SPATIAL DEPENDENCE OF GEOCHEMICAL ELEMENTS IN A SEMIARID AGRICULTURAL FIELD .2. GEOSTATISTICAL PROPERTIES

Experimental variograms may be used to infer the spatial structure of geochemical elements. This information is needed to control the transport of toxic elements through the unsaturated zone. Geostatistical properties of total soil contents for 20 major and trace element were investigated for a soil in northern Tunisia. The analysis showed that all elements have a clear spatial structure. Several elements displayed a significant trend that was removed by fitting the raw data to a second-order polynomial. Variograms for the residuals showed that most elements reach sills at ranges of approximate to 10 to 20 m. Exceptions are Co with a range of approximate to 1 m and Zn with a range of approximate to 5 m. The elements Be and Sr have larger ranges of approximate to 30 m. Calculation of direction-dependent variograms showed that most elements depended; on direction. Autocorrelation analysis of the residuals indicated no spatial correlation. The ranges found in this study cad be;sed in sampling strategies to obtain independent values of geochemical elements.