Raised boglands are threatened habitats. Boglands are wetlands that accumulate peat and they contain important populations of specialised animals, birds, fungi and plants.
Lille Vildmose contains more than 50% of the raised bogland in Denmark. However, decades of peat cutting and farming have left the central area severely damaged. Of the original 55 km2 of raised bogland in Lille Vildmose, only 20 km2 is preserved today.
Design, tendering & supervision
Ramboll has carried out detailed design, tendering and supervision for the nature restoration of the degraded bogland at Smidie Fenner and Tofte Mose, as well as the restoration of the lake Birkesø.
Raised bogland to be protected and restored
The main purpose of the project was to restore areas of drained bogland and to improve the conditions to develop new areas of raised bogland. The area has been used for excavation of sphagnum for commercial use and for agriculture and as a result, drainage is a serious threat.
Recorded as a Ramsar area
A Ramsar area is defined as a wetland site of international importance under the Ramsar Convention established by UNESCO. The entire project in Lille Vildmose has been recorded as a Ramsar area, not only because of the biodiversity it contains, but also because of the area’s ability to absorb, remove and sequester CO2 from the atmosphere.
According to the Danish Nature Agency, calculations show that the restoration of Lille Vildmose will reduce CO2 emissions by 14,000 tonnes per year. While the bog was decomposing, it discharged 5,000 tonnes of CO2 per year. These emissions have now been cut and the added mosses absorb 9,000 tonnes of CO2 per year.
Restoration of Lake Birkesø
Lake Birkesø has an area of 1.2 km2 and it has been restored by cutting off drainage canals and establishing a new dike around parts of the area with a controlled outlet. The outlet from Tofte Sø now enters Birkesø instead of being discharged to the sea via a canal. Infiltration through the dike is prevented by vertical membranes. The rise in water level has resulted in about 700 m of the existing asphalt road being raised and about 2 km of new gravel road has been built. The average water depth is now approximately 1 m.
Ramboll designed three bird islands for the lake. The islands have had ditches dug around them to maintain a water level even during dry spells, which secures the habitat from foxes. Furthermore, there are three bird observation posts for visitors and in front of these areas and we increased the water depth to prevent reed growth, which would block the view to the bird islands. These initiatives have made Lake Birkesø a popular site for bird enthusiasts.
Protection of the edges of Tofte Mose
In Tofte Mose we have designed two new waterproof dikes. The dikes will prevent the drainage of the perimeter of the raised bogland. Drainage of the bog has been prevented by establishing new earth-filled dams up towards Tofte Mose. The raised water level will directly impact 80 hectares of raised bogland and generally improve conditions on much larger areas. A vertical membrane has been established in the dams, and this will prevent drainage from Tofte Mose. The surface water drainage from Tofte Mose is delayed via a system of cross dams and the water is directed to the new Lake Birkesø.
Restoring bogland at Smidie Fenner and Purker Fenner
In the neighboring areas of Smidie Fenner and Purker Fenner we have stopped the drainage and raised the water level with small dikes and established overflow structures to control the water level. At Smidie Fenner all drainage ditches have been blocked with overflow structures and the outlet from the area is controlled with dikes and overflow structures. The water level can be controlled to ensure suitable water level for developing the growth of sphagnum.
This is a long-term project as the sphagnum layer will grow just a few millimeters a year.