Abstract:
The Water Framework Directive (WFD) 2000/60/EC aims to achieve both a good ecological and physicochemical status of all surface water bodies, and a good chemical and quantitative status of groundwater resources by 2021. Currently, the implementation of this goal appears to be a difficult task. Despite the great efforts made by the stakeholders in the last decades, the majority of Europe’s water bodies still do not meet the requirements. On a European scale, around 38 per cent of water pollution is caused by chemical and organic agricultural wastes. In addition, the unregulated waste disposal from livestock farms into streams and lakes is also a serious problem. Nutrient enrichment causing eutrophication is the main effect from these unsustainable anthropogenic practices. Although during the last years the water bodies in Bulgaria tend to maintain relatively good hydro-ecological status, the discharge of agricultural chemicals and the disposal of household wastes remain the main polluting activities, particularly in rural areas. This study presents an assessment of the physicochemical properties and water quality of the Tsibritsa River (NW Bulgaria) – a small lowland stream, situated in an extensive agricultural region with cultivation of cereal crops. The main river body springs from the Fore-Balkans and flows as a right tributary into the Danube River within the Danube Plain. The length of the Tsibritsa River is 87.5 km and its drainage basin covers an area of 933.6 km2 . The catchment area is covered by arable lands polluting the surface water bodies due to the discharge of soil runoff containing fertilizers, manures and pesticides. Furthermore, the release of untreated wastewater from livestock farms and domestic sources in the small settlements without urban sewerage systems is also problematic. The input data includes information about ten physicochemical water quality parameters – pH, electrical conductivity (EC), dissolved oxygen (DO2 ), ammonium nitrogen (N-NH4 ), nitrite nitrogen (N-NO2 ), nitrate nitrogen (N-NO3 ), total nitrogen (N-tot), orthophosphates (P-PO4 ), total phosphorus (P-tot) and five-day biochemical oxygen demand (BOD5 ), measured at one water sampling point located near to the river’s mouth. A total of 60 samples for each variable, recorded during the period 2003–2017 have been used. The analysis has been conducted in compliance with the reference values stated in the National Regulatory Framework (Regulation 4/2012). The general water quality status has been determined according to the “one out – all out” principle, by the element with the worst status out of all physicochemical elements. The descriptive statistics (mean, minimum and maximum values) and a correlation matrix between each pair of two variables have been computed. The Canadian Council of Ministers of the Environment Water Quality Index (CCME WQI) for an overall assessment has also been applied. Its calculation is conducted according to the values for “Good status”, recommended for surface water bodies of type R8 (Regulation 4/2012). Results show increased concentrations of nitrate nitrogen (NNO3 ), total nitrogen (N-tot), total phosphorus (P-tot) and orthophosphates (P-PO4 ) (up to 40 times above the threshold values for “Good quality status”, stated in Regulation 4/2012). Over 50 per cent of these variables have been assessed to be of “Moderate status”. Those results can be explained by the excessive use of chemical substances in agriculture and the release of untreated wastes from livestock farms into the river channel. At the same time, some of the physicochemical parameters have been assessed as ones of “Excellent status”, e.g. EC and DO2 . The correlation matrix between various variables shows the following strong, positive relationships (r>0.9): “N-NO3 – N-tot” and “P-PO4 – P-tot”. These physicochemical parameters are indicative for organic pollution. According to the “one out – all out” principle and due to the significant excesses in the values of nitrates and phosphates, the overall physicochemical status of the Tsibritsa River is assessed as “Moderate”. The annual values of CCME WQI vary from 38.9 (2004) to 74.0 (2015), which means the water is “severely impaired” and “slightly polluted”, respectively. The calculation of CCME WQI shows an overall worsening of water quality in 2004, 2007 and 2008. Then, because of the failure of six physicochemical parameters (N-NH4 , N-NO3 , N-tot, P-PO4 , P-tot, BOD5 ), the status is categorized as “Poor”, meaning water quality is impaired and the conditions usually depart from the natural levels. On the other hand, in 2011, 2013, 2014, 2015, 2016 and 2017, due to the failure of two or three parameters (N-NO3 , N-tot, P-PO4 ), the CCME WQI indicates “Fair status”, which means water quality is usually protected and the conditions sometimes depart from the desirable levels. Although a positive trend in water quality parameters is detected after 2011, the CCME WQI generally shows “Marginal” and “Poor” ratings. In order to achieve better physicochemical conditions and to maintain good water quality of the Tsibritsa River, the adoption of sustainable land use practices and the construction of urban wastewater treatment plants are recommended.