Afanasyev S. Structure of biota of the river systems as indicator of their ecological status

Thesis comprehends results of the long-term hydrobiological studies of the river nets of Ukraine. Peculiarities of structural organization of biota of the mountainous and lowland river systems of different natural-climatic zones are determined. On this basis theoretical principles of assessment of ecological status of the river basins have been developed, where as fundamental provisions are used establishment of the reference hydrobiological, hydromorphological and hydrochemical characteristics for each water body and their comparison with actual data. Principles have been suggested and typification of the river systems have been carried out taking into consideration physical-geographical (ecoregion, size, elevation above sea level, geological structure of the riverbed), data on historical-geographic peculiarities of the river net forming and actual species composition of the aquatic organisms. Impact of anthropogenic factors (pollution, forest-cutting, drainage amelioration of the flood lands) on biotic communities has been investigated. Role of natural factors (flow processes, quality of substrate, water level fluctuation and catastrophic floods) in the biota's structure forming has been determined. Biota's response to the volley pollution discharges has been revealed. Mechanisms of maintaining and restoration of the river biota's structure under the impact of natural and anthropogenic factors have been established and investigated. Assessment of ecological status of the model river basins of the Tisa River and Prypiat' River has been carried out. Theoretical background, concept apparatus and methodology of the ecological risks assessment, arising from impact of the point pollution sources on the river ecosystems has been developed.