Abstract

This study systematically analyzed the geochemical characteristics of the Taehwa River water to examine the natural factors and human activities influencing changes in its major chemical composition. The Taehwa River flows through the major industrial city of Ulsan and eventually into the sea, where it is impacted by both anthropogenic pollution and natural processes such as rock weathering. In the upstream region, the weathering of igneous and sedimentary rocks plays a dominant role, resulting in high ratios of ions such as Ca, Mg, and HCO₃. Additionally, the weathering of igneous rocks in the upper reaches contributes to elevated Si ratio. However, as the river flows downstream, the ratios of Cl and SO₄ ions increase greatly due to human activities, such as the discharge of industrial effluents, domestic wastewater, and agricultural runoff. In the downstream areas, the mixing of seawater causes a significant rise in Na and Cl ratios, indicating the influence of seawater on the river water. Regarding heavy metals, their concentrations generally increase from upstream to downstream. Zn and As, in particular, show relatively high levels due to nearby industrial activities and abandoned mines, while other heavy metals exhibit irregular variations depending on the location. This study identifies the spatial distribution and origins of major ions and heavy metals in the Taehwa River, providing fundamental data for understanding how rivers respond to natural weathering and human activities.

Keywords the Taehwa River, weathering, human activity, pollution, heavy metal