污染水稻田中土壤含砷量的空间变异特征

Spatial distributions of arsenic in contaminated paddy soils

利用地统计学方法研究在长期淹水和频繁干湿交替影响下污染水稻田中砷的小尺度空间分布特征。采用变异函数定量描述含砷量分布特征 ,用克立格插值法对表层土壤未测点的含砷量进行最优估计 ,并绘制含砷量等值线分布图。结果表明 ,来自表面污染源的砷进入农田土壤后主要积累在耕层 0～ 2 0cm中 ,对 4 0～ 80cm土壤影响不大。耕层土壤含砷量半方差值呈有规律持续增加趋势 ,可用直线方程很好地拟合。表层土壤含砷量存在很好的空间结构性 ,高砷区出现在进水口附近 ,并以其为中心呈斑块状向周围扩散 。

Spatial distribution characteristics of arsenic in the As contaminated paddy soils which were long term submerged with frequent dry/wet alternations at small scales were studied using geostatistics method The spatial distribution features were quantitatively described by variogram Based on the variograms, Kriging interpolation was performed, and the distribution maps were produced The result showed that arsenic from polluted source mainly accumulated in 0 20cm of soil profile, and arsenic concentrations in 0 20 cm layer were always higher than those in 20 40cm layer The arsenic concentration in 80 100 cm had an increasing trend comparing to that in 60 80 cm However, arsenic concentrations at depth of 40 80cm were not greatly influenced Average arsenic concentration in heavy contaminated paddy soils was 97 1 mg/kg, while that in low contaminated paddy soil was 36 4 mg/kg Soil arsenic concentration decreased with the increase of distance between As source and paddy soil The variograms of arsenic in the surface soil persistently increased and could be fitted by linear equation. Arsenic in soil layer of 0 20cm had good spatial structures Heavy As contaminated sites were found at the water entrances that were centered around the entrances This indicated the soils were secondly polluted by both irrigating water and surface water with elevated levels of arsenic The results also suggested that geostatistics could be applied to evaluate the status of arsenic contaminated soils, which is a necessary precondition for carrying out remediation