Evaluation of the dynamic mobilization of vanadium in tributary sediments of the Three Gorges Reservoir after water impoundment

The Three Gorges Reservoir (TGR) is the largest water resource protection zone in China, and environmental safety is crucial to its operation. For both aqueous and sediment phases, diffusive gradients in thin films (DGT), total vanadium (V) concentration (C-Total-V), and community Bureau of Reference (BCR) sequential extraction data were used to measure the pollution characteristics, horizontal and vertical distributions of DGT-labile V, and the dynamic mobilization of V in a typical tributary (the Meixi River) of the TGR. The results showed that C-Total-V in the surface sediments were obviously higher than the background values in sediment and soil, indicating a potential anthropogenic input of V in this area. A positive relationship was found between total organic carbon (TOC) and C-Total-V in the sediments, indicating that the pollution characteristics of V were associated with TOC. In addition, horizontal and vertical distributions of the fluxes of DGT-labile V (F-DGT-V) varied among the four DGT probes. In the same DGT probe, the horizontal distributions (0-6 mm, 6-12 mm and 12-18 mm) of F-DGT-V were similar in the overlying water; however, the values showed a poor coincidence with those recorded in the sediment. The vertical distribution of F-DGT-V in the same DGT probe showed similar tendencies. In fact, C-DGT-V is significantly negatively correlated with C-DGT-Fe, demonstrating that V had an inversely diffusive tendency with Fe. Moreover, diffusion fluxes of V at the sediment-water interface illustrated that the release characteristics of V varied among the sampling sites. In addition, the BCR fraction of V in the surface sediments of the four sampling sites showed that V mainly existed in the residual fraction (88.04-88.57%). The concentrations of DGT-labile V (C-DGT-V) were considerably lower than the non-residual fractions (the sum of exchangeable, reducible, and oxidizable fractions) measured by BCR sequential extraction. Correlation analysis showed that C-DGT-V had no correlation with non-residual V fractions, indicating that it is doubtful whether BCR extraction alone can be used to predict the bioavailability of V in this study. (C) 2017 Elsevier B.V. All rights reserved.