Factor-cluster profiling of water quality in the Southern Bug Basin
DOI:
https://doi.org/10.26565/2410-7360-2026-64-24Keywords:
surface waters, Southern Bug, hydrochemical profile, state monitoring, organic pollution, nutrients, mineralization, maximum permissible concentration, clustering, pollution indexAbstract
Introduction. The Southern Bug River Basin is one of the largest water-management systems of Right-Bank Ukraine, where natural runoff seasonality combines with sustained pressure from urbanized areas, agriculture, municipal wastewater, and industry. Existing studies either assess isolated water-quality indices, apply multivariate statistics without regulatory interpretation, or treat Ukraine at a generalized inter-basin level, so a reproducible basin-scale profile combining multiyear averages, seasonality, regulatory exceedances, and site typology is lacking for the Southern Bug. The purpose of the study was to perform factor-cluster and regulatory-index profiling of longterm hydrochemical series for rivers of the Southern Bug Basin, identifying reaches dominated by organic, nutrient, or mineralization-salinity pollution and ranking sites by hydrochemical risk. The object is surface waters of rivers within the Southern Bug Basin; the subject is the long-term structure of hydrochemical indicators, their seasonal variability, regulatory exceedances, and cluster profiles of monitoring sites.
Methods. The analysis used processed data of the state surface-water monitoring system of the State Water Agency of Ukraine for 13 January 2003 – 18 March 2026 (5,654 records, 95 sites). After plausibility control, 57 technical extremes were removed. Multiyear mean concentrations and seasonal profiles were calculated for organicoxygen, nutrient, and mineralization-salinity blocks. Exceedance ratios and violation frequencies were computed against domestic-use and fishery-use reference values, and a screening index I6 was built as the mean of the six highest partial exceedance ratios per site. Indicators were robustly standardized, visualized by principal component analysis, and grouped by k-means clustering.
Results. Under domestic-use reference values, the most frequent exceedances were COD (42.9% of samples), permanganate oxidizability (40.8%), and BOD5 (14.8%). Under fishery-use reference values, violations were far more widespread: BOD5 – 60.4%, COD – 42.9%, sulphates – 42.4%, permanganate oxidizability – 40.8%, nitrites – 31.5%, ammonium nitrogen – 18.8%. Seasonal profiles revealed oxygen-regime stress in summer (mean dissolved oxygen 7.60 mg/dm³ versus 10.80 mg/dm³ in winter), with higher COD and permanganate oxidizability in the warm period. PCA showed the leading components reflect nutrient enrichment and mineralization-salinity processes. Clustering of 48 sites yielded three profiles: organic-oxygen (43 sites, basin-wide background pressure), mineralization-salinity (3 sites), and nutrient (2 sites, upper reaches). The highest I6 values occurred near the Bug Estuary, the lower Inhul River in Mykolaiv, and the upper Southern Bug downstream of Khmelnytskyi; under fishery-use values, upper-basin sites showed a sharp risk increase, with ammonium nitrogen as the limiting factor.
Conclusions. Combining multiyear and seasonal profiling with regulatory exceedance analysis and cluster typology provides an objective, reproducible screening tool for the Southern Bug Basin. Organic-oxygen loading dominates basin-wide, nutrient enrichment forms a distinct risk pattern in the upper reaches, and mineralization-salinity pollution is spatially localized. The identified priority sites give a scientific basis for optimizing the monitoring network and planning water-protection measures, without substituting for official ecological-status classification.
