"Etude de la distribution des métaux lourds dans les ripisylves de l’oued Rhumel."

Abstract

"Wadi Kebir-Rhumel, surrounded by a more or less degraded riparian forest and interspersed with wide pieces of completely denuded land, is bordered throughout by a main road probably to be contaminated by heavy metals, particularly lead (Pb), zinc (Zn) and cadmium (Cd). The present study has for objectives to determine the role of tamarisk grove in the soil contamination by heavy metals. For this purpose, ten sites were selected along the Wadi Kebir-Rhumel so as to have a side by side plot with vegetation and bare plot. In each plot, soil samples were collected in a central band and, on either side of it, on the side of the road and the edge of the wadi. Tamarisk leaves have been a sampling means. The concentrations of Pb, Cd and Zn were determined by ICP-OES in the washed, unwashed leaves and soils. These, have also been the determination of the organic matter, pH, electrical conductivity, the total limestone (CaCO3), cation exchange capacity and the particle size. The results show significant differences between the washed and unwashed leaves of tamarisk from the viewpoint of the contents of Pb, Zn and Cd, suggesting an atmospheric origin of their contamination by heavy metals. The determination of the correlation coefficients shows, for soils with vegetated plots, that the retention of Pb was by the organic matter and clay, that of Zn by clay and Cd by pH and manganese. In bare plots, retention Pb and Cd is governed by pH, CEC and silt, whereas Zn is by iron and manganese. The analysis of variance revealed the contents of Pb, Zn, Cd, organic matter and clay for the plots under vegetation, particularly in the middle of the tamarisk, significantly greater than in the bare plots. It comes out from this study that the efficiency of tamarisk grove in the retention of metallic trace elements is the results of an important accumulation of Pb and Zn following the retention of great quantities of clay and organic matter."