Quantifying Hyporheic Zone and Hydrochemical Stability under Seasonal Variability

The hyporheic zone (HZ), a critical interface between surface water and groundwater, plays a key role in controlling water quality, nutrient cycling, and ecosystem resilience. This study quantitatively investigates the depth and hydrochemical stability of the HZ in contrasting geological settings—a limestone-dominated upstream and a gneiss-dominated downstream region—using hydraulic gradient measurements, temperature profiles, and hydrochemical data collected across four seasons (spring, summer, fall, winter) between 2021 and 2022. Key parameters, including hydraulic gradients (dh/dl), temperature, and Saturation Index (SI), were collected seasonally from a representative streambed. The study incorporated δ18O, δD and δ13C isotopic data to determine mixing ratios between surface and groundwater and their effects on the HZ boundary dynamics. Advanced numerical modeling, including Darcy’s law and heat transfer equations, was employed to delineate the spatial and temporal variability of the HZ. Our results reveal a significant correlation between seasonal shifts in hydroclimatic factors (precipitation, evaporation, and temperature variability) and HZ, demonstrating its dynamic nature. Increased precipitation during the wet season enhanced mixing processes, resulting in elevated SI values and potential carbonate mineral saturation, while the dry season exhibited reduced mixing and undersaturation conditions. These findings suggest that seasonal hydroclimatic factors profoundly influence the chemical and physical stability of the HZ, impacting water resource management and ecosystem resilience.

This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (grant numbers 2019R1A6A1A03033167). This subject is supported by Korea Ministry of Environment as "The SS(Surface Soil conservation and management) projects; 2019002820004.