沂河小埠东橡胶坝蓄水段表层沉积物中重金属的分布及生态风险评价

摘要

Six kinds of heavy metals in the surface sediment and surface water in the Yihe River were monitored in order to study the effects of the Xiaobudong Rubber Dam on distribution and accumulation of heavy metals in the surface sediment. Samples from eight sites were collected during the dry, wet, and normal seasons. The results showed that the average contents of As, Cd, Cr, Cu, Hg and Pb in the surface sediment were 6. 65, 0.40, 71.21, 42.48, 0. 15 and 41.54 mg/kg, respectively, which were 2.85 × 103-3.04 × 105 times higher than those in surface water meeting Grade I of China's national Environmental Quality Standard for Surface Water ( GB 3838-2002). Furthermore, the contents of the heavy metals in the sediment increased down the reservoir from the dam, which indicated the acceleration of heavy metal enrichment by the dam. Assessment of the ecological risk of the metals in the surface sediment suggested that As presented low risk, while Cd, Cr, Cu, Hg and Pb presented moderate risk during the water-filling stage. The average risk levels of the metals in the surface sediment were ranked in the order of Cr > Cu > Pb > Hg > Cd > As. It could be concluded that the dam is a contaminant trap where heavy metals accumulate gradually as a result of bydrodynamic changes.%为探讨沂河小埠东橡胶坝对蓄水段表层沉积物中重金属分布和富集的影响,在该河段设置了8个监测站位,分别于枯水期、丰水期、平水期监测了表层沉积物和水体中6种重金属的含量.结果表明:表层沉积物中w(As)、w(Cd)、w(Cr)、w(Cu)、w(Hg)和w(Pb)的平均值分别为6.65、0.40、71.21、42.48、0.15和41.54 mg/kg,而表层水体中重金属质量浓度均符合GB 3838-2002《地表水环境质量标准》Ⅲ类标准；蓄水段沉积物浓缩系数为2.85×103 ～3.04×1O5,并且坝前表层沉积物中重金属含量从上游到下游递增,说明橡胶坝的建成促进了沉积物中重金属的富集；采用沉积物质量基准(SQG)方法评价表明,蓄水段As处于低风险水平,Cd、Cr、Cu、Hg和Pb均处于中等风险水平,其风险水平Cr＞ Cu ＞Pb＞ Hg＞ Cd ＞As.建坝后水动力条件的改变是坝前沉积物中重金属富集的主要原因.