Equipamento inderbitzen modificado para simulação da erosão hídrica em amostras de solo indeformado

Several devices have been developed to assess soil losses by water erosion. However, they rarely assess the combined effects of raindrop impact and surface runoff together with vegetation cover on varying slopes. This study aimed to design and validate an equipment, on laboratory scale, to evaluate the effect of water erosion on undisturbed soil samples with and without plant cover, as well as to assess the kinetic energy of simulated rain and the resultant shear stress at varying runoff intensities. The equipment is composed of a rainfall simulator, an adjustable stand for different slopes and falling heights, and a runoff ramp for testing undisturbed soil samples measuring 15 x 20 x 40 cm (height, width, and length). In this study, the equipment simulated and evaluated the effect of precipitation and runoff on soil losses, allowing to obtain different values of the kinetic energy of precipitation and runoff. For a f low rate of 12 L min-1 and slope of 35%, the shear stress could reach up to 8 Pa. Furthermore, the equipment showed the effect of vegetation cover and slope on soil losses in different granulometric fractions (< 0.106 mm, 0.106 to 0.25 mm, 0.25 to 0.5 mm, 0.5 to 1.0 mm, 1.0 to 2.0 mm, and > 2.0 mm), revealing the potential of its use in several erosion studies on a laboratory scale.Diversos equipamentos foram desenvolvidos para a avaliação das perdas de solo por erosão hídrica. No entanto, raramente eles avaliam o efeito do impacto das gotas de chuva e do escoamento superficial em conjunto com a cobertura vegetal em diferentes declividades. Este estudo objetivou projetar e validar um equipamento, em escala de laboratório, para avaliar o efeito da erosão hídrica em amostras indeformadas de solo, bem como avaliar a velocidade de queda e tamanho das gotas de chuva simulada na superfície do solo e a intensidade do escoamento superficial em amostras com e sem cobertura vegetal. O equipamento é composto de um simulador de chuva, um suporte ajustável para diferentes declividades e alturas de queda e uma rampa de escoamento para testar amostras de solo indeformadas, com 15 x 20 x 40 cm (altura, largura e comprimento). Neste estudo, o equipamento simulou e avaliou o efeito da precipitação e do escoamento superficial nas perdas de solo, possibilitando a obtenção de diferentes valores de energia cinética de precipitação e escoamento. Para uma vazão de 12 L min-1 e inclinação de 35%, a tensão de cisalhamento pode chegar a 8 Pa. Além disso, o equipamento evidenciou o efeito da cobertura vegetal e da declividade nas perdas de solo em diferentes frações granulométricas (< 0,106 mm, 0,106 a 0,25 mm, 0,25 a 0,5 mm, 0,5 a 1,0 mm, 1,0 a 2,0 mm, e > 2,0 mm), demonstrando o potencial do seu uso em diversos estudos de erosão em escala de laboratório

Soil and water losses in eucalyptus plantation and natural forest and determination of the USLE factors at a pilot sub-basin in Rio Grande do Sul, Brazil

Monitoring water erosion and the factors that control soil and water loss are essential for soil conservation planning. The objective of this study was to evaluate soil and water losses by water erosion under natural rainfall in eucalyptus plantations established in 2001 (EF2), and 2004 (EF1), native forest (NF) and bare soil (BS), during the period of 2007 to 2012; and to determine the USLE factors: rain erosivity (R), erodibility (K) of a Red Argisol and the cover-management factor (C) for EF1, EF2 and NF at a pilot sub-basin, in Eldorado do Sul, RS, Brazil. The R factor was estimated by the EI30 index, using rainfall data from a gauging station located at the sub-basin. The soil and water losses were monitored in erosion plots, providing consistent data for the estimation of the K and C factors. The sub-basin presented an average erosivity of 4,228.52 MJ mm ha-1 h-1 yr-1. The average annual soil losses em EF1 and EF2 (0.81 e 0.12 Mg ha-1 year-1, respectively) were below of the limit of tolerance, 12.9 Mg ha-1 year-1. The percentage values of water loss relating to the total rainfall decreased annually, approaching the values observed at the NF. From the 5th year on after the implantation of the eucalyptus systems, soil losses values were similar to the ones from NF. The erodibility of the Red Argisol was of 0.0026 Mg ha h ha-1 MJ-1mm-1 and the C factor presented values of 0.121, 0.016 and 0.015 for EF1, EF2 and NF, respectively

Assessing sediment yield and streamflow with SWAT model in a small sub-basin of the Cantareira System

