Abstract

 
 
 The paper relevancy is determined by the need to substantiate the feasibility of restoring the ecosystem of the Sasyk estuary after its transformation into a reservoir (1978) and the unsuccessful desalination by the Danube waters for irrigation purposes. The paper is aimed at assessment of the possible inflow of fresh water to the Sasyk estuary from the Kohylnyk and Sarata rivers and their role in the formation of fresh water balance in the first half of the 21st century according to the climate change scenarios RCP4.5 and RCP8.5. The main calculation method is the ‘climate-runoff’ model, which uses meteorological data as input data. Estimates of freshwater inflow into the estuary-reservoir are provided for various calculation periods: before 1989 (before the beginning of significant climate change in the North-Western Black Sea Region); in the period of 1989-2018 according to the hydrometeorological observations; in 2021-2050, according to the averaged data from 14 runs of scenarios RCP4.5 and RCP8.5 under the EVRO-CORDEX project. Estimates of the average long-term values of freshwater inflow in natural conditions and the conditions transformed by water management activity were obtained for each calculation period. It is found that owing to changes in the regional climate for the period of 2021-2050, the total inflow of freshwater from rivers to the estuary in natural conditions will decrease by 23.5 % (by RCP4.5) and by 38.5 % (by RCP8.5) in comparison with the reference period (before 1989). Taking into account the impact of artificial reservoirs, the reduction in the river runoff will be 52.1 % (by RCP4.5) and 64.7 % (by RCP8.5). It is defined, that in case of renaturalization of the Sasyk reservoir into the estuary and the water inflow cut-off from the Danube river, the changes in climatic conditions expected in the first half of the 21st century, combined with water management activity, will result in the increased deficit of annual freshwater balance of the Sasyk reservoir up to 62 % under the RCP4.5 scenario and up to 75 % under the RCP8.5 scenario compared to the period before the emergence of climate change (before 1989). This change must be considered in scientific substantiation of the project on a reversion of the Sasyk Reservoir to the original status of the estuary to ensure such conditions of water exchange with the sea (for compensation of the water balance deficit), which will prevent the long-term trend of salinization.
 
 
Highlights
The urgency of providing estimates of freshwater inflows into the Sasyk estuary based on climate change scenarios in the 21st century is determined by the directions of the Strategy (IPCC, 2014) to reduce the climate change effects and consequences
This study is related to the existence of risks of the loss of biodiversity and the ecosystem functions and services of the Sasyk water body in the case of its renaturalization into the estuary owing to the reduced freshwater inflow in modern climate conditions and those expected in the 21st century
According to the ‘climate-runoff’ model developed by OSENU (Odessa State Environmental University), the estimates of freshwater inflow from the Kohylnyk and Sarata rivers to the Sasyk estuary are provided
Summary
The urgency of providing estimates of freshwater inflows into the Sasyk estuary based on climate change scenarios in the 21st century is determined by the directions of the Strategy (IPCC, 2014) to reduce the climate change effects and consequences. The main task of this study is to substantiate the feasibility of restoration of the functioning of the Sasyk water body as an estuary, which in the last century for irrigation purposes was converted into a reservoir by separating it from the sea and desalination with the Danube waters. The research object includes changes in the freshwater inflow from the rivers Kohylnyk and Sarata to the Sasyk reservoir (estuary) depending on climatic conditions and water management activities. The subject of research is the assessment of possible changes in the inflow of freshwater from the rivers Kohylnyk and Sarata into the lake under the climatic conditions of the first half of the 21st century. The water quality in the estuary currently remains unsatisfactory: a high mineralization of water is maintained, and the maximum permissible concentrations of chlorides, sulphates, heavy metals, phenols and pesticides
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