Effect of dams on hydrological parameters and the structure of benthic molluscs: case study in Dnieper river basin

Spatial changes in the structure of benthic mollusk's assemblage were examined in the regulated peneplain rivers Psel and Vorskla, Dnieper Basin. Both rivers run within the area of the eastern Ukraine forest-steppe zone. Both rivers are regulated by dams. The sample points were located upstream and downstream the dams.In the Psel River the high water transparency and current velocity from 80 to 30 km upstream the dam diminished with a distance to the dam. The river length from 30 to 0 km upstream the dam is characterized by the conditions typical for reservoir. Eleven taxa of living mollusks have been traced at the bottom in the riverbed: all taxa found within the section of the river before the reservoir (80–30 km upstream the dam), total density ranged between 175 and 1420. Within the reservoir the number of taxa decreased to 5, density did not exceed 85 ind. m−2. Similar trend of mollusks distribution were observed in Vorskla River.The research showed a detrimental effect of dam on the mollusk fauna. One of the most imporant effects is the loss of rare and protected species such as Unio crassus and U. pictorum.