5·12汶川大地震后涪江绵阳段沉积物重金属污染评价

Evaluation of Heavy Metal Pollution in the Sediments from Mianyang Section of Fu River after the Earthquake in Wenchuan on May 12

为探明5·12特大地震对涪江绵阳段重金属沉积特征的影响,对涪江绵阳段（平武县至三台县,5·12地震带横穿调查江段）沿江9个点位的沉积物重金属含量进行了采样分析。结果显示：沿江各点位Cd、Cr、Zn含量变幅较大,Cd超标2~12倍,具有明显的富集作用。由各元素间相关性分析可知：5种重金属元素来源大致相同,这与涪江绵阳段沉积物主要来源于地震后破碎冲积物有关。总体而言,上游沉积物重金属含量高于下游,佐证了地震后新产生的碎屑沉积物降低了地震带下游河流表层沉积物中重金属含量。涪江支流安昌沉积物对Cr、Cd、Cu、Pb具有明显富集作用,可知工业源也是重金属重要来源。内梅罗指数法和潜在生态风险评价法均表明：平武到青义属于重度污染和中度污染区,绵阳市区到三台属于未污染状态。涪江绵阳段综合评价为中度污染,首要污染因子为Cd。

In this paper, 9 point locations along Mianyang section of Fu River（From Pingwu County to Santai County, the survey section crossed by the earthquake zone） were sampled for analysis of the contents of heavy metals in the sediments to study the impacts of the earthquake in Wenchuan on May 12 on the enrichment of heavy metals in the sediments. The results showed that amplitude of the contents of Cd, Cr and Zn varied greatly, with the content of Cd exceeding the standard limit by 2 ~12 times, indicating that enrichment was obvious. According to the results of correlation analysis, it was deduced that along the river section, 5 heavy metals were originated from the same resource, which was related to the similar geological feature that the sediments were mainly from the broken alluviums after the earthquake. Generally, the spatial distribution showed that the contents of heavy metals were higher in the upper reaches than in the lower reaches, proving that the classic deposits generated after the earthquake reduced the contents of heavy metals in the surface sediments of the downstream. Besides, the distinct enrichment of Cr, Cd, Cu and Pb in the sediments of Anchang River, which was the tributary of Fu River flowing through Mianyang City, indicated that industrial emissions were also key sources of heavy metals. By use of Nemerow index and potential ecological risk evaluation methods, it was showed that the river section from Pingwu to Qingyi was heavily or moderately polluted, but that from Mianyang City to Santai was not polluted. In all, Mianyang section of Fu River was moderately polluted with Cd as the main pollution factor.