Identificação de fontes de produção de sedimentos em uma bacia hidrográfica de encosta

Abstract

Land use outside of its agricultural suitability is the main cause of degradation of natural resources due to anthropogenic activities. Agricultural activities are among those that most disturb the environment, exposing the soil to the action of water erosion and accelerating the transfer of sediments into bodies of water. In recent years, the fingerprinting method for identifying sources of sediment has been successfully used throughout the world; however, such studies in Brazil are still incipient. This study aims to estimate the proportion of contribution of the major sources of sediment production from a hillside catchment area with the predominance of shallow soils and less intensive family agriculture. This catchment area is located in the central region of the State of Rio Grande do Sul, and the predominant land use is native forest, followed by native grassland, shrubland, annual crops, and a few areas of forestry (eucalyptus) and urbanized development. For identification of the sources of erosion, the fingerprinting method was used, which compares the soil from different sources and the sediments found in suspension in the drainage canal, using tracer elements. The largest contributions in sediment production are derived from soil surface erosion. For the first monitoring period, relative sediment production of 60 % from unpaved roads at point T2, 100 % of the sampling grid at point T3, and 77 % of the sampling grid at point T4 was identified. For the second monitoring period, unpaved roads had a relative contribution of 81 % of the suspended sediments at point T2 and 76 % at point T3. For point T4, the greatest contribution was the sampling grid with 82 %. The method was sensitive enough to detect changes in the contribution of each source due to the characteristics they presented for the type of catchment area studied.