Hidrológiai Közlöny 1986 (66. évfolyam)

4-5. szám - Hegedűs János: A Duna fitoplanktonja Budapest felett (1659. fkm): I. Mennyiségi viszonyok

270 HIDROLÓGIAI KÖZLÖNY 1086. (56. FIVF., 4—5. SZÁM Key words: 2. In February and November it ranged between 1 and 2 million. 3. Differences were detected in the data for March and October. In some years, such as 1972, 1975 and 1976, the mild winters resulted in sufficiently high water temperatures in March already, so that the monthly means were higher than 10 million/litre. The alga counts in October are influenced by the river regime, water temperature and solar radiation. In favourable combination these resulted in alga counts around 19 million/litre, otherwise the monthly means dropped to as low as 800,000/litre. 4. Between April and September, under favourable river regime and meteurological conditions, monthly mean alga counts of 20 to 25 million/litre were observed. The peak alga counts in the Danube were 40 to 50 million per litre. Even higher values were registered on ten occasions, the absolute maximum being 79,342,000/litre. Alga counts above 15 million/litre are considered high in Danube water. The number and duration of such periods depended primarily on the river regime, the number varying from 1 to 6 in any single year. In the periods with high alga counts the peak occurred normally 9 to 13 days after the onset of the period. In periods of long duration two, occasionally three peaks were observed. The daily changes in the alga counts were also very wide. The maximum rise registered was 21.6, while the maximum drop 27.1 million/litre. Based on the results of these quantitative algological studies a compilation has been prepared for predicting the percentage probability of high and low alga counts in the individualy months. phytoplankton, Danube, diatomaeeous algae