The aims of the study are twofold: firstly to obtain a better understanding of the biogeochemical processes influencing the immobilization and/or remobilization of metals in the sedimentary phase of the Scheldt estuary; secondly to estimate possible fluxes of metals from the sediment to the aqueous phase of the estuary. Six sites in the Scheldt estuary, chosen as a function of bottom characteristics and salinity gradient, are studied seasonally. Earlier research programmes about the behaviour of trace metals in the Scheldt improved our knowledge in that field, but let still many unknowns. One of them is what will be the forthcoming dissolved metal contents in the Scheldt. Firstly, it is very uncertain how the large amounts of metals, stored in the sediment, will react in future. Secondly, the dissolved metal concentrations are depending on a (large) number of waterquality variables such as pH, O2, Cl, DOC, turbidity etc....Through the influence of the planned sanitation of BOD discharges, the waterquality variables will be (stongly) modified in future. This leads to the proposed research on the buffering activity of the metals stored in the aquatic sediments, and the Inf'luence of the planned BOD reduction on the metal concentrations. The former Institute for Nature Conservation was a partner in this project