Stochastic Simulation of Spatial Distribution and Uncertainty Assessment of Heavy Metal in Paddy Soil
水稻土重金属空间分布的随机模拟和不确定评价

Ordinary kriging and sequential Gaussian simulation (SGS) were used to estimate and simulate spatial distribution of heavy metal Cu in paddy soil in Hang-Jiang-Hu plain, and sequential indicator simulation (SIS) was used to assess the probability of Cu content exceeding the predefined threshold. The results indicated that north region in the study area has high Cu content. The spatial distribution of Cu obtained by ordinary kriging was continuous and smooth, whereas that obtained by the SGS was relatively discrete and fluctuant. The results of the SIS indicated that the conditional probability of Cu content exceeding the threshold of 35 mg/kg was greater than 80% in the north area, whereas in south area the probability of Cu content exceeding 35 mg/kg was less than 10%. Based on the joint probability statistics, the spatial uncertainty (multi-points uncertainty) obtained from the SIS was used to assess the reliability of delineation for regions suspected of contamination. The result showed that assessment of spatial uncertainty are more strict than that of single-point uncertainty. Therefore, it is more acceptable and convinced that these two approaches of uncertainty assessment were used simultaneously for delineating the contaminated area.