Water erosion modeling in the watersheds of the rivers Lontra and Manoel Alves Pequeno, Tocantins State, Brazil

Water erosion is one of the main factors that lead to the process of soil degradation, with impacts ranging from reducing productivity to losses of natural resources. Thus, this work aimed to estimate soil losses performing RUSLE model and to verify the effect of changes in land use changes, from 1990 to 2007, in the watersheds of the rivers Lontra and Manoel Alves Pequeno, Tocantins State-Brazil. Water erosion in the river Lontra ranged from "slight" (51.3%) in the central region of the basin (dominance of flat relief and forest land use), to "extremely high" (24.6%), in the range that goes from the north to the west (dominance of pasture land use and more declining relief). In the watershed of Manoel Alves Pequeno the erosion class "slight" (52%) was distributed along the basin, due to most soils had low erodibility and with most of the area covered by cerrado. While the "extremely high" class (6.7%), occurred in the northern and western part due to pasture land use, and in the eastern part due to the greater slope. Temporal evaluation of soil loss evidenced that there were no significant variations in the period studied. However, in the watershed of river Lontra, from 2000 to 2007, occurred a 0.3% reduction of the "extremely high"; at the wathershed Manoel Alves Pequeno, from 1990 to 2007, there was a gradual increase in the soil erosion rate.