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Improving status of coastal lagoon Tryggelev Nor, Denmark - IMAGE (Tryggelev Nor)
Date du début: 1 avr. 2002, Date de fin: 30 juin 2006 PROJET  TERMINÉ 

Background Tryggelev Nor is one of several coastal lagoon areas that disgorges into the Baltic Sea. This particular area is located both within an SPA and an SCI on the island of Langeland at the sourthernmost tip of Denmark. Over the years, the lagoon has suffered from increasing eutrophication and stagnation, which has severely negatively affected the conservation status of both the lagoon itself and its resident bird populations, such as the bittern (Botaurus botaurus) and the spotted crake (Porzana porzana). Many of the problems can be traced back to the draining of the nearby Nørreballe Nor in 1883 to make way for new agricultural fields. This effectively removed one of the principal natural water filtering systems leading to the lagoon. Action was taken in the 1990s to reduce the more diffuse sources of agricultural pollution through the application of the Nitrates Directive and the use of agri-environmental schemes, but the fact remained that the lagoon itself was still highly eutrophic, since it no longer had the means of flushing out the nitrogen-rich waters that had built up over the last half century. Tryggelev Nor is a central part of a wetland network in the region, that also includes Piledybet, Ristinge Nor, Klise Nor, Gulstav Mose and Keldsnor. Thus, to improve this network and the biological diversity of coastal wetlands in the region, improvement of the conservation status of Tryggelev Nor would be a key objective. Objectives To obtain a favourable conservation status of the coastal lagoon in Tryggelev Nor and to improve the ecological conditions for a number of bird species of Annex I of the Birds Directive, for example Botaurus stellaris, Circus aeruginosus, and Porzana porzana, the trophic state of Tryggelev Nor had to be changed towards a much more nutrient-poor state, the hydrological state improved, the management of the salt meadows addressed and the biotopes increased in the area. The LIFE-Nature project intended to address this problem by reducing the nitrogen load in the whole wetland area by 70%. It would achieve this by constructing a salt water inlet into the lagoon to help flush out the accumulation of nutrients and reestablish a more natural water exchange between the sea and the lagoon. The nearby Norrebolle Nor would also have its water level raised to create a freshwater lake with surrounding reed beds and wet meadows. Not only would this help to increase the retention capacity of the wetlands but it would also create new habitats and improved breeding conditions for birds. In this respect a number of specific objectives were formulated as means to meet the overall objective: (1) to ensure that water in Tryggelev Nor is exchanged 4-5 times during the summer to reduce the availability of nutrients; (2) to improve the retention capacity of the catchment to an equivalent of 19 tonnes of nitrogen per year; (3) to obtain a stable water table in the reedbed to protect it against desiccation, (4) to obtain appropriate grazing of 44 ha of salt meadows, (5) and to enlarge the area with a well-functioning reed bed by at least 15 ha and the area of open fresh water by 69 ha. This enlargement of existing wetland habitats would occur on land which was intensive agricultural fields at the beginning of the project. Once the restoration work was done, management contracts for extensive grazing would be drawn up to ensure the long-term maintenance of the whole site. As agriculture continues to decline, more and more stakeholders are turning towards rural tourism as an alternative source of revenue. Therefore, a number of small-scale visitor facilities, such as a bird observation tower and trail, would be developed to further encourage nature-friendly tourism to the area. Results All project actions have been accomplished and implemented, creating the conditions for a favourable conservation status of the coastal lagoon in Tryggelev Nor. The monitoring results show that the nutrient load via the new lake, Nørreballe Nor, has decreased and this creates the possibility for the area to develop into a rich wetland area with a wide variety of breeding birds. The plant community of Nørreballe Nor is dominated by early succession plants of wet nature types. All the meadows are grazed by cattle and the vegetation will be kept low. The composition of the vegetation on the Tryggelev Nor salt meadows is almost unchanged before and after the construction works. The population density of the core species - Botaurus stellaris, Circus aeruginosus, Porzana porzana – of the project has either increased or remained unchanged. However, the development cannot be ascribed to the physical changes implemented in the project - the composition of aquatic plants shows no clear trends. Whilst sea water intrusion has not yet had any effect on the plant communities, monitoring indicates that the intrusion of seawater to the coastal lagoon has increased. However, the intrusion is determined by climatic factors more than the tide. It is expected that the sea water will wash out nutrients stored in the coastal lagoon sediment. The nitrogen input to Tryggelev Nor has decreased by 60% due to improved retention capacity (the Nørreballe Nor lake) in the catchment. The external phosphorus input has not yet decreased but this is expected to happen when the new lake becomes more ecologically stable. No clear trends in oxygen concentration can be seen. As a result of stratification in some parts of the lagoon, oxygen depletion was observed for some periods. A technical solution with tidal valves was established in the summer of 2006 to prevent stratification.

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