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Trilateral Wadden Sea Plan Eighth Trilateral
Governmental Conference
on the Protection of the
Wadden SeaStade, Germany,
October 22, 1997
3 Salt Marshes The habitat type salt marsh includes all mainland and island salt marshes, including the pioneer zone. The brackish marshes in the estuaries are also considered part of this habitat type (Leeuwarden Declaration Annex I).
Salt marshes are typical Wadden Sea habitats of great beauty, diversity and attractiveness for visitors to the Wadden Sea area and they are important and unique habitats.
NATURALLY DEVELOPED SALT MARSHES have a drainage system of irregular, winding gullies, sometimes a pioneer zone, and - in the course of time - formations of salt marsh cliffs between older parts on the one side, and pioneer zones on the bordering tidal flats on the other. The remains of the natural salt marshes can be found on the landside of dune areas, and in some places, along the mainland coast.
ARTIFICIAL SALT MARSHES are salt marshes which have developed through active human interference, like shelter, by means of brush wood groynes. They are mainly situated in places where natural developments would not have led to salt marsh formation.
SUMMER POLDERS are embanked parts of the salt marshes with dikes that are high enough to prevent flooding during the growing season. The frequency of inundation varies between only once per 2 or 3 years to several times per year, depending on the height of the dikes. Remains of natural gullies and salt marsh cliffs can sometimes be found. When inundation takes place during winter, the influence of the sea water on the vegetation is often negligible. The soil is saturated with fresh water and the sea water is drained off very rapidly within a few days after flooding.
Status The present salt marsh area is, mainly as a result of embankments, much smaller than it used to be. Moreover, many of the remaining salt marshes are heavily influenced by human use. With the exception of some locations in Denmark and Lower Saxony, almost all natural mainland salt marshes have been embanked in the past, some only as a summer polder, but most of them as polders on the land side of a sea dike. Salt marshes and summer dikes are important elements of the coastal protection strategy.
Most of the artificial salt marshes on the Wadden Sea islands have an almost natural geomorphology, whereas most mainland artificial salt marshes have a geomorphology that is dominated by human structures: brushwood groynes, ditches and ground dams.
The artificial salt marshes are considered an additional advantage resulting from embankments, although created at the expense of natural tidal areas.
Targets An increased area of natural salt marshes.
An increased natural morphology and dynamics, including natural drainage patterns of artificial salt marshes, under the condition that the present surface area is not reduced.
An improved natural vegetation structure, including the pioneer zone, of artificial salt marshes.Favorable conditions for migrating and breeding birds.
Assessment Large areas of natural and artificial salt marshes have been embanked in the past. This has not only caused a considerable loss of this typical Wadden Sea habitat, but also reduced the volume of the tidal basin considerably. These losses have been compensated for, at least partly, on the islands where new salt marshes developed in the shelter of sand dikes and on the mainland through the stimulation of sedimentation. Most of the island salt marshes have developed in a natural way, whereas the mainland salt marshes must be regarded as largely artificial.
The main interference with the natural development of salt marshes and summer polders is caused by coastal protection and land reclamation activities. The intensive drainage of the 'normal' management practice of the land reclamation areas is, at least partly, beneficial for agriculture.
Agricultural activities, mainly grazing and drainage, but also the application of fertilizer and pesticides, affect the natural vegetation structure and, consequently, the faunal composition.The effects of a reduction of the volume of the tidal basin, in the light of sea level rise and bottom subsidence, are not quite well understood. There is, however, the danger that these combined processes will cause a reduction of the area of tidal flats.There are indications that this might result in some areas in the reduction of the area of the salt marshes.
How to proceed The possibilities for the development of new natural salt marshes are restricted. The best way to increase the area of natural salt marshes is through improving natural conditions in existing salt marshes. The natural morphology and dynamics of the salt marshes must be enhanced through reduction of interference with natural processes. For example, artificial drainage systems should be modified in such a way that they become self sustaining. In order to improve the natural vegetation structure and the conditions for birds, the grazing pressure must, where necessary, be reduced.
Disturbance of birds through hunting and recreational activities should be reduced as much as possible.
Outbankment of summer polders, excluding the summer dikes of the Halligen, because these protect the inhabitants, is a very good instrument to enlarge the salt marsh region, provided socio-economic and coastal protection aspects are considered as well. It can yield salt marsh areas without interference with natural geomorphological processes. Ecologically valuable habitats can be restored, in case of summer polders, on relatively old and high salt marshes. Such salt marshes are rare and their restoration is of utmost importance for the restoration of the total richness of the mainland salt marsh habitats.
