionation factors for CH4 production (α AM and α HM ), CH 4 oxidation (α MO ), and plant-mediated CH 4 transport (α TP ). The sensitivity analysis indicated that the δ13C-CH 4 is highly sensitive to the factors associated with microbial metabolism (α AM , α HM , and α MO ). The model framework simulating stable C isotopic dynamics provides a robust basis for better constraining and testing microbial mechanisms in predicting CH 4 cycling in peatlands.