In this study, we have investigated the water quality and flow rate at the 4 sites of main stream and 8 sites of the branch stream of Nam river from April, 2006 to 2008, and analyzed the effects on Nam river with the purpose of using the data for as the fundamental information for water quality improvement and water resource management in the water system of Nam river downstreams.
1) The flow rate at 4 sites of the main stream and 8 sites of the branch stream increased during the rainy season between June and August, and continuously decreased during the dry season starting from autumn to winter. The BOD water quality status at each site of the main stream was stable in between 1.9∼3.0 mg/L with no large variation, so that it was between ‘Good’ and ‘A Little Good’ by the life environment standards. On the other hand, BOD of the inflow branch streams such as Panmuncheon, Nabulcheon, Gajoacheon and Yongacheon was between 2.7∼6.7 mg/L to be ‘A Little Good’ to ‘A Little Bad’ by the life environment standards and it was much dependent on the precipitation. The average COD of the branch streams, Panmun, Gajoa and Yonga was 8.6 mg/L, 6.5 mg/L and 5.6 mg/L, respectively, which were relatively high. The COD of the main stream was relatively stable with no large variation. The SS of the branch streams had large variation, while that of the main stream was relatively stable. The T-N of Panmun, Gajoa and Yonga was about 2∼3 times higher than that of the main stream. The T-P, the target substance of the second year’s total water pollution loads, of Panmun, Gajoa and Yonga was relatively higher than other sites. Other investigation items showed similar tendency.
2) The results of correlation analysis with Pearson correlation coefficient showed that BOD and COD, BOD and TOC, and COD and TOC at the 4 sites of the main stream had high correlation with each other. At Site 1, BOD and COD, BOD and TOC, and COD and TOC showed high correlation with the correlation coefficients of 0.663, 0.668 and 0.872, respectively. At Site 5, the correlation coefficients were 0.604 for BOD and COD, 0.829 for COD and TOC. Also, the correlation coefficients at Site 11 were 0.735 for BOD and COD, 0.644 for BOD and TOC, and 0.809 for COD and TOC. At Site 12, the correlation coefficients were 0.763 for BOD and COD, 0.730 for BOD and TOC, and 0.753 for COD and TOC, showing high correlation.
3) We have also analyzed the correlation between Chl-a and major factors at the 4 sites of the main stream. At Site 1, the correlation coefficient of Chl-a and the water temperature was -0.312, and that of Chl-a and T-P was -0.248. At Site 5, the correlation coefficient of Chl-a and the water temperature was -0.378, and that of Chl-a and DO was 0.239, showing their low correlation, and there was no specific correlation in between other items. At Site 11, the correlation coefficient of Chl-a and pH was 0.225, that of Chl-a and COD was 0.293, that of Chl-a and T-P was 0.485. At Site 12, the correlation coefficient of Chl-a and BOD was 0.612, that of Chl-a and COD was 0.682 and that of Chl-a and T-P was 0.449, showed high correlation.
4) We have investigated the eutrophication by using Trophic state index (TSI) at the 4 sites of the main stream of Nam river. At Site 1, the TSI from 2006 to 2008 was 49, 55, and 51, respectively, indicating mesotrophic state. At Site 2, the TSI was 52, 58, and 55, respectively, indicated mesotrophic state. In contrast, the TSI at Site 11 was 59, 66, and 63, and the TSI at Site 12 was 61, 67, and 66, showing that eutrophic state already took place. The N/P ratio at all the 4 sites of the main stream was higher than 16 by DIN/DIP and T-N/T-P, indicating that phosphorus is acting as the limited nutrient.