中文摘要：

为了研究湘江中游江段沉积物中重金属的污染特征及生态风险，于枯水期在株洲段和衡阳段采集了6个断面的18个沉积物；测定了沉积物中Cd、Ph、Zn、Cu的总量、形态及生物有效性，利用地积累指数法和单因子指数法分析了其污染程度与等级，并评价了湘江重金属污染治理的成效。结果表明：（1）湘江中游4种典型重金属（Cd、Pb、Zn、Cu）含量远高于湖南省土壤背景值，分别为背景值的83．1-1178．7、4．46-15．9、2．88-16．1和3．35-6．22倍；整体上看，重金属含量由上游往下游呈逐渐增加趋势。（2）湘江中游各采集点沉积物重金属的交换态比例不高，无定型铁锰氧化物结合态占很大比例，有较高的二次污染风险。（3）湘江中游沉积物中各重金属的生物可利用性差异显著，霞湾镇和松柏镇生物可利用性最高的是Cu，其余各采集点均为Cd。（4）与GB15618-1995《土壤环境质量标准》中二级标准比较，各采集点Cd、Pb、Zn、Cu含量均已超标；其中污染最严重的是Cd，已达到强一极强的污染程度。（5）湘江流域重金属污染的综合治理已一定程度上降低了湘江沉积物重金属污染的生态风险。

英文摘要：

In order to study characteristics and ecological risk of heavy metal pollution in the sediments of the middle reaches of Xiangjiang River, 18 sediment samples were collected from 6 cross-sections of the Zhuzhou and Hengyang Sections of the river （ 3 samples per cross section） during the dry season for analysis of heavy metals and their total contents, chemical forms and bioavailabilities. Heavy metals pollution was analyzed by degree and graded with the geoaccumulation index method and single-factor index method, and effect of governance of the Xiangjiang River was evaluated. Results show as follows ： （ 1 ） The contents of four typical heavy metals （ Cd, Pb, Zn and Cu） were much higher than their respective background values in the soil of Hunan Province, being 83.1-1 178. 7, 4.46-15.9, 2. 88-16. 1 and 3.35-6. 22 times as high, respectively. On the whole, contents of the heavy metals rose gradually from the upper reaches to lower reaches; （2） Of the heavy metals in the sediment samples, the fraction of exchangeable form was rather low in proportion and the fraction of amorphous Fe-Mn oxides was in dominance, posing a high risk of secondary pollution ; （3） The heavy metals in the sediments differed sharply in bioavailability. In the cross-sections at Xiawan Town and Songbai Town, the element the highest in bioavailability was Cu and in the other cross-sections, it was Cd; （4）According to Grade II criteria ofthe China Environmental Quality Standard for Soils （GB 15618-1995）, Cd, Pb, Zn and Cu all exceeded the threshold values, with Cd in particular, which reached the severe-extremely severe level ; and （5） After years of comprehensive pollution control, heavy metal pollution in the sediment of the river has been lowered by a certain degree and hence their ecological risks.