Matthews and Fung 1987
, and I. Fung, 1987: Methane emissions from natural wetlands: Global distribution, area, and environmental characteristics of sources. Global Biogeochem. Cycles, 1, 61-86, doi:10.1029/GB001i001p00061.
A global data base of wetlands at 1° resolution has been developed from the integration of three independent global, digital sources: (1) vegetation, (2) soil properties and (3) fractional inundation in each 1° cell. The integration yielded a global distribution of wetland sites identifies with in situ ecological and environmental characteristics. The wetland sites have been classed into five major wetland groups on the basis of environmental characteristics governing methane emissions. The global wetland area derived in this study is ~5.3×1012 m2, approximately twice the wetland area previously used in methane-emission studies. Methane emission was calculated using methane fluxes for the major wetland groups, and simple assumptions about the duration of the methane-production season. The annual methane emission from wetlands is ~110 Tg, well within the range of previous estimates (11-300 Tg). Tropical/subtropical peat-poor swamps from 20°N to 30°S account from ~30% of the global wetland area and ~25% of the total methane emission. About 60% of the total emission comes from peat-rich bogs concentrated from 50-60°N, suggesting that the highly seasonal emission from these ecosystems is the major contributor to the large annual oscillations observed in atmospheric methane concentrations at these latitudes.