[Mobilization and transformation of phosphorus from water-soil interface of flooded soil]

Mobilization and transformation of phosphorus from water-soil interface of flooded agricultural soils is a concern, and it has been a leading cause of eutrophication of lakes and rivers. Using PVC soil trough, we modeled the mobilization and transformation of P, ferrous iron, ferric iron, dissolved organic carbon (DOC) between soil floodwater and porewater induced by flooding, and characterized the main factors that contributed to phosphorus release by using the principal component-partial least squares method. This study shows that flooding soils induced significant release of phosphate to the floodwater over a 54-d period. Cumulative phosphate content in floodwater was 16 times as much as in porewater. The changes that occurred among the inorganic P forms during flooding were also invested. Significant changes in the inorganic P fractions Fe-P, Al-P, Ca-P, and O-P occurred in soil during flooding. Typically, the Ca-P fraction was almost unchanged during flooding. The others decreased, and Fe-P contents during flooding decreased by 30.4%-72% of its initial value, which significantly contributed to the release of phosphate to floodwater and porewater. The major factors that affected the floodwater phosphate release were Eh, ferrous iron, ferric iron, and dissolved organic carbon (DOC). The factor that affected the porewater phosphate release was DOC. The predominant mechanism of DOC induced floodwater P release was ligand-enhanced dissolution, and that induced porewater P release was competitive sorption. Furthermore, ferric iron in porewater affected the porewater P release.