Grazing marsh
Encyclopedia
Grazing marsh is a British Isles
term for flat, marshy grassland in polder
s. It consists of large grass fields separated by fresh or brackish ditches, and is often important for its wildlife.
s and salt marsh
to make polders (though the term "polder" is little used in Britain). Polders in Britain are mostly drained by gravity, rather than active pumping. The original tidal drainage channels were augmented by new ditches, and flap valves in the sea walls let water drain out at low tide
and prevent the sea or tidal river from entering at high tide. Constructing polders in this way is called inning or reclaiming from the sea.
Grazing marshes have been made in most lowland estuaries
in Britain, often leaving only the river channel and the lowest part of the estuary tidal. In a few cases (such as Newtown
Harbour on the Isle of Wight
, and Pagham Harbour
in West Sussex
) the sea walls have been breached, and the estuaries have returned to a tidal state. Grazing marshes have also been made on low-lying open coasts.
Many grazing marshes were inned in stages, and the old sea walls (called counter walls) may be found marooned far from the current sea wall. Land levels on either side of a counter wall often differ by several metres. Paradoxically, the lower side is the land inned earlier, because sediment continued to build up on the side that remained tidal.
, White-fronted Goose
and Bewick's Swan
. Many of these birds are hunted by predators such as Peregrine
and Marsh Harrier
.
In summer, waders such as Common Redshank
, Eurasian Curlew
and Northern Lapwing
breed.
The ditches often have a range of salinity, depending on how close to the sea wall they are. The more saline ditches host specialist brackish-water plants and animals. These include, for example, the rare brackish amphipod Gammarus
insensibilis and sea club-rush (Bolboschoenus maritimus). Fresher ditches may support rare animals, such as the great silver water beetle (Hydrophilus piceus) and the great raft spider
(Dolomedes plantarius), and a wide range of pondweeds (Potamogeton
and relatives).
The grassland vegetation usually has a fairly small number of species, but those present are often scarce elsewhere, such as sea arrowgrass
(Triglochin maritimum), divided sedge (Carex divisa) and strawberry clover Trifolium fragiferum.
, often using pumped drainage to lower the water levels enough to grow crops. The low ditch levels and agricultural runoff combine to remove much of the aquatic wildlife, although the arable fields may still be used by some wintering wildfowl.
Some areas of grazing marsh and other polder land have been used to recreate tidal habitats by a process of managed retreat
.
Many of the larger areas of grazing marsh bear nature conservation designations, including Site of Special Scientific Interest
, Special Protection Area
, Special Area of Conservation
and Ramsar Site.
British Isles
The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
term for flat, marshy grassland in polder
Polder
A polder is a low-lying tract of land enclosed by embankments known as dikes, that forms an artificial hydrological entity, meaning it has no connection with outside water other than through manually-operated devices...
s. It consists of large grass fields separated by fresh or brackish ditches, and is often important for its wildlife.
History
Grazing marshes were created from Medieval times by building sea walls (earth banks) across tidal mudflatMudflat
Mudflats or mud flats, also known as tidal flats, are coastal wetlands that form when mud is deposited by tides or rivers. They are found in sheltered areas such as bays, bayous, lagoons, and estuaries. Mudflats may be viewed geologically as exposed layers of bay mud, resulting from deposition of...
s and salt marsh
Salt marsh
A salt marsh is an environment in the upper coastal intertidal zone between land and salt water or brackish water, it is dominated by dense stands of halophytic plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh...
to make polders (though the term "polder" is little used in Britain). Polders in Britain are mostly drained by gravity, rather than active pumping. The original tidal drainage channels were augmented by new ditches, and flap valves in the sea walls let water drain out at low tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
and prevent the sea or tidal river from entering at high tide. Constructing polders in this way is called inning or reclaiming from the sea.
Grazing marshes have been made in most lowland estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
in Britain, often leaving only the river channel and the lowest part of the estuary tidal. In a few cases (such as Newtown
Newtown, Isle of Wight
Newtown is a small hamlet on the Isle of Wight, in England. In medieval times it was a thriving borough.Newtown is located on the large natural harbour on the Island's north-western coast, now mostly a National Nature Reserve owned and managed by the National Trust.The Caul Bourne stream running...
