Wetlands play an important role in the hydrology of a catchment; they can provide water storage at times of diminishing water levels, they can buffer against flooding downstream during times of prolonged rainfall, suspended sediments can settle in the slow flow of a wetland, and wetland vegetation can absorb organic pollutants.
Wetlands encompass a mosaic of wet habitats, some permanent, others ephemeral. Seasonal wet pasture, networks of ditches, ephemeral hollows, permanent ponds, emergent swamp communities, can all be features of a wetland.
Floodplain and coastal grazing marsh is now a recognised UK Biodiversity Action Plan Priority Habitat.
Grazing marsh ditches are of special importance for biodiversity, they support especially species-rich aquatic macroinvertebrate assemblages, particularly water beetles.
This landscape type provides habitat for unusually high numbers of rare species.
Wetlands are sensitive to development, to water quality and quantity issues, and to unsympathetic ditch management.
Ditch networks can be surveyed using a combination of netting techniques to cover a wide range of vegetative habitat types.
Buglife methodology, using a combination of aquatic vegetation, aquatic macroinvertebrate assemblages and environmental parameters, can be used to assess the status of ditch systems.
The conservation value of a ditch or ditch system can be assessed using species richness and diversity indices and the Community Conservation Index (CCI).
The invertebrate species conservation status score and invertebrate habitat quality score can assess the relative rarity and the fidelity of a ditch assemblage to coastal and floodplain grazing marsh habitats.
The Species Quality Index provides an evaluation of the value of a wetland, based on the relative richness and rarity of its water beetle assemblage.