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Coastal Saltmarsh

Alnmouth Saltmarsh - English Nature/peter Wakely

Saltmarsh occurs on soft, shallow shores in sheltered coastal areas and estuaries. It generally occupies the upper, vegetated portions of intertidal mudflats, lying approximately between mean high water neap tides and mean high water spring tides. Characteristic species include glasswort Salicornia spp., sea aster Aster tripolium and common saltmarsh grass Puccinella maritima. The plant species found in saltmarsh show a clear zonation according to the frequency of inundation by tidal waters.

Saltmarsh is a highly specialised and productive habitat which supports a flora which is adapted to cope with seawater. Many invertebrates, including GB red data book and nationally scarce species, are confined to saltmarshes. Areas with a high structural and plant diversity, particularly where freshwater seepages provide a transition from fresh to brackish conditions, are particularly important for invertebrates.

Saltmarshes are important feeding grounds for migrating and wintering bird species, including wigeon, teal, and redshank. The seeds of saltmarsh plants may also attract feeding flocks of twite and snow bunting.

Saltmarsh, like other intertidal areas, dissipates wave energy thus reducing the risk of damage to sea defences and flooding of low-lying areas.

Current status

Coastal saltmarsh is widely distributed around the UK coastline and is believed to cover some 45 500 ha. However, just over ten sites account for 60% of the total resource. Historically, large areas of saltmarsh have been lost as a result of land claim for agriculture and industry. As a result, the upper and transitional zones of saltmarsh have become comparatively scarce in England.

Within the North East, saltmarsh is found in all of the Region’s estuaries. The habitat is particularly concentrated within Northumberland with the largest area being found at Lindisfarne.  In other some areas, such as in the tidal stretches of the Tyne and in parts of Tees Valley, the saltmarsh has been reduced to little more than a belt of halophytic (salt-loving) plants. The regional resource is small by UK standards, amounting to a little over 1% of that in England. This is because of a limited supply of sediment, lack of suitable sites for the accumulation of fine sediments, and the land claim of several formerly extensive saltmarshes on estuaries. Since the Industrial Revolution, land reclamation has greatly reduced the amount of saltmarsh found on the Tyne, Wear and Tees.

The largest areas of saltmarsh within the region are notified as SSSI. The Lindisfarne SPA and the Teesmouth and Cleveland Coast SPA both contain sizable areas of saltmarsh. The saltmarsh at Lindisfarne also forms part of the Berwickshire and North Northumberland Coast cSAC.

Threats

  • Erosion of the seaward edge of saltmarshes may occur because of rising sea levels and an increase in wave energy. Sediments are usually deposited further up the shore but this is not possible where coastal defences are in place. This can lead to saltmarsh being lost because of the ‘squeeze’ which takes place between the rising sea and the fixed sea defences. Industrial development and other forms of land reclamation can lead to the loss of saltmarsh communities.
  • Pollution incidents and chronic poor water quality, including increases in nutrient levels, can damage the habitat and the species it supports.
  • Cord-grass Spartina anglica colonization reduces the diversity of saltmarsh vegetation and the value of the habitat as a feeding ground for birds.
  • Coastal defences and other engineering works can disrupt the natural coastal processes of erosion and deposition needed for the maintenance of intertidal habitats such as saltmarsh.
  • Recreational and sporting use of saltmarshes can cause disturbance to important bird populations.
  • Overgrazing may cause damage on some sites, affecting both breeding birds and saltmarsh vegetation.

Opportunities for protection and enhancement

  • Saltmarsh at Holy Island is managed as part of the Lindisfarne National Nature Reserve by Natural England.
  • The Environmental Stewardship scheme has the option of making payments for the creation of inter-tidal habitats, such as saltmarsh, in agreed areas.
  • The Northumberland 4Shores project is creating new areas of saltmarsh and other interidal habitats through selective removal of sea defences