Hydro-sedimentological models might be useful tools for investigating the effectiveness of soil and water conservation practices. However, evaluating the usefulness of such models requires that predictions are tested against observational data and that uncertainty from model parameterization is addressed. Here we aimed to evaluate the capacity of the SWAT model to simulate monthly streamflow and sediment load in the Posses creek catchment (12 km2), Southeast Brazil. The SUFI-2 algorithm from SWAT-CUP was applied for calibration, testing, uncertainty, and sensitivity analysis. The model was calibrated and initially tested using discharge and sediment load data, which were measured at the catchment outlet. Additionally, we used soil loss measurements from erosion plots within the catchment as independent data for model evaluation. Average monthly streamflow simulations obtained satisfactory results, with Nash-Sutcliffe coefficient (NSE) values of 0.75 and 0.51 for the calibration and testing periods, respectively. Sediment load simulations also displayed satisfactory results for calibration (NSE = 0.65) and testing (NSE = 0.52). However, the comparison with independent plot data revealed that SWAT severely overestimated hillslope erosion rates and compensated it with high sediment channel deposition. Moreover, the model was not sensitive to the parameters used for calculating hillslope sediment yields. Therefore, it should be used with caution for evaluating the interactions between land use, soil erosion, and sediment delivery. We found that the commonly used outlet-based approach for model calibration and testing can lead to internal misrepresentations, and models can reproduce the right answer for the wrong reasons

CHARACTERIZATION OF HEADWATERS PEATS OF THE RIO ARAÇUAÍ, MINAS GERAIS STATE, BRAZIL

Peatlands are soil environments that accumulate water and organic carbon and function as records of paleo-environmental changes. The variability in the composition of organic matter is reflected in their morphological, physical, and chemical properties. The aim of this study was to characterize these properties in peatlands from the headwaters of the Rio Araçuaí (Araçuaí River) in different stages of preservation. Two cores from peatlands with different vegetation types (moist grassland and semideciduous seasonal forest) from the Rio Preto [Preto River] headwaters (conservation area) and the Córrego Cachoeira dos Borges [Cachoeira dos Borges stream] (disturbed area) were sampled. Both are tributaries of the Rio Araçuaí. Samples were taken from layers of 15 cm, and morphological, physical, and chemical analyses were performed. The 14C age and δ13C values were determined in three samples from each core and the vertical growth and organic carbon accumulation rates were estimated. Dendrograms were constructed for each peatland by hierarchical clustering of similar layers with data from 34 parameters. The headwater peatlands of the Rio Araçuaí have a predominance of organic material in an advanced stage of decomposition and their soils are classified as Typic Haplosaprists. The organic matter in the Histosols of the peatlands of the headwaters of the Rio Araçuaí shows marked differences with respect to its morphological, physical, and chemical composition, as it is influenced by the type of vegetation that colonizes it. The peat from the headwaters of the Córrego Cachoeira dos Borges is in a more advanced stage of degradation than the peat from the Rio Preto, which highlights the urgent need for protection of these ecosystems/soil environments

CHARACTERIZATION OF HEADWATERS PEATS OF THE RIO ARAÇUAÍ, MINAS GERAIS STATE, BRAZIL

Peatlands are soil environments that accumulate water and organic carbon and function as records of paleo-environmental changes. The variability in the composition of organic matter is reflected in their morphological, physical, and chemical properties. The aim of this study was to characterize these properties in peatlands from the headwaters of the Rio Araçuaí (Araçuaí River) in different stages of preservation. Two cores from peatlands with different vegetation types (moist grassland and semideciduous seasonal forest) from the Rio Preto [Preto River] headwaters (conservation area) and the Córrego Cachoeira dos Borges [Cachoeira dos Borges stream] (disturbed area) were sampled. Both are tributaries of the Rio Araçuaí. Samples were taken from layers of 15 cm, and morphological, physical, and chemical analyses were performed. The 14C age and δ13C values were determined in three samples from each core and the vertical growth and organic carbon accumulation rates were estimated. Dendrograms were constructed for each peatland by hierarchical clustering of similar layers with data from 34 parameters. The headwater peatlands of the Rio Araçuaí have a predominance of organic material in an advanced stage of decomposition and their soils are classified as Typic Haplosaprists. The organic matter in the Histosols of the peatlands of the headwaters of the Rio Araçuaí shows marked differences with respect to its morphological, physical, and chemical composition, as it is influenced by the type of vegetation that colonizes it. The peat from the headwaters of the Córrego Cachoeira dos Borges is in a more advanced stage of degradation than the peat from the Rio Preto, which highlights the urgent need for protection of these ecosystems/soil environments

