程海沉积物重金属时空变化及人为污染与潜在生态风险

沉积物重金属污染是影响湖泊等水体环境质量与健康的主要因素之一.通过对程海9个沉积短岩芯中10种金属元素含量的分析,在~(210)Pb与~(137)Cs定年的基础上,研究了沉积物中重金属含量与污染的时空变化特征;采用潜在生态风险指数法与沉积物质量基准法、并参考重金属污染水平,评估了表层沉积物重金属的潜在生态风险.结果表明,各岩芯不同年代沉积物中,除了Cd含量变化较大之外(变异系数为0.59),其余各金属元素含量变化均较小(变异系数小于0.20);空间上,各岩芯之间每一种金属的平均含量差异较小,最大值与最小值的比值为1.2~1.8,显示了不同湖区重金属较为相似的富集规律.沉积物中主要污染元素为Cd、Pb和Hg,其中Cd和Pb污染始于20世纪80年代中期;近十年来Cd污染程度稍有下降,但仍呈中等污染水平,而Pb污染程度持续增加,属于弱污染水平;Hg污染始于20世纪90年代末期,呈弱污染水平;而As、Cu和Zn仅在部分近表层沉积物呈现较弱污染.空间上,沉积物中重金属污染水平并未表现出明显的趋势.除了大气沉降(主要为有色金属冶炼释放)输入之外,程海沉积物重金属污染还可能受到农业面源与生活污水排放的影响.表层沉积物中As、Cu、Ni、Pb和Zn具有较低的潜在生态风险,Hg和Cd具有中-高潜在生态风险.

Spatio-temporal Variations, Contamination and Potential Ecological Risk of Heavy Metals in the Sediments of Chenghai Lake

Heavy metals pollution in the sediments is one of the main factors impacting the water quality and ecosystem health. In this study, concentrations of ten metals in nine sediment cores from the Chenghai Lake were determined. Chronology of a typical core (CH2012) was constructed by the ²¹⁰Pb and ¹³⁷Cs dating method. The spatio-temporal variations in concentrations and contamination characteristics of As, Cd, Cu, Hg, Ni, Pb, and Zn were evaluated. The potential eco-risks of heavy metals in the surface sediments were studied by combining the ecological risk index and sediment quality guidelines (SQGs) assessment as well as their pollution levels (enrichment factors, EF). The metal concentrations in each sediment core showed little vertical change with coefficients of variation of less than 0.20, except for Cd, whose coefficient of variation was 0.59. Spatially, the average concentrations of each metal showed minor difference among the cores, with ratios ranging from 1.2 to 1.8, suggesting similar sedimentary characteristics of metals in the whole lake. Cd and Pb were influenced by anthropogenic contamination that has started in the mid-1980s. The pollution level of Cd decreased in the past decade and still belongs to the moderate pollution degree, whereas the pollution level of Pb increased continually and could be classified as the weak pollution degree. The Hg contamination began in the late 1990s, with EFs ranging from 0.9 to 1.6, belonging to the weak pollution degree. The As, Cu, and Zn pollution occurred mainly near the surface sediments with weak pollution degrees. Spatially, there were no obvious trends in pollution levels of the metals. The heavy metals pollution is mainly influenced by atmospheric deposition that originates from non-ferrous metal smelting emissions, as well as agricultural and domestic discharges. As, Cu, Ni, Pb, and Zn in the surface sediments have low potential ecological risks, whereas Hg and Cd may pose middle-high potential risks.