东北平原区地块尺度土地质量地球化学评价合理采样密度研究

选择吉林省公主岭市大岭地区作为东北平原区典型代表区域开展土壤元素空间变异性、经典统计学合理取样数及不同采用密度数据空间插值对比研究.结果表明:①受地形平坦及成土母质相对单一等因素影响,研究区土壤元素空间变异性总体较小,大部分以轻中度变异为主(变异系数<15%),受人为因素影响较大的Cd、Hg变异系数分别为35.3%、136.6%,属于高度变异.②经典统计学确定的研究区合理采样数为80,该样本量可在95%的置信区间及允许误差为30%的条件下反应区内土壤元素含量的均值与方差,但因未考虑样本的空间属性,不足以反应区内土壤元素空间变异特征,具有一定的局限性.③通过对均匀抽稀后4种不同采样密度数据与实测数据空间插值对比研究,在定量评估空间插值相对误差、地块预测值相对误差及预测等级与实测等级一致性的基础上,结合土地质量地球化学调查工作精度要求,提出研究区地块尺度地球化学评价工作合理采样密度为8个点/km2,该密度可在确保评价精度的前提下,大幅减少采样数量和工作成本.上述结论为东北平原及类似地区大面积开展地块尺度土地质量地球化学评价工作提供了关键的技术支撑,对进一步完善土地质量地球化学评价方法技术具有重要意义.

Reasonable sampling density for land parcel scale geochemical assessment on land quality in Northeast China Plain

In order to identify the reasonable sampling density for land parcel scale geochemical assessment on land quality in Northeast China Plain,the authors studied spatial variability of elements in soils as well as reasonable sampling size based on classic statistics and conducted a thorough comparison of interpolation accuracies at four sampling densities in a typical area in Gongzhuling City of Jilin Province. As the area is dominated by flat land and the soils parent materials are mainly homogeneous sediments,most of elements in soils in this area display a minor to moderate variability,Cd and Hg which are sensitive to human activities have a significant higher coefficient of variation of 35.3% and 136.6%,respectively. Classic statistics show that sampling size of 80 is sufficient for providing a reliable estimation of mean and variance for the elements concentration in soils in this area( under a P value of 95% and Ertolerance level of 30%);however,classical statistics could not make out the spatial allocation of soil properties at the unsampled locations. By comparing the relative error of spatial interpolation,the predicted value for land parcel and the predicted classes at four sampling densities,the authors suggest that the reasonable sampling density is 8 samples per square kilometer for land parcel scale geochemical assessment on land quality in the study area and similar areas in the Northeast China Plain,considering the tolerance level of Er( relative error) for the geochemical assessment on land quality. The results obtained by the authors may help optimize soil sampling density in land parcel scale geochemical assessment.