The bioaccumulation performance of reeds in a pilot scale Constructed Wetland for removal of heavy metals in polluted river treatment (Xi'an, China)

To obtain a comprehensive understanding of the accumulation and distribution of heavy metals in constructed wetland, the Phragmites australis, growing in a pilot scale artificial wetland, dealing with the polluted Zaohe River in Xi'an (Shaanxi, China), were sampled and the concentration of Cd, Cr, Cu, Ni, Pb and Zn in reeds was investigated. The results showed that the Zn, Cu and Cr concentration of reed declined obviously along the first three sampling points near the entrance of the wetland, which infers that the heavy metals removal function by reed mainly reacts in the area of about 30 m range closer to the wetland entrance. Meanwhile, it was figured out that there are two different partition patterns of heavy metal absorbed and accumulated by Phragmites australis in this wetland. In particular, the concentration and allocation percentage of Cu in tissues of reeds follows the sequence of root > stem > leaf, which are high and partitioned evenly among the root, stem and leaf tissues. Meanwhile the Cd, Cr, Ni, Pb and Zn concentration follows another sequence of root > leaf > stem, and the concentrates of Cd, Cr, Ni, Pb and Zn in root tissue are significantly higher than in the stem and leaf. In addition, by calculating the bioaccumulation factor and transfer coefficient, the result showed that Cd and Cu can be enriched by reed root and the enrichment capability is relatively weak for Cr. The migration ability of Cu, Pb, Cd, Ni and Zn from root to leaf is stronger than the transfer ability from root to stem. While, Cu and Zn have the strong ability of migration from reed root to the ground parts.