Above- and below-ground methane fluxes and methanotrophic activity in a landfill-cover soil

摘要

Landfills are a major anthropogenic source of the greenhouse gas methane (CH_4). However, much of the CH_4 produced during the anaerobic degradation of organic waste is consumed by methanotrophic micro organisms during passage through the landfill-cover soil. On a section of a closed landfill near Liestal, Switzerland, we performed experiments to compare CH_4 fluxes obtained by different methods at or above the cover-soil surface with below-ground fluxes, and to link methanotrophic activity to estimates of CH_4 ingress (loading) from the waste body at selected locations. Fluxes of CH_4 into or out of the cover soil were quantified by eddy-covariance and static flux-chamber measurements. In addition, CH_4 concentrations at the soil surface were monitored using a field-portable FID detector. Near-surface CH_4 fluxes and CH_4 loading were estimated from soil-gas concentration profiles in conjunction with radon measurements, and gas push-pull tests (GPPTs) were performed to quantify rates of microbial CH_4 oxidation. Eddy-covariance measurements yielded by far the largest and probably most representative estimates of overall CH_4 emissions from the test section (daily mean up to ～91,500 μmol m~(-2)d~(-1)), whereas flux-chamber measurements and CH_4 concentration profiles indicated that at the majority of locations the cover soil was a net sink for atmospheric CH_4 (uptake up to -380 μxnol m~(-2)d~(-1)) during the experimental period. Methane concentration profiles also indicated strong variability in CH_4 loading over short distances in the cover soil, while potential methanotrophic activity derived from GPPTs was high (V_(max)~ 13 mmol L~(-1)(soil air) h~(-1)) at a location with substantial CH_4 loading. Our results provide a basis to assess spatial and temporal variability of CH_4 dynamics in the complex terrain of a landfill-cover soil.