Water Quality Survey and Evaluation in the Backwater Area of the Pengxi River in the Three Gorges Reservoir

Since the first impoundment of the Three Gorges Reservoir in 2004,algal blooms have broken out for several times in the Pengxi River,the largest tributary on the north shore of the reservoir area.In order to evaluate water quality in the backwater area of the Pengxi River and analyze the causes of eutrophication,water quality in the backwater area of the Pengxi River was monitored from 2007 to 2009 and evaluated based on Environmental Quality Standards for Surface Water(GB3838-2002) of China and Carlson Trofic State Index.It was found that the concentrations of total nitrogen(TN) and total phosphorus(TP) in the Pengxi River were high and eutrophication or serious eutrophication of the water body was detected all the year round.The situation in Shuangjiang Bridge Ferry was more serious than that in Gaoyang and Quma Ferries.Concentrations of TN and dissolved oxygen(DO) showed no obvious trend of variation with seasons,while the concentration of TP,chlorophyll a(Chla) and secchi depth(SD) exhibited a pronounced seasonal fluctuation.In addition,concentration of TP and Chla in summer and fall were higher than in winter and spring,while SD showed an opposite tendency.According to this study,the concentration of TP is the major cause of eutrophication and non-point source pollution is the main source of TP in the backwater area in the Pengxi.