Keywords: 
• heavy metals /
• pollution /
• ecological risk /
• trend /
• Dongting Lake /
• surface sediments

Abstract: Although there are many studies on heavy metals in Dongting Lake sediments, the information regarding heavy metal ecological risk and its trend is little. This paper discussed the heavy metal ecological risk of surface sediments in Dongting Lake and its trend, based on sampling analysis of 9 representative monitoring sites in February 2012 and April 2013 and some historical monitoring data. Hakanson's Potential Ecological Risk Index (RI)Method was employed in this paper. The results show that the contents of Cd, Hg, As, Cu and Pb in surface sediments range from 0.60 mg·kg^-1 to 20.7 mg·kg^-1, 0.090 mg·kg^-1 to 0.640 mg·kg^-1, 10.4 mg·kg^-1 to 83.7 mg·kg^-1, 17.9 mg·kg^-1 to 70.9 mg·kg^-1 and 16.9 mg·kg^-1 to 95.8 mg·kg^-1, respectively. The descending order is as follows:Pb > Cu > As > Cd > Hg. The potential ecological risk of heavy metals in surface sediments of Dongting Lake can be arranged as Cd > Hg > As > Pb > Cu. Cd and Hg are the main heavy metal risk pollutants, and Cd isthe primary pollutant. The RI values of the whole lake are between 117.10 and 589.80, with an average value of 289.99. The spatial distribution of RI average values has certain characteristics. South Dongting Lake is the highest area, West Dongting Lake is the middle one, and East Dongting Lake is the lowest region. According to the classification standard proposed by Hakanson, the Cd in South Dongting Lake has extremely high ecological risk. The ecological risk level of Dongting Lake is medium. In terms of the preliminary analysis, the ecological risks of other heavy metals have risen, to some extent, in the past 30 years, except Hg. And Cd's rising trend is obvious. The heavy metal ecological risk level in Dongting Lake has changed from low risk to medium. Therefore, heavy metal pollution control in Dongting Lake basin should focus on Cd in Xiangjiang River and Zishui River.