The modelling of soil-process functional units based on three-dimensional soil horizon cartography, with an example of denitrification in a riparian zone

This article aims to propose an approach for estimating the three-dimensional (3D) variability of denitrification. The concept of functional horizons is applied to the process of biological denitrification and 3D soil horizon cartography is used to estimate its spatial variation. On one hand, detailed fieldwork (186 pedological auger holes) was undertaken to map 3D horizon distribution within a 3-ha riparian area using Geographical Information Systems (GIS). On the other hand, three classes of denitrifying capacities were defined according to the distribution of the denitrifying enzyme activity of 51 samples. The relationship between the process of denitrification and the cartography is assessed through soil characteristics, which both differentiate soil horizons and control the process of denitrification: organic carbon and textural fractions. This allows a class of denitrifying capacity to be attributed to each soil horizon. This information was inserted into the 3D soil horizon cartography and the denitrifying functional horizons could be delimited. With this approach, field criteria are used and variations of the 3D distribution of denitrification are considered in order to estimate the spatial variation of denitrification within the riparian area being studied.