南方典型矿区农业小流域耕地土壤重金属空间分布特征及污染评价

为了解我国南方典型矿区所在流域的耕地土壤重金属含量空间分布特征及其污染状况，对所选取的小流域内耕地土壤6种重金属(Cd、 As、 Mn、 Cu、 Zn和Pb)的总量进行测定，运用空间插值方法分析典型矿区小流域尺度重金属含量的空间分异特征，并采用地累积污染指数法与潜在生态危害指数法进行了生态风险评价.结果表明，小流域内耕层(0～20 cm)土壤中Pb、 Zn、 Cu、 As和Cd的含量均值分别高出背景值约11.9、3.8、8.2、4.7和14.2倍，样品超过农用地土壤污染风险筛选值的比例分别为24%、56%、75%、44%和48%, Zn和Mn呈现中等变异，Pb、 As、 Cu和Cd则发生了强变异，表明小流域内存在明显的重金属富集现象；空间分析结果显示，耕地土壤6种重金属的空间分布有明显的一致性特征，即在矿业活动区及其下游和小流域西部乡镇街道处存在富集，在流域主河道干流两侧存在部分重金属的高值点，表明研究区内最主要的污染来源是矿冶活动及污染河水灌溉；地累积污染指数法与潜在生态危害评价结果表明，小流域内存在重金属复合污染，尤以Cd污染的程度最高，河流干流两侧耕地生态风险等级最高.

Spatial Distribution Characteristics and Assessment of Heavy Metal Pollution in Cultivated Soil of Agricultural Small Watershed in Typical Mining Area in South China

In order to clarify the spatial distribution characteristics and the present situation of heavy metal pollution in cultivated soil of a typical mining basin in southern China, the contents of Cd, As, Mn, Cu, Zn, and Pb in cultivated soil in the selected small watershed were determined, and the spatial distribution characteristics of heavy metals were analyzed using the spatial interpolation method. Further, the ecological risk was evaluated using the geo-accumulation index and potential ecological risk coefficient (PERC). The results showed that the average contents of Pb, Zn, Cu, As, and Cd in the topsoil (0-20 cm) in the small watershed were approximately 11.9, 3.8, 8.2, 4.7, and 14.2 times that of the background value in Hunan soil, respectively. Compared with the soil risk screening value of agricultural land, the over-standard rates of Pb, Zn, Cu, As, and Cd were approximately 24%, 56%, 75%, 44%, and 48%, respectively. Zn and Mn showed medium variation, whereas Pb, As, Cu, and Cd showed strong variation, which indicated that there was an obvious enrichment of heavy metals in the small watershed. The spatial analysis results showed that there was an obvious consistent characteristic of six heavy metals in the topsoil, that is, there was enrichment in the mining activity area and its downstream and the township streets in the west of the small watershed. Additionally, there were high value points of some heavy metals on both sides of the main river, indicating that the main pollution sources in the study area were mining and metallurgy activities and sewage irrigation. The results of the geo-accumulation index and potential ecological risk index showed that there was compound pollution of heavy metals, in which the degree of Cd pollution was the highest, and the soil of both sides of the river could pose the strongest potential ecological risk.