Papers by Carla Semiramis Silveira
Revista Brasileira de Geofísica, 2017
ABSTRACT. In the present work, we describe our experience with digital petrophysics, enhancing ou... more ABSTRACT. In the present work, we describe our experience with digital petrophysics, enhancing our choices for performing the related tasks. The focus is on the use of ordinary personal computers. To our best knowledge, some of the information and hints we give cannot be found in the literature and we hope they may be useful to researchers that intend to work on the development of this new emerging technology. We have used micro-scale X-ray computed tomography to image the rock samples and, in that sense, we address here the issue of the corresponding image acquisition and reconstruction parameters adjustment. In addition, we discuss the imaging resolution selection and illustrate the issue of the representative volume choice with the aid of two examples. The examples corroborate the notion that it is much more challenging to define a representative volume for carbonate samples than for sandstone samples. We also discuss the image segmentation and describe in details the Finite Elem...
Perspectivas Medicas, 2012
Fatores de risco relacionados ao ato cirúrgico em puérperas com infecção de sítio cirúrgico.
The accumulation of trace metals in environmental archives is controlled by climatic and geochemi... more The accumulation of trace metals in environmental archives is controlled by climatic and geochemical processes. Mercury (Hg), a major global pollutant, is released into the environment via natural and anthropogenic sources. Being susceptible to longrange transport, it poses a threat to both human and environmental health. To understand how climatic and biogeochemical processes affect Hg cycling and accumulation in the environment, Hg profiles in environmental archives are studied. Here, we study mercury records from marine sediment cores GL-1248 and ODP1077 collected from the continental slope off northeastern Brazil, and the Congo deep-sea fan area respectively. Our objective is to gain insights into the dynamics of mercury accumulation in the African and South American continents (known t to be highly vulnerable to climate change), to climate forcing.
Scientific Reports, 2018
Seafloor methane release can significantly affect the global carbon cycle and climate. Appreciabl... more Seafloor methane release can significantly affect the global carbon cycle and climate. Appreciable quantities of methane are stored in continental margin sediments as shallow gas and hydrate deposits, and changes in pressure, temperature and/or bottom-currents can liberate significant amounts of this greenhouse gas. Understanding the spatial and temporal dynamics of marine methane deposits and their relationships to environmental change are critical for assessing past and future carbon cycle and climate change. Here we present foraminiferal stable carbon isotope and sediment mineralogy records suggesting for the first time that seafloor methane release occurred along the southern Brazilian margin during the last glacial period (40-20 cal ka BP). Our results show that shallow gas deposits on the southern Brazilian margin responded to glacial−interglacial paleoceanographic changes releasing methane due to the synergy of sea level lowstand, warmer bottom waters and vigorous bottom currents during the last glacial period. High sea level during the Holocene resulted in an upslope shift of the Brazil Current, cooling the bottom waters and reducing bottom current strength, reducing methane emissions from the southern Brazilian margin. Methane is an important greenhouse gas and alterations in its atmospheric concentration have been associated with changes in global temperature over orbital and millennial timescales 1. Appreciable quantities of methane are sequestered in marine sediments in the form of ice-like gas hydrate deposits (ca. 1,600-2,000 Pg of C) 2 and shallow subsurface gas deposits, which are sensitive to changes in environmental conditions on the seafloor 3-5. Changes in pressure (i.e. sea level changes), bottom water temperature and bottom current strength have been the main triggers for seafloor gas methane seepage 6-9. A decrease in pressure and an increase in bottom water temperature and flow speed have great potential to destabilize gas deposits and release considerable amounts of methane to the ocean 3,10. An appreciable amount of methane released from seafloor gas deposits is consumed by microorganisms in the water column, potentially altering seawater carbonate chemistry and promoting ocean acidification 11. A portion of the released methane may reach the atmosphere, and significantly contribute to global warming 2,11 , although the amount of methane that reaches the atmosphere is still debated 12. An in-depth understanding of the temporal evolution and mechanisms related to seafloor gas methane release are critical for assessing ancient changes in the climate and chemistry of the oceans and the atmosphere, with potential consequences for future global carbon cycle and climate projections 2,11. The calcareous shells of benthic foraminifera living in cold seep habitats have more negative stable carbon isotopic (δ 13 C) values compared to the same species living in non-seep environments (see supplementary information) 13-15 because of the incorporation of negative δ 13 C from ambient methane 16. Recent laboratory culture experiments using pressure chambers to expose deep-water foraminifera species to labeled methane showed that
Anuário do Instituto de Geociências, 2002
In hydrologic and hydrogeological studies, environmental isotopes have been used as a tool to ide... more In hydrologic and hydrogeological studies, environmental isotopes have been used as a tool to identify provenience, quantify recharge and establish aquifer age. The aim of this work is to present a historic retrospective of the use of this technique in Brazil, focusing on study cases in Northeastern, Amazon and Paraná Basin regions. In addition, some comments on the main advances of this technique on a world basis, in contrast with the restrict use in Brazil help to promote a discussion on the perspectives and unfolding of this use at national level.
