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.

In this study, we examined the concentration and spatial distribution of heavy metals in groundwater and surface water around the Erdenet ore mining using the Heavy Metal Pollution Index (HPI). The study was carried out in June and September of 2021. In total, 59 water samples were collected randomly from 20 groundwater and 13 surface water sites. We examined 53 heavy metals in the water samples and compared them with water standards including MNS 0900:2018, MNS 4586:1998, and MNS 4943:2015. As the result, we detected 10 out of 53 heavy metals in groundwater and surface water samples. Concentrations of the heavy metals were relatively different between sites. At sites near the mining zone, mean concentrations of Mn (435 µg/L) and Mo (936 µg/L) were above the highest permissible values of the MNS 0900:2018 standard but As (1.30 µg/L) and U (4.65 µg/L) were below the permissible values of the standard. For the groundwater sites, mean concentration of the Sr (1520 µg/L), Cd (0.43 µg/L) and Ni (4.89 µg/L) were below the permissible value of the MNS 0900:2018 standard. 72.2 percent of the total surface water sites were considered at medium to high risks or ecologically risky by the HPI. Hence, we conclude that the Erdenet ore mining area is polluted by heavy metals and further assessment of the environmental status is necessary to evaluate ecological risk. Эрдэнэтийн уурхай орчмын газрын доорх болон гадаргын усны хүнд металлын бохирдлын судалгаа ХУРААНГУЙ Энэхүү судалгааны ажлаар бид Эрдэнэтийн зэсийн үйлдвэр орчмын газрын доорхи болон гадаргын усан дахь хүнд металлын элементийн агууламжыг тодорхойлж, тархалтын зураглалыг хүнд металлын бохирдлын түвшний индекс (HPI) ашиглан боловсруулав. Судалгааны ажлыг 2021 оны зун (6-р сар) болон намар (9-р сар) хийж гүйцэтгэлээ. Усны чанарын судалгааны ажлын хүрээнд нийт 59 сорьцыг санамсаргүйгээр гадаргын усны 13, газрын доорхи усны 20 цэгээс авч шинжилсэн. Бид усны хүнд металлын үр дүнд боловсруулалт хийхдээ 53 хүнд металлыг тодорхойлж, MNS 0900:2018, MNS 4586:1998 болон MNS 4943:2015 стандартуудтай тус тус харьцуулсан. Судалгааны дүнд бид 53 хүнд металлаас 10-ийг гүний болон гадаргын усны дээжинд илрүүлсэн. Хүнд металлын агууламж цэг хооронд харьцангуй ялгаатай байв. Үйлдвэрийн бүсэд байрлах хэд хэдэн цэгт Mn (435 мкг/л) болон Mo (936 мкг/л)-ны дундаж агууламж холбогдох стандарт (MNS 0900:2018)-ын зөвшөөрөгдөх дээд хэмжээнээс өндөр агууламжтай байсан бол As (1.30 мкг/л) болон U (4.65 мкг/л) стандартад заасан хэмжээнээс бага агууламжтай байв. Харин газрын доорхи усан дахь Sr (1520 мкг/л), Cd (0.43 мкг/л) болон Ni (4.89 мкг/л)-ийн дундаж агууламж MNS 0900:2018 стандартаас бага байна. Судалгаанд хамрагдсан гадаргын усны цэгийн 72.2% нь HPI индексээр дундаас өндөр эрсдэлтэй буюу экологийн хувьд эрсдэлтэй гэж үзэхээр байна. Эндээс дүгнэхэд үйлдвэрийн район орчмын ус нь хүнд металлаар бохирдсон байгаа тул түүний экологийн эрсдэлийг үнэлэхэд цаашид байгаль орчны төлөв байдлын үнэлгээ шаардлагатай. Түлхүүр үгс: Эрдэнэтийн уурхай, хүнд металл, хүнд металлын бохирдлын түвшний индекс газрын доорх ус, гадаргын ус

