English summary - Natuurherstel Nieuwkoop
Restoration plan for the important bird area "Nieuwkoopse Plassen"
Nieuwkoopse Plassen are part of the Holland-Utrecht low fenland region which is called the Groene Hart (transl. Green Heart) of the Netherlands. This nature area of 2,000 hectares is among the most important wetland regions in the Netherlands.
Nieuwkoopse Plassen is a low fenland which has come about by peat accumulation. It contains a large variety of vegetations that are characteristic of open waters, quagmires (calciferous swamps with Cladium Mariscus 53.3, habitat priority type), reedlands and swamp forests. These vegetations provide a suitable habitat for various characteristic reedland and marshland birds, such as Bittern (Botaurus stellaris) priority bird species, Purple heron (Ardea purpurea), Marsh harrier (Circus aeruginosus), Black tern (Chlidonias niger), Common tern (Sterna hirundo) and Bluethroat (Luscinia svecica).
The nature values of Nieuwkoopse Plassen are, however, endangered, that is to say the first stages of water and terrestrialisation vegetations have practically disappeared and consequently bird species typical of this region are becoming extinct; a species as Little bittern (Ixobrychus minutus) has entirely disappeared, whereas other breeding birds are sharply decreasing in number (Purple heron, Bittern, Great reed warbler (Acrocephalus arundinaceus) and Savi’s warbler (Locustella luscinioides). The decline is the result of a combination of causes, i.e.: poor water quality, acidity, dehydration of the vegetation which results in a more rapid succession to rough reedlands and swamp forests. Besides there is considerable erosion of the standing baulks consisting of reed and alder wood .
Several years ago some remedial measures were introduced to improve the water quality: the incoming water is dephosphated and pollutant sources within the area are treated. This has produced good results, i.e. the return of stone worts (Chara) and Najas marina to the area. Subsequently, Natuurmonumenten together with the provincial autorities of Zuid-Holland have worked out a plan for the restoration of the area. This plan constitutes four projects:
1) Recovering the vegetations of waters, terrestrialised land and quagmires by removing the dehydrated mud bottoms of the broads in the region. By removing the mud the phosphate deposit will be restricted and the water quality improved.
2) Restoration of aciduous and dried up reedland by cutting sods of the reedlands which have roughened and are now holding only a small number of species. By removing the thick aciduous top layer and by digging furrows the reedland will then be under the influence again of the clean surface water. This will yield favourable conditions for the development of a species-rich reedland.
3) Installing wooden sheet piling so that the banks are no longer subject to water and wind erosion. In this way the banks of precious reedlands and quagmires can be protected.
4) Developing 15 hectares of reedland on recently acquired parcels of grassland, after they have first served temporarily as a mud storage area. If possible, this reedland will be set up as a helophyt filter, so that the adjoining nature reserve “De Haak” (valuable water and reed vegetations) can be supplied with the desired water quality.
Recovery of the vegetations of waters, terrestrialized zones, quagmires and reedlands will offer the bird species which are characteristic of this nature reserve a considerably improved breeding and foraging biotope. By realizing this project the uniqueness of this nature reserve in the western part of the Netherlands can be preserved.