LAUSR

Abstract As the world's largest water diversion project, the South-to-North Water Diversion Project in China will have potential environmental effects on the Miyun Reservoir (MYR). However, Cu is a toxic pollutant, and the potential risk of Cu remobilization in MYR soils after water impoundment remains unknown. Riparian soils (five land use types and three vertical elevations) were collected from the MYR before water impoundment. Soil properties, total concentrations of Cu in soils (Ctotal-Cu) and pore water (Csol-Cu), and chemical fractions were measured. Diffusive gradients in thin films (DGT) and the DGT-induced fluxes in soils (DIFS) model were applied to investigate Cu availability. The average Ctotal-Cu was higher than the Chinese background values, indicating potential anthropogenic input of Cu. No significant influences of land use types/vertical elevations on DGT-labile Cu (CDGT-Cu) and Ctotal-Cu were observed. A significant positive relationship between CDGT-Cu and Csol-Cu showed that CDGT-Cu can effectively predict bioavailable Cu fraction in MYR soils, whereas CDGT-Cu had no correlation with different chemical fractions measured by European Community Bureau of Reference (BCR) geochemical fractionation, suggesting that BCR chemical fractions cannot reflect Cu mobility in MYR soils. Risk assessment code showed a low risk of Cu remobilization in MYR soils, but a reducing environment would cause higher mobilization of Cu associated with Fe/Mn oxides after water impoundment. Moreover, the DIFS model reported a deficient soil resupply capacity; this agreed with low R values, which were mostly attributed to the limited available pool of Cu in the soil solid phase.