Trip reports
Indoor Meeting: RSPB LOCH OF STRATHBEG RESERVE
RSPB Image
Tuesday, 3 March 2009
A variety of waterfowl uses the loch, including Shoveler, Teal and Goldeneye: Pochard numbers are smaller than formerly with about sixty birds. Mute Swans stay on the loch to moult while Whooper Swans spend the winter there.
The catchment area of the Savoch Burn is agricultural land. In 1820 the burn was canalised so that it ran in a straight line into the loch. The water quality in the loch has deteriorated as the burn carried silt, nitrates and phosphates, forming eighty percent of the pollution of the loch. The water is a green-tinged, turgid mess of microscopic algae which does not provide nutriment for birds. So the ecosystem of the loch lacks vegetation on which birds can feed. Islands - which provide nesting sites - in the loch have disappeared, nine in 1950 being reduced to three in 2004. Uncontrolled water levels led to excessive flooding. The wet fen, with invasive rushes and woody scrub, was a habitat unfavourable for birds.
To improve the reserve a number of remedial measures were identified. To upgrade the water quality it would be necessary to slow the flow of the Savoch Burn into the loch. This was achieved by diverting the burn into a wide, shallow channel running through an extensive reed bed so that water could just flood out amongst the reeds. In this meandering channel the burn deposited silt and nutrients, removing both before reaching the loch. In the loch an island was to be stabilised and enlarged as a platform for nesting birds.
Invasive scrub had to be removed from the thirty-five hectares of designated fen wetland and a large area of rushes had to be removed from the grassland.
Most water from the reserve drains into the loch and thence to the sea. Water levels had to be controlled as at high tide and in heavy rain, water cannot drain into the sea. Control structures were needed to hold water on the flood plain for longer rather than just allowing it to flood into the loch from where it might not be able to escape. One and a half kilometres of shallow drains were to be excavated on the Savoch Low Ground and over six kilometres of existing drains cleaned. Six new concrete weirs were to be built around Savoch Low Ground and the new reed bed. These would permit the adjustment of the flow of water through key points by slowing down the rate of flow in places to maximise the nutrient stripping and to divert water into certain areas to maximise storage and ensure the wetlands stay wet. In addition four pipe sluices were to be installed for micro-management of water levels on the Savoch Low Ground.
A major constraint was time. The work had to be carried out after the 10th of July when the breeding season was over and before the 5th of September when the geese return, a period of nine weeks. So what seemed to be eighteen months work would be constrained into two periods each of nine weeks in consecutive years. Permission to carry out the work had to be agreed by bodies such as Scottish Natural Heritage and funding had to found.
It was important to appoint a contractor who could do all the work - moving soil, cutting down scrub and trees, ditching and building an island. And it had to be done in the time available. No company in Scotland had the equipment to undertake all the work and only two serious offers came from the south of England. The company chosen does only ecological restoration, has impressive pieces of machinery for the various tasks and also does the work at cost for conservation bodies.
In the first year the trees bordering the Savoch Burn were removed. In the second year the burn was diverted into its new channel and the old one filled in. Fish in the old channel were caught and relocated, these included over two hundred trout and in excess of twenty thousand brook lampreys, which were not known previously to be in Strathbeg. A further complication was the population of water voles which had to safeguarded.
To make an established reed filtration system through which the new course of the burn would wend its way, one thousand one cubic metre blocks of soil with reeds were translocated to form the basis of the reed bed. Over 2,500 cubic metres of slurry and peat were removed from an old silt trap
and a deep channel dug in the reed bed to make a habitat suitable for Bitterns. Bittern, Bearded Tit and Water Rail have been seen in the new reed bed but no Marsh Harriers yet.
Levelling the grassland was a complex operation, designed to minimise the translocation of soil. The height profile of the whole area was mapped then soil moved from high areas to the nearest low areas. Topsoil was scraped up and replaced to keep the nutrients. In all 25,000 cubic metres of soil were moved. The ground was then reseeded and became green quite quickly.
To restore the wet fen almost thirty hectares of invasive scrub had to be removed. This formidable task was done with a massive machine which just mowed down the trees then removed the timber but which, in spite of its size, presented a large surface area to the ground thus causing minimal damage to the soil structure. The huge volume of wood was consigned to a special incinerator which burned at about 800 oC and, at night, the glow of the metal jacket could be seen half a mile away. A garden bonfire would produce one ton of ash per hectare of wood but such was the intensity of the heat in this one that a volume of less than three skips was produced and later disposed of by burying.
The control of water levels in the wetlands was another concern, the main problem being the removal of water. Invasive scrub had to be removed from the wet fen to replace it with open sward and to allow grazing to be reinstated.
The area of thirty-five hectares of rushes was cleared to restore wet fen. The cut rushes amounted to over 1,200 cubic metres which were eaten by either livestock or geese or rotted down. Within three weeks of cutting the rushes, the area was colonised by a variety of plants.
To recreate the island, 450 metres of monorail were laid down, some of it constructed on site, to carry the materials across an area of wet fen then over the water to the site. The perimeter of the island was constructed of piles made of compressed, recycled plastic bags then almost eight hundred tons of materials were used to form the island with an area of 550 square metres. On the new island, one pair of Common Terns nested in 2006, a colony of Lesser Black-backed Gulls nested in 2007 and 400 Arctic terns nested in 2008 the but all the chicks died.
After many years, access to the airfield hides has been agreed with the Ministry of Defence and a road constructed so that cars no longer have to pass across the fenced area at the building.
The Scottish Environmental Protection Agency built a hut to protect equipment, costing £30,000, installed to monitor the solutes in the Savoch Burn. Unfortunately the hut blew over and the custom-built equipment destroyed. The hut has been restored and the parts of the replacement monitoring equipment are acquired as they become available.
Has spending over a million pounds, much of it from European Union sources, been a success? It is too soon to determine whether water quality in the loch has improved. Lapwings have changed the area where they breed. Three pairs of Redshanks displayed on low ground, the first time for twenty years. The ground with wet tussocks looks perfect for Snipe although they have yet to avail themselves of it. A pair of Avocets mated and made a scrape but stayed for only five or six days, a pair of Wood Sandpipers were seen mating and scraping and six male Ruff displayed and two females mated but no nests was found. A pair of young Marsh harriers built a nest then abandoned it. Most of Scotland's population of Garganey, in the form of seven males and five females, produced a minimum of two nests and several broods.
Future projects include maintaining and controlling the plant cover both on the wet fen and on the grassland by grazing cattle, probably Highland, using a herd about thirty strong. It is desirable to remove from the loch the accumulation of silt which has a volume of rather less than thirty thousand cubic metres. More extensive late cutting of grassland is proposed to encourage Corn Buntings to nest on fields in the Reserve and to provide a mosaic of species-rich grasslands and hedgerows of native species, which will provide a range of food and nest sites for a mix of farmland birds. This work can go ahead as funding for it has been obtained. It is also intended to increase the network of footpaths.
A large and appreciative audience was impressed by such a detailed and interesting description of the changes affected at Strathbeg and by the work Dominic and his team had put in to bring the project to fruition.