Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 17
Biogeosciences, 13, 5021–5041, 2016
https://doi.org/10.5194/bg-13-5021-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 5021–5041, 2016
https://doi.org/10.5194/bg-13-5021-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Sep 2016

Research article | 12 Sep 2016

Biogeochemical modeling of CO2 and CH4 production in anoxic Arctic soil microcosms

Guoping Tang1, Jianqiu Zheng2, Xiaofeng Xu3, Ziming Yang1, David E. Graham2,4, Baohua Gu1, Scott L. Painter1,4, and Peter E. Thornton1,4 Guoping Tang et al.
  • 1Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
  • 2Biosciences Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
  • 3Biology Department, San Diego State University, San Diego, CA 92182, USA
  • 4Climate Change Science Institute, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA

Abstract. Soil organic carbon turnover to CO2 and CH4 is sensitive to soil redox potential and pH conditions. However, land surface models do not consider redox and pH in the aqueous phase explicitly, thereby limiting their use for making predictions in anoxic environments. Using recent data from incubations of Arctic soils, we extend the Community Land Model with coupled carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) enables us to approximately describe the observed pH evolution without additional parameterization. Although Fe(III) reduction is normally assumed to compete with methanogenesis, the model predicts that Fe(III) reduction raises the pH from acidic to neutral, thereby reducing environmental stress to methanogens and accelerating methane production when substrates are not limiting. The equilibrium speciation predicts a substantial increase in CO2 solubility as pH increases, and taking into account CO2 adsorption to surface sites of metal oxides further decreases the predicted headspace gas-phase fraction at low pH. Without adequate representation of these speciation reactions, as well as the impacts of pH, temperature, and pressure, the CO2 production from closed microcosms can be substantially underestimated based on headspace CO2 measurements only. Our results demonstrate the efficacy of geochemical models for simulating soil biogeochemistry and provide predictive understanding and mechanistic representations that can be incorporated into land surface models to improve climate predictions.

Publications Copernicus
Download
Short summary
We extend the Community Land Model coupled with carbon and nitrogen (CLM-CN) decomposition cascade to include simple organic substrate turnover, fermentation, Fe(III) reduction, and methanogenesis reactions, and assess the efficacy of various temperature and pH response functions. Incorporating the Windermere Humic Aqueous Model (WHAM) describes the observed pH evolution. Fe reduction can increase pH toward neutral pH to facilitate methanogenesis.
We extend the Community Land Model coupled with carbon and nitrogen (CLM-CN) decomposition...
Citation