The article presents the results of study on the ecological state of Slana River (Slovakia) and an assessment of catastrophic pollution due to the mine water leakage from the Siderit iron ore mine (village of Nižná Slana). The geological structure of the siderite deposit is described, the organization of geochemical data monitoring is analyzed using trend analysis and a correlation matrix for ecological and hydrochemical tasks. The study has confirmed the increased content of Fe, Ni, Mn, sulfates and As (components of the ore formation). Spatial assessment of pollution was carried out using mathematical modeling and the Google Earth platform. It was identified that in the zone of mine water leakage, there is an increase in temperature, a low level of dissolved oxygen, a reduced pH and high concentrations of sulfates, Mg, Fe, As, Co, Zn. Analysis of spatial changes showed nonlinear (parabolic) dynamics of pollutant distribution. Correlation analysis revealed a strong positive relationship between pH and dissolved oxygen (90% probability), nitrates, sulfates, nitrogen (70–85%), Fe–sulfates, sulfates–nitrates, Mg–COD. Negative correlation (70–80%) is characteristic of Mg–nitrates, nitrates–dissolved solids (TDS), Ca–TDS. Environmental harm of metals is exacerbated by hardness, salinity and organic matter in water. Toxic metals (Zn, Pb, Cu, Cd) form insoluble sulfides, carbonates, precipitate (oxides/hydroxides) or co-precipitate with Fe, Mn, Al, with different redistribution rates. A combination of methods is recommended for the purification of Slana River: mechanical, physicochemical and biological with algolization of strain Chlorella vulgaris Polikarp. Optimal conditions for the development of Chlorella microalgae have been determined.
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