Global carbon exchange and methane emissions from natural wetlands: Application of a process‐based model

Wetlands are one of the most important sources of atmospheric methane (CH 4 ), but the strength of this source is still highly uncertain. To improve estimates of CH 4 emission at the regional and global scales and predict future variation requires a process-based model integrating the controls of climatic and edaphic factors and complex biological processes over CH 4 flux rates. This study used a methane emission model based on the hypothesis that plant primary production and soil organic matter decomposition act to control the supply of substrate needed by methanogens ; the rate of substrate supply and environmental factors, in turn, control the rate of CH 4 production, and the balance between CH 4 production and methanotrophic oxidation determines the rate of CH 4 emission into the atmosphere. Coupled to data sets for climate, vegetation, soil, and wetland distribution, the model was used to calculate spatial and seasonal distributions of CH 4 emissions at a resolution of 1° latitude x 1° longitude. The calculated net primary production (NPP) of wetlands ranged from 45 g C m -2 yr -1 for northern bogs to 820 g C m -2 yr -1 for tropical swamps. CH 4 emission rates from individual gridcells ranged from 0.0 to 661 mg CH 4 m -2 d -1 , with a mean of 40 mg CH 4 m -2 d -1 for northern wetland, 150 mg CH 4 m -2 d -1 for temperate wetland, and 199 mg CH 4 m -2 d -1 for tropical wetland. Total CH 4 emission was 92 Tg yr -1 . Sensitivity analysis showed that the response of CH 4 emission to climate change depends upon the combined effects of soil carbon storage, rate of decomposition, soil moisture and activity of methanogens.