Little Assynt Lochs Project Invertebrate Communities of a Gneiss Catchment Little Assynt Lochs Project 2010 Little Assynt Lochs Project Report for Culag Community Woodlands Trust By Caroline Bowes May 2011 Funded by the Sutherland Partnership Environmental Fund, which was supported by Leader and Scottish Natural Heritrage 2 Caroline Bowes: email - [email protected] Abstract The Little Assynt Lochs Project is a study of the aquatic ecosystem on the Little Assynt Estate. Existing ecological records relating to the estate have been sought out. These have been collected in a single spread sheet. A survey of several small lochs in one catchment on the estate has shown that the invertebrate assemblage of the aquatic ecosystem is not abundant, but is reasonably diverse. The members of invertebrate communities identified are mainly acid-tolerant, pollution-sensitive taxa, and as such are consistent with the flora, geology and land-use of the area. Figure 1: Little Assynt Estate Boundary and Deer Fence. Composite map compiled from Ordnance Survey map and data from SNH (Ordnance Survey of Great Britain) Estate Boundary -x-x-x-x Deer Fence Contents Abstract ...................................................................................................................................... 3 Introduction ................................................................................................................................ 5 Aims and Objectives .................................................................................................................. 5 Background ................................................................................................................................ 5 Management ........................................................................................................................... 5 Geology .................................................................................................................................. 6 Ecology................................................................................................................................... 6 Terrestrial ........................................................................................................................... 6 Aquatic ............................................................................................................................... 7 Desk Study ................................................................................................................................. 7 Lochs survey .............................................................................................................................. 9 Methods Used ....................................................................................................................... 10 Sample Point Selection .................................................................................................... 10 Sample collection ............................................................................................................. 10 Sorting, Fixing and Preservation of Samples. .................................................................. 11 Identification .................................................................................................................... 11 Results ...................................................................................................................................... 11 Loch Leitir Easaidh .......................................................................................................... 13 Loch na h-Innse Fraoich .................................................................................................. 20 `Lochan a’ Mhanaich ....................................................................................................... 27 Loch Torr an Lochain ...................................................................................................... 32 Loch 5 .............................................................................................................................. 35 Loch 6 .............................................................................................................................. 38 Summary of Data ................................................................................................................. 42 Taxa by Frequency of Appearance .................................................................................. 42 Species List ...................................................................................................................... 43 Fauna Distribution Charts ................................................................................................ 44 Interpretation of the results .................................................................................................. 47 Conclusion ............................................................................................................................... 49 Bibliography ............................................................................................................................ 50 Appendices ............................................................................................................................... 52 Appendix 1- Spread sheets containing ecological data sets relating to NC12 ..................... 52 Appendix 2 – Spread sheet containing data from Little Assynt Loch Survey ..................... 52 Little Assynt Lochs Project 2010 Introduction The Little Assynt Lochs Project was a study of aquatic habitats on the Little Assynt Estate. The Little Assynt Estate is owned and managed by the Culag Community Woodland Trust which has provided funding for the project. The remit of the projectwas to gather together and consolidate any accessible information from previous studies, whilst providing fresh information about aquatic ecosystems on Little Assynt from a baseline study of a group of lochs. All this information will be stored in a central data-base. The findings of the project will be used to inform future management of the estate and to support the objectives of the Sutherland Biodiversity Action Plan (2003). Aims and Objectives The Project had four objectives, as follows: 1. A desk study to track down and collate existing information. 2. Compilation of a data-base to store existing and future information. 3. A base-line survey of a group of lochs on the estate. 4. Production of a report evaluating the findings from the above. The aim of the project is to provide an accessible store of information about the aquatic ecosystems on Little Assynt and to provide a base-line from which future monitoring can be carried out. Background The Estate consists of around 1200 hectares of dry and wet heath, blanket bog and other communities, overlying the base rock of Lewisian gneiss, which is interspersed with dykes of basic and ultrabasic rock. These dykes take the form of linear ridges and trenches cutting through the landscape. Hollows in the Lewisian gneiss have filled with water, becoming lochs, while depressions in the overlying peat form smaller bog-pools. The resulting landscape is often referred to as “cnoc and lochan”. The underlying rock affects the fertility and composition of the soil and the area has a diverse flora. This consists predominantly of communities associated with nutrient poor acid soils, interspersed with areas of vegetation more often associated with mineral-rich soils. Management There is little evidence for settlement in the Little Assynt area in prehistoric times. This may be the result of its generally infertile, acid soils or it may be that the evidence for settlement has been obliterated. The area was settled and farmed from medieval times and evidence for that can be seen around the estate in the form of sheilings, occasional ruined buildings and remnants of lazybeds. Land-use changed at the time of the clearances in the early 19th century. From this point onwards the area was used primarily for sheep grazing. Some form of woodland management appears to have been practised on the estate prior to the clearances. Evidence for this lies in trees with the characteristic growth pattern of pollards. (Noble & Bangor-Jones, 2005). The Little Assynt Estate was purchased by the Culag Community Woodland Trust in November 2000 (CCWT). Culag Community Woodland Trust is a charity set up in 1995 to promote and manage local woodlands for the community. Since coming 5 Little Assynt Lochs Project 2010 under the management of the CCWT a large part of the estate has been enclosed within a deer fence. This has resulted in two very different habitats, one in which the natural vegetation is kept cropped by deer and one in which natural regeneration occurs unhindered. The two areas show some marked contrasts. Extensive tree planting has also been carried out using native species and a network of footpaths has been constructed. Geology The base rock at Little Assynt is Lewisian gneiss. This is around 3000 million years old, formed by metamorphosis of the parent rock by heat, pressure and folding during a period of tectonic instability in the Precambrian period. Lewisian gneiss is a hard, often acidic rock, providing few nutrients to the overlying soil. The Lewisian gneiss on the Little Assynt Estate is interrupted by dykes composed of comparatively mineral-rich basic and ultrabasic rock. These dykes consist of magmatic material which intruded into fissures in the Lewisian