Difference between revisions of "Coastal grazing marsh"

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Coastal grazing marsh lies towards the most maritime end of the spectrum of coastal wet grasslands. The general term ‘lowland wet grassland’ can be applied to virtually all river valley grasslands and coastal marshes <ref>Ward, D., 1994. Management of lowland wet grassland for breeding waders. British Wildlife, 6/2, 89-98.</ref> (Ward 1994). This article describes the main features of coastal grazing marsh.
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==Introduction==
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Two principal features are important in defining the ‘coastal’ nature of the lowland wet grassland: its origins and the degree of maritime influence. A general term of ‘coastal wet grassland’ is used to describe those grasslands which lie on the margins of tidal influence, but are subject to some, often limited maritime influence. More specifically ‘coastal grazing marsh’ is applied to sites where the coastal wet grassland is derived from marine sediments (mostly those from which [[Salt marsh definition|salt marsh]] devlops).
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===Lowland wet grassland===
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Wet grassland can occur in any areas of low-lying land where the soil is subjected to varying water levels. Impeded drainage, flooding as a result of river banks over-topping or excessive precipitation are among the factors helping to create permanent or seasonally wet grasslands. Those which are unploughed and traditionally managed as grazing pasture or used for hay, with little use of artificial fertiliser, tend to have a rich flora and fauna.
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===Coastal wet grassland===
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What distinguishes coastal wet grassland from lowland wet grassland which happens to lie near the sea, is the nature of the soil and/or the influence of saline water. Their origins are usually the result of drainage of swamps and other low-lying wetlands derived from marine sediments around the margins of tidal embayments. These enclosures may date back to ‘Roman Times’ as in the case of the Wash (the Fenland Basin) and Romney Marsh (c200AD) in Kent. Precise definitions are difficult because the marine sediments may be overlain by river alluvium as relative sea level movements alter the landward limits of tidal influence. Although now largely intensive agriculture, the fenland basin around the Wash, for example, is derived from the enclosure of freshwater and brackish swamps and salt marshes. The Ouse Washes in Cambridgeshire lie adjacent to the canalised river Ouse which stretches many miles inland and is influenced by tidal water along much of its length. The extent of saline water intrusion today is limited, and only occurs in the lowest tidal reaches of the river. Pevensey Levels on the south coast in East Sussex was formed on the site of a former inlet <ref>Steers, J.A., 1969. ''The Coastline of England and Wales''. 2nd edition. Cambridge University Press, Cambridge.</ref> (Steers 1969) but today has no saline influence. Other coastal wet grasslands may receive limited saline water intrusion from seepage zones through coastal barriers or as a result of overtopping by the sea. There will be gradations from brackish to freshwater, especially in the drainage ditches.
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==Coastal grazing marsh==
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Coastal grazing marsh is a specific term applied to land derived from the enclosure of salt marsh. Coastal grazing marsh is recognised as a distinct habitat type in Great Britain (Section 11.2.17 of the SSSI Guidelines define it as “Enclosed, unimproved or semi-improved saltmarsh.”). These areas represent some of the most recent (within the last 200-300 years) enclosures. The habitat is something of an anomaly in European terms and not recognised in the classification used to identify Special Areas of Conservation (European Commission 1999). It is defined by the presence of permanent and semi-permanent grassland, drainage ditches and enclosing earth dykes. Features of the original marsh are present including old creek lines. Saline waters derive from seepage zones through the sea walls and intrusion of sea water along channels which may remain partially open to the tide. As with other wet grasslands the wildlife interest has developed alongside the traditional use of the land for agricultural, notably grazing or hay-making.
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From the above it might be inferred that these definitions are mutually exclusive and easy to identify. However this is far from the case and historically the drainage and enclosure of tidal lands, such as those around the Wash inevitably include transitions between saltmarsh, brackish water swamps and fresh water fens. The Norfolk Broads are also derived from fen peat deposits though in this case many of the wetlands are the result of excavations. This area includes Halvergate Marshes “perhaps the finest coastal grazing marsh in Britain, replete with extensive transitions to freshwater ditches.” (Dargie 1993). According the definitions used above these areas are coastal wet grasslands rather than ‘coastal grazing marsh’ but this serves to emphasise the problems associated with habitat definition.
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Coastal grazing marsh is best considered as a sub-set of coastal wet grassland. The principal components which help to define these systems include:
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 Sea walls;
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 Saline seepage areas;
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 Vehicle rutted ground;
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 Grassland (alongside the sea wall);
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 Counter ditches (alongside sea wall);
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 Grazing marsh;
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 Cattle poached areas;
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 Dredged spoil heaps;
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 Fleet (former tidal channel);
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 Reed beds and scrub (after Gray, 1977 p. 257).
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This description relates to land derived from saltmarsh enclosure. Although this falls within a general term “reclaimed land” used by Gray (1977) he makes a distinction between two types of reclaimed land, based on the method of reclamation. The former involves the enclosure of an intertidal surface, usually saltmarsh covered, the land has unique character and is described as “permanent” retaining a high wildlife interest (the ‘coastal grazing marsh’ as defined above). This is distinguished from “temporary” land derived from newly enclosed bare surfaces, subsequently developed for more intensive uses. The latter involves either pumping dry the existing tidal mud, or infilling the void behind a sea wall with imported material. This may include dredged sediments from the seabed or other material such as refuse. It is suggested these broad definitions provides a useful basis to undertake an assessment of the particular qualities of the Dibden Bay SINC provided next.
  
