Using sediment resuspension to immobilize sedimentary phosphorus

The response of the transformation of internal phosphorus (P) to resuspended sediment was investigated in the sediment-water system under different disturbance intensity. The sediments and overlying water were collected from Taihu Lake, a typical shallow lake. The concentrations of particulate P (PP) and dissolved inorganic P (DIP) in the water phase and algal available P (AAP) and P fractions in the sediments and suspended particle characteristics were evaluated in laboratory-simulated experiments. The results show that dissolved oxygen (DO) in the overlying water increased continuously and pH decreased slightly under sediment resuspension. The concentration of ammonia nitrogen (NH₄⁺-N) showed a distinct decline, indicating that sediment resuspension promotes the penetration of DO into the sediments. It was also favor of the formation of metal oxides and hydroxides, inducing soluble amorphous metal compounds oxidized to insoluble crystalline metal compounds under disturbance condition. This resulted in the increase of refractory P in sediment compared with the static conditions. Sediment resuspension is beneficial to long-term P retention. This can be confirmed by the increase of maximum P adsorption amount (Q_max) and the decrease of the degree of P saturation (DPS) and equilibrium P concentration (EPC₀). This is the main explanation of DIP decrease in the overlying water. It is indicating that sediment resuspension not only improves the redox environment in the sediment-water system but also enhances P retention capacity.