Rationate: In recent years, global warming, climate change, environmental pollution driven by human activities, expansion of settlement areas, and mining operations within the Tuul river basin have been increasingly recognized as major factors affecting the river’s water quality, pollution levels, and flow regime [1, 3].
In particular, air and soil pollution in Ulaanbaatar, the quality and composition of effluent from the central wastewater treatment plant, water use by thermal power plants and boilers, as well as increasing domestic and industrial water consumption, continue to exert pressure on the Tuul river system [4, 6]. In addition, gold mining activities in the Zaamar area further contribute to the deterioration of water quality.
These combined pressures highlight the growing vulnerability of the Tuul river ecosystem and underline the need for detailed, spatially differentiated assessment of water quality along its course, especially within and downstream of urbanized areas. Objective: The objective of this study is to assess and evaluate the level of pollution in the Tuul river by spatially dividing the river into zones based on the results of chemical analysis. Materials and Methods: This study utilized water quality data obtained from laboratory analyses of Tuul River water samples conducted by the Information and Research Institute of Meteorology, Hydrology and Environment between 2022 and 2024. The data were accessed and used with official permission from the relevant authority.
The study was designed as a descriptive cross-sectional analysis. The research area was divided into three zones and 14 monitoring sites. A total of 373 water samples were analyzed based on 15 chemical parameters. Ethics: Before initiating the study, the research methodology and procedures were reviewed and approved by the Ethics Committee of Ach Medical University. An official request was submitted to the National Agency for Meteorology and Environmental Monitoring to obtain permission for the use of research data, and the data were used upon receiving approval.
To assess the water quality of the Tuul river, a statistical analysis was conducted on 15 key parameters across Zones 1, 2, and 3 using SPSS and Microsoft Excel. The study calculated arithmetic means and standard deviations to evaluate the data. A total of 373 samples, collected from 14 monitoring points within these three zones over a three-year period, were included in the analysis. Results: The three-year average concentrations of water quality indicators differed across Zones 1, 2, and 3. In Zones 2 and 3, key indicators including dissolved oxygen, biochemical oxygen demand (BOD), chemical oxygen demand (COD), ammonium nitrogen, mineral phosphorus, and chromium corresponded to Class IV and V levels of surface water quality classification, indicating heavy to extreme pollution. Conclusion
1. The chemical indicators reflecting the water quality and pollution level of the Tuul River show clear spatial variation along its course. The upper reach entering the city is relatively unpolluted, the central urban section experiences noticeable contamination, and the downstream section accumulates the highest level of pollution.
2. The main surface water pollution indicators in Zones 2 and 3 fall within heavily polluted (IV) and very heavily polluted (V) categories, indicating a strong influence of human activities and urbanization.
3. The average fluoride concentration in all zones exceeds the permissible limit defined by relevant standards by 2.5–3.9 times. Consumption of surface water with elevated fluoride levels may lead to fluorosis in humans, while livestock drinking water along the Tuul River may experience reduced productivity and disruption of normal bone structure development.