Influence of human impacts on Albeluvisol analysed by X-ray microfluorescence: relative evolution of the transforming front at the tongue scale.

In this paper we studied the nature and hierarchy of the processes responsible for soil evolution as a function of land use (forest and culture). Albeluvisols were chosen as a pedological model for this study. Iron, manganese, calcium, potassium and trace elements were used as indicators of the soil processes. Their spatial distribution was mapped along tongues of Albeluvisols at a pluri-centimetric scale, using X-ray microfluorescence. In both land use, Fe distribution was shown to be closely related to the soil colour variation along the tongues. Nickel and Cu followed the same distribution. Zinc was almost functioning as Fe with the difference that this element was not lost from the transition zone identified between the bleached tongues and the ochre volumes representative of the illuvial horizon. Under forest, the Fe and Mn redox fronts were closely associated that allows mapping them on the same thin section. Manganese disappeared from the neighbourhood of the iron redox front under agriculture. This was interpreted as a slow down of the iron redox process due to pH increase while Mn redox process was not modified. In addition, under forest, Ca seems totally leached. Liming causes an increase of Ca concentrations in the whole soil profile. This Ca is in an exchangeable form principally located at the interface between white and ochre volumes. We concluded that by liming, Man induced drastic changes in the kinetic of redox process in Albeluvisols over 200 years showing at the same time the extreme rapidity of these processes.