Saturday, 15 July 2006
136-10

Hydrological and Geomorphological Implications of Different Types of Soil Surface Crusts in Semiarid Rangelands in Se Spain.

Albert Sole-Benet1, Yolanda Cantón2, Gabriel DelBarrio1, Roberto Lázaro1, and Juan Puigdefábregas1. (1) E.E.Z.A./C.S.I.C., General Segura, 1, Almeria, Spain, (2) Universidad de Almeria, La Cañada de San Urbano, Almeria, Spain

Rangelands are widespread in SE Spain due to the scarcity of precipitation. Quite recent subsidies to reforest rangelands and abandoned agricultural fields essentially consider soil depth as viability criteria, omitting soil surface characteristics as crucial indicators of soil quality. It is known that rock fragment cover and surface crusting play an essential role in the hydropedological properties of dryland soils. In this communication it is shown how different types of surface crusts from rangelands in SE Spain contribute significantly to explain the hydropedological behavior of their soils and how we can derive recommendations for their sustainable management. Soil properties including particle size, bulk density, aggregate stability, infiltration rate, water repellency, pH, organic matter content, CaCO3, EC, and SAR, were statistically processed with topographic attributes derived from digital elevation models and with soil surface characteristics including roughness and rock fragment cover and type of surface crust (several types of structural crusts including sieving crusts, erosion crusts, depositional crusts, and several types of biological crusts), as well as soil moisture evolution below these crust types. Significant relationships were found between soil texture and structure, terrain attributes (slope gradient and aspect, contributing area etc) and the types of soil crust. It may be observed that the different types of studied soil crust occupy different parts of the distribution range of each topographic variable. Moreover, the occurrence conditions of a particular type of structural crust, the “coarse pavement sieving crust”, widespread in the Betic ranges (southern Spain), has been determined. This type of crust is mostly found in abandoned fields and its morphology changes along the slope, under bare soil and under perennial plants and also according to the age of perennial plants. Some types of biological crusts and the coarse pavement sieving crust behave as mulches as they preserve soil moisture longer than other ground cover types and also reduce erosion, however they might reduce infiltration, increasing runoff. The effect of this additional runoff has to be evaluated at catchment scale to assess the combined impact of these effects, and the potential for water harvesting from crusted areas to feed adjacent vegetated areas. A rainfall-runoff spatially distributed model based in the hydropedological behaviour of these surface crusts at plot scale, is used to predict runoff patterns across small catchments on contrasted lithology. The results show the influence of the spatial distribution of ground cover types, including the different surface crusts, on the overall runoff, all of which is of great importance for the sustainable management of these rangelands.

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