Erosión y desertificación.-How development and disturbance of biological soil crust do affect runoff and erosion in drylands? PDF

Abstract

ABSTRACT Deserts and semiarid ecosystems (shrublands and grasslands) are the largest terrestrial biome, covering more than 40% of the Earth's terrestrial surface and Biological Soil Crusts (BSCs) are the predominant surface type in most of those ecosystems covering up to 70% of its surface. BSCs have been demonstrated to be very vulnerable to disturbance due to human activities and their loss has been implicated as a factor leading to accelerate soil erosion and other forms of land degradation. Incorporation of the response of different type of soil crusts and the effects of their disturbance is likely to improve the prediction of runoff and water erosion models in arid and semi-arid catchments. The aim of this work is to analyse the influence of BSC development and the impact of crust disturbance on infiltration and erosion. Extreme rainfall simulations at microplots scale were performed in two semiarid ecosystems with different lithology and conditions of occurrence of BSCs: El Cautivo and Amoladeras. Moreover, open plots were set in the field to examine the response under natural rainfall, and contributing area was estimated from a 1 centimetre resolution DEM built from laser scan height records. Our results demonstrated that the stage of development of the undisturbed BSCs affects infiltration and erosion with an increase in the infiltration rate and a decrease in erosion as crust development is higher. Crust disturbance affected infiltration and erosion: trampling caused the highest runoff rates and crust removal the highest erosion, nevertheless, the effects of crust disturbance on erosion were lower for Amoladeras, an area with a flat topography and a coarser soil texture. At both sites, under extreme rainfalls, although crust removal enhanced infiltration at the beginning of the rain, the early development of a new physical crust increases runoff until reaching similar runoff rates as undisturbed crusts. The responses of BSCs to extreme simulated rainfall and to natural rains were compared to evaluate when the differences among BSCs in different degree of development are more accentuated in order to identify critical thresholds to incorporate in runoff and erosion models.