The hydrographic basin of the Scheldt covers a heavily populated and industrialised region and drains waters extremely polluted due to uncontrolled discharges.
In this partially stratified estuary, the mixing process of fresh and salt water is responsible for an important deposition of the suspended load of the river in a restricted area corresponding to the harbour of Antwerp. This important shoaling is explained by the physico-chemical properties of the suspended matter and the hydrodynamical characteristics of the estuarine region.
The mud accumulated in the estuary contains high levels of organic matter and heavy metals, and the sedimentation process contributes markedly to the removal of pollutants from the surface water. Mass-balances of input, output in the estuary and accumulation in the sediments were estimated for various pollutants. The role of the sediments on the oxygen budget was deduced from the previous mass-balances.
Large concentrations of nutrients persist in the brackish water zone where oxygen is available and turbidity is low. As a consequence, this zone is eutrophied and diatom blooms are frequent.