ABSTRACT Agriculture intensification in Southern Brazil’s subtropical regions combined with the frequent occurrence of erosive rainfall has rendered the area a global water erosion hotspot. In this scenario, understanding and regulating erosion processes at the river catchment scale is critical for mitigating soil and water resource degradation. Traditional methods for tracing sediment sources are expensive and time-consuming and justify the development of alternative approaches. Therefore, in this study, we employed diffuse reflectance spectroscopy analyses in the ultraviolet-visible (UV-VIS), near-infrared (NIR), and mid-infrared (MIR) ranges, combined with multivariate models and spectral pre-processing techniques to estimate sediment source contributions in a homogeneous subtropical catchment (Conceição River, 804 km²). Soil samples (n = 181) were collected to characterize the four potential sediment sources, including: cropland (n = 78), stream bank (n = 36), unpaved road (n = 40) and pasture (n = 27). Moreover, 44 sediment samples were collected, including suspended sediment (n = 8), fine sediment deposited on the riverbed (n = 15), and suspended sediment samples collected in the water column during storm events (n = 21). Vector machine (SVM) model outperformed the others, with better accuracy and reliability. While UV-VIS spectra proved less effective due to soil homogeneity across the catchment, NIR and MIR spectra provided valuable information for discriminating sediment sources. Furthermore, reducing the number of potential sources (from four to three or two) improved model predictions, especially when distinguishing between surface sources (cropland and pasture) and subsurface sources (unpaved roads and stream banks). The study’s findings shed light on the power of efficient and cost-effective alternative methods for assessing sediment sources, which are vital for promoting effective erosion control and sustainable land management in similar regions. Brazils Brazil s hotspot scenario degradation timeconsuming time consuming approaches Therefore study ultravioletvisible ultraviolet visible UVVIS, UVVIS UV VIS , (UV-VIS) nearinfrared near infrared NIR, (NIR) midinfrared mid (MIR ranges preprocessing pre processing Conceição River 80 km². km² km . km²) n 181 78, 78 78) 36, 36 36) 40 27. 27 27) Moreover 4 8, 8 8) 15, 15 15) 21. 21 21) SVM (SVM others reliability Furthermore from two predictions banks. banks banks) studys costeffective cost (UV-VIS (NIR 18 7 3 2 1

ABSTRACT Strategies to mitigate degradation and ensure food and water security are among the main challenges in agricultural development. Unconsolidated information about the positive impact of conservationist practices on productivity increase is fundamental for their adoption by farmers. This study evaluated if the saved rainfall excess in catchment with terrace generates higher soybean and corn yield due to greater water availability in the crop rooting zone. Experiments were conducted in southern Brazil during the agricultural years of 2016/17 (soybean) and 2017/18 (corn) in two paired zero-order catchments (~2.4 ha) with similar topography and soil properties. One catchment has no terraces, while the other has five broad-based terraces as a complementary practice to control runoff. Soybean and corn yield was compared between catchments through five paired transects, totaling 47 sampling points. The fraction of available water (FAW – the current in relation to the total available water) was monitored at two points in each catchment, one at the base and the other at the top, considering the elevation. The FAW was monitored with CS616 probes at eight soil layers (from 0.00 up to 1.60 m) at each point during the crop growth cycle. The FAW was higher in the terraced catchment than the non-terraced catchment during the soybean (14 %) and corn (8 %) cycles. The terraced area provided higher soybean (12 %) and corn (10 %) than the non-terraced area. These results highlight the importance of terraces to increase productivity by managing runoff on hillslopes, indicating the potential of terraces to mitigate water deficits.

ABSTRACT Several management practices can increase soil water storage capacity, but their effectiveness to minimize the adverse effects of drought depends on their potential to increase the soil available water to plants. Terracing is an effective option to increase soil water storage, but its effect on available water to plants in no-tillage system is still a knowledge gap. In this study, we monitored soil water content at eight layers down to 1.6 m in two zero-order paired catchments for 16 months. Presence of five broad-based terraces in one of the catchments was the main difference between the two. Water availability to plants over time was expressed as a fraction of available water capacity (FAW). Positive differences of FAW between the terraced and non-terraced catchments were noticed over periods of rainfall shortage, but they were barely perceptible in periods of abundant rainfall. Over the 16 months, the frequency of FAW higher than 0.75 was between 46 and 50 % in the non-terraced catchment, and between 67 and 75 % in the terraced catchment. This benefit of terracing is more noticeable in thicker upper-section of the soil profile evaluated and with greater number of terraces upstream from the point of observation. We concluded that terracing in no-tillage turn excess rainfall into noticeable positive increases in available water to plants in the following periods of rainfall shortage.

