Gustavo Henrique Merten

The identification of sediment sources in a small urban watershed in southern Brazil: An application of sediment fingerprinting

Soil particles eroded from the land surface and transported into rivers by runoff are considered one of the main components of non‐point source pollution in urban watersheds. These particles also serve as a vector for a wide variety of both organic and inorganic constituents. As a result, the identification of sediment sources in an urban watershed is necessary not only to understand erosion dynamics, but also to help implement more effective measures to control and/or remediate non‐point source pollution. The present study employs sediment ‘fingerprinting’ to determine the main sediment sources in a small residential urban watershed (0.83 km2) on the outskirts of Porto Alegre in southern Brazil. Based on an evaluation spanning 12 rainfall events, the results show that paved and unpaved roads and the stream channel itself contribute, on average, 46%, 23%, and 31%, respectively, to the suspended sediment flux in the watershed. Furthermore, the source contributions varied both between events and over the course of a single event. This appears to imply that source contributions, at least to some extent, depend on local precipitation patterns. The results from this study indicate that the level of uncertainty in source ascription tends to decline with increasing numbers of tracers; hence, successful sediment fingerprinting and source ascription in complex hydrologic environments, such as urban watersheds, may require the use of a large number of chemical and/or physical tracers.

Digital soil mapping using multiple logistic regression on terrain parameters in southern Brazil

Soil surveys are necessary sources of information for land use planning, but they are not always available. This study proposes the use of multiple logistic regressions on the prediction of occurrence of soil types based on reference areas. From a digitalized soil map and terrain parameters derived from the digital elevation model in ArcView environment, several sets of multiple logistic regressions were defined using statistical software Minitab, establishing relationship between explanatory terrain variables and soil types, using either the original legend or a simplified legend, and using or not stratification of the study area by drainage classes. Terrain parameters, such as elevation, distance to stream, flow accumulation, and topographic wetness index, were the variables that best explained soil distribution. Stratification by drainage classes did not have significant effect. Simplification of the original legend increased the accuracy of the method on predicting soil distribution.

The expansion of Brazilian agriculture: Soil erosion scenarios

Abstract During the next 10 years Brazil’s agricultural area will expand to meet increased domestic and worldwide demand for food, fuel, and fiber. Present choices regarding land use will determine to what degree this expansion will have adverse effects that include soil erosion, reservoir siltation, water quality problems, loss of biodiversity and social conflict, especially around indigenous reservations. This paper presents an up-to-date inventory of soil erosion in Brazil caused by crop and livestock activities and provides estimates based on three different hypothetical land-use scenarios to accommodate the expansion of Brazilian agricultural activity by 2020: Scenario 1 – expansion of cropping into areas of natural vegetation, without adoption of conservation practices; Scenario 2 – expansion of cropping into areas of degraded pasture, without adoption of conservation practices; Scenario 3 – expansion of cropping into areas of degraded pasture, together with conservation practices in 100% of the expanded area. The worst-case scenario involves expansion of agriculture into areas of native vegetation in the Brazilian Savannah (Cerrado) and Brazilian rainforest (Amazon) biomes, and could increase total soil erosion in Brazil (currently about 800 million metric tons a year) by as much as 20%. In the best-case scenario, crop expansion under a conservation agriculture model would utilize currently degraded pasture, especially in the Savannah ( circa 40 million hectares), reducing soil erosion in Brazil by around 20%. For this to occur, however, a national soil and water conservation policy needs to be implemented in Brazil to support a sustainable model of agriculture in which the environment can be preserved as much as possible.

Use of the swat model for hydro-sedimentologic simulation in a small rural watershed

Modelos matematicos apresentam grande potencial para serem utilizados como instrumento de apoio ao planejamento de uso da terra, com o proposito de melhorar a qualidade do solo e da agua. A utilizacao de um modelo, no entanto, deve ser antecedida de uma etapa inicial, a fim de verificar o desempenho dele em simular corretamente os processos hidrologicos e erosivos de um dado local. O modelo SWAT (Soil and Water Acesamente Tool) foi desenvolvido nos Estados Unidos para avaliar os efeitos da agricultura conservacionista sobre os processos hidrologicos e de qualidade de agua na escala de bacia. Esse modelo foi inicialmente proposto para ser utilizado sem a necessidade de calibracao, o que dispensaria o uso de dados hidrossedimentologicos medidos. Nessa condicao, o modelo SWAT foi avaliado em uma pequena bacia rural (1,19 km²) localizada nas encostas basalticas do Estado do Rio Grande do Sul, onde culturas de cobertura associadas com o cultivo minimo vem sendo empregadas pelos agricultores para controlar o processo erosivo. Valores simulados pelo modelo SWAT foram comparados com dados hidrossedimentologicos medidos. Como resultado da simulacao, verificou-se que o escoamento superficial e o total, para a escala de tempo diaria, foram considerados insatisfatorios (valores de COE < 0,5). Ja as mesmas simulacoes para as escalas mensal e anual apresentaram resultados sensivelmente melhores. Com relacao ao processo erosivo, verificou-se para todos os anos que a producao de sedimentos simulada, quando comparada com os valores observados, foi insatisfatoria para as simulacoes diarias e mensais (valores de COE < -6) e superestimou em mais de 100 % a producao de sedimentos anual.

