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

Within the Ebro valley, the Zaragoza province contains the largest area of gypsiferous soils in Spain. Previous mapping of the gypsum outcrops has bee n the starting point for this study of the soils developed on them. In this paper, gypsiferous soils are differentiated according to geological age, l ithological facies and other depositional features. The most abundant gypsi ferous soils correspond to Tertiary outcrops, where a typical catena includ es Leptosols on the crest of the hillslopes, Regosols on the talus and Gyps isols on the valley bottom. Gypsiferous soils, developed on the Triassic Ke uper facies and Quaternary materials, occupy a relatively small area. The g ypsiferous soils have been mapped at a scale of 1:200000. A CAD software pa ckage has been used for digitizing the soil units. A digital elevation mode l 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 cl assified according to slope and precipitation. In the Zaragoza province, th e gypsiferous soils (Lithic and Eutric Leptosols, Petric, Calcic and Haplic Gypsisols, Gypsic Regosols, Gypsic Solonchaks) occupy a total area of 2296 19 ha (13% of the area of the province). 25% of the gypsiferous soils occur within the semiarid area (annual rainfall < 400 mm) indicating that climat e is the main limiting factor for soil conservation, because of the fragili ty of gypsiferous soils, special care must be taken with land use operation s on the 18137 ha with slopes above 10 degrees. The knowledge of the distri bution of gypsiferous soils in relation to topographic and climatic factors provides an important basis for soil conservation and management. (C) 1998 Elsevier Science B.V. All rights reserved.