Saline Lagoons

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Saline Lagoons

1. Habitat Definition

Saline lagoons are essentially bodies of saline water, either natural or artificial, that are partially (but not completely) separated from the adjacent sea. Typically they lie adjacent to the sea and are separated from it by a shingle or sandy beach or sand dune system through which sea water either percolates or infiltrates through a narrow channel; these are known as 'true' lagoons. Other types of lagoon may be created as ponded waters in depressions on soft sedimentary shores or in depressions separated from the sea by a rocky shore or artificial construction such as a sea wall. Old coastal gravel pits frequently become brackish through sea water percolation (often via drainage ditches) and these also qualify as saline lagoons. In the wider sense, such brackish drainage ditches should also be regarded as linear saline lagoons. Sea water exchange in saline lagoons may occur through a natural or artificial channel or by percolation either through or over the sand/shingle barrier. They retain a proportion of their sea water at low tide and, depending on the extent of sea water infiltration and the amount of fresh water input from ground and surface water sources, they may develop as brackish, fully saline or hyper-saline water bodies. Salinity levels often vary within a lagoon; for example a lagoon may be fully saline adjacent to its connection with the sea but largely fresh water adjacent to a stream inflow at the other end. Saline lagoons generally contain soft sediments, which support filamentous green and brown algae and often charophytes and tassel weeds as well. They are important for their invertebrate fauna, which can be divided into essentially freshwater species, brackish/marine species and lagoon specialists. In addition, the habitat is important for birds, particularly waders, wildfowl and some seabirds such as gulls and cormorants.

2. Current Status and Distribution [top]

Saline lagoons are a nationally rare habitat type and are listed on Annex 1 of the EC Habitats Directive as a habitat of international conservation importance; it is estimated that they cover just 5% of the European coastline, though in global terms they cover some 1 3%. In England the total area of saline lagoons is some 1300 ha with 450 ha being occupied by a single site (Chesil Fleet in Dorset). In Sussex, saline lagoons cover a total of 69.57 ha (183.86 ha including the additional pits at Rye Harbour and Pett - see below) of which 55.27 ha (134.82 ha) is protected by SSSI and/or LNR status and 17.7 ha is defined as 'true' saline lagoon (after Barnes 1988). Table 1 lists the saline lagoons in Sussex. According to Smith & Laffoley (1992) the gravel pits at Rye Harbour (with the exception of Ternery Pool) and the Crumbles, and the pools at Pett Levels, are freshwater and do not qualify as saline lagoons. However, Barry Yates (manager of Rye Harbour LNR) has confirmed that all the pits at Rye Harbour, plus the Pert Level pools have some level of salinity due to sea water inflow and should therefore all be included as saline lagoons.


Saline Lagoons

3. Importance of the Habitat [top]

3.1 Biological

Saline lagoons are important for both the plant and invertebrate communities they contain, some of which are reliant on this habitat. In addition there are a few plant species which are lagoon specialists. Bamber et al (1991) estimated that there are 40 known specialist lagoon species in Britain. Recent developments have shortened this list somewhat and those species that are currently thought of as lagoon specialists are listed in Appendix 1. Of particular note in the county context are Ivell's sea anemone Edwardsia ivelli, which is known only from Widewater in West Sussex and which may now be extinct, starlet sea anemone Nematostella vectensis and tentacled lagoon worm Alkmaria romijni, which occur at Slipper Mill and Peter Ponds (the former also used to occur at Pagham Lagoon but may now be extinct there), and lagoonal sand-shrimp Gammarus insensibilis which is found at Birdham Pool and Thorney Great Deep. Another globally rare hydroid Clavopsella navis, only occurs at Widewater in the UK (this species is no longer regarded as a true lagoon specialist). Ivell's and starlet sea anenomes, and lagoonal sand-shrimp are also legally protected under Section 5 of the Wildlife & Countryside Act (1981).

Beaked Tasselweed Ruppia maritima used to occur commonly in Widewater; it had more or less disappeared by the 1970s but 3 small clumps were found in a small area of the lagoon in 1997 (Irving 1997) indicating a partial recovery. This is a species which would normally indicate a healthy lagoon. Since 1985, Widewater has been dominated by mats of the green alga Cladophora sp., which could indicate eutrophication of the site although in this case it is probably also a result of falling water levels in the lagoon. The rare foxtail stonewort Lamprothamnium papulosum occurs in Thorney Great Deep.

