A study on natural and anthropogenic changes of chemical compositions in the Nakdong river in Korea

The Nakdong river is the longest river in South Korea and about sixty metalliferous mines have been operated since the 1930s. So, the environmental issues have occurred due to mine tailings, which were derived from mining activities located in the basin. In this study, thirty three river samples were collected from branches affected by tailings of each eleven-mine and main stream that meets the branches. Field parameters were measured in situ and major cations, anions, trace elements and water isotopes were determined at the Korea Basic Science Institute. The purpose of this study was, thus, to evaluate whether the mines positioned upper catchment affect on chemical variations of the Nakdong river where bedrocks mostly consist of quartize. Most water samples that dominantly were influenced by chemical weathering are on a weathering line [HCO3+2 SO4 : 2 (Ca + Mg) = 1:1]. However, six samples have shown excess sulfate that were below the 1:1 line and these samples were mostly from the streams around the Seokpo refinery and Sambo mine branch, which were consistent with the results by principle component analysis (PCA). Also, three samples near farmlands can be separated into a group by PCA because of high concentrations of nitrate. Based on the chemical and PCA results, we believe that the chemical compositions of the river have been affected by the mine tailings and agricultural contaminants. However, it is necessary to understand how the contaminants were derived from other inputs, such as synthetic fertilizer, soil, and atmospheric deposition.