Marshland habitat audit

The term `marshland' has been chosen to cover the following wet terrestrial habitats: bog, swamp, fen, wet marginal vegetation, wet marshy grassland and ditches. The following habitats also occur in association with marshland but are covered by other audits: fen carr (Woodland); floodplain grassland (Grazing Marsh and Floodplain Grassland); and reedswamp (Reedbed).

Marshland habitat has been highlighted as a priority for nature conservation in the UK due to dramatic declines in area and distribution throughout Europe during the last century. Marshland habitat within London is now relatively rare and fragmented. There are approximately 273 ha of marshland in Greater London. Marshland areas are more frequent in outer London boroughs and are effectively absent from the inner London boroughs. London's marshlands support a rich diversity of plant and animal communities.

The main present day threats to London's marshland resource are development, water abstraction, pollution and lack of, or inappropriate, management. Fen and bogs will be particularly threatened by drying out and succession to woodland, whereas wet marginal vegetation can be seriously affected by water-borne pollution, development and unsympathetic maintenance, for example vegetation clearance at inappropriate times of the year. Wet marshy grassland can be very easily damaged or destroyed by relatively minor drainage schemes, particularly those associated with `improvements' to agricultural land, golf courses, parks and other amenity land.

Existing degraded marshland habitats can be enhanced or new marshland habitats created when designing new flood-defence projects or refurbishing existing ones by incorporating schemes which aim to reduce the incidence of flooding by reducing direct run-off through containment of floodwaters in balancing ponds and flood-storage lagoons. Marshlands can also be restored or rehabilitated as part of the after use of mineral workings. At present many existing gravel pits are restored as deep-water pits or returned to agricultural use.

Existing high quality marshland habitats can be conserved by the preparation of Water Level Management Plans which identify the water budget for a particular site and how this can be effectively managed with respect to conflicting demands. At many smaller sites, the biggest threat to marshlands - drying out and succession - can be tackled relatively inexpensively by control of water levels.