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A Comparison of Three Kriging Methods Using Auxiliary Variables in Heavy-Metal Contaminated Soils

Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan, R.O.C.

^* Corresponding author (dylee{at}ccms.ntu.edu.tw).

ABSTRACT

Characterization of the spatial distribution of pollutants in contaminated soils is important for risk assessment and soil reclamation. In this study, three kriging methods using auxiliary variables, cokriging, kriging combined with regression, and kriging combined with Q-mode factor analysis, were used for interpolation of heavy metal concentrations in a contaminated site. The three interpolation methods were evaluated for whether or not they could make better use of an auxiliary variable for estimation of the spatial distribution of heavy metals. A heavy metal contaminated site about 10 ha in area, situated in Taoyuan, Taiwan, was studied. The results demonstrate that better use of the auxiliary variable in interpolations of the target variable was made using kriging combined with regression compared to using cokriging or kriging combined with Q-mode factor analysis. The results also show that the spatial distribution patterns of the target variables estimated using kriging combined with Q-mode factor analysis were more similar to those estimated using kriging combined with regression than were those estimated using cokriging. In addition, kriging combined with regression and kriging combined with Q-mode factor analysis could avoid negative estimates, which occur in cokriging. Moreover, both of them were more robust than cokriging. Simultaneous estimation of spatial distributions of several target variables using an auxiliary variable was demonstrated for the kriging combined with Q-mode factor analysis procedure. However, for only one target variable, kriging combined with regression was simpler and less cumbersome than cokriging.