The aim of this research is to provide the assessment of water quality with a wider scheme of interrelations between the water quality parameters and locations using a reliable visual approach of multicriteria PROMETHEE and GAIA methods. The case study of one of the largest and regionally most important catchment areas on the territory of the Republic of Serbia—the Tisa River Basin—was therein used. The analysis of water quality included scenarios for warm (summer), cold (winter), and average annual period. A partial and complete ranking of locations according to the quality of water was performed by applying the PROMETHEE method and expanded afterward by GAIA method analysis to point out critical locations with endangered water quality (M6, M4, and M11). Identified locations were then investigated in more detail using spider web graphs that revealed water quality variables of concern (PO4-P and N) and indicated the causes of its occurrence. The obtained results are in accordance with the results of physical and chemical tests that are regularly conducted by the official government agencies for environmental protection and the reports that are presented to the public. The presented approach can easily be applied to any water body to point out both the locations with reduced water quality and the specific parameters (causes) that affect the reduction of water quality at these locations, thereby enhancing and strengthening usual water quality assessments as well as water resources management in general.

Nutrient pollution represents an ongoing problem and a great challenge to water resources management around the world. Therefore, the aim of this paper is to contribute to the efforts of the water resources management in considering a problem of the nutrient pollution of water from a multicriteria decision-making point of view. The combined PROMETHEE and GAIA analysis in this paper included indicators of nutrients in the water (total nitrogen, nitrite, nitrate, ammonium ion, total phosphorus, and orthophosphates) to rank and evaluate significant sites along the Danube River flow through Serbia. Furthermore, the ecological quality status of the water was determined which places the Danube River into the category of “good” to “moderate” water quality. The results represent a detailed evaluation of the sites with increased nutrient content, associated with the most dominant parameters of nutrient indicators affecting water pollution at each site. The main sources of nonpoint pollution are of anthropogenic origin reflected in agricultural applications of pesticides and fertilizers, together with natural contamination of ground and water sources, while pollution from point sources arises from industrial waste waters as well as from domestic activities. Minimizing the application of fertilizers and pesticides is a way to control pollution from agricultural activities while, at the same time, a proper wastewater treatment is needed to reduce point sources, although financial aspects and lack of funds are limiting factors of this control in Serbia. Therefore, the findings in this paper could serve environmental scientists and water resources managers as a starting point in identifying key sources of nutrient pollution in water, as well as industry experts and national authorities in expanding strategies and taking long-term measures to reduce the input of nutrients into the valuable Danube River.

The assessment of the Danube water pollution in this study was conducted based on the content of total nitrogen (N) and total phosphorus (P) in the water samples collected from three measuring stations on the Danube River in Serbia. The stations were selected with the intention to depict the three points of the flow of the river through Serbia, namely, the input, center and output profile of the river. The values of the indicators of nutrients were observed annually in the time period from 2013 to 2015, as the average value of monthly measurements at each station, and compared with the limit values prescribed by the Regulations on limit values of pollutants in the surface and ground waters and sediments. In addition, the paper presents the three-year trend of changes in the value of the observed parameters in order to determine certain regularity of changes in the content of nitrogen and phosphorus in the water. Also, fluctuations in the value on a monthly basis are also taken into consideration and are presented in this paper in order to see all possible deviations and trend of changes per annum. The results obtained in this paper showed that nutrient concentrations have exceeded prescribed limit values which put the water quality of the Danube River into class III according to current regulations in Serbia, indicating the nutrient pollution of the Danube at the observed locations. The three-year trend of changes points to the tendency of the linear growth of nutrients in the aquatic ecosystem of the Danube which are endangering the quality of water, and this is an alarm signal and urgent call for the implementation of appropriate protective measures.