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Dieren en planten

Water en land

Coastal areas   Salt marshes   Biotope   

Mens en Milieu

Salt marsh (the Slufter on Texel), Ecomare

Salt marshes

Salt marshes are pieces of land directly bordering shallow tidal areas, such as the Wadden Sea; they are bare of dunes and dikes. Salt marshes only flood over with seawater during extremely high water levels. Sand and mud particles suspende in the seawater can then subside. The particles fall between the vegetation and do not easily wash away. In this way, salt marshes gradually expand and grow higher. Salt marshes are also found in the delta area.

  • Salt bath
    Sea lavender during an extremely high tide, Ecomare

    There is a big difference between low and high marshes. Low marshes are almost always inundated with water during high tide while high-lying marshes only flood during tidal storms.

    Due to the regular salt bath on the marshes, only those plants resistant to a high salinity level in the soil are able to grow. Salt marshes form an extremely rare type of nature area, containing a unique flora and fauna.

  • Salt marshes along the flats and in the Dutch delta region
    Sheep on the North-Groningen salt marsh, Ecomare
    Sheep on the North-Groningen salt marsh, Ecomare

    Distribution of the salt marshes in the tidal region and the Delta.
    In the Netherlands, salt marshes can be found in the delta region as well as in the wadden region.
    Some of the well-known salt marshes in the Netherlands are the Slufter and the Schorren on Texel, the Boschplaat on Terschelling, the Nieuwlandsreid on Ameland and the Oosterkwelder on Schiermonnikoog. Large marshes on the mainland can be found to the east of Lauwersoog, on the south side of the Dollard and to the west of Holwerd (North-Frisian outer dikes). Altogether, the surface area of the salt marshes in the wadden region in 2000 was around 6200 hectares. According to the goals of the European Water Framework Directive, this must increase to 15,000 hectares.
    Some marshes are still expanding at places, while others are eroding due to storms or a change in currents. At such places, there is a sharp changeover from bare mud flats to salt marsh, in the form of a marsh cliff a few decimeters in height. In such a cliff edge, it is easy to see how the marsh is built up from thin layers of sand and mud. Expansion and erosion can occur simultaneously within a marsh: even though the marsh grows higher, erosion occurs along the areas bordering the sea. Not all marshes are created naturally. The marshes along the coast of Groningen and Friesland were formed over many centuries with the help of human hands: the Salt Marsh Works.
    Salt marshes form in sheltered coastal regions; the weak current gives the sand and mud particles suspended in the seawater a chance to precipitate. In the Wadden Sea, around 3.5 million cubic meters of sand and mud precipitates every year. The precipitation is not the same everywhere: so much mud can precipitate on a mud flats layer for layer in tranquil places that the land is high enough above the water surface for salt marsh plants to grow. Characteristic species for salt marsh vegetation are salicorn, sea lavender, annual seablite, sea purslane, sea aster and sea wormwood.
    A salt marsh has obvious vegetation zones. Starting from the seaside, one first finds a zone with salicorn and tussocks of cord-grass. Sea meadow grass grows in the next zone higher up on the marsh, close to the high-tide waterline. Midway up the marsh grows sea lavender, sea wormwood, sea purslane, sea aster and salt-marsh sand spurry. This part of the marsh is only flooded with salt water during extremely high floods. The plants that are not as tolerant to salt water are found on the high part of the marsh. Species such as thrift, red fescue and sea couch are found here, as well as normal land plants.
    In the early Middle Ages, an extremely large part of what now is the provinces of Groningen, Friesland and North Holland consisted of extensive salt marshes, interchanged with lakes, peat swamps and man-made hills: terps or wierdes. This landscape lay behind a beach ridge with dune regions that were broken open in various places, allowing seawater free play. The Zuiderzee, the Wadden Sea, the Middle Sea and the Lauwers Sea together formed a shallow tidal region in which a very gradual transition existed from practically fresh water via brackish to salt water.

    The people in this unique landscape were mostly livestock farmers. They allowed their animals to graze on the marshes. The settlements lay on the higher parts, where crop farming took place on a very modest scale when soil conditions permitted. Taking into account safety and the need for more agricultural land, one began protecting higher lying lands with dikes: the first form of land reclamation. Gradually, the technique improved and one could abstract larger pieces of salt marsh from the influence of seawater. Even later, it was discovered that water could be pumped out of a lake with the help of wind energy: the first polders. Complete sea channels were eventually closed off: the Zuiderzee and Lauwers Sea became Lake IJssel and Lauwers Lake. Via these forms of land reclamation and polder formation, the aerial of the salt marshes in the wadden region in the past 5 centuries was reduced to what is now left over: more than 2800 hectare on the islands, more than 1800 hectare along the mainland coast and around 800 hectare in the Dollard.
    In the 1960s, there were still plans to impolder at least half of the Wadden Sea. Due to community protests against these plans, the Waddenvereniging (Society for Preservation of the Wadden Sea) was founded, which consequently succeeded in preventing most of the land reclamation in the Wadden Sea.
    The present management of the marshes varies per area. There are a number of marshes where nothing is being consciously done. Nature has free-play here and can develop on its own. The best known example where no management takes place is Rottumeroog. A drift dike is maintained on the Oosterkwelder on Schiermonnikoog, past the natural dunes. Marshes are often grazed in order to delay the succession. Someone taking a stroll through the Slufter on Texel could suddenly be walking through a flock of sheep. Or roaming around the Nieuwlandsreid on Ameland, one could run into cattle.