[Analysis of Water Quality Change and Its Driving Factors of the Xiaoqing River Estuary in Recent Ten Rears]

According to the monitoring data of pollutant concentration in the Xiaoqing River estuary from 2008 to 2017, 13 pollutants affecting water quality were selected. The trends of changes in water quality were identified mainly by the pollution index method, and the driving factors affecting water quality changes were quantitatively and qualitatively analyzed by the Spearman and Pearson correlation analysis method and the principal component analysis. The results showed that the water quality of the Xiaoqing River estuary was improved and the pollution was greatly reduced from 2008 to 2017. The pollution factors were still above the limits to varying degrees; COD and petroleum were the most serious pollutants, TP came second, and the remaining pollutants basically met the water quality standards of the Ⅲ. The pollution degree of petroleum, COD, NH₄⁺-N, NO₂^--N, and As showed an overall downward trend, and the pollution degree of TP, NO₃^--N, Cu, Pb, Zn, Cd, Hg, and Cr⁶⁺ showed an upward trend to different degrees. Social and economic factors were the main driving factors affecting the water quality of the Xiaoqing River. The discharge of pollutants and the changes in land use type led to serious water pollution overall in the Xiaoqing River, whereas the improvement of sewage treatment rate and the implementation of water environmental protection policy were the main factors affecting the water quality improvement of the Xiaoqing River. Natural factors were the secondary driving factors affecting the water quality of the Xiaoqing River. Climate and hydrological factors, such as temperature, sunshine duration, precipitation, and instantaneous runoff, also indirectly affected the water quality to different degrees.