基于柱状底泥污染状态的环保清淤深度确定:以长荡湖为例

Determination of environmental dredging depth based on the pollution status of columnar sediments:A case study of Changdang Lake

以长荡湖环保清淤工程为例,研究清淤区域柱状底泥中污染物(TN、TP、OM和8种重金属)分布特征,提出基于柱状底泥厚度及污染物垂直分布特征的清淤深度确定方法。在计划实施清淤区域,底泥中TN、TP和OM质量分数随深度变化的总体趋势不明显,不同层底泥中污染物质量分数变化范围较大。TN和TP分别为418~1 840和100~1 120 mg·kg^(-1),随着深度的增加,TN平均值略有降低趋势,而TP平均值稍有增加趋势。表层底泥的重金属潜在生态风险指数明显高于底层,底泥中8种重金属质量分数随深度增加而降低,其中,Zn的质量分数最高,为33.9~359 mg·kg^(-1),而Hg质量分数最低,为0.002~0.23 mg·kg^(-1)。其余重金属(Cr、Cu、Ni、As、Cd和Pb)质量分数分别为24.9~114、4.3~95.0、12.4~55.8、1.02~17.9、0.05~7.78和6.28~59.9 mg·kg^(-1)。综合分析,长荡湖环保清淤深度设定为10~35 cm,建议在实施环保清淤工程时,优先选择底泥中重金属潜在生态风险指数较高的区域,并妥善处理Cd质量分数较高的底泥及其尾水。

This study takes the environmental dredging project of Changdang Lake(CDL)as an example,examining the pollution characteristics of pollutants(TN,TP,OM,and eight kinds of heavy metals)in the columnar sediments of the dredging area.A method for determining the dredging depth based on the thickness of the columnar sediment and the vertical distribution characteristics of pollutants was proposed.In the planned dredging area,the overall content of TN,TP and OM content in the sediments did not show clear trends with the change of depth,due to large variations in the contents in different sediment layers.The content of TN and TP ranged from 418 to 1840 mg·kg^(-1) and 100 to 1120 mg·kg^(-1),respectively.With increasing depth,the average content of TN showed a slight decrease,while that of TP showed a slightly increasing trend.In addition,the potential ecological risk index of heavy metals in the surface sediments was significantly higher than that in the bottom layer.Heavy metal contents in the sediments decreased with increasing depth.Among them,Zn had the highest content,ranging from 33.9 to 359 mg·kg^(-1),while Hg had the lowest content,ranging from 0.002 to 0.23 mg·kg^(-1).The contents of Cr,Cu,Ni,As,Cd,and Pb ranged from 24.9 to 114 mg·kg^(-1),4.3 to 95.0 mg·kg^(-1),12.4 to 55.8 mg·kg^(-1),1.02 to 17.9 mg·kg^(-1),0.05 to 7.78 mg·kg^(-1),and 6.28 to 59.9 mg·kg^(-1),respectively.Upon comprehensive analysis,the environmental dredging depth of CDL is set at 10 to 35 cm.It is recommended that areas with higher ecological risks of heavy metals in the sediments are prioritized during environmental dredging.Additionally,proper handling of sediments with a high Cd content and its tailwater is advised.