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Layer: Coastal Lagoon (ID: 13)

Parent Layer: Conservation Objectives Habitats

Name: Coastal Lagoon

Display Field: datasetName

Type: Feature Layer

Geometry Type: esriGeometryPolygon

Description: <metadata></metadata> <keywords> life science, ecology</keywords> Coastal lagoons are areas of shallow, coastal salt water, wholly or partially separated from the sea by sandbanks, shingle or, less frequently, rocks. Lagoons show a wide range of geographical and ecological variation; five main sub-types have been identified in the UK, on the basis of their physiography, as meeting the definition of the Annex I habitat type. 1. Isolated lagoons. These are separated completely from the sea or estuary by a barrier of rock or sediment. Seawater enters by limited groundwater seepage or by over-topping of the sea barrier. Salinity is variable but often low. Isolated lagoons are often transient features with a limited life-span due to natural processes of infilling and coastal erosion. 2. Percolation lagoons. These are normally separated from the sea by shingle banks. Seawater enters by percolating through the shingle or occasionally by over-topping the bank (e.g. in storms). The water level shows some variation with tidal changes, and salinity may vary. Since percolation lagoons are normally formed by natural processes of sediment transport, they are relatively transient features, which may be eroded and swept away over a period of years or decades or may become infilled by movement of the shingle bank. 3. Silled lagoons. Water in silled lagoons is retained at all states of the tide by a barrier of rock (the sill). There is usually little tidal rise-and-fall. Seawater input is regular (i.e. on most tides) and although salinity may be seasonally variable, it is usually high, except where the level of the sill is near to high tide level. These lagoons are restricted to the north and west of Scotland and may occur as sedimentary basins or in bedrock (where they are called oban). Muddy areas are dominated by filamentous green algae, amongst which may be colonies of rare charophytes, such as foxtail stonewort Lamprothamnium papulosum. There may be beds of tasselweed Ruppia spp. and, in the deeper most stable lagoons, eelgrass Zostera marina. 4. Sluiced lagoons. Sluiced lagoons are formed where the natural movement of water between the lagoon and the sea is modified by artificial structures, such as a culvert under a road or valved sluices. Communities present in sluiced lagoons vary according to the type of substrate and salinity, but may resemble those of silled lagoons. 5. Lagoonal inlets. Seawater enters lagoonal inlets on each tide and salinity is usually high, particularly at the seaward part of the inlet. Larger examples of this sub-type may have a number of different basins, separated by sills, and demonstrate a complete gradient from full salinity through brackish to freshwater. This salinity gradient significantly increases the habitat and species diversity of the sites in which it occurs.

Definition Expression: N/A

Copyright Text: National Parks and Wildlife Service

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