Geochemical behaviour of heavy metals in a sedimentation area of the rivers Rhine and Meuse

The Biesbosch, situated in the delta of the rivers Rhine and Meuse in The Netherlands, is considered an important freshwater tidal area, although the tidal amplitude has decreased as a result of the implementation of the Delta Worles. Due to the decrease in flow rates since the closure ofthe area by sluices in 1970, the Biesbosch has developed into a semi-stagnant sedimentary basin, in which deposition of fine-grained highly contaminated calcareous sediments takes place. Dutch environmental policy aims at nature development in this area by increasing the number and area of wetlands to enlarge the intertidal area. To achieve a sustainable situation in which environmental and ecological factors are also considered, the long-term behaviour of contaminants and their ecotoxicological effects should be well recognised (Chapter 1). The behaviour and the bioavailability of heavy metals in (temporarily) waterlogged soils and sediments is strongly coupled to the variation and intensity ofredox processes. The purpose of this study was to describe the redox chemistry and mobility ofheavy metals of sediments and hydric soils in the Biesbosch, as well as their emission to the groundwater and surface water. The results of this study are also used to evaluate environmental quality criteria to assess potential metal toxicity of sediments