Anuário do Instituto de Geociências, 2018
A 180 ha area in the headwater of Paquequer watershed, a drainage system located at the Teresópol... more A 180 ha area in the headwater of Paquequer watershed, a drainage system located at the Teresópolis municipality, was selected for the evaluation of chemical weathering from collected river water samples in February and August 2013 in a granitic-gnaissic substrate free of direct anthropogenic influence for being located in a conservation unit (Serra dos ÓrgãosNational Park). The study area has a native forest cover, an altitude range of 1100-1900 m and an average annual rainfall of 2800 mm. The dissolved elements (Na, Mg, Ca, K, Si, Al) were analyzed by inductively coupled plasma spectrometries and the anions Cl and SO42-, by ion chromatography. These results, combined with the concentration data of nitrogen and phosphorus compounds (Alvim, 2016), the atmospheric deposition (Rodrigues, 2006), and the litogeochemistry (Zorita, 1979; Tupinambá, 1999; Tupinambá et al., 2012) were used to generate the dissolution model of mineral, employing the PHREEQC software. The mass balance indicat...
Anuário do Instituto de Geociências, 2014
A bacia de drenagem do rio Paquequer (269 km²) faz parte da região hidrográfica do rio Paraíba do... more A bacia de drenagem do rio Paquequer (269 km²) faz parte da região hidrográfica do rio Paraíba do Sul e situa-se no município de Teresópolis no estado do Rio de Janeiro. A sua litologia é representativa dos granitos e gnaisses da Região Sudeste do Brasil. Objetiva-se avaliar o processo de intemperismo destas rochas e a mobilidade dos elementos químicos através da hidrogeoquímica fluvial. Foram amostrados 15 pontos fluviais (com medição de vazão e parâmetros físico-químicos) sendo 9 no canal principal e 6 nos principais afluentes. As amostras foram analisadas por ICP-MS para Si, Fe, Mn, Al, Cu, Ni, Cr, Zn, Ba, Rb, Sr, Pb, Cd e Co e por cromatografia de íons para Na+ , K+ , Mg2+ e Ca2+. Dados da literatura referentes à composição elementar destas rochas foram utilizados. A hidrogeoquímica fluvial é dominada por Na, Ca e Si. Os metais Pb, Cd, Co e Cr apresentaram valores muito baixos refletindo a baixa abundância nas rochas e a inexistência de fontes antrópicas industriais. As concentr...
