|IPA Factsheet - Colonsay|
Site Description Colonsay is an island in the Scottish Inner Hebrides, about 8 miles (13 km) in length and reaching 3 miles (4.8 km) at its widest point. Colonsay IPA comprises a string of three freshwater lochs extending around two miles, from north-east to south-west, across the centre of the Hebridean Island of Colonsay. Loch Fada is notable for its rich diversity of aquatic flora. Of particular interest are the rare Slender Naiad Najas Flexilis and six-stamened waterwort Elatine hexandra. Loch Fada is also designated as a Special Area of Conservation (SAC) on account of its importance for the slender naiad and otters, as well as for the quality of its freshwater habitat (specifically the lochs’ oligotrophic to mesotrophic standing waters). The Machrins is a dune system that lies on the west coast of Colonsay and is a designated IPA for stoneworts. The three lochs comprising Colonsay IPA have a low nutrient status and support rich assemblages of aquatic and fringing vegetation. Low nutrient level waterbodies are rare in the UK and are threatened due to their vulnerability to nutrient enrichment. Of the oligotrophic lochs occurring on the Hebridean Islands of Islay, Jura and Colonsay, Loch Fada is notable for its rich diversity of aquatic flora. The site includes areas of loch shore which are seasonally inundated. This inundation has led to the evolution of fen and wet meadow habitats which support diverse plant communities and good numbers of wildfowl and waders.
Botanical Significance BSBI VCR form: Baldellia ranunculoides. Also Nitella flexilis agg; Chara virgata. The Red Data Book listed slender naiad Najas flexilis, a species with a UK distribution restricted to north-west Scotland occurs extensively on the bottom of the central Loch Fada. Records for slender naiad Najas flexilis at Loch Fada date back to 1902, and its continued presence was confirmed as recently as 1999. It is the single known Colonsay locality for the species and is representative of the south-western part of the species’ range in Scotland. Colonsay is a hot spot for stoneworts with seven species recorded. Chara virgata and Nitella flexilis agg./Nitella opaca are scattered in lochs on the island, but the bulk of the diversity occurs at the Machrins. This dune system contains a number of flushes, pools and a small loch. Exposure to the west ensures some saline influence form windborn spray. Five species have been recorded recently, namely Chara aspera, C. contraria, C. hispida, C. virgata and C. vulgaris, whilst the nationally rare Tolypella glomerata has been recorded in the past and is most probably still present Stewart, N.F. (2004).
General Habitat Description
Conservation Issues Site condition monitoring carried out at Loch Fada in 2004 found The open water transition fen and vascular plant assemblage feature of Loch Fada were found to be in favourable condition (2004), however the oligotrophic loch feature of the site was concluded to be in unfavourable condition due to the presence of the invasive non-native species of waterweed Elodea nuttallii. The presence of the invasive non-native species Elodea nuttallii within Loch Fada is cause for concern as it may spread across the site and out-compete native plant species present within the lochs. The results of further site condition monitoring should determine whether continued monitoring of the spread of E. nuttallii is necessary or whether active management is needed to attempt to eradicate this species from the site. The threat of nutrient enrichment to the Loch comes mainly from fertiliser inputs to the surrounding agricultural land, although these are currently at low levels. Other pollution possibilities are domestic waste and aerial pollution. At present the levels are not causing concern and regular water chemistry monitoring will be established to ensure that any adverse trends can be detected and acted upon. The stonewort Chara vulgaris has been recorded from Balnahard Dunes at the north-eastern end of the island and there is an old record for Chara contraria from Kiloran Bay. Both of these systems may be worth further investigation Stewart, N.F. (2004).