闽江大樟溪下游沿线湿地沉积物中重金属分布特征及生态风险评价

Distribution Characteristics and Ecological Risk of Heavy Metals in Sediments of Wetland Along the Lower Reach of the Dazhang Stream(Min River)

基于2018年7月采集的大樟溪下游沿线湿地表层沉积物样品,探讨了6种重金属(Pb、Cr、Cu、Zn、Ni、Cd)的沿程分布特征,并运用地累积指数法(Igeo)和潜在生态风险指数法(RI)对其生态风险进行了评估。结果表明,湿地沉积物中重金属的平均含量整体表现为Zn>Pb>Cr>Cu>Ni>Cd,且其沿程变化较为一致,而这主要取决于沉积物粒度组成、磁学参数、pH、EC和有机质的沿程分布。湿地沉积物中的6种重金属含量均于桃花洲、耕櫵亭、方庄村和奥莱时代出现较低值,原因主要与4个采样点的采砂活动改变了河流水沙条件使得沉积物发生粗化有关。湿地沉积物中6种重金属之间均存在极显著正相关关系(P<0.01),说明其具有同源性,并可能代表了一个因采砂/采石活动以及建筑/生活垃圾堆放导致的复合污染源。大樟溪下游沿线湿地大部分样点的Pb处于轻度污染状态,而Cd处于中度污染状态。6种重金属平均单项潜在生态风险指数(E■)表现为Cd>Pb>Ni>Cu>Cr>Zn,Cd具有强生态风险。所有样点重金属的平均RI值为228.62,说明湿地整体处于中等生态风险。研究发现,尽管大樟溪下游沿线湿地沉积物中的重金属含量相比闽江上游其它支流和闽江中下游河段处于一个较低水平,但其Pb、Cd污染及生态风险(特别是Cd)仍较为突出,故下一步在加强对沿线湿地管控时应给予特别重视。

The surface sediments in wetland along the lower reach of the Dazhang Stream were sampled in July 2018 and the concentrations of six heavy metals(Cr,Ni,Cu,Zn,Pb and Cd)in samples were determined to evaluate their distribution characteristics and ecological risks according to the geoaccumulation index(Igeo)and the potential ecological risk index(RI).Results showed that the average contents of heavy metals in sediments generally followed the sequence of Zn>Pb>Cr>Cu>Ni>Cd and their variations along the lower reach were consistent,which mainly depended on the distributions of grain composition,magnetic parameters,pH,EC,and organic matter along the lower reach.The levels of six heavy metals in sediments of Taohuazhou,Gengjiaoting,Fangzhuangcun and Aolaishidai were very low,which might be due to the sand mining activities at the four sampling sites.The sand mining activities could alter the conditions of flow and sediment in river,resulting in the coarsening of sediments in wetland.Significantly positive correlations were observed among the six metals in sediments(P<0.01),indicating that they might have similar source which represented a combination of sand mining/quarrying wastes and construction/living wastes.The Pb in sediments of most sampling sites was in an unpolluted to moderately polluted status,while Cd was in a moderately polluted status.The average single potential ecological risk indices(E■)of six heavy metals in sediments generally followed the order of Cd>Pb>Ni>Cu>Cr>Zn,and Cd showed a high ecological risk.The average RI value of heavy metals in all sampling sites was 228.62,implying that the wetland along the lower reach,as a whole,was in a moderately ecological risk.The study found that although the levels of heavy metals in sediments of wetland along the lower reach of the Dazhang Stream were much lower compared with the other branches in the upper reach of the Min River and the main stream of middle and lower reaches of the Min River,the pollution of Pb and Cd(particularly Cd)and their ecological risks were still very serious.Thus,in the next step,more attentions should be especially emphasized to strengthen the management of wetlands along the lower reach of the Dazhang River.