Methane flux in the Great Dismal Swamp

Abstract

Methane is an important component of the biogeochemical cycle of carbon with potentially critical roles in both atmospheric chemical and radiation transfer processes1–4. Limited evidence is available which suggests an increase in global tropospheric methane during the last decade5,6. To understand and assess the possibility and implications of temporal variations in atmospheric methane requires improved quantitative knowledge of methane sources and sinks. We report here methane flux measurements made over a 17-month period in the Great Dismal Swamp, Virginia. These flux measurements indicate that Great Dismal Swamp soils can act as both a source and sink for atmospheric methane. In a waterlogged condition, swamp soils are a net source of methane to the atmosphere with seasonal variations in emission rates from <0.001 to 0.02 g CH4 m−2 day−1. During drought conditions, swamp soils consume atmospheric methane at rates of <0.001 to 0.005 g CH4 m−2 day−1. While these results should not be extrapolated to all swamp soils, they illustrate the potential complexity of processes which regulate net flux of methane between wetland soils and the atmosphere.