ABSTRACT The objective of this paper was to evaluate the quality of water drained after the use of the knife-roller (an implement used to incorporate rice residues after harvest), the partial global warming potential (pGWP) and straw decomposition as a result of postharvest field management of irrigated rice. The experiments were conducted during the 2018 and 2019 offseason and the treatments consisted of several water drainage periods (0, 3, 6, 9 and 12 days) after a field pass with a knife-roller. In addition, a nonflooded harvest treatment without straw management was included. Analysis of drainage water three days after a pass with the kniferoller showed a reduction in total soluble solids by 94% compared to zero days. Nitrogen and soluble phosphorus were not influenced by the treatments. However, potassium levels increased as the drainage period increased, which is related to the period between harvest and drainage. As the electrical conductivity is influenced by the concentration of ions, it showed the same response curve as the potassium levels and, for pH, there were small oscillations influenced by the temperature. The total CH4 emission and the pGWP were higher when the water depth remained for a longer period. However, the N2O emissions were higher in the absence of soil submersion. Water should be drained three days after a pass with the knife-roller in order to reduce potassium loss and suspended solids as well as pGWP. The use of the knife-roller accelerated the process of straw decomposition in relation to the unmanaged straw treatment.

ABSTRACT The objective of this study was to evaluate the distribution pattern of total organic carbon (TOC) and total nitrogen (TN) in the native field soil profile and Eucalyptus sp. The study was carried out in native field and in eucalyptus plantations with 20, 44, 180 and 240 months, located in Santa Maria and Manoel Viana, RS, Brazil. The decay rate (k) of the TOC and TN contents up to 1.2 m depth was determined by the graphical, numerical and mathematical method using the third order negative exponential model. The content of TOC and TN deep in the soil showed a third order negative exponential distribution. However, the methods used to estimate the decay rate generate differences in TOC and TN contents along the soil profile.

A caracterização de componentes da paisagem e de suas relações na Estação Experimental de Silvicultura de Santa Maria - RS e o monitoramento da variação temporal solo/paisagem entre os anos de 1987 e 2009 (22 anos) foram realizados, por meio de levantamentos de campo e mapeamento digital da cobertura vegetal, relevo e solos. Cruzaram-se informações do histórico de uso e ocupação do solo, de transecções realizadas em 2009, do modelo numérico do terreno, de mapas de cobertura vegetal para 1987 e 2009 e de solos. Derivou-se assim um caráter transitório dos componentes da paisagem, entre o Rebordo do Planalto Sul-Riograndense e a Depressão Central do Rio Grande do Sul, com uma descaracterização das fitofisionomias naturais e existência de conflitos de uso do solo, bem como a influência do relevo e da gênese dos solos sobre o desenvolvimento fitofisionômico. Houve expansão, em 22 anos, dos cultivos de Eucalyptus e Pinus, e da floresta nativa sobre o campo antrópico, principalmente em áreas com Argissolos Bruno-Acinzentados e Argissolos Vermelhos.

The characterization of landscape components and their relationships for the Forestry Experimental Station of Santa Maria,Rio Grande do Sul state, Brazil, and the monitoring of soil-landscape temporal variation between the years 1987 and 2009 (22 years) were performed by means of field surveys and digital mapping vegetation, soil and topography. Crossed the historical information of use and occupation of transects conducted in 2009, the digital terrain model, maps of land cover for 1987 and 2009 and soil, thus deriving a transitory component landscape, between the plateau border Southern and Central Depression of Rio Grande do Sul state, with a distortion of the natural vegetation types and conflicts of land use, as well as the influence of topography and soil genesis on the vegetation development. There was expansion in 22 years of Eucalyptus and Pinus crops and the natural forest on the anthropic field, especially in areas with Argissolos Bruno-Acinzentados and Argissolos Vermelhos.

