Image-analytically derived conceptual model of Albeluvisol morphological degradation induced by artificial drainage in France
Résumé
Soils are a non-renewable resource and evolve through time in response to changes in land-use and environmental conditions. To predict this soil evolution requires the development of mechanistic modelling. Only a few attempts of this kind exist in the literature, and these often use an extremely simplified representation of soil structure, with the soil being frequently considered as a succession of homogeneous "boxes". In this paper we have quantified the evolution of the soil structure during pedogenesis using image analysis. This analysis was performed along a sequence of morphological degradation in an Albeluvisol perpendicular to a drain. These soils, which are commonplace in Europe, are characterised by horizons consisting in a juxtaposition of soil volumes differing in texture (silty to clayey) and colour (ochre, pale-brown, white-grey and black). The image analysis approach was based on these differences in colour and combined i) a supervised training method using ERDAS IMAGINE® to assign the different pixels to the different types of soil volumes and ii) ARCInfo™ for characterisation of the morphology of the different soil volumes. The organisation of the different volumes in space suggests that ochre volume is transformed to pale-brown one and then to grey-white one, whilst black volume is formed within the residual ochre one, due to precipitation of Mn. As the process progresses along the drainage sequence, progressive indentation and final disintegration of the ochre volume are responsible for the release of the black volume into the pale-brown matrix. Ochre volume alteration takes place mainly at the border of the volume which is indicated by the geometry of the pale-brown and ochre volumes. Finally, the formation of the white-grey volume from the pale-brown one occurs in the core of the latter, mainly by eluviation, and is centripetal. We conclude that soil structure needs to be considered when modelling pedogenetic soil evolution.[br/] Highlights ► Drainage significantly modifies the soil structure on a tenths of years time scale. ► Surface and connectivity of soil volumes are key parameters for soil processes. ► Connection of soil volume previously disconnected is a threshold in soil evolution. ► Soil structure evolution is crucial for the expression of soil processes.