This thesis addresses the geochemical aspects of AVS (Acid Volatile Sulfide) and SEM (Simultaneously Extracted Metals) in floodplain lake sediment, its spatial distribution in floodplain lakes and dynamics over time, the link with effects on single species (bioassays), as well as the impact of excess SEM on the in situ benthic community, in one consistent methodological approach. Using this approach the SEM-AVS concept is thus evaluated on various levels from geochemical through ecotoxicology towards ecology. Furthermore, the aspect of spatial and temporal variability is addressed. For the case studies in the field, several floodplain lakes located in the floodplain area Afferdensche and Deestsche Waarden along the Waal branche of the Rhine were selected. Occasionally, this selection was extended towards other floodplain lakes along the Rhine branches. The main goal of this research is a) to explore the actual risks of trace metals to benthic communities in floodplain systems and b) to evaluate the SEM-AVS concept as a tool to assess bioavailable concentrations of trace metals in dynamic floodplain sediment