Wadden Sea region
The wadden region begins near Den Helder in the Netherlands and ends at the peninsula Skallingen in Denmark. The area consists of around 30% of the Dutch, 20% of the Danish and 60% of the German coasts. In total, the region has around fifty islands and large, high-lying sandbanks. There is some debate as to whether or not the impoldered sea clay areas and the former island of Wieringen should also be counted within the wadden region.
The size of the islands in the region is determined by the strength of the tide. In the Netherlands, the difference between high and low tide is less than in Germany and Denmark. The force of the flood wave is also less here, so that the Dutch islands suffer less erosion than the German and Danish islands. That is evident when looking at the size of the islands. Even the sea channels between the islands grow larger the more one moves in an easterly direction through the wadden region.
This means that the Wadden Islands become smaller from west to east. In the German Bight, there are hardly any islands at all. More water needs to flow in and out of the region behind the sea channels per tide than in the west, resulting in larger and wider sea channels and smaller islands. Almost all of the islands are formed from sand from the North Sea floor, which has been thrown onto sandbanks due to a southern movement of the coast long ago. Afterwards, dunes formed and were held down by plant growth. Exceptions are Texel (with a core dating back to the Pleistocene) and Sylt (dating back to the Tertiary).
The formation of the Wadden Sea
Around 7000 years before Christ, a tidal area lay between the Doggersbank and the present coast. When sea level rose, this region shifted south. In 5000 B.C., the coast lay only several kilometers west of the present coast. Sea-level rise declined since 4000 B.C., while the sediment supply remained high. Therefore, the channels were filled for the most part with deposited mud and large peat marshes formed behind the closed row of dunes. Tidal flats were only in the northeast.
The peat bogs no longer expanded since Roman Times and the banks were washed away by the rising sea level. Most of the peat washed away during the Middle Ages and the Wadden Sea filled up with water.
Further formation of the wadden region in the Netherlands
In the Netherlands, the Marsdiep and the Zuiderzee formed in the Middle Ages. Halfway through the Middle Ages, people began to build dikes, which put a halt to the Wadden Sea shifting landwards. The Lauwerszee and the Dollard were formed during large storm floods, but the Wadden Sea could not expand. In fact after the Middle Ages, the Wadden Sea grew smaller due to impoldering. Most of the marshes along the edges of the mainland were reclaimed. The Zuiderzee was dammed in 1932 follwed by the Lauwerszee in 1969. Since that time, the coastline has hardly changed, but the natural processes of the wandering sandbanks and channels still continues.
Characteristics of the Wadden Sea
With high tide, the water enters through the large channels and floods the flats. During low tide, the water drains away through the creeks back through the large channels. The flats are sandier at places where there is a lot of current or wave action, such as by the sea channels. The finer particles of mud settle at places where it is tranquil during the high tide period. The flood mountain flows along the sea channels of the Wadden Sea from southwest to northeast, arriving earlier on the west side of the island than on the east side. The flood waves of the western and eastern sea channels meet on the east side of the island. This meeting point is called 'slack water'.
The tide: rhythm and nourishment for the tidal flats
The tide is the most distinguishing process in the Wadden Sea region. Twice a day, when the tide rises, the area receives a new supply of nutrients. These nutrients form the foundation for an intricate food web. Different species of algae, seaweed, plants, worms (rag-worms and lugworms), molluscs (for instance mussels, cockles and Baltic tellin) and crustaceans (prawns, hermit crabs and barnacles) ingest the nutrients. These plants and animals are consumed by other animals. Crabs, starfish, fish and bird are just a few of the animals which prey upon these species. The seals, in turn, prey upon the fish, which is mainly flatfish in the Wadden Sea. Young seals will also eat shrimp.
Beside nutrients, the rising tides also transport pollution into the region. Heavy metals, PAHs, PCBs and other organic chlorinated compounds are the most prominent pollutants. However, oil and suspended refuse also have tremendous effects on the ecosystem. Every once in awhile, a different material suddenly arrives in the area in relatively large amounts, usually indicating that an accident has occurred on board a ship. Containers carrying poisonous substances fall overboard. The small bags of herbicides which fell off a ship in January 1994 are a vivid example. Fortunately for the Wadden Sea, only a few of these bags reached the area.
Usually, rich feeding grounds also have a high bio-diversity. The wadden region is a very rich feeding ground. However, the number of species which are found in the area is relatively low. This is due to the fact that the wadden region is a very dynamic ecosystem. When sandbanks are exposed to the air, many changes take place. The temperature fluctuates and the oxygen level is continually changing. Even the salinity of the water varies due to the fluctuating freshwater input. The bottom of the wadden region is also dynamic. Erosion and sedimentation are constantly occurring.
Although one often speaks of the 'tidal region', several types of landscapes can be categorized. Within the area, brackish water and coastal areas can be distinguished from the tidal flats, marshes, beaches, dunes and cultivated land. Every area has its own characteristic flora and fauna.
Man and the tidal flats
The influence of man in the wadden region manifests itself at various levels. Fishing is popular, especially for mussels, cockles and shrimps. Beside the professional fishermen, there are many sport fishermen who go fishing on the flats for a day. The wadden area also attracts nature lovers and many aquatic sport and beach enthusiasts. Furthermore, gas is exploited on Ameland and on the mud flats, and sand is extracted in some special areas. The Defence Department performs military exercises in the Lauwersmeer area, on the Vliehors and on the Razende Bol. Den Helder, Harlingen, Delfzijl and the Ems harbour are important areas for many industrial activities, which means busy shipping routes cutting through the region.
Source: de Vleet, Ecomare
