Abstract:
The hydrological characteristics of water basins in Pernik region, Bulgaria have been badly worsened since the summer of 2019. This study was performed in the low-flow period of December 2019 and covered eight sampling stations along the Struma River between Studena dam and Pchelina dam, region of the town of Pernik. The analytical data obtained and the calculated threshold pollution indices of the single nutrients PO4 3-, NO2 – , NO3 – and NH4 + and their integrated threshold pollution indices showed water pollution in respect of PO4 3- and NH4 + . The concentrations of PO4 3- at all stations, of NH4 + ions in the waters after Pernik city, and of NO3 – and NO2 – before Pchelina dam exceeded the respective maximum allowed concentrations (MAC) according to the Bulgarian legislation. The waters were pure in respect of the trace metals Al, Fe, Co, Ni, Cu, Zn, Cd, and Pb; only Mn exceeded its MAC. The chemical species of the trace metals were calculated by thermodynamic modeling and discussed on the base of the “Hard and Soft Acids and Bases” (HSAB) principle.