Impact of industrial and domestic wastewater on the water quality of the Tundzha River, Bulgaria

In the modern world, the anthropogenic pressure on water bodies is the result of the complex interaction of various factors. The different resources of pollution have a different degree and duration of influence on the state on the waters. Industry is a major user of water resources. The effects of industrial water pollution are harmful to both animals and plants as well as humans. Another key source of pollution of water bodies is a municipal sector. This research focuses on the cumulative pressures exerted mainly by industry and municipal waste management infrastructure, in the context of insufficient wastewater treatment. The main aim of this study was to obtain an assessment of water quality state of the Tundzha River, Bulgaria through analysis of ten physicochemical characteristics for the period 2016-2021. In the present study were applied the methods of analysis and synthesis, comparative method, mathematical and statistical methods, graphical method, cartographical method and complex index for evaluation of the river water quality (Canadian Water Quality Index - CCME WQI, 2001). The findings reveal that sections of the river located downstream show consistently degraded water quality, with parameters exceeding permissible thresholds under European Water Framework Directive 2000/60 standards and its equivalent criteria in Bulgarian law (Regulation H-4/2012 for characterization of surface waters). The river Asenovska before flowing into the Tundzha River has the worst quality of river water. Extreme maximum values have been established at this point for the indicators – N-NH4 - 116,33 mg/l, N-NO3 – 93,67 mg/l, N-NO2–110,67 mg/l and P-PO4 – 68 mg/l for 2021. The scientific and applied contributions of the obtained results are predetermined by the scarce researches on the qualitative state of the Tundzha River. The main conclusions in this study could be a good basis in the preparation of specific policies for sustainable management and use of river waters in the presented basin