Application of multiple-isotope and groundwater-age data to identify factors affecting the extent of denitrification in a shallow aquifer near a river in South Korea

Kaown, Dugin; Koh, Eun-Hee; Mayer, Bernhard; Kim, Heejung; Pak, Tong-gyu; Park, Byeong-Hak; Lee, Kang-Kun

Application of multiple-isotope and groundwater-age data to identify factors affecting the extent of denitrification in a shallow aquifer near a river in South Korea | Application d’un traçage multi-isotopique et de lal datation des eaux souterraines pour identifier l’extension de la dénitrification dans un aquifère superficiel près d’une rivière, en Corée du Sud Aplicación de datos de isótopos múltiples y de edad del agua subterránea para identificar los factores que afectan el grado de desnitrificación en un acuífero poco profundo cerca de un río en Corea del Sur 利用多个同位素和地下水年龄数据确定影响南韩一条河流附近浅层含水层反硝化程度的因素 Aplicação de dados de multi-isótopicos e de datação de águas subterrâneas para identificar fatores que afetam a extensão da desnitrificação em um aquífero raso nas proximidades de um rio na Coréia do Sul

2018

The extent of denitrification in a small agricultural area near a river in Yangpyeong, South Korea, was determined using multiple isotopes, groundwater age, and physicochemical data for groundwater. The shallow groundwater at one monitoring site had high concentrations of NO₃-N (74–83 mg L⁻¹). The δ¹⁵N-NO₃ values for groundwater in the study area ranged between +9.1 and +24.6‰ in June 2014 and +12.2 to +21.6‰ in October 2014. High δ¹⁵N-NO₃ values (+10.7 to +12.5‰) in both sampling periods indicated that the high concentrations of nitrate in the groundwater originated from application of organic fertilizers and manure. In the northern part of the study area, some groundwater samples showed elevated δ¹⁵N-NO₃ and δ¹⁸O-NO₃ values, which suggest that nitrate was removed from the groundwater via denitrification, with N isotope enrichment factors ranging between −4.8 and −7.9‰ and O isotope enrichment factors varying between −3.8 and −4.9‰. Similar δD and δ¹⁸O values of the surface water and groundwater in the south appear to indicate that groundwater in that area was affected by surface-water infiltration. The mean residence times (MRTs) of groundwater showed younger ages in the south (10–20 years) than in the north (20–30 years). Hence, it was concluded that denitrification processes under anaerobic conditions with longer groundwater MRT in the northern part of the study area removed considerable amounts of nitrate. This study demonstrates that multi-isotope data combined with physicochemical data and age-dating information can be effectively applied to characterize nitrate contaminant sources and attenuation processes.

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