Produção de sedimentos na microbacia do Córrego Seco em Tabapuã - SP
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Data
2020-02-28
Autores
Freire, Poliana Mara Reis
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Universidade Estadual Paulista (Unesp)
Resumo
O aporte de sedimentos oriundos de áreas agrícolas tem efeitos adversos nos corpos d´água, como córregos e rios numa bacia hidrográfica. Em geral, os processos erosivos no solo são a principal fonte de produção destes sedimentos. Neste estudo foi dado atenção para estimar e mapear a distribuição espacial da produção de sedimentos, utilizando a taxa de transferência de sedimentos (SDR) e a Equação Universal de Perda de Solo Revisada (RUSLE) na microbacia do Córrego Seco (BBV). Especificamente, objetivou-se identificar áreas de produção de sedimentos e prioritárias para a conservação do solo em dois cenários no cultivo de cana-de-açúcar. Na BBV 165 pontos amostrais, georreferenciados, espaçados de 50 em 50 m, permitiram estabelecer a distribuição espacial dos fatores erosividade da chuva (R), (K) erodibilidade do solo (K), fator comprimento e inclinação do declive (LS), manejo e cobertura do solo (C), e (P) práticas conservacionistas (P), em dois cenários de cobertura do solo por resíduos de cana-de-açúcar: Cenário 1, 50% de cobertura; Cenário 2, 90% de cobertura. Para cada ponto dentro das Unidades de Resposta Hidrológica (HRU’s) estabelecidas com o SWAT (Soil and Water Assessment Tool) a erosão (A) e a SDR foi estimada. Com a associação RUSLE/SDR a produção de sedimentos (SY) foi estimada ponto a ponto. Métodos geoestatísticos (Análise Semivariográfica e Interpolação por Krigagem ordinária) permitiram avaliar a distribuição espacial de A e SY para os dois Cenários testados. A produção total anual de sedimento na BBV é de 178,0 t no Cenário 1 e de 115,9 t no Cenário 2, valores altos de SY (>2,4 t ha-1 ano-1) e moderados (1,2 a 2,4 t ha-1 ano-1) correspondem a 10,7% e 85,3% do total da produção de sedimentos na área da BBV. Estes valores mais críticos são devidos ao solo mais susceptível à erosão (Argissolos), maiores valores de LS e alta erosividade local. Além desses fatores a densidade de drenagem alta nas HRU, correspondentes as áreas com SY moderada e alta no Cenário 1 e SY moderada no Cenário 2, predispõem o terreno à erosão. As áreas mais críticas ocorrem na região noroeste da BBV, onde as HRU apresentam fatores que determinaram os níveis de SY estimados. O método de estimar a produção de sedimento (SY) integrado a SDR e RUSLE pode ser repetido em outras sub-bacias da Bacia do Rio São Domingos. As estimativas de produção de sedimentos, obtidas neste estudo, e a sua espacialização demonstraram um papel fundamental das práticas de manejo no cultivo de cana-de-açúcar. Elas permitem identificar fontes não-pontuais de poluição e de produção de sedimentos identificando áreas de manejo, as quais deverão receber práticas de manejo específicas para fins de conservação do solo e da água.
