Influences of micro-relief patterns and plant cover on runoff related processes in badlands from Tabernas (SE Spain)

Soil surface morphology, soil thickness and their evolution strongly affect infiltration processes. Badland surfaces are characterised by a substantially low plant cover and a reduced soil development controlled by high erosion rates. In the badlands of Tabernas (Almeri´a, SE Spain), the soil surface morphology exhibits a marked spatial variability, caused by different processes under moisture and temperature alternations in different slope aspects. Previous studies on the area have revealed. the different hydrologic behaviour of North- and South-facing surfaces. In this paper, we go into more detail trying to establish the influences of both micro-relief patterns and plant cover on the hydrological behaviour of sixteen representative soil surfaces from the badlands of Tabernas. Rain simulations at a constant intensity of 55 mm/h have been carried out on 16 circular plots of 0.24 m2, during 30 min, to evaluate runoff, infiltration, and sediment production parameters. Surface morphology has been evaluated by image analysis of photographs, before and after the simulations the following parameters have been considered: plant cover and type, length and width of cracks, and stoniness. Surface roughness was determined with a laser profile meter. Runoff and erosion responses have been gathered in three and four groups, respectively, which are related to differences in slope gradient, soil depth and surface morphology. Runoff is positively correlated with slope gradient and negatively correlated with plant cover and total cover. Erosion is negatively correlated with lichen cover, with non-cryptogamic plant cover, with total cover and with surface area occupied by cracks. In some aspects, Tabernas badlands have an hydrological behaviour similar to other badlands described elsewhere (i.e., shallow moisture penetration, short times to runoff, different responses in runoff). However, they are particular in the following: (a) apparent morphological stability after rainfall events of high magnitude and intensity, along with high sediment production associated either from micro-rills that follow open cracks in the regolith, or from overland flow on bare, crusted, silty surfaces; (b) runoff enhancement by surface roughness through the channelling effect of the sealed depressions among pedestals and mounds of crustose lichens.