Table 1 List of saline lagoons in Sussex (* 'true lagoon' )

Pett Pool I

Pert Pool 2

Pett Pool 3

Pett Pool 4

Horseshoe Pool

Winchelsea Beach Pond
Percolation pool

Nook Drain

Long Pit

Narrow Pit

*Rye Harbour Lagoon, (Ternery Pool)
Percolation pool


Wader Pool
Sluiced pond

Northpoint Pit
part SSSI

Northpoint Pit (small)

Camber Pit 1

Camber Pit 2

Camber Pit 3

Scotney Court
borders SSSI

Hooe Level Ponds, Pevensey Levels
Isolated lagoon

Norman's Bay Lagoon, Pevensey levels
Sluiced pond
TQ 690058

Newhaven Tide Mills
Sluiced pond
TQ 459002

Ox-bow Lake,
Sluiced pond
TV 517990

Cuckmere Haven

Tidal Pool, Cuckmere Haven
Sluiced pond
TV 516979

The Scrape, Cuckmere Haven
Sluiced pond
TV 518977

Brighton Marina Undercliff Lagoon
Sluiced pond
TQ 340033

Percolating pool
TQ 200042

*Little Spit Lagoon, Pagham Harbour
Percolating pool
SZ 882962

*Pagham Lagoon
Percolating pool
SZ 884970

*Church Norton Shore Lagoons (The Severals), Pagham Harbour
Percolating pooi
SZ 873947

Saltmarsh Channel Lagoon, Pagham Harbour
Sea inlet
SZ 855963

Sidlesham Ferry. Pagham Harbour
Sluiced pond
SZ 855964

Birdham Pool
Sluiced pond
SNCI (50% of it)
SU 825010

Slipper Mill Pond, Emsworth
Sluiced pond
SU 753056

Peter Pond, Emsworth
Sluiced pond
SU 753058

Saline lagoons are also important for the birds (especially waders, wildfowl and seabirds) which use them as feeding and roosting sites. Locally breeding ringed plover use the shallows and margins of saline lagoons for feeding and a wide variety of migrating waders also feed in the invertebrate-rich margins and shallows. Dunlin, redshank and ringed plover regularly feed in Widewater and the Newhaven Tide Mills and the last species also breeds on the adjacent shingle at these sites. Deeper lagoons also support dabbling and diving ducks in winter and on migration and gulls use them as roosting sites. In hard weather and during storms, lagoons may also be used by sea duck, grebes and divers. Saline lagoons are often separated from the sea by sand dunes or vegetated shingle which are important habitats in their own right.

3.2 Geological and Geomorphological

Many saline lagoons are former river tributaries which become separated from the main river by the natural movement of coastal shingle, through the process of longshore drift, thus becoming isolated shingle spit lagoons. This is the favoured theory for the formation of Widewater (although some believe that it is an artificial lagoon, or borrow pit, created in the 19th century in order to build a landward sea defence prior to drainage of the marsh land to the north). Thus the coastal process of longshore drift appears to have been primarily responsible for the formation of the natural lagoons of Widewater, Ternery Pool, Little Spit Lagoon, Pagham Lagoon and The Severals, although the main geological importance is generally in the shingle barriers rather than in the lagoons themselves.

4. Importance for the People, Local Community and Cultural Significance [top]

Saline lagoons are often visited by birdwatchers due to the special bird species they attract. Widewater also attracts walkers, joggers and cyclists, while Newhaven Tide Mills attracts walkers and people using the adjacent beach. Birdham Pool and Slipper Mill Pond and Peter Ponds are also readily accessible and heavily used by the adjacent residents, other local people and visitors. A recent survey at Widewater showed that most local people use the area for exercise (walking, jogging and cycling) with birdwatching being the second most popular activity. This survey also showed that over half of the people surveyed wanted Widewater to be maintained as a natural resource, in recognition of its natural value (although a quarter of those surveyed most of them youngsters, wanted to see it developed as a recreational facility). Slipper Mill Pond and Peter Pond attract many visitors to the town of Emsworth, which generates additional revenue for the town.

On a less positive note lagoons frequently become polluted, often with resulting eutrophication, and are also frequently used as unofficial rubbish dumps. This detracts from both the scenic and the biological value.

