CH4MODwetland: A biogeophysical model for simulating methane emissions from natural wetlands

Wetlands are among the most important sources of atmospheric CH4, but the size of this source remains highly uncertain. We developed a biogeophysical model called CH4MODwetland to assess CH4 emissions from natural wetlands. The model adopted the rationale of CH4MOD that simulates CH4 emission from irrigated rice paddies, and focused on the supply of methanogenic substrates in natural wetlands that differ from the supply in the rice paddy. CH4MODwetland was validated against independent field measurements of CH4 emissions from different wetland sites, including marshland in the Sanjiang Plain (northeast China), peatland in the Ruoergan Plateau (southwest China), fen in Saskatchewan (Canada) and bogs in Michigan (USA). Model validation showed that CH4MODwetland is generally capable of simulating the seasonal and interannual variations in CH4 emission from different sites, while it overestimated CH4 emissions from the bog vegetated with Carex oligosperma in Michigan for 2 out of 3 years. Further investigation by running a different model (Wetland-DNDC) showed similar outcomes for the latter case. The simulated seasonal and/or annual amounts of CH4 emissions at different sites agreed with the observed results and yielded an R2 of 0.84 (n=14). The root mean-squared error, mean deviation and model efficiency were 29.7%, −11.8% and 0.79, respectively. Sensitivity analysis of the model suggested that the standing water depth of the wetland and the air temperature could significantly affect CH4 emissions. We conclude that, in general, the CH4MODwetland model can simulate CH4 emissions from wetlands under various conditions (climate, soil and plant species). Further improvements of CH4MODwetland should focus on the enhancement of its descriptive power for key processes, as well as on its re-calibration and verification using spatiotemporal measurements across a wider domain so that it can be more applicable to various wetlands.