城市绿地土壤质量监测样点二阶前向抽样优化方法——以上海市为例

The second-order forward selection sampling optimization method for monitoring soil quality of urban green space:A case study of Shanghai City

在设计城市绿地土壤监测体系时,如何在已有的监测点位上使用易操作、低成本且兼顾代表性的优化方法是亟待解决的技术难题。本研究以上海市绿地土壤质量监测优化为目标,提出一套针对二阶前向抽样布局优化的技术工作框架。在运用三明治空间模型、Kriging插值方法评估现有点位精度的基础上,针对土壤指标空间相关性和分异性特征,使用空间模拟退火算法在已有点位上增加监测点位进行监测布点系统优化,并使最终方案满足空间分层抽样对采样点数量的最低要求。结果表明:针对上海市绿地土壤的营养元素和重金属元素,现有监测样点采样方差基本低于均值的10%,但在浦东新区、静安、虹口和徐汇区的部分元素代表性需要进一步优化。全市新增350个点可改进精度的64.5%。本研究提出的多目标协同改善的城市绿地土壤监测点位优化布局方法能兼顾精度和成本,有效协助城市管理者合理布设城市绿地监测体系。

In the processes of designing urban green land soil monitoring system,there is a technical problem with respect to optimize the existing monitoring sites through an easy-to-operate,low-cost and representative optimization method which considers multiple soil quality indices.Aiming at the optimization of soil quality monitoring of urban green space in Shanghai,we proposed a technical framework for the optimization of the second-order forward sampling.The Sandwich spatial sampling model and Kriging interpolation method were used to evaluate the accuracy of existing point positions.Spatial simulated annealing was used to add extra points on the existing sampling system,considering the spatial characteristics of spatial autocorrelation and heterogeneity of various soil indicators.Then,the final scheme was used to test whether the optimal design number could meet the minimum number requirement of the stratified sampling method.The results showed that the sampling variance of the existing monitoring sites was lower than 10%of the mean values of nutrients and heavy metals concentrations in Shanghai green space soils.However,the representativeness of certain elements in Pudong,Jing’an,Hongkou and Xuhui Districts needed to be improved.The mean Kriging variance could be reduced by 64.5%by adding 350 monitoring sites.This multi-objective optimization method balances the equity between the accuracy and the cost,and helps city managers to build a reasonable monitoring program for urban green space.