Micro- and macrofauna of benthic invertebrates of the estuary section of the Mokra Moskovka, a small river in the City of Zaporizhzhia

Abstract

Nowadays, in the period of scientific and technological progress, the anthropogenic impact on the environment keeps increasing. At the same time, its forms and its degree are very diverse. The study of aquatic ecosystems, including ecosystems of small rivers, is one of the applied environmental researches. Small rivers form water resources, hydrochemical composition and water quality of medium and large rivers. They form natural landscapes and contribute to human economic activities.
 Most of the indicators classify the current environmental state of small and medium rivers of Zaporizhzhia Region as unsatisfactory. The main reason for this situation is an excessive anthropogenic load on environmental systems of small rivers that have a noticeable reaction to any interference. One of the consequences of this process includes siltation of small rivers. A small river Mokra Moskovka is not an exception to the above-described characteristics of aquatic ecosystems. The river flows through the territory of Zaporizhzhia Region and its lower part of about 11 km long flows in the densely built-up part of the City of Zaporizhzhya. The mouth section of the Mokra Moskovka River is 2.6 km long and runs through the territory of Aleksandrovsky and Kommunarsky districts of Zaporizhzhia from the river's mouth to the Zaporizhzhia-1-Zaporizhzhia-2 railway bridge. Over the years of its existence, the mouth section of the small river's bed silted up considerably and has an unsatisfactory condition. This is due to the rising of the Kakhovka Reservoir water level and daily fluctuations of the Dnipro's water level that together lead to the reverse movement of water masses and emergence of stagnant phenomena within the studied portion of the river's bed. In addition, the outlets of the municipal rainwater drainage system present a significant source of the sediment, debris and pollutants entering the river.
 In order to improve the environmental condition of the Mokra Moskovka and remove its silt sediments within the bounds of the city, the riverbed was being cleared during 2004-2013. Our data indicate that the thickness of the river's silt sediments reaches 1.0-1.5 m in some places. To restore and maintain favorable hydrological regime and sanitary condition of the mouth section of the Mokra Moskovka it is planned to clean the mouth section of the river channel from silt sediments using hydromechanization technologies and dredging mechanisms in 2022-2023 (scheduled activities).
 The research is aimed at studying the structural organization of the bottom fauna of the estuary section of a small river Mokra Moskovka within the urban ecosystem. The work is based on the results of our own hydrobiological research. During the observation that took place in 2021 53 species of benthic invertebrates were recorded at the mouth of the watercourse. It was found that, out of the total number, 21 species belonged to the macrozoobenthos and 32 – to the benthic microfauna groupings. The conducted saprobiological assessment of the studied river sections for the indicated organisms of micro- and macrozoobenthos revealed that the surveyed part of the watercourse belongs to the α-mesosaprobic zone and is classified as "polluted waters" according to the surface water quality classification. In order to improve the environmental condition of the mouth section of the Mokra Moskovka River it is necessary to implement certain measures of biological water treatment using modern biotechnological solutions developed in Ukraine.