Einfluss von Überflutungsereignissen auf Redoxspannung und Zusammensetzung der Bodenlösung von Auenböden

Regarding the influence of flooding on the redox potential of alluvial soils and the composition of the soil solution, it could be demonstrated that the manifold abiotic effects substantially impede a precise prediction. The small-scale spatial pattern of highly variable soil characteristics, (e. g. content of organic matter, porosity, relative elevation, position) and the climatic and hydrological imponderabilities, as well, do not allow an extrapolation on large scales, but permit a prognosis for well-defined locations. The present study has shown that it is not possible to deduce the redox potential only from the water-saturation-level of a layer. In order to avoid a decrease of the redox potential at high water contents, a minimum content of redox sensitive substances is necessary in the soil. Even in layers with a high content of reactive organic substances, the reaction velocity of breakdown of reactive organic matter considerably depends on the soil temperature. The great variability of the redox potentials within the soil layers is a characteristic feature for the studied alluvial soils. Evaluating potential changes of the redox potential and a significant change in the composition of the soil solution e. g. as a result of a relocation of the dike, it should be taken into consideration that a periodical flooding of alluvial soils is an essential element of an intact river floodplain ecosystem. Therefore, the redox processes in the soils have to be assigned to the intended river floodplain dynamics. Negative effects, such as an increasing phosphorus load, which results from retried water logging of areas previously drained by ditch systems with balanced water supply, are tolerable effects.