Abstract: Sediment is an important endogenous source of phosphorus for the lake water environment.Due to climate change and human activities, the water level of Poyang Lake shows dramatic seasonal fluctuation.However, the effect of these seasonal dry-wet alternations on the endogenous release of phosphorus(P) from sediment remains unclear.In this paper, six silty loam sediment columns and six sand sediment columns were collected from the Fuhe River estuary into the Poyang Lake.Dry-wet alteration and long-term flooding scenarios were simulated respectively in the laboratory over a 45-day incubation to explore the effect of dry-wet alteration on sediment P form and endogenous release rate.The results showed that:(1) dry-wet alteration promoted the release of P in sediments, with organic-P as the main form.The maximum P release rates of silty loam and sandy sediments under dry-wet alteration could reach up to 2.59 mg/(m2·d) and 1.97 mg/(m2·d) respectively, 4～5 times higher than those in long-term flooding conditions.(2) Under dry-wet alteration, iron-aluminum bound P(Fe/Al-Pi) in sediment decreased, while weakly adsorbed P(WA-P),potentially active organic-P(PA-Po) and moderately active organic-P(MA-Po) increased.Calcium bound P(Ca-Pi) and non-active P(NA-Po) remained stable.(3) During long-term flooding, Fe/Al-Pi increased, while MA-Po which can be mutually transformed with Fe/Al-Pi decreased.The easily released P(WA-P,PA-P) and inactive P(Ca-Pi,NA-Po) showed no significant changes.Those results suggest that dry-wet alteration promotes the transformation of Fe/Al-Pi to MA-Po,further converting into easily released P(WA-Pi and PA-Po),thereby facilitating endogenous P release in the sediment.