Application of the water quality index in the Timok River basin (Serbia)

The paper presents an analysis of water pollution carried out on the basis of the combined physico-chemical Serbian Water Quality Index (WQI) in the Timok River basin. The analysis covers various parameters (oxygen saturation, Five-Day Biochemical Oxygen Demand or BOD 5 , ammonium ion concentration, pH value, Water Total Nitrogen or WTN, Total Suspended Solids or TSS, orthophosphate concentration, electrical conductivity, temperature and the fecal coliform bacteria parameter) the values of which were calculated for four hydrological stations within the basin. The data obtained at each measurement station were averaged using the annual arithmetic average mean. The annual WQI values were calculated for a twenty-five year period (1990–2014) and they were in the range between 12 and 92, which means that the quality of water varied, ranging from “very bad” to “excellent”. The obtained results were interpreted and the watercourse quality was assessed using the comparison of water quality indicators according to the Serbian Classification of Surface Waters and the WQI method. The worst water quality was recorded in the Borska Reka River. Certain SWQI values are the result of water quality changes caused by wastewater from human settlements, industrial facilities, agricultural sources and illegal waste disposal sites in the basin.