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3.1 Trilateral policy and management 3.1.1 The general trilateral policy regarding salt marshes aims at adequately protecting salt marshes in order to allow natural processes to take place within this habitat, with special emphasis on flora and fauna. To this end, all salt marshes shall be brought under legal protection, insofar this has not yet been done, and Best Environmental Practice will be applied in salt marsh protection and development, taking account of experiences with local concepts and measures.
Salt Marsh Area
3.1.2 The trilateral policy takes as starting point that the present area of salt marshes will not be reduced and that, where possible, the area of natural salt marshes will be extended.
3.1.3 The long-term goal is to limit human interference with the salt marshes, except for the edges of the marshes which may need protection against erosion. In working towards this long-term goal, the interest of cultural history, coastal protection and private rights should be taken into account.
3.1.4 The present artificial salt marsh area can be protected against erosion because the size of the land reclamation salt marshes along the mainland is, generally, still far below the total size of the mainland salt marshes in a more natural situation without sea walls.
3.1.5 An increase of the salt marsh area will be aimed for through the restoration of salt marshes by opening summer dikes, provided that it is in line with the Targets for the region, socio-economic conditions and coastal protection requirements. The Halligen are protected by summer dikes for the security of the inhabitants. There is no intention to open these dikes.
Coastal Protection
3.1.6 The interests of nature protection and sea defence measures will be further harmonized, taking into account that the safety of the inhabitants is essential.
3.1.7 As a principle, it is prohibited to embank salt marshes and loss of biotopes through sea defence measures will be minimized. Reinforcement of existing dikes will be carried out on the location of existing dikes and, preferably, on the land side. (Reference to 4.1.2).
3.1.8 The application of Best Environmental Practices for coastal protection will be enhanced.
3.1.9 In general, clay for sea defence will be extracted behind the dikes. In special cases, i.e. where there is urgent and sudden need and if no other deposits behind the dikes are available, or if the extraction of suitable material is ecologically balanced, the extraction of clay may be allowed in front of the dike. In this case, the extraction shall be carried out in such a way that the environmental impact is kept to a minimum and permanent or long lasting effects are avoided and, if this is not possible, compensated.
Natural Dynamics
3.1.10 The natural drainage of salt marshes will be increased by reducing drainage works where possible and practicable and by introducing more environmentally friendly digging methods.
3.1.11 It is the aim to reduce and/or diversify grazing in order to increase the diversity of vegetation and associated animal species in salt marshes, with the exception of those areas where grazing is necessary for coastal protection measures.
3.1.12 It is the aim to reduce disturbance caused by recreation and tourism by introducing and applying information systems and/or temporal and spatial zoning. (Identical with 5.1.8).
3.1.13 The application of natural and artificial fertilizers and pesticides and other toxic substances on the salt marshes will be stopped.
Infrastructural works
3.1.14 New infrastructural works which have a permanent or long-lasting impact should not be established in salt marshes.
3.1.15 Infrastructural works which are necessary for the supply of the islands and the Halligen with, amongst others, gas, water and electricity, or other utilities, shall be carried out in a way that the environmental impact on the Wadden Sea is kept to a minimum and permanent, or long lasting, impacts are avoided. (Identical with 4.1.14).
3.1.16 New licenses for the construction of pipelines in the salt marshes for the transport of gas and oil shall not be issued unless such measures are necessary for imperative reasons of overriding public interest. In that case, the method of construction and the planning of the location line shall be such that the environmental impact on the Wadden Sea ecosystem is kept to a minimum and permanent, or long lasting, negative impacts are avoided. (Reference to 4.1.13).
3.2 Trilateral projects and actions 3.2.1 A study into the possible effects of enhanced sea level rise by a Trilateral Expert Group to be established under the coordination responsibility of the competent authorities and, on the basis of these studies, the development of proposals for future integrated coastal defence and nature protection policies. (Identical with 4.2.1, 5.2.2, 7.2.1).
3.2.2 The investigation of existing salt marsh maintenance works and methods and possibilities for enhancing more natural drainage patterns.
The investigation of existing agricultural use of the salt marshes and methods for improving the quality of the salt marshes.
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