ABSTRACT 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.

ABSTRACT Through the lack or non-use of conservationist criteria for adequate land use and management, the scarcity of natural resources becomes ever more evident. This study aimed to analyze the origin of the sediments in the Posses catchment, municipality of Extrema, state of Minas Gerais, Brazil, throughout the fingerprinting technique and portable X-ray fluorescence. Samples from soils under agriculture, pasture, and roads; and from the subsoil of theses land uses were taken in a widespread and representative manner from the entire Posses catchment. Lag deposits and river bed sediment samples were collected downstream from the catchment outlet. A total of 45 geochemical elements were analyzed in the samples by a portable X-ray fluorescence device (pXRF). The outlier test, Kruskal-Wallis test, multivariate discriminant analysis, and a mixing model were used to estimate the contribution of each source in relation to the sediments that arrive at the mouth of the catchment. The elements selected as geochemical tracers were Sr, Al2O3, Ba, Rb, Ti, Fe, and Zn, which combined correctly discriminated 81 % of the sediment sources. The largest and smallest proportion of sediment from the Posses catchment outlet comes from rural roads and agriculture, respectively. The contribution of the subsoil was higher for lag deposits or lower for river bed sediments, than the pasture. There was a low degree of uncertainty (<8 %) for predictions made by the model employed. The types of use, selected as potential sediment sources in the Posses catchment, are adequately discriminated through the geochemical tracers quantified through the pXRF. The fingerprinting technique estimates that the contributions to outlet sediments are dominated by rural roads, following by subsoil or pasture (depending on the type of sediment evaluated) and by agriculture. The sediment sampling strategies used in this study provided similar results for the period studied. Our results showed the potential of the fingerprinting technique and the pXRF for use as tools by the program of Payment for Environmental Services in the monitoring of catchment areas.

ABSTRACT The use of Unmanned Aerial Vehicles (UAVs) and Structure from Motion (SfM) techniques can contribute to increase the accessibility, accuracy, and resolution of Digital Elevation Models (DEMs) used for soil erosion monitoring. This study aimed to evaluate the use of four DEMs obtained over a year to monitor erosion processes in an erosion-degraded area, with occurrence of rill and gully erosions, and its correlation with accumulated rainfall during the studied period. The DEMs of Geomorphic Change Detection (GCD) of horizontal and vertical resolutions of 0.10 and 0.06 m were obtained. It was possible to detect events of erosion and deposition volumes of the order of 2 m3, with a volumetric error of ∼50 %, in rills and gullies in the initial stage denominated R and GS-I, respectively. Events of the order of 100 m3, with a volumetric error around 14 % were found for advanced gullies, a segment denominated GS-II. In the three studied erosion situations, the deposition volume increased with the accumulated rainfall. The segments R and GS-I presented an inverse relationship between erosion volume and accumulated rainfall during the studied period. This behaviour can be explained by the dynamics of the deposition and erosion volumes during the erosion process. In the GS-II segment, erosion and deposition volumes were proportional and a direct relation with the cumulative rainfall over the studied period and a low percentage of volumetric error were found.

ABSTRACT Several soil conservation practices are used to reduce water erosion and ensure sustainable agriculture. An effective crop management practice is intercropping, in which two or more crops with different architectures and vegetative cycles are grown simultaneously in the same area. We hypothesized that intercropping of corn and jack-bean increases soil cover and reduce soil erosion by water in comparison to monocropping. The objective of this study was to evaluate the effects of different crop systems on soil cover and on soil erosion by water. Soil and water losses from a Typic Hapludox were measured under the following systems: corn cultivation (CO), jack-bean cultivation (JB), intercropping of corn and jack-bean (IC), and bare soil (BS), as a reference for maximum erosion rates. For each crop system, erosion plots with dimensions of 12 × 4 m were set up in the field on a 0.12 m m−1 slope gradient. The experiment was carried out under natural rainfall, over three crop seasons (November to March) from 2011 to 2014. The soil cover index of the systems was monitored during crop growth, and rainfall erosivity for the crop seasons was calculated according to the EI30 index to interpret soil and water losses. A set of linear mixed models was fitted to relate soil losses to rainfall erosivity, crop systems, and soil cover. The average rainfall erosivity in the study area was 6,132 MJ mm ha−1 h−1 per crop season. The results indicate that water losses are directly related to erosivity and are less influenced by soil cover and cultivation systems than the soil losses. A linear maximum value of the soil cover index was achieved 70 days after sowing. Intercropping exhibited greater soil cover than single crops. Total soil losses from the three seasons display the trend: BS > CO > JB > IC. The best fitted model of the linear mixed models indicates that soil loss responses are strongly correlated with rainfall erosivity and soil cover, which nullified the influence of the crop systems in the model.

RESUMO Identificar e classificar áreas quanto ao risco de perda de nutrientes são passos importantes para o manejo integrado de bacia hidrográfica. O objetivo deste estudo foi aplicar o modelo Índice P na bacia hidrográfica das Posses, Extrema-MG. O Índice P foi empregado sobre as condições atuais de uso da terra na bacia hidrográfica das Posses e na simulação de dois cenários: cenário 1, o fertilizante P foi aplicado para todos os usos, exceto para florestas nativas e, cenário 2, além do fertilizante P ser aplicado da mesma forma que no cenário 1, considerou-se que as Áreas de Proteção Ambiental referentes as matas ciliares e nascentes fossem totalmente restituídas. Considerando o uso atual, quase toda a bacia hidrográfica (91,4%) apresentou baixo risco de perda de P. O maior Índice de P foi associado a lavouras e plantações de eucalipto. No cenário 1, as pastagem apresentaram Índice P baixo (15,1%), médio (45,5%), alto (27,1%) e muito alto (12,3%). No cenário 2, as Áreas de Proteção Ambiental promoveram uma redução de 37,6% no risco de perda de P do cenário 1. Dessa forma, os resultados do modelo indicam que o reflorestamento de matas ciliares pode reduzir o risco de perdas de P no caso do aumento do uso de fertilizantes. O Índice P é uma potencial ferramenta para promoção do uso criterioso de fertilizantes e de práticas conservacionistas na bacia hidrográfica das Posses.

ABSTRACT Identifying and ranking nutrient loss risk areas are important steps towards integrated catchment management. This study aimed to apply the P index model at the Posses catchment, south of the state of Minas Gerais, Brazil. We applied the P index for the current land use at the Posses catchment and for two hypothetical scenarios: scenario 1, in which P fertilizer was applied to all land uses, except for native forests; and scenario 2, which considered the use of P fertilizer as in scenario 1, and that the Environmental Protection Areas referring to the riparian forests and springs were totally restored. Considering current land use, almost the whole catchment area (91.4%) displayed a low P loss risk. The highest P index was associated to croplands and eucalyptus plantations. Regarding scenario 1, areas under pasture fell into the low (15.1%), medium (45.5%), high (27.1%) and very high (12.3%) P index categories. Environmental Protection Areas on scenario 2 decreased the P loss risk from the scenario 1 in 37.6%. Hence, the model outputs indicate that the reforestation of buffer zones can decrease P loss risk in the case increasing use of P fertilizer. The P index model is a potential support tool to promote judicious use of fertilizers and conservation practices at the Posses catchment.

RESUMO Modelos de terreno de rios são usados para análise de mudanças geomorfológicas e para simulações hidrológicas. Estes modelos são interpolados a partir de pontos batimétricos. A batimetria fluvial é geralmente conduzida através de seções transversais, o que pode acarretar em uma malha amostral esparsa. Métodos híbridos de krigagem, como krigagem por regressão (KR) e co-krigagem (CK), empregam a correlação com preditores auxiliares, além da auto-correlação entre variáveis, na predição da variável resposta. Neste estudo, sugere-se que a distância ortogonal de um ponto até a linha de centro do talvegue de um rio pode ser usada como covariável para KR e CK. Considerando-se que a variabilidade da cota do leito do rio é abrupta transversalmente a direção do fluxo, espera-se que quanto maior a distância euclidiana de um ponto até o talvegue, maior será sua elevação. O objetivo deste estudo foi avaliar o uso da covariável proposta em métodos híbridos de krigagem para a predição espacial da topografia do leito de rios. Para tanto, foi realizada uma validação externa, em que seções transversais foram usadas para interpolação e dados levantados entre as seções consistiram na amostra de teste. Os resultados da KR e CK foram comparados aos da krigagem ordinária. A KR apresentou a menor REQM. No mapa resultante da KR, o talvegue foi preservado nas lacunas não amostradas entre as seções, enquanto os demais métodos subestimaram a profundidade do talvegue nestes espaços. Assim, conclui-se que a KR pode melhorar a predição espacial de dados batimétricos fluviais.

ABSTRACT Terrain models that represent riverbed topography are used for analyzing geomorphologic changes, calculating water storage capacity, and making hydrologic simulations. These models are generated by interpolating bathymetry points. River bathymetry is usually surveyed through cross-sections, which may lead to a sparse sampling pattern. Hybrid kriging methods, such as regression kriging (RK) and co-kriging (CK) employ the correlation with auxiliary predictors, as well as inter-variable correlation, to improve the predictions of the target variable. In this study, we use the orthogonal distance of a (x, y) point to the river centerline as a covariate for RK and CK. Given that riverbed elevation variability is abrupt transversely to the flow direction, it is expected that the greater the Euclidean distance of a point to the thalweg, the greater the bed elevation will be. The aim of this study was to evaluate if the use of the proposed covariate improves the spatial prediction of riverbed topography. In order to asses such premise, we perform an external validation. Transversal cross-sections are used to make the spatial predictions, and the point data surveyed between sections are used for testing. We compare the results from CK and RK to the ones obtained from ordinary kriging (OK). The validation indicates that RK yields the lowest RMSE among the interpolators. RK predictions represent the thalweg between cross-sections, whereas the other methods under-predict the river thalweg depth. Therefore, we conclude that RK provides a simple approach for enhancing the quality of the spatial prediction from sparse bathymetry data.

RESUMO O monitoramento da erosão hídrica e o conhecimento dos fatores que causam perdas de solo e água são essenciais para o planejamento conservacionista do solo. Objetivou-se com esse trabalho avaliar as perdas de solo e água por erosão hídrica, sob chuva natural, em plantios de eucalipto estabelecidos em 2001 (FE2) e 2004 (FE1), floresta nativa (FN) e solo descoberto (SD), no período de 2007 a 2012; e determinar os fatores da USLE: erosividade da chuva (R), erodibilidade (K) de um Argissolo Vermelho e o fator cobertura vegetal (C) para FE1, FE2 e FN, em sub-bacia hidrográfica piloto, em Eldorado do Sul, RS. O fator R foi estimado pelo índice EI30, a partir de dados pluviométricos obtidos em estação climatológica instalada na sub-bacia. As perdas de solo e água foram monitoradas em parcelas experimentais, fornecendo dados consistentes para a estimativa dos fatores K e C. A sub-bacia apresentou uma erosividade média de 4.228.52 MJ mm ha-1 h-1 ano-1. As perdas médias anuais de solo em FE1 e FE2 (0.81 e 0.12 Mg ha-1 ano-1, respectivamente) foram muito abaixo do limite de tolerância 12,9 Mg ha-1 ano-1. Os valores percentuais de perdas de água relativos à precipitação pluvial total decresceram anualmente, aproximando-se dos valores observados em FN. A partir do 5º ano após implantação dos sistemas de eucalipto o comportamento dos mesmos foi semelhante ao da FN, no tocante à erosão hídrica. A erodibilidade do ArgissoloVermelho foi de 0,0026 Mg ha h ha-1 MJ-1 mm-1 e o fator C apresentou valores de 0,121, 0,016 e 0,015 para FE1, FE2 e FN, respectivamente.

ABSTRACT 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.

Nas regiões tropicais, o desgaste provocado no solo por ação das águas da chuva, ou seja, a erosão hídrica é a mais importante forma de degradação do solo. Visto que os plantios florestais de eucalipto estão inseridos em ecossistemas sensíveis às perturbações antrópicas em razão de ocorrência de plantações em solos com baixos teores de argila, com baixa fertilidade natural e grande parte das plantações estabelecidas em antigas áreas agrícolas e de pastagens degradadas, surge a necessidade do entendimento dos processos que regem a erosão hídrica e suas relações com as perdas de solo e água nos sistemas florestais. Objetivaram-se com este trabalho calcular os valores de erosividade da chuva (fator R - EI30), estimar a tolerância de perda de solo (T) para as classes representativas nas áreas de estudo, avaliar as perdas de solo e água por erosão hídrica e verificar a influência, por meio de análise de componentes principais (ACP), de atributos físicos e matéria orgânica do solo sobre a erosão hídrica em florestas de eucalipto no estádio de pós-plantio. Os tratamentos constituíram de diferentes sistemas de manejo dos resíduos e da disposição de plantio (nível e desnível), em dois biomas distintos, Cerrado e Floresta, e solo descoberto. Os solos foram classificados como Latossolo Vermelho distrófico típico textura média-alta fase floresta (LVd1) e Latossolo Vermelho distrófico típico textura média-baixa fase cerrado (LVd2). O estudo foi realizado em áreas experimentais de plantio de eucalipto localizadas no município de Três Lagoas, na bacia do Rio Paraná, no leste do Mato Grosso do Sul. O índice de erosividade anual obtido foi de 6.792,7 MJ mm ha-1 h-1 ano-1. Os valores de T variaram de 9,0 a 11,0 Mg ha-1 ano-1, para o LVd2 e LVd1, respectivamente. As perdas de solo apresentaram valores em torno de 0 a 0,505 Mg ha-1 no LVd1 e de 0 a 0,853 Mg ha-1, no LVd2. A ACP evidenciou-se eficiente na discriminação dos sistemas de manejo em razão da interação entre os atributos físicos e matéria orgânica do solo e suas relações com a erosão hídrica, possibilitando visualizar de forma clara a influência do manejo sobre esses atributos e a relação de ambos com as perdas de solo e água.

In tropical regions, the damage caused to soil by rainwater, i.e., soil erosion, is the most significant form of soil degradation. In Brazil, eucalyptus plantations are mainly located in ecosystems sensitive to anthropogenic disturbances for reasons such as the occurrence of plantations in soils with low clay contents, soils with low natural fertility, and most plantations being established on areas previously occupied by agriculture or by degraded pastures. Thus, the need arises for understanding the processes that control water erosion and their relationship to soil and water losses in forest systems. The aim of this study was to calculate the values of rainfall erosivity (R factor - EI30), to estimate tolerance to soil loss (T) for the representative soil classes in the areas under study, to evaluate soil and water losses by water erosion, and, through the use of principal component analysis (PCA), to verify the influence of soil physical attributes and soil organic mater (SOM) on water erosion in the post-planting stage, with minimum tillage. Treatments consisted of different systems of waste management and planting arrangements (contour and downslope) in two distinct biomes, cerrado (tropical savanna) and forest, and bare soil. The soils were classified as Latossolo Vermelho distrófico típico (Oxisol), upper-middle texture in forest phase (LVd1), and Latossolo Vermelho distrófico típico (Oxisol), medium-low texture in cerrado phase (LVd2). The study was conducted in experimental areas of eucalyptus plantations located in Três Lagoas, in the Parana River basin, eastern Mato Grosso do Sul, Brazil. The annual erosivity index obtained was 6,792.7 MJ mm ha-1 h-1 yr-1. The T values ranged from 9.0 to 11.0 Mg ha-1 yr-1 for LVd2 and LVd1, respectively. Soil losses for eucalyptus plantation were well below the tolerance limits for the soil classes studied, at 0 to 0.505 Mg ha-1 in LVd1, and 0 to 0.853 Mg ha-1 no LVd2. Among the forest systems, eucalyptus under contour planting with maintenance of the residue was closest to native vegetation in relation to soil and water losses. The PCA proved to be effective in discriminating management systems based on the interaction between physical properties and soil organic matter and their relationship to water erosion, enabling clear visualization of the influence of soil management systems on these properties and their relationship to soil and water losses.

A erosão hídrica é responsável por perdas de solo, água, carbono orgânico e nutrientes, sendo esta a principal forma de degradação dos solos brasileiros. Dessa forma, objetivou-se, com este trabalho, avaliar a influência de três plantas de cobertura, em dois sistemas de manejo, no controle da erosão hídrica em um Argissolo, no sul de Minas Gerais. As plantas de cobertura utilizadas foram o feijão-guandu, feijão-de-porco e milheto, em dois sistemas de manejo (plantio em nível e em desnível no sentido do declive), sendo que uma parcela sem cobertura vegetal foi mantida como testemunha. Para a quantificação das perdas de solo, água, carbono orgânico e nutrientes utilizaram-se parcelas de 4 x 12 m em que a maior dimensão obedeceu ao sentido do declive, de 9 %, sob chuva natural. Os meses de dezembro e janeiro apresentaram a maior erosividade, porém elevada quantidade de chuvas erosivas foram detectadas durante todo o período chuvoso. O plantio em nível proporcionou maior redução da erosão hídrica em comparação ao plantio em desnível, conforme era de se supor. O feijão-de-porco cultivado em nível obteve os menores valores de perdas de solo, água, nutrientes e matéria orgânica.

Water erosion is responsible for soil, water, carbon and nutrient losses, turning into the most important type of degradation of Brazilian soils. This study aimed to evaluate the influence of three cover plants under two tillage systems on water erosion control in an Argisol at south of Minas Gerais state, Brazil. The cover plants utilized in the study were pigeon pea, jack bean and millet, under contour seeding and downslope tillage. Experimental plots of 4 x 12 m, with 9% slope, under natural rainfall were used for the quantification of losses of soil, water, nutrients, and organic matter. One experimental plot was kept without plant cover (reference). Higher erosivity was observed in December and January, although a great quantity of erosive rainfall was detected during the whole raining period. Contour seeding provided a greater reduction of water erosion than downslope tillage, as expected. The jack bean under contour seeding revealed the lowest values of soil, water, nutrients and organic matter losses.