Sediment input from agricultural areas has adverse effects on water bodies such as streams and rivers in a river basin. In general, soil erosion processes are the main source of production of these sediments. In this study attention was given to estimate and map the spatial distribution of sediment production, using the Sediment Transfer Rate (SDR) and the Universal Equation of Revised Soil Loss (RUSLE) in the Córrego Seco watershed (BBV). Specifically, the objective was to identify sediment production areas and priorities for soil conservation in two scenarios in sugarcane cultivation. In the BBV 165 sampling points, georeferenced, spaced 50 m apart, allowed establishing the spatial distribution of rain erosivity factors (R), (K) soil erodibility (K), slope length and steepness factor (LS), soil management and cover (C), and (P) conservation practices (P), in two scenarios of soil cover by sugarcane residues: Scenario 1, 50% cover; Scenario 2, 90% cover. For each point within the Hydrologic Response Units (HRU's) established with the SWAT (Soil and Water Assessment Tool) erosion (A) and SDR was estimated. With the RUSLE/SDR association the sediment production (SY) was estimated point by point. Geostatistical methods (Semivariographic Analysis and Interpolation by Ordinary Krigagem) allowed to evaluate the spatial distribution of A and SY for the two Scenarios tested. The total annual sediment production in BBV is 178.0 t in Scenario 1 and 115.9 t in Scenario 2, high values of SY (>2.4 t ha-1 year-1) and moderate (1.2 to 2.4 t ha-1 year-1) correspond to 10.7% and 85.3% of the total sediment production in BBV area. These more critical values are due to the soil more susceptible to erosion (Ultisol), higher LS values and high local erosivity. In addition to these factors the high drainage density in the HRU, corresponding to the areas with moderate SY and high SY in Scenario 1 and moderate SY in Scenario 2, predispose the land to erosion. The most critical areas occur in the northwestern region of BBV, where the HRU have factors that determined the estimated SY levels. The method of estimating sediment production (SY) integrated with SDR and RUSLE can be repeated in other sub-watersheds of the São Domingos River Basin. Sediment production estimates, obtained in this study, and their spatialization demonstrated a fundamental role of management practices in sugarcane cultivation. They allow the identification of diffuse sources of pollution and sediment production by identifying management areas, which should receive specific management practices for soil and water conservation purposes.
Sediment input from agricultural areas has adverse effects on water bodies such as streams and rivers in a river basin. In general, soil erosion processes are the main source of production of these sediments. In this study attention was given to estimate and map the spatial distribution of sediment production, using the Sediment Transfer Rate (SDR) and the Universal Equation of Revised Soil Loss (RUSLE) in the Córrego Seco watershed (BBV). Specifically, the objective was to identify sediment production areas and priorities for soil conservation in two scenarios in sugarcane cultivation. In the BBV 165 sampling points, georeferenced, spaced 50 m apart, allowed establishing the spatial distribution of rain erosivity factors (R), (K) soil erodibility (K), slope length and steepness factor (LS), soil management and cover (C), and (P) conservation practices (P), in two scenarios of soil cover by sugarcane residues: Scenario 1, 50% cover; Scenario 2, 90% cover. For each point within the Hydrologic Response Units (HRU's) established with the SWAT (Soil and Water Assessment Tool) erosion (A) and SDR was estimated. With the RUSLE/SDR association the sediment production (SY) was estimated point by point. Geostatistical methods (Semivariographic Analysis and Interpolation by Ordinary Krigagem) allowed to evaluate the spatial distribution of A and SY for the two Scenarios tested. The total annual sediment production in BBV is 178.0 t in Scenario 1 and 115.9 t in Scenario 2, high values of SY (>2.4 t ha-1 year-1) and moderate (1.2 to 2.4 t ha-1 year-1) correspond to 10.7% and 85.3% of the total sediment production in BBV area. These more critical values are due to the soil more susceptible to erosion (Ultisol), higher LS values and high local erosivity. In addition to these factors the high drainage density in the HRU, corresponding to the areas with moderate SY and high SY in Scenario 1 and moderate SY in Scenario 2, predispose the land to erosion. The most critical areas occur in the northwestern region of BBV, where the HRU have factors that determined the estimated SY levels. The method of estimating sediment production (SY) integrated with SDR and RUSLE can be repeated in other sub-watersheds of the São Domingos River Basin. Sediment production estimates, obtained in this study, and their spatialization demonstrated a fundamental role of management practices in sugarcane cultivation. They allow the identification of diffuse sources of pollution and sediment production by identifying management areas, which should receive specific management practices for soil and water conservation purposes.
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Palavras-chave
Erosão do solo, SDR, RUSLE, SWAT, Sub-bacias, Soil erosion, sub-watersheds