Influence of sediment concentration on different forms of phosphorus concentration in main stream of Three Gorges Reservoir

Phosphorus, no matter dissolved and particulate forms, is an important index for water quality assessment and pollution control supervision.It is of great significance to study influence of sediment concentration variation on the concentration of different phosphorus forms.In this paper, the main stream of Three Gorges Reservoir(TGR) was selected as the research object, and the Mann-Kendall nonparametric test method and Pearson correlation coefficient were used to analyze the influence of sediment concentration on the concentration of different forms of phosphorus, such as total phosphorus, dissolved phosphorus and particulate phosphorus.The results showed that:(1) From2003to2019,the average flow of monitoring sections in the main stream of the TGR hasn't changed significantly, however the sediment concentration decreased significantly.(2) The total phosphorus concentration in the mainstream of the TGR gently fluctuating upward from2003to2012,and continued to decline from2013to2019; the concentration of dissolved phosphorus increased first and then decreased, and the peak value of each section appeared in2013and2014.The concentration of particulate phosphorus decreased in a fluctuated way.(3) Compared with the average concentration from2003to2012,the total phosphorus concentration in cloudy waters decreased by about40%,the total phosphorus concentration in clarified waters decreased by about25%,the particulate phosphorus decreased by about65%.The dissolved phosphorus at Zhutuo Section at the end of the reservoir and Cuntan Section in the varied backwater area increased by about60%,and the dissolved phosphorus in Qingxichang and Wanxian sections in the perennial backwater area increased by about20% and12% respectively.The ratio of dissolved phosphorus to clarified total phosphorus also increased rapidly, with dissolved phosphorus/clarified total phosphorus reaching over68% from2013to2019.(4) Under the influence of new water and sediment regimes, phosphorus concentrations of different forms in the mainstream of the TGR have changed significantly.Dissolved phosphorus which is most easily used by plankton, has become the main form of phosphorus in the mainstream of the TGR.This study can provide scientific basis for nutrient control and management in the TGR area.