| Popis: |
The algal growth potential (AGP) in water samples from the Drava River (stream-km 23.37, 22.00, 21.32, 20.44 and 17.69), as well as the influence on the AGP due to adding phosphates (final concentration of 0.028 ; 0.056 ; 0.169 g l-1) and nitrates (final concentration 0.180 an 0.360 g l-1) was investigated by miniaturized bioassay method. According to the classification for waters of Middle Europe, the Drava River belongs to the category of oligo to meso-mesoeutrophic waters. The water level of the Drava and the Danube had a significant influence on the AGP in the original water samples of the Drava River. Phosphates stimulated the growth of Chlorella kessleri in cases of lower values of algal biomass in original water samples of the Drava River. During the period of investigation (April-September 1997) P was the growth-limiting factor. The addition of nitrates to the water samples had a stimulating effect on the growth of the algal biomass during the spring of 1997. On the basis of AGP results, heavy metals and toxic substances were mostly present during the period of investigation. Results of former chemical analyses indicated continued pollution of the Drava River near Osijek due to insufficiently purified waste waters. Since samples were taken at polluted spots, the composition of wastewater varied during the chosen stream kilometers. |
