TRANSPORT AND TRANSFORMATION OF TRACE-METALS IN THE SCHELDT ESTUARY

Water samples collected along the Scheldt estuary during several cruis es were analysed for fundamental physico-chemical parameters and for d issolved and particulate trace metals (Cd, Co, Cr, Cu, Mn, Ni, Ph and Zn). Mean suspended matter concentration and upstream dissolved concen trations of Ni, Cr and Mn are increasing with river discharge, suggest ing a resuspension of fluid mud and release of dissolved elements from interstitial waters. Dissolved and particulate Ni and Cr behave conse rvatively during estuarine mixing, while Mn is removed from the dissol ved phase and Cd, Cu and Zn are on the contrary mobilized. The distrib ution coefficients, K-D's, show at low salinities the following sequen ce Cd > Cu > Zn > Ni. The K-D's of Cd, Cu and Zn are well correlated w ith dissolved oxygen content suggesting a redissolution of sulphide pr oduced in the anoxic part of the estuary. The analysis of suspended ma tter in the upper Scheldt confirms the high contamination of this estu ary for Cd, Cr, Cu, Pb and Zn. The long residence time of the water in the estuary, due to its small river discharge and large tidal influen ce and the important variations of the river input make it difficult t o estimate metal fluxes to the North Sea, without the use of an elabor ated coupled hydrodynamical/biogeochemical model. (C) 1997 Elsevier Sc ience B.V.