 
"Coastal grazing marsh" is one of the habitat sub-categories within the section dealing with biodiversity of coastal and marine habitats and ecosystems. This forms part of Theme 7.  
 
"Coastal grazing marsh" is one of the habitat sub-categories within the section dealing with biodiversity of coastal and marine habitats and ecosystems. This forms part of Theme 7.  
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==References==
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<references/>
  
 
[[Category:Coastal grazing marsh]]
 
[[Category:Coastal grazing marsh]]
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Revision as of 13:31, 28 November 2007

Category:Stub
Category:Revision


Coastal grazing marsh lies towards the most maritime end of the spectrum of coastal wet grasslands. The general term ‘lowland wet grassland’ can be applied to virtually all river valley grasslands and coastal marshes [1] (Ward 1994). This article describes the main features of coastal grazing marsh.


Introduction

Two principal features are important in defining the ‘coastal’ nature of the lowland wet grassland: its origins and the degree of maritime influence. A general term of ‘coastal wet grassland’ is used to describe those grasslands which lie on the margins of tidal influence, but are subject to some, often limited maritime influence. More specifically ‘coastal grazing marsh’ is applied to sites where the coastal wet grassland is derived from marine sediments (mostly those from which salt marsh devlops).

Lowland wet grassland

Wet grassland can occur in any areas of low-lying land where the soil is subjected to varying water levels. Impeded drainage, flooding as a result of river banks over-topping or excessive precipitation are among the factors helping to create permanent or seasonally wet grasslands. Those which are unploughed and traditionally managed as grazing pasture or used for hay, with little use of artificial fertiliser, tend to have a rich flora and fauna.

Coastal wet grassland

What distinguishes coastal wet grassland from lowland wet grassland which happens to lie near the sea, is the nature of the soil and/or the influence of saline water. Their origins are usually the result of drainage of swamps and other low-lying wetlands derived from marine sediments around the margins of tidal embayments. These enclosures may date back to ‘Roman Times’ as in the case of the Wash (the Fenland Basin) and Romney Marsh (c200AD) in Kent. Precise definitions are difficult because the marine sediments may be overlain by river alluvium as relative sea level movements alter the landward limits of tidal influence. Although now largely intensive agriculture, the fenland basin around the Wash, for example, is derived from the enclosure of freshwater and brackish swamps and salt marshes. The Ouse Washes in Cambridgeshire lie adjacent to the canalised river Ouse which stretches many miles inland and is influenced by tidal water along much of its length. The extent of saline water intrusion today is limited, and only occurs in the lowest tidal reaches of the river. Pevensey Levels on the south coast in East Sussex was formed on the site of a former inlet [2] (Steers 1969) but today has no saline influence. Other coastal wet grasslands may receive limited saline water intrusion from seepage zones through coastal barriers or as a result of overtopping by the sea. There will be gradations from brackish to freshwater, especially in the drainage ditches.

