Zooplankton and zoobenthos of the Mokra Sura river

Purpose. To study the spatial distribution of structural and functional indicators of zooplankton and zoobenthos during the period of maximum development of hydrobiocenosis in the contaminated and conditionally clean sites of the Mokra Sura river being under antropogenic pressure. Methodology. During the collection and subsequent laboratory processing of zooplankton and zoobenthos samples, we used the standard conventional hydrobiological methods. In order to rank the studied river sites, we used the combined index of the community state (CICS) based on the structural-functional indicators of zoobenthos. Findings. The research results have shown that the species composition of zoobenthos and zooplankton of the Mokra Sura river included many saprobiontic species such as oligochaetes, chironomids and rotifers, which were developed significantly in some sites under the effect of eutrophication and silt accumulation in the presence of anthropogenic pollution. The above-mentioned processes cause inhibition of the life activity of such filter feeders as mollusks and crustaceans being the most powerful zooplanktonic and zoobenthic agents of self-cleaning. The highest numbers of zooplankton and zoobenthos development were recorded in front of the point of the emergency discharge of right-bank sewage water (stimulating effect of organic pollution) while the lowest numbers were registered near the tire plant (combined effect of both chemical sewage pollution and silt accumulation). In the «Dnipro - Zaporizhzhia highway» site, low numbers of zooplankton development were the result of silt accumulation, whereas the zoobenthos biomass turned out to be the highest due to the intensive development of oligochaetes. Planktonic saprobiontic rotifers dominated in the site located in front of the sewage discharge whereas bdelloid rotifers dominated in the upstream sites of the river. The dominance of planktonic and benthic saprobiontic rotifers caused the highest saprobity indices in these sites. According to CICS index, the sites of 3 km and 2 km upstream from the river mouth were the purest ones as indicated by the greatest development of filter feeding crustaceans and the lowest indices of saprobity compared to the other sites studied. These results indicate a very effective biogenic detoxification and precipitation of toxic substances entering the river in the above-mentioned areas, as well as dilution effects of large water masses from the Dnieper River in the mouth areas of its tributaries Originality. For the first time, the ecological state of the selected sites of the Mokra Sura River was assessed on the basis of the results of a comprehensive study of the structural and functional indicators of zooplankton and zoobenthos during the maximum development of their hydrobiocenosis. Practical value. The obtained results can be used for hydroecological monitoring to detect the dangerous ecological state of small rivers and to prevent further degradation of the ecosystems of small rivers as well as for calculation of fish losses caused by sewage water effects.