Erosão em uma microbacia em desertificação no médio curso do Rio Salitre, BA

Abstract

The aim of this work is to evaluate the laminar erosion of a micro-basin (16 ha) in process of desertification, in order to identify the causes of its degradation. The study area is located in the middle course of the Salitre River, located in Campo Formoso, state of Bahia. For that, data on soil, topography and use and occupation of the area were collected. Topography characterization used unmanned aerial vehicle (UAV) with precision optical equipment. The Universal Soil Loss Equation (USLE) was parameterized and applied to calculate gross erosion, whose value, multiplied by the sediment delivery ratio (SDR), allowed the estimation of sediment production due to laminar erosion. This value was compared to the rate of soil formation in the region. Additionally, the ages of 53 pedestals were calculated, micro elevations that resisted laminar erosion due to the presence of roots. The results show that the average annual soil production in the micro-basin was 71 Mg ha-¹, a magnitude from three to one hun dred times greater than the rate of soil formation at the area. The annual tolerance limit for soil loss is 1 Mg ha-¹, a value seventy times lower than the sediment production in the micro-basin, a strong evidence that the area is under a high state of degradation, which continues to increase. It is verified that 80% of the micro-basin presents a high risk of vulnerability to desertification. According to the dating of the pedestals, two mo ments proved to be of great relevance: the first, when 16% of the pedestals started, indicates a driving force that boosted erosion in the 1960s. Among the main facts that may have facilitated the erosion is the construction of a side road in the upper part of the micro-basin. The second moment, when the formation of 80% of the pedestals began, corresponds to the 1990s, when there was a resurgence of the intense cultiva tion of Agave sisalana in the region, which included production on steep slopes without conservative practices. Between these two moments there was a pause in the 1980s, when virtually no pedestals were formed. During this period there was a drastic reduc tion in the cultivation of Agave sisalana in the basin. This leads us to point out the construction of the side road and the cultivation of Agave sisalana on the slopes as the most likely factors that triggered the intense degradation of the area. After 2010, there was a considerable reduction in the generation of new pedestals. The micro-basin is in an advanced process of degradation by water erosion, and the region must be rec ognized among those that are in desertification.