Description Waddenzee and Zeeland delta
Introduction
The Waddenzee (Wadden Sea) and the Zeeland delta are the two large areas in the Netherlands in which tidal influence is very visible. Tidal areas, by nature very dynamic, are where alternating processes of erosion and accretion create new pioneer situations.
Many plant and animal species are adapted to tidal environments and can cope with their habitat being submerged by the incoming tide every day. These species are largely restricted to tidal zones. Almost all the tidal areas in the Netherlands are designated nature reserves.
The variation in duration of submergence, currents and salinity produces a great range of ecotopes in the tidal area. However, the quality and area of many of these ecotopes (including saltmarshes and mussel beds) are currently at risk because of human interventions. Some ecotopes have disappeared, such as the transitional zones between saltmarshes and marsh.
Saltmarshes are the higher-lying vegetated parts of the tidal area. Many of their characteristic plant species rarely occur in other habitats. They are important nesting areas for ducks, waders and sea birds like gulls and terns, and serve as high tide roosts for birds that forage on the mudflats.
Tidal flats are unvegetated. Mudflats are extensions of the mainland (extending from dikes or saltmarshes). They contain much fine sediment (silt). Sand flats are separated from the land by tidal channels, and because the currents are faster, they are sandier. Tidal flats have an important function as spawning and nursery areas for fish. They are also the habitat of bottom-dwellers such as lugworms, cockles and mussels and are important foraging areas for birds.
Zeeland delta, Waddenzee and dammed inlets
The damming of inlets, particularly the Zuiderzee, Haringvliet and Grevelingen, has had huge repercussions for the Waddenzee and Zeeland delta. It has removed tidal influence and has resulted in the water behind the dams becoming less saline. The Grevelingen is still classified as a tidal area because of its salinity, but in other areas, particularly the Oosterschelde, tidal influence has diminished. The damming of inlets has reduced the area of saltmarsh in the Zeeland delta and also the area of shallow flats that are important for birds. Ranker vegetation is encroaching in the saltmarsh, as a result of vegetation succession.
Various human interventions have caused much of the natural dynamics of the Zeeland delta to disappear, with the result that pioneer situations are less common. As a result, pioneer species like the Kentish plover and little tern are endangered.
The beds of eelgrass have all but disappeared from the Zeeland delta and Waddenzee, and with them an entire ecosystem has been lost.
Some species have profited from the changes in the Oosterschelde that occurred after the storm surge barriers were constructed. They include the lobster, which likes the increased salinity, reduced currents and clearer water, and the sea squirt. And in the Oosterschelde certain exotics have greatly increased in number.
