This study investigates the hydrological, ecological, and socio-economic responses of Ugii Lake—a freshwater body in semi-arid Central Mongolia—to climate variability and anthropogenic pressures. Seasonal field surveys conducted during the spring, summer, and fall of 2023–2024 revealed notable spatial and temporal variation in water quality, with pH ranging from 7.54 to 8.87, EC from 316 to 645 µS/cm, and turbidity between 0.36 and 5.76 NTU. Total dissolved solids (TDS) values and ionic compositions indicated increased salinization in some zones, particularly those exposed to high evaporation and shoreline disturbance. Heavy metal analysis identified elevated levels of aluminum, manganese, and zinc at several sampling points; however, concentrations generally remained within national environmental standards. Vegetation surveys showed that disturbed areas—especially those affected by grazing and tourism—exhibited reduced native plant diversity and dominance of invasive species. Socio-economic interviews with local herders and stakeholders indicated that 67.3% of households experienced declining livestock productivity, and 37.1% reported increased allergies or respiratory symptoms linked to deteriorating environmental conditions. Despite some ongoing conservation efforts, respondents expressed dissatisfaction with enforcement and impact. These findings highlight the need for community-driven, integrated lake management strategies that address environmental degradation, climate adaptation, and rural livelihood security.

This research work was performed within the framework of the project titled “The survey on the drinking water quality of settlement areas of Tuv province, conclusion and recommendation” implemented at the Institute of Geography and Geoecology, MAS in 2021, and some of the research results are summarized in this article. We took totally 16 samples from the water supply wells at the center of 8 soums. Performed by physicochemical, micro-elements, and bacteriological analysis, and determined the chemical composition, quality and pollution parameters and the quality and composition. We determined the quality of underground water was evaluated by calculating the water quality index (WQI). As regards the anions, the first most prominent water types are the Ca-[HCO3] (50%), the second Х-[HCO3] (43.7%), the third Ca-[HCO3-SO4 2- ] (6.3%) and groundwater was dominated by mixed type of water. From the study results, in case of mineralization, groundwater at 50% surveyed locations belongs to fresh, 50% belongs to freshly or relatively high mineralization. In case of hardness, groundwater at 43.7% belongs to softish, 50% belongs to moderately hard and the remaining 6.3% to hard, respectively. According to the analysis of microelements, the uranium concentration (U 33-176 µg/l) was 1.1-5.86 times higher than the drinking water standard, strontium concentration (Sr 2021µg/l) was 21 μg/l more (1 out of 16), and nitrate concentration (NO3 63.0 mg/l) was 1.26 times more (1 out of 16) of the total groundwater samples. Total 11 samples collected from sampling points and the water supply wells covered by the survey does not meet the requirements of Drinking water. Hygienic requirements, and assessment of quality and safety MNS 0900:2018 standard by any or several parameters. Төв аймгийн баруун урд бүсийн ундны усны чанар, найрлага Хураангуй: Хүн ам баталгаат ундны ус хангамжийн үйлчилгээ хүртэж байгаа эсэхийг тогтоох зорилгоор ундны усны чанарын судалгааг аймаг тус бүрээр судалсан. Энэхүү судалгааны нэг болон 2021 онд хэрэгжсэн “Төв аймгийн төв, суурин газрын ундны усны чанарын судалгаа, дүгнэлт, зөвлөмж” гэрээт ажлын хүрээнд 27 сумын худаг уст, цэг хамрагдан физик, химийн үзүүлэлт болон бичил элемент, бактерлогийн шинжилгээг хийж химийн шинж чанар, найрлага, бохирдлыг тодорхойлсон судалгааны үр дүнгээс баруун урд бүсийн 8 сумын нутаг дэвсгэрээс нийт 16 худаг уст, цэгийн нарийвчилсан судалгааны үр дүнд боловсруулалт хийж, чанар найрлагыг тогтоон, газрын доорх усыг усны чанарын индекс (УЧИ-WQI)- ээр үнэлсэн. Судалгааны дүнгээс харахад тус судалгааны талбайд гидрохимийн шинж чанараараа 50% Ca-[HCO3], 45.81% Na-[HCO3], 12.51% Ca-[Mg]-HCO3, 43.7% холимог-[HCO3] найрлагатай ус тархсан байна. Судалгаанд хамрагдсан нийт уст цэгүүд нь эрдэсжилтийн хувьд цэнгэг болон цэнгэгдүү ангилалд хамаарч байгаа бол хатуулгийн хувьд маш зөөлөн, зөөлөн ус байхгүй, нийт уст цэгийн 43.7% нь зөөлөвтөр, 50% нь хатуувтар, 6.3% нь хатуу устай ангилалд тус тус хамаарч байна. Судалгаанд хамрагдсан уст цэгүүдээс 3 уст цэгт ураны (U 33-176 мкг/л) агууламж ундны усны стандартаас 1.1-5.86 дахин их, хүнцэл (As 36.7 мкг/л) 1 худгийн усанд 5.86 дахин их, стронций (Sr 2021 мкг/л) 1 худгийн усанд 21 мкг/л ээр их, нитратын ион ( NO3 - 63.0 мг/л) 1 уст цэгт 1.26 дахин их тус тус илэрсэн байна. Шинжилгээний дүнгээр нийт уст цэгийн 11 нь буюу 68.75% нь аль нэг юм уу хэд хэдэн үзүүлэлтээрээ “Хүрээлэн буй орчин, эрүүл мэндийг хамгаалах аюулгүй байдал. Ундны ус эрүүл ахуйн шаардлага, чанар, аюулгүй байдлын үнэлгээ” MNS 0900:2018 ундны усны стандартын шаардлага хангахгүй байна. Түлхүүр үг: газрын доорх ус, усны чанарын индекс, хатуулаг, хүнцэл, уран.

