西溪国家湿地公园底泥重金属污染风险评价

Assessment on Heavy Metal Pollution in Sediment of Xixi National Wetland Park in Hangzhou City

对杭州西溪湿地不同水体干扰和沉积过程干扰类型的底泥重金属进行研究,分析了底泥表层和剖面重金属Cu、Zn、Cr、Pb、Cd、Hg和As的含量及分布特征,探讨不同湿地保护措施和水体干扰类型等因素对底泥重金属含量的影响及重金属的可能来源,在此基础上,运用单因子污染指数、Hkanson潜在生态风险指数和基于沉积物质量基准的方法对底泥污染的生态风险进行了评价。结果表明,底泥7种重金属含量平均值均低于《土壤环境质量标准》(GB15618-1995)的二级标准。除Hg和As外,其他元素含量平均值高于当地土壤元素背景值。重金属元素间的不同相关性指示底泥污染物的多种来源。Zn和Cd在底泥中的含量要明显高于土壤,指示底泥中有不同于土壤的重金属污染来源。空间上,底泥污染物的分布与人为活动干扰的强度具有较为密切的关系,景区外围样点污染物含量要高于景区内样点,且景区外围样点重金属污染物仍然处于一个增加的趋势,而景区内污染物输入则呈现为减少的态势。水体类型对底泥重金属的影响一般表现为封闭池塘和大水面中底泥重金属元素含量高于普通河道中的含量。Hkanson潜在生态风险评价表明,西溪湿地的整体生态风险较轻微,元素中Cd和Hg具有中等生态风险,其余为轻微生态风险。基于沉积物质量基准的风险评价结果则有所不同。

Heavy metals in sediments of Xixi Wetland were researched. Effects of protection measures, sediment dredging and water types on heavy metal content were discussed. The results indicated that mean contents of Cu, Zn, Cr, Pb, Cd, Hg and As were lower than the second grade standard of Chinese environmental quality standards for soils （GB 15618-1995 ）. Hg and As were lower than the background values of agriculture soils in Hangzhou City, while Zn, Cr, Pb and Cd were higher than that. The various correlations of heavy metals indicated a multisource of sediment pollutants. Zn and Cd contents in sediments were higher than that in soils, which indicated different sources of heavy metals in sediment and soils. Spatially, the pollutant contents were lower in center wetland （first phase project） than that in outside. And the accumulation of heavy metals had been reduced in center wetland, while it was improved in outside areas which were being disturbed by human activities more frequently. Heavy metal contents were higher in sediment of closed pounds or big pools than that in general watercourses aswater types had also effects on the heavy metal contents in sediment. The Hakanson integrated potential ecological risk of Xixi was light as the mean integrated index was low （110.9）. Cd and Hg were in medium levels, which had the heaviest contribution to integrated potential ecological risk, while other 5 metals had low levels of risk. And the results concluded from American National Oceanic and Atmospheric Administration of Sediment Quality Guidelines for the sediment risk assessment was different comparing with the Hakanson＇ s.