First attempt to apply whole-lake food-web manipulation on a large scale in The Netherlands |
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Authors: | Van Donk E Grimm M P Gulati R D Heuts P G M de Kloet W A van Liere L |
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Institution: | (1) Provincial Waterboard of Utrecht, P.O. Box 80300, 3508 TH Utrecht, The Netherlands;(2) Present address: Department of Nature Conservation, Aquatic Ecology Section, Agricultural University, P.O. Box 8080, 6700 DD Wageningen, The Netherlands;(3) Witteveen & Bos, Consulting Engineers, P.O. Box 233, 7400 AE Deventer, The Netherlands;(4) Limnological Institute, ‘Vijverhof’ laboratory, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands |
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Abstract: | Lake Breukeleveen (180 ha, mean depth 1.45 m), a compartment of the eutrophic Loosdrecht lakes system, was selected to study
the effects of whole-lake foodweb manipulation on a large scale. In Lake Loosdrecht (dominated by filamentous cyanobacteria),
due to water management measures taken from 1970–1984 (sewerage systems, dephosphorization) the external P load has been reduced
from 1.2 g m−2 y−1 to 0.35 g m−2 y−1. The water transparency (Secchi-depthca. 30 cm), however, has not improved. The aim of the food-web manipulation in Lake Breukeleveen was not only to improve the
light climate of the lake, but also to study if the successfull effects observed in small lakes (a few ha) can be upscaled.
In March 1989 the standing crop of planktivorous and bentivorous fish populations was reduced by intensive fishery, fromca. 150 kg ha−1 toca. 57 kg ha−1. The lake was made unaccessible to fish migrating from the other lakes and it was stocked with large-sized daphnids and 0+ pike. However, water transparency did not increase in the following summer and autumn 1989, which is in contrast with great
improvement in the light conditions previously observed in smaller lakes. The main explanations for the negative outcome in
Lake Breukeleveen are: 1) the rapid increase of the planktivorous fish biomass and carnivorous cladocerans, predating on the
zooplankton community; 2) suppression of the large daphnids by the high concentrations of filamentous cyanobacteria; 3) high
turbidity of the lake due to resuspension of bottom material induced by wind, unlike in smaller lakes, and thus inability
of submerged macrophytes to develop and to stabilize the ecosystem. |
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Keywords: | Biomanipulation whole-lake experiment lake restoration Lake Breukeleveen planktivore fish Daphnia predation |
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