Geoscience Reference
In-Depth Information
Photo: Michael Raw
dramatically speeded up, but in turn
Spartina anglica
is
replaced by sea poa (
Puccinella maritima
), especially
where the grass is intensively grazed.
Puccinella
withstands
the grazing and trampling of sheep and cattle much better.
The value of salt marshes is twofold. First, they support
a distinctive flora and fauna and contribute much to
coastal biodiversity. Second, they provide a buffer to wave
energy and coastal erosion processes, thus reducing the
cost of coastal flood defences. The history of human
impact on salt marshes in the United Kingdom has been
one of reclamation by building sea walls, then reclaiming
land behind the wall for agriculture. Large-scale erosion
of marshes by the sea has also been a problem, especially
in southern and eastern England. One estimate is that 25
per cent of the salt marsh in Essex has been lost since 1965.
The main reasons appear to be related to relative sea-level
rise, increased storminess of the climate, and reductions
in sediment input by coastal development that interrupts
coastal processes (Morris
et al
. 2004). Since 1992 'managed
coastal retreat' or 'managed realignment', whereby the
sea wall is deliberately breached to form new intertidal
habitat, has been advocated by several conservation
agencies, including the Environment Agency, English
Nature (now Natural England) and the Wildlife Trusts.
Examples are: Tollesbury (1995); Freiston shore, north-
west Wash, Lincolnshire (2002); Paul Holme Strays (2003)
and Alkborough Flats (2005), the largest project in
Europe, both on the river Humber. Another large project
is at Abbot's Hall Farm on the river Blackwater estuary,
Essex, where a 3.4 km breach of the sea wall created 84 ha
of new salt marshes. The project is managed by the Essex
Wildlife Trust, and funded by the Wildlife Trusts (WT),
the Heritage Lottery Fund (HLF), the Environmental
Agency (EA), and the Department of Environment,
