Abstract: In order to investigate heavy metal pollution and its potential ecological risk in surface sediments of urban lakes in Nanjing,samples of sediments in five urban lakes(Lake Xuanwu,Lake Yueya,Lake Zixia,Lake Pipa and Lake Qianhu)were collected for analysis of concentrations of six heavy metals,i.e. Cd,Cr,Cu,Ni,Pb and Zn using the inductively coupled plasma-atomic emission sepectrometry (ICP-AES),and potential risks of the pollutants were assessed with the geo-accumulation index method and the potential ecological risk index methods,separately.Results show that the concentrations of the heavy metals in the lake sediments were in the range of 0.8-5.1mg?kg^-1 for Cd,10.3-67.6 mg?kg^-1 for Cr,6.2-70.5mg?kg^-1 for  Cu,undetectable -53.2 mg?kg^-1for Ni,12.9-55.9 mg?kg^-1for Pb and 40.6-456.3 mg?kg^-1 for Zn.Analysis with the geo-accumulation index method that the six heavy metals followed the order of Cd>Zn>Pb>Cu>Ni>Cr in accumulation degree.Cd was at the level varying from moderate-on-the-severe-side to severe in accumulation.Risk assessment using the potential ecological risk index method showed that among the five lakes,Lake Yueya ranked the first in heavy metal pollution of the surface sediment and was followed by Lake Qianhu,Lake Zixia,Lake Pipa an Lake Xuanwu.The first three lakes were in the category of moderate in ecological risk,while the last two were in the category of low in ecological risk.     In order to investigate the heavy metal pollution status and its potential ecological risk in surface sediment of the urban lakes in Nanjing, the concentrations of six heavy metals including Cd, Cr, Cu, Ni, Pb and Zn were analyzed by inductively coupled plasma-atomic emission spectrometry (ICP-AES) in five urban lakes (Lake Xuanwu, Lake Yueya, Lake Zixia, Lake Pipa and Lake Qianhu). In addition, potential risks were assessed by geo-accumulation index and the potential ecological risk index methods, respectively. The results indicated that the concentrations of heavy metals ranged from 0.8~5.1 mg/kg-1 for Cd，10.3~67.6 mg/kg-1 for Cr，6.2~70.5 mg/kg-1 for Cu，not detected~53.2 mg/kg-1 for Ni，12.9~55.9 mg/kg-1 for Pb and 40.6~456.3 mg/kg-1 for Zn, respectively, in the surface sediments of the five lakes. Results of the geo-accumulation index method indicated that the surface sediments were heavily polluted by Cd (the calculated geo-accumulation indexes Igeo of Cd were all higher than 2.0 except for Lake Pipa). Meanwhile, other metals such as, Zn, Pb and Cu were also within different pollution status (Igeo ranged from 0.1 to 2.0). Based on the potential ecological risk index method, the pollution degree of heavy metals in surface sediments of Lake Yueya was the most seriously with the potential ecological risk index (RI) of 280.0. Meanwhile, Lake Qianhu and Lake Zixia were also belonged to the moderate ecological risk status (the potential ecological risk indexes (RI) were 164.4 and 161.2, respectively), while Lake Pipa (RI =81.7) and Lake Xuanwu (RI =131.7) were in slight ecological risk status.

Key words: heavy metal, urban lake, sediment, geo-accumulation index, potential ecological risk index, Nanjing