Coastal grazing marsh

Coastal grazing marsh is a specific term applied to land derived from the enclosure of salt marsh. Coastal grazing marsh is recognised as a distinct habitat type in Great Britain (Section 11.2.17 of the SSSI Guidelines define it as “Enclosed, unimproved or semi-improved saltmarsh.”). These areas represent some of the most recent (within the last 200-300 years) enclosures. The habitat is something of an anomaly in European terms and not recognised in the classification used to identify Special Areas of Conservation (European Commission 1999). It is defined by the presence of permanent and semi-permanent grassland, drainage ditches and enclosing earth dykes. Features of the original marsh are present including old creek lines. Saline waters derive from seepage zones through the sea walls and intrusion of sea water along channels which may remain partially open to the tide. As with other wet grasslands the wildlife interest has developed alongside the traditional use of the land for agricultural, notably grazing or hay-making. From the above it might be inferred that these definitions are mutually exclusive and easy to identify. However this is far from the case and historically the drainage and enclosure of tidal lands, such as those around the Wash inevitably include transitions between saltmarsh, brackish water swamps and fresh water fens. The Norfolk Broads are also derived from fen peat deposits though in this case many of the wetlands are the result of excavations. This area includes Halvergate Marshes “perhaps the finest coastal grazing marsh in Britain, replete with extensive transitions to freshwater ditches.” (Dargie 1993). According the definitions used above these areas are coastal wet grasslands rather than ‘coastal grazing marsh’ but this serves to emphasise the problems associated with habitat definition. Coastal grazing marsh is best considered as a sub-set of coastal wet grassland. The principal components which help to define these systems include:  Sea walls;  Saline seepage areas;  Vehicle rutted ground;  Grassland (alongside the sea wall);  Counter ditches (alongside sea wall);  Grazing marsh;  Cattle poached areas;  Dredged spoil heaps;  Fleet (former tidal channel);  Reed beds and scrub (after Gray, 1977 p. 257).

This description relates to land derived from saltmarsh enclosure. Although this falls within a general term “reclaimed land” used by Gray (1977) he makes a distinction between two types of reclaimed land, based on the method of reclamation. The former involves the enclosure of an intertidal surface, usually saltmarsh covered, the land has unique character and is described as “permanent” retaining a high wildlife interest (the ‘coastal grazing marsh’ as defined above). This is distinguished from “temporary” land derived from newly enclosed bare surfaces, subsequently developed for more intensive uses. The latter involves either pumping dry the existing tidal mud, or infilling the void behind a sea wall with imported material. This may include dredged sediments from the seabed or other material such as refuse. It is suggested these broad definitions provides a useful basis to undertake an assessment of the particular qualities of the Dibden Bay SINC provided next.

"Coastal grazing marsh" is one of the habitat sub-categories within the section dealing with biodiversity of coastal and marine habitats and ecosystems. This forms part of Theme 7.

References

  1. Ward, D., 1994. Management of lowland wet grassland for breeding waders. British Wildlife, 6/2, 89-98.
  2. Steers, J.A., 1969. The Coastline of England and Wales. 2nd edition. Cambridge University Press, Cambridge.


The main author of this article is Doody, Pat
Please note that others may also have edited the contents of this article.

Citation: Doody, Pat (2007): Coastal grazing marsh. Available from http://www.coastalwiki.org/wiki/Coastal_grazing_marsh [accessed on 9-07-2020]