Abstract
Ulaanbaatar (UB), the capital of Mongolia, is one of the fastest-growing cities in the developing world. Due to increasing demand driven by rapid population and industrial growth, sustainable water resource management is required. Therefore, we investigated sustainability in UB from the perspective of water quality. During five sampling campaigns, we collected 135 water samples (58 from bedrock wells, 44 from shallow wells tapped into the alluvial aquifer, 24 from rivers, and 9 from springs). The hydrochemistry of the water samples was controlled by two major processes: NO3 contamination, and silicate and carbonate mineral weathering. The groundwater samples could be classified into three groups based on their NO3 levels and spatial distribution. Group 1 had natural background NO3 levels (median: 1.7 mg/L) and silicate weathering–dominant water–rock interactions and was distributed in the alluvial aquifer along the floodplain. Group 2 was dominated by carbonate weathering processes, had a maximum NO3 concentration of 47.4 mg/L, and was distributed between the riverbank and upslope area; overall, it reflected ongoing contamination. Group 3 was distributed in the upslope Ger districts and showed significant NO3 contamination (range: 64.0–305.4 mg/L) due to dense and poor living conditions. The stable isotope signatures indicated that the city’s major water supply from riverbank filtration (i.e., Group 1 wells) mixed dynamically with the river; therefore, it showed no sign of NO3 contamination. However, the isotope values and bedrock groundwater quality of wells in Groups 2 and 3 implied that they were closely connected, with the same water source, and showed a strong potential for expanding NO3 contamination toward Group 1 wells. To support sustainable development in UB, the implementation of appropriate institutional measures to protect and preserve water resources, with systematic spatio-temporal monitoring and a focus on Ger districts, is crucial.
Highlights
Mongolia, a landlocked country in central Asia, has a total area of about 1.5 million km2 and an average altitude of 1580 m
Residents living on the outskirts of the city in Ger districts use hand-dug wells as independent sources of water or purchase water at kiosks that function as local distribution centers for water pumped from the alluvial aquifer [7]
We evaluated the sustainability of UB from the perspective of water-resource quality issues
Summary
A landlocked country in central Asia, has a total area of about 1.5 million km and an average altitude of 1580 m. Industrial, and economic center of Mongolia, Ulaanbaatar (UB) is one of the fastest-growing cities in the developing world [3]. Rapid industrial development, including that in textiles, tanning, food processing, energy production, communications, and construction, is concentrated primarily in UB and has attracted people from rural areas, resulting in significant. Water 2018, 10, 750 growth in the city’s population from about 0.5 million in 1989 to 1.2 million in 2016 [4,5]. The rapid introduction of rural people into the city and the residential areas along the hillslope surrounding it (Ger districts) has caused many issues, including those related to water supply and waste treatment infrastructure
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