title: Hydrogeochemistry and isotopic tracing of nitrate contamination of two aquifer systems on Jeju Island, Korea.
abstract: The groundwater of Jeju Island (Republic of Korea) is vulnerable to contamination because its aquifers are mainly composed of highly permeable geological units and its agricultural fields are often exposed to excessive use of predominantly synthetic fertilizers. In the Gosan area of Jeju Island, we investigated nitrate contamination in both a perched aquifer above an impermeable clay bed and the regional groundwater beneath this aquitard. The δO and δD values indicate that the perched groundwater is recharged by local precipitation, whereas the regional groundwater is recharged mainly by regional flow from an adjacent mountainous region. The perched groundwater contained very high NO-N concentrations of up to 87 mg/L. The isotopic composition of nitrate in the perched groundwater showed that synthetic fertilizers applied in high excesses of crop N needs were the main cause of aquifer pollution. Elevated nitrate concentrations were also observed in the regional groundwater especially after precipitation events. Concentration and isotopic data revealed that the inflow of shallow perched groundwater along the poorly cemented or uncemented annulus of regional groundwater wells was one of the main reasons for the nitrate contamination observed in the regional groundwater. In both aquifers, δN and δO values showed that the sources of nitrate were derived from synthetic fertilizers that had been recycled in the soil zone by nitrification and in some portions of the perched aquifer (dissolved oxygen concentrations <2 mg/L) indicated that denitrification occurred locally.
authors.affiliation: School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea.
authors.forename: Eun-Hee
authors.initials: EH
authors.lastname: Koh
authors.forename: Dugin
authors.initials: D
authors.lastname: Kaown
authors.forename: Bernhard
authors.initials: B
authors.lastname: Mayer
authors.forename: Bong-Rae
authors.initials: BR
authors.lastname: Kang
authors.forename: Hee Sun
authors.initials: HS
authors.lastname: Moon
authors.forename: Kang-Kun
authors.initials: KK
authors.lastname: Lee
mesh_terms: D004784:Environmental Monitoring; D055593:Geological Phenomena; D060587:Groundwater / Q000737:chemistry*; D062312:Islands; D009566:Nitrates / Q000737:chemistry*; D009587:Nitrogen Isotopes / Q000737:chemistry; D056910:Republic of Korea; D014874:Water Pollutants, Chemical / Q000737:chemistry*; D014881:Water Supply
chemical_list: D009566:Nitrates; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical