Contrasting Groundwater Nitrate Levels and Temporal Trends: A 15-Year Regional Assessment in Jeonbuk Province, South Korea

Long-term groundwater monitoring is essential for assessing nitrate contamination, yet regional concentration patterns may obscure changes at individual wells. This study examined groundwater NO3-N concentrations and temporal trends using 15 years (2010–2024) of data from 57 wells at 38 monitoring sites in Jeonbuk Province, South Korea. Mann–Kendall tests, Sen’s slope estimates, and Spearman correlations were used to evaluate temporal changes and their associations with land use and environmental characteristics. Regional nitrate concentrations fluctuated without a consistent directional pattern, while 11 wells showed increasing trends, 11 decreasing trends, and 35 no significant trend. Wells with decreasing trends had a higher median long-term NO3-N concentration (7.55 mg/L) than those with increasing trends (3.45 mg/L), although the difference was not statistically significant. Long-term nitrate concentrations were generally higher in western agricultural lowlands and associated with geographic gradients and selected agricultural land uses, whereas temporal trends showed limited associations with the examined environmental variables. These findings indicate that existing nitrate contamination levels and temporal changes provide distinct information. Integrating long-term concentrations with well-specific trends can help identify persistent contamination and emerging deterioration, supporting more targeted groundwater monitoring and management.