Extractable trace metals in soils of Siwa oasis as related to soil variables and productivity

Abstract EN

Nine soil profiles were chosen to represent the pedological and productivity variations along Siwa Oasis, from which 27 soil samples were collected from the subsequent depths.

The relevant morphological, physical and chemical characteristics of soils were presented.

Nine trace metals (Fe, Mn, Zn, Co, Ni, Sr, and Cd) were chemically extracted using DTPA.

The results indicate that the amounts of chemically extractable Fe, Mn, Zn and Co are relatively higher in the medium-textured soils while the contents of the other studied trace metals are more pronounced in the coarse- texturedsoils.

Except for chemically extractable Fe, the highest contents of trace metals characterize the poorly productive soils.

In all cases, Cd is below the detection level.

Depthwise distribution of extractable trace metals does not portray any specific pattern pertaining to locality, soil variations, productivity level and specify of metal except in few cases.

Computation of the weighted means of the studied trace metals reveals that the medium-textured soils attain relatively higher weighted means of Fe, Mn, Cu, Zn and Co while the reverse is true for Ni, Pb and Sr.

This could be explained on basis of soil genesis, formation, intermixing of multi-parent materials and multi depositional regimes of the studied soils.

Moreover, weighted means of trace metals are generally higher in the moderately and poorly productive soils with few exceptions.

Nevertheless, none of the studied trace metals approached the maximum acceptable concentrations for environmental pollution.

To figure out the relationship between chemically extractable heavy metals and soil variables, statistical analyses were performed.

These analyses reveal that Fe, Zn, Co, and Pb are negatively correlated with soil PH while Fe, Zn, Pb and Sr are positively correlated with HCO3 Cobalt is positively correlated with Fe while being negatively correlated with Mg.

Nickel is the only heavy metal that has a highly significant positive correlation with CaCO3 (Fig.

15).

Strontium exhibits positive correlations with soil salinity and its individual components except for HCO3-. Moreover, Mn and Co are highly significant positively correlated with silt and clay while Zn and Pb are positively correlated with sand.