Biomanipulation by introduction of herbivorous zooplankton. A helpful shock for eutrophic lakes? |
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Authors: | Theiss J Zielinski K Lang H |
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Institution: | (1) Institut für Entwicklung und Forschung Dr. Vielberth KG, Im Gewerbepark B49, D - 8400 Regensburg, Federal Republic of Germany |
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Abstract: | In 1988 and 1989Daphnia magna were introduced into the Gewerbepark Pond and into the University Pond, and also into a limnocorral (10 m diameter, 5 m deep)
in Postfelden Reservoir. Limnological parameters were regularly monitored in all the three water bodies over three months
or longer. The objective of the experiments was to induce a clear-water period in turbid eutrophic waters by direct manipulation
of the zooplankton community. Introduction of four million individuals ofD. magna (10 ind. 1−1) caused a long lasting clear-water period in the limnocorral. While Secchi-disc transparency in the reservoir decreased from
1.3 m to<1 m during summer, transparency increased to a stable level of about 4 m in the corral. Despite very low phytoplankton
biomass,D. magna was still abundant. The experiment was terminated after three months because of oxygen depletion in the corral. In the Gewerbepark
Pond 3.3 million individuals ofD. magna (0.6 ind. 1−1) were introduced at the beginning of August. The daphnids soon increased 60-fold in their density causing a persistently
high water transparency and low phytoplankton biomass up to November. Ammonia concentration rose steeply, whereas that of
nitrate and oxygen decreased. Subsequently in summer, concentrations of chlorophyll as well as of inorganic phosphorus and
nitrogen were extremely low. Instead of the phytoplankton,Elodea canadensis grew enormously and covered 12% of the pond surface. The biomanipulation experiment in University Pond failed, probably due
to predation by carp. |
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Keywords: | biomanipulation lake restoration eutrophication food web Daphnia magna limnocorral |
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