草原土壤重金属含量空间变异与污染评价——以大庆市及周边地区为例

重金属是危害草原生态健康的主要污染物之一,迄今有关大庆市及周边地区草原土壤重金属含量、空间变异和污染程度的研究鲜见报道。本文通过野外调查采样,应用地统计学,结合经典重金属污染评价方法,分析了大庆市及周边地区草原土壤Cd,Cr,Pb,Cu,Zn,Ni,Hg及As含量的空间变异与污染程度,结果表明:研究区8种重金属含量具有中等空间异质性,变异系数在28.3%~58.5%。8种重金属元素可以用指数模型、高斯模型和球状模型拟合,Cd,Cr,Pb,Cu,Zn,Ni和As的块金值/基台值C₀/(C₀+C)]在25%~75%,其空间变异由结构性变异(母质、地形等)和非结构性因素(人类活动)共同引起,Hg的C₀/(C₀+C)]>75%,即非结构性因素对其的影响大。土壤重金属含量呈斑块状、条带状、点状和环岛状分布特征。研究区8种重金属的超背景值率较高,表现为累积的特征。As和Ni的分别有23.7%和1.7%的采样点重金属含量超过《国家土壤环境质量标准》(GB15618-1995)2级标准限值。地积累指数评价表明,As存在轻度污染风险,其他重金属无单因子污染风险。潜在生态风险评价表明,8种重金属元素均不存在潜在生态风险。大庆市及周边地区草原土壤重金属呈现空间中等强度变异,个别重金属元素存在超标现象,土壤质量整体良好。

Spatial Variability of Steppe Soil Heavy Metal Content and Contamination Assessment: A Case Study of Daqing City and the Surrounding Areas,China

Soil heavy metal pollution is a potential hazardous factor to grassland ecology health. Given this, studies focused on heavy metal content, spatial variability and the degree of contamination in soil of Daqing city and the surrounding areas are fresh. In the study, contents of Cd, Cr, Pb, Cu, Zn, Ni, Hg and As in the steppe soil of Daqing city and the surrounding areas were analyzed after field investigation. The spatial variability of those heavy metal elements mentioned above and their pollution potential in the region were evaluated by using geo-statistics combined with classic heavy metal pollution assessment methods. The results showed that: Heavy metal contents varied in middle level in terms of spatial distribution in the soil with variation coefficients ranged from 28.3% to 58.5%, eight kinds of heavy metal elements could be simulated through exponential model, Gauss model and spherical model. Indexes C₀/(C₀+C) of Cd, Cr, Pb, Cu, Zn, Ni and As were in the range of 25%~75% showing that the contents were determined by structural factors, such as soil parent material, topography and the factors of non-structural , such as human activities, while C₀/(C₀+C) of Hg was more than 75% indicating that they were mainly affected by the factors of non-structural and human activities. The distribution pattern of heavy metal content in the region presented as patchy, banded,point and island modes. Contents of the eight kinds of heavy metal elements in the soil of the region showed a trend of accumulation. However, content of 23.7% and 1.7% sampling points of As and Ni were above the soil threshold levels of the Second Grade criteria of "the Chinese environmental quality standard" (GB 15618-1995). There was the mild pollution risk of As in the soil of the region as showed in the Geo-accumulation index, whereas there was no pollution risk of other tested elements. No potential risk was detected for eight kinds of heavy metals analyzed by the single factor ecological risk index and the total potential ecological risk index. Heavy metal contents of soil in Daqing city and the surrounding areas had the spatial variation of moderate intensity. Though individual heavy metal elements exceeded the soil threshold levels of the Second Grade criteria of "the Chinese environmental quality standard" (GB 15618-1995), overall the soil quality is good.