Geochemistry and isotope compositions of the Han River, South Korea : implications for water-rock interaction

In order to investigate processes and factors controlling the chemical and isotopic compositions of the Han River, seasonal studies were carried out. The North Han River was much lower in the concentrations of total dissolved solids (TDS), dissolved inorganic carbon and major ions than the South Han River, but higher in SiO2 concentration, sulfur isotopic values of sulfates and Sr isotopic ratios. This indicates that the chemical and isotopic compositions of the Han River waters were strongly controlled by the geology of their drainage basins: silicate rocks in the North Han River and carbonate rocks in the South Han River. The oxygen and hydrogen isotopic values of the waters were higher in summer than in the other seasons, resulting from evaporation in the dams. The sulfur isotopic values of sulfates were relatively higher in the North Han River (5.90+/-1.46 per mil) than in the South Han River (3.48+/-0.73 per mil). This implies that dissolved sulfate in the North Han River might be derived from deposition of atmospheric sulfates, whereas in the South Han River from oxidation of sulfide minerals in the abandoned poly-metallic deposits and the sedimentary rocks distributed over the upstream as well as deposition of atmospheric sulfates. The Sr isotopic ratios in the North Han River were much higher than those in the South Han River, reflecting water-rock interaction with different rock types. This work was supported by a grant (3-2-1) from the Sustainable Water Resources Research Center of 21st Century Frontier Research Program.