HYDROLOGICAL CHARACTERISTICS OF THE DNIESTER ESTUARY BY SURVEYS IN THE SUMMER’S OF 2003–2019

Abstract

Problem Statement and Purpose. The Lower Dniester delta and the Dniester estuary are very important because they are natural filters of the river water from pollution and suspended matter, as well as they are the habitat of a large number species of flora and fauna. The construction of reservoirs on the Dniester River in past completely changed the hydrological regime of the river itself and of the Dniester estuary. For these reasons a constant environmental monitoring of the aquatic environment are required. Since 2002 Odessa I. I. Mechnikov National University has been carrying out a wide range of environmental studies in the Dniester estuary, one of aspects of which is observation of hydrological characteristics. The purpose of this paper is to study long-term changes in transparency, temperature and electrical conductivity of the Dniester estuary water in the summer periods of 2003–2019. Materials & Methods. Measurements of transparency, temperature and electrical conductivity of water in the Dniester estuary in the indicated years were carried out according to standard methods at 19 ecological stations. Statistical processing, analysis and mapping of the measurements results were conducted in EXCEL, ARCGIS, SURFER software’s. Data analysis was based on a graphical representation of the spatial distribution of characteristics, as well as by identifying the features of long-term changes in these characteristics. Main Results and Conclusions. On the basis of the summer surveys during 2003–2019 more than double decrease of water transparency mean values in the Dniester estuary has been established. It was found that the maximum transparency values were observed in the central parts of the estuary, far from settlements. For theseyears, an increase of the mean water temperature for the estuary northern part and its decrease in the middle and southern parts has been recorded. Also, for the summer period of these years, an increase of the mean water electrical conductivity in all parts of the estuary was established. The established features of spatial distribution of hydrological characteristics indicate to the river runoff, intrusion of seawater into the estuary, and wind activity as the determining factors in formation of the estuary hydrological regime. Recorded long-term trends of the means transparency values decreasing and the means temperature and electrical conductivity increasing of the Dniester estuary water in the summer of 2003–2019 are considered as consequences of the river discharge decreasing due to long-term climatic changes over Europe and man regulation of river flow.