SHALLOW LAKES The importance of drawdown and sediment removal for the restoration of the eutrophied shallow Lake Kraenepoel (Belgium) Jeroen Van Wichelen Æ Steven Declerck Æ Koenraad Muylaert Æ Ivan Hoste Æ Vanessa Geenens Æ Jochen Vandekerkhove Æ Erik Michels Æ Niels De Pauw Æ Maurice Hoffmann Æ Luc De Meester Æ Wim Vyverman Ó Springer Science+Business Media B.V. 2007 Abstract Lake Kraenepoel (Belgium) is a shal- low lake (22 ha), divided in two basins since 1957 by a shallow dike. The lake was used for fish farming until World War II and was drawn down about every 5 years to harvest fish. Despite its dense historical carp population, it had clear water and a rich Littorelletea vegetation. During the course of the 20th century, the lake became eutrophic and the Littorelletea vegetation degraded. The northern basin, which was still drawn down about every decade after 1957, retained its clear water and had a dense sub- merged macrophyte vegetation. The southern basin, which was never drawn down after 1957 and which received direct surface water inputs, had become a turbid shallow lake with phyto- plankton blooms in summer. In 2000, efforts were taken to restore the lake: the entire lake was drawn down, the fish community was biomanipu- lated, nutrient-rich surface water inputs were diverted from the southern basin and sediments were removed (only in the northern basin). Fish biomanipulation and sediment removal were suc- cessful in the northern basin, as nutrient levels declined and the Littorelletea vegetation recov- ered. In the southern basin, sediment analyses indicated that drawdown resulted in sediments with a lower water and organic matter content and water column turbidity decreased after the draw- down. But pH in the southern basin declined to <4, probably because sulphides in the sediment were oxidized during drawdown and sediment desiccation. In contrast, desiccated sediments were removed from the northern basin and pH did not decline below 6 after restoration. In spite of the still high dissolved nutrient concen- trations, phytoplankton biomass declined signifi- cantly in the southern basin, probably due to acidification. However, no Littorelletea species colonised the lake bottom in the southern basin. Thus, lake drawdown may be a useful Guest editors: R. D. Gulati, E. Lammens, N. De Pauw & E. Van Donk Shallow lakes in a changing world J. Van Wichelen (&) Á K. Muylaert Á V. Geenens Á W. Vyverman Laboratory of Protistology and Aquatic Ecology, Ghent University, Ghent, Belgium e-mail: jeroen.vanwichelen@UGent.be S. Declerck Á J. Vandekerkhove Á E. Michels Á L. De Meester Laboratory of Aquatic Ecology, Catholic University Leuven, Leuven, Belgium I. Hoste National Botanic Garden of Belgium, Meise, Belgium N. De Pauw Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, Ghent, Belgium M. Hoffmann Laboratory of Terrestrial Ecology, Ghent University, Ghent, Belgium 123 Hydrobiologia (2007) 584:291–303 DOI 10.1007/s10750-007-0611-z