Geochemistry characteristics of sediment phosphorus in a typical area prone to deposition in the Three Gorges Reservoir

Study region: The mainstream reach from Zhongxian to Yunyang in the Three Gorges Reservoir. Study focus: In this study, the modified sequential extraction method (SEDEX) and diffusive gradients in thin films technique (DGT) were utilized to reveal geochemistry characteristics of sediment phosphorus (P) in a typical mainstream reach from Zhongxian (ZX) to Yunyang (YY) in the Three Gorges Reservoir (TGR). A hydrodynamic model was established for the study reach to clarify hydrodynamic characteristics in the pro-TGR and post-TGR periods and its effects on sediment deposition and P release. New hydrological insights for the region: Results illustrated that total phosphorus (TP) in the surface sediments was about 693.31-805.92 mg/kg, and inorganic phosphorus (IP) and organic phosphorus (OP) were 648-781 mg/kg and 23-45 mg/kg. Ca-bound P (Ca -P) made a major contribution (39.18-54.08%) to TP. Vertical distribution of labile P has a positive correlation with Fe (II) and S( -II), respectively, and labile P exhibited a synchronous change with Fe(II). Diffusion flux (Fd) of labile P was about 0.32-0.56 mg/(m2 & sdot;d), and the sediment paid a role as P source during the sampling period. Affected by the operation of the TGR, velocity and sediment carrying capacity (S*) reduced significantly in the study reach. The velocity was about 1.0-3.0 m/s and 0.0-0.7 m/s, and S* ranged from 0-10 kg/m3 and 0-0.1 kg/m3 in the pro-TGR and post-TGR periods, respectively. A highlight of this work is that impacts of hydrodynamics on P mobility in a typical mainstream reach prone to deposition are systematically investigated by recreating the hydrodynamic processes in the pro-TGR and post-TGR periods.