Characteristics on Spatiotemporal Variations of Surface Water Environmental Quality in Tuojiang River in Upper Reaches of Yangtze River Basin

Tuojiang River is one of the most important tributaries among the Upper Reaches of Yangtze River basin. In order to characterize of the water quality variations and the prevention focus of Tuojiang River basin,this paper presents analyses in its four periods of the year,month,quarter and water period using single factor evaluation and rank correlation coefficient method,based on the monitoring data of water quality in 36 monitoring sections in Tuojiang River Basin from 2010 to 2017, the results show that the water quality of Tuojiang River basin was generally in a polluted state,but has a positive trend. Total phosphorus (TP) was the primary pollutant. The standard rate of water quality monitoring sections in basin shows a trend of increasing first,then decreasing and then increasing again. The water quality index changed significantly during the year,which reached its minimum in wet season and reached the maximum in dry season. Besides,the water quality of the main stream was better than that of the tributary. The spatial variability of TP and ammonia nitrogen (NH₃-N) concentrations were weak,and the spatial variability of chemical oxygen demand (COD) and biochemical oxygen demand (BOD₅) concentrations were strong. Although the water environmental quality of Tuojiang River basin has changed,the pollution problem that Tuojiang River basin faced is still grim. Therefore,it is necessary to attach great importance to the control of pollution source,especially the prevention of TP in future.