Abstract

Over the past decade, BOD5 has improved somewhat in Korea’s major rivers and reservoirs, but CODMn is increasing. The purpose of this study is to investigate the loading characteristics of refractory organic matter (ROM) in two tributaries(Juwon stream and Pumgok stream) that enter Daecheong Reservoir, which is the most important drinking water sources in the Geum River basin. Agricultural reservoirs are located upstream of the two tributary streams, and monitoring is performed upstream and downstream of the reservoirs. The ROM was extracted into hydrophilic(Hi) and hydrophobic(Ho) organic substances using the XAD rasin method. The monitoring of upstream and downstream of Juwon and Pumgok streams showed that COD and TOC were higher at downstream than those of upstream monitoring stations. The TOC/DOC ratio was also higher at downstream stations. However, the POC was higher in the upstream monitoring stations, and this result seems to be due to the fact that most upstream watersheds consist of forests. The results of XAD analysis showed that the hydrophobic ratio was higher than that of hydrophilic, and hydrophobic organic matter was mostly classified as humic acid.
The Ho / Hi ratio increased during the rainy season, but decreased during the dry season. It was confirmed that the Ho component including HoA is the main component that flows into the streams during rainfall. As a result of the survey in 2016, the total organic carbon loading into the Daecheong Reservoir from the Juwon stream was 3470.6 kg/yr and the RDOC was 49.3%. On the other hand, the total organic carbon load flowing through the Pumgok stream was 6009.1 kg/yr and the POC was 46.5%. The correlation analysis between TOC and DOC showed a strong positive correlation(p < 0.01).
The results of this study provide important information to understand the characteristics of the refractory organic material load in tributary streams flowing into the Daecheong Reservoir and show that efforts to reduce natural organic matter from the watershed are necessary to control the continuous increase of COD.