Evaluation of water quality for the Nakdong River watershed using multivariate analysis

• The water quality characteristics were evaluated by conducting multivariate statistical analysis.
• The first factors were shown to be nutrient salts (TN, TP) and organic pollutants (TOC, COD).
• The priorities of required water quality were determined according to the water quality pollution level.

Water quality observation data were collected from 20 representative monitoring sites located in the main stream of the Nakdong River and its major tributaries between 2008 and 2012. Based upon these data, the water quality distribution and characteristics of each river were evaluated by conducting multivariate statistical analysis for 12 pollution indicators using SPSS-17.0. Monitoring site T8 passing through the city of Daegu and monitoring site M5 located downstream of the Nakdong River exhibited high-concentration tendencies. The monitoring sites located near the city and midstream and downstream of the Nakdong River exhibited high pollution levels in the investigation. To analyze the spatial and temporal variations in the water quality at 20 major monitoring sites in the Nakdong River watershed, principal component and factor analyses were conducted by separating the average water quality data based upon (a) monitoring site, and (b) season. As a result, three factors were obtained for (a), and (b), respectively. In the Nakdong River watershed, the first factor was shown to be nutrient salts (total nitrogen and total phosphorus) and organic pollutants (total organic carbon and chemical oxygen demand), and as a result of cluster analysis, two statistically significant groups were classified. The results of multivariate statistical analysis indicated that the monitoring sites with high levels of pollution were mostly those sites going through the heart of the city or the sites affected by residential sewage directly, as well as the sites located midstream and downstream of the Nakdong River. The water quality pollution level was calculated based upon the above study results, and the priorities for water quality improvement items required in future watershed management were determined in order to facilitate efficient water quality management.