Complex multivariate water quality impact assessment on Krivaja River

Abstract This study assesses the water quality of the upper course of the Krivaja River in northern Serbia, part of the Tisza and Danube catchments. The analysis focuses on a 2 km stretch with the highest pollution levels, using monitoring data from 2014 to 2017 and synthetic surface water pollution indicators. A total of 96 samples were collected at 6 different surface water sampling points, 16 per site. Wastewater were collected from 4 sampling points, 16 before its inflow into the Krivaja River and 32 as effluent. Surface water sampling where taken in accordance with SRPS EN ISO 5667-3:2007, and wastewater with SRPS ISO 5667-10: 2007 methods. Analyses of metals in water samples were carried out by atomic absorption spectroscopy, and nitrogen and phosphorus compounds were measured by UV spectrophotometry. Comparison with national standards revealed extremely high pollution levels: COD exceeded limits by 43 times, BOD 5 by 76 times, total nitrogen by 23 times, and N-NH 3 by 211 times. Nickel concentrations also surpassed the European Union Directive 2013/39/EU limits. The Nemerow index values (27.6–102) highlighted heavily polluted discharge sources, such as animal feed production. Cluster analysis confirmed these findings. Key pollutants include organic indicators (COD, BOD 5 , KMnO 4 ), nutrients (NO 2 − , NO 3 − , TN, N-NH 3 ), TSS, Cl − , and Fe. Metals (Mn, Zn, Ni, Pb, Cu, Cr, Cd, As) showed minor variations, minimally impacting the overall score. Poultry wastewater exhibited significant quality fluctuations, ranging from moderately to heavily polluted (PIW = 4.05–8.20). The primary cause of poor water quality is inadequate wastewater treatment in the region. Urgent measures are needed to mitigate pollution and restore the Krivaja River’s ecological integrity.