Individual study: Restoration of a former oligotrophic softwater lake by reducing the inflow of calcareous surface water and removal of the organic sediment layer; Lake Beuven, Brabant, the Netherlands
Roelofs J.G.M. (1996) Restoration of eutrophied shallow softwater lakes based upon carbon and phosphorus limitation. Aquatic Ecology, 30, 197-202
The study summarised here examined water quality and vegetation development of a formerly soft water lake (Beuven) in the Netherlands, which in the late 1960s become very eutrophic and relatively alkaline as a result of the inflow of nutrient-rich, calcareous water, originating from run-off from fertilised agricultural land. Almost all submerged aquatic macrophytes disappeared within a few years; only small populations persisted in shallow water. In 1986 restoration was attempted.
Study site: Beuven is a shallow lake (70 ha; max. depth 1.5 m) lying in a 2,300 ha heathland east of Eindhoven, south-eastern Netherlands (51º24N, 5º39E). In the past, the lake was mainly fed by rainwater and water from its small catchment. Until the 1960s, the water was dominated by submerged aquatic plants of the 'Littorelletea' community, including shoreweed Littorella uniflora, quillwort Isoetes echinospora, water lobelia Lobelia dortmanna, six-stamened waterwort Elatine hexandra, Echinodorus repens and floating-leaved water-plantain Luronium natans.
Lake restoration: In 1986, most of the dense reed Phragmites australis vegetation that had colonized and the accumulated muddy organic sediment layer was removed. The alkalinity was reduced by controlling the inflow of the calcareous stream water. Plant monitoring had been undertaken prior to restoration (1976-1985) and this was continued for 10 years after restoration (1986-1995).
After restoration, between 1986 and 1995 the characteristic 'softwater' submergent and emergent plant species (rare or absent from 1976-1985) re-established. L.uniflora became dominant and other species belonging to the Littorelletea very abundant e.g. E.hexandra, needle spike-rush Eleocharis acicularis and marsh St.John's-wort Hypericum elodes.
Despite great improvements in water quality after 1986, it became evident that the lake was become slightly over-acidic (due to atmospheric deposition) and poorly buffered again. A small part of the lake was isolated by a dam. When necessary, water from the inflowing stream could be let into this area and retained; here the nitrogen and phosphorus load decreases by 80-90% within two weeks. This relatively calcareous, nutrient-poor water is then released into the large part of the lake to prevent acidification and to maintain the inorganic carbon in the water layer at low levels.
Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://www.springerlink.com/content/c8607x8426412703/fulltext.pdf