5. Benefits to Local Economy

Certain lagoons in Sussex attract large numbers of visitors. In particular, Rye Harbour attracts many people from outside the area (up to 10,000 a year) many of whom visit the hide overlooking Ternery Pool. This benefits the local economies of Rye Harbour, where people park their cars, and of Rye itself. As already discussed, Widewater attracts many visitors, although most of these (with the exception of birdwatchers) are actually visiting the beach and adjacent footpath rather than the lagoon itself.


Saline Lagoons

6. Trends and Threats [top]

6.1 Trends

Saline lagoons are a rare habitat in Britain and Europe and are also highly transient features, at least in geological terms. Barnes (1980) considered that most natural lagoons would last for less than 1 000 years. Due to coastal processes, the shingle beach and sand dune barriers tend to move inland, gradually encroaching on the lagoon behind them. Over time this will result in the infilling of the lagoon, hence their geologically short lifespan. If there is development on the landward side of the lagoon then this process may be accelerated as there is no room for any landward extension of the lagoon. Lagoons may also be destroyed by severe storms breaching the natural barrier and creating a bay. However, the lagoons in Sussex do not appear to be under immediate threat from this process as the natural barriers are quite extensive and are also monitored and maintained by the Environment Agency as part of their coastal defence work. Many lagoons are very shallow and if they are only slightly saline, natural succession ~vi]l ultimately coIlvert them to fen carr or reed swamp. Thus there is a natural tendency for saline lagoons to be destroyed over time. Under natural conditions, this loss would be compensated for by the formation of lagoons in other areas. However, along the heavily built up Sussex coastline the scope for natural creation of lagoons is extremely limited. Therefore the long term trend will be for saline lagoons to gradually disappear from the Sussex coastline.

However, saline lagoons can be created artificially with good examples in Sussex being the 'scrape' on the eastern side of the Cuckmere Haven and the wader pool at Rye Harbour. The 'scrape' in the Cuckmere was specifically created as a lagoon and could be used as an example of how lagoons can be created in the area to compensate for the artificial and natural losses that are occurring. There is considerable potential for the creation of further artificial lagoons at Rye Harbour.

Saline lagoons have a tendency to become eutrophic over time, primarily due to pollution (as at Widewater), and this will disrupt the delicate ecosystem of the habitat. Pollution may be carried in the water supply to the lagoon (for example leaching of agricultural runoff) or be inputted directly (for example sewage and rubbish). The problem is compounded at Widewater as there is no outflow and pollutants therefore accumulate in the lagoon.

6.2 Threats

Pollution and development are the main threats to the saline lagoons occurring in Sussex. Most of the information on pollution has come from Widewater, but much of it is applicable to other Sussex lagoons. At Widewater, heavy metals have entered the lagoon as a result of sewage from nearby sea outfalls percolating through the shingle bank in the seawater, and also directly from the dumping of refuse such as old paint tins (Everett 1993). It is thought that some of the pollution here may be from coal waste used to build up the sea defence in the post-war period. Runoff of pesticides from adjacent gardens and dog-fouling along the shore are two other sources of pollution at Widewater. Pollution of Widewater has been estimated as moderate with the most serious threat coming from direct dumping of items such as oil and paint cans; even minute quantities of contaminants such as oil and paint, directly inputted, may prove lethal to the flora and fauna of lagoons as they are quite enclosed ecosystems with limited and slow water exchange. The number of specialist lagoon species at Widewater declined by 50% between 1931 and 1993 (Everett 1993).

Development is a threat to some of Sussex's lagoons. Although many of them lie within protected sites such as the Rye Harbour and Pagham Harbour Local Nature Reserves, the Newhaven Tide Mills are under continuing threat from development along the northern shore. Widewater has been a LNR since 1997, but designation as a SSSI (once conditions there are appropriate) would add further protection to this site. Slipper Mill Pond and Peter Pond at Emsworth have been threatened by development schemes to drain surface water from nearby housing estates through them. One such attempt has been resisted, but another is now in progress. These are not protected sites (they are SNCIs) and legal protection would help to prevent such schemes from being approved.

Sea defence works often interrupt the natural process of longshore drift, upon which the natural formation of lagoons in Sussex is dependent. Ironically, sea defences may therefore also protect some natural lagoons by preventing this same natural process which would ultimately destroy them.

