Landscape system mapping of the humid Baturité massif and its semi-arid piedmont (Northeastern Brazil): a multilayer integration of environmental parameters
Résumé
The Baturité massif is the erosional remnant of an Early Cretaceous rift shoulder. Humid bioclimatic conditions on this upstanding residual relief contrast with the semi-arid conditions of the surrounding plain (‘Sertão’). Located about 100 km to the south of Fortaleza (Ceará, NE Brazil), the study area exhibits a characteristic vegetation continuum between evergreen forest, or ‘mata atlântica’, of the humid zone and deciduous ‘caatinga’ of the semi-arid piedmont via a semi-deciduous forest belt delimiting a sub-humid transition zone. Systematic soil successions and landform variations were also identified through this topo-climatic framework. The objective of this work was to develop a method of soil-landform mapping that accounts adequately for the new pedogeomorphogical observations made in the field. The survey was performed using GIS techniques based on the integration of a SRTM-derived digital elevation model, topographic maps at 1:100,000, digital geological data, Landsat imagery, and available soil maps. The GIS survey also allowed to take into consideration other fundamental environmental parameters such as rainfall distribution and water balance calculations that are useful to understanding soil distribution and mesoscale topographic patterns. The resulting soil-landform map captures the key features of the regional pedogeomorphic landscapes: (1) the humid Baturité massif is characterised by a summit surface (800-900 m a.s.l.) which is the domain of multiconvex topography, monosiallitic weathering and associated low-activity-clay Acrisols; (2) a sub-humid peripheral area of highly dissected landscape (200-800 m) shows a shallowness in weathering and soil profiles (Lixisols); (3) in the semi-arid plain (0-200 m), the ‘Sertão’ is a landscape of dissected pediplain with shallow bisiallitic grus that supports red Luvisols and brown Cambisols; (4) the sedimentary piedmont is composed of basal Neogene clastic sediments covered by paleosols (Lixisols) and of Pleistocene aeolian sands marked by poorly developed soils (Arenosols).