The growth of ferromanganese (FeMn) crusts on soft substrates is uncommon. FeMn crusts generally ... more The growth of ferromanganese (FeMn) crusts on soft substrates is uncommon. FeMn crusts generally accrete on hard-rock surfaces, where sedimentation rates are low and the rocks free of sediment cover. Here we use X-ray Powder Diffraction, Fourier Transform-Infra Red spectroscopy, Raman spectroscopy, X-ray Computed Micro-Tomography, Scanning Electron Microscopy and Particle Size Distribution analysis to investigate FeMn crusts associated with a porous, weakly consolidated, and bioturbated siltstone consisting mainly of authigenic palygorskite. FeMn crusts occur both on the surface of the siltstone and as FeMn lining and/or infilling of bioturbation burrows. Our results show that variations in the water redox conditions lead to a micrometric alternation of hydrogenetic vernadite and diagenetic todorokite and asbolane. These variations affected the oxidation state of Mn, which increased during the diagenetic formation of todorokite. The mineralogy of the FeMn oxides lining bioturbation ...
Weathering and pollution of the Paquequer watershed (Teresopolis, RJ) were evaluated based on the... more Weathering and pollution of the Paquequer watershed (Teresopolis, RJ) were evaluated based on the mineralogy of suspended sediments and the stream hydrogeochemistry. Fifteen sampling points along the main river channel and major tributaries were selected. The composition of suspended sediment shows mainly kaolinite, gibbsite and quartz, which indicate monosialitization process from rocks. Hydrogeochemistry is dominated by 1) Silica (H4SiO4) from weathering, 2) Chloride (Cl-) from rainfall and sewage sources and 3) Sodium (Na+ ) from all three sources. Na+/H4SiO4 ratio proved to be a very good pollution indicator in gneiss granitic watersheds as Paquequer watershed. Wastewater comes to Paquequer river downstream Serra dos Orgaos National Park. The polluted points are mainly inside the city, along the main stream and the affluent (Fisher) that drains the landfill.
Anuário do Instituto de Geociências - UFRJ
Uma área de 180 ha na cabeceira da bacia hidrográfica do Paquequer, sistema de drenagem situado n... more Uma área de 180 ha na cabeceira da bacia hidrográfica do Paquequer, sistema de drenagem situado no município de Teresópolis, foi selecionada para avaliação do intemperismo químico a partir de amostras de água fluvial coletadas em fevereiro e agosto de 2013 em substrato granito-gnaissico e local livre de influência antrópica direta, por estar inserido no Parque Nacional da Serra dos Órgãos. A área estudada possui cobertura de mata nativa, altitude variando de 1100 a 1900 m e precipitação média anual de 2800 mm. Os elementos dissolvidos (Na, Mg, Ca, K, Al, Si) foram determinados por espectrometrias atômicas com plasma indutivamente acoplado e os ânions Cl -e SO 4 2-, por cromatografia iônica. Esses resultados, assim como os dados de concentração de compostos nitrogenados e fosfatados (Alvim, 2016), de deposição atmosférica local (Rodrigues, 2006) e de composição litogeoquímica Tupinambá, 1999; Tupinambá et al., 2012) foram usados para gerar o modelo de dissolução de minerais, empregando o software PHREEQC. O balanço de massa apontou o Na como principal espécie química produto de intemperismo. Os dados mineralógicos mostram plagioclásio, quartzo, k-feldspato e biotita como mais abundantes no substrato, dentre os quais, unicamente o plagioclásio possui sódio em sua composição. De acordo com a série de Goldich (estabilidade mineral ao intemperismo), o plagioclásio foi identificado como principal mineral intemperizado desta assembleia, sendo consumido em uma taxa de 649 mol ha -1 ano -1 formando os minerais caulinita e gibbsita, e contribuindo com a liberação de no mínimo 818 mol ha -1 ano -1 e no máximo 1490 mol ha -1 ano -1 de sílica dissolvida (valor medido). Considerando o plagioclásio como o principal mineral responsável pelo fluxo de Na, a partir de cálculos estequiométricos associados à proporção de Si, estimou-se que a partir do intemperismo apenas do mineral plagioclásio, o solo deveria ser composto por 14% de caulinita e 86% de gibbsita em percentual molar relativo às duas fases minerais, o que está de acordo com os valores determinados no solo por difração de raio X (7% caulinita e 93% gibbsita).
