Methane emissions, groundwater levels and redox potentials of common wetland soils in a temperate-humid climate

Typical groundwater soils in a temperate-humid climate were investigated for the relationship between methane emissions and dynamic (groundwater level, redox status) as well as static soil properties over 2 years (July 1996 to July 1998, weekly probing, static chamber). High unit area emissions, like annual (5-73 g CH4 m(-2) yr(-1)) or mean daily fluxes (15-244 mg CH4 m(-2) d(-1)) were observed at the wetter sites. Oxidation seemed to be the controlling subscale process for the emissions observed: Time with Eh above -75mV in the upper 20 cm was inversely correlated to net CH4 fluxes (nonlinear). Two factors, namely groundwater level and the quality of soil organic matter (SOM), built a factor hierarchy to control methane emission. Thereby SOM is strongly influenced by the land use practices, for example, erosional and depositional processes in a catchment. Soil morphology corresponded to static (e.g., Mn-d, Fe-d) and dynamic soil properties like groundwater level or redox potentials. Because the linkage to Eh regional or global scale methane emissions may be estimated by coupling unit area emissions to soil maps based on soil morphology (e.g., soil taxonomy). Calculations of our own results exemplified (1) the significance of a representative set of unit areas for each climatic zone and (2) the potential importance of the temperate climatic zone for global methane budget.