Simulation of methanogenesis in the mathematical model ecosys

A biologically-based approach to the modelling of CH4 transformations in soil would likely be of general use in the estimation of soil–atmosphere CH4 exchange as part of global climate studies. Such an approach was adopted as part of the ecosys modelling project to simulate the interrelated activities of anaerobic fermenters and H2-producing acetogens, of acetotrophic and hydrogenotrophic methanogens and of autotrophic methanotrophs. The simulation of these activities was based on the stoichiometries and energetics of the transformations mediated by each microbial community. Model results were tested with published data for CH4 emission during anaerobic incubation of soils amended with different plant residues. The model reproduced within experimental error observed changes with temperature in CH4 emission rates and in CH4-to-CO2 emission ratios caused by different residue amendments. These changes were driven in the model by the dynamics of growth and respiration by fermentative and methanogenic communities under different temperatures and residue amendments. Growth yields of methanogenic communities in the model were consistent with growth yields observed in other studies, but specific growth rates in the model were somewhat lower. Because the model represents basic microbial behaviour during CH4 transformation, its use will likely improve the confidence with which changes in soil–atmosphere CH4 exchange can be estimated under hypothesized changes in soils, climates and management. However testing of the model should be extended to more complex conditions of transient anaerobiosis under natural temperatures to establish confidence in its predictive capability for soil–atmosphere CH4 exchange.