两种取样尺度下土壤重金属空间变异特征研究

Determination of the characteristics of soil heavy metal spatial variability with two soil sampling scales

通过在两种取样尺度下采集重庆地区土壤样品，测定土壤重金属As、Hg、CA、Pb、Cr含量，研究不同取样尺度下地统计学方法对土壤重金属空间分析的实用性和空间插值质量。研究结果表明，除小尺度中As、CA、Cr呈正态分布，小尺度中的Pb、Hg和大尺度中As、Hg、CA、Pb、Cr均呈偏态分布。各重金属变异系数存在明显空间变异（CV介于23．2％～24．1％），小尺度下空间变异较小，大尺度下空I＂1变异大。在两种取样尺度下，土壤重金属均存在典型的半方差结构，表明采用地统计学方法进行重金属空间变异分析是可行的。在小尺度下，各重金属块金系数介于0．112～0．736之间，表明具有强或中等空间自相关；在大尺度下，块金系数介于0．301～0．570之间，表明具有中等空间自相关。空间插值和交互检验结果表明，As、Cr、Hg、CA在小尺度下的空间估测结果能准确地反映变量的空间变异，在大尺度下估值有偏差，Pb在两种尺度下的估测结果均有偏差。

Soil samples were collected with two sampling scales in Chongqing and their As, Hg, Cd, Pb and Cr levels measured to study the feasibility and adaptability of geostatistics in analyzing soil spatial variability of heavy metals. Results indie.ate that As, Cd and Cr on the small scales show normal symmetrical distribution, but Pb, Hg on the small scales and As, H.g, Cd,Pb and Cr on the large scales show skewed distribution. The CV of different heavy metals are between 23.2 % 24.1%, showing a significant spatial variability. High spatial variability exists under large scales, while low spatial variability occurs under small scales. Typical semivarigram structure observation of samples on the two scales show that the geostatistical analytical method can correctly analyze soil heavy metal spatial variability, regardless of the size of the sampiing scale. On small scales, heavy metal has strong spatial or medium auto-correlation with nugget values between 0.112～0.736. On large scales,heavy metal has medium auto-correlation with nugget values between 0.301 ～ 0.570. Spatial interpolations and cross validations show that the spatial forecast results of As, Cr, Hg and Cd on small scales precisely reflect their spatial variability;and on large scales, the estimated results somewhat warp. The estimated result for Pb deviates on all scales.