North Atlantic area
Scotland -Orkney islands
Scotland is rich in freshwater and wetland habitats with its high rainfall and rugged, glaciated landscape. Clean water is an essential resource for people but is also vital to wild plants and animals; and wetland vegetation helps to maintain that water quality.
Scotland has generally high quality rivers and lochs. The condition of the water play an important role for Scotland biodiversity, health, enjoyment of countryside and economy.
From small ponds to the deep and mysterious Loch; from isolated lowland bogs to the vast Marshes, Scotland’s wet places support many important habitats and species. (1)
The reference sites selected in this macroarea are located in the Highlands, one of three Scotland’s regions. In particular, ecosystems are in the Orkney Islands.
Orkney (Scottish Gaelic: Arcaibh) also known as the Orkney Islands, is an archipelago in northern Scotland, situated 16 kilometres north of the coast of Caithness. Orkney comprises approximately 70 islands of which 20 are inhabited
From an administrative point of view, Orkney is one of the 32 council areas of Scotland.
The largest island is “Mainland” (area of 523.25square kilometers), relatively densely populated (75% of Orkney’s population) and has much fertile farmland. The island is mostly low-lying (especially East Mainland) but with coastal cliffs to the north and west and two sizeable lochs: the Loch of Harray and the Loch of Stenness.
In addition to the Mainland, most of the islands are in two groups, the North and South Isles.
The northern group of islands is the most extensive and consists of a large number of moderately sized islands, linked to the Mainland by ferries and by air services. Farming, fishing and tourism are the main sources of income for most of the islands. The centre of the island is moorland and the island’s main industries have been peat extraction and limestone quarrying.
The southern group of islands surrounds Scapa Flow. Hoy is the second largest of the Orkney Isles.
Glacial striation and the presence of chalk and flint erratics that originated from the bed of the North Sea demonstrate the influence of ice action on the geomorphology of the islands.
The islands are mainly low-lying except for some sharply rising sandstone hills on Hoy, Mainland and Rousay and rugged cliffs on some western coasts. The superficial rock ,that characterizes the islands, is almost entirely Old Red Sandstone, mostly of Middle Devonian age.
Nearly all of the islands have lochs, but the watercourses are merely streams draining the high land. The coastlines are indented, and the islands themselves are divided from each other by straits generally called “sounds” or “firths”.
The tidal currents, or “roosts” as some of them are called locally, off many of the isles are swift, with frequent whirlpools. The islands are notable for the absence of trees, which is partly accounted for by the amount of wind.
Orkney has a cool temperate climate that is remarkably mild and steady for such a northerly latitude, due to the influence of the Gulf Stream. (2)
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North Atlantic area Scotland -Orkney islands
Lagoons: General description and ecological characteristics
Lagoons may be clustered together on particular stretches of coasts, where they are dependent on local physical processes, such as sediment transport systems. Such clusters have been considered particularly important for the conservation of lagoon structure and function. Some lagoon types found in this area, are rare elsewhere in Europe. They are a priority habitat type.
The water in coastal lagoons can vary in salinity from brackish (owing to dilution of seawater by freshwater) to hypersaline (i.e. more salty than seawater as a result of evaporation). The plant and animal communities of lagoons vary according to the physical characteristics and salinity regime of the lagoon, and consequently there are significant differences between sites.
Although, compared to other marine habitats, there is usually only a limited range of species present, they are especially adapted to the varying salinity regimes of lagoons and some are restricted to lagoon habitats. The vegetation may include Fucus ceranoides, beds of eelgrass Zostera spp., tasselweed Ruppia spp., and pondweeds Potamogeton spp., or stoneworts such as foxtail stonewort Lamprothamnium papulosum. In more rocky lagoons, communities of fucoid wracks Fucus spp., sugar kelp Laminaria saccharina, and red and green algae are also found.
The fauna is often characterised by mysid shrimps and other small crustaceans, worms that burrow into the sediment, molluscs, and some fish species. Species that are particularly found in lagoons and consequently have restricted distributions in the UK include starlet sea anemone Nematostella
vectensis, lagoon sandworm Armandia cirrhosa, lagoon sand-shrimp Gammarus insensibilis and foxtail stonewort L. papulosum.
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 (Jackson and McLeod 2000).
- 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 lifespan due to natural processes of infilling and coastal erosion. - Percolation lagoons.
These are normally separated from the sea by shingle banks. Seawater entersby 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. - 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. - 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. - 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. (3)
References
- http://www.snh.gov.uk/
- http://en.wikipedia.org/wiki/Orkney
- Joint Nature Conservation Committee. 2007. Second Report by the UK under Article 17 on the implementation of the Habitats Directive from January 2001 to December 2006. Peterborough: JNCC. Available from: www.jncc.gov.uk/article17
- Roff, J.C., Taylor, M.E., 2000. National framework for marine conservation – a hierarchical geophysical approach. Aquatic conservation: marine and freshwater ecosystems, 10, 209-223