Groundwater is the most important natural source for supplying of drinking water around the world, especially in rural areas. The 14^th khoroo (sub-district) of Khan-Uul district of Ulaanbaatar is only one khoroos where its inhabitants engage in animal husbandry and agriculture, which play an important role in the district’s economic growth, faces an increasing shortage of groundwater due to population and economic growth in the agriculture sector in the sub-district. In this study, we present the hydro-chemical characteristics and spatial distribution of aquifer using GIS and multivariate statistical approaches. During the sampling periods, a total of 51 groundwater samples were collected from 46 deep wells and 5 shallow wells in the area between October and November 2019. Samples included parameters of anions and cations (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^-, SO₄^2-, NO₃^-, HCO₃^-) and EC. Data from all the samples were subject to cluster and component analysis. As a result, three clusters were defined and it was established that the dominant groundwater type is HCO₃^-Ca²⁺-Na⁺. The parameter of Mg²⁺ and Ca²⁺ were not set in the permissible limits of the second and third clusters. Principal component analysis (PCA) illustrated that the northern part of the study area is greater affected to anthropogenic activities and aquifer mineralogy. Moreover, it found that Ca²⁺ and Mg²⁺ correlated with each other, which could be helpful in site specific monitoring of groundwater quality. The results of the study will contribute to management and quality control of the groundwater in the city.

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.

In this study, 176 groundwater samples were collected along the floodplain of the Kherlen River to assess seasonal variations in groundwater quality. Sampling was conducted three times: twice during the spring and once during the autumn. The analysis included the use of a Piper diagram, a Gibbs diagram, and correlation analysis to evaluate temporal and spatial variations in groundwater hydrochemistry. The results revealed significant seasonal fluctuations in the concentrations of HCO₃⁻, Ca²⁺, Na⁺, Fe, F⁻, and NO₃⁻, with more pronounced spatial variations during the spring due to the dilution effect of precipitation. In both seasons, the majority of groundwater samples were classified under the Ca-HCO₃ hydrochemical type, while a few samples were identified as Na-HCO₃ and Mixed-HCO₃ types. The findings indicated that the groundwater in the study area mainly originated from rock-water interactions, with only a few samples linked to evaporation mechanisms. High Na⁺/(Na⁺+Ca²⁺) ratios and low Cl⁻/(Cl⁻+HCO₃⁻) ratios suggest that groundwater chemistry is primarily influenced by the weathering of carbonate and silicate minerals. Additionally, cation exchange processes, specifically the replacement of Ca²⁺ by Na⁺, were found to actively contribute to the hydrogeochemical evolution of the aquifer system. Correlation analysis further demonstrated that groundwater salinity is predominantly controlled by dissolved ions, as evidenced by strong positive correlations between EC and TDS. Significant associations among major ions, including Ca²⁺, Mg²⁺, Na⁺, and HCO₃⁻, highlight the influence of geochemical processes such as dolomite dissolution and the weathering of sodium-rich minerals. The positive correlation between nitrate and Ca²⁺/Mg²⁺, along with its negative correlation with HCO₃⁻, points to anthropogenic impacts-particularly from agricultural inputs-as significant contributors to groundwater contamination. These findings underscore the need for improved land and water management practices to safeguard groundwater quality in the region.

River water quality is crucial as rivers support multiple uses in human needs as well as in sustaining the aquatic ecosystems. In this study, we assessed the physicochemical characteristics and water quality of the Delgermurun River Basin (DRB). We collected water samples from 16 sites along the Delgermurun River and its tributaries in June 2024. Eleven physicochemical parameters were measured onsite, and a permanganate index (CODMn) was analyzed in the laboratory. Seven heavy metals (Mn, Zn, Co, Ni, Mo, As, and Cd) were analyzed at SGS IMME Mongolia LLC, a certified laboratory. Principal component analysis (PCA) was used to explore variations in physicochemical characteristics, while water quality index (WQI) and heavy metal pollution index (HPI) were calculated to assess overall water quality of the DRB. According to the PCA, pH, turbidity, water temperature (Temp.), total dissolved solids (TDS), and elevation contributed the most to variation across the DRB. The highest values of pH, turbidity, and Temp. were found at lower sites (DELBugsei, DELG03, and DELW01), while the highest TDS was recorded at DELR02. In terms of the water quality, WQI and HPI values ranged from 0.04 to 0.1 and 5.98 to 29.20, respectively, remaining within the category of “very clean” by WQI and level of lower pollution by HPI (MNS 4586:1998). Our findings indicate that physicochemical parameters and water quality varied across the DRB, but it remains suitable for potable use. Our results can inform future water resource management, for example, identifying and protecting critical habitats, such as those for the endangered taimen (Hucho taimen), and contributing to the conservation of the DRB ecosystem.