Methane Emissions from Natural Wetlands in the United States: Satellite-Derived Estimation Based on Ecosystem Carbon Cycling

Abstract

Wetlands are an important natural source of methane to the atmosphere. The amounts of methane emitted from inundated ecosystems in the United States can vary greatly from area to area. Seasonal temperature, water table dynamics, and carbon content of soils are principal controlling factors. To calculate the effect of wetlands (and their potential conversion to other land uses) on global greenhouse gas emissions, information on area covered by various wetland types is needed, along with verified projections of spatial variation in net methane emissions. Both of these variables are poorly known, and estimates are largely unavailable at the country level. Nationwide satellite datasets for the coterminous United States (excluding Alaska) have been combined with ecosystem model predictions of monthly net carbon exchange with the atmosphere to produce the first detailed mapping of methane fluxes from natural wetlands on a monthly and annual basis. The Carnegie?Ames?Stanford Approach (CASA) model?s predicted mean emission flux of methane from wetlands of the continental United States totaled 5.5 Tg CH4 per year. Ranked in terms of total annual flux, the 10 states with the highest predicted emissions (not considering Alaska) are all located in the Great Lakes region and the southern coastal regions of the country.