Medinets V.I.

Purpose. To reveal seasonal changes in phytoplankton quantitative characteristics including biodiversity and species composition of potentially dangerous (toxic) species. Methods. Phytoplankton sampling in Odessa bay coastal waters and sample analyses were carried out using standard methodologies. The samples were preserved using formalin. Microscopes HUND−H600 and OLYMPUS−BH2 have been used for sample analyses. Classification of microalgae and Cyanobacteria was done according to the standards of the international database. Results. Analysis of the main abiotic factors influencing the state of phytocene has been carried out. In the species composition, 238 species of phytoplankton belonging to 11 classes have been registered: diatoms − Bacillariophyceae, dinophytes − Dinophyceae, green − Chlorophyceae, Cyanobacteria, Prymnesiophyceae, Euglenoidea, Chrysophyceae, Cryptophyceae, Dictyochophyceae, Choanoflagellatea. It was shown that the dominant phytoplankton species were Bacillariophyceae, Dinophyceae, Chlorophyceae and Cyanobacteria. For the first time, 11 freshwater species of dinophytes were registered in the Zmiinyi Island area. Statistical interconnections between phytoplankton metrics and abiotic characteristics were analysed. Development of 54 phytoplankton species, which refer to the group of potentially harmful (toxic) was registered; out of this number, 21 reached blooming level. Conclusions. The main abiotic factors determining the state of phytoplankton and its seasonal changes are salinity and transparency. During 2016−2017, 4 seasonal maximums of microalgae development were registered in the photic layer of the Zmiinyi Island coastal waters (in spring, summer, autumn and winter), which corresponded to the terms of the normal periodicity of the Black Sea phytoplankton vegetation. Comparison of modern maximum values with similar data obtained in previous years, allows us to conclude that a significant increase in the quantitative characteristics of phytoplankton took place in 2016−2017. The quality of water in the surface layers in the Zmiinyi Island area assessed using the main metrics of phytoplankton was much lower than that in the bottom water layers, which was caused by the Danube River discharge impact, first of all, observed in the surface layers of water.

Purpose. The study of the features of long-term changes of the Dniester Estuary hydrological regime main characteristics in 2012-2017 based on the results of annual surveys performed by Odessa National I. I. Mechnikov University. Methods. Measuring of the water transparency, temperature and electrical conductivity in the surface and near-bottom layers were carried out using standard techniques with Secchi disk and portable HACH analyser with temperature and conductivity sensors. Results. Based on the studies performed, almost two times decrease in water transparency values in summer of 2012-2017 has been established compared with the same period of 2003-2011. It was shown that the maximum transparency values were observed in the southern part of the estuary, where the presence of seawater is almost constant. Analysis of electrical conductivity spatial distribution has revealed practically constant influence effect of seawater intrusion in the southern part of the estuary, especially in the bottom layer, and periodical influence effect in the middle and northern parts. Significant increasing of the range of water temperature and electrical conductivity variations in the Dniester Estuary has been recorded in summer 2012-2017 comparison with summer 2003-2011. Conclusions. The established peculiarities of hydrological characteristics’ spatial distribution indicate that river discharge and intrusion of marine water are the most important factors determining the Dniester Estuary hydrological regime. Increase of temperature and conductivity of the Dniester Estuary water in summer 2012-2017 in comparison with 2003-2011 was registered. An anomalous penetration of marine waters into most part of the estuary was detected in July 2016, which in the past was observed for the last time in 2011.