Hydrogeochemical conceptualization of granitic-urban area for sustainable water resource management: a case study of Daejeon, Korea.

Groundwater is increasingly vital under growing demand and climate pressures, making its effective management essential for sustainable use. A thorough understanding of hydrogeochemical processes is therefore critical to secure water quality and guide resource development. This study develops a conceptual model of a granitic aquifer in Daejeon, Korea, representing a typical weathered-fractured system under mixed urban and green land-use conditions. An integrated approach was applied, combining conventional geochemical analysis, multivariate statistics, geochemical modeling, and strontium isotope tracing. The results highlight silicate weathering as the dominant control on groundwater chemistry, validated by 87Sr/86Sr ratios (~ 0.716). Mineral-water interactions explain nearly half of the observed variance, mainly through the weathering of silicate minerals to secondary clays, which promote ion exchange processes. Anthropogenic activities, particularly agriculture and land use, account for ~ 15% of the variation, indicating localized contamination risks in the lowland areas. The conceptual model, supported by natural tracers, demonstrates that groundwater evolves from a Ca-HCO3 type in recharge zones to mixed types, such as Ca(Na)-HCO3 and Ca-Cl, along downgradient flow paths. This hydrogeochemical evolution reflects the combined effects of progressive mineral weathering and superimposed anthropogenic influences.By capturing both natural processes and human impacts, this study advances the understanding of hydrogeochemical dynamics in granite-based aquifers. The proposed conceptual framework provides a basis for predicting groundwater evolution and emphasizes the urgent need for sustainable management of these vulnerable resources in rapidly urbanizing regions.