Impact of burial conditions on NO₃^--N source apportionment in groundwater: Insights from PCA-APCS-MLR and MixSIAR methods

Abstract. NO₃^--N contamination in groundwater poses a significant threat to drinking water safety and ecosystem health, with accurate source identification being crucial for effective pollution control. Previous studies on NO₃^--N source apportionment in groundwater have largely neglected aquifer burial conditions. In this study, groundwater samples from aquifers with varying burial conditions were collected and analyzed using an integrated approach combining hydrochemical analysis (PCA-APCS-MLR) and stable isotope mixing modeling (MixSIAR) to identify and quantify NO₃^--N pollution sources. The results demonstrate that NO₃^--N concentrations in 75 % of the groundwater samples exceeded the WHO drinking water standard. PCA-APCS-MLR analysis revealed that the dominant NO₃^--N sources in unconfined groundwater and confined groundwater were chemical fertilizers (52.5 %) and manure & sewage (53.9 %), respectively. The MixSIAR model further identified soil nitrogen (58 %) and manure & sewage (37.9 %) as the primary contributors to NO₃^--N in unconfined and confined groundwater, respectively. These findings suggest that unconfined groundwater in regions with high soil nitrogen reserves is at persistent risk of NO₃^--N contamination. In addition, neglecting aquifer burial conditions would introduce absolute errors of 22 %–24 % in source apportionment results obtained from both PCA-APCS-MLR and MixSIAR approaches. This study highlights that aquifer confinement must be rigorously considered as a critical factor in NO₃^--N source identification and pollution control strategies to enhance the accuracy of source apportionment and the effectiveness of management measures.