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Rapport sur l'état des connaissances de la biodiversité 2000-2010

Marshlands and other wetland environments

Why marshland and other wetlands are important for the Département

  • They provide an important home for rare or threatened wildlife at different levels;
  • They constitute a refuge and staging area for numerous species of birds (Shorebirds, reedbed passerines or for wintering (ducks);
  • They act as natural floodplains
  • They constitute an area to relax, to go walking for families (i.e. the Romelaëre Nature Reserve welcomes 100,000 visitors a year)
  • They are important for water quality (through filtering)

Major conservation and public access projects

  • Removing harvested vegetation or extensive grazing, allowing open environments to be maintained;
  • Pollarding willow to support cave-dwelling species;
  • Restoring the river banks employing ‘soft’ methods, using living or dead vegetation (fascines and branches, etc.);
  • Implementing a public access plan designed to limit the disturbance of wildlife and plant life being trodden on (including the construction of walkways, observatories, etc.).

A few statistics

  • The wetlands account for only 3% of Département’s surface area (approximately 23,000 ha).
  • 12% of the natural habitats of the ENS in the Pas-de-Calais are classed as wetlands (approximately 470 ha).
  • 2 % of marshlands and wet areas are protected by the Département’s ENS conservation strategy.

The surface area of the wetlands in the North-Pas de Calais has dropped from 30 to 40% of the territory 40 years ago to 2% today (Report on Wetlands Sage Sensée, 2005). This brutal disappearance can be attributed to various causes. Regarded as unhealthy and non-productive zones, they have been subjected to urban pressure, the development of urban infrastructures (government planning projects, urban sprawl) or have even been drained.

Today, the wetlands are the focus of an international recognition, and their role as natural floodplains, in purifying water, and also in preserving local biodiversity has been recognized. As a result, they are now being included in various planning documents (e.g.: the blue belt network in town planning documents) are also the focus for the implementation of adapted management styles.

Their presence is dependent on the site being well managed and left undisturbed. 50% of the region's nesting population of Bittern are to be found at the Marais Audomarois.

The Bearded Reedling (Panurus biarmicus) seen here ringed at the Wissant marshlands, and the Bittern (Botaurus stellaris) are excellent indicators for how well the reed beds are being conserved.


Importance for Insects

  • 97 species of insects , including 33 that are remarkable;
  • 45 species of Dragonflies observed, representing 96% of the Département's diversity;
  • 21 species of remarkable Dragonflies, including the Southern Damselfly (Coenagrion mercuriale) and the Orange Spotted Emerald (Oxygastra curtisii), two species listed in the National Action Plan, aimed at protecting their habitat;
  • Crickets and Grasshoppers are less common in this type of environment, owing to their preference for hot and dry environments but those that can be seen are often of interest for the natural heritage;
  • Certain species of Orthoptera have a real preference for these environments: the European Mole Cricket (Gryllotalpa gryllotalpa), the Short-winged Conehead (Conocephalus dorsalis), the Large Marsh Grasshopper (Stethophyma grossum), etc.
  • These habitats are of major interest for other families of water insects (including Coleoptera, Ephemera, and Diptera).

They are of major importance for Dragonflies.

Importance for Amphibians and Reptiles

  • 14 species of Amphibians, (including 8 remarkable ones) representing 93% of the diversity in the Département;
  • There is a major conservation issue with regard to 3 species in sharp decline: the Common Parsley Frog (Pelodytes punctatus), mainly a land-dwelling species, the Common Midwife Toad (Alytes obstetricans) and the Great Crested Newt (Triturus cristatus);
  • 4 Species of reptiles; and are especially important with regard to the grass snake (Natrix natrix);

These groups are good indicators for the quality of the wetlands

Importance for Birds

  • 96 species identified, including 20 remarkable ones
  • There is a major conservation issue for the in-land wetlands the Marais Audomarois and the Romelaëre Nature Reserve ;
  • Presence of the Eurasian Bittern (Botaurus stellaris) at Saint Omer, Marais de Guînes, and the Baie de Wissant;
  • Presence of the little Bittern (Ixobrychus minutus), a species in decline and the Bearded Reedling (Panurus biarmicus);
  • Presence of numerous species dependant on reed-beds and water-willow wetlands;
  • Coastal Wetlands (Platier d’Oye Nature Reserve, Baie d’Authie), supporting large bird colonies (Mediterranean Gull Ichthyaetus melanocephalus, Sandwich Tern Thalasseus sandvicensis).

