Water quality assessment of the Nam River, Korea, using multivariate statistical analysis and WQI

Water quality assessment using water quality index (WQI) is performed based on major variables reflecting the river characteristics. We evaluated the water quality of tributaries of the Nam River in South Korea. We analyzed the tributaries spatial characteristics using cluster analyses and selected the main water quality variables (Cluster 1: chemical oxygen demand [COD], total organic carbon [TOC], total nitrogen, and total phosphorus; Cluster 2: water temperature [WT], dissolved oxygen [DO], COD, and TOC; Cluster 3: WT, DO, electrical conductance, COD, and TOC) of the clustered rivers. The WQI for each tributary was calculated using variables selected post statistical analysis. We verified that the WQI calculated in this study was similar to the annual change in water quality of the target river. Finally, it was analyzed that performing river water quality evaluation using the major variables selected using statistical analysis reflects the current water quality status of the river in more detail. (WQI grade was S1 Good (63.0), S2 Poor (53.3), S3 Excellent (98.4), S4 Poor (48.4), S5 (Excellent (100.0), S6 Good (77.6), S7 Good (76.2), S8 Good (76.5), S9 Good (69.9), S10 Excellent (81.5), S11 Good (71.2), S12 Good (63.1), and S13 Good (63.5).) Our method effectively reduced the number of variables required for index calculation compared with WQI methods of the MOE. Further, the reduced number of variables simplified the analysis process, reduced analysis time, and enabled water quality assessment that reflected the water quality characteristics of the river to be evaluated.