Influence of the Šance Reservoir on the benthic diatoms of the Ostravice River

This contribution deals with the comparison of several physical and chemical parameters and algae periphyton in the Ostravice River above and below the Šance Reservoir. The Šance Reservoir on the Ostravice River (North Moravia) is a typical deep reservoir with the hypolimnetic outflow during the period of stratification. The reservoir serving as drinking water supply was filled up in 1969. Temperature, pH, conductivity and concentrations of oxygen and nitrogen compounds, as well as the phyto-periphyton changes (focussed on diatoms and assessment of saprobity) were followed in the five profiles on the Ostravice River. Special attention was done on the morphological variability of the diatom species Fragilaria arcus (EHRENBERG) CLEVE. Two profiles studied were located on the reservoir inflows, three below the reservoir dam. The decrease of oxygen concentrations, pH, conductivity and saprobity was observed below the dam. Concerning water temperature, the decrease of summer water temperature values and increase of water temperature in winter were found below the reservoir. While the concentrations of NO2- and NH4+ and the morphological variability of the species Fragilaria arcus were not significantly different in the profiles studied, the NO3- concentrations were higher below the dam