Estimation of releasing fluxes of sediment phosphorous in the Three Gorges Reservoir during late autumn and early winter

In order to investigate the internal contamination load sources in the Three Gorges Reservoir(TGR),a field sampling campaign was carried out in November and December 2010.Phosphate contents(PO3-4-P) were determined in 6 mainstream and 9 estuary sediment cores of sediment-water interface in the TGR.The results showed that the PO3-4-P concentrations of pore water in sediments from tributaries and the corresponding overlying water were higher than those from the mainstream.The PO3-4-P contents in tributaries and mainstream ranged from 9.59-29.79 μg·L-1 and 9.01-25.36 μg·L-1,respectively.Based on calculations using the Fick's First Law,sediments located at GuoJiaba and Xiaojiang estuaries were the 'sink' of P,and the fluxes of sediment PO3-4-P were estimated to be-0.63 mg·(m2·a)-1and-0.60 mg·(m2·a)-1,respectively.In other areas,PO3-4-P diffused from the pore water to the overlying water,and the diffusive fluxes were in the range of 0.15-2.47 mg·(m2·a)-1.With the assumption that molecular diffusion was the main process by which nutrients were transported from the pore water to the overlying water and the water body in the TGR was evenly mixed,the contribution of sediment phosphorus to the water body was only-0.011-0.098%.So far,with the Three Gorges Reservoir sediments as the internal contamination load sources,the phosphorous release didn't significantly influence the water quality.The sediments in the TGR may be a large P source in a period of future time after the external P source is controlled efficiently.