Environmental hydrochemical characteristics of groundwater in Dnieper Prysamarya as state indicator of reference and destructive biogeocenoses

In the paper, there is a characteristic of hydrochemical properties of the groundwater lying within the river valley of Samara Dniprovska, on the steppe plakor areas, under the automorphic soils and the water of the Samara River. In characterizing of the hydrochemical properties of the groundwater the author came from the fact that the groundwater, according to the previous studies (Kotovich, 2010, 2014), with varying degrees of share participation, is an integral part of the water balance of forest ecosystems and used by the wood vegetation. Based on the landscape principle of groundwater formation there are those that lie within the valley of the river Samara, as well as the groundwater of steppe plain regions with automorphic soils and areas with developed gullies and ravines. The groundwater of the river valley for its hydrochemical properties is not homogeneous, and there is a clear binding of hydrochemical indicators to the main geomorphological elements with typical for them soil cover. It was established that the groundwater of flood plain lying directly in the area of undermining near the town of Ternivka is the most mineralized – 1928 mg/dm3, due to slow water exchange with surface water because of sedimentation of the surface. Out of the influence of undermining zone the floodplain groundwater do not differ from the zonal groundwater; its mineralization is 1560–1050 mg/dm3. The groundwater of sandy terraces of the Samara river valley has azonal signs, namely – reduced salinity (110–150 mg/dm3), hydrocarbonate and calcium ion composition and acidic reaction of pH (4,5–5,7). It is noted that due to favorable filtration properties of sandy soil, salt concentration varies synchronously with the fluctuations of groundwater level. At the same time in the area of coal mining with transformed soil and hydrological conditions the groundwater has a higher salinity than the groundwater, lying outside the influence of mine water drainage, while the dynamics of change in mineralization lags behind fluctuations in the groundwater level for more than three and a half months. Within the third terrace of the Samara river valley the mirror of the groundwater begins at a depth of 1,5 m. The total mineralization – 2640 mg/dm3 – is significantly higher than in the groundwater of the first and the second terraces. The ion composition is dominated by sodium and chloride ions, and the pH reaction is close to neutral. The groundwater of the watershed areas between the Samara and Oril rivers lies at a considerable depth – 20 m, has mineralization of 2100 mg/dm3, and the ionic composition is dominated by chloride ions and calcium. At the same time, the groundwater in the area of developed network of gullies and ravines has a lower mineralization – 650 mg/dm3. It can be assumed that the differences are related to the terms of draining of aquifers. Analysis of long-term data of salinity in the Samara river demonstrated an increase in this index from 1738 mg/dm3 in 1929 to 3540 mg/dm3 in 2006.