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An investigation of rainfall characteristics, erosivity and soil erosion on Round Island, MauritiusCalvert, Darren Rhett 02 1900 (has links)
Round Island is a small (208 ha) islet of volcanic origin located 22.5 km north east of mainland Mauritius and has been classified as a nature reserve since 1957. Two sites were chosen for the installation of environmental monitoring equipment. A series of Gerlach troughs were installed to capture surface sediment transported by runoff, which were used to document sediment yields and determine the particle size distribution. Overall, rainfall and erosivity on Round Island is far less, when compared to mainland Mauritius. However, erosivity from Round Island (2,314.76 MJ.mm.ha-1.h-1.yr-1) is slightly above the global average of 2,190 MJ.mm.ha-1.h-1.yr-1. In terms of sediment transport, the annual sediment movement rates for Round Island were established during this study (0.1248 t.ha-1.yr-1) and were found to be considerably lower than Mauritius (10 t.ha-1.yr-1), as well as other tropical island such as Kauai (0.86 t.ha-1.yr-1) and O’ahu (0.6 t.ha-1.yr-1). Thus, although the estimated rates of soil erosion are very low for humid tropical regions, these rates only reflect the contemporary environmental conditions and cognisance of the landscape history should be incorporated into assessments of soil erosion / Geography / M. Sc. (Geography)
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MONITORAMENTO E MODELAGEM MATEMÁTICA DOS PROCESSOS HIDROSSEDIMENTOLÓGICOS EM BACIAS HIDROGRÁFICAS FLORESTAIS NO SUL DO BRASIL / MONITORING AND MODELING OF HIDROSSEDIMENTOLOGIC PROCESSES IN FORESTRY WATERSHED IN SOUTHERN BRAZILRodrigues, Miriam Fernanda 31 October 2011 (has links)
The effect of eucalyptus forests in hidrossedimentologic processes has been little explored
by the scientific community, which results in a database containing information related to
these incipient effects, especially at the watershed scale. The monitoring and the
mathematical modeling are recognized as effective tools of science to supply the lack of
information, particularly in natural resource management, in the representation and
prediction of these processes. In this sense, the aim of this study was to describe the
monitoring data to assess effects of eucalyptus cultivation in the hidrossedimentological
processes, to calibrate the input parameters and to verify the potential application of the
Limburg Soil Erosion Model (LISEM) in the representation of watershed hydrological
processes embedded with forest cover. The study was conducted in two forest watersheds
located in Eldorado do Sul - RS, and the watershed has an area of 94.46 ha and drainage
sub-watershed, which is embedded in the amount and terms of the watershed, has a
drainage area of 38.86 ha. The hidrossedimentometrical monitoring began in February 2011
and was conducted within the limits of the watershed in two automatic sections, composed of
linigraph, turbidimeters and pluviographs. This work has included monitoring over a period of
six months from 02/16/2011 to 08/15/2011. The sediment yield was determined by
multiplying the data of sediment concentration and flow. The model LISEM was calibrated
from six different rain events. The model input parameters were obtained through surveys
conducted in the watershed and literature data. To evaluate the model ability in representing
the hydrological processes hydrographs measured in the watershed exutory were used. The
monitoring results demonstrated that periods with higher rainfall volume presented a
significant increase in peak flows in relation to the driest intervals, as well as an increase in
the suspended sediments concentration in the watershed and in the sub-watershed. The
events with greater rainfall intensity demonstrated that the smallest drainage area of the subwatershed
generated faster answers in flow and sediment concentration. For the watershed,
in most events occurred flood wave attenuation with least steeply sloping and lowest
hydrograph peaks than the sub-watershed. Specifically, the sediment yield was 38.41 and
33.65 t km-2, during the six months of monitoring for the watershed and for the subwatershed,
respectively. The magnitude of sediment yield was 0.77 t ha-1 yr-1 for the
watershed and 0.67 t ha-1 yr-1 for the sub-watershed. The LISEM model was able to
reproduce adequately the peak flow and direct runoff for the six events used for calibration.