Quaternary Science Reviews
Abstract The sediment core GL-1248, collected from the continental slope off northeastern Brazil,... more Abstract The sediment core GL-1248, collected from the continental slope off northeastern Brazil, was used to reconstruct mercury (Hg) variations in NE South American continental margin and understand its variability in response to paleoclimate changes over the past 128 ka. Mercury concentrations in GL-1248 ranged between 14.95 and 69.43 ng/g, showing a glacial-interglacial pattern with higher (lower) concentrations in the glacial period (interglacial period). Parallel trends of Hg and XRF-Fe plots suggest that following atmospheric Hg deposition onto the continent, Hg is incorporated with Fe compounds before transportation and eventual immobilization at the NE Brazil continental slope. Peaks of Hg and Fe/Ca ratio peaks occurred concurrently during certain Heinrich Stadials, indicating that Hg is transported from the continent alongside fluvial sediments during periods of increased precipitation and erosion in NE Brazil continent. Mercury concentrations varied with periodicities of 56 ka and 900 yr suggesting glacial-interglacial changes and millennial-scale variability, respectively. Total Hg and total organic carbon are poorly correlated, although the latter likely influenced Hg sequestration into marine sediments during millennial-scale events between 60 ka and 30 ka. Altogether, our results suggest that the atmosphere is the primary source of Hg to GL-1248 and glacial-interglacial climate variations were the major determinant of atmospheric Hg deposition. Furthermore, increased precipitation during millennial-scale events played a secondary role by enhancing Hg transport to the continental slope of NE Brazil.
Anuário do Instituto de Geociências - UFRJ
The mountainous region of Rio de Janeiro has a history of natural disasters. The aim of this stud... more The mountainous region of Rio de Janeiro has a history of natural disasters. The aim of this study was to understand the hydrology of this region. A dataset (up to 70 years) from four rainfall gauges and three stream gauges in Piabanha watershed (2065 km 2 ) was used for this purpose. Mean annual rainfall ranged from 2900 mm (at the headwaters) to 1250 mm in the central area of the watershed. The results showed good correlation between rainfall and stream gauges data. There is a seasonal pattern of dry winters (average month rainfall ranging from 15 to 90 mm) and 20 m 3 /s mean monthly discharge at the watershed outlet and a rainy summer (average month rainfall ranging from 150 to 450 mm) and 80 m 3 /s mean monthly discharge at the watershed outlet. The historical rainfall and discharge dataset showed a cyclicity of about 15 years bounded by the driest years. The most catastrophic events that occurred in the mountainous region of Rio de Janeiro were during the years around the top of the rainfall and discharge cycles. According to the historical trend the last cycle began at 1999 and the present moment (2015)(2016) matches the end of a drier period. However during this last cycle rainfall and discharge trends are not very clear. Together with an increase of great magnitude natural disasters frequency in recent years this may be a sign of an anthropogenic effect.
Journal of Applied Geophysics
Abstract Recent studies have indicated that the accurate identification of carbonate rock types i... more Abstract Recent studies have indicated that the accurate identification of carbonate rock types in a reservoir can be employed as a preliminary step to enhance the effectiveness of petrophysical property modeling. Furthermore, rock typing activity has been shown to be of key importance in several steps of formation evaluation, such as the study of sedimentary series, reservoir zonation and well-to-well correlation. In this paper, a methodology based exclusively on the analysis of 1H-NMR (Nuclear Magnetic Resonance) relaxation responses – using data mining algorithms – is evaluated to perform the automatic classification of carbonate samples according to their rock type. We analyze the effectiveness of six different classification algorithms (k-NN, Naive Bayes, C4.5, Random Forest, SMO and Multilayer Perceptron) and two data preprocessing strategies (discretization and feature selection). The dataset used in this evaluation is formed by 78 1H-NMR T2 distributions of fully brine-saturated rock samples from six different rock type classes. The experiments reveal that the combination of preprocessing strategies with classification algorithms is able to achieve a prediction accuracy of 97.4%.
