DISTRIBUTION OF TRACE-METALS IN SUSPENDED MATTER OF THE SCHELDT ESTUARY

The distribution of trace metals (Ni, Co, Cr, Zn, Cu, Cd, Pb, Mn) in s uspended matter and sediments collected in the Scheldt estuary is inve stigated as a function of grain size, Al and particulate organic carbo n (POC) content. Normalized trace-metal content with respect to Al all ows characterization of the origin of the solids and evaluation of the ir degree of contamination. The suspended matter exhibits strong chang es in chemical composition in the tidal zone, indicating mixing of hea vily contaminated particles of continental origin with less contaminat ed marine particles. Flood events strongly influence the trace-metal c ontent of the suspended matter by inducing resuspension processes and intensive transfer of solid material from the river system to the sea. The evolution of the composition of the particles in the mixing zone of the estuary indicates that the trace elements do not behave conserv atively and that they are also affected by the changing physico-chemic al conditions (salinity, pH, redox) observed in the Scheldt. In order to gain a better understanding of the origin and behaviour of the part iculate trace elements in the estuary, a mixing model of suspended mat ter based on the conservative property of Al is proposed, which enable s quantification of the proportion of marine vs. continental solids an d to detect non-conservative behaviour of trace elements.