Utilização de P-Index em uma bacia hidrográfica através de técnicas de geoprocessamento

Due to problems caused by eutrophication of lakes and reservoirs, the identification of phosphorus source areas is important for planning the control of agriculture-related water pollution. This study applied a method designed to identify these phosphorus source areas, called P-Index, which is based on combining data layers related to soil phosphorus availability and phosphorus transport processes. The method was used for studying the Salto Reservoir waterbasin, in Sao Francisco de Paula, in the State of Rio Grande do Sul, Brazil. Data related to phosphorus availability, intensity of transport processes, and distance to waterways were combined to yield a map of phosphorus contribution classes, which showed that almost the entire study area was considered to have low phosphorus contribution potential. A few small areas, corresponding to potato and garlic fields that received heavy chemical fertilization, were classified as having high phosphorus contribution potentials.

Método "fingerprinting" para identificação de fontes de sedimentos em bacia hidrográfica rural

In this study, the fingerprinting method was used to identify sediment sources in a small rural watershed located in a mountainous region in southern Brazil. This watershed represents a typical agricultural ecosystem, in which smallhold farmers cultivate tobacco in marginal areas, with severe consequences to the natural resources. The identification of sediment sources, based on analysis of sediments transported in suspension, enables an evaluation of which areas are truly contributing to sediment production and, therefore, to make inferences about the polluting potential of these sediments. The study considered the main limitations of this method, as well as its potential in the identification of sediment sources. Through classification, it was possible to identify the relative contribution of these different sources, with fields and roads being predominant. Results showed that the contribution from these two sources varied over time and that the relative proportion of the contribution from each source varied according to management and soil cover in the fields and maintenance work performed in the roads. The average contribution from fields and roads was 64 and 36%, respectively.

Impact on sediment yield due to the intensification of tobacco production in a catchment in Southern Brazil

A producao de fumo no sul do Brasil tem causado um profundo impacto no meio ambiente, resultando em alta de producao de sedimentos e diminuindo a qualidade da agua. Programas publicos tem se esforcado para resolver estes problemas com a implementacao de praticas de controle de erosao. 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 automaticos de medicao da vazao e precipitacao 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 frequencia das vazoes de estiagem e medias, e um aumento de 25% na producao 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 area dedicada ao cultivo de fumo em 2003, devido ao aumento no preco do fumo.

Simulação da dinâmica do carbono do solo numa microbacia rural pelo modelo Century

The objective of this study was to combine the Century model with geoprocessing and remote sensing techniques, in order to evaluate spatial-temporal dynamics in total organic carbon (TOC). The study was carried out in a small rural watershed in Northeastern of Rio Grande do Sul State, Brazil. The area was initially under forest cover, which was progressively converted to agriculture in a period of 80 years. The proper calibrating of the model, especially in terms of TOC decomposition parameters, during the initial years of tillage, was essential to produce a coherent simulation of TOC values. Regarding the spatial distribution of TOC, it was observed that greatest impact of soil management on original contents occurred in the areas under cultivation since 1925, which showed a decline of 58.2% in TOC. The Century model integration with a geographic information system makes it possible the study of spatial-temporal dynamics of TOC and the performing of TOC distribution inventories.

Monitoramento de bacias hidrográficas para identificar fontes de sedimentos em suspensão

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.

Análise qualitativa e quantitativa da histerese entre vazão e concentração de sedimentos durante eventos hidrológicos

The relationship between flow rate - Q and suspended sediment concentration - SSC demonstrates complex temporal patterns during hydrologic events, which are governed by geomorphology, land use, soil management and rainfall. This fact has important implications for understanding and describing erosive processes and sediment production in catchments. These patterns can be evaluated by their loop hysteresis characteristics on the graph of SSC vs. Q. In this study, the hysteresis effect was analyzed for 19 rainfall events in a rural catchment in Southern Brazil. The events were separated in two groups in relation to soil management (with and without soil management practices). The events were classified according to the type of hysteresis, and a hysteresis index (HI) was calculated to evaluate the magnitude of the difference in phase. Results show that the hysteresis pattern was a clockwise loop, indicating that the peak SSC occurred before the peak Q, which represents rapid mobilization and transfer of sediment in the catchment. The HI was not statistically different between the two periods studied, although there is evidence that the conservation practices do have some influence on the index.