The objectives of the study were to analyze water quality and ecological stream health in the watershed of Nonsan Stream. For a comprehensive analysis of the stream sites, multimetric assessment model of FAI were applied to diagnose the ecological health and the national biological monitoring data were used.
Water quality were compared among the seasons of premonsoon, monsoon and postmonsoon. In the upstream region, water quality got worse in the postmonsoon than the premonsoon season. In the downstream region, water quality got better in the postmonsoon than the premoonson season. In the lentic system(reservoir), water quality got better after the summer rainfall.
In the empirical model analysis, based on the nutrient(N, P) and CHL-a, phosphorus(P) acted as a limiting factor to control the primary production of phytoplankton. The regression analysis of CHL-a for total phosphorus(TP) showed that P was greater predictor in the reservoir system(R²=0.26, p<0.0001) than the streams(R²=0.04, p=0.0449).
According to fish community analysis, The downstream region(diversity index: 2.42, dominance index: 0.37) was higher diversity than the upstream region. It means that fish community analysis did not match with water quality. The FAI analysis means that FAI value was higher in the upstream region(FAI=68.8; B-grade; good condition) than the downstream region(FAI=40.6; C-grade; fair condition).
Overall, the study suggests that Water Quality, based on nutrient(N, P) and organic matter(BOD, COD), was not good and the ecological stream health, based on the FAI multi-metric model values, also was not good due to intensive farming and waste water treatment in the watershed. Especially, downstream water quality and ecological health were worse than the upstream's. Efficient stream and reservoir managements are required for the ecosystem restoration.