Abstract
Accurately estimating methane (CH4) flux is critically important for investigating and predicting the biogeochemistry-climate feedback. Better simulating CH4 flux requires explicit representations of microbial processes on CH4 dynamics because all processes for CH4 production and consumption are actually carried out by microbes. A microbial functional group based module was developed and tested against an incubation experiment. The module considers four key mechanisms for CH4 production and consumption: methanogenesis from acetate or single-carbon compounds and CH4 oxidation using molecular oxygen or other inorganic electron acceptors. These four processes were carried out by four microbial functional groups: acetoclastic methanogens, hydrogenotrophic methanogens, aerobic methanotrophs, and anaerobic methanotrophs. This module was then linked with the decomposition subroutine of the Community Land Model, and was further used to simulate dynamics of carbon dioxide (CO2) and CH4 concentrations from an incubation experiment with permafrost soils. The results show that the model could capture the dynamics of CO¬2 and CH4 concentrations in microcosms with top soils, mineral layer soils and permafrost soils under natural and saturated moisture conditions and a temperature gradient of -2 °C, 3 °C, and 5 °C. Sensitivity analysis confirmed the importance of acetic acid’s direct contribution as substrate and indirect effects through pH feedback on CO2 and CH4 production and consumption. This study suggests that representing the microbial mechanisms is critical for modeling CH4 production and consumption; it is urgent to incorporate microbial mechanisms into Earth system models for better predicting the behavior of the climate system.
