Hydrochemistry and isotope geochemistry of Song Stream, a headwater tributary of the South Han River, South Korea

Abstract

To investigate the geochemical and isotopic characteristics of a headwater tributary of the South Han River, we analyzed major elements, stable isotopes of oxygen, hydrogen, carbon, and sulfur, and strontium (Sr) isotopes of stream and groundwater samples collected from the Song Stream watershed in summer 2003. The stream water samples of the study area were divided into three water types, among which dissolved ion concentrations differed considerably. Our results strongly indicate that the chemical composition of Song Stream is controlled by silicate and carbonate weathering, as well as anthropogenic contamination, and variations in major dissolved ions and Sr isotopic ratios are mainly correlated to lithological variations in the watershed. The dissolved loads of the main channel of Song Stream are largely controlled by carbonate dissolution. Thus, the water chemistry of the main channel is probably dominated by the chemical weathering of carbonates, even where carbonates comprise only a minor proportion of the bedrock geology. The Sr isotopes and Mg/Ca molar ratios indicate that a dolomite end-member may exist in the study area, which would be compatible with the cationic characteristics of Song Stream. All groundwater samples from the study area, except for one, had significantly high nitrate concentrations (0.75–2.42 mmol/L) that exceeded the drinking-water standard and possibly resulted from both sewage and agricultural inputs.