Saline Lagoons - Habitat Action Plan

Ref 1/H2 Habitat Action Plan 2
Plan Author: Norfolk Wildlife Trust
Plan Co-ordinator: Coastal BAP Topic Group
Final Draft 31 December 1998
Under Review December 2000
Final revised draft May 2006

 

Action Plan Summary

Current Status

National Status

  • Lagoons in the UK are essentially bodies, natural or artificial, of saline water partially separated from the adjacent sea. They retain a proportion of their sea water at low tide and may develop as brackish, full saline or hyper-saline water bodies.
  • The largest lagoon in the UK is in excess of 800 ha (Loch of Stenness), although the rest are much smaller and some may be less than 1 ha. Lagoons can contain a variety of substrata, often soft sediments which in turn may support tasselweeds and stoneworts as well as filamentous green and brown algae. In addition, lagoons contain invertebrates rarely found elsewhere. They also provide important habitat for waterfowl, marshland birds and seabirds. The flora and invertebrate fauna present can be divided into three main components: those that are essentially freshwater in origin; those that are marine/brackish species; and those that are more specialist lagoonal species. The presence of certain indigenous and specialist plants and animals makes this habitat important to the UK's overall biodiversity.
  • There are several different types of lagoons, ranging from those separated from the adjacent sea by a barrier of sand or shingle ('typical lagoons'), to those arising as ponded waters in depressions on soft sedimentary shores, to those separated by a rocky sill or artificial construction such as a sea wall. Sea water exchange in lagoons occurs through a natural or man-modified channel or by percolation through, or overtopping of, the barrier. The salinity of the systems is determined by various levels of fresh water input from ground or surface waters. The degree of separation and the nature of the material separating the lagoon from the sea are the basis for distinguishing several different physiographic types of lagoon.

Norfolk Status

  • All sites are within the North Norfolk Coast SAC except Snettisham lagoons, which lie within the Wash and North Norfolk Coast SAC. The North Norfolk ones also lie within the North Norfolk SPA/Ramsar site and the Wash ones within the Wash SPA/Ramsar site. See Table 1.
  • They can be artificial or natural and are characterised by a range of salinities from brackish to hyper saline. They vary greatly in size (see Table 2). They support certain specialist invertebrates and plants which add to the UK's biodiversity. Norfolk lagoons are important for Paramysis nouveli (a shrimp), Nematostella vectensis (starlet sea anemone) and Gammarus insensibilis (lagoon sand shrimp). The latter two species are included in Schedule 5 of the Wildlife and Countryside Act; Nematostella is also a biodiversity Priority Species.
  • Within Norfolk, saline lagoons are of three basic types: the salt marsh creek relic pools and the percolation pools behind the Blakeney spit, and the abandoned gravel pits at Snettisham.
  • Reference should be made to 'Assessment of saline lagoons within Special Areas of Conservation' by Bamber (EN Research Report 235, 1997). Snettisham Pits data from RSPB.

Table 1: Area of saline lagoon biotopes in Norfolk (after Bamber 1997)

Habitat Type

Site

Muddy sand dominated by annelid worms.

Broadwater, Holme; Salt Holes, Holkham; Salthouse Broad and West of Gramborough Hill, Salthouse.

Muddy sand but poor worm fauna because of disturbance.

Broadwater, Holme; Seahorse Pond, Cley; Little Eye and East of Gramborough Hill, Salthouse.

Deep mud with lugworms dominant.

Salt Holes, Holkham; Abraham’s Bosom, Wells; New Moon Pit and Arnold’s Marsh, Cley; Salthouse Broad.

Firm sand with Corophium dominant.

Arnold’s Marsh, Cley.

Submerged vegetation dominated by Ruppia and Enteromorpha.

Broadwater, Holme; Salt Holes, Holkham; Abraham’s Bosom, Wells; Half Moon Pit, New Moon Pit and Arnold’s Marsh, Cley; Salthouse Broad and West of Gramborough Hill, Salthouse.

No details currently available.

Snettisham Pits.

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Current factors affecting the habitat in Norfolk

There are a number of factors potentially affecting the conservation status of saline lagoons in Norfolk, including:

  • Phragmites encroachment;
  • Recreational use;
  • Coastal erosion;
  • Beach regrading;
  • Dehydration;
  • Cattle;
  • Hypertrophication.

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Current Action in Norfolk

Current action for saline lagoons in Norfolk includes:

  • The installation of a new sluice at Broadwater;
  • Measures to make the temporary lagoons at Little Eye permanent.
  • The development of a monitoring strategy for Snettisham Pits.

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Action Plan Objectivesand Targets

National

  • Maintain the current area (c.5,200 ha) of coastal saline lagoons.
  • Maintain the current number and distribution of coastal saline lagoons.
  • Maintain and improve, as necessary, the quality of coastal saline lagoons as measured by the retention of lagoonal specialist BAP Priority and Red Data Book species where these occur.
  • Create, by the year 2015, 120 ha of saline lagoon.

Norfolk

  • Maintain extent and condition of the existing lagoons consistent with the development of a naturally functioning coastline.
  • Create 5ha of new lagoon to make up for losses due to natural factors by 2010.

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