This study presented the hydrochemical characteristics of groundwater in the “Songinohairkhan district”. We collected 111 samples from deep and dug wells in 2020 and major ions and pollution indicators were analyzed in the laboratory, and calculated the Water Quality Indices (WQI). The most dominant water type was first Ca-HCO₃ (70.3%), the second was Mg-HCO3, Mg-[Ca]-HCO₃ (15.3%), the third was Ca-mixed and Ca-[Na]-mixed (2.7%), the fourth was Ca-CI (0.9%). In the case of mineralization, about 0.9% of the groundwater showed very fresh, 75.7% was fresh, 20.7% was freshly or relatively high mineralization, and 2.7% was salty. However, in the case of hardness, 15.3% was soft, 53.2% was softish, 23.4% was slightly hard, 3.6% was hard, and 4.5% was very hard. About 12.6% of the samples were dominated by magnesium and manganese concentrations exceeded the standard of drinking water in the 21 samples (18.9%) which was 1.1-3.16 times higher than the permissible level of the standard. Additionally, As, Sr, and U were found to be higher than the MNS0900:2018 standard in some groundwater. The WQI indicated that the groundwater samples were excellent (65.8 %), good (27%), poor (4.5%), very poor (1.8%), and 0.9% of the samples showed unsuitable water for drinking purposes. Generally, in the study region, fresh and softish water was distributed and most of the samples were suitable for drinking water standards. The Emelt, Tolgoit, and Bayankhoshuu areas have groundwater with relatively high mineralization and hardness. In other words, about 18% of groundwater does not meet the above standard in one or several parameters.

The study described in this article aimed to assess the hydrochemical characteristics and heavy metal pollution index of groundwater in the Gorkhi Terelj of Nalaikh district, located in the northeast part of Ulaanbaatar, Mongolia. In this study, we have used 91 groundwater samples, which were collected in 2020. In recent years, tourism has been developing rapidly in this region of Gorkhi Terelj National Park and the tour companies and enterprises in this area are using groundwater for all purposes. Thus, by conducting a research on the quality and composition of groundwater of the region will be significant importance on providing fresh and safe drinking water supply to foreign and domestic tourists. We determined physicochemical and microelement parameters in the selected wells and the results were compared to the Mongolian drinking water standard MNS0900:2018 and WHO 2011. According to our studies the predominant hydrochemical type of groundwater was Ca-HCO₃ (97.8%). In the case of mineralization, about 67% of groundwater wells showed very fresh, and 32.9% was fresh. However, in the case of hardness, 47.2% was very soft, 35.1% was soft, and 17.5% was medium-hard. The most of the microelements were found below the standard levels. But some heavy metals were very high. The uranium concentration varied from 0.073 to 642 μg/L; it surpassed the WHO drinking water standard (30 μg/L) at 30.7% of sampling sites. The concentration of arsenic (As 0.19-49.5 μg/L) in 6 water samples was 1.45-4.95 times higher than the WHO level and MNS0900:2018 standard level, molybdenum (Mo 0.2-77.5 µg/L) was 1.1 times higher in 1 sample, and manganese (Mn 6.0-1599 mg/l) was 1.1-15.9 times higher in 6 water samples. The groundwater quality was calculated with a heavy metal pollution index (HPI). Calculation of the heavy metal pollution index (HPI) showed that 62.6% of the samples showed “very good”, “good” (19.7%; HPI 26.67-50.72), “poor” (7.69 %; HPI 52.19-74.81), “very poor” (1.09%; HPI 88.21), and 8.79% of the samples showed unsuitable for drinking purpose (HPI 110.4-304.9).