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

Abstract

The extent of denitrification using multiple isotopes, groundwater age, and physicochemical data for groundwater was compared in a small agricultural area near a river in Yangpyeong, South Korea. In 2014, the shallow groundwater at one site had high concentrations of NO3-N (74-83 mg L -1 ). The δ 15 N-NO3 values for groundwater in the study area ranged between +9.1 and +24.6‰ in June and +12.2 to +21.6‰ in October. High δ 15 N-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 δ 15 N-NO3 and δ 18 O-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 δ 18 O 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 of the study area (10-20 years) than in the north (20-30 years). Hence we conclude that denitrification processes under anaerobic conditions with longer MRT of groundwater 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.

Dual isotopes of nitrate in Korean fertilizers and their application for identifying nitrate sources

“…The average δ O values were 2.6 ± 2.5‰ and 19.3 ± 2.6‰ for inorganic fertilizer (IOF, n = 19), 14.7 ± 7.7‰ and 5.9 ± 4.9‰ organic fertilizers (OF, n =30), and 10.9 ± 6.7‰ and 16.0 ± 6.1‰ for plant-based compound fertilizer (PCF, n = 24), respectively. The combined δ O values of nitrate from previous studies (Lee et al, 2008;Koh et al, 2010;Choi et al, 2011;Cheong et al, 2012;Shin et al, 2014;Kim et al, 2015;Kaown et al, 2018) in South Korea superimposed on the revised fields of nitrate from fertilizers determined in this study. Main factors determining the isotopic ranges were shown in italic.…”

“…In addition, our results revealed that the nitrate sources in groundwater collected from eastern part of the study area were mainly derived from organic fertilizer including manure, while those in groundwater collected from the other parts was attenuated by denitrification processes (Kaown et al, 2018). A study conducted in mid-western South Korea investigated the sources of nitrate in the shallow groundwater of an agricultural area, and indicated that it is derived predominantly from several sources; i.e., septic waste, inorganic fertilizers, and atmospheric deposition (Koh et al, 2010).…”

“…Many studies conducted in various countries have used a typical cluster of δ O values (Kendall, 1998) to determine nitrate sources and understand the reactions in the study area. In many previous studies in South Korea, both of the isotopes have been determined to trace nitrate sources in groundwater and surface water (Lee et al, 2008;Koh et al, 2010;Choi et al, 2011;Cheong et al, 2012;Shin et al, 2014;Kaown et al, 2018). To evaluate our results, the isotope data from previous Korean studies were plotted on the revised fields of O determined in this study (Fig.…”

Vertical Nitrate Migration And Denitrification Zones In The Regional Recharge Area (Lwowek Region, Poland)

“…Groundwater in shallow unconfined groundwater systems is easily contaminated by nitrate because of high vulnerability to pollution from the surface 6,7,8 . However, besides the fact that contamination is usually less effective in deep wells 9 , in some cases, nitrate contamination can also appear in deeper parts of the flow system 10 .…”

“…The isotopic composition of nitrate, represented by δ 15 N-NO3 and δ 18 O-NO3 values, can be used to distinguish nitrate sources in groundwater 7,19,20 . This technique is also used to document denitrification in the system 8,17,21 . The traditional physical and chemical measurements (water level, major ion composition, geochemical investigation, etc.)…”