Abstract: Distribution characteristics and interfacial diffusion fluxes of seven heavy metals (Co, Ni, Cu, Zn, As, Cr, and Pb) were examined in the overlying water and sediment porewater from four sampling sites from Aha Reservoir in summer and winter, to understand the pollution status of dissolved heavy metals in the water body. Results showed that the average concentrations of dissolved heavy metals in the overlying water from Aha reservoir were lower than the standard of Grade I of Environmental Quality Standard for Surface Water (GB 3838-2002) and the Sanitary Standard for Drinking Water (GB 5749-2006) in China. Concentrations of As, Co and Cr in the bottom water increased during the anoxic period in summer, and the vertical changes of all heavy metals during the mixed season in winter were not significant. The mean concentrations of heavy metals in pore water were significantly higher than that in overlying water. There were significant positive correlations among Co, Ni and As, indicating their migration and transformation processes being affected by the iron-manganese cycle in Aha Reservoir. Concentrations of Cu, Zn and Pb had a positive correlation with the same pollution source. Results from the analysis of the diffusion fluxes of heavy metals at the sediment-water interface (SWI) showed that Zn remained negative diffusion, which indicated that sediment had a good adsorption effect on Zn. Co, Ni, As and Pb showed positive values at the SWI. The concentration of As reached 2.07 μg·cm^-2·a^-1 in summer, which may impose a greater release risk on the overlying water. Our results demonstrated that the pollution control of heavy metals had achieved remarkable results in the past decade in Aha Reservoir.

Key words: UV-B radiation, Yuanyang terraces, local rice variety, lodging index, culm wall thickness.