Spatial analysis of gypsiferous soils in the Zaragoza province (Spain), using GIS as an aid to conservation

Abstract

Within the Ebro valley, the Zaragoza province contains the largest area of gypsiferous soils in Spain. Previous mapping of the gypsum outcrops has been the starting point for this study of the soils developed on them. In this paper, gypsiferous soils are differentiated according to geological age, lithological facies and other depositional features. The most abundant gypsiferous soils correspond to Tertiary outcrops, where a typical catena includes Leptosols on the crest of the hillslopes, Regosols on the talus and Gypsisols on the valley bottom. Gypsiferous soils, developed on the Triassic Keuper facies and Quaternary materials, occupy a relatively small area. The gypsiferous soils have been mapped at a scale of 1:200 000. A CAD software package has been used for digitizing the soil units. A digital elevation model of the Zaragoza province has been created from the digitized topography. The geographical information system, IDRISI, has been used to integrate all the spatial information generated and to produce maps of the soil types classified according to slope and precipitation. In the Zaragoza province, the gypsiferous soils (Lithic and Eutric Leptosols, Petric, Calcic and Haplic Gypsisols, Gypsic Regosols, Gypsic Solonchaks) occupy a total area of 229 619 ha (13% of the area of the province). 25% of the gypsiferous soils occur within the semiarid area (annual rainfall<400 mm) indicating that climate is the main limiting factor for soil conservation, because of the fragility of gypsiferous soils, special care must be taken with land use operations on the 18 137 ha with slopes above 10°. The knowledge of the distribution of gypsiferous soils in relation to topographic and climatic factors provides an important basis for soil conservation and management.