Sea level rise is also a potential quite serious threat to lagoons. Relative sea level rise is currently estimated to be at least 6mm per year along this stretch of coast (3 mm due to sea level rise and 3 mm due to land sinking) and as it is estimated that about 120 ha (or 10%) of England s saline lagoons will be lost to sea level rise in the next 20 years or so (figures from the National Saline Lagoon HAP), this has serious implications for those in Sussex. Global warming and climite change is also likely to have an effect on this delicate ecosystem, although it is not fully known what this might be.

7. Potential [top]

The creation of the scrape at Cuckmere Haven and the wader pool at Rye Harbour has shown that there is potential for creating artificial saline lagoons along the Sussex coast. Maximum use should be made of this potential, especially considering that there is little chance of saline lagoons forming naturally along the Sussex coast, due to the various coastal defence schemes and heavy development. Suitable areas for lagoons should be identified with a view to creating as much of this habitat as possible, providing that doing so does not threaten or compromise other important natural habitats.

There is also potential for improving the quality of existing lagoons, for example by ensuring that suitable water levels are maintained and pollution affecting the sites is dealt with and eliminated. The current situation at Widewater has shown that minimising pollution and ensuring adequate water levels are essential in maintaining saline lagoons in a healthy state.

8. Current Action [top]

8.1 Site Protection

Most of the saline lagoons in Sussex are protected by their SSSI and/or LNR status. Newhaven Tide Mills, Brighton Marina, Birdham Pool, Slipper Mill Pond/Peter Pond at Emsworth and some of the gravel pits in the Camber area are the only lagoons which currently have no protection. Although it has been a LNR since 1997 and despite being the county's most important lagoon (at least historically), Widewater is currently not in a good enough condition to qualify for designation as a SSSI. The problems at Widewater are being addressed (the water levels are currently significantly higher than they were in the drought years of the late 1980s) but it may still be some time before Widewater improves sufficiently to meet the criteria for designation as a SSSI. Peter Brett Associates have recently completed a hydrological investigation of Widewater, on behalf of the Environment Agency and English Nature, which has resulted in several recommendations for improving the state of the lagoon. The most suitable of these are currently the subject of a feasibility study by the Environment Agency.

8.2 Site Management

A management plan for Widewater was produced in 1993, but it has only been partly implemented. This has recently been updated however. The lagoons within Pagham Harbour and Rye Harbour should have specific management guidelines drawn up as part of the LNR management plans if this has not been done already. Site Management Statements produced for landowners by English Nature may also be used to guide management for any lagoons within SSSIs which are under private ownership.

9. Existing Agri-environment Schemes [top]

No agri-environment schemes are available for this habitat. However, such schemes are available for scrape creation, which can be used to create new lagoons.

10. Objectives [top]

The national objectives, taken from the National Saline Lagoon HAP, are as follows:

a The current number, area and distribution of coastal lagoons should be maintained and enhanced. There are at present some 5200 ha of known saline lagoonal habitats in the UK.

b Create, by the year 2010, sufficient lagoonal habitat to offset losses over the last 50 years. It is considered that even with a great deal of effort it will be possible to produce only very indicative figures of losses over the last 50 years. Instead it should he accepted that there has been some loss during this period and to focus on creating new habitat, using the target of 120 ha referred to herein (the amount of habitat which it is estimated will be lost from 1992-2022 as a result of sea level rise). If any figures were to be obtained there should be an attempt to distinguish between losses due to natural processes and due to human activities.

c Recent evaluations estimated that 38 English lagoons were lost in the latter half of the 1980s (this is an estimate which should be taken as an indication of the fact that saline lagoon habitat has been lost over the last 50 years). In 1992 the creation of at least 120 ha of lagoon habitat over the following 20 years was considered attainable and necessary within England just to keep pace with projected losses. It is considered that this figure should be used as the target for creation of new saline lagoon habitat to offset previous losses. Future losses should be compensated for where feasible as and when they arise, creating new habitat as near to the original site as possible.

The key Sussex objectives are:

  1. To prevent net loss of lagoon habitats caused by development or land reclamation.
  2. To allow natural formation/evolution of lagoons wherever possible.
  3. To maintain water quality and quantity and eliminate pollution from all sources, and to maintain the biodiversity interest in all lagoons.
  4. To determine the hydrology of all the lagoons of Sussex, to enable appropriate management techniques to be applied.
  5. To identify areas for lagoon creation and restoration, including during flood defence projects.
  6. To manage the recreational use of lagoons. including the use of zoning. to minimise disturbance to wildlife.
  7. To increase public awareness and appreciation of this important habitat, for example through interpretation boards at targeted lagoons and the involvement of local people in managing lagoons.