Composição lignocelulósica e isótopica da vegetação e da matéria orgânica do solo de uma turfeira tropical: I - composição florística, fitomassa e acúmulo de carbono Lignocellulosic and isotopic composition of vegetation and soil organic matter of a tropical peat: I floristic composition, biomass and carbon stock

A matéria orgânica do solo (MOS) é um dos grandes reservatórios de carbono (C) da Terra e constitui um dos principais componentes do ciclo do C. Turfeiras, ambientes acumuladores de MOS, são produto da decomposição de vegetais, que se desenvolvem e se acumulam em ambientes saturados com água, sendo o estádio inicial da sequência de carbonificação. A fitomassa participa de forma marcante no ciclo global do C, armazenando em torno de 85 % de todo o C terrestre acima do solo. O tecido vegetal é composto principalmente por lignina, celulose e hemicelulose, constituindo até 85 % da biomassa seca. As plantas discriminam C de forma diferenciada, em razão de seu ciclo fotossintético (C3, C4 e CAM). As turfeiras da Serra do Espinhaço Meridional (SdEM-MG) são colonizadas por vegetação de Campo Limpo Úmido (CLU) e de Floresta Estacional Semidecidual (FES), onde ocorrem espécies dos ciclos fotossintéticos C3 e C4. Este trabalho objetivou avaliar a contribuição dessas duas fitofisionomias para o acúmulo de MOS, por meio da avaliação da fitomassa e da composição lignocelulósica e isotópica da vegetação e da MOS. A turfeira estudada localiza-se na SdEM e ocupa 81,75 ha. Para a estimativa da fitomassa do CLU e da FES, foram marcadas três parcelas de 0,5 x 0,5 m em cada fitofisionomia, onde todos os indivíduos da parcela foram cortados e armazenados. Para as análises isotópicas e lignocelulósicas da vegetação, identificaram-se as espécies dominantes em cada fitofisionomia. Amostras de solo foram coletadas em três locais representativos sob cada fitofisionomia, a cada 5 cm de profundidade, até 50 cm. Foram extraídas a celulose e a lignina das folhas das 15 espécies dominantes e das 60 amostras de turfeira para quantificação e determinação dos valores de &#948;13C e &#948;15N. Para datação da MOS, o 14C foi determinado em três profundidades, sob o CLU e a FES. A produção da fitomassa da FES foi muito superior à produção da do CLU. Os sinais isotópicos e a composição lignocelulósica da vegetação e da matéria orgânica do solo evidenciaram que a turfeira foi formada pela deposição de matéria orgânica da vegetação que a coloniza. O crescimento vertical e a taxa de acúmulo de C foram muito mais elevados sob a FES do que sob o CLU.<br>Soil organic matter (SOM) is one of the major reservoirs of carbon on Earth and is one of the key contributors to the carbon cycle. Peatlands are natural accumulators of organic matter commonly derived from decomposing plant residues in water-saturated environments, and represent an initial stage of a much longer pedogenic pathway leading to carbonification. The soil biomass markedly influences the global carbon cycle, accounting for approximately 85 % of all carbon on the Earth's surface. Plant tissues are mainly composed of lignin, cellulose and hemicelluloses, representing as much as 85 % of their dry biomass. Plants usually discriminate carbon differentially, according to their photosynthetic cycle (C3, C4 and CAM). The vegetation of the bogs in the southern domain of Serra do Espinhaço (SdEM; Brazil) consists mostly of moist grassland (CLU) and semideciduous forest (FES), with species of both C3 and C4 cycles. This study was designed to discriminate the contribution of these two vegetation types to the accumulation of soil organic matter by an analysis of the biomass and of the lignocellulosic and carbon isotopic composition and SOM. The studied peat is located in SdEM and covers an area of 81.75ha. Three 0.5x0.5m plots were marked per vegetation type, to delimit the sampling areas, for which biomass of CLU and FES were estimated. All plants per plot were cut and adequately stored to preserve as much of their fresh characteristics as possible. To characterize the isotopic and lignocellulosic composition of the vegetation, the species of each vegetation type were systematically identified according to their main botanic characteristics. Soil samples were collected at three representative sites under each vegetation type, at intervals of 5 cm, down to a depth of 50 cm. Cellulose and lignin were extracted from leaves of 15 dominant species and 60 peat samples, to quantify and determine the values of &#948;13C and &#948;15N. The 14C was determined at three depths under CLU and FES. The biomass production under FES was much higher than the biomass production under CLU. The isotopic signals and lignocellulosic composition of the vegetation and SOM confirmed that this peat was originated by the deposition of organic matter from the colonizing vegetation. The vertical growth and the carbon storage rates are much higher under FES than under CLU

