Stability of soil organic matter in two northeastern German fen soils: the influence of site and soil development

Peatland soils play an important role in the global carbon (C) cycle due to their high organic carbon content. Lowering of the water table e.g. for agricultural use accelerates aerobic secondary peat decomposition and processes of earthification. Peatlands change from C sinks to C sources. We characterized soil organic matter (SOM) with special attention to human impact through drainage. Our aim was to gain knowledge of SOM quality and soil-forming processes in drained fen soils in northeastern Germany. Through techniques of representative landscape analysis, we identified two typical and representative sampling sites in different stages of land use, representing the most important hydrogenetic mire types in northeastern Germany. We adapted chemical fractionation procedures which include hot water extraction (C-hwe and N-hwe) for determination of the labile fraction. Furthermore, a stepwise acid hydrolysis procedure was performed to measure the chemical recalcitrant part of SOM as it is more resistant to biodegradability. Total organic C decreased with increasing human impact and intensity of drainage. Conversely, C-hwe and N-hwe concentrations increased with increasing drainage and human impact. In contrast, the more recalcitrant fractions increased with soil depth. Generally, there is a lack of existing data about SOM quality and the factors controlling its stability and decomposition in fen soils. For northeastern German fen soils, the data are even more inadequate. Influence of drainage seems to overlap natural influences of site on SOM quality. The used extraction scheme was suitable for the chemical fractionation of SOM into labile and more recalcitrant parts.