Fontes de produção de sedimentos e índices ambientais de uso da terra como indicadores de vulnerabilidade ambiental de uma bacia hidrográfica rural

Abstract

Small drainage wathersed are more susceptible to environmental impacts related to human activities possessing vulnerability processes that may lead to degradation, pollution and/or contamination of sites. In this context, studies on small drainage basins and their environmental dynamics are crucial to understanding the environmental impact of human activities. This study encompasses three central knowledge axes of a rural drainage basin used as a drinking water supply. The selected basin is the Epaminondas Hydrographic wathershed, which corresponds to 70% of the drainage and supply area of the Santa Bárbara wathershed, which is responsible for 60% of the drinking water supply of Pelotas’s municipality, a southern city in the state of Rio Grande do Sul, Brazil. The Epaminondas Basin has an area of 33 km2 , where various activities are undertaken, such as the production of vegetables, grains, beef cattle, mining, and leisure sites. The predominant soils are Argissolo at the middle and upper layers of the basin; Planossolo in the lower layer; Cambissolo and Neossolo associations in the highest layer, Gleissolo near Santa Bárbara dam. Studies were conducted in the sediments and phosphorus adsorptive processes in the soil, relating the dynamics of sediment production and their originating sources, with pollution and contamination processes by Cu, Fe, Mn and Zn metals. The dynamics of sediments, production, and sources were conducted using the fingerprinting technique widely used in the Rio Grande do Sul state. The study pertinent to the pollution methods and/or contamination by Cu, Fe, Mn and Zn metals was developed using the Geoaccumulation index, the contamination factor, and the enrichment factor, specifying the pollution/contamination degree and their possible sources. For the study of the phosphorus adsorptive processes in the soil, indexes were used to indicate the soil capacity in receiving phosphate fertilizer doses without loss and the eutrophication process of water bodies. At the end of the study, it was observed that the variables used for the composition of the fingerprinting technique were not sufficient to identify the sources of sediments. Thus, no contamination and accumulation by the chosen metals were verified in the metal dynamics study, demonstrating the need to investigate further soil use and erosion and its impacts on the basin sediments. The phosphate fertilization and the adsorption capacity studies showed that the basin soils still could receive more doses of phosphate fertilizers but with caution to avoid environmental contamination and eutrophication of water bodies. In summary, the three studies revealed the impact of natural and human activities on the basin, showing that continuous monitoring studies are necessary to avoid significant environmental damages that could adversely affect the water supply for the surrounding inhabitants.