Site Code
Country: United Kingdom
Central coordinates: 58.99075275o [58o 59' 26" North], -3.11206982o [3o 6' 43" West]
Administrative region: Scotland Northern Isles (Orkney)
Area: 2906 ha
Altitude: 0 - 133
Site Description
Loch of Harray and Loch of Stenness
The two largest lochs in Orkney form an important natural heritage site. Harray Loch drains a shallow basin in the centre of the West Mainland. Its waters flow into the Stenness Loch, the largest brackish lagoon in the UK, through a narrow channel at Brodgar, which in turn is open to the sea at the Brig O’ Waithe. The waters of the lochs range from marine at the seaward entrance of Stenness to freshwater in Harray with variability between marine and freshwater within Stenness itself. The associated flora and fauna is diverse comprising predominantly brackish and marine species in Stenness and freshwater species in Harray, with a transition zone in the vicinity of the Bridge of Brodgar.
Both lochs provide an important wintering ground for a wide variety of wildfowl, including Pochard (Atteal), Tufted Duck, Scaup and Goldeneye (Gowdie Duck). A very rare caddis fly Triaenodes reuteri, previously recorded only in Kent, Essex and Yorkshire is found in the loch. It is also the only Scottish home for the snail Theodoxus fluviatilis commonly found in the calacareous rivers of England.
Loch of Isbister and the Loons
Loch of Isbister and the Loons are located on the west mainland, between Marwick and Twatt, in the parish of Birsay. The site is a wetland site of national importance for its botanical and ornithological interest. The Loch of Isbister and the Loons has developed into Orkney’s best basin-mire complex as peripheral vegetation has encroached into the open water of Loch of Isbister and is internationally important as a high quality example of a nutrient rich water body.
The rich habitat provides a nationally important breeding ground for a range of birds including: wigeon Anas Penelope, mallard Anas platyrhynchos, teal Anas crecca, tufted duck Aythya fuligula, red breasted merganser Mergus serrator, shoveler Anas clypeata and shelduck Tadorna tadorna. The site is also notified for its nationally important breeding population of pintail, supporting on average 6% of the British population. The site is used by an internationally important number of otters.
Stromness Heaths and Coasts
This part of the west coast of Orkney is important for coastal geomorphology, providing the best examples of the distinctive sandstone and flagstone cliffs and associated features of Orkney. At Yesnaby and Gaulton good examples of cliff sections of the Lower Old Red Sandstone Yesnaby Group and the Middle Old Red Sandstone Flagstones are exposed, separated by an intervening unconformity. This is important evidence of the regional relationship between these two sets of Devonian sediments typical of the Orcadian basin. The south Stromness coast is the best section through the lower part of the Middle Old Red Sandstone (Stromness Flagstone Group), showing very diverse lake and playa basin sediments.
Botanical Significance
Noted for stoneworts, habitat and vascular plants interest.
Loch of Harray and Loch of Stenness
Harray Loch is important for its large number of Potamogeton (pond weed) species (9), three of which, P. filiformis, P. praelongus and P.friessi are nationally scarce. This assemblage is unusual, representing a broad spectrum of nutrient requirements.
Loch of Harray and Loch of Stenness are sites of European importance for stoneworts (Stewart, 2004). Loch of Stenness is connected to the sea through a narrow channel and is brackish: stoneworts were confined to the parts of the loch most remote from the sea connection, where the salinity is lower. Three rare brackish species have been recorded; Chara baltica, Chara canescens, and Tollypella nidifica. Only T. nidifica has been confirmed in recent years, present as a small population in the Bay of Voy in 1994, here in one of its only three British sites, but not re-found subsequently. The salinity of the site has increased since the 1920s when the other species were recorded, possibly die to higher tides resulting from the building of the Churchill Barriers across the eastern entrances of Scapa Flow. It may now be too brackish for stoneworts (Stewart, 2004).
Loch of Harray, which is separated from loch of Stenness only by a valved culvert, is freshwater and contains five stonewort species (Chara aspera, C. curta, C. contraria, C. virgata and Tolypella glomerata), although two others (Chara baltica and C. globularis) have not been confirmed recently. Extensive beds of slender stonewort species, particularly Chara contraria are found in the deeper water and strong populations of nationally scarce Chara curta in the shallows at the southern end (Stewart 2004).
Loch of Isbister and the Loons
This site is Orkney’s best example of a basin fen and sits in a shallow natural basin, fed by burns and springs. Over thousands of years, vegetation has gradually encroached on the Loch of Isbister and formed a range of habitats, including peatland. Relatively small differences in water levels and soil fertility across the site favour different plant species and give rise to the complex mosaic of vegetation that characterises the site today. The site in particular contains excellent examples of vegetation that forms on the margins of lochs. The mosaic of habitats supports a very rich variety of wetland plants, including autumnal water-starwort Callitriche hermaphroditica, slender-leaved pondweed Potamogeton filiformis, the regionally scarce fragrant orchid Gymnadenia conopsea and abundant stoneworts (Chara aspera, C. contraria, C. curta, C. globularis,C. virgata and C. vulgaris).
Stromness Heaths and Coasts
Along the clifftops, extreme exposure to wind and salt spray has produced some of the best and most extensive areas of maritime grassland and maritime heath anywhere in the UK. Red fescue Festuca rubra, thrift Armeria maritima, spring squill Scilla verna and sea plantain Plantago maritima are just some of the plants that carpet the maritime grassland. The site is also a Special Area of Conservation because of its internationally important coastal vegetation. In places where cliff-top communities are strongly influenced by the sea, species such as sea plantain and thrift are co-dominant. These cliff-top communities grade into mosaics of maritime heath and grassland. The heathland is the largest area of of the distinctive northern lichen-rich maritime European dry heaths in the UK. The coastal heath is often rich in species and is dominated by dwarf shrubs such as common heather Calluna vulgaris, bell heather Erica cinerea, an unusual maritime form of crowberry Empetrum nigrum. and creeping willow Salix repens, along with lichens, a variety of grasses, sedges and wildflowers such as mountain everlasting Antennaria dioica and wild thyme Thymus serpyllum. The seaward transition to maritime grassland includes herb-rich sedge dominated vegetation. The nationally scarce Scottish primrose Primula scotica thrives locally in this maritime heathland and grassland mosaic. The largest Primula scotica colonies occur near Yesnaby.
There is a natural landward transition from the more maritime plant communities into areas of wind-pruned acidic heath. Heathland away from the zone of maritime influence is naturally less species-rich. Throughout the heathland there are base-rich flush and mire communities which support a wide range of grasses, sedges and flowering plants.
Loch of Banks
The area is rich in nutrients and supports a wide variety of wetland plants, including a large stand of reeds, willow scrub, creeping willow Salix repens, sedges, bog-rush Juncus effusus, yellow flag iris Iris pseudacorus, branched bur-reed Sparganium erectum and meadow sweet Filipendula ulmaria.
Management guidance notes
Loch of Isbister/Loch of Stenness
Loch of Stenness
Stromness Heaths and Coast
Notes
None