They are of major importance as nesting, staging and wintering areas

Importance for Mammals

  • 25 species of mammals, including 6 remarkable ones and 14 species of chiroptera. The level of diversity can vary depending on the shape and character of the different sites;
  • Water bodies are used as hunting grounds by numerous bats;
  • Ponds and other wet micro-zones are home to the Eurasian Water Shrew (Neomys fodiens), a protected species.

They provide areas for refuge, feeding, spawning and for giving birth.

Importance for Fish

  • 30 species of fish living in the wetland areas, including 7 remarkable ones;
  • Importance can vary depending on the different ENS: 28 sites can support fish;
  • Large areas, like the Saint Omer marshlands and the Marais de Guînes, support a variety of fish (24 species have been identified in the Marais Audomarois for instance);
  • A diverse variety of species are dependent on the mosaic of different environments with the marshlands and wetlands;
  • Some of the ENS that are surrounded by major waterways, like the Vallée de l’Aa support the development of the European Eel (Anguilla anguilla), a critically endangered species;
  • Presence of the Northern Pike (Esox lucius), which is a good indicator for the quality of the sites (underwater willow wetlands and grasslands that are liable to flooding).

They are of major importance as spawning grounds, in addition to other water bodies.

Importance for Flora and related environments

  • 888 species of vegetation , including 56 quite remarkable ones and 32 of the most remarkable;
  • These environments allow the survival of unique and particularly threatened species on a regional and even national level;
  • Topographic gradients (notably gentle slopes), edaphic conditions (peat clay, sand) ensure the presence of a diversified plant life: more than 450 species of plants on the Marais de Condette Nature Reserve;
  • They are of great importance for certain species, like the Meadow Thistle (Cirsium dissectum L.) which can be found in limited parts of only one of the ENS (Dunes de Berck).

The wetlands are the refuge of an exceptional and threatened natural heritage

The ENS have a major role in regard to the wetlands, especially in light of the threats faced by these ecosystems on a national scale (waste depositing, closure due to lack of maintenance, alluvial deposits, pollution etc..).

The major wetlands found in the ENS are:

The large wetland complexes: Marais de Guînes and Marais Audomarois with their several ENS, including the Romelaëre Nature Reserve, are sought after areas for the nesting, migration and wintering of more than 150 species of Birds. Other ENS supporting smaller wetlands are also remarkable, like the Marais de Condette Natural Reserve or the Marais de Tardinghen.

The back littoral marshlands like those found at the Marais de Wissant are appealing areas, offering an immense variety of habitats supporting plant and animal life.

The dune slacks and the polder meadows form additional habitats to the back littoral marshlands. These two types of environments can be found at the Nature Reserves at Platier d’Oye and Baie de Canche.

The wet grasslands, typically found at the Marais Audomarois are abundant with an important, remarkable diversity of plant life.

Isolated water bodies or areas connected to waterways can easily be found in the ENS. Depending on their shape and character, they can attract mainly Amphibians or Fish (as in the Vallée de l’Aa for instance).

Permanent and vernal ponds are very interesting micro-habitats located on the slag heaps, in woods, meadows, dunes, heathlands, grasslands, etc. Depending on their level of vegetation, they can provide homes to different types of species and may be used for feeding, resting or reproduction.

The former mining sites’ settling basins, like the 9/9bis at Oignies are located in a very urban and industrialised environment where large wetlands are otherwise scarce.

The coastal wetlands are mainly stop off areas or places of refuge sought by migrating and wintering birds (Conchil le Temple).

To learn more about the wetlands in the ENS.

État des connaissances de la biodiversité des ENS du Pas-de-Calais, chapitre VI.1.4, les marais, une zone de refuge pour une biodiversité devenue peu ordinaire. (Only available in French)