Modelling the effect of catena position and hydrology on soil chemical weathering

Abstract. The sensitivity of chemical weathering to climatic and erosional forcing is well established at regional scales. However, soil formation is known to vary strongly along catenas where topography, hydrology, and vegetation cause differences in soil properties and possibly chemical weathering. This study applies the SoilGen model to evaluate the link between topographic position and hydrology with the chemical weathering of soil profiles on a north-south catena in southern Spain. Pedogenesis was measured and simulated in seven selected locations over a 20000-year period. A good correspondence between simulated and measured chemical depletion fraction (CDF) was obtained (R2 = 0.47). An important variation in CDF values along the catena was observed, although the position along the catena alone, nor by the slope gradient, explained this variation well. However, the hydrological variables explained the observed trends better. A positive trend between CDF data and soil moisture and infiltration and a negative trend with water residence time was found. The model sensitivity was evaluated with a large precipitation gradient (200–1200 mm yr−1). While a marked depth gradient was obtained for CDF with precipitation up to 800 mm yr−1, a uniform depth distribution was obtained with precipitation above 800 mm yr−1. The basic pattern for the response of chemical weathering to precipitation is a unimodal curve, with a maximum around a mean annual precipitation value of 800 mm yr−1. Interestingly, this corroborates similar findings on the relation of other soil properties to precipitation and should be explored in further research.