Black Sea estuaries are phenomenon of geological nature and are not only an important component of the Black Sea geoecosystem, but also they are important component of local and regional ecological, socioeconomic systems of the coastal territory of Ukraine. Affecting the livelihoods and wellbeing of the population of these systems, estuaries from ancient times have attracted the attention of researchers. Unfortunately, the ecological status of these reservoirs has been worsening over the last decades because of the complex of reasons that require comprehensive study, analysis, development and implementation of a specific system of action, which cannot be realized without knowing at least the major milestones in the history of the research of these unique formations. Based on the published materials, information on the history of studies of estuaries of the northwestern Black Sea coast has been systematized. The history of the research has been reproduced in chronological order for the largest estuaries of the Black Sea, taking into account the current level of their study and identifying the main problems regarding their ecological status. The article gives a brief description of the current conditions and status of the largest Black Sea estuaries and some facts from the history of their research. In order to preserve the natural value of estuaries for their further research and rational use, the authors propose to use the methodology, the basic component of which is the geoecosystem paradigm, and henceforth study each estuary as a complete geoecological system taking into account all its components (subsystems), elements and conditions, which affect the formation and functioning of all components and the system as a whole. Geoecosystem paradigm together with a certain ecological and economic approach will allow to study in detail the geoecological conditions of water area of estuaries and adjacent territories, to evaluate their geoecological systems in terms of the prospects for their provision of certain services to the individual and / or society. Geoecosystem paradigm also allows to draw conclusions on optimizing the use of resources of these estuaries.

The Dniester Estuary is a unique natural object that was formed and exists within the transitional area between the geoecosystems of the Black Sea and the mainland, which determines its hydrological regime, features of bottom sediments, quality characteristics of water and other properties. The Dniester Estuary should be considered as a separate and integral geoecosystem, which is composed of interdependent subsystems. Today, anthropogenic activity has a great influence on the state of the estuary, especially the role of the military factor is growing, which is explained by hostilities and destruction in the region where the reservoir is located. In order to assess changes and ensure effective use of reservoir resources in the future, a comprehensive analysis of the pre-war state of the Dniester Estuary is absolutely necessary. The article summarizes the existing information about the bottom sediments of the Dniester Estuary and the unknown results of the expedition research of the reservoir, which were carried out by the authors in 2020-2021. 35 samples of the rocks of the shore and the bottom of the reservoir, as well as 25 samples of water from the bottom layer, were taken. A primary lithological description, an analysis of the granulometric composition of sands, and the content of heavy metals (Pb, Cr, Cu, Cd, Zn) were carried out for samples of bottom and coastal sediments. Maps of the distribution of some of them in the bottom sediments of the reservoir were built, as well as a comparison of the content of these metals with the content in the bottom sediments of adjacent territories, adjacent soils, in the bottom sediments of other estuaries of the northwestern Black Sea region, as well as with existing regulatory characteristics. Elevated concentrations of Pb were established. In the article, the authors present the results of their own research into the regularities of the distribution of pH parameters, redox potential, salinity, and mineralization of water, and for some samples, the powers of the ambient equivalent dose of gamma radiation were determined. A map of the distribution of mineralization values of the southwestern part of the reservoir was constructed. Features of dependence of parameters of mineralization and salinity on pH values were established. The authors identified the main climatic and geomorphological factors affecting and controlling the geoecosystem of the estuary. The article is illustrated with the author's photographs.

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The Black Sea estuaries are unique natural formations that havegreat geoecological and recreational importance. But their ecological state is almost critical and requires developing effective measures to preserve them and restore the geoecological balance. On the basis of literary and field materials, the article analyzes the information about the history of research of estuaries within the northwest coast of the Black Sea. The current state and problematic situations in the study of their morphology, dynamics and regime are determined, the current problems for each estuary are emphasized. On the basis of field geological and geomorphological investigations and remote sensing data, the features of gravitational geological processes within the coastal zones are characterized. Changes in the morphology of the coastline and estuary areas during 2015–2020 are analyzed. Modern hydrological characteristics and features of ecological condition of these estuaries are given. Perspectives of further research of these objects are determined. To preserve the natural value of the estuaries as a unique transition zone between sea and land (geoecoton), the geoecological research approachis proposed to use