The study on heavy metal distribution in the sediment of middle tidal flat in Yangtze Estuary, China

The heavy metal distribution in the tidal flat has great effect on the estuary environment. The study aims to find the heavy metal distribution mechanism in the sediment of a middle tidal flat in Yangtze Estuary, China. The effects of grain size, the redox cycle of Fe, Mn during early diagenesis and post-depositional migration, and humic acid on the distribution of heavy metals have been studied extensively. Surface and core sediments from middle tidal flat of eastern Chongming Island were collected and analyzed the content of element Al, Cu, Cr, Fe, Mn, Pb, Zn, Zr and humic acid. The results showed that grain size, the geochemistry of Fe, Mn during early diagenesis and post-depositional migration, and humic acid had significant effect on the distribution of heavy metals. Copper, Fe, Mn, Pb and Zn mainly accumulated in the fine particles. Copper, Pb and Zn had similar seasonal variation in surface sediment and similar vertical distribution in the four seasons with Al, Fe, Mn and humic acid. Copper, Pb and Zn remobilized after deposition together with redox-sensitive elements Fe and Mn and accumulated in the redox boundary. Peak value of heavy metals, Fe, Mn and humic acid was observed in the four seasons at different depths at the redox boundary. Zirconium and Cr had opposite distribution than the other heavy metals.