How do changes of water table level affect CH4 fluxes between soil and atmosphere in an acidic fen?
P 4.3 in Climate change research
The greenhouse gas methane (CH4) has a GWP of 25 and reached an atmospheric concentration of 1774 ppbv in 2005. In soils CH4 is mainly produced by methanogenic bacteria (CO2 reduction and acetate fermentation), but CH4 also can be consumed by methanotrophic bacteria. The CH4 fluxes of an acidic fen soil in the Fichtelgebirge were measured during two consecutive years. In 2008 the effects of experimentally induced drying (followed by a rewetting event) on the dynamic of the CH4 fluxes were studied. As opposed to this there was a flooding experiment conducted the next year. For these experiments six plots (each ~21m²) were installed. Three of them were not manipulated and served as control. In 2008 drought was induced for the three manipulation plots by a roof construction and drainage ditches for eight weeks. In the following year the manipulation plots were flooded by an irrigation system for eighteen weeks. CH4 fluxes between soil and atmosphere were measured with a closed chamber method by analysing changes of CH4 concentrations over time by gas chromatography. To determine the CH4 concentration and the δ13C values of CH4 from soil profiles, soil gas samples were taken from six different depths and were analysed via “Pre-Con-GC-IRMS coupling”. The fen acted temporarily and localised as a slight CH4 sink. During the drought and flooding period no differences in terms of the CH4 fluxes between soil and atmosphere could be found. Measurements of CH4 concentrations and isotope signatures along soil profiles provided insight into sequences of CH4 production and consumption processes, which are much more complex than simple gas exchange between soil surface and atmosphere makes belief.