Hydrogeochemistry and Isotopic Tracing of Nitrate Contamination of Two Aquifer Systems on Jeju Island, Korea
- Eun-Hee Koha,
- Dugin Kaowna,
- Bernhard Mayerb,
- Bong-Rae Kangc,
- Hee Sun Moona and
- Kang-Kun Lee *a
- a School of Earth and Environmental Sciences, Seoul National Univ., Seoul 151-747, South Korea
b Dep. of Geoscience, Univ. of Calgary, 2500 University Dr. NW, Calgary, AB, Canada T2N 1N4
c Institute of Environmental Resources Research, Munyeonro 2, Jeju City, Jeju Special Self-Governing Province 690-700, South Korea. Assigned to Associate Editor Christian Stamm
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 δ18O 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 NO3–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, δ15N and δ18O 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.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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