小型河流库坝建设对河道重金属元素分布的影响

Effects of a dam on heavy metal distribution in sediment in a small-scale river

【目的】研究小型河流库坝建设对河道沉积特征及重金属元素分布特征的影响。【方法】以淮河4级支流索河三仙庙水库至丁店水库段为研究对象,依据水流方向及库坝位置将其分为上、中、下3段,分别采用单因素方差分析和冗余分析,对3段的表层沉积物及下表层沉积物粒度特征,以及As、Cr、Pb、Cd、Cu、Hg和Zn共7种重金属元素进行了分析和评价。【结果】表层和下表层沉积物各粒度组分和有机碳含量基本相同,但表层重金属含量略高,表明库坝建设后该区域沉积环境总体上较为稳定,而重金属污染有所加重;3段间的水文条件差异较大,上段常处于相对断流状态,沉积物中砂粒含量较多,中段水流较小,粉粒和黏粒等粒径较小的沉积物粒度组分含量较高,下段常年积水,但水位变化较大,沉积物特征与上段相似;重金属元素分布特征显示其在中段的含量均高于上段和下段;有机碳在中段的含量极显著高于其在上、下段的含量。【结论】总体上,库坝建设改变了河流的水文条件,影响沉积物特征,对重金属元素分布影响较大,使得中段重金属元素相对容易富集。

【Objective】Study the effects of a dam on heavy metal distribution in sediments.【Methods】We used a twostep approach to understand the influence of a dam on sediment deposition and heavy metal distribution.The first step was to evaluate the effects of dam construction on sedimentary characteristics based on the changes in hydrological conditions by using One-way analysis of variance（ANOVA）.The second step applied redundancy analysis to examine the relationship between heavy metals（As,Cr,Pb,Cd,Cu,Hg and Zn） contents and the physical and chemical properties of sediments,including grain size distribution and organic carbon content.The Suo River was selected as the study area,which was divided into three parts（up,middle and down） according to the direction of the water flow and the position of the dam.【Result】The hydrological conditions in each part showed marked differences：the up part regularly showed a state of river blanking,the middle part had low water flow,and the down part always contained water.The reservoir-dam construction affected these characteristics and distribution of sediments.Analyses results of grain size distribution showed silt and clay depositions were higher in the middle part than those recorded in the up and down parts.Silt represented the largest proportion of sediments in all samples,whereas clay comprised the lowest percentage.Reservoir-dam construction resulted in an abundance of tiny grains of sediment in the middle part,and the organic matter also deposited in the middle part,depending on the flow regime and flow rate of the river.One-way ANOVA analysis showed that the distributions of heavy metals contents were high in the middle part,except Cr and Cu.Redundancy analysis showed that the grain size played a significant role in controlling heavy metal content in sediments,as the content tended to increase with declining grain size.【Conclusion】Overall,reservoir-dam construction increased the risk of heavy metal pollution by changing the hydrological conditions.