Characterization of phosphorus storage and release fluxes at the sediment-water interface of lakes in typical agricultural and irrigation areas: a case study of Chagan Lake in western Jilin, China.

Endogenous phosphorus release from sediments is a major cause of eutrophication in water bodies. To investigate the endogenous phosphorus morphological features and migration patterns in lakes under the influence of agricultural irrigation areas, we analyzed the changes of polymorphic phosphorus content in lake sediments under irrigation withdrawal conditions based on field sampling tests and sediment phosphorus release dynamics simulation experiments and used the diffusive flux method to determine the flux of phosphorus release from the sediment-water interface (SWI). The results showed that: (1) Data from encrypted sampling during the receding period revealed total phosphorus (TP) of lake water decreased from 0.11 mg/L to 0.05 mg/L, and TP of sediment increased from 723.53 mg/kg to 955.89 mg/kg. (2) The order of polymorphic phosphorus content of sediments at the lake inlet before the irrigation period was Fe-Al bound phosphorus (NaOH-nrP) > insoluble phosphorus > Fe-Al oxide bound phosphorus (NaOH-rP) > Calcium bound phosphorus (Ca-P) > Fe-Mn chelated phosphorus (BD-P) > active phosphorus. Interconversion between sedimentary polymorphic phosphorus is more drastic after the irrigation period. (3) The phosphorus forms extracted from sediments were ranked as insoluble phosphorus > NaOH-nrP > NaOH-rP > active phosphorus > Ca-P > BD-P. Insoluble phosphorus is the predominant form of phosphorus in sediments. (4) The TP exchange fluxes between the SWI by the diffusive flux method were 0.30 mg/(m2·h) and -0.33 mg/(m2·h) respectively. Receding water conditions promote sediment adsorption of TP from overlying water. The research findings establish a theoretical foundation for endogenous phosphorus from lake sediments in agricultural irrigation areas.