Fragilidade ambiental aos processos erosivos na bacia hidrográfica do Ribeirão do Mandaguari, oeste do estado de São Paulo, Brasil
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Data
2019-01-07
Autores
Vagula, Paulo Roberto [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Até o início do século XX grande parte do oeste do estado de São Paulo estava coberta por vegetação nativa. Ainda nas primeiras décadas as florestas foram substituídas por cultivos agrícolas e pastagens. As transformações causadas pelos agentes sociais e econômicos não consideraram as dinâmicas naturais das paisagens, produzindo a quebra do equilíbrio até então existente e provocando impactos como a alteração dos processos morfodinâmicos. Assim, mesmo depois de décadas de uso da terra para a produção agrícola e para a pecuária, os estudos de fragilidade ambiental são de grande relevância, uma vez que permitem apontar as áreas mais propensas a formação de processos erosivos. Esta pesquisa tem como objetivo principal analisar a fragilidade ambiental aos processos erosivos na bacia hidrográfica do Ribeirão do Mandaguari, oeste do estado de São Paulo, Brasil. Para tanto, fundamenta-se na análise fisiográfica e na análise comparativa de três mapas síntese: mapa da fragilidade do relevo, mapa da fragilidade potencial e mapa da fragilidade ambiental emergente. A metodologia adotada para a determinação da fragilidade ambiental baseou-se naquela proposta por Ross (1994) com as devidas adequações para a área de estudo. A aplicação dessa metodologia requereu uma base de dados com variáveis referentes à morfologia do terreno, tipos de solo, além do uso da terra e cobertura vegetal. Para a definição dos níveis de fragilidade da variável “relevo” utilizaram-se as classes de declividades e a curvatura do terreno. Para a definição dos níveis de fragilidade da variável “solos” foram considerados as características de textura, estrutura, plasticidade, grau de coesão das partículas e profundidade/espessuras dos horizontes dos diversos tipos de solos. Para a variável “uso e cobertura da terra” considerou-se o grau de proteção que cada tipo de cobertura oferece aos solos face aos processos erosivos induzidos pela ação das águas pluviais. A partir da análise ponderada dessas variáveis foram obtidos três produtos cartográficos. O primeiro deles, o mapa de fragilidade do relevo, obtido a partir da curvatura e da declividade do terreno, apontou a predominância de média fragilidade aos processos erosivos. O mapa de fragilidade potencial, obtido a partir das características do relevo e dos diversos tipos de solos presentes na bacia, apontou a predominância das áreas classificadas como de fragilidade alta. Já o mapa de fragilidade ambiental emergente, obtido a partir do mapa de fragilidade potencial e do uso da terra na bacia, apontou o predomínio de áreas classificadas como de fragilidade muito alta. A pesquisa mostrou que a maior parte da bacia hidrográfica pode ser considerada como altamente frágil ao desenvolvimento de processos erosivos, o que pode causar danos ambientais, assoreamento de cursos d’água e prejuízos econômicos aos proprietários rurais.
Until the beginning of the 20th century, much of western São Paulo was covered by native vegetation. Even in the first decades the forests were replaced by agricultural crops and pastures. The transformations caused by the social and economic agents did not consider the natural dynamics of the landscapes, breaking the existing balance and provoking impacts such as the alteration of the morphodynamic processes. Thus, even after decades of land use for agricultural production and livestock, studies of environmental fragility are of great relevance, since they allow us to point out the areas most prone to the formation of erosive processes. This research has the main objective to analyze the environmental fragility to the erosive processes in the watershed of Ribeirão do Mandaguari, west of the state of São Paulo, Brazil. For this, it is based on the physiographic analysis and the comparative analysis of three synthesis maps: map of the fragility of the relief, map of the potential fragility and map of the emerging environmental fragility. The methodology adopted for the determination of the environmental fragility was based on that proposed by Ross (1994) with the appropriate adaptations for the study area. The application of this methodology required a database with variables related to soil morphology, soil types, besides land use and vegetation cover. In order to define the fragility levels of the "relief" variable, the slope classes and the curvature of the terrain were used. In order to define the fragility levels of the soil variable, the characteristics of texture, structure, plasticity, degree of cohesion of the particles and depth / thickness of the horizons of the different types of soils were considered. For the variable "land use and land cover", the degree of protection that each type of cover is offered to the soils in view of the erosive processes induced by the action of rainwater. From the weighted analysis of these variables. Three cartographic products were obtained. The first one, the map of fragility of the relief, obtained from the curvature and slope of the terrain, pointed the predominance of medium fragility to the erosive processes. The map of potential fragility, obtained from the characteristics of the relief and the different types of soils present in the basin, pointed out the predominance of the areas classified as high fragility. The map of emerging environmental fragility, obtained from the map of potential fragility and land use in the basin, pointed out the predominance of areas classified as very fragile. Research has shown that most of the river basin can be considered as highly fragile to the development of erosive processes, which can cause environmental damage, silting up streams and economic losses to rural landowners.
Until the beginning of the 20th century, much of western São Paulo was covered by native vegetation. Even in the first decades the forests were replaced by agricultural crops and pastures. The transformations caused by the social and economic agents did not consider the natural dynamics of the landscapes, breaking the existing balance and provoking impacts such as the alteration of the morphodynamic processes. Thus, even after decades of land use for agricultural production and livestock, studies of environmental fragility are of great relevance, since they allow us to point out the areas most prone to the formation of erosive processes. This research has the main objective to analyze the environmental fragility to the erosive processes in the watershed of Ribeirão do Mandaguari, west of the state of São Paulo, Brazil. For this, it is based on the physiographic analysis and the comparative analysis of three synthesis maps: map of the fragility of the relief, map of the potential fragility and map of the emerging environmental fragility. The methodology adopted for the determination of the environmental fragility was based on that proposed by Ross (1994) with the appropriate adaptations for the study area. The application of this methodology required a database with variables related to soil morphology, soil types, besides land use and vegetation cover. In order to define the fragility levels of the "relief" variable, the slope classes and the curvature of the terrain were used. In order to define the fragility levels of the soil variable, the characteristics of texture, structure, plasticity, degree of cohesion of the particles and depth / thickness of the horizons of the different types of soils were considered. For the variable "land use and land cover", the degree of protection that each type of cover is offered to the soils in view of the erosive processes induced by the action of rainwater. From the weighted analysis of these variables. Three cartographic products were obtained. The first one, the map of fragility of the relief, obtained from the curvature and slope of the terrain, pointed the predominance of medium fragility to the erosive processes. The map of potential fragility, obtained from the characteristics of the relief and the different types of soils present in the basin, pointed out the predominance of the areas classified as high fragility. The map of emerging environmental fragility, obtained from the map of potential fragility and land use in the basin, pointed out the predominance of areas classified as very fragile. Research has shown that most of the river basin can be considered as highly fragile to the development of erosive processes, which can cause environmental damage, silting up streams and economic losses to rural landowners.
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Palavras-chave
Fragilidade ambiental, Processos erosivos, Bacia hidrográfica, Geomorfologia, Solos, Environmental fragility, Erosive processes, Drainage basin, Geomorphology, Soils