Saturday, 15 July 2006
136-1

Sieving Crusts and Water Repellency.

Albert Sole-Benet1, Sergio Contreras1, Juan Puigdefábregas1, and Yolanda Cantón2. (1) E.E.Z.A./C.S.I.C., General Segura, 1, Almeria, Spain, (2) Universidad de Almería, La Cañada de San Urbano, Almería

Soils from abandoned fields over mica schist colluvia in Almería (SE Spain), have developed layers of sorted particles below a surface stony pavement. The soil micromorphology of the surface 5 cm shows a progressively downward finer washed-out layer (from gravel to coarse sand) under layered by a very fine sandy washed-in layer, compacted, crusted-like, only crossed by the roots of sparse bushes, shrubs and eventually annual plants. Such layers are interpreted as a sieving crust, though its hydrological behavior differs to what previous literature reports. Both the macroporosity (evaluated by image-analysis of polished impregnated blocks) and water repellency of the sieving crust (evaluated by the Water Drop Penetration Time, WDPT), provide key elements to explain the hydropedological behaviour of these soils specially in the first stages of a rainfall event. As only the washed-in layer of the sieving crust shows hydrophobicity (WDPT = 6 to 30 s), some elements of discussion are provided to consider water repellency as a key element in the formation and further evolution of sieving crusts in such environment. Once the subsurface fine-particle layer of the sieving crust outcrops, giving an erosion crust, due to the removal by erosion of the upper layers, the hydrological behavior changes, with consequences for the further soil evolution. Moreover, the spatial variability of these layers regarding both morphology and physical properties, which change along the hillslope, under bare soil and under perennial plants, and also with the age of land abandonment, provide key elements for the understanding of the hydropedological behaviour at hillslope scale. Knowing how these sieving crusts form and evolve, and their exact relationship with water repellency, are important points for designing adequate soil management and conservation.

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