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Universidade de Sao Paulo (2017)

Interações pedogeomorfológicas em bacia de drenagem no semiárido baiano

Pacheco, Jucelia Macedo

Titre : Interações pedogeomorfológicas em bacia de drenagem no semiárido baiano

Soil-geomorphology interactions in drainage basin in the semi-arid Bahia

Auteur : Pacheco, Jucelia Macedo

Université de soutenance : Universidade de Sao Paulo

Grade : Doutora em Geografia Fisica 2017

This work is part of the process of research and knowledge of the evolution of the landscape from the interaction between soil and relief, i.e., a soil geomorphological approach. Aiming to contribute to and disseminate the knowledge of the geo- and biodiversity of the Brazilian semiarid, where studies such as this one is rare, we investigated an area in the northeast of Bahia, near the Nova Soure municipality. The drainage basin was picked as the unit of spatial analysis because, even in semiarid conditions, we understand it to provide the best comprehension of the relationships between shapes and materials, such as soil coverage. The Natuba stream drainage basin we investigate in this study is geologically situated in the Tucano Sul sedimentary basin, itself part of the Recôncavo-Tucano-Jatobá rift. Geomorphologically, the basin is part of the Itapicuro tablelands, formed by surfaces of planation and dissection. The investigation involved office, field, and laboratory stages, including : literature and conceptual review, gathering of cartographic material, image processing, geoprocessing to produce maps, area survey and fieldwork, profile description and sampling, laboratory analysis, and thin section microscopy. We adopted different scales to study the soil-relief relationship. At the basin-scale, the study comprised the identification and description of morphopedological compartments. At the slope-scale, the study was derived from the description and characterization of soils along transects between morphopedological compartments. Finally, at the detail-scale we observed the microstructures on slides, using petrographic microscopes. Results indicate that the basin is soil-diverse and that its variety and distribution is intimately related to the variation of the lithofacies of the Marizal Formation and to relief processes such as superficial and subsuperficial erosion of fine material (clays). The Quartzarenic Neosols, more frequent in the higher regions of the basin, are differentiated by the clay content, mineral composition, and the relative distribution of groundmass. These distinctions were interpreted as products of the influence of water circulation, substantiating the importance of the relief in the soil genesis. At the lower regions of the basin, the soil is more diverse : Acrisols, Luvisols, Chernozems, Fluvisols, and Planosols occur. Fertility, mineralogy and micromorphological organization of the soils are typical of the original material enduring conditions of weathering that are characteristic of the semiarid. Furthermore, the soils are related to the erosive processes that affect the slopes and form, for instance, the textural gradient as a result of elutriation (Acrisols and Luvisols) or sedimentation (Planosols). Generally, the basin soils are interlinked via the redistribution of material throughout the landscape. This context, therefore, expresses the importance of considering both pedogenesis and morphogenesis when examining the evolution of the semiarid landscape.


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