TY - JOUR
T1 - Groundwater contamination assessment in Ulaanbaatar City, Mongolia with combined use of hydrochemical, environmental isotopic, and statistical approaches
AU - Batsaikhan, Bayartungalag
AU - Yun, Seong Taek
AU - Kim, Kyoung Ho
AU - Yu, Soonyoung
AU - Lee, Kyung Jin
AU - Lee, Young Joon
AU - Namjil, Jadambaa
N1 - Funding Information:
This study was initially supported by the Korea Environment Institute (KEI) and was prepared for a doctoral thesis by the first author in February 2017. The completion of this study was supported from Korea Environmental Industry & Technology Institute (KEITI) through the Subsurface Environment Management (SEM) Project, funded by the Korea Ministry of Environment (MOE) ( 2018002440002 ). Dr. Ariunzul Yangiv helped us with field work for hydrogeologic knowledge. The comments and suggestions from four anonymous reviewers have helped to improve and clarify this manuscript.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2021/4/15
Y1 - 2021/4/15
N2 - Ulaanbaatar City, Mongolia is rapidly becoming urbanized and attracts great attention because of environmental issues. This study was performed to assess the status of groundwater quality in Ulaanbaatar at an early but growing stage of urbanization, focusing on nitrate contamination in relation to land use. Along with high total dissolved solids and NO3− concentrations, significant contamination of groundwater is indicated by positive loadings of NO3−, Cl− and δ15N-NO3− along the first principal component of the principal component analysis (PCA). Based on the concentrations and δ15N values of nitrate, groundwater is classified into two groups: Group I (baseline quality) and II (contaminated). Nitrate in Group II water in urbanized (esp. peri-urban) areas is higher in concentration (> 10 mg/l NO3−) and N-isotopic values (> 10‰ δ15N-NO3−), while pristine hydrochemistry is observed restrictedly in grassland and forest areas. Other ions (e.g., Cl− and SO42−) are also higher in Group II water. The δ15N-NO3− values in Group II water in combination with the spatial distribution on the land use map indicate that nitrate originates from untreated sewage effluents including pit-latrine leakage in peri-urban areas, while nitrate in Group I water originates from soil organic matter. The relationship between nitrate concentrations and δ2H (and δ18O) values of water suggests that nitrate enrichment is also influenced by evaporation during groundwater recharge. With the help of PCA for compositional data, we suggest a hydrochemical index for groundwater contamination assessment; i.e., the Groundwater Quality Index (GQI) that consists of three variables (concentrations of dissolved silica, nitrate and chloride) and can be used to delineate zones vulnerable to nitrate contamination as a crucial step for the efficient monitoring and management of groundwater quality. The study results suggest an urgent need for the management of unsealed pit latrines that are common in peri-urban areas with high population density.
AB - Ulaanbaatar City, Mongolia is rapidly becoming urbanized and attracts great attention because of environmental issues. This study was performed to assess the status of groundwater quality in Ulaanbaatar at an early but growing stage of urbanization, focusing on nitrate contamination in relation to land use. Along with high total dissolved solids and NO3− concentrations, significant contamination of groundwater is indicated by positive loadings of NO3−, Cl− and δ15N-NO3− along the first principal component of the principal component analysis (PCA). Based on the concentrations and δ15N values of nitrate, groundwater is classified into two groups: Group I (baseline quality) and II (contaminated). Nitrate in Group II water in urbanized (esp. peri-urban) areas is higher in concentration (> 10 mg/l NO3−) and N-isotopic values (> 10‰ δ15N-NO3−), while pristine hydrochemistry is observed restrictedly in grassland and forest areas. Other ions (e.g., Cl− and SO42−) are also higher in Group II water. The δ15N-NO3− values in Group II water in combination with the spatial distribution on the land use map indicate that nitrate originates from untreated sewage effluents including pit-latrine leakage in peri-urban areas, while nitrate in Group I water originates from soil organic matter. The relationship between nitrate concentrations and δ2H (and δ18O) values of water suggests that nitrate enrichment is also influenced by evaporation during groundwater recharge. With the help of PCA for compositional data, we suggest a hydrochemical index for groundwater contamination assessment; i.e., the Groundwater Quality Index (GQI) that consists of three variables (concentrations of dissolved silica, nitrate and chloride) and can be used to delineate zones vulnerable to nitrate contamination as a crucial step for the efficient monitoring and management of groundwater quality. The study results suggest an urgent need for the management of unsealed pit latrines that are common in peri-urban areas with high population density.
KW - Groundwater Quality Index (GQI)
KW - Nitrate contamination
KW - Peri-urban, Mongolia
KW - Sewage and pit latrine
KW - Urbanization
KW - Water chemistry and environmental isotope
UR - http://www.scopus.com/inward/record.url?scp=85092664864&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2020.142790
DO - 10.1016/j.scitotenv.2020.142790
M3 - Article
C2 - 33069480
AN - SCOPUS:85092664864
SN - 0048-9697
VL - 765
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 142790
ER -
