THE VINNE (Zoutleeuw)

6th European Conference on Ecological Restoration Ghent, Belgium, 8-12/09/2008 THE VINNE (Zoutleeuw) 1 2 Ingrid Beerens – Greet Swinnen 1 [email protected] Flemish Land Agency, Diestsevest 25, 3000 Leuven, [email protected] 2 Flemish Agency for Nature and Forests, Waaistraat 1, 3000 Leuven, Keywords: natural eutrophic lake, hydrological measures, restoration of water dynamics Introduction The Vinne is a provincial domain situated about 2 km from the city centre of Zoutleeuw. It is designated as a special protection area “forests and calcareous heaths of Haspengouw”. The Vinne depression is thought to be created through glacial formation. The lake that developed later was fed with water from the Kleine Gete and surrounding streams and with ground and rain water. It was drained in 1850 to plant poplars. Historical data (maps, texts, etching, flora, see figure 1) show the existence of the largest natural lake in Flanders, with a varied fish population and unique vegetation. Figure 1. Ferraris map and etching from before the drainage (VLM) Further investigation of the ecohydrology showed that a partial restoration of the lake was possible. In order to preserve the Vinne farm and the walking paths in the fringe zone a smaller (68ha) and less deep (1m) lake was proposed. The original system differs from the current (restored) system because surrounding streams are no longer connected with the lake. The current lake is fed only by ground and rain water. Since the Vinne has formed an isolated hydrological system since 1850 no external water has ended up in the lake and the input of nutrients has been rather limited. Natuurpunt launched the idea of restoring the lake in the beginning of 1980, starting a psychological ripening process. In 1998 the planning began in order to restore the lake through the instrument nature development. The works were executed in 2004-2005. Materials and methods To create the lake a number of preparatory works were done. 50 ha of poplars were felled, branchwood and stems as well as mulch were locally removed (see figure 2). Debris banks were dug off locally. Pasture grids and recreation infrastructure were constructed. The water quality was improved through water purification (connection with the sewerage of the Vinne farm and a small water purification for the waste water of four houses). In 2004 the pumps were stopped. 18 months later the lake was filled. 1 Towards a sustainable future for European ecosystems – Providing restoration guidelines for Natura 2000 habitats and species Spontaneous grafting of fishes is improbable. In 2005 pike was introduced (1,400 individuals of 6 weeks old) to control the topmouth gudgeon population. In the winter a maximum water level is maintained. The superfluous water is pumped away, refreshing a part of the water mass in the winter months. In the summer the water level decreased naturally with 16 cm in 2005, 5 cm in 2006 (wet summer) and 22 cm in 2007. The reed is mowed in cycles. In the spring of 2008 artificial nesting rafts for black terns were placed. Figure 2. Photos of the works (VLM) Results and discussion In 2006 and 2007, two years after the lake was restored, the area was extensively monitored. Mainly non-rooting aquatic plants established rapidly and became very abundant (lemnids, Riccia fluitans, Utricularia australis). So far, rooting aquatics remain sparse and limited to a few tolerant species such as Potamogeton crispus and P. pusillus. Large patches of perennial reed and Typha latifolia developed. At this early stage, it is still unclear to which extent the reed vegetation will expand further (it now nearly covers 50% of the lake) (see figure 3). Many nature managers fear that the lake will rapidly dry out, but it is too early to tell. Decomposition of abundant organic material causes turbidity and oxygen consumption, inducing an outbreak of botulism in 2007. Figure 3. The Vinne before and after the restoration (VLM) 2 6th European Conference on Ecological Restoration Ghent, Belgium, 8-12/09/2008 Many reed and marsh birds reappeared. Among the more remarkable breeding birds are Bittern (Botaurus stellaris), Little Bittern (Ixobrychus minutus), Black-necked Grebe (Podiceps nigricollis) and Whiskered Tern (Chlidonias hybridus). Black Terns (Chlidonias niger) occur in relatively large numbers during migration