Geostatistical Analyses of the Spatial Variation of Soil Cadmium in Rice Producing Area in the Luxian County, China

In recent years, much attention has been paid to the problem of farmland soil contamination by heavy metals in China. Cadmium (Cd) is an important heavy metal which can cause adverse ecological effects, in particular, can be easily accumulated by rice plants. On the basis of determining the concentrations of Cd in 303 farmland soil samples from the rice producing area in the Luxian County, Sichuan Province, China, the spatial variability and distribution character of the relevant data were further analyzed using geostatistical methods. The results of the exploratory spatial data analysis showed that there was the autocorrelation of soil Cd and the experimental semivariogram was isotropic. The spherical model and the exponential model were used to match the experimental semivariogram. The results of the cross-validation showed that the exponential model with sill could best simulate the experimental semivariogram. Ordinary kriging were used to estimate the Cd distribution in the study area. The significant correlation between the estimated values and the monitoring values was found. No system errors could be tested. The areas with high soil Cd presented the strip belt-shaped. At the same time, the high soil Cd concentration patches and the low soil Cd concentration patches show relative decentralization distribution character. This distribution character testified that non-point pollution and atmospheric precipitation were the main sources of soil Cd contamination in the study area. In addition, the spatial distribution character was also affected by wasterwater irrigation from polluted rivers in the study area.