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The German Wadden Sea

Les noms des biens figurent dans la langue dans laquelle les Etats parties les ont soumis.

Allemagne (Europe et Amérique du nord)

Date de soumission : 20/09/1999
Critères: (vii)(viii)(ix)(x)
Catégorie : Naturel
Soumission préparée par :
NationalparkverwaltungNiedersächsisches Wattenmeer
Etat, province ou région :

Federal states of Schleswig-Holstein, Hamburg and Niedersachsen


Ref.: 1357

Description

The coastline of the south-eastern North Sea is formed by a large intertidal transition zone, the Wadden Sea. With a length of about 450 km and an expanse of up to 30 km the Wadden Sea is the largest coherent tidal wetland in the world with all components characteristic for a gently sloping down soft bottom coast with a medium tidal range. As a postglacial formation - just about 10 000 years old - it is a young and highly dynamic ecosystem, still depending and constantly reacting on the forces of wind and waves and a changing sea level. Sand and, where the conditions for sedimentation it allows, mud are the natural soil components. With about 7300 km² the German part covers more than 60 % of the Trilateral Wadden Sea (The Netherlands, Germany, Denmark).

The Wadden Sea ecosystem consists of different subsystems which are interconnected: intertidal sand and mudflats, subtidal gullies and channels, barrier islands and salt marshes. Large bays and estuaries are included. In a typical order sandbanks or barrier islands with beaches, dunes and salt marshes arise from the deeper offshore zone of the North Sea. Landward, behind the barrier islands the landscape is formed by intertidal flats and gullies and at the mainland coast in many parts salt marshes exist in front of the dikes which today protect the marshland along nearly the whole mainland coast of the Wadden Sea. These salt marshes are relics of a belt of marine -, brackish -, and freshwater marshes which formed the transition between the sea and the land in ancient times before the construction of dikes which started about 1 000 years ago.

As a transboundary ecosystem the Wadden Sea is highly productive. Plankton from the coastal North Sea transported to the Wadden Sea by the tides twice a day together with the high primary production on the tidal flats, mainly from benthic diatoms, are the basis of the high secondary production by benthic animals like worms, molluscs or crayfish. These animals are the food source of breeding and migrating birds as well as for a number of fish species which permanently live in the Wadden Sea. Other fish species need the area as main nursery ground and spend the first one or two years of their lifetime in the Wadden Sea before they migrate to the open North Sea.

For birds on the East Atlantic Flyway the function of the Wadden Sea as a main staging area needed for refuelling their fat reserves is indispensable for their migration from the breeding grounds in the arctic tundra of northeast Canada, Greenland, Scandinavia and North Siberia to the wintering grounds in Europe and West - and South Africa and for their migration back to the breeding grounds. It is estimated that 10 to 12 million birds pass through the area and stay here for shorter or longer periods each year. For more than 20 bird species, the Wadden Sea is an indispensable reproduction area.

Organic matter from the coastal waters and from the rivers debouching into the southern North Sea is deposited on the tidal flats and will be decomposed. Thus, the Wadden Sea also plays an important roll in the water purification process of the North Sea. As an ecosystem widely open to the adjacent North Sea and with a permanent water exchange, many of the processes and functions proceeding in the Wadden Sea have effects on a much wider scale.

Valeur universelle exceptionnelle

Satements of authenticity and/or integrity

The Wadden Sea contains all subsystems in their natural and functional coherence in a sufficient size. The undisturbed character of large parts of the Wadden Sea, let natural morphodynamic processes the freedom to occur. Biological processes depending on, and affecting geomorphology can be found on many scale levels, from seasonal microphytobenthos mats gluing the sediment together or the large tidal flat areas formed by the bioturbation activities of lugworms up to salt marshes raising the sediment level and growing with sea level rise. Anthropogenic influences are well regulated, a set of ecotargets is internationally agreed on by the governments of the neighbouring states and monitored to safeguard the integrity.

Comparison with other similar properties

The Wadden Sea is the largest coherent tidal flat ecosystem in the temperate zone of the world. But not only the large size and the coherency are unique, the completeness of subsystems, processes and structures, morphological as well as biological, underline the outstanding position.

Many tidal flat systems of the World are closely related to rivers and their deltas (e.g. Kakadu National Park in Australia and Sundarbans mangrove forest in Bangladesh,) form the inner parts of bays or (e.g. The Wash in Great Brittan) or neighbouring quite mountainous regions (e.g. Gros Morne National Park in Canada). Beside their size, these tidal flat areas differ strongly from the Wadden Sea in a morphological and geological point of view. The tidal flat system of the Yellow Sea, partly in north east China and along the Korean West Coast has some functional similarities to the Wadden Sea, e.g. the importance for migrating birds, but differs strongly in geology, morphology and habitats. The coast is dominated by a rocky shoreline and a mountainous hinterland and islands or by estuaries and river deltas. A barrier island - tidal flat - marsh land system as in the Wadden Sea is absent. The only tidal flats system, which is to some extent comparable, is the Banc d'Arguin National Park in Mauritania. This, however, is tropical-subtropical in character, has no barrier islands and very sheltered regions.

The Wadden Sea is dominated by large intertidal flats which are exposed at low tide and display a progressively shoreward-fining grain-size gradient. It commences with sand flats in the seaward sections, followed by mixed flats and finally mud flats along the mainland shore. By contrast, the tidal flats of similar systems in other parts of the world are almost entirely occupied by eel grass meadows (e.g. the Ria Formosa in southern Portugal) or cord-grass marshes (e.g. the east coast of the U.S.A.). This fundamental difference in outward appearance produced by natural vegetation is due to a high supply of fine-grained sediments in the latter cases which has enabled the grass meadows and marshes to encroach entire sand flats by the capture and accretion of mud.

The sites to which the Wadden Sea compares most with as a coastal marine wetland are:

  • Donana (1974), but the Wadden Sea supports the largest population of migratory birds on the flyway;
  • Greater St. Lucia (1999): the Wadden Sea coast continues for about 500 km and is the longest unbroken stretch of mudflats world wide.
  • The Ria Formosa is of a much smaller size, not containing similar dune and saltmarsh systems, while there also is a lack of very silty parts.
  • The barrier systems of North/South Carolina and Georgia (US East coast) have similar geomorphological characteristics but are very different from an ecological point of view because the intertidal flats are covered with Spartina, while these in the Wadden Sea are bare or partly covered by sea grasses (Zostera sp.).
  • The barrier systems of Louisiana can not be compared because they have such a small tidal range that the majority of the sandbanks are permanently covered by the sea.

There is no similar area in northern latitudes to be found.