Harbour on the Isle of Wight
Isle of Wight
The Isle of Wight is a county and the largest island of England, located in the English Channel, on average about 2–4 miles off the south coast of the county of Hampshire, separated from the mainland by a strait called the Solent...
, and Pagham Harbour
Pagham Harbour
Pagham Harbour is a natural harbour on England's south coast. It is south of the city of Chichester and near the towns of Pagham and Selsey.Geographically it is the smallest and most easterly of the harbours of the Solent....
in West Sussex
West Sussex
West Sussex is a county in the south of England, bordering onto East Sussex , Hampshire and Surrey. The county of Sussex has been divided into East and West since the 12th century, and obtained separate county councils in 1888, but it remained a single ceremonial county until 1974 and the coming...
) the sea walls have been breached, and the estuaries have returned to a tidal state. Grazing marshes have also been made on low-lying open coasts.
Many grazing marshes were inned in stages, and the old sea walls (called counter walls) may be found marooned far from the current sea wall. Land levels on either side of a counter wall often differ by several metres. Paradoxically, the lower side is the land inned earlier, because sediment continued to build up on the side that remained tidal.
Wildlife
Wintering wildfowl are characteristic of grazing marshes, often including large flocks of Eurasian Wigeon, Brent GooseBrent Goose
The Brant or Brent Goose, Branta bernicla, is a species of goose of the genus Branta. The Black Brant is an American subspecies. The specific descriptor bernicla is from the same source as "barnacle" in Barnacle Goose, which looks similar but is not a close relation.-Appearance:The Brant Goose is...
, White-fronted Goose
White-fronted Goose
The Greater White-fronted Goose is a species of goose. The Greater White-fronted Goose is more closely related to the smaller Lesser White-fronted Goose...
and Bewick's Swan
Bewick's Swan
The Tundra Swan is a small Holarctic swan. The two taxa within it are usually regarded as conspecific, but are also sometimes split into two species, Cygnus bewickii of the Palaearctic and the Whistling Swan, C. columbianus proper, of the Nearctic...
. Many of these birds are hunted by predators such as Peregrine
Peregrine Falcon
The Peregrine Falcon , also known as the Peregrine, and historically as the Duck Hawk in North America, is a widespread bird of prey in the family Falconidae. A large, crow-sized falcon, it has a blue-gray back, barred white underparts, and a black head and "moustache"...
and Marsh Harrier
Marsh harrier
The marsh harriers are birds of prey of the harrier subfamily. They are medium-sized raptors and the largest and broadest-winged harriers. Most of them are associated with marshland and dense reedbeds...
.
In summer, waders such as Common Redshank
Common Redshank
The Common Redshank or simply Redshank is an Eurasian wader in the large family Scolopacidae.- Description and systematics :...
, Eurasian Curlew
Eurasian Curlew
The Eurasian Curlew, Numenius arquata, is a wader in the large family Scolopacidae. It is one of the most widespread of the curlews, breeding across temperate Europe and Asia...
and Northern Lapwing
Northern Lapwing
The Northern Lapwing , also known as the Peewit, Green Plover or just Lapwing, is a bird in the plover family. It is common through temperate Eurasia....
breed.
The ditches often have a range of salinity, depending on how close to the sea wall they are. The more saline ditches host specialist brackish-water plants and animals. These include, for example, the rare brackish amphipod Gammarus
Gammarus
Gammarus is an amphipod crustacean genus in the family Gammaridae. It contains more than 200 described species, making it one of the most speciose genera of crustaceans...
insensibilis and sea club-rush (Bolboschoenus maritimus). Fresher ditches may support rare animals, such as the great silver water beetle (Hydrophilus piceus) and the great raft spider
Great raft spider
The great raft spider or fen raft spider is a European species of spider in the Pisauridae family. Like other Dolomedes spiders, it is semi-aquatic, hunting its prey on the surface of water...
(Dolomedes plantarius), and a wide range of pondweeds (Potamogeton
Potamogeton
Potamogeton is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed...
and relatives).
The grassland vegetation usually has a fairly small number of species, but those present are often scarce elsewhere, such as sea arrowgrass
Sea Arrowgrass
Triglochin maritima is a variety of arrowgrass found in brackish marshes, freshwater marshes, wet sandy beaches, fens, damp grassland and bogs. It has a circumboreal distribution, occurring throughout the northern Northern Hemisphere...
