Die Massenentwicklung der Geißelalge Uroglena americana (Alk.) Lemm in Trinkwassertalsperren Thüringens und ihre Bekämpfung

Abstract

AbstractA mass development of Uroglena americana with cellular densities of up to 13.5 · 106 and 86.106 cells/l, was observed in two drinking‐water reservoirs. In the first case the development remained confined to the upper 20 m, in the second case there occurred a gradual shift of the maximum to deeper zones from May to July with decreasing cellular densities down to a depth of 35 m. Laboratory experiments for the control of the algae development were performed in order to protect the drinking‐water resources from potential impairments of odour and taste. Samples of the storage‐reservoir water with 20.106 cells/l of Uroglena were concentrated up to 1.25 … 12.5 mg/l Ca(OH)2 (pH‐values of 7.2 … 9.6) by addition of calcium hydroxide and observed for 39 h. First impairment of the cells of Uroglena is detectable at 5 mg/l Ca(OH)2 after 15 h, an immediate effect can be observed at 7.5 mg/l Ca(OH)2 together with increased sedimentation, also Gymnodinium and Cryptomonas having been damaged. Thereupon a successful control of Uroglena by liming up to pH‐values above 8.0 is possible. The application of lime to outdoor areas was not necessary, in the final analysis, since the drinking‐water quality could be secured by the optimum choice of the intake depth of raw water with a maximum of 4.103 to 77.103 cells/l.