Eight sediment cores were taken from Lake Ketelmeer, a sedimentation area of the Rhine River, located in the central part of The Netherlands. Priority pollutants (eight metals, six planar and mono‐ortho polychlorinated biphenyls, seven polychlorinated dibenzo‐p‐dioxins, 10 polychlo‐rinated dibenzofurans, and eight polycyclic aromatic hydrocarbons) were determined in all or in a selected number of cores. Present‐day and historical levels of pollutants since the late 1930s were established through the use of radionuclide time tracers (137Cs, 134Cs) and area‐specific geological time markers. Postdepositional redistribution of pollutants and possible transformations were evaluated by analyzing sediment top‐layer samples that were taken in 1972. Disappearance in the anaerobic sediment was observed for several chlorinated biphenyls, dioxins, and furans, Disappearance of the chlorinated compounds may be caused by microbial dechlorination reactions in the anaerobic lake sediment. For the persistent metals and polycyclic aromatic hydrocarbons, as well as for the somewhat changed concentrations of chlorinated aromatics, trends in the concentration profiles during the last five decades are described. Rather low concentrations of almost all studied chlorinated compounds were observed in the early 1940s. These low levels were in contrast to the metal and PAH concentrations, which were already high in the late 1930s and were lowered during the second world war. For all studied compounds, maximum concentrations were found between 1955 and 1975. Cadmium and nickel levels remained high until 1980. The highly toxic 2,3,7,8‐tetrachlo‐rodibenzo‐p‐dioxin reached concentrations up to 400 ng/kg in the mid‐1960s. Recently deposited sediments showed lower pollutant levels. The levels of lead, arsenic, and all studied PAHs were the lowest observed in the past five decades.

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The contribution of erosion of bed sediment to the load of metals leaving Lake Ketelmeer, a shallow lake in the Netherlands fed by the IJ ssel branch of the River Rhine, is reported . Transport of suspended matter and associated trace metals was measured using both centrifuges and sediment traps at several locations in the lake . Mass balances of suspended matter and heavy metals were calculated using data from these field measurements .Metal/scandium-ratios were used to identify the source of the suspended matter in the lake . Since the bed sediment is more polluted than the suspended sediment entering the lake, higher metal/scandiumratios were found for bottom sediment in the lake compared with those for suspended matter entering the lake from the River IJssel . Using the metal/scadium-ratio in suspended matter from the lake, it was calculated that bottom sediments made up 43% of the suspended matter leaving the lake . This implies an erosion flux of bottom sediment of 16 g M-2 d -1 . For cadmium, mercury, chromium and zinc, this erosion process accounts for more than 50% of the pollutant load leaving Lake Ketelmeer and entering Lake IJsselmeer .

Suspended matter and sediments in the catchment areas of European rivers are often highly polluted. A forecast of sediment quality in relation to discharges is of importance in formulating policy pertaining to emission reduction and sediment sanitation. The model Horizon has been developed to predict the sediment quality in the long term under various emission reducing scenarios. The model schematics consist of a description of the Rhine, the Meuse and the large lakes and basins in The Netherlands. The model calculates the concentration of eight inorganic and five organic micro pollutants in surface water, suspended matter and the sediment under the influence of processes such as sorption, evaporation, degradation, sedimentation, resuspension and burial. The principles underlying the model, the modelled pollutants, the schematics and the modelled physical/chemical processes are briefly discussed. The model input, calibration, validation and model errors follow. The predictions show that emission reductions more far reaching than the Rhine Action Programme (RAP) are needed to meet the Quality Objective 2000,set out in the Dutch National Policy Document on Water Management.