Predicting Ni dynamic mobilization in reservoir riparian soils prior to water submergence using DGT and DIFS

The South-to-North Water Diversion Project has been initiated to address the problem of water shortages in north China. However, the environmental impact of this project is currently unclear, especially for the geochemical process of toxic trace metals in reservoir riparian soil following water submergence. The mobility of Ni in Miyun Reservoir riparian soil samples was investigated using diffusive gradients in thin films (DGT), considering five different land use types and three vertical elevations. The DGT-induced fluxes in soil (DIFS) model was applied to simulate the kinetics of Ni mobilization in the soil. The results showed that the average concentration of Ni was 36.58 mg/kg, which was slightly higher than the corresponding background values reported for both Beijing and China. Coincidentally, the highest concentrations of both total Ni and DGT-labile Ni (C_DGT-Ni) were observed at the same site (recreational area), indicating that anthropogenic activities may have contributed to the release of Ni. Land use type and vertical elevation had no significant influence on C_DGT-Ni. In addition, C_DGT-Ni was positively correlated with reducible fraction, C_DGT-Fe, C_DGT-Mn, and TOC, indicating that Ni in the soils was adsorbed mainly on the Fe/Mn oxides and organic matter. Moreover, the low values of R (C_DGT-Ni/C_sol-Ni, R < 0.25) indicated that the replenishment of Ni from the solid phase was poor, and the rate of Ni desorption was considerably lower than its depletion rate, thus leaving only a small proportion of Ni was available.