O conhecimento das principais fontes difusas de produção de sedimento pode aumentar a eficiência de utilização dos recursos públicos, investidos em estratégias de gestão em bacias hidrográficas, que visem mitigar a transferência de sedimentos aos cursos d'água. Objetivou-se com este trabalho avaliar as fontes de sedimentos numa bacia hidrográfica rural de cabeceira com predomínio de cultivos anuais sob plantio direto e com intensa e inadequada exploração dos recursos naturais, por meio da quantificação da contribuição relativa das estradas e das lavouras na produção global de sedimentos. A bacia hidrográfica está localizada no município de Júlio de Castilhos, Rio Grande do Sul. O período de estudo foi de maio de 2009 a abril de 2011. Para a identificação das fontes, foi utilizado o método fingerprinting, que compara os solos de diferentes fontes e os sedimentos que são encontrados em suspensão no canal de drenagem, usando elementos traçadores. O manejo inadequado do solo nas áreas de lavoura, a falta de planejamento das vias de acesso e a ausência de práticas de controle do escoamento superficial, que sejam compatíveis com a fragilidade condicionada pelos solos e pelo relevo da bacia hidrográfica, têm provocado o surgimento de processos erosivos acelerados com efeitos negativos ao agricultor e à sociedade. As estradas apresentam alta porcentagem de contribuição na transferência de sedimentos, mas a contribuição das áreas de lavoura aumenta em precipitações pluviais de alta magnitude. Isso evidencia que a magnitude dos eventos de chuva influencia a proporção de contribuição entre as fontes ao longo do ano na bacia hidrográfica, interferindo no processo de mobilização de sedimentos e nutrientes em direção à rede de drenagem.

Knowledge of the main diffuse sources of sediment production can enhance efficiency in use of public resources invested in management strategies that seek to mitigate sediment transfer to waterways from catchment areas. The aim of the present study was to evaluate the sediment sources in a rural catchment with predominance of annual crops under a no-tillage system and with intense and inappropriate exploitation of natural resources (soil and water) by quantifying the relative contribution of roads and croplands in the overall production of sediments. Inappropriate exploitation is a result of a lack of planning of crop production areas and access pathways, both from the point of view of their location in the landscape, and of management practices which are incompatible with the conditions of soil fragility and relief. The catchment is located in the municipality of Julio de Castilhos, State of Rio Grande do Sul. The period under study was from May 2009 to April 2011. For identification of the sources we used the fingerprinting method, which compares the soils from different sources and the sediments in suspension in the drainage canal using tracer elements. Inadequate soil management in croplands, the lack of planning of access roads, and the absence of control practices for surface runoff compatible with the fragility brought about by the soil and topography of the watershed have caused the emergence of accelerated erosion with negative effects for the farmer and society. Roads represent a high percentage of contribution to sediment transfer, but the contribution of cropland increases with rainfall of high magnitude. This shows that the magnitude of rainfall events affects the proportion of contribution among sources throughout the year in the catchment area, affecting the process of mobilization of sediments and nutrients towards the drainage system.

A degradação dos recursos hídricos está intensamente relacionada à atividade agrícola. O objetivo deste trabalho foi avaliar a influência do uso do solo e de alguns componentes ambientais na qualidade da água superficial na microbacia do rio Campestre, município de Colombo, Paraná. Foram analisados os atributos físicos e químicos (nitrogênio Kjeldahl, amônio, nitrato, fósforo total, turbidez, pH, temperatura, condutividade elétrica, sólidos totais, demanda biológica de oxigênio, demanda química de oxigênio e oxigênio dissolvido). A coleta das amostras de água foi realizada mensalmente por um ano em oito pontos, distribuídos em três sub-bacias. De modo geral, a qualidade da água foi inferior na sub-bacia com maior porcentagem de agricultura, sendo influenciada também pelas porcentagens de floresta, área de preservação permanente com agricultura e área de contribuição da sub-bacia. Na estação de verão, provavelmente em razão da maior precipitação pluvial e do uso do solo, ocorreram as maiores concentrações de N Kjeldahl e N particulado, bem como de condutividade elétrica, pH e turbidez. Todos os atributos analisados, exceto o P total, estavam de acordo com a Resolução Conama nº 357/2005, para água doce de classe 1. No entanto, cabe ressaltar que o monitoramento realizado referiu-se ao escoamento de base e não representou uma condição de descarga, já que a maioria das coletas não foi realizada durante ou próxima do evento de precipitação.

