Saline 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 seawater at low tide and may develop as brackish, full saline or hyper-saline water bodies.
Saline lagoons are an important and relatively scarce habitat due to the special conditions that are required for their formation. They support unique invertebrates, such as the lagoon cockle and ostracods, and are important for waterfowl, marshland birds and seabirds. The presence of certain indigenous and specialist plants and animals make this habitat important to the UK's overall biodiversity and has led to the listing of saline lagoons as a priority habitat under the EU Habitats Directive.
Kent has a high proportion of the national saline lagoon resource. There are currently 242 hectares of saline lagoons in Kent, which represents 16% of the total resource for England (total English resource is 1,474ha, according to English Nature's inventory primarily undertaken in 1992). The largest areas are at Cliffe Pools (142ha) and Murston (46ha).
The majority of Kent's saline lagoon resource is on the landward side of hard sea defences. These lagoons depend on continued saline influence through overtopping, leaky sluices and saline intrusion, and would be threatened if improvements to sea walls reduced these inputs. Realignment of sea walls could also reduce the extent of the habitat, or lead to changes in quality. These changes may be offset by the development of new habitat in front or behind the realigned defences. However, any realignment at the larger sites (Cliffe and Murston) would probably result in the loss of a larger area of the habitat than would reform naturally.
Pollution, in particular nutrient enrichment leading to eutrophication, can have major detrimental effects. Nutrient inputs can come from sewage discharges, agricultural run-off or industrial sources.
Artificial control of water (sea and fresh) to lagoons can have profound influences on the habitat. Changes to the salinity regime can result in changes to the communities of species that survive in the lagoon.
Lagoons may be lost to infilling as part of anthropogenic impacts from coastal development.
Lagoons may suffer from natural degradation, if they are not managed, including gradual infilling with sediment and encroachment with vegetation.
Coastal flood management and climate change – Changes to the management of coastal sea defences could alter the extent or quality of Kent's saline lagoon resource. Sea level rise, due to climate change, may pose a threat to existing lagoons where sea walls start to overtop more frequently and alter the salinity regime, or where realignment of defences is considered that would result in the loss of lagoons. Realignment in areas currently without lagoons may also result in opportunities to create new lagoons as part of the sustainable management of the coast.
- The majority of saline lagoons in Kent are designated as Sites of Special Scientific Interest (SSSIs). Public bodies (eg. EA, local authorities, water companies) have a duty to conserve and enhance SSSIs when carrying out their functions.
- The saline lagoons in Kent that are not SSSIs, at Barton Point Coastal Park and Cuxton, are Local Wildlife Sites (SNCIs).
- Westminster Dredging and RSPB are working in partnership to use dredged material to restore the lagoons at Cliffe Pools to a more natural profile and shallower depth. This will benefit lagoonal specialist invertebrates along with breeding bird species.
- English Nature's Saline Lagoon Habitat Inventory (available on their website www.english-nature.org.uk) has mapped Kent's saline lagoon resource in electronic format, and also records various physical and chemical data.
To maintain the extent of saline lagoons in Kent.
To achieve condition for existing saline lagoons through appropriate management.
To restore and enhance neglected saline lagoons
To create/expand areas of saline lagoon.