International Journal of River Basin Management, 2016
ABSTRACT Mineralogy and geochemistry of the total suspended sediment (TSS) from a granite-gneiss ... more ABSTRACT Mineralogy and geochemistry of the total suspended sediment (TSS) from a granite-gneiss watershed in southeast Brazil brought light to geogenic and anthropogenic sources. TSS was sampled in 15 points along the Piabanha watershed in summer (February 2013) and winter (August 2013). The Piabanha watershed (2 × 103 km2) is located in the mountainous region of Rio de Janeiro, and it is an affluent of the Paraiba do Sul River, the most important river from the Brazilian southeastern coast. TSS mineralogical analyses were performed with X-ray powder diffraction. Geochemical analysis was done with energy dispersive X-ray fluorescence. Quartz, kaolinite and gibbsite were dominant in the TSS mineralogy, followed by feldspar and mica. Granite and gneiss rocks contribution in the TSS have a common mineralogical and geochemical source. But the alluvial deposits from river banks might have been responsible for the differences between summer and winter samples. The major features in TSS from geogenic sources were SiO2, Al2O3, MgO, Ga2O3, Nb2O5, Rb2O, K2O, SrO, ZrO2 and TiO2. The good correlation on the Si:Al molar ratio suggested that the source area is intensely weathered. Pollution features (sewage source) were given by significant TSS concentration of Fe2O3, MnO, ZnO, CuO, As2O3, CaO, Na2O, P2O5 and SO3.
Geociencias, 2012
RESUMO-A bacia do rio Paquequer (269 km 2), município de Teresópolis, região serrana do Estado do... more RESUMO-A bacia do rio Paquequer (269 km 2), município de Teresópolis, região serrana do Estado do Rio de Janeiro é ocupada por floresta, vegetação em diferentes estágios de sucessão vegetal e uma expressiva área urbana ao longo do vale principal do rio. Objetivouse caracterizar hidrologicamente a bacia com base em uma série temporal de chuva e vazão. Na área ocorrem granitos e gnaisses com latossolos e cambissolos. Dados de precipitação e de vazão foram coletados entre junho/2007 e maio/2009. A cabeceira é mais chuvosa (2800 mm/ano) que a foz da bacia (1400 mm/ano), com o mesmo padrão sazonal de chuvas. Chuvas acima de 10 mm na cabeceira, são suficientes para gerar hidrógrafa (lagtime de até 24 horas) na foz, distante 38 km. Uma precipitação extrema (20 mm/h) ocasiona um aumento de até 9,5 vezes da vazão, o fluxo máximo é influenciado pela condição antecedente e o lagtime é de 6-20 horas. Fluxos rápidos têm grande importância na vazão do rio, principalmente no verão, mascarando a contribuição dos fluxos subsuperficial e subterrâneo. A área urbana, as grandes declividades, solos rasos e muitos afloramentos rochosos explicam este comportamento hidrológico. O conhecimento gerado pode subsidiar um sistema de alerta para as frequentes enchentes no núcleo urbano de Teresópolis. Palavras-chave: hidrologia, hidrógrafa, tempo de resposta, Paquequer. ABSTRACT-C.S. Silveira & K.V. de Souza-Hydrological relationship between rainfall and discharge temporal range in a multiple land use drainage basin in Teresópolis, RJ, Brazil. Paquequer basin (269 km 2), is located in Teresópolis, a mountainous region of Rio de Janeiro state. It is covered by forest, vegetation in different ecological succession stages and a meaningful urban area along the river main valley. The basin was hydrological characterized based on rainfall and discharge analysis from a temporal range. Granites and gneisses are covered by latosoils and cambisoils. The hydrological data (rainfall and discharge) were collected between June/2007 and May/2009. The headwater is more rainy (2800 mm/year) than the basin outlet (1400 mm/year), but the seasonal rainfall pattern is the same. Headwater rainfall above 10mm is enough to form a hydrograph at the basin outlet (38 km away), within 24 hours. Under extreme precipitation (above 20 mm/h) discharge increases up to 9.5 times, peak discharge is controlled by antecedent flow condition and the average lagtime is 6-20 hours. Fast flows are very important in the stormflow, mainly in summer, hiding subsurface and subterranean flow contributions. The urban areas, the presence of great slopes, shallow soils and rocky outcrops explain this hydrological behavior. The results developed can be used in a flooding warning system to help city management.
