Avaliação dos modelos de predição da erosão hídrica MEUPS e WEPP: contribuição em bacias hidrográficas
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2016-03-07
Autores
Moraes, Isabel Cristina [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A intensificação do uso das terras torna-se cada vez mais evidente em função da crescente produção de alimentos à população humana. A aplicação de práticas inadequadas às múltiplas funcionalidades do solo tem provocado a erosão hídrica acelerada como um dos principais processos de degradação deste recurso. No esforço de colaborar em estudos de conservação dos solos, avaliaram-se os modelos preditivos de erosão hídrica MEUPS – Equação Universal de Perda de Solo Modificada (Williams, 1975) e WEPP – Water Erosion Prediction Project (Laflen, 1991) por meio da comparação das estimativas de perda de solo com dados empíricos de parcelas experimentais de pinos de erosão. A variabilidade de parâmetros envolvidos nas simulações motivou a definição de duas bacias hidrográficas de características hidrossedimentológicas distintas, as bacias do ribeirão Jacutinga (Rio Claro – SP) e do córrego do Monjolo Grande (Ipeúna - SP), para avaliar o comportamento erosivo em solos oriundos de argilitos e arenitos, respectivamente. No período experimental de junho/2013 a agosto/2014, parcelas experimentais de 1 m2 foram monitoradas em diferentes condições de declividade, posição topográfica, forma da vertente e cobertura vegetal – pastagem, cana-de-açúcar, e vegetação ripária, e em solo descoberto. Nos Argissolos e Cambissolos de textura argilosa foram registradas perdas de 0,018 a 0,066 ton/ha.ano-1, e deposição entre 0 e 0,026 ton/ha.ano-1, e nos Neossolos Quartzarênicos e Argissolos de textura arenosa, houve predomínio deposicional, entre 0,004 e 0,085 ton/ha.ano-1, e perdas de 0,002 a 0,11 ton/ha.ano-1. As maiores perdas estão associadas a maiores porções das frações de areia fina e silte, e fraca agregação pelos baixos teores de argila e matéria orgânica. O maior percentual de cobertura vegetal foi determinante para as menores perdas, evidenciando maior fator de proteção do solo por plantio direto que por plantio convencional. As simulações foram realizadas para o ano experimental e para eventos específicos de chuva: Evento 1 - intensidade superior a 50 mm/h, e Evento 2 – intensidade inferior a 14 mm/h. A avaliação dos modelos foi dada pelos coeficientes de determinação (R2), de Pearson (PR2) e de Nash-Sutcliffe (COE), sendo o último o mais eficiente. A MEUPS foi simulada com obtenção do comprimento de rampa (L) pelo método automático (Desmet e Govers, 1996) e manual (distância linear). As estimativas foram satisfatórias a muito boas (COE médio > 0,7) principalmente nos solos argilosos com predomínio das perdas, e com fator L manual. No WEPP, foram realizadas simulações pelo módulo vertente (software WEPP) e bacia (GeoWEPP – versão do WEPP em SIG). Em todas as simulações do WEPP vertente foram obtidos resultados insatisfatórios (COE < 0). No GeoWEPP, as estimativas dadas em classes de perda e deposição apresentaram classes coincidentes aos registros das parcelas, entre 20% e 90% em solos argilosos e entre 40% e 50% nos solos arenosos. As melhores estimativas ocorreram para chuvas de baixa intensidade, evidenciando a inadequação do modelo em eventos extremos e em condições tropicais. Ressalta-se que o período experimental representa um ano atípico de chuva, com baixos índices pluviométricos em comparação às médias anuais históricas. Considerando os valores superestimados do WEPP e GeoWEPP, apenas a MEUPS mostrou-se adequada como ferramenta para estudos de erosão hídrica, evidenciando a contribuição deste modelo na gestão do uso da terra e no planejamento de sistemas agrícolas e práticas conservacionistas.
The land use intensification becomes more and more evident due the growing of food production and supply to the human population. The application of inadequate practices to the multiple functions has shown the accelerated water erosion as a major degradation processes for this resource. In an effort to colaborate for soil conservation studies, this research aimed to evaluate the predictive models of erosion MUSLE – Modified Universal Soil Loss Equation (Williams, 1975) and WEPP – Water Erosion Prediction Project (Laflen, 1991) by comparing the estimated soil loss and empirical data from pins experimental plots. The variability of simulated parameters led the definition of two watersheds with different hydrossedimentological characteristics, watershed of stream Jacutinga (Rio Claro – SP/Brazil) and stream Monjolo Grande (Ipeúna – SP/Brazil) to assess the erosive behavior in soils derived from mudstones and sandstones, respectively. In the experimental period of June/2013 to August/2014, experimental plots of 1 m2 were monitored in different conditions of slope, topographic position, slope shape and vegetation cover - grazing, sugarcane, riparian vegetation and bare soil. In Lixisols and Cambisols clayey the losses registered were 0.018 to 0.066 ton/ha.year-1 and deposition between 0 and 0.026 ton/ha.year-1 , and in Quartzarenic Neosols and Lixisols of sandy texture, where dominated depositional process, between 0.004 and 0.085 ton/ha.year-1 , and the losses were 0.002 to 0.11 ton/ha.year-1 . The greatest losses are associated with the largest portion of fine sand and silt fractions, and weak aggregation by low levels of clay and organic matter. The highest percentage of vegetation cover was crucial for smaller losses, showing greater soil protection factor for direct plantation which in conventional tillage. The simulations were performed for the experimental year and specific rainfall events: Event 1 - intensity greater than 50 mm/h, and Event 2 - intensity less than 14 mm/h. The evaluation of the models was given by the coefficients of determination (R2 ), Pearson (PR2 ) and NashSutcliffe (COE), the latest being the most eficiente one. The MUSLE was simulated obtaining the ramp length (L) by the automatic method (Desmet and Govers, 1996) and manual (linear distance). Estimates were satisfactory to very good (average COE> 0.7) especially in clay soils with predominance of soil losses, and manual factor L. For WEPP, the simulations were performed by hill module (WEPP software) and watershed (GeoWEPP – GIS version for WEPP). In all aspects, WEPP simulations have obtained unsatisfactory results (COE < 0). In GeoWEPP, the estimatives given in loss and deposition classes showed coincidence of classes and records of the plots between 20% and 90% in clayey soils, and between 40% and 50% in sandy soils. The best estimates occurred for low intensity rains, pointing out the inadequacy of this model in extreme events and in tropical conditions. It is emphasized that the rain in the experimental period atypical, with low rainfall compared to historical annual averages. Considering the overestimated values of WEPP and GeoWEPP, only MUSLE was adequate as a tool to water erosion studies, especially for the contribution of this model in land use management, in the planning of agricultural systems and conservation practices.
The land use intensification becomes more and more evident due the growing of food production and supply to the human population. The application of inadequate practices to the multiple functions has shown the accelerated water erosion as a major degradation processes for this resource. In an effort to colaborate for soil conservation studies, this research aimed to evaluate the predictive models of erosion MUSLE – Modified Universal Soil Loss Equation (Williams, 1975) and WEPP – Water Erosion Prediction Project (Laflen, 1991) by comparing the estimated soil loss and empirical data from pins experimental plots. The variability of simulated parameters led the definition of two watersheds with different hydrossedimentological characteristics, watershed of stream Jacutinga (Rio Claro – SP/Brazil) and stream Monjolo Grande (Ipeúna – SP/Brazil) to assess the erosive behavior in soils derived from mudstones and sandstones, respectively. In the experimental period of June/2013 to August/2014, experimental plots of 1 m2 were monitored in different conditions of slope, topographic position, slope shape and vegetation cover - grazing, sugarcane, riparian vegetation and bare soil. In Lixisols and Cambisols clayey the losses registered were 0.018 to 0.066 ton/ha.year-1 and deposition between 0 and 0.026 ton/ha.year-1 , and in Quartzarenic Neosols and Lixisols of sandy texture, where dominated depositional process, between 0.004 and 0.085 ton/ha.year-1 , and the losses were 0.002 to 0.11 ton/ha.year-1 . The greatest losses are associated with the largest portion of fine sand and silt fractions, and weak aggregation by low levels of clay and organic matter. The highest percentage of vegetation cover was crucial for smaller losses, showing greater soil protection factor for direct plantation which in conventional tillage. The simulations were performed for the experimental year and specific rainfall events: Event 1 - intensity greater than 50 mm/h, and Event 2 - intensity less than 14 mm/h. The evaluation of the models was given by the coefficients of determination (R2 ), Pearson (PR2 ) and NashSutcliffe (COE), the latest being the most eficiente one. The MUSLE was simulated obtaining the ramp length (L) by the automatic method (Desmet and Govers, 1996) and manual (linear distance). Estimates were satisfactory to very good (average COE> 0.7) especially in clay soils with predominance of soil losses, and manual factor L. For WEPP, the simulations were performed by hill module (WEPP software) and watershed (GeoWEPP – GIS version for WEPP). In all aspects, WEPP simulations have obtained unsatisfactory results (COE < 0). In GeoWEPP, the estimatives given in loss and deposition classes showed coincidence of classes and records of the plots between 20% and 90% in clayey soils, and between 40% and 50% in sandy soils. The best estimates occurred for low intensity rains, pointing out the inadequacy of this model in extreme events and in tropical conditions. It is emphasized that the rain in the experimental period atypical, with low rainfall compared to historical annual averages. Considering the overestimated values of WEPP and GeoWEPP, only MUSLE was adequate as a tool to water erosion studies, especially for the contribution of this model in land use management, in the planning of agricultural systems and conservation practices.
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Palavras-chave
MEUPS, WEPP, Erosão hídrica laminar, Modelagem ambiental, Parcelas experimentais, Water erosion, Environmental modeling, MUSLE, Experimental plots