Jean Paolo Gomes Minella

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.

Simulating Landscape Sediment Transport Capacity by Using a Modified SWAT Model.

Sediment delivery from hillslopes to rivers is spatially variable and may lead to long-term delays between initial erosion and related sediment yield at the watershed outlet. Consideration of spatial variability is important for developing sound strategies for water quality improvement and soil protection at the watershed scale. Hence, the Soil and Water Assessment Tool (SWAT) was modified and tested in this study to simulate the landscape transport capacity of sediment. The study area was the steeply sloped Arroio Lino watershed in southern Brazil. Observed sediment yield data at the watershed outlet were used to calibrate and validate a modified SWAT model. For the calibration period, the modified model performed better than the unaltered SWAT2009 version; the models achieved Nash-Sutcliffe efficiency (NSE) values of 0.7 and -0.1, respectively. Nash-Sutcliffe efficiencies were less for the validation period, but the modified models NSE was higher than the unaltered model (-1.4 and -12.1, respectively). Despite the relatively low NSE values, the results of this first test are promising because the model modifications lowered the percent bias in sediment yield from 73 to 18%. Simulation results for the modified model indicated that approximately 60% of the mobilized soil is deposited along the landscape before it reaches the river channels. This research demonstrates the modified models ability to simulate sediment yield in watersheds with steep slopes. The results suggest that integration of the sediment deposition routine in SWAT increases accuracy in steeper areas while significantly improving its ability to predict the spatial distribution of sediment deposition areas. Further work is needed regarding (i) improved strategies for spatially distributed sediment transport measurements (for improving process knowledge and model evaluation) and (ii) extensive model tests in other well instrumented experimental watersheds with differing topographic configurations and land uses.

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.

Combining visible-based-color parameters and geochemical tracers to improve sediment source discrimination and apportionment.

Parameter selection in fingerprinting studies are often time-consuming and costly because successful fingerprint properties are generally highly site-specific. Recently, spectroscopy has been applied to trace sediment origin as a rapid, less expensive, non-destructive and straightforward alternative. We show in this study the first attempt to combine both geochemical tracers and color parameters derived from the visible (VIS) spectrum in a single estimate of sediment source contribution. Moreover, we compared the discrimination power and source apportionment using VIS-based-color parameters and using the whole ultra-violet-visible (UV-VIS) spectrum in partial last square regression (PLSR) models. This study was carried out in a small (1.19 km(2)) rural catchment from southern Brazil. The sediment sources evaluated were crop fields, unpaved roads, and stream channels. Color parameters were only able to discriminate unpaved roads from the other sources, disabling its use to fingerprint sediment sources itself. Nonetheless, there was a great improvement in source discrimination combining geochemical tracers and color parameters. Unlike VIS-based-color parameters, the distances between sediment sources were always significantly different using the whole UV-VIS-spectrum. It indicates a loss of information and, consequently, loss of discriminating power when using VIS-based-color parameters instead of the whole UV-VIS spectrum. Overall, there was good agreement in source ascription obtained with geochemical tracers alone, geochemical tracers coupled with color parameters, and UV-VIS-PLSR models, and all of them indicate clearly that the main sediment source was the crop fields, corresponding to 57 ± 14, 48 ± 13, and 62 ± 18%, respectively. Prediction errors for UV-VIS-PLSR models (6.6 ± 1.1%) were very similar to those generated in a mixed linear model using geochemical tracers alone (6.4 ± 3.6%), but the combination of color parameters and geochemical tracers decreases the prediction error (5.4 ± 2.0%). Therefore, the use of VIS-based-color parameters combined to geochemical tracers can be a rapid and inexpensive way to improve source discrimination and precision of sediment source apportionment.

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.

Runoff of genotoxic compounds in river basin sediment under the influence of contaminated soils

Contaminated sites must be analyzed as a source of hazardous compounds in the ecosystem. Contaminant mobility in the environment may affect sources of surface and groundwater, elevating potential risks. This study looked at the genotoxic potential of samples from a contaminated site on the banks of the Taquari River, RS, Brazil, where potential environmental problems had been identified (pentachlorophenol, creosote and hydrosalt CCA). Samplers were installed at the site to investigate the drainage material (water and particulate soil matter) collected after significant rainfall events. Organic extracts of this drained material, sediment river samples of the Taquari River (interstitial water and sediment organic extracts) were evaluated by the Salmonella/microsome assay to detect mutagenicity and by Allium cepa bioassays (interstitial water and whole sediment samples) to detect chromosomal alterations. Positive mutagenicity results in the Salmonella/microsome assay of the material exported from the area indicate that contaminant mixtures may have drained into the Taquari River. This was confirmed by the similarity of mutagenic responses (frameshift indirect mutagens) of organic extracts from soil and river sediment exported from the main area under the influence of the contaminated site. The Allium cepa test showed significant results of cytotoxicity, mutagenic index and chromosome aberration in the area under the same influence. However, it also showed the same similarity in positive results at an upstream site, which probably meant different contaminants. Chemical compounds such as PAHs, PCF and chromium, copper and arsenic were present in the runoff of pollutants characteristically found in the area. The strategy employed using the Salmonella/microsome assay to evaluate effects of complex contaminant mixtures, together with information about the main groups of compounds present, allowed the detection of pollutant dispersion routes from the contaminated site to the Taquari River sediment.

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.

Contribuição das fontes de sedimentos em uma bacia hidrográfica agrícola sob plantio direto

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.

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.