Revista Brasileira de Geomorfologia, 2010
Este trabalho tem como objetivos principais apresentar e analisar, por meio de Sistema de Informa... more Este trabalho tem como objetivos principais apresentar e analisar, por meio de Sistema de Informação Geográfica, a distribuição espacial dos parâmetros ambientais, na escala 1:50.000, e discutir a possível influência destes na dinâmica hidrológica de chuvavazão da bacia do Paquequer. Este rio (5ª ordem, 30 km de comprimento) nasce na Serra dos Órgãos e drena 269 km2 para o vale do Paraíba do Sul. A pluviosidade anual varia de 1500 mm a jusante da bacia até mais de 3000 mm na cabeceira e as chuvas predominam no verão. Em 1996, a vegetação da bacia era composta por um mosaico de diferentes estágios de sucessão ecológica até Floresta Ombrófila Densa - Mata Atlântica, em fragmentos de diferentes tamanhos, e 25 % da área com uso urbano/rural. Na bacia ocorrem 3 unidades geológicas (Granito Teresópolis, Batólito Serra dos Órgãos (gnaisse) e Unidade Rio Negro (migmatito). Os afloramentos rochosos (5 % da área) são importantes feições da paisagem (principalmente no Granito Teresópolis). As ...
Geociencias, 2012
Introdução Materiais, métodos e técnicas Área de estudo Coleta e tratamento das amostras Análise ... more Introdução Materiais, métodos e técnicas Área de estudo Coleta e tratamento das amostras Análise mineralógica Análises químicas Análise estatística Resultados e discussão Mineralogia em suspensão Hidrogeoquímica fluvial Indicadores de poluição Fosfato Razão Na + /H 4 SiO 4 Análise estatística multivariada Conclusões Agradecimentos Referências bibliográficas RESUMO -O processo de intemperismo e a contribuição antrópica foram caracterizados na bacia de drenagem do rio Paquequer (Teresópolis, RJ) através da mineralogia do sedimento em suspensão e da hidrogeoquímica fluvial. Foram amostrados quinze pontos ao longo do canal principal do Paquequer e seus principais tributários. A mineralogia do material em suspensão é dominada pela caulinita, gibbsita e quartzo, indicando o processo de monossialitização das rochas. Os principais constituintes inorgânicos solúveis das águas fluviais da bacia do rio Paquequer são: 1) a sílica (H 4 SiO 4 ), advinda do intemperismo; 2) o cloreto (Cl - ), proveniente da água da chuva e dos lançamentos de esgotos domésticos; e o sódio (Na + ), procedente dessas três fontes. A razão Na + /H 4 SiO 4 mostrou ser um bom indicador de poluição atribuída à descarga de esgotos domésticos em bacias de drenagem gnáissica-granítica, como a do Paquequer. A jusante dos limites do Parque Nacional da Serra dos Órgãos, as águas do Paquequer passam a receber lançamentos de esgotos domésticos. Os pontos de amostragem mais poluídos do canal principal do Paquequer foram aqueles situados dentro do perímetro urbano de Teresópolis e no córrego Fisher, um tributário que drena o aterro sanitário municipal. Palavras-chave: Bacia de drenagem, intemperismo, hidrogeoquímica, poluição hídrica, esgotos domésticos. ABSTRACT -Weathering and pollution of the Paquequer watershed (Teresópolis, RJ) were evaluated based on the mineralogy of suspended sediments and the stream hydrogeochemistry. Fifteen sampling points along the main river channel and major tributaries were selected. The composition of suