滇池沉积物中重金属垂向分布及污染评价

Vertical distribution and pollution assessment of heavy metals in sediment of Dianchi Lake

目前,对滇池沉积物中重金属的研究大多侧重于表层沉积物,对于重金属垂向分布规律的研究较少。用原子吸收光谱仪的火焰模式测定了云南滇池草海和外海各6个采样点沉积物中的4种重金属元素(Zn、Cu、Cr、Cd)的含量,对沉积物中重金属元素的垂向分布规律进行了分析,并应用地质累积指数法和Hakanson潜在生态危害指数法对沉积物中的重金属污染进行了评价。结果表明:滇池草海沉积物中重金属质量比高于外海。滇池外海中4种重金属平均质量比排序为:Zn>Cu>Cr>Cd,而草海中4种重金属平均质量比排序为:Zn>Cu>Cr≈Cd。除了Cr,草海沉积物内其它3种重金属质量比随深度增加而减小的趋势明显,外海这种趋势不明显。结合地质累积指数法和Hakanson潜在生态危害指数法评价出滇池整体上Cd的污染程度最为严重,其次是Zn和Cu,Cr污染程度最小。草海的重金属污染程度明显高于外海,草海呈现从南到北重金属污染越发严重的趋势,而北边靠近五家堆湿地公园处污染又有所减轻。随区域变化,外海的重金属污染没有明显的变化规律。

At present, most of the studies on heavy metals in the sediments of Dianchi Lake focus on the surface sediments, but there are few studies on the vertical distribution of heavy metals. Concentrations of four kinds of heavy metals including Zn, Cu, Cr and Cd in the sediments of 12 different areas of Dianchi Lake were investigated with flame atomic absorption spectrometer. Vertical distribution of the metals in the lake sediment were analyzed. The differences degree of heavy metal pollution in Caohai sub-lake and Waihai sub-lake were discussed. Pollution of heavy metals in sediment was analyzed by geological accumulation index method and Hakanson Potential Ecological Hazard Index method. Results show that: the concentrations of heavy metals in sediment of Caohai sub-lake are higher than those in sediment of Waihai sub-lake. The order of average mass ratio of four heavy metals in sediment of Waihai sub-lake are Zn > Cu > Cr > Cd, while the order of average mass ratios of four heavy metals in Caohai sub-lake are Zn > Cu > Cr ≈ Cd. Except Cr, the concentrations of other three metals decrease with increasing depth in the sediments of Caohai sub-lake. This trend is not obvious in Waihai sub-lake. Assessment results based on geo-accumulation index and potential ecological risk index show that the pollution status of Cd is the most serious, followed by Zn and Cu, and the pollution degree of Cr is minimum in all sampling sites. The pollution status of Caohai sub-lake is more serious than that of Waihai sub-lake. From the south area to the north area, the metal pollution becomes more and more serious in Caohai, while the pollution is decreased near the Wujiadui wetland park. There is no obvious change of the heavy metal pollution with the change of region in the Waihai sub-lake.