References
1. Bezsonnyi, V., & Nekos, A. (2023). Analysis of the environmental risk of water bodies in conditions of military danger. 17th International Conference Monitoring of Geological Processes and Ecological Condition of the Environment, Monitoring 2023. https://doi.org/10.3997/2214-4609.2023520153
2. Bezsonnyi, V., Plyatsuk, L., Ponomarenko, R., & Tretyakov, O. (2023). Assessment of ecological safety of a surface water object. 17th International Conference Monitoring of Geological Processes and Ecological Condition of the Environment, Monitoring 2023. https://doi.org/10.3997/2214-4609.2023520155
3. Bezsonnyi, V. (2022). Assessment of environmental risks from the impact of domestic and industrial effluents. 16th International Conference Monitoring of Geological Processes and Ecological Condition of the Environment, Monitoring 2022. https://doi.org/10.3997/2214-4609.2022580218
4. Gupta, S., & Gupta, S. K. (2021). A critical review on water quality index tool: Genesis, evolution and future directions. Ecological Informatics, 63, 101299. https://doi.org/10.1016/j.ecoinf.2021.101299
5. Chidiac, S., El Najjar, P., Ouaini, N., El Rayess, Y., & El Azzi, D. (2023). A comprehensive review of water quality indices (WQIs): History, models, attempts and perspectives. Reviews in Environmental Science and Bio/Technology, 22, 349-395. https://doi.org/10.1007/s11157-023-09650-7
6. Mogane, L. K., Masebe, T., Msagati, T. A. M., & Ncube, E. (2023). A comprehensive review of water quality indices for lotic and lentic ecosystems. Environmental Monitoring and Assessment, 195, 926. https://doi.org/10.1007/s10661-023-11512-2
7. Akhtar, N., Syakir Ishak, M. I., Ahmad, M. I., Umar, K., Md Yusuff, M. S., Anees, M. T., Qadir, A., & Ali Almanasir, Y. K. (2021). Modification of the Water Quality Index (WQI) process for simple calculation using the Multi-Criteria Decision-Making (MCDM) method: A review. Water, 13(7), 905. https://doi.org/10.3390/w13070905
8. Muniz, D. H. F., & Oliveira-Filho, E. C. (2023). Multivariate statistical analysis for water quality assessment: A review of research published between 2001 and 2020. Hydrology, 10(10), 196. https://doi.org/10.3390/hydrology10100196
9. El Azhari, H., Cherif, E. K., Sarti, O., Azzirgue, E. M., Dakak, H., Yachou, H., Esteves da Silva, J. C. G., & Salmoun, F. (2023). Assessment of surface water quality using the Water Quality Index (IWQ), multivariate statistical analysis (MSA) and Geographic Information System (GIS) in Oued Laou Mediterranean Watershed, Morocco. Water, 15(1), 130. https://doi.org/10.3390/w15010130
10. Wang, Z., Jia, D., Song, S., & Sun, J. (2023). Assessments of surface water quality through the use of multivariate statistical techniques: A case study for the watershed of the Yuqiao Reservoir, China. Frontiers in Environmental Science, 11, 1107591. https://doi.org/10.3389/fenvs.2023.1107591
11. Yao, R., Wang, X., Chen, J., & Liu, S. (2022). Hydrochemical analysis, principal component analysis and clustering for water quality evaluation: A case study in the Northern Sichuan Basin. Frontiers in Environmental Science, 10, 907872. https://doi.org/10.3389/fenvs.2022.907872
12. Mammeri, A., Tiri, A., Belkhiri, L., Salhi, H., Brella, D., Lakouas, E., Tahraoui, H., Amrane, A., & Mouni, L. (2023). Assessment of surface water quality using Water Quality Index and discriminant analysis method. Water, 15(4), 680. https://doi.org/10.3390/w15040680
13. Barrie, A., Agodzo, S. K., Frazer-Williams, R., Awuah, E., & Bessah, E. (2023). A multivariate statistical approach and water quality index for water quality assessment for the Rokel River in Sierra Leone. Heliyon, 9(6), e16196. https://doi.org/10.1016/j.heliyon.2023.e16196
14. Gaur, N., Sarkar, A., Dutta, D., Gogoi, B. J., Dubey, R., & Dwivedi, S. K. (2022). Evaluation of water quality index and geochemical characteristics of surface water from Tawang India. Scientific Reports, 12, 11698. https://doi.org/10.1038/s41598-022-14760-3
15. Zhalmagambetova, U., Assanov, D., Neftissov, A., Biloshchytskyi, A., & Radelyuk, I. (2024). Implications of Water Quality Index and multivariate statistics for improved environmental regulation in the Irtysh River Basin (Kazakhstan). Water, 16(15), 2203. https://doi.org/10.3390/w16152203
16. Akiner, M. E., Chauhan, P., & Singh, S. K. (2024). Evaluation of surface water quality in the Betwa River Basin through the Water Quality Index model and multivariate statistical techniques. Environmental Science and Pollution Research, 31, 18871-18886. https://doi.org/10.1007/s11356-024-32130-6