11. Targets and Costs [top]

11.1 Targets

  • All significant areas of saline lagoon should be formally protected by the end of 2001.
  • All protected areas of saline lagoon should have a written management statement/management plan by 2003 (including any that only have SNCI status).
  • A hydrological survey of Widewater should be completed by April 2000, with a view to providing recommendations on how to maintain appropriate water levels at the site. (This has now been completed).
  • Widewater lagoon should meet the criteria for designation as a SSSI by2003.
  • Create 10 ha of saline lagoon habitat in Sussex by 2010.
  • Ensure that all significant lagoons in Sussex have been mapped and surveyed for lagoon specialist species by 2003.

11.2 Costs

Hydrological survey of Widewater (already done) £4000

To implement the recommendations of the Widewater hydrological survey £10,000

Create 5 ha of saline lagoon by 2010 £10,000

Survey and map lagoons £13,000

N.B. All these are rough estimates and will no doubt be modified as the HAP is implemented.

12. Action Plan [top]

The Species Action Plan for Ivell's sea anenome, drawn up by the UK Biodiversity Group, recommended surveying Widewater by 1998 to determine whether this species still survives there. This was done, with negative results, but the surveys were not very intensive (the main one was over two days in September 1997) and it is felt that ongoing survey/monitoring work should take place over the next five years to give a clearer picture of this species' status.


13. Monitoring and Review [top]

This Habitat Action Plan will be monitored annually by English Nature (Sussex & Surrey Team) in conjunction with the Sussex Biodiversity Partnership, with a full review carried out at five year intervals. Monitoring will include checking up on the implementation by the relevant Lead Agency of the Action points identified in the Action Table.


14. References [top]

Folkestone to Selsey Bill Natural Area Profile, 1998 English Nature.

Coastal Vegetated Shingle Habitat Action Plan, 1999 Sussex Biodiversiry Partnership

UK Biodiversity Group Tranche 2 Action Plans ,Vol. V maritime species and habitats, 1999

English Nature

Bamber, R.N., Batten, S.D., Sheader, M. & Bridgewaer, N .D. (1992) On the ecology of brackish water lagoons in Great Britain. Aquatic Conservation 2: 63-94

Barnes, R.S.K. (1980) Coastal Lagoons. Cambridge University Press, Cambridge.

Barnes, R.S.K. (1988) The coastal lagoons of Britain: an overview. Nature Conservancy Council CSD report No 933

Bratton, J.H. (1991) British Red Data Books: 3. Invertebrates other than insects. Joint Nature Conservation Committee

Downie, A.J. (1996) Saline Lagoons and Lagoon-like Saline Ponds in England. English Nature Science No 29

Everett, S. (1993) Widewater Lagoon Management Plan. Eiiglish Nature Science No 16

Irving, R.A. (1997) Survey of Widewater Lagoon, Lancing, West Sussex, 16 & 17

September 1997. WorldWide Fund for Nature, UK

Shirt, D.B. (1987) Red Data Books: 2. Insects. Nature Conservancy Council

Smith, B.P. & Laffoley, D. (1992) A directory of saline lagoons and lagoon like habitats in England, 1st edition. English Nature Science No 6

15. Consultation [top]

The following were consulted during the preparation of this Habitat Action Plan: Phil Griffiths (Environment Agency), Sarah Dawkins (RSPB), Graham Roberts & Neil

Mitchell (West Sussex County Council), Alex Tait (East Sussex County Council), Matthew Thomas (Brighton & Hove Unitary Authority), Barry Yates (Rye Harbour LNR, ), Rob Carver (Pagham Harbour LNR), Henri Brocklebank & Don Baker (Sussex Wildlife Trust), Paul Gilliland (EN Maritime Team), Anne de Potier (Chichester Harbour Conservancy), Robert Irving, Vic Howard (Friends of Widewater Lagoon), Dr. Y.R. Fares (University of Surrey), Martin Sheader (University of Southampton), Brian Banks (EN Kent Team), Ian Pearson (EN Hampshire team).

16. Appendices [top]