How do changes of water table level affect N2O fluxes between soil and atmosphere in an acidic fen?
P 4.4 in Climate change research
The concentration of the long-lasting greenhouse gas nitrous oxide (N2O) increases by about 0.3% yr-1 in the atmosphere and reached in 2005 319 ppbv. N2O produced by microorganisms through nitrification or denitrification in soils is considered to be mainly responsible for this increase. However, N2O also can be consumed by denitrification. In this study we compared the effects of experimentally induced drying (followed by a rewetting event) and flooding on N2O fluxes of an acidic fen soil in the Fichtelgebirge. Three of six plots (each ~21m²) 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. The N2O fluxes were measured using the „closed chamber”-method in combination with a “photoacoustic infrared-analyser”. To determine the N2O concentration and the δ15N values of N2O from soil profiles, soil gas samples were taken from six different depths and were analysed via “Pre-Con-GC-IRMS coupling”. With increasing drought the fen acted temporarily as an N2O sink. The effect was reversed after rewetting. During the flooding no differences in terms of the N2O fluxes from the soil to the atmosphere could be found. Measurements of N2O concentrations and isotope signatures along soil profiles provided insight into sequences of N2O production and consumption processes, which are much more complex than simple gas exchange between soil surface and atmosphere makes belief.