Abstract

The Kumho River flows through volcanic and sedimentary rocks at upstream and downstream regions and also through industrial district including dyeing complex before it meets the Nakdong River, and as a result, many factors can influence the geochemistry of river water. The concentrations of dissolved ions generally increased as it flows downstream. The concentrations of cations are in the order of Ca>Na>Mg>K, and those of anions are HCO₃>SO₄>Cl>NO₃. These results show that the weathering of sandstone and shale containing carbonate including calcite caused the enrichment of Ca and HCO₃. At first 4 sampling sites, Si contents are relatively high mainly
due to the weathering of silicate minerals of volcanic rocks. However, Na and SO4 contents are higher at downstream sites due to the industrial and municipal sewage. Piper diagram also shows that the geochemical patterns changed from Ca-HCO₃ to Ca-Cl/Ca-SO₄ and Na-Cl/Na-SO₄ type. When comparing the samples collected in May and July, the concentrations of dissolved ions in July are generally lower than those in May, which indicates that dilution by precipitation played an important role. In July the relative concentration of Ca increased, indicating that Ca in soils probably from fertilizer were mixed into the river water by precipitation. The river waters are mainly
from precipitation. The dissolved ions are mainly from weathering of carbonate minerals and pollutants from municipal sewage and discharged water from industrial complex. The composition of oxygen and deutrium isotope in July showed higher values, which is contrary to the amount effect, maybe due to Youngchon Dam. The nitrogen isotope showed lower values in July than those in May, which can be interpreted to indicate mixing of nitrate from soils and fertilizer in the cultivated land by the heavy rain. The isotope composition of nitrate increased downstream, indicating that the influence of sewage and animal manure also increased downstream.

Keywords the Kumho River, river water, weathering, precipitation, isotope