On the other hand, the peak time and shape of the hydrograph did not have adequate fit. / O efeito das florestas de eucalipto nos processos hidrossedimentológicos tem sido pouco
explorado pela comunidade científica, o que resulta em banco de dados contendo informações
incipientes relacionadas a esses efeitos, principalmente na escala de bacias. O monitoramento e
a modelagem matemática são reconhecidos como eficientes ferramentas científicas para suprir a
carência de informações, principalmente na gestão dos recursos naturais, na representação e na
predição desses processos. Nesse sentido, objetivou-se com este estudo, descrever os dados
do monitoramento, avaliar os efeitos dos cultivos de eucalipto nos processos
hidrossedimentológicos, calibrar os parâmetros de entrada e verificar o potencial de aplicação do
modelo Limburg Soil Erosion Model (LISEM) na representação dos processos hidrológicos de
bacias hidrográficas embutidas, com cobertura florestal. O estudo foi desenvolvido em duas
bacias hidrográficas florestais situadas em Eldorado do Sul RS, sendo que a bacia possui área
de drenagem de 94,46 ha e a sub-bacia, que se encontra à montante e embutida em relação à
bacia, possui área de drenagem de 38,86 ha. O monitoramento hidrossedimentométrico teve
início em fevereiro de 2011 e foi realizado no exutório das bacias, em duas seções automáticas,
compostas de linígrafos, turbidímetros e pluviógrafos. O presente trabalho contemplou o
monitoramento durante um período de seis meses, de 16/02/2011 a 15/08/2011. Os resultados
do monitoramento demonstram que os períodos com maior volume de precipitação
apresentaram aumento significativo nos picos de vazão em relação aos intervalos mais secos,
assim como aumento na concentração de sedimentos em suspensão, para a bacia e para a subbacia.
Os eventos com maior intensidade máxima de precipitação demonstraram que a pequena
área de drenagem e o relevo mais acentuado da sub-bacia geraram respostas rápidas na vazão
e concentração de sedimentos. Para a bacia hidrográfica, na maioria dos eventos, ocorreu
amortização da onda de cheia com hidrogramas menos íngremes e ocorrência após o pico de
vazão da sub-bacia. A produção de sedimentos foi de 38,41 e 33,65 Mg km-2, durante os seis
meses de monitoramento para a bacia e para a sub-bacia, respectivamente. O modelo LISEM foi
calibrado a partir de seis eventos de chuva. Os parâmetros de entrada utilizados para o modelo
foram obtidos por meio de levantamentos realizados na bacia e de dados da literatura. Para
avaliar a capacidade do modelo em representar os processos hidrológicos, foram utilizados
hidrogramas medidos no exutório da bacia. A análise estatística aplicada foi o teste BIAS (Erro
(%)) para os parâmetros vazão de pico, escoamento superficial direto e tempo de pico. Para
avaliar a eficiência do modelo em reproduzir adequadamente o formato dos hidrogramas, foi
utilizado o Coeficiente de eficiência Nash-Sutcliffe (COE) para os seis eventos utilizados na
calibração. O modelo LISEM foi capaz de reproduzir adequadamente a vazão de pico e o
escoamento superficial direto para os seis eventos utilizados na calibração, indicado pelos
baixos erros percentuais. Por outro lado, o tempo de pico e a forma do hidrograma não
apresentaram ajuste adequado, indicado pelos elevados erros e valores negativos para o erro e
para o COE, respectivamente.
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Analysing the Interactions between Water-induced Soil Erosion and Shallow LandslidesAcharya, Govind January 2011 (has links)
Water-induced soil erosion and shallow landslides interact with each other and need to be studied in an integrated approach to understand hillslope sediment yields. The principal aim of this thesis was to study and model soil erosion and shallow landslides in an integrated way. The thesis presents results from laboratory and catchment-scale studies and modelling.
A laboratory flume under a rainfall simulator was used for shallow landslide and soil erosion experiments using sandy and silty loess soils. In the experiments, landslide initiation, retrogressions and slip surface depths were measured and monitored directly or by using video camera recordings. Sediment and runoff were collected from the flume outlet every minute during landslides and every 10 minutes before and after landslides. Changes in the soil slope, after landslides, were recorded. Initially, six experiments including two repetitions were conducted using sandy soils at a 30º and 10º compound slope configuration, but with different soil profile depths. The experimental results showed that total and landslide-driven sediment yields were affected by the original soil profile depth; the greater the depth, the higher the sediment yield. Later, twelve other experiments were conducted on different slopes using silty loess soils. The experimental observations were used to validate an integrated modelling approach which includes WEPP for runoff and soil erosion modelling, a slope stability model for simulating shallow landslides, and a simple soil redistribution model for runout distance prediction. The model predictions were in good alignment with the observations. In all (sandy and silty loess) experiments, peak sediment discharges were related to the landslide events, proximity to the outlet and landslide volume. The post-failure soil erosion rate decreased as a function of changes in the slope profile.
The GeoWEPP-SLIP modelling approach was proposed for catchment-scale modelling. The approach simulates soil erosion using the Hillslope and Flowpath methods in WEPP, predicts shallow landslides using a slope stability model coupled with the WEPP’s hillslope hydrology and finally uses a simple rule-based soil redistribution model to predict runout distance and post-failure topography. A case study application of the model to the Bowenvale research catchment (300 ha) showed that the model predictions were in good agreement with the observed values. However, the Hillslope method over-predicted the outlet sediment yield due to the computational weighting involved in the method. The Hillslope method predicted consistent values of sediment yield and soil erosion regardless to the changes in topography and land-cover in the post-failure scenarios. The Flowpath method, on the other hand, predicted higher values of sediment yield in the post-failure vegetation removal scenario. The effects of DEM resolution on the approach were evaluated using four different resolutions. Statistical analyses for all methods and resolutions were performed by comparing the predicted versus measured runoff and sediment yield from the catchment outlet and the spatial distribution of shallow landslides. Results showed that changes in resolution did not significantly alter the sediment yield and runoff between the pre- and post-failure scenarios at the catchment outlet using the Hillslope method. However, the Flowpath method predicted higher hillslope sediment yields at a coarser resolution level. Similarly, larger landslide areas and volumes were predicted for coarser resolutions whereas deposition volume decreased with the increase in grid-cell size due to changes in slope and flowpath distributions. The research conducted in the laboratory and catchment presented in this thesis helped understand the interactions between shallow landslides and soil erosion in an integrated approach.
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A numerical model of watershed erosion and sediment yieldLopes, Vicente Lucio,1952- January 1987 (has links)
A physically based, distributed parameter, event oriented, nonlinear, numerical model of watershed response is developed to accommodate the spatial changes in topography, surface roughness, soil properties, concentrated flow patterns and geometry, and land use conditions. The Green and Ampt equation with the ponding time calculation for an unsteady rain is used to compute rainfall excess rates. The kinematic wave equations are used to describe the unsteady one-dimensional overland and channel flow. The unsteady and spatially varying erosion/deposition process on hillslopes and channel systems is described dynamically using simultaneous rates of sediment entrainment and deposition rather than the conventional approach using steady state sediment transport functions. To apply the model the watershed is represented by a simplified geometry consisting of discrete overland flow planes and channel elements. Each plane or channel is characterized by a length, width, and a roughness parameter. For channel elements, a cross-section geometry is also needed. A modular computer program called WESP (Watershed Erosion Simulation Program) is developed to provide the vehicle for performing the computer simulations. Rainfall simulator plots are used to estimate infiltration parameters, hydraulic roughness, and soil erodibility parameters for raindrop impact and overland flow. The ability of the model to simulate watershed response (hydrograph and sedigraph) to a variety of rainfall inputs and antecedent soil moisture conditions is verified using data collected on two small watersheds. The good agreement between the simulated watershed response and the observed watershed response indicates that the governing equations, initial and upper boundary conditions, and structural framework of the model can describe satisfactorily the physical processes controlling watershed response.
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Evaluating soil erodibility parameters with mini-JET under various soil moisture conditionsNguyen, Gia Huynh Truong January 1900 (has links)
Master of Science / Department of Biological & Agricultural Engineering / Aleksey Y. Sheshukov / Soil erosion is one of the main reasons for agricultural land degradation in the world. Losses of land because of high soil erosion rates and rapidly expanding population result in significant reduction of cultivated land area per capita, and shortage of food on the global scale. Soil erosion can be a major source of sediment in the aquatic systems leading to reduction of organism population and poor water quality. Many factors affect soil erodibility, such as, soil properties, rainfall, topographic features, land use, and management practices, among others. The impacts of soil moisture content, however, are not well understood and. therefore, the primary goal of this study was to quantify two soil erodibility parameters, the erodibility coefficient and critical shear stress, under different soil moisture conditions using the jet erosion test (JET).
The JET test uses the apparatus (called mini-JET) that creates an impinging jet of water into the soil and records the resulting scour depth over time. The scour depth time series are then fitted into a non-linear soil erosion equation, yielding the sought values of erodibility parameters. For this study, more than 40 soil samples were collected from several sites in Kansas, processed, and prepared to conduct JET tests in the lab setting. The effects of tillage and soil moisture content were of interest to this study. The results showed varied effects of soil type and sample soil moisture condition on the scour depth development and parameters sensitivity. The critical shear stress decreased and the erodibility coefficient increased with the increase of initial moisture content for clay loam soil, while critical shear stress did not change for sandy loam soil. The study also revealed higher erosive properties of soil collected from the tilled field compared to the no-till field.
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Estimation of agricultural soil erosion and surface water quality trends in the Cheney Lake watershedBontrager, Austin January 1900 (has links)
Master of Science / Department of Agronomy / Nathan Nelson / Phosphorus and sediment runoff are the primary cause of eutrophication in Cheney Lake, the primary water source for Wichita, Kansas. Best Management Practices (BMPs) such as no-till farming practices and nutrient management can be implemented to reduce phosphorus runoff on high-risk agricultural fields. Past efforts have established BMP use in this watershed, although the effectiveness of these efforts has not been evaluated. The goals of this project were to identify any existing water quality trends in the Cheney Lake watershed, estimate the current distribution of erosion in the watershed, and evaluate the placement of BMPs with regards to field-scale erosion risk. Parametric, multi-linear regression and non-parametric, seasonal Mann-Kendall analyses were used to identify trends in the Total Suspended Solids (TSS) and Total Phosphorus (TP) of grab samples from the North Fork Ninnescah River. A Geographic Information System (GIS) model based on the Revised Universal Soil Loss Equation (RUSLE) was used to estimate watershed-scale erosion, prioritize agricultural land for BMP placement, and evaluate existing placement of BMPs within the Cheney Lake watershed. No detectible trends were identified in the water quality data due to stream variability, frequency of sampling, or absence of actual improvement in water quality. Additional sampling must be done to detect any trends in the future. BMPs were implemented on 13% of prioritized field area, and 11% of non-prioritized field area. Conservation Reserve Program (CRP) fields were placed on 14% of prioritized field area, and 5% of non-prioritized field area. No-till practices were implemented on 13% of prioritized field area, and 18% of non-prioritized field area. The top 20% eroding fields were identified given current conditions, and account for approximately 56% of the watershed-wide erosion. The GIS method has demonstrated utility in evaluating past erosion control measures for the watershed and in informing future decisions concerning BMP placement.
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Studie a posouzení protierozních opatření v katastrálním území ZábornáBŮŽKOVÁ, Jana January 2019 (has links)
The diploma thesis deals with an assessment of cadastral territory, which is going through a complex land consolidation. For these purposes, the cadastral area Záborná, that is located in the Vysočina Region, was selected. The main objective of this work is to compare the current state of the territory, in terms of erosion, with the area where the erosion control measures were proposed. Erosion will be calculated using by Wischmeier-Smith's universal soil loss equation. In this cadastral area, it will be necessary to assess in terms of climate, geology and hydrology.
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Análise da redistribuição do \"fallout\" do 137Cs na avaliação da erosão e deposição de sedimentos em sistemas de manejo de solo sob Cerrado / Erosion and sediment deposition evaluation on slopes under different tillage systems in the Cerrado region using the 137Cs fallout techniqueArthur, Robson Clayton Jacques 31 March 2010 (has links)
No Brasil, a expansão das áreas agrícolas é o fator mais impactante da agricultura sobre os recursos naturais. Com a crescente ocupação do Cerrado pela agricultura, uma série de problemas ambientais decorrentes do desmatamento como a erosão e a compactação do solo estão surgindo causando transformações radicais na paisagem natural pela retirada de quase toda sua vegetação nativa. O sistema de plantio convencional (SPC) tem sido considerado uma forma de manejo inadequado pelas suas conseqüências freqüentemente irremediáveis de compactação e perdas de solo, ao passo que o sistema de plantio direto (SPD) possibilita a manutenção das condições do solo mais próximas ao ambiente natural, reduzindo assim as taxas de erosão hídrica. Este trabalho teve por objetivo avaliar a eficiência da mata ripária na retenção dos sedimentos originados por três sistemas de preparo de solo através da técnica da análise da redistribuição do fallout do 137Cs, da Equação Universal de Perdas de solo (EUPS) e de alguns parâmetros físicos e químicos indicadores das condições estruturais do solo, em Goiatuba e Jandaia-GO. Nas três áreas estudadas, com auxilio de um trado tipo caneca, foram tomados perfis de solo em três camadas de 20 cm (0-20, 20-40 e 40-60 cm) em pontos distintos localizados ao longo de transeções lineares no sentido do declive até a mata ciliar localizada a jusante das áreas de estudo. Nas matas ciliares de cada área de estudo foram abertas trincheiras e amostras de solo coletadas para avaliação da atividade de 137Cs e dos parâmetros físicos e químicos dos solos. As amostras de solo coletadas nas transeções e trincheiras (TFSA) foram analisadas quanto à atividade de 137Cs em um detector de raios gama (GEM-20180P, EG&ORTEC) acoplado a um analisador multicanal. Na comparação das médias usou-se o teste de Tukey ao nível de 5% de significância. Os resultados obtidos indicaram que os três sistemas de manejo do solo apresentaram elevadas taxas de erosão e deposição de sedimentos e as matas ciliares à jusante das áreas sob SPC, SPD e pastagem, receberam grandes quantidades de sedimentos. Entre essas, somente a mata ciliar da área de SPC foi capaz de reter os sedimentos com eficiência. As características distintas dos três locais de estudo sugerem que a eficiência da mata ciliar na retenção dos sedimentos gerados na área agrícola e na pastagem, dependente do comprimento e da declividade das vertentes e da largura da mata ciliar. Quanto aos parâmetros físicos avaliados, observou-se que a pastagem e o SPD são os sistemas de manejo de solo que apresentaram melhores condições de preservação do solo em relação ao SPC. Os sistemas de manejo do solo provocaram alterações nos parâmetros físicos e químicos, comparados com a mata ciliar, destacando-se a menor resistência à penetração sob SPC e maior no SPD e pastagem; diminuição na agregação dos solos sob SPC e SPD e aumento sob pastagem e decréscimo nos teores de matéria orgânica e cálcio sob todos os sistemas de manejo / In Brazil, the expansion of agricultural areas causes several problems on natural resources. With the increasing occupation of the Cerrado region by agriculture, a series of environmental problems like deforestation, soil erosion and soil compaction are appearing and causing radical transformations in the natural landscape due to removing almost all native vegetation. The conventional tillage system (CTS) is considered an inadequate form of soil management for its frequently irremediable consequences of soil compaction and soil erosion, and the no till system (NTS) makes the maintenance of the soil conditions possible, leving them close to the natural environment, thus reducing rates of soil erosion. The objective of this work was to evaluate the efficiency of riparian forests in the retention of sediments originated for three different tillage systems, through the fallout 137Cs redistribution technique, the Universal Soil Loss Equation (USLE) and some physical and chemical parameters that indicate the structural conditions of the soils of Goiatuba and Jandaia-GO. In the three areas, soil profiles were collected in three layers of 20 cm (0-20, 20-40 and 40-60 cm) at distinct points located along linear transects in the direction of the maximum slope until the riparian forest. In the riparian forest of each area, trenches were opened and soil was sampled to evaluate the activity of 137Cs and the physical and chemical parameters of soil. Detection of the activity of 137Cs was made with a gamma ray detector model (GEM-20180P, EG& ORTEC) connected to a multichannel analyzer. The comparison