Análise geoambiental dos processos erosivos numa área de expansão urbana: estudo de caso da Bacia do Rio dos Cachorros, São luís - Maranhão

Abstract

Soils play a fundamental role in the life of the planet, supporting agriculture, construction, and ecosystems. They provide nutrients and support to plants, in addition to regulating water and sheltering different organisms, which is vital for productivity and environmental balance. Understanding their formation and the importance of sustainable use is essential for the conservation of this precious and non-renewable resource. This research aims to analyze the morphopedological units in the Cachorros River basin, in order to identify the interrelationships between the distribution of gullies and land use. The methodological procedures consisted of: bibliographic surveys – in this stage, scientific, technical, and institutional materials were consulted and reviewed; cartographic surveys – cartographic data were collected and organized, including topographic maps, satellite images, Digital Elevation Models (DEMs), and thematic shapefiles; fieldwork – aimed at verifying in situ the geomorphological features, soil types, vegetation cover, and occurrence of erosive processes; Thematic map creation – these were created using software, based on the processing and cross-referencing of data obtained in previous stages; and laboratory analysis – soil samples collected in the field were subjected to physical and chemical analyses in the laboratory, following methodologies standardized by Embrapa (2017). The Cachorros River basin presents a predominance of Itapecuru Group lithology (69.10%) and a relief characterized by dissected plateaus (79.60%). The slope is mostly gentle, between 0 and 5% (65.70%), with rectilinear planar curvature (81.93%) and altitudes ranging from 12 to 22 m (29.18%). In pedological terms, Yellow Latossos of medium texture stand out (34.52%), mainly associated with natural vegetation (21.31%); industrial (12.96%) and urban (12.44%). Soil erodibility analysis indicates that 44.58% of the basin is slightly erodible, while 34.46% is highly erodible. Susceptibility to sheet erosion is predominantly moderate (48%), with low erosive potential (44.24%) and medium potential (37.06%). Compartments CMP2 and CMP3 are the most vulnerable, presenting steeper slopes and the occurrence of Argisols and Latosols. Morphological and physical analyses of the soils reveal colors ranging from reddish-yellow to yellowish-red, predominantly sandy texture, angular to subangular structure, and consistency ranging from extremely hard to loose. Soil density values ranged from 0.94 to 1.73 g/cm³, and particle density from 2.5 to 3.07 g/cm³. Porosity ranged from 25.22% to 58.95%, and granulometry showed sand (57.05%) as the dominant fraction, with clay between 4% and 23%, and silt up to 19.95%, classifying most samples as loamy sand. It is concluded that the basin lacks adequate environmental planning, suffering significant impacts from mining activities and the formation of gullies. The study reinforces the importance of morphopedological analysis as a fundamental t