土壤元素异常成因研究及生态风险评价

山区岩石与水系沉积物,对山前平原土壤物质组成具有控制作用。土壤地球化学调查,查明北京某地区土壤存在着大面积同心圆状的镉、铜、铅等多金属元素异常。研究表明,西北侧山区分布着种类繁多的岩浆岩、变质与沉积岩,但与山前土壤具有高度正相关的元素组合特征的主要是燕山期中酸性岩浆杂岩体,而且杂岩体周边及其下游的BY沟水系沉积物中的多金属元素也呈现出明显的高背景含量特征。同时,铅同位素组成亦指示山前平原土壤铅与山区岩浆岩铅、沉积岩铅具有一致的物质来源,从而证实山前土壤多金属元素异常主要来源于山区岩浆杂岩体。由于山前平原土壤呈现为碱性且农田仅种植旱地作物,故富含多金属的土壤对农作物生长的生态风险程度低下。

The Element Abnormal Genetic Research of soil and Its Ecological Risk Assessment

Soil materials in piedmont plain are controlled by rocks and stream sediments in mountain areas. Soil geochemical survey shows that there are wide ranges of concentric circle of multi metal element abnormality such as Cd, Cu, Pb and so on in a region of Beijing, where the magmatic rocks, sedimentary rocks and metamorphic rocks are wide distributed. Of them, the Yanshanian intermediate acidic magmatic complexes’ elements are high positively correlated with piedmont plain soil. There are high content characteristics of multi-elements obviously in stream sediments of the magmatic complexes and its downstream sediments of Baiyang valley. Lead isotope composition supports that lead in soil has consistent source of material with lead in mountain magmatic and sedimentary rocks. So it is proved that the multi metal element abnormalities in piedmont plain are mainly derived from magmatic complexes. Because of the alkaline soil and cultivated land crops, the ecological risk of multi-metal elements soil in piedmont plain to the growth of crops is low.