Abstract: The spatial-temporal variation characteristics of total phosphorus (TP) in the Thirteenth Five-Year Plan period are examined in this paper based on the TP data of 590 river sections and 116 lakes and reservoir points in the Yangtze River Basin monitored by the National Examination Network. Results revealed a decline trend of TP concentration in the Yangtze River Basin in the Thirteenth Five-Year Plan period,with the annual average concentration dropping from 0.106 mg/L in 2016 to 0.072 mg/L in 2020. TP concentration in 93.2% sections of the mainstream of Yangtze River decreased,with the annual average concentration reducing from 0.092 mg/L in 2016 to 0.059 mg/L in 2020. Minjiang River,Tuojiang River and Wujiang River witnessed apparent decrease (over 50%) of TP concentration,while the mainstream of Yangtze River experienced a rise of TP concentration due to the inflow of major tributaries including Minjiang River,Tuojiang River,Wujiang River and Hanjiang River. TP concentration at 62.9% of lake and reservoir sites decreased compared with that in 2016. Taihu lake and Chaohu Lake suffered from high TP concentration in autumn,Dongting Lake,Poyang Lake and Danjiangkou Reservoir in winter,and Dianchi Lake in summer. The research finding reflects the positive results of water pollution prevention and control in the Yangtze River Basin on the one hand,and offers reference for the in-depth control of TP pollution in the Yangtze River Basin on the other.

Key words: total phosphorus, temporal-spatial variation, influencing factors, Thirteenth Five-Year Plan period, Yangtze River Basin