Water degradation is strongly related to agricultural activity. The aim of this study was to evaluate the influence of land use and some environmental components on surface water quality in the Campestre catchment, located in Colombo, state of Parana, Brazil. Physical and chemical attributes were analyzed (total nitrogen, ammonium, nitrate, total phosphorus, electrical conductivity, pH, temperature, turbidity, total solids, biological oxygen demand, chemical oxygen demand and dissolved oxygen). Monthly samples of the river water were taken over one year at eight monitoring sites, distributed over three sub-basins. Overall, water quality was worse in the sub-basin with a higher percentage of agriculture, and was also affected by a lower percentage of native forest and permanent preservation area, and a larger drainage area. Water quality was also negatively affected by the presence of agriculture in the riparian zone. In the summer season, probably due to higher rainfall and intensive soil use, a higher concentration of total nitrogen and particulate nitrogen was observed, as well as higher electrical conductivity, pH and turbidity. All attributes, except for total phosphorus, were in compliance with Brazilian Conama Resolution Nº 357/2005 for freshwater class 1. However, it should be noted that these results referred to the base flow and did not represent a discharge condition since most of the water samples were not collected at or near the rainfall event.

A variabilidade espacial das características do solo torna a estimativa da infiltração de água altamente dependente da escala de análise. Muitos trabalhos necessitam de informações da dinâmica da infiltração para descrever o mecanismo de outros processos associados à água, aos sedimentos ou aos solutos. O objetivo deste trabalho foi utilizar duas estratégias metodológicas para a estimativa da infiltração na escala de bacia. Os parâmetros de dois modelos de infiltração foram ajustados a um conjunto de dados coletados durante dois anos de monitoramento, em 77 eventos de chuva-vazão ocorridos sob diferentes condições de uso e manejo do solo numa bacia hidrográfica rural de 1,2 km². Os resultados dos ajustes para os dois modelos de infiltração na escala de bacia foram comparados com aqueles obtidos para dois métodos pontuais de estimativa da infiltração. Com o conjunto de dados do monitoramento, foi possível definir um modelo de infiltração para a bacia monitorada. Além disso, os resultados indicaram que a comparação realizada entre os valores dos modelos com os pontuais são fortemente dependentes da escala de análise; isto é, as medidas pontuais revelaram valores médios de taxa de infiltração alta para a bacia em estudo. Todavia, observações no campo indicaram baixa infiltração, principalmente nas áreas saturadas onde condicionam o escoamento superficial nessa bacia, ao contrário dos resultados pelos modelos de estimativa, que apresentaram menor ordem de magnitude dos valores estimados de infiltração, em razão, entre outros, da maior incorporação dos fatores controladores do processo em seu método.

The spatial variability of soil characteristics makes the estimation of water infiltration highly dependent on the scale of analysis. Many studies require information on the dynamics of infiltration to describe the dynamics of other processes associated with water, sediment and solutes. This study aims to use two methodological strategies to estimate water infiltration at the catchment scale. The parameters of two infiltration models were fitted to a data set collected over two years of monitoring (77 rainfall-runoff events) occurring under different land use and management conditions in a rural catchment of 1.2 km². The results of fitting to the two infiltration models at the catchment scale were compared with those obtained from two site-specific methods for estimating infiltration. With the set of monitoring data, it was possible to establish an infiltration model for the monitored catchment area. Furthermore, the results indicate that the comparison between values from the models and site-specific values are strongly dependent on the scale of analysis. That is, the site-specific measures showed mean values of high infiltration rates for this catchment, but field observations indicate low infiltration, especially in saturated areas, which affect runoff in this catchment area. This is in contrast with the results obtained by the estimation models, which present a lower order of magnitude for the estimated values of infiltration, due to the greater incorporation of factors controlling the process in their methodology, among other aspects.

Índices topográficos (IT) obtidos computacionalmente a partir do modelo numérico de elevação do terreno (MNE) têm sido incorporados em algoritmos computacionais aplicados na simulação de processos hidrológicos, erosivos e de transporte de poluentes. Por meio desses índices, zonas de acúmulo de umidade em uma bacia hidrográfica, por exemplo, podem ser previstas espacialmente através de IT, que levam em consideração efeitos de orientação de drenagem e declividade do terreno. Este trabalho tem como propósito o de apresentar uma revisão bibliográfica sobre esse tema e de demonstrar a aplicabilidade desses índices por meio de alguns exemplos, aplicada à modelagem agrícola e ambiental.

Topographic indices obtained computationally from the numerical model of elevation have been incorporated into computer algorithms and used in hydrological simulating processes, erosion and pollutant transport. Through these indices, zones of water accumulation in a catchment, for example, can be predicted using topographic index that take into account the slope orientation and land slope. This study aims to present a review of the literature on this topic by means of some examples applied in agricultural and environmental modelling.

