Evaluation of Nitrate Reduction Potential Using Field Water Quality Parameters of the Hyporheic Zone in the Tandoncheon Stream, Daejeon, Korea

The hyporheic zone is a transitional interface between surface water and groundwater that is characterized by distinct physicochemical conditions and plays a key role in various biogeochemical processes. This study aims to investigate the formation and characteristics of the hyporheic zone in the Tandoncheon Stream, Daejeon, South Korea, and evaluate its potential for water quality improvement. Field measurements of water temperature, electrical conductivity, and pH were conducted along vertical profiles, and grain size distribution and dissolved organic matter properties were analyzed to characterize hyporheic flow and potential redox transitions. Results showed a gradual decrease in water temperature with depth in the hyporheic zone, indicating groundwater discharge influence. Sediment samples from the hyporheic zone exhibited multimodal grain size distributions, primarily composed of sand and silt, reflecting selective sedimentation under variable hydraulic conditions. Using the PHREEQC geochemical model, we simulated nitrate denitrification reactions under varying organic matter concentrations. The modeling results indicated that nitrate reduction can proceed effectively in the presence of sufficient organic matter leading to increased N<sub>2</sub> and bicarbonate concentrations under reducing conditions. These findings highlight the potential role of the hyporheic zone in attenuating oxidized contaminants such as nitrate and emphasize its value in groundwater recharge and water quality management strategies.