17. Roy, B. N., Roy, H., Rahman, K. S., Mahmud, F., Bhuiyan, M. M. K., Hasan, M., Bhuiyan, A.-A. K., Hasan, M., Mahbub, M. S., Jahedi, R. M., & Islam, M. S. (2024). Principal component analysis incorporated water quality index modeling for Dhaka-based rivers. City and Environment Interactions, 23, 100150. https://doi.org/10.1016/j.cacint.2024.100150
18. Hammoumi, D., Al-Aizari, H. S., Alaraidh, I. A., Okla, M. K., Assal, M. E., Al-Aizari, A. R., Moshab, M. S., Chakiri, S., & Bejjaji, Z. (2024). Seasonal variations and assessment of surface water quality using Water Quality Index (WQI) and Principal Component Analysis (PCA): A case study. Sustainability, 16(13), 5644. https://doi.org/10.3390/su16135644
19. Jo, C. D., Choi, S. Y., & Kwon, H. G. (2024). Statistical analysis of water quality change by total maximum daily load policy stage. Applied Water Science, 14, 176. https://doi.org/10.1007/s13201-024-02239-7
20. Alfaleh, A., Ben Khedher, N., & Alviz-Meza, A. (2023). Is the entropy-weighted water quality index a suitable index for evaluating the groundwater quality in Ha'il, Saudi Arabia? Water Science and Technology, 88(3), 778-797. https://doi.org/10.2166/wst.2023.230
21. Bezsonnyi, V., Tretyakov, O., Plyatsuk, L., Ponomarenko, R., & Davydova, O. (2025). Seasonal and spatial dynamics of entropy-weighted water quality assessment in surface waters of Ukraine. Visnyk of V. N. Karazin Kharkiv National University, Series Geology. Geography. Ecology, 62, 384-400. https://doi.org/10.26565/2410-7360-2025-62-29
22. Bezsonnyi, V. (2025). Entropy-weighted model for assessing the environmental safety of surface waters in the Southern Bug river basin. Visnyk of V. N. Karazin Kharkiv National University. Series Geology. Geography. Ecology, (63), 516-529. https://doi.org/10.26565/2410-7360-2025-63-38
23. Naddeo, V., Zarra, T., Pervez, M. N., Papamichael, I., Zorpas, A. A., Li, C.-W., Klontza, E., Lekkas, D. F., & Belgiorno, V. (2023). A comparative analysis of ecological status assessment in river water quality under the European Water Framework Directive. Case Studies in Chemical and Environmental Engineering, 8, 100477. https://doi.org/10.1016/j.cscee.2023.100477
24. Wuijts, S., Van Rijswick, H. F. M. W., Driessen, P. P. J., & Runhaar, H. A. C. (2023). Moving forward to achieve the ambitions of the European Water Framework Directive: Lessons learned from the Netherlands. Journal of Environmental Management, 333, 117424. https://doi.org/10.1016/j.jenvman.2023.117424
25. Zhu, M., Wang, J., Yang, X., Zhang, Y., Zhang, L., Ren, H., Wu, B., & Ye, L. (2022). A review of the application of machine learning in water quality evaluation. Eco-Environment & Health, 1(2), 107-116. https://doi.org/10.1016/j.eehl.2022.06.001
26. Uddin, M. G., Rahman, A., Taghikhah, F. R., & Olbert, A. I. (2024). Data-driven evolution of water quality models: An in-depth investigation of innovative outlier detection approaches-A case study of Irish Water Quality Index (IEWQI) model. Water Research, 255, 121499. https://doi.org/10.1016/j.watres.2024.121499
27. State Water Agency of Ukraine. (2026). Surface water monitoring. URL: https://www.davr.gov.ua/monitoring-poverhnevih-vod1 [in Ukrainian]
28. On approval of the Methodology for assigning a surface water body to one of the classes of ecological and chemical status: Order of the Ministry of Environmental Protection of Ukraine No. 5, January 14, 2019. URL: https://zakon.rada.gov.ua/go/z0127-19 [in Ukrainian]
29. On approval of hygienic standards for the quality of water bodies for drinking, domestic and other needs of the population: Order of the Ministry of Health of Ukraine No. 721, May 2, 2022. URL: https://zakon.rada.gov.ua/go/z0524-22 [in Ukrainian]
30. On approval of methodological recommendations for the development of maximum permissible discharge standards for pollutants discharged into water bodies with return waters: Order of the Ministry of Environmental Protection of Ukraine No. 173, March 5, 2021. URL: https://zakon.rada.gov.ua/go/v0173926-21 [in Ukrainian]
31. European Parliament and Council. (2000). Directive 2000/60/EC establishing a framework for Community action in the field of water policy. Official Journal of the European Communities, L327, 1-73. http://data.europa.eu/eli/dir/2000/60/oj
32. APHA, AWWA, & WEF. (2023). Standard Methods for the Examination of Water and Wastewater (24th ed.). APHA Press. https://secure.apha.org/imis/ItemDetail?iProductCode=978-087553-2998&CATEGORY=BK
33. ISO. (2018). ISO 5667-3:2024 Water quality - Sampling - Part 3: Preservation and handling of water samples. https://www.iso.org/standard/82273.html
