VALIDATION OF A SIMPLE MODEL TO PREDICT EFFICIENCIES OF METHANE OXIDATION SYSTEMS

摘要

On a large scale test field (1060 m~2) methane emissions were monitored over a period of 30 months. During this period, the test field was loaded at rates between 0.7 and 2.2 L CH4 m~(-2) h~(-1). The total area was subdivided into 60 monitoring grid fields at 17.68 m~2 each, which were individually surveyed for methane emissions and methane oxidation efficiency. The latter was calculated by a CO2-CH4 gradient method. The base flux to each grid field was backcalculated from the data on methane oxidation efficiency and emission. Resolution to grid field scale allowed the analysis of the spatial heterogeneity of all considered fluxes. Predictions of the methane oxidation potential were estimated with the simple model Methane Oxidation Tool using soil temperature, air filled porosity and water tension as input parameters. It was found that the test field could oxidize over 80 % of the injected methane. The MOT predictions seemed to be realistic albeit the higher range of the predicted oxidations potentials could not be challenged because the load to the field was too low. Spatial and temporal emission pattern were found indicating heterogeneity of fluxes and efficiencies in the test field. No constant share of direct emissions was found as proposed by the Methane Oxidation Tool albeit the mean share of emissions throughout the monitoring period was in the range of the expected emissions. However these were more likely explained by a sporadic overloading of the field than by actual direct emissions.