Stuart Nattrass

Methane is an important greenhouse gas, contributing 22% to the increased radiative forcing over 150 years, and emissions from wetlands are key to its global dynamics. A general model of methane dynamics is presented that emphasizes the impact of external climate factors on methane production and oxidation. The model consists of two uncoupled bacterial populations, each following a logistic growth pattern, and a third differential equation, dependent on these two populations, that represents the concentration of stored methane in wetland soils. This is related to methane emissions into the atmosphere. Several simplified models are also presented to demonstrate the development of the model from the basic processes occurring in the soil. Analysis of the model shows a stable equilibrium point for the methane concentration. This equilibrium is subject to short-term forcing by climate, specifically changes in temperature and water table depth. Parameters for this model are then fitted to real data taken from a wetland site in Teesdale, and this forcing is shown to account for much of the observed variation in methane emissions. An attempt to extend this model to longer time scales is made, by considering the average climate. This extension is shown to be unsuccessful through considering Taylor's theorem and its implications for the model. Finally, a simplistic approximation to climate change is made, and the consequences of these changes on methane emissions predicted by the model are presented. These consequences are found to include negative feedback, where the change in climate eventually results in lower emissions of methane.