 |
 |
 |
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
 |
 |
 |
Index
Education |
Introduction |
Fundamentals |
Management |
Restauration |
Protection |
Summary |
||||||||||||||
Foodchain Control as a Long-term Management Strategy
Biological procedures for restoring waters acquire greater significance when considering global and regional aspects and also against the background of rising costs for disposal and deployment of energy: All biological procedures for restoring waters are orientated towards reducing concentrations of nutrients, pollutants or phytoplanktons by controlling the growth factors (nutrients, light, grazing).
Controlling the food web
One method of controlling
eutrophication in standing waters is the top down control of the food web
(biomanipulation). Disturbing biovolumes can already be reduced in waters
used for the production of drinking water by deliberately intervening in
the food chain fish - zootoplankton - phytoplankton. The fact that phytoplankton
contents appear in waters "clear water states" in spite of relatively high
nutrient pollution is a starting point for considering whether to encourage
this stated in a suitable way. These "clear water states" are caused by
larger zooplankters (primarily water fleas, genus Daphnia, > 1mm), which
basically have the phytoplankton as their basic food and which filter this
very effectively out of the water.
The concept of manipulating the food chain (biomanipulation) is based on the control or encouragement of this large zooplankton by intervening in the final link of the food chain in the lake, the fish. The desired effect continues like a cascade through the whole food chain (Figure).
The reduction of fish that consume zooplankton encourages the propagation of large zooplankters. The increased filtering capacity of the zooplankton causes a reduction in the algae biomass with an increased water clarity (visible depth). Sufficient reduction of the external pollution means biomanipulation can to bring about long term lowering of the phosphate pollution by phosphate fixation on particles and sedimentation and reduction in the phytoplankton biomass even within the lake itself.
Benndorf J., Schultz H., Benndorf A., Unger R., Penz E., Kneschke H., Kossatz K., Dumke R., Horning U., Kruspe R. and Reichel S. (1988): Food-web manipulation by enhancement of piscivorous fish stocks: Longterm effects in the hypertrophic Bautzen reservoir. Limnologica 19. 97-110.
Große N., Clasen J., Hoehn E., Horn W., Ketelaars H. A. M., Müller U., Scharf W., Willmitzer H. und Benndorf J. (1998): Der Einfluß des Fischbestandes auf die Zooplanktonbesiedlung und die Wassergüte. GWF, Wasser - Abwasser 139, 15. 30 - 35.
WILLMITZER, H., 1995: Biomanipulation zur Sanierung von Seen und Talsperren. In: Wasserwirtschaft, Wassertechnik 3/95, Berlin, 20-22.
Willmitzer, H., M.-G. Werner und W. Scharf, 2000: Fischerei und fischereiliches
Management an Trinkwassertalsperren. Technische Information Nr. 11, Arbeitsgemeinschaft
Trinkwassertalsperren. Oldenbourg-Verlag, München, 103 S.
