Hydro-ecological relations in the Delta Waters

Grevelingen. Lake Veere and Krammer-Volkerak, the area of salt marshes
Fn the South-West Netherlands has been dwished and is at the moment
no more than ca. 30% of that in 1990. If we Look at the area of higher
salt marshes thi. decline is even more dramstical. Especially these
higher salt marshes are a valuable and rare type 05 ecosystem, with d
number of endangered animal and plant species. For this reason kigh
priority must be given to conserve the remaining 5aSt marshes in the
Oosterschelde and Westerschelde. In the Oosterschelde the sediment
balance indicates that there are hardly any perspecti~es for the
development of large new salt marshes. On the other hand the largest
part of the remaining saltmarsh area is formd in the eaptern part of
the Westersdtelde (ca. 80%). Enviromnent is under great pressure here
hecause of chemical pollutiw of water and soil (Bijlsma and Kuipers.
1989) and the predicted eroaion as a consequence of the proposed
enlargwnt of the shipway to Antwerp.
However, there are also a lot Of positive effects as a consequence of
the works. In the first years after the r~mplation of the dams, in the
new habitats impostant populations of breeding birds have been
established, including several rare species. Many of these were
formerly quite connnoo, in our country on shores, in marshes or
extensively used agricultural Land. They have declined iII recent years
because of drabage or more inteneive hu)aan use of their original
habitats. For. some species of terns and waders (e.g. Sandwich Tern.
Little fern, Kentish Plover, Avo~et) the Delta area is now one of the
wst important breeding grou&
Eurape.
in the Netherlands or even in Western
For wintering buds the situation is quite swlar. Large numbers of
herbivorous waterfowl like geese and ducks forage now on the grassland
of the former tidl flats and salt mrshcs. The West-European
population of the Barnacle Goose winters almost completely in the
Kefherlands and this species visits the grasslands along the
Haringvliet since long. However, its original habitats strongly
diminished here because of the public water works and the change of
agricultural grassland in arable fields. Thanks to a nature management.