Composição lignocelulósica e isótopica da vegetação e da matéria orgânica do solo de uma turfeira tropical: II - substâncias húmicas e processos de humificação Lignocellulosic and isotopic composition of vegetation and soil organic matter of a tropical peat: II humic substances and humification processes

Grande parte da matéria orgânica de Organossolos das turfeiras é composta por substâncias húmicas, formadas pela transformação de resíduos orgânicos pelos microrganismos do solo e pela polimerização dos compostos orgânicos em macromoléculas resistentes à degradação biológica. Os processos de humificação da matéria orgânica do solo (MOS) ainda são pouco compreendidos e o conhecimento sobre os precursores das substâncias húmicas é limitado, sendo apresentadas rotas diferentes para a formação dessas substâncias. Contudo, em todas as rotas, destaca-se a participação da lignina. Isótopos estáveis (13C, 15N) podem ser utilizados para rastrear processos de humificação da MOS, por meio da identificação de seus precursores. Este trabalho teve como objetivo avaliar comparativamente a composição isotópica da vegetação das fitofisionomias que colonizam uma turfeira tropical de altitude composta de Campo Limpo Úmido (CLU) e de Floresta Estacional Semidecidual (FES), em relação à composição isotópica das substâncias húmicas da MOS. A turfeira estudada ocupa 81,75 ha. Para as análises isotópicas e lignocelulósicas da vegetação, foram identificadas as espécies dominantes em cada fitofisionomia. Amostras de solo foram coletadas em três locais representativos sob cada fitofisionomia, a cada 5 cm de profundidade, até 50 cm. As substâncias húmicas dessas amostras foram fracionadas, assim como calculados os valores de &#948;13C e &#948;15N nas frações húmicas, respectivamente a partir da determinação dos isótopos estáveis 12C e 13C e 14N e 15N. Os teores de lignina e seus valores de &#948;13C são mais elevados na vegetação e MOS sob FES em relação à vegetação e MOS sob CLU. Os teores de humina são mais elevados entre as substâncias húmicas na MOS, sob as duas fitofisionomias; os de ácidos húmicos são mais elevados na MOS sob CLU, em relação à FES; e os de ácidos fúlvicos são mais elevados na MOS sob a FES, em relação ao CLU. O &#948;13C da lignina apresenta similaridade elevada em relação ao &#948;13C da humina, dos ácidos húmicos e dos ácidos fúlvicos. As variações na composição lignocelulósica das espécies que colonizam o CLU e a FES promovem diferenças nas taxas e nos produtos da humificação da MOS.<br>Much of the organic matter of a typical peat consists of humic substances, mainly formed via humification of organic residues, decomposed by soil microorganisms, and by the polymerization of organic compounds to functional macromolecules, which are normally more resistant to degradation. The fundamental pathways governing the humification of soil organic matter (SOM) are not well understood so far, and most available data about the identified chemical precursors of humic substances and the main chemical routes by which they are transformed in the peat environment are still poorly understood. What is clear is that all routes involve lignin as a chemical intermediate. Stable isotopes (&#948;13C, &#948;15N) can be used to trace humification processes of the soil organic matter (SOM), by identifying their precursors. The purpose of this study was to compare the isotopic composition of vegetation materials from the two bog vegetation types that colonize a tropical highland peatland: moist grassland (CLU) and semideciduous forest (FES), based on the isotopic composition of humic substances of SOM. The whole area of the studied peatland occupies 81.75 ha. To identify the isotopic and lignocellulosic vegetation composition, materials of the dominant species of each vegetation type were sampled. Soil samples were collected from three representative sites per vegetation type, at intervals of 5 cm from the surface down to a depth of 50 cm. The humic substances were isolated from these samples; signals of &#948;13C and &#948;15N were determined for the humic fractions. The lignin and and &#948;13C values were higher in vegetation and SOM under FES than in SOM under CLU. Humin contents were high in SOM under both vegetation types; the levels of humic acids were higher in SOM under CLU than in FES; fulvic acid contents were higher in SOM under FES than CLU. The 13C values for lignin were highly similar to those for humic acids and fulvic acids. Variations in the lignocellulosic composition of the species that colonize the CLU and FES promote different rates and SOM humification products