Impacts of irrigation systems on vertical and lateral metals distribution in soils irrigated with treated wastewater: Case study of Elhajeb-Sfax

Abstract

Treated wastewater irrigation, usually, leads to the increase of metals contents in soils and affects their mobilities and distributions. The aim of this study is to evaluate the effects of treated wastewater irrigation systems on the vertical and lateral distribution of metals in soils. Two irrigated sites with treated wastewater were chosen. The first is composed of a calcisol soil type, irrigated since 17 years with a furrow irrigation system. The second one, fluvisol, irrigated since 4 years with a bowl irrigation system. In both sites, a vertical soil sampling is made as a pedological profile in the irrigated soil and the non irrigated one (control). Moreover, in the calcisol, another lateral soil sampling is carried out in the same direction of irrigation water flux. All the soils samples were characterised by their major and metal contents as well as some soils physicochemical properties. To evaluate the vertical distribution of metals in soils, two parameters are calculated: the logRatio and the isovolumetric mass balance as qualitative and quantitative tools respectively.In the irrigated calcisol, the logRatio shows a slight enrichment of metals in the upper soil layer mainly for Cr. The isovolumetric mass balance confirms this trend for Cr but, in contrast, the stocks of Zn and Cu in the soil have decreased. The logRatio for the fluvisol reveals an accumulation of all the metals in a new created horizon at 90 cm of the depth. Quantitatively, the stocks of Cr, Zn and Cu, in this soil, have increased. However, in the case of calcisol, the furrow irrigation system favors the lateral distribution of metals rather than the vertical variability.