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This article in JEQ

  1. Vol. 30 No. 3, p. 894-903
     
    Received: Mar 6, 2000


    * Corresponding author(s): dylee@ccms.ntu.edu.tw
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doi:10.2134/jeq2001.303894x

Using Rank-Order Geostatistics for Spatial Interpolation of Highly Skewed Data in a Heavy-Metal Contaminated Site

  1. Kai-Wei Juanga,
  2. Dar-Yuan Lee *a and
  3. Timothy R. Ellsworthb
  1. a Graduate Institute of Agricultural Chemistry, National Taiwan Univ., Taipei, 106 Taiwan
    b Dep. of Natural Resources and Environmental Sciences, Univ. of Illinois, Urbana–Champaign, IL 61801

Abstract

The spatial distribution of a pollutant in contaminated soils is usually highly skewed. As a result, the sample variogram often differs considerably from its regional counterpart and the geostatistical interpolation is hindered. In this study, rank-order geostatistics with standardized rank transformation was used for the spatial interpolation of pollutants with a highly skewed distribution in contaminated soils when commonly used nonlinear methods, such as logarithmic and normal-scored transformations, are not suitable. A real data set of soil Cd concentrations with great variation and high skewness in a contaminated site of Taiwan was used for illustration. The spatial dependence of ranks transformed from Cd concentrations was identified and kriging estimation was readily performed in the standardized-rank space. The estimated standardized rank was back-transformed into the concentration space using the middle point model within a standardized-rank interval of the empirical distribution function (EDF). The spatial distribution of Cd concentrations was then obtained. The probability of Cd concentration being higher than a given cutoff value also can be estimated by using the estimated distribution of standardized ranks. The contour maps of Cd concentrations and the probabilities of Cd concentrations being higher than the cutoff value can be simultaneously used for delineation of hazardous areas of contaminated soils.

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Copyright © 2001. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.30:894–903.