SHORT AND LONG TERM EFFECTS OF BIOTURBATION ON SOIL EROSION AND SOIL DEVELOPMENT IN AN ARID ENVIRONMENT

Short and long term effects of faunal activity on soil erosion and soil development had been largely overlooked by geomorphologists; especially in arid areas. A study of hillslopes runoff and erosion processes in the Negev desert indicated systematic differences in sediment concentrations and erosion rates between rocky and colluvial surfaces. Erosion rates were always higher on the former than on the latter. Field observations drew attention to an intense burrowing and digging activity conducted mainly by Isopods and Porcupines. The monitoring of this activity, based on a grid system, which consists of rows, 5 m wide, lasted ten years. Data obtained suggest a strong link between the spatial pattern of bioturbation and that of soil erosion. The study also examines, through feedback processes, the regulatory role of bioturbation on soil moisture and soil forming processes. Due to bioturbation two distinct environments were recognized. The upper, rocky, hillslope areas are characterized by a positive feedback. High runoff and erosion rates remove salt from the soil, preventing salt accumulation. At the same time the colluvial slope sections absorb, at most rainstorms, all runoff generated over the upper rocky slope sections leading over time to soil salinization.