Testing the robustness, to changes in process, of a scaling relationship between soil grading and geomorphology using a pedogenesis model

Using the mARM1D pedogenesis model (which simulated armouring and weathering processes on a hillslope) previous work by Cohen found a strong log-log linear relationship between the size distribution of the soil (e.g. d50), the contributing area and the local slope. However, Cohen performed his simulations using only one set of grading data, one climate, one geology and did his simulations over a relatively limited range of area and slope combinations. A model based on mARM, called SSSPAM, that generalises the modelled processes has been developed, and calibrated to mARM. This calibration was used as the starting point for a parametric study of the robustness to changes in environmental conditions and weathering conditions of the area-slope and d50 relationship, different initial soil gradings and weathering conditions, different geology, and a broader range of area and slope combinations. This parametric study assessed the influence of changes in the model parameters on the soil evolution results. These simulations confirmed the robustness of the area-slope and d50 relationship discovered by Cohen using mARM. We also demonstrated that the area-slope-diameter relationship is not only true for d50 but for the entire grading range (e.g. d10, d90). The results strengthen our confidence in the generality of the log-log linear scaling relationship between area, slope and soil grading. The paper will present the results of our parametric study and will highlight the potential uses of the relationship for digital soil mapping and better characterization of soils in environmental models.