Theoretical consideration of methane emission from sediments

A stationary theory of gas emission from sedimentary (active) layers of wetlands is developed. The theory takes into account methane generation in a sedimentary layer (W-1) and its depth dependence, (W-1 (z)), the solubility, determined by Henry's constant (K-1), and the mobility of methane molecules set by the methane diffusion coefficient (D-1). The exponential dependence of methane generation rate decay with depth is considered in more detail. The penetration of atmospheric nitrogen into the active layer is also taken into consideration. It is shown that the value of diffusion methane flux from sedimentary layers is proportional to rootK(1)D(1)P(0)W(10) where P-0 characterizes the atmospheric pressure and W-10 characterizes the maximum generation rate. Coefficients relating the diffusion methane flux to the rootK(1)D(1)P(0)W(10) value are calculated for the different depth dependencies of methane generation rate. The values of these coefficients are not much different from unity for most real cases. (C) 2002 Elsevier Science Ltd. All rights reserved.