I have a large data set of simultaneous CO2 and CH4 soil efflux data from across the surface of an active landfill. Data was collected using a West Systems Accumulation Chamber and infrared gas analysers. I now want to assess the cumulative methane oxidation from the ratio of CH4 to CO2 provided by the flux data.

My understanding is that bacteria within the soil convert CH4 to CO2 decreasing the size of the CH4/CO2 as the gas moves through the porous cover/waste. However, the degree to which CH4 oxidation occurs is dependent upon the gas velocity. At high flux rates there may not be enough time for microbial catabolism of the CH4 resulting in little or nil methane oxidation and high flux rates. A simple X-Y plot of the CH4 and CO2 flux data support this hypothesis. The same plot also demonstrates that at high fluxes the CH4/CO2 mass flux ratio is identical to that of the source gas ratio determined from repeat subsoil gas and well head gas compositional sampling using a LFG analyzer (volumetric CH4, CO2, O2 concentrations) indicating minimal/nil oxidation. I’m now attempting to assess the relationship between mass flow and methane oxidation and was hoping for some recommendations?

The reason I’m trying to calculate the cumulative CH4 oxidation rate is in order to make a comparison between the CH4 output measured directly and that determined by multiplying the CO2 output by the source gas ratio - but this requires a robust and defensible measure of CH4 oxidation. As this is an active landfill there is no/little soil material only municipal waste and cover comprised of screened aggregate so I am not overly concerned about the role of soil respiration derived CO2 over the CH4/CO2 ratio.