A ocupação da Bacia do Rio das Velhas relacionada aos tipos de solo e processos erosivos

Abstract

With the intention of avoiding the occurrence of erosive processes and the environmental damages that these cause to the hydrographic basin, it is important to know the influence that the soil characteristics, together with the way in which it is occupied, can have on environmental degradation. With this in mind, this study attempted to establish the relationships that exist between the type of soil, its use and the occurrence of erosive processes. The main aim of this study was, therefore, to analyse the principal uses of the soils in the basin of the Rio das Velhas, associating them with the main types of soil and the related erosive processes. For this, the agricultural potential of the soil was considered, and once this had been done, along with the soil characteristics, parameters such as relief and hydro availability, whichcontribute greatly towards explaining the occurrence of erosion, were also taken into account. In order to achieve these objectives, geoprocessing resources were used. The Mapinfo software was used to work with georeferenced databases developed by environmental bodies and institutions concerned with the recuperation and the environmental conservation of the region of the study. Four different thematic maps were used: Soil type, Soil use, Agricultural potential and Erosive processes. Each thematic map was separated into levels, with each level corresponding to an item in the key, that is, a type of soil, a way in which the soil is used and a class of agricultural potential, respectively. Next, these levels were superimposed, generating other thematic mapswhich showed the spatial relationship between the parameters, or themes, analysed. In this way, it was demonstrated that the mining, which is the main economic activity of the region, has a spatial distribution which is better explained by the geological formation than by the type of soil, being concentrated in two small areas of the basin: one in the extreme south in the area known as the Ferriferous Quadrilateral, where the exploitation of iron ore occurs on Neossolos Litolicos; and the other to the north of the metropolitan region of Belo Horizonte, Brazil, where the exploitation of lime is predominant in limestone deposits of the Bambuí group. In spite of the environmental degradation provoked by this activity, the erosive processes in the regions where it is carried out are relatively stable or natural. As examples of agricultural uses, in the region there are occurrences of farms, pasture and silviculture. The farms are of little significance and the majority are concentrated on Latossolos,where the occurrence of accelerated erosive processes, even though in small areas, has been verified. The pasture, however, occupies a significant area in all of the soil types, including land with good farming potential. The occurrence of pasture on Cambissolos of restricted potential for natural or planted pasture is responsible for the greatest area of accelerated erosive processes in the basin. Silviculture, in turn, is carried out mainly on Latossolos; this association also results inerosive processes in their accelerated form. The natural vegetation is concentrated in the east and south of the basin. In the east, the very nature of the Serra do Espinhaço (espinhaço mountain range), where the pasture is found, makes its degradation nonviable, since the relief is fairly step and the soils are shallow, creating problems for the occupation of this land. In the south, the creation of the Unidades de Conservaçao (conservation units) contributes to maintaining a state of relative preservation. In these regions, the erosive processes, when they occur, are of low intensity. It was verified that the erosive processes occur as much in more easily erodible soils, such as Cambissolos, as in those that are less easily erodible, such as Latossolos. This shows thatinadequate management practices can be determining factors in the occurrence of accelerated erosion in any type of soil. The use of soils of higher agricultural potential for less demanding cultivation, such as pasture and silviculture was also observed, as well as the occupation of soils with restrictions for more demanding cultivation, such as farming. This demonstrated that, beyond the soil characteristics, other factors such as the economic and cultural circumstances of the society interfere significantly in its use.