THE OOSTERSCHELDE ESTUARY, A CASE-STUDY OF A CHANGING ECOSYSTEM - AN INTRODUCTION

During the period 1980-1990 long-term physical, chemical and ecologica l studies were carried out, to study the changes induced by the buildi ng of a storm-surge barrier in the mouth of the Oosterschelde estuary and two large auxiliary compartment dams in the rear ends of the estua ry. The storm-surge barrier was constructed in the mouth of Oostersche lde estuary (SW Netherlands) during the period 1979-1986. The barrier allows the tides to enter the estuary freely, and, on the other hand, the barrier guarantees safety for the human population and their prope rties when a stormflood threatens the area. Oosterschelde estuary is i solated from the river input, the rear ends of the ecosystem were sepa rated from the estuary by sea-walls and the strongly decreased tidal e xchange with the North Sea induced sheltered circumstances. The Ooster schelde changed from a turbid estuary into a tidal bay, and yet primar y production responses appear to be robust and resilient, and the biol ogical communities showed only quantitative shifts from the dominance of specific species assemblages to other assemblages. In many cases pr edicted changes in the structure of the biological communities could n ot be verified owing to the large natural variability mainly caused by physical factors (e.g. temperature).