Restoration of Salinity in the Sivash Bay to Natural Levels after the Closure of the North Crimean Canal

The paper analyzes the salinity dynamics in the Sivash Bay after the closure of the NorthCrimean based on the data from field research carried out by MHI RAS in 2014–2020. Recent field data are compared with the literature data obtained in the period before the commissioning of the North Crimean Canal. Salinity in water samples taken during 18 expeditions to the Eastern and Southern Sivash at over 100 stations was determined using the refractometric method. It was shown that after the closure of the North Crimean Canal in 2014, there was a steep increase in salinity in the Eastern and Southern Sivash. It was determined that in the area of the Sivash Bay, the haline field changes non-uniformly. The data analysis showed that salinity increases from north to south (from the Eastern to Southern Sivash), moreover salinity values in the Southern Sivash can be several times higher than those in the Eastern Sivash. In spring 2014, salinity in the Eastern Sivash varied from 27 to 33 ‰, and in 2020, 6 years after the closure of the Canal, salinity increased significantly at all stations reaching 60–70 ‰. These values are comparable to those obtained before the start of the Canal in the 1950s. The highest salinity values were observed in the South Sivash: in 2013, it was 54 ‰ and in summer 2020, for the first time since the North Crimean Canal became operational, it reached 110 ‰, which almost corresponds to the salinity level observed in 1969.

Structural and Optical Characteristics of Aqueous Solutions of Acetic Acid

A refractometric method, coupled with molecular dynamics study, attenuated total reflection Fourier transform infrared (ATR FT-IR), and Raman spectroscopy, was used to determine optical characteristics of concentration features of aqueous solutions of acetic acid. Measurements of the refractive index of aqueous solutions of acetic acid in the wide range of acetic acid concentrations (∼ 0 ÷ 1 mole fraction) in a solution at a room temperature were conducted. Maximum value of refractive index was detected at a concentration of ∼0.3 mole fraction. The deviation from the parabolic form of the dependence of the refractive index on the concentration occurs at a concentration of ∼0.8 mole fraction. As far as we know, this deviation has been observed for the first time. The maximum is attributed to the largest number of molecular interactions between water and acetic acid molecules, while the deviation is associated with the parallel orientation of acetic acid molecules. To identify the reconstructing of molecules in the system, FT-IR and Raman spectra of these solutions at a concentration of ∼0.3 and ∼0.8 mole fraction were recorded and compared with pure solutions. The data obtained by using ATR FT-IR and Raman spectroscopy support the idea that the refractometric method is sensitive to determine the structural states of aqueous solutions of acetic acid.