Hydrogeochemical and isotopic investigations of the Han River basin, South Korea

Abstract

Summary The Han River, the largest river in South Korea draining approximately 26,000 km 2 , comprises two major tributaries: the North and the South Han Rivers. Seasonal and spatial variations in the major ion chemistry and isotope compositions of the Han River were monitored for one year at 14–23 locations, covering about 80% of the entire drainage basin. Compared to the South Han River (SHR), the North Han River (NHR) was much lower in total dissolved solids (TDS), Sr, and major ion concentrations, but higher in Si concentration, δ 34 S SO 4 values, and 87 Sr/ 86 Sr ratios. These observations suggest strong influence of prevailing rock types in the drainage basins on the chemical and isotopic compositions of the river waters. These are silicate rocks in the NHR basin and carbonate rocks in the SHR basin. The headwaters of the NHR basin, where several flood control dams have been constructed, show enrichment in deuterium and oxygen-18, indicating evaporative loss. The δ 34 S SO 4 data suggest dissolved sulfates in the NHR and SHR are mostly derived from atmospheric deposition, and variable mixtures of atmospheric deposition and sulfide oxidation, respectively. The 87 Sr/ 86 Sr ratios are much higher in the NHR (0.71793–0.72722) than in the SHR (0.71495–0.71785) with one exception, indicating weathering of Precambrian and Mesozoic granitic rocks and marine carbonates, respectively.