Abstract:

Total contents of Pb，Cd，Ni，Zn，Cr and Mo in sediments of Xuanwu lake，a shallow urban lake，were determined，and the chemical fractions of these metals were also investigated using BCR’s sequential extraction procedure to evaluate the vertical distribution of metals in the sediment and their potential mobility.The results showed that metal total contents were in the order of  Zn (14880~24412 mg/kg)>Cr (11255~13578 mg/kg)>Mo (5519~7730 mg/kg)>Ni (4142~4981 mg/kg)>Pb (857~2005 mg/kg)>Cd (129~173 mg/kg).Except for Pb，all these contents exceeded the background values of soils in Nanjing city.In the 50 cm sediment profile，Pb and Cd were mainly in the oxidizable and residual fractions，while Mo，Ni，Zn and Cr distributed mainly in the residual fraction.The vertical distribution of total metal contents and their fractions varied greatly.Because the pH of the sediment of Xuanwu lake leaned to acidic or nearneutral (582~713)，it can be assumed that the exchangeable and reducible fractions are vulnerable，and the risk can be high for the potential release of Zn，Mo，Ni and Cd.The abundant organic matter (80%~110%) in the sediment reveals the potential mobility of oxidizable fraction，which can be degraded over the time.The high percentages of Pb (7550%) and Cr (4238%) in the oxidizable fraction imply the potential risk of mobility.Enough attention must be paid to the risk of heavy metals release during the processes of pollution control of urban lakes.