水稻土重金属空间分布的随机模拟和不确定评价

以杭嘉湖平原为样区,利用普通克立格法和序贯高斯模拟方法对土壤Cu的空间分布进行估值和模拟,并利用序贯指示模拟进行不确定性评价.结果表明,样区北部区域土壤Cu含量较高.由普通克里格法得到的土壤Cu的空间分布整体比较连续,具有明显的平滑效应,估值结果数据的分布频率趋于平缓.序贯高斯模拟结果整体分布相对离散,突出了原始数据分布的波动性,其模拟结果数据的分布频率相对集中.以35 mg·kg-1作为土壤Cu含量的阈值进行的序贯指示模拟结果显示,在土壤Cu含量较高的北部地区超过阈值的概率超过80%,而南部很多相对含量低的地区该概率值都低于10%.以超阈值概率为0.85和0.75来选取Cu的高污染风险区进行空间不确定评价结果表明,联合概率比单点统计的概率更为严格,在划分较大范围污染区域时,最好同时采用联合概率来进行信度评价.

Stochastic Simulation of Spatial Distribution and Uncertainty Assessment of Heavy Metal in Paddy Soil

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.