Alterações do uso e cobertura da terra e avaliação da resistência à erosão da bacia hidrográfica do Rio Gualaxo do Norte

Abstract

Landscape transformation brought on by men/nature relationship, often favors the degradation of the environment. These changes can be the result of natural processes - coming exclusively from nature’s dynamic-, anthropic actions or a combination of both. To understand the processes of change through time is essential for decision making and interpretation of the environment. The aim of this study is to identify changes in land use and land cover as well as to analyze erosion resistance in the Gualaxo do Norte river basin in Minas Gerais. The Gualaxo do Norte basin integrates the Rio Doce basin and a portion of it is part of Quadrilátero Ferrífero. In 2015 the basin was hit by the Fundão mining dam rupture in the municipality of Mariana, which caused serious impacts both environmentally and socially. Considering this setting this paper was structured in two sections, first identifying changes in land use and land cover in the basin in the past decade (2008-2018) and then assessing the erosion resistance in the basin. To map land use and cover satellite images from Landsat -5, Landsat-8 and Sentinel-2 were used. We applied object-oriented classification method also considering the specific spectral signature, like shape and compacity. We used the Nearest Neighbor algorithm for the classifications, and they were validated by a control matrix created through image analysis with Google Earth Pro and control points determined in field campaigns. The assessment of erosion resistance was done through weighting of variables and attributes of variables that play a part in erosive processes in the basin. The considered variables were related to soils, geology and relief. The basin presents eight main land use and cover classes that in the 10 years analyzed have gone through major or minor changes, such as the considerable increase in exposed soil area. We have also found that the river basin displays three great environments, the first predominantly represented by mining activities, in the upper course; the second represented by silviculture and forest formation in the middle course and the third typically made of fields in many areas of pasture in the lower course. In terms of erosion resistance, we have found areas more fragile as well as more resistant in the basin along with the anthropic pressures upon it. Unlike conventional erosion models - the floodplain and fluvial terraces are usually areas of aggradation - due to the presence of mining tailings the physical features of floodplains and terraces have become unstable and fragile to erosive processes. This diagnosis and analysis can be useful to support decision making in the study area, subsidizing discussion and intervention measures in order to recover degraded areas, to preserve and to identify areas to be prioritized for urgent actions.