Днестровский лиман

Purpose. Determination of long-term changes in bacterioplankton number in the Dnistrovskiy Estuary in 2003-2018 and data usage for aquatic environment quality assessment. Methods. Bacterioplankton number determination was done using direct microscopy method under microscope with magnification of 1200. Ecological classification of surface waters quality adopted in Ukraine was used for water trophic status assessment. Results. Changes of bacterioplankton quantitative characteristics in summer periods of 2003-2018 have been analyzed. Tendency of increase in bacteria quantity has been revealed in the past eight years, as well as the waters’ trophic status increase from polytrophic in summer periods of 2003-2005, 2007-2009 and 2015-2016 to hypertrophic in 2011-2014 and 2017-2018. Maximal out of all the years bacterial number was identified in July 2012 that exceeded the peak value in the end of past century. Existence of statistical connections between bacterioplankton and water conductivity, transparency, chlorophyll a, pheophytin and total phosphorus were shown. Conclusions. It has been established that microbiological regime forming in the Dnistrovskiy Estuary took place under the influence of natural processes of organic matter production and pollution factors that revealed themselves the most in the middle and southern parts of the estuary. Among the aquatic environment parameters controlled bacterioplankton number, like chlorophyll a, reflected the changes of the Dnistrovskiy Estuary trophic state the most realistic way. At that, index of bacterioplankton is indispensible for indication of water pollution with organic matter of anthropogenic origin.

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.