长江流域沿江镉异常源追踪与定量评估的方法技术研究:以长江流域安徽段为例

A methodology of tracking sources of cadmium anomalies and their quantitative estimation in the Yangtze River basin.

长江全流域性的Cd异常是被中国正在进行的多目标地球化学调查发现的重大生态环境问题。以长江流域安徽段为研究对象,对沿江镉异常源追踪与定量评估的方法技术进行了系统研究。通过对安徽段长江干流及其主要支流悬浮物中元素含量的测量查明:悬浮物是流域内重金属元素大跨度迁移的主要载体;Cd在悬浮物中的富集程度远远大于其他重金属元素,这或许正是Cd可以形成沿江流域性异常的主要原因;长江干流悬浮物中重金属元素含量的变化明显受到沿江支流的影响。安徽段长江干流及其主要支流重金属元素输出通量定量计算结果表明:秋蒲河是安徽段重金属元素输出通量最大的支流,每年在安徽段长江两岸土壤中沉积下约4.45t的Cd。利用悬浮物加密测量、1∶5万土壤测量和岩石测量对顺安河流域Cd异常源追踪结果显示:内生金属矿床特别是铅锌矿是悬浮物中Cd的最大的供应源。采用河漫滩沉积物分层采样技术和同位素测年技术,初步恢复了研究区Cd等重金属元素沉积和污染的地球化学历史,对研究区Cd等重金属元素异常的未来演变趋势进行了预警预测。

The cadmium anomalies are spreading along almost the whole Yangtze River basin. This is the major ecological environmental issue discovered by the Multi-purpose Geochemical Investigation that is being carried out in China. By taking the Anhui section of the Yangtze River basin as its object, a systematical study on methodology of the source tracking and quantitative estimation of the Cd anomalies has been made in the pa- per. By determining contents of elements in suspended matters in the Anhui section of the trunk stream and main tributaries of the Yangtze River, it is shown that the suspended matters are the main carriers of heavy metals for long distance migrations; the concentration of Cd in the suspended matters is much higher than those of other heavy metals, this may be the main reason for forming the Cd anomalies spreading along the whole Yangtze River basin; and the tributaries of the Yangtze River have significant influences on the variations of heavy metal contents in the suspended matters in its trunk stream. The quantitative computation of output flow of heavy metals for the trunk stream and main tributaries for the Anhui section of the Yangtze River shows that the largest output flow of heavy metals is from the Qiupu River, with roughly 4.45 t of Cd deposited in soils along either bank of the Anhui section of the Yangtze River. Results of source tracking of Cd anomalies along the Shun＇an River by detailed survey of suspended matters, soil survey on a scale of 1 ： 50 000 and rock survey indicate that endogenetic mineral deposits, especially Pb-Zn deposits, are the largest suppliers of Cd in the suspended matters. With techniques of layer sampling of sediments on alluvial beds and isotopic agedetermination, we have primarily reconstructed the geochemical history of sedimentation of Cd and other heavy metals and of their pollutions, and have made the prediction and early warning of evolution of anomalies of Cd and other heavy metals.