Contribution of nitrate-nitrogen concentration in groundwater to stream water in an agricultural head watershed
Chung‐Mo Lee, Se‐Yeong Hamm, Jae-Yeol Cheong, Kangjoo Kim, Heesung Yoon, Moon-Su Kim, Jinsoo Kim
Abstract
This study characterized nitrate-nitrogen (NO3–N) concentrations in groundwater and stream water in an agricultural head watershed in South Korea and identified the pollution load of NO3–N as a result of the groundwater entering streams using field surveys, analyses of chemical constituents, and numerical modeling. The mean NO3–N concentration in groundwater was 7.373 mg/L, which is approximately 1.9 times higher than concentrations found in stream water. The groundwater and stream water samples belonged to the Ca–HCO3 type. The concentration of NO3–N in groundwater tended to increase in the lowland areas downstream. There was seasonal variations of NO3–N in both the groundwater and stream water samples, with increases in concentration during the dry season (January–April) and decreases during the wet season (June–October). The NO3–N load in stream water to that in groundwater (R) was higher during the wet season (September) than the dry season (March), with R distinctly increasing in upstream areas relative to downstream areas, indicating that during the wet season, a large amount of NO3–N is introduced into stream water from groundwater. By analyzing the relationship between groundwater and stream water and through NO3–N transport modeling, it was revealed that in the watershed, the nitrate-N load in stream water is greatly augmented by inputs from groundwater, particularly in the middle and downstream areas.