title: Identifying the sources of nitrate contamination of groundwater in an agricultural area (Haean basin, Korea) using isotope and microbial community analyses.
abstract: An integrated study based on hydrogeochemical, microbiological and dual isotopic approaches for nitrate and sulfate was conducted to elucidate sources and biogeochemical reactions governing groundwater contaminants in different seasons and under different land use in a basin of Korea. The land use in the study area is comprised of forests (58.0%), vegetable fields (27.6%), rice paddy fields (11.4%) and others (3.0%). The concentrations of NO3-N and SO4(2-) in groundwater in vegetable fields were highest with 4.2-15.2 mg L(-1) and 1.6-19.7 mg L(-1) respectively, whereas under paddy fields NO3-N concentrations ranged from 0 to 10.7 mg L(-1) and sulfate concentrations were ~15 mg L(-1). Groundwater with high NO3-N concentrations of >10mgL(-1) had δ(15)N-NO3(-) values ranging from 5.2 to 5.9‰ and δ(18)O values of nitrate between 2.7 and 4.6‰ suggesting that the nitrate was mineralized from soil organic matter that was amended by fertilizer additions. Elevated concentrations of SO4(2-) with δ(34)S-SO4(2-) values between 1 and 6‰ in aquifers in vegetable fields indicated that a mixture of sulfate from atmospheric deposition, mineralization of soil organic matter and from synthetic fertilizers is the source of groundwater sulfate. Elevated δ(18)O-NO3(-) and δ(18)O-SO4(2-) values in samples collected from the paddy fields indicated that denitrification and bacterial sulfate reduction are actively occurring removing sulfate and nitrate from the groundwater. This was supported by high occurrences of denitrifying and sulfate reducing bacteria in groundwater of the paddy fields as evidenced by 16S rRNA pyrosequencing analysis. This study shows that dual isotope techniques combined with microbial data can be a powerful tool for identification of sources and microbial processes affecting NO3(-) and SO4(2-) in groundwater in areas with intensive agricultural land use.
authors.affiliation: School of Earth and Environmental Sciences (BK21 SEES), Seoul National University, Seoul 151-747, South Korea.
authors.forename: Heejung
authors.initials: H
authors.lastname: Kim
authors.affiliation: School of Earth and Environmental Sciences (BK21 SEES), Seoul National University, Seoul 151-747, South Korea. Electronic address: dugin1@snu.ac.kr.
authors.forename: Dugin
authors.initials: D
authors.lastname: Kaown
authors.affiliation: Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary T2N 1N4, Alberta, Canada.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Mayer
authors.affiliation: Department of Geology, Kangwon National University, Chuncheon 200-701, South Korea.
authors.forename: Jin-Yong
authors.initials: JY
authors.lastname: Lee
authors.affiliation: Planning and Management Group, Korea Environment Institute, Sejong 339-007, South Korea.
authors.forename: Yunjung
authors.initials: Y
authors.lastname: Hyun
authors.affiliation: School of Earth and Environmental Sciences (BK21 SEES), Seoul National University, Seoul 151-747, South Korea.
authors.forename: Kang-Kun
authors.initials: KK
authors.lastname: Lee
mesh_terms: D000383:Agriculture; D004784:Environmental Monitoring; D060587:Groundwater / Q000737:chemistry* / Q000382:microbiology; D009566:Nitrates / Q000032:analysis*; D056910:Republic of Korea; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical
keywords: Agriculture; Land use; Microbial communities; Nitrate; Stable isotopes; Sulfate