Cherkez Ye. A.

Purpose. To study hydrodynamic prerequisites of forming and to assess the volume of subaqueous discharge of Upper-Sarmatian aquifer into the Kuyalnyk Estuary. Objects and methods. Hydrodynamic model determining changes in direction and volume of exchange between groundwater and surface water of estuary based on the ratio of levels (pressures) has been taken as the methodological basis. Results. It has been established based on many years’ hydrogeological and hydrological observations (1950 - 2016) that water exchange between groundwater and surface water of the estuary, depending on changes of hydrogeodynamic conditions with time, is characterized by both up and down flows. The results of calculation of specific discharge of water exchange between Upper-Sarmatian aquifer and surface water of the estuary show that after a long (30 - 40 years) period of water down filtration from the estuary just after mid-90th of last century a slow process of estuary refilling with groundwater started. As of 2016, the subaqueous constituent of the estuary ground feeding makes around 20% of the total water volume in the estuary. Conclusions. Assessing water balance of the Kuyalnyk Estuary, together with traditional factors forming its hydrogeological regime (atmospheric precipitation, river discharge, surface run-off and evaporation), one should take into account spatial and temporal changes in subaqueous constituent of the estuary groundwater feeding.

Purpose. Assessment of bottom sediments accumulation rate for two areas of the Kuyalnyk Estuary using radionuclide method. Methods. The study has been done in two areas of the Kuyalnyk Estuary: the middle part near Kovalivka village and the lower part to the north from the sanatorium, using the standard methods of sedi-ment columns sampling and gamma-spectrometric analysis of radionuclides concentration. Results. Based on the results of the studies of 2016, layer-by-layer concentrations of Cesium-137, Potassium-40, Radium-226 and Torium-232 were determined. Analysis of vertical profiles of Cesium-137 concentrations enabled us to assess, for the first time, the intensity of sediments accumulation in two areas of the estuary for the periods 1962-1986-2016, which later were used for indicative dating of anomalies in the distribution of natural radionuclides Potas-sium-40, Radium-226 and Torium-232 concentrations. Conclusions. It has been shown that in the lower and middle parts of the Kuyalnyk Estuary the average rate of sediments accumulation in 1986 – 2016 made 0.8±0.1 mm/year and 1.8±0.2 mm/year respectively. In 1962-1986 sediments accumulation rate was prac-tically the same in both parts of the estuary and made 1.9±0. mm/year. The average values for the period 1962-2016 made 1.6±0.1 mm/year and 1.8±0.2 mm/year for the lower and middle parts of the estuary respectively. It has been proposed to perform additional mineralogical studies for more precise dating of the sediment layers accumulated before 1962 and to use radionuclide method for determination of sediment accumulation rate in other water bodies of the Black Sea region.

One of the main reasons for the necessity of our study was the fact that previous researchers used only model experiments on the impact of dilution of sulfuric mud on seawater and did not take into account in their conclusions the fundamental foundations of the functioning of ecosystems, such as the cyclicity of the salt and hydrological balance and the cyclic functioning of biocenosis in Ecosystem of the estuarine complex.Purpose. Revealing of real biological consequences of the Kuyalnik Estuary filling with big amounts of marine water in 2014-2016. Methods. Standard methods of hydrological, hydrochemical, hydrobiological and microbiological studies. Results. Based on the comprehensive studies the analysis of dynamics of the Kuyalnik Estuary ecosystem’s main physicochemical and hydrobiological characteristics has been performed, first of all of species composition, abundance and biomass of phytoplankton, bacterioplankton, zooplankton and concentrations of photosynthetic pigments. It has been shown that the studied biological characteristics have seasonal variations, the main reasons of which are changes in temperature and mineral content of the estuarine water, as well as the cases of gypsum sedimentation observed in summer of 2015 and 2016. Conclusions. Feeding of marine water did not achieve the expected result of stable estuarine water freshening, but worsened the situation with the unique biocoenosis. The current methodology of the estuary refilling with marine water causes negative consequences, which aggravate with each next feeding of marine water into the estuary and will accrue and entail the irreversible processes and complete degradation of the estuary’s ecosystem. We propose to focus on the restoration of the freshwater flow of the Big Kuyalnik River and the search for other engineering solutions.