洞庭湖主要入湖口表层沉积物重金属分布特征与生态风险评价

尽管针对洞庭湖沉积物中重金属的研究工作较多,但缺乏针对其主要入湖口的研究。基于2014年12月和2015年6月对洞庭湖主要入湖口表层沉积物中重金属调查,分析了重金属含量的时空分布特征,并采用一致性沉积物质量基准法对其生态风险进行了评价。结果表明,Cd、Hg、As、Cu、Pb和Zn的平均含量分别为3.27、0.190、27.10、39.8、38.0和157.8 mg·kg-1,其大小顺序为ZnCuPbAsCdHg,Cd和As含量出现超过土壤环境质量三级标准的现象,是主要的重金属污染物。Cd、As、Pb和Zn等4种重金属含量的最高值均出现在湘江入湖口,Cu含量的最高值出现在资水入湖口,Hg含量以沅江入湖口最高,除Pb外,其他5种重金属在湘江和资水入湖口的含量均大于平均值,表明湘江和资水入湖口污染较为严重;汛期与非汛期6种重金属的含量均无显著性差异(P0.05)。6种重金属生态风险大小顺序为AsCdZnPbCuHg,各入湖口生态风险大小顺序为湘江入湖口资水入湖口沅江入湖口汨罗江入湖口澧水入湖口长江"三口"新墙河入湖口,其中湘江和资水入湖口为较高生态风险,其他入湖口为较低生态风险。入湖河流是洞庭湖湖体沉积物重金属污染的主要来源,在一定程度上,入湖河流沉积物中重金属的含量对洞庭湖湖体沉积物中重金属污染状况起着决定性作用,因此,洞庭湖流域重金属污染防控应以入湖河流为主,其中尤以湘江和资水为重点。

Distribution and Ecological Risk Assessment of Heavy Metals in Surface Sediments from Main Tributary Entrances of Dongting Lake

Although there are many studies on heavy metals in sediments from Dongting Lake,but the study on heavy metals in sediments from main tributary entrances of Dongting Lake is still lacking.The spatial-temporal distribution of heavy metal contents was analyzed,and the ecological risk assessment of heavy metals was conducted using the Consensus-Based Sediment Quality Guidelines based on the investigation of heavy metal contents in surface sediments of main tributary entrances of Dongting Lake in December 2014 and June 2015.The results showed that the average contents ofCd,Hg,As,Cu,Pb and Zn were 3.27,0.190,27.10,39.8,38.0 and 157.8 mg · kg-1,respectively,and the descending order was as follows:Zn＞Cu＞Pb＞As＞Cd＞Hg.The contents of Cd and As exceeded the standard of Class Ⅲ of Environment Quality Standard for Soils (GB 15618-1995) in some sites,indicating Cd and As were the main heavy metal pollutants.The maximum values of Cd,As,Pb and Zn were observed in lake entrance of Xiangjiang River,the maximum value of Cu was observed in lake entrance of Zishui River,and the maximum value of Hg was observed in lake entrance of Yuanjiang River.The contents of heavy metals in lake entrances of Xiangjiang River and Zishui River were greater than the averages except Pb,indicating the pollution of lake entrances of Xiangjiang River and Zishui River was more serious.No significant differences were found in the contents of Cd,Hg,As,Cu,Pb and Zn between flood season and non-flood season (P＞0.05).The PEC-Qi values in descending order was As＞Cd＞Zn＞Pb＞Cu＞Hg,and the ∑ PEC-Qi values in descending order was lake entrance of Xiangjiang River＞lake entrance of Zishui River＞lake entrance of Yuanjiang River＞lake entrance of Miluo River ＞lake entrance of Lishui River＞three outlets of Yangtze River＞lake entrance of Xinqiang River.There were higher ecological risk in lake entrances of Xiangjiang River and Zishui River,while there were lower ecological risk in other tributary entrances.The inflow rivers were the main sources of heavy metal pollution in sediments from Dongting Lake body.To a certain extent,the heavy metal contents of inflow rivers contributed most to the heavy metal pollution in surface sediments from Dongting Lake body.The inflow rivers should be given priority in heavy metal pollution prevention and control in Dongting Lake basin,especially focusing on Xiangjiang River and Zishui River.