Distribution and stabilization of organic carbon in Danubian floodplain soils

Floodplain soils are assumed to act as sinks for organic carbon (OC). To date, our knowledge on OC distribution and stabilization in these soils is only weak. We investigated OC stocks at 76 sampling sites in the Danubian floodplains and conducted density fractionation of selected soil samples. The soils were found to contain huge stocks of OC. The distribution (horizontal and vertical) of OC stocks and other soil properties is highly heterogeneous and determined by sedimentation dynamics. First results of density fractionation of organic matter (OM) and aggregate stability tests indicate that soils developed under different sedimentation conditions differ in the relevance of the different OM stabilizing mechanisms. Occlusion of OM within aggregates is more important in soils developed under dynamic sedimentation conditions, whereas formation of organo6mineral complexes is determining OM stabilization in soils developed under static sedimentation conditions. Testing aggregate stability is crucial to assess OM stabilization.