Abstract

Major ions and nitrogen isotopic analyses were performed to determine the geochemical characters and to identify the source of nitrate of the shallow groundwater around agricultural field in the Youngdong area. The pH value of groundwater ranges from 60. to 8.2 (pH 7.2, mean). The average of EC, Eh and DO is 369 μS/cm (70~729 μS/cm), 165.6 mV (29~383.2 mV), 4.3 mg/L (1.8~8.0 mg/L) respectively. The ion concentraion of groundwater was in the order of Ca²⁺>Na²⁺>Mg²⁺>K²⁺ and HCO₃>NO₃>SO₄²>Cl>F^-. Most of groundwater is Ca-HCO₃ type. The groundwater was affected by water-rock interaction in the shallow depth. Some groundwater is Ca-Cl or Na-HCO₃ (2.5%) type that was due to agricultural activities. The NO₃_N concetration of grondwater range from 10.2 mg/l to 26.9 mg/l, which show that this area is under nitrate pollution. δ¹⁵N-NO₃ value of the groundwater is the origins of are a combination of animal wastes and man-made fertilizers.

Keywords agricultural field, groundwater, nitrate, δ¹⁵N