and there are about 20 breedings on the artificial nests. A large breeding colony of Black-headed Gull (Larus ridibundus; up to presumably 6,000 birds) has developed, which has caused a nutrient problem. The stubs of the poplars and the broad reed zone offer many breeding opportunities for the gulls. These stubs were not removed to keep down the costs, but they now cause problems when mowing the reed. The gulls, however, also have a positive influence, through the protection they offer against birds of prey. To decrease the brooding opportunities for gulls the water level was temporarily increased with 20 cm in 2008 and about 20 hectares of reed were mowed. The Vinne is important to foraging bats as can be seen by the large numbers and the presence of six to eight species, such as Myotis daubentonii, M. nattereri, Nyctalus noctula, Plecotus spec. The fish community of the Vinne is still in a pioneer stage and a limited number of species are present: Topmouth gudgeon (Pseudorasbora parva), Three-spined stickleback (Gasterosteus aculeatus), Nine-spined stickleback (Pungitius pungitius), Pike (Esox lucius) and Carp (Cyrpinus carpio). Because of the combination of open water, marsh and fringing woodland, the dragonfly diversity is considerable (38 species), with high densities of common species and populations of a few more specialized species (Aeschna isosceles, Lestes dryas, Aeschna juncea, Ceriagrion tenellum). Chemical analysis of the surface water has shown that the lake is moderately eutrophic in seven sample locations, and hypertrophic in one location (due to former discharge of domestic waste water). The transparency was measured in eight places; it is averagely 40 cm, whereas ideally it should be at least 100 cm. The overall development of the domain (exhibition, traffic safety, walking paths, playground, cycle path, bird hides, cafeteria, … ) has led to an obvious increase in the number of visitors. Figure 4. Photos from before, during and after the restoration (ANB, VLM) Conclusions The social context was of overriding importance to obtain means and public support for the restoration of the lake. The results of the lake restoration are spectacular for Flanders, concerning avifauna and dragonflies. It is important to thoroughly consider the conditions and not give in on ecological priorities (water depth, tree stem removal) to avoid problems. The change of management must be properly assisted. 3 Towards a sustainable future for European ecosystems – Providing restoration guidelines for Natura 2000 habitats and species Since the lake is still in a pioneer phase it is too early to draw conclusions. Further monitoring is necessary to be able to assess the evolution of the lake. After five and again after ten years it will be monitored extensively. Aside from internal eutrophication and guanotrophication (gull plague) nutrient inputs through spillover of stored manure from an adjacent farm are a cause of concern. The evolution of the water quality and the growth of reed must be monitored closely. The area became very popular for tourism. People can visit the area via attractive wooden tracks through the marsh and bird hides are provided (see figure 5). The large number of visitors proves the need for this type of high quality nature areas for recreation. Local people complain about the increase of mosquitoes and noise from the Black- headed gulls. Figure 5. recreative infrastructure (VLM) Acknowledgements Several institutions cooperated on the nature development project: VLM, ANB, Natuurpunt and the province Flemish Brabant. This project is a success thanks to the perseverance, insight and knowledge of the people concerned. References - Aerts S., Beerens I., Swinnen G. (11/2002). Projectuitvoeringsplan het Vinne. Vlaamse Landmaatschappij, Diest, Belgium - Lambrechts J., Aubroeck B., HendrickxP., Gabriëls J., De Vocht A., Van der Wijden B., Hendig P. (2006-2007). Monitoringsrapport T+2, Aeolus in opdracht van VLM, Leuven, Belgium - De Wilde M., Huybrechts W., De Becker P. (1998-1999). Ecohydrologische studie van het Vinne. Instituut voor natuurbehoud in opdracht van de provincie Vlaams-Brabant - Messiaen S. (5/2003). Monitoringsplan en inventarisatie van de huidige toestand voor het natuurinrichtingsproject het Vinne. VLM. Diest. Belgium 4 .

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