Simulation of methanotrophy in the mathematical model ecosys

Oxidation by soil-based methanotrophs is an important sink for methane in the soil and atmosphere. Methanotrophy should therefore be explicitly represented in models of CH4 transfer between soils and the atmosphere. The model for methanotrophy proposed here is based on the kinetics of CH4 oxidation, as controlled by the biomass and specific activity of aerobic methanotrophs and by soil heat, CH4 and O2 transfers. Energy yields from CH4 oxidation drive the growth of methanotrophs and thereby the kinetics of oxidation. Rates of atmospheric CH4 oxidation simulated by this model were consistent with rates of oxidation measured at different temperatures and water contents in soil columns. Steep vertical profiles of gaseous CH4 concentration in the model indicated that oxidation was limited by CH4 diffusion through soil. This indication was confirmed by the low sensitivity of oxidation to soil temperature and the high sensitivity of oxidation to soil water content. At higher soil temperatures and water contents, limitations to O2 diffusion in the model caused CH4 to be generated deeper in the soil profile. Consequent increases in CH4 concentrations closer to the soil surface caused more rapid oxidation, which caused CH4 emission to be much lower than CH4 generation. Such reduction is consistent with that measured over soil profiles in which an aerobic zone overlies an anaerobic one. The biologically-based approach to the modelling of CH4 oxidation proposed here is likely to find general application in the simulation of CH4 transfer between soils and the atmosphere.