FINE SEDIMENTS IN THE OOSTERSCHELDE TIDAL BASIN BEFORE AND AFTER PARTIAL CLOSURE

Changes in the budget of fine sediments in the Oosterschelde have been measured. These are related to the partial closure of the tidal basin . Before the engineering works, soil texture of most of the basin was sandy. After the works, unconsolidated fine sediments occurred at seve ral locations throughout the Oosterschelde, mainly in the deeper parts of channels and on musselbeds. Fine sediments accumulate due to the r eduction in current velocities. Most of the fine sediment comes from t he North Sea; internal sources of fine sediments (primary production a nd erosion of intertidal flats) are of minor importance. Due to the wo rks, the direction of net transport of fine sediments has changed from an export (before the works) into an import. A qualitative discussion of the underlying processes is presented. The changes in the budget o f fine sediments have both positive and negative ecological consequenc es. Muddy deposits on dike slopes have reduced hard bottom macrozooben thos. The reduced nutrients input due to reduced fresh water input has not resulted in a reduced primary production because it is counter-ba lanced by a decrease in turbidity.