铅锌矿尾砂重金属污染物对不同土地利用类型土壤性质影响的典范对应分析

广西阳朔思的村铅锌矿尾矿砂坝坍塌造成了大面积农田污染,已往报道多集中在金属矿山开采过程中产生的废液及大量固体废弃物堆砌而造成的环境污染,较少关注因尾矿砂坝坍塌所造成的这种土壤重金属特殊污染模式。本文运用典范对应分析(CCA)研究铅锌矿尾砂坝坍塌对不同土地利用类型(玉米地、柑橘园、水稻田)造成的重金属(铅、锌、铜、镉)污染以及对土壤理化性质(有机碳、碱解氮、速效磷、速效钾、阳离子交换量、碳氮比、pH值)的影响。CCA分析结果表明,研究区污染以铅、锌、镉为主,铜次之,其中锌和镉的空间分布格局受土地利用类型的影响更明显,并且镉对水稻田产生的环境风险最高。此外,在土壤中尾矿砂分布不均的前提下,土地利用类型是造成土壤重金属污染空间分布不同的重要驱动力,受土壤质地和矿砂性质的影响,重金属污染引起的酸化效应在供试土壤中不明显,使得CCA图中pH值所代表的点远离重金属箭头连线;阳离子交换量距重金属连线较近,受重金属影响明显并随重金属污染的加剧而减小;碱解氮、速效磷、速效钾等速效养分受重金属污染的影响并不显著,但与施肥配比和农业管理密切相关;有机碳与重金属箭头连线分布象限相同且包裹于其中,与重金属质量分数呈正相关关系,相较于玉米地和柑橘园,水稻田中有机碳积累量更大,达到18.14 g/kg,可能因稻田中微生物的碳源代谢利用能力明显降低,土壤中有机碳的矿化分解受阻,导致水稻土中有机碳的积累。此外,尾矿砂作为土壤重金属的持续性释放源,尽管对土壤的基本理化性质尤其是速效养分的影响并不明显,但能够通过影响土壤微生物群落间接影响土壤碳循环。

Canonical Correspondence Analysis for Soil Properties and Heavy Metal Pollution from Pb-Zn Mine Tailings in Different Land Use Types

The collapse of the lead-zinc mine tailing dam in Sidi village (Yangshuo, Guangxi Zhuang Autonomous Region, and SW China) led to the spread of mining waste spills on the farmland along the river. Past reports concentrated on environmental pollution caused by metal mining process, and were less focused on the special pattern of heavy metal pollution caused by the dam collapse. Canonical correspondence analysis (CCA)was employed to reveal the relationship between heavy metal contamination and soil properties in different land use types around the polluted area. 12 soil samples from rice paddy fields, 12 from corn fields and 9 from citrus orchards were collected from the surface layer (0-20 cm) to analyze SOC, AN, AP, AK, CEC, C/N, pH, total and DTPA-extractable Pb, Zn, Cu, Cd. The results show that Pb-Zn mine tailing sand is a multi-mineral orebody of which Pb, Zn and Cd are the main pollutants and Cd is the environmental risk key factor controlling the soil quality. The spatial distribution pattern of Pb and Zn affected by land use type is more obvious. Moreover, from the arrow distribution of heavy metals, it can be seen that the heavy metal pollution was relatively more serious in the rice paddy fields than in the corn fields and citrus orchards. From the distance between the heavy metals arrow and the soil properties point, the combined pollution of Pb, Zn, Cu and Cd decreased CEC content and increased SOC concentration, but had only small effects on soil pH value and available nutrients (AN, AP, AK). There existed positive significant correlations between heavy metals and SOC.The SOC content in rice paddy fields was 18.14 g/kg, and had the significant statistical differences with other land use types. In summary, Pb-Zn tailing sands as the sustained release source of heavy metals have the consecutive inputting mechanism into the soil, which inhibited microbial communities' metabolism, resulting in carbon accumulation, and then influenced the carbon cycle in the area.