Development of Reservoir Water Quality Index (WQI) Based on Long-term Physicochemical Parameters and Their Spatio-temporal Variations

The main objectives of this study were to develop a Water Quality Index (WQI) model based on the physicochemical parameters in Daecheong reservoirs by using datasets of 1995-2016. The parameters included total phosphorus (TP), total nitrogen (TN), biological oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), chlorophyll (CHL), electrical conductivity (EC), dissolved oxygen (DO) and hydrogen ion concentrations (pH). The results had showed that physicochemical parameters varied spatially and temporarily as well as were correlated. TP was the most important key regulating factor for chlorophyll growth in the reservoirs. Seasonal summer TP influenced the autumn algal growth. The concentrations of total phosphorus (TP) was highest during the summer season (36±2 μgL^-1) while it was lowest in the winter season (15±1 μgL^-1). Summer monsoon directly influences the concentrations of total phosphorus in the reservoirs. Overall, the calculated WQI value suggested that site 1 (129.44) was in poor condition whereas sites 2 (116.06), 3 (103.51), 4 (89.3), 5 (82.007) and 6 (90.22) were in fair condition.