Higher dissolved oxygen levels promote downward migration of phosphorus in the sediment profile: Implications for...

Lake restoration (typically sediment dredging) commonly involves producing a new sediment-water interface (SWI). This study comprehensively investigated the migration and transformation of P during the formation of a new SWI under different dissolved oxygen (DO) levels in the overlying water, based on Fe/Al-rich sediment. The results suggest that DO had a profound effect on the 0-7 cm sediment layer properties and higher DO levels in the overlying water resulted in the diffusion of DO deeper into the sediments. Importantly, besides preventing Fe reductive dissolution and sulfides competition, higher DO levels inhibited the release of P from sediment by inducing the mitigation of P from the upper (0-3 cm) into the bottom (3-7 cm) sediments. The migration of P was found to be closely related to the interactions between organic matter and Al, Fe, and Ca in the sediment profile caused by higher DO levels in overlying water. Particularly, the decrease in organic matter in the upper sediments increased the mobility of Ca and promoted aging of Al and Fe, which increased the migration of the different forms of P. The increased organic matter in the bottom sediments retained the mobile Ca and increased amorphous Fe, which immobilized the P that had migrated from the upper sediments. These results demonstrate the relatively high mobility of P in the upper sediments and the importance of P immobilization capability of bottom sediments on regulating P release from SWI under higher DO levels in overlying water. Accordingly, measures for lake restoration with producing a new SWI were recommended to be applied in combination with P immobilization method to develop more feasible strategies.