(Triglochin maritimum), divided sedge (Carex divisa) and strawberry clover Trifolium fragiferum.
Conservation
Many grazing marshes have been converted into arable landArable land
In geography and agriculture, arable land is land that can be used for growing crops. It includes all land under temporary crops , temporary meadows for mowing or pasture, land under market and kitchen gardens and land temporarily fallow...
, often using pumped drainage to lower the water levels enough to grow crops. The low ditch levels and agricultural runoff combine to remove much of the aquatic wildlife, although the arable fields may still be used by some wintering wildfowl.
Some areas of grazing marsh and other polder land have been used to recreate tidal habitats by a process of managed retreat
Managed retreat
In the context of coastal erosion, managed retreat allows an area that was not previously exposed to flooding by the sea to become flooded by removing coastal protection...
.
Many of the larger areas of grazing marsh bear nature conservation designations, including Site of Special Scientific Interest
Site of Special Scientific Interest
A Site of Special Scientific Interest is a conservation designation denoting a protected area in the United Kingdom. SSSIs are the basic building block of site-based nature conservation legislation and most other legal nature/geological conservation designations in Great Britain are based upon...
, Special Protection Area
Special Protection Area
A Special Protection Area or SPA is a designation under the European Union Directive on the Conservation of Wild Birds.Under the Directive, Member States of the European Union have a duty to safeguard the habitats of migratory birds and certain particularly threatened birds.Together with Special...
, Special Area of Conservation
Special Area of Conservation
A Special Area of Conservation is defined in the European Union's Habitats Directive , also known as the Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora...
and Ramsar Site.
Examples of grazing marsh
- Pevensey LevelsPevensey LevelsThe area known as the Pevensey Levels is a Site of Special Scientific Interest notified under Section 28 of theWildlife and Countryside Act 1981. It is an area of marshland situated between Bexhill in the east, Pevensey in the west and Hailsham in the north...
in East SussexEast SussexEast Sussex is a county in South East England. It is bordered by the counties of Kent, Surrey and West Sussex, and to the south by the English Channel.-History:... - Romney MarshRomney MarshRomney Marsh is a sparsely populated wetland area in the counties of Kent and East Sussex in the south-east of England. It covers about 100 mi ² .-Quotations:*“As Egypt was the gift of the Nile, this level tract .....
in KentKentKent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
and East SussexEast SussexEast Sussex is a county in South East England. It is bordered by the counties of Kent, Surrey and West Sussex, and to the south by the English Channel.-History:... - The Somerset LevelsSomerset LevelsThe Somerset Levels, or the Somerset Levels and Moors as they are less commonly but more correctly known, is a sparsely populated coastal plain and wetland area of central Somerset, South West England, between the Quantock and Mendip Hills...
- The Thames EstuaryThames EstuaryThe Thames Mouth is the estuary in which the River Thames meets the waters of the North Sea.It is not easy to define the limits of the estuary, although physically the head of Sea Reach, near Canvey Island on the Essex shore is probably the western boundary...
marshes in KentKentKent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
and EssexEssexEssex is a ceremonial and non-metropolitan county in the East region of England, and one of the home counties. It is located to the northeast of Greater London. It borders with Cambridgeshire and Suffolk to the north, Hertfordshire to the west, Kent to the South and London to the south west...
. - Marshes along the River WantsumRiver WantsumThe River Wantsum is a tributary of the River Stour, in Kent, England. Formerly, the River Wantsum and the River Stour together formed the Wantsum Channel, which separated the Isle of Thanet from the mainland of Kent...
in KentKentKent is a county in southeast England, and is one of the home counties. It borders East Sussex, Surrey and Greater London and has a defined boundary with Essex in the middle of the Thames Estuary. The ceremonial county boundaries of Kent include the shire county of Kent and the unitary borough of...
– formerly the Wantsum Channel separating the Isle of ThanetIsle of ThanetThe Isle of Thanet lies at the most easterly point of Kent, England. While in the past it was separated from the mainland by the nearly -wide River Wantsum, it is no longer an island ....
from the mainland - Moss Valley, DerbyshireMoss Valley, DerbyshireThe Moss is a brook in North East Derbyshire, England.When Rother Valley Country Park was built in 1980s, they used water from The Moss to fill the lakes.-Name:The name of the river derives from Moss Beck, which means 'stream through marshy ground'....