Water Resources Sustainability of Ulaanbaatar City, Mongolia
Naranchimeg Batsaikhan, Jae Lee, Buyankhishig Nemer, Nam Woo
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).
... e hydrochemistry of the water samples was controlled by two major processes: NO 3 contamination, and silicate and carbonate mineral weathering. The groundwater samples could be classified into three groups based on their NO 3 levels and spatial distribution. Group 1 had natural background NO 3 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 NO 3 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 NO 3 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 NO 3 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 NO 3 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.