Produktionsbiologische Aspekte der Entwicklung eines mit nährstoffreichem Wasser gespeisten künstlichen Sees

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Summary

From 1969 until 1972 the development of the plankton and benthos biocenoses was investigated in a just originating lake. The lake was fed with water from a polluted brook containing up to 2800 μg/I phosphate and up to 28.5 mg/I NO₃⁻. In the middle of 1971 the filling was completed and thereby the influx of nutrients ceased. The water volume of the lake is 10.4 million m³, the maximum depth 37.5 m. The high amount of nutrients caused an intense growth of phytoplankton. The maximum cell numbers rose every year, they reached 90,000/ml one year after the end of the nutrient influx. The minima were lowest during the first winter, during the following years the decrease of the cell numbers in winter was less and less. Despite some mass growths of centric diatoms the major part of the phytoplankton consisted of Cryptophyceae and Chlorophyceae. Cyanophyta were of no importance. During the first year the zooplankton consisted of rotifers and copepods only. Cladocera appeared during the second summer for the first time. The benthic fauna consisted mainly of chironomids during the first two years, later on tubificids were predominant.