Quoted from: Li, Tingting, Yao Huang, Wen Zhang, and Changchun Song. "CH4MODwetland: A biogeophysical model for simulating methane emissions from natural wetlands." Ecological Modelling 221, no. 4 (2010): 666-680. https://doi.org/10.1016/j.ecolmodel.2009.05.017 

We accept the CH4MOD model's hypothesis (Huang et al., 1998a, Huang et al., 2004) that methanogenic substrates are derived from plants via root exudates and from the decomposition of organic matter. Methane production rates are determined by the availability of methanogenic substrates and by the influence of environmental factors. Plant-mediated transport is the primary mechanism of CH4 emission, and CH4 emission via ebullition is significant in the early stages of plant growth.

Compared with rice paddies, plants in wetlands are not harvested at the end of the growing season. The decomposition of plant litter supplies substrates for methanogens. On the other hand, wetland ecosystems accumulate great amounts of organic matter in a thick sod layer (Bertness, 1988, Frolking et al., 2001, Gorham et al., 2003, Zhang et al., 2008) that also becomes a source of methanogenic substrates. We pay special attention to the substrates derived from the decomposition of above- and below-ground plant litter and soil organic matter in the CH4MODwetland model. Fig. 1 shows the conceptual explanation for modeling the processes of methane production, oxidation and emission from natural wetlands.

 

Fig. 1. Conceptual explanation for modeling the processes of methane production, oxidation and emission from natural wetlands (modification to Huang et al., 1998a). The arrow lines represent mass flow or interactions between defined quantities.