Model comparisons of methane oxidation across a management gradient: Wetlands, rice production systems, and landfill

Abstract

Abstract. Through model experiments we quantitatively examined fractional methane oxidation and net methane emissions using three model systems which encompass a management gradient from pristine (wetlands) to managed (rice production) to highly engineered (landfills). Fractional methane oxidation is rarely determined in situ; thus our goal was to cross-compare modeling results and major drivers to field and laboratory data for this important parameter in both pristine and managed systems. In the models, management factors are typically introduced as combinations of theoretical relationships, empirical functions, or scaling factors which drive net emissions through forcing of water table variations, availability of degradable organic carbon substrates, input and cycling of major nutrients, variability in plant communities, physical properties for gaseous transport, and indigenous capaci .ty of soils for methane oxidation. The net methane emission and fractional oxidation vary by orders of magnitude within and among the three model systems, yet each model was quite consistent in its predictive ability. This study lays the groundwork for a more unified, modular approach to modeling methane emissions from soil sources where both natural (climatic and ecological) and anthropogenic factors are important drivers. BackgroundMethane is a radiatively important trace gas whose current atmospheric mixing ratio is 1.8 ppmv,--2.5 times greater than it is important to establish which factors control changes in emissions for specific sources. This can best be done through the application of models which have been validated at appropriate scales for discrete sets of field observations. For all methanogenic-methanotrophic systems, models rely on a mass balance to describe net methane emissions to the atmosphere as a function of (1) methane production rates, (2) methane transport rates through soil, water (ebullition), and plant systems, and (3) processes which reduce the bulk methane available for transport (methanotrophic oxidation and landfill methane recovery). Of particular importance is the role of methanotrophic methane oxidation, which is capable of reducing net emissions to the atmosphere in all terrestrial settings. it is thus necessary to model the opposing rates of methanogenesis and methanotrophy, linked through soil transport processes, to determine the net methane emission to the atmosphere ( Figure 1). In extreme circumstances, methane oxidation capacities in soils can exceed the rate of methane transport from deeper methanogenic zones, resulting in oxidation of atmospheric methane [Yavitt et al., 1988; Bognet et al., 1997a].In this paper, we focus on three field-validated models for net methane emissions from wetlands, rice production, and landfills: (1) wetland model [Walter et al

A process-based inventory model for landfill CH4emissions inclusive of seasonal soil microclimate and CH4oxidation

“…The microclimate data are then utilized to estimate the rate of microbial CH 4 oxidation based on the empirical relationship with temperature and soil moisture [ Spokas and Bogner , 2011]. However, even though the in situ oxidation rate (g CH 4 m −2 d −1 ) would be the preferred measure for oxidation within a particular soil cover in a particular climate, it is not currently possible to quantify this oxidation rate in the field; instead, one must rely on numerical modeling coupled to laboratory studies [ Bogner et al , 2000].…”

“…Many components have both default settings as well as settings which can be customized by the user based on field measurements or site management practices. Such site‐specific practices including various cover materials and engineered gas recovery are extremely important for landfill settings which, compared to other CH 4 ‐emitting settings such as wetlands or rice production systems, represent a highly managed endpoint [ Bogner et al , 2000].…”

Physical Controls on Methane Ebullition from Reservoirs and Lakes

“…Methane generation is strongly temperature dependent, and temperate-latitude environments show much greater seasonal variation in methane flux than tropical environments (e.g., Walter and Heimann, 2000). In natural and man-made wetlands, methane flux can also be strongly dependent on depth of the water table (Bogner et al, 2000).…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…Because plants efficiently evacuate CH 4 to the atmosphere by passive diffusion or mass flow through stems (Chanton and Dacey, 1991), they improve CH 4 oxidation efficiency by decreasing ebullition (Bosse and Frenzel, 1998;Grunfeld and Brix, 1999). Understanding the proportion of CH 4 efflux that occurs by these three pathways is essential for modeling the response of natural wetlands, rice paddies and landfills to management or climate change (Bogner et al, 2000).…”