Microbial processes of CH 4 production in a rice paddy soil: model and experimental validation

Abstract

The importance of different anaerobic processes leading to CH 4 production in rice paddies is quantified by a combination of experiments and model. A mechanistic model is presented that describes competition for acetate and H 2/CO 2, inhibition effects and chemolithotrophic redox reactions. The model is calibrated with anaerobic incubation experiments with slurried rice soil, monitoring electron donors and electron acceptors influencing CH 4 production. Only the values for maximum conversion rates ( V max) for sulphate and iron reduction and CH 4 production are tuned. The model is validated with similar experiments in which extra electron donors or electron acceptors had been added. The differences between model estimates without kinetic parameter adjustments and experiment were not significant, showing that the model contains adequate process descriptions. The model is sensitive to the estimates of V max, that are site dependent and to the description of substrate release, that drives all competition processes. For well-shaken systems, the model is less sensitive to chemolithotrophic reactions and inhibitions. Inhibition of sulphate reduction and methanogenesis during iron reduction can however explain acetate accumulation at the start of the incubations. Iron reduction itself is most probably retarded due to manganese reduction.