of averages was made using the Tukey test at 5% level of significance. The results indicated that, the three soil tillage systems presented high rates of soil erosion and deposition of sediments and the riparian forest of the areas under CTS, NTS and pasture, located downstream received great amounts of sediments, and that only the riparian forest of CTS was capable to trap the sediments with efficiency. The distinct characteristics of the three studied areas suggest that the efficiency of the riparian forest to retain the sediments generated in the agricultural and pasture areas, depends on the length and the slope of the transects, and of the width of riparian forest. Through the physical and chemical parameters it was observed that the pasture and the NTS were the soil tillage systems that presented the best conditions of soil preservation in relation to the CTS. The tree soil tillage systems caused alterations in the physical and chemical parameters, compared with the riparian forest, mainly by a lower resistance to penetration under CTS and a greater resistance in the NTS and pasture systems; reduction in soil aggregation under CTS and NTS and an increase under pasture, and decrease of organic matter and calcium under all tillage systems
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Förorenade markers påverkan på grundvatten vid ökad erosion till följd av ett förändrat klimat : Kartläggning av erosionsrisk för MIFO – riskklass 1 och 2 i anslutning till Umeälven i Umeå kommunPersson, Matilda January 2019 (has links)
The purpose of this study was to investigate how increasing erosion, caused by increasing precipitation due to climate change, could have an effect on groundwater. Four maps were created using ArcGIS 10.4.1 (ArcMap). The maps include information from climate scenario RCP 8.5 referring to a baseline period from 1961 to 1990, flowage by natural casual factors like water storage or shifting rainfalls, and the geographical representation showing diversity of soil types within Umeå municipality. Each map was analyzed with the risk classification method referred to as - Methods for Inventories of Contaminated Site (MIFO). The study was limited to sites with objects of risk class 1 and 2. The results of the study showed that changes in climate can have a direct impact on precipitation in Västerbotten (Umeå municipality). With increased precipitation the risk of flooding increases in watercourses, which in this study refers to Umeälven. The result showed a high variability of soil erosion in areas near Umeälven where groundwater storage for water supplies were found. Three objects with preliminary class 2 were identified in this area. Other studies have shown that increasing rainfall may, affect soil stability and cause increased soil erosion, and therefore increase the mobility of metals in the soil. The conclusion of this study is that increased precipitation due to a changing climate could cause an increase soil erosion and landslides. This could increase mobility and erosion of soil contaminated with heavy metals and potentially contaminate important areas downstream Umeälven.
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A Erodibilidade do solo em sistema de plantio direto aumenta com o tempo de manejoPereira, Adalberto Alves 23 June 2017 (has links)
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Previous issue date: 2017-06-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Nos últimos anos tem-se ampliado as discussões em torno da eficiência do sistema de plantio direto na conservação do solo e da água, principalmente em áreas com longos períodos de uso contínuo. Desta forma, o objetivo deste trabalho foi testar se a erodibilidade do solo aumenta em sistema de plantio direto manejado por longos períodos de tempo. Este trabalho foi desenvolvido em quatro áreas agrícolas cultivadas sob sistema de plantio direto com diferentes tempos de manejo (6; 17; 24 e 38 anos) e uma área de floresta (controle) localizadas na região Centro-Sul do Paraná, microrregião de Guarapuava. A avaliação da erodibilidade dos solos foi realizada sob chuva simulada em laboratório utilizando amostras indeformadas de solo, cada amostra foi submetida a duas simulações de chuva, uma com solo em umidade de campo e outra com solo saturado. Durantes as simulações foram coletados a água e os sedimentos transportados pelo efeito salpico e pelo escoamento superficial e subsuperficial. A determinação do percentual de agregados da massa total de solo e de macroagregados foi realizada por via úmida. Para isto, foram coletadas amostras em cinco pontos (escolhidos aleatoriamente) no topo do solo (0,0-0,1 m) em cada área. A estabilidade de agregados foi determinada através do diâmetro médio ponderado, diâmetro médio geométrico e índice de estabilidade de agregados. As áreas apresentaram baixo coeficiente de escoamento superficial. O escoamento superficial não apresentou diferença significativa entre as áreas de Floresta, Plantio direto com 6 anos, Plantio direto com 17 anos e plantio direto com 24 anos de manejo, na simulação em umidade de campo. Com o solo saturado não houve diferença significativa entre as áreas, mas com tendência de aumento do escoamento com o tempo de manejo. Inversamente ao escoamento superficial, o escoamento subsuperficial (infiltração) apresentou redução com o tempo de manejo. A perda total de solo apresentou elevação de acordo com o tempo de manejo em ambas as repetições. A área Plantio direto com 38 anos de manejo foi a única a demonstrar diferença em relação às demais áreas manejadas e a floresta. Da perda de solo total mais de 80% foi representada pelo salpico em todas as parcelas e repetições, a perda por escoamento superficial foi inferior a 5%. Os indicadores de agregação da massa total de solo não apresentaram diferença significativa entre as diferentes áreas avaliadas. Quando se avalia o índice de estabilidade de agregados por classe de macroagregado, observa-se que as classes de 4-8 mm e 2-4 mm são os que sofrem maior efeito e melhor representam a degradação do SPD após longo período de manejo. Os macroagregados apresentaram redução do carbono orgânico relacionado com o tempo de manejo. observou-se correlação do índice de estabilidade de macroagregados com as perdas de solo em pelo menos uma das simulações (umidade de campo e/ou umidade saturada), principalmente nas classes com tamanho superior a 2 mm. Mesmo o sistema de plantio direto sendo considerado um sistema conservacionista, e apresentando vantagens em relação a outros sistemas de manejo, este apresenta degradação das propriedades físicas após longo período de manejo (>24 anos), evidenciado pela redução da estabilidade de macroagregados e do teor de carbono orgânico, assim como aumento das taxas de perda de solo. / In recent years, it to discussions the efficiency of the no tillage system in soil and water conservation has been expanded, especially in areas with long periods of continuous use. In this way, the objective of this work was to test if the soil erodibility increases in no-till of long-term. This work was developed in four agricultural areas under no-tillage system with different management times (6; 17; 24 and 38 years) and forest area located in the Centro-Sul region of Paraná, Guarapuava microregion. The soil erodibility was performed with laboratory rainfall simulations using undisturbed soil samples, and each sample was submitted to two rain simulations, one in soil moisture field capacity and the other in saturated soil. During the simulation, the water and the sediments transported by the splash effect and the surface and subsurface flow were collected. The stability of aggregates of the total soil mass and macroaggregates was performed by wet method. For this, samples were collected at five points (randomly chosen) at the top of the soil (0.0-0.1 m) in each area. The stability of aggregates was determined through the weighted average diameter, geometric mean diameter and aggregate stability index. The areas presented low coefficient of surface runoff. The runoff showed no significant difference between the areas of forest, no-tillage 6 years, no-tillage 17 years and no-tillage 24 years, in simulation with field moisture. With the saturated soil there was no significant difference between the areas, but with tendency to increase the runoff with the management time. Conversely to the surface runoff, the subsurface flow (infiltration) presented reduction with the management time. The soil loss presented elevation according to the management time in both repetitions. The no-tillage 38 years area was the only one to show difference in relation to the other managed areas and the forest. Of the soil loss, over 80% was represented by the splash in all plots and repetitions, the loss by surface runoff was less than 5%. The aggregation indicators of the total soil mass did not present a significant difference between the different evaluated areas. When evaluating the aggregate stability index by class of macroaggregate, it is observed that the class of 4-8 mm and 2-4 mm are the ones that suffer the greatest effect and better represent the degradation of the no-tillage after a long period of management. The macroaggregates presented reduction of organic carbon related to the time of management. It was observed a correlation of stability index of macroaggregates with the soil losses in at least one of the simulations (field moisture and / or saturated moisture), especially in class with a size greater than 2 mm. Even the no-tillage system being considered a conservationist system, and presenting advantages over other management systems, it presents degradation of the physical properties after a long period of management (> 24 years), evidenced by the reduction of the stability of macroaggregates and the content of organic carbon, as well as increased rates of soil loss.
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