Study on release potential of sediment phosphorus under water level fluctuation in Poyang Lake and suggestions on assessment

In order to investigate the effect of alternation of wetting and drying on phosphorus release from lake sediments, this paper studied the process of phosphorus release from sediments driven by water level fluctuation of Poyang Lake based on basic data and simulation test, and gave some suggestions for total phosphorus(TP)assessment of the lake.The results showed that the water level of Xingzi Hydrological Station fluctuated in 2020～2022,and the maximum water level difference were 15.01,11.42 m and 12.69 m, respectively, resulting in a highly dynamic lake area.The exposed area at the lowest water level reached 3433.92,3442.40 km2 and 3618.36 km2,respectively, with a large area of sediments experiencing the alternation of wetting and drying.The results of simulation test showed that the average TP release fluxes from the sediments of Nanjishan and Qinglan Lake sections experienced bare-exposure to sunshine-flooding were 16.67 mg/(m2·d)and 13.23 mg/(m2·d),respectively, in the early stages of simulation.Considering the characteristics of TP composition and the influence of water level fluctuation in Poyang Lake, it was suggested that soluble reactive phosphate(SRP)or total dissolved phosphorus(TDP)should be used as the phosphorus assessment parameter instead of TP for Poyang Lake, and the threshold should be dynamically adjusted.When the water level of Xingzi Hydrological Station was lower than 11.00 m, the river standard should be used for the assessment.