Simulative analysis of vegetation on CH4 emission from landfill cover soils: Combined effects of root-water uptake, root radial oxygen loss, and plant-mediated CH4 transport

Abstract

Vegetation on landfill cover soil plays a complicated role in methane (CH4) transport, oxidation, and emissions. This study proposes an improved theoretical model that couples the effects of root-water uptake, radial oxygen loss (ROL), plant-mediated CH4 transport, and microbial CH4 oxidation for capturing water-gas-heat flow and CH4 oxidation in landfill unsaturated cover soil. Parametric studies were conducted to investigate the combined effect of transpiration rate (Tp), ROL rate, root architecture, and root depth on CH4 oxidation. The simulation results indicate that the effect of root-water uptake on CH4 oxidation depends on the initial water content. When the water content was <15%, 10% more CH4 was emitted to the atmosphere from vegetation-covered areas than from bare areas. More than 23% CH4 was oxidized when the initial water content was 35% owing to improved aeration. Plants with a parabolic root architecture are more efficient in CH4 oxidation than other root architectures under wet conditions. However, under dry conditions, roots with a parabolic architecture could release more CH4 to the atmosphere. The CH4 oxidation was significantly enhanced when the ROL rate (oxygen released per unit root surface area per unit time) was higher than 1.0 × 10−4 mol/m2·s. Plants are the dominant pathway for CH4 release, and more than 31% of input CH4 was emitted to the atmosphere from plants directly when the initial water content was 35%. This implies that high water-demand plants with parabolic root architectures in dry climate require frequently irrigation to improve the CH4 oxidation efficiency. In wet climate, plant some species with high water-demand, high ROL capacity, and parabolic root architecture would be feasible strategies for landfill CH4 mitigation.