Programas de conservação do solo e da água que utilizam a bacia hidrográfica como unidade de planejamento têm sido amplamente empregados. Um componente importante desses programas se refere à implantação de projetos de monitoramento hidrossedimentométrico e de qualidade de água para avaliar o impacto nos recursos hídricos das práticas introduzidas. Entretanto, em alguns casos, os resultados obtidos pelos projetos de monitoramento têm sido pouco conclusivos, devido a limitações dos procedimentos experimentais adotados. Esta revisão explora metodologias de avaliação que combinam técnicas tradicionais de monitoramento com técnicas de identificação de fontes de sedimentos que contribuem para elucidar os efeitos das práticas conservacionistas na produção de sedimentos em bacias hidrográficas e também a inter-relação dinâmica entre as fontes de sedimentos.

Soil and water conservation programs frequently use catchments as planning units. An important follow-up component of these programs is the installment of hydrosedimentometric and water quality monitoring projects to evaluate the impact of the practices introduced. However, in some cases, these monitoring projects have yielded inconclusive results, mostly due to procedural limitations. This review explores methods that combine traditional monitoring techniques with sediment source identification to further elucidate the impact of conservation practices on sediment yield in the catchment and dynamic interactions between different sediment sources.

Métodos de representação espacial para o cálculo do fator topográfico (LS) da Equação Universal de Perda de Solo Revisada (RUSLE) têm sido utilizados para estimar a erosão do solo e a produção de sedimentos em bacias hidrográficas. Esses procedimentos baseiam-se nas equações tradicionalmente empregadas para determinação do fator LS e em informações que caracterizam a forma das vertentes derivadas do modelo numérico de elevação (MNE). Neste estudo foram analisados dois métodos de representação espacial utilizados no cálculo do fator LS em modelos matemáticos de erosão e produção de sedimentos em bacias hidrográficas. A análise foi realizada em quatro bacias rurais de relevo movimentado. Os valores de LS obtidos pelos métodos de representação espacial foram comparados entre si e com valores de LS determinados pelo método tradicional com levantamento em campo. Resultados mostraram que os valores de LS gerados pelos métodos de representação espacial apresentam diferenças significativas entre si, sendo dependentes do procedimento de cálculo e do método utilizado para determinar a direção de fluxo no MNE. Também foi verificado que os valores numéricos do fator LS determinados pelos métodos de representação espacial apresentam diferenças em relação àqueles estimados pelo método tradicional.

Methods of spatial representation to calculate the topographic factor (LS) of the Revised Universal Soil Loss Equation (USLE) have been used to estimate soil erosion and sediment yield of watersheds. These procedures are based on equations traditionally used to determine the LS factor and information that characterize the hillslope forms and processes, derived from the Digital Elevation Model (DEM). Two computational methods commonly used to calculate LS factor in soil erosion and sediment yield models were analyzed in this study. The analysis was performed in four small rural watersheds with hilly terrain. The LS values obtained by the methods of spatial representation were compared with each other with LS values measured by the traditional method. Results show significant differences of the computer-generated LS values, which were related to the calculation procedure and the method used to determine the DEM flow direction. Differences were also observed between the numeric values of the LS factor determined by methods of spatial representation and in the field.

A condutividade hidráulica do solo saturado (Kθs) é uma propriedade com grande variabilidade, o que exige a utilização de um número maior de determinações para que sua descrição possa ser feita adequadamente pela função densidade de probabilidade normal. Consequentemente, há aumento de trabalho e de tempo para a obtenção dos resultados, principalmente se as determinações forem feitas com equipamentos de pouca praticidade. A construção de equipamentos de maior praticidade e o desenvolvimento de ferramentas computacionais podem tornar o processo de análise mais rápido e preciso. Com esse objetivo, foi construído um permeâmetro de carga decrescente e desenvolvido um software para a aquisição de dados. As medidas de Kθs obtidas com esses equipamentos, em amostras de um Argissolo, mostraram menor variabilidade, avaliada pelo coeficiente de variação, o que resultou em maior precisão das determinações. Além disso, o tempo de análise foi reduzido em 30 %.

The soil saturated hydraulic conductivity (Kθs) is a property with great variability, which requires the use of a greater number of determinations so that they can be described by the normal probability density function. Consequently, there is an increase in time and labor to obtain Kθs results if determined by conventional equipment. The use of more practical equipment and computational tools allows a faster and more accurate analysis. With this aim a falling head permeameter was built and a software for data acquisition was developed. Values of Kθs obtained with this equipment in Hapludalf samples showed less variability, as assessed by the coefficient of variation, resulting in more precise measurements. Moreover, the time of analysis was reduced by 30 %.

Os sedimentos oriundos de áreas agrícolas são importante fonte de poluentes para os ecossistemas aquáticos. Existem várias fontes de sedimentos na escala de uma bacia hidrográfica rural, como lavouras, pastagens, florestas, rede fluvial e estradas. Cada uma tem características diferentes na magnitude de contribuição e potencial de contaminação. Identificar a origem dos sedimentos é fundamental na compreensão da taxa de emissão de sedimentos e no manejo dos sedimentos erodidos na escala de bacia. Este trabalho foi desenvolvido com o propósito de identificar as principais fontes de sedimentos de duas bacias rurais de cabeceira no Sul do Brasil, as quais são representativas do sistema agrário e das características fisiográficas da região. A metodologia utiliza a comparação entre os solos de diferentes fontes e os sedimentos em suspensão, usando traçadores naturais. A análise discriminante encontrou um grupo de variáveis capazes de distinguir as fontes de sedimentos. Com base na análise de classificação, as contribuições relativas de cada fonte nas bacias de Agudo e Arvorezinha foram, respectivamente: lavouras (68,3 e 55,5 %), estradas (28,1 e 37,6 %) e rede fluvial (3,6 e 6,9 %). Os resultados mostram que, além da contribuição predominante das lavouras, as erosões nas estradas e na rede fluvial contribuem significativamente para produção total de sedimentos nas bacias, demonstrando a importância dessa informação para controle da erosão do solo e manejo dos sedimentos na escala de bacia hidrográfica.

Sediments in agricultural areas represent a significant source of pollution of aquatic environments. There are many different sediment sources at the level of a rural catchment (e.g. crop fields, pastures, forests, river banks, and roads), with different magnitude of contribution and contaminant potential. The identification of the sediment origin is important to understand the sediment transport rate and the management of sediment eroded at the catchment scale. The goal of this work was to identify the main sediment sources of two rural headwater catchments in southern Brazil, representative of the regional agrarian system and physiographic characteristics. The methodology was based on a comparison between soils of different sources and the eroded sediments using natural tracers. A set of variables was found by the discriminant soil analysis to distinguish the sources. Based on the classification analysis, the relative contribution of each source to the eroded sediments in the Agudo and Arvorezinha catchments was, respectively: crop fields 68.3 and 55.5 %, roads 28.1 and 37.6 % and bank erosion 3.6 and 6.9 %. Results show that besides the major contribution coming from crop fields, erosion from roads and drainage represents a significant part of the total sediment. Such information is essential to control soil erosion and for sediment management at the catchment scale.

A produção de fumo no sul do Brasil tem causado um profundo impacto no meio ambiente, resultando em alta de produção de sedimentos e diminuindo a qualidade da água. Programas públicos têm se esforçado para resolver estes problemas com a implementação de práticas de controle de erosão. Para avaliar o impacto destes programas, uma pequena bacia rural (1,33km²) em Arvorezinha, no estado do Rio Grande do Sul, tem sido monitorada desde 2001. Instrumentos automáticos de medição da vazão e precipitação foram instalados na bacia e os sedimentos foram medidos com um amostrador manual do tipo DH48. Apesar de ter chovido menos em 2003, houve um aumento significativo na freqüência das vazões de estiagem e médias, e um aumento de 25% na produção de sedimentos em 2003 (91Mg km-2 year-1) comparado com 2002 (73Mg km-2 year-1). Estes resultados podem ser explicados por um aumento de 37,7% na área dedicada ao cultivo de fumo em 2003, devido ao aumento no preço do fumo.

Tobacco production in Southern Brazil has caused a profound impact in the environment, resulting in heavy sediment yields and diminishing water quality. Public programmes have attempted to address these problems by encouraging the implementation of erosion control practices. To evaluate the impact of these programmes, a small rural catchment (1.33km²) in Arvorezinha county, in the state of Rio Grande do Sul, Brazil, has been monitored since 2001. Instruments to automatically monitor flow rate and precipitation were installed in the catchment and sediment has been measured manually using a DH-48 sampler. Despite lower rainfall in 2003, there was a significant increase in the frequency of low and average flow rates, and sediment yield increased 25% in 2003 (91Mg km-2 year-1), compared with 2002 (73Mg km-2 year-1). These results can be explained by a 37.7% increase in the area dedicated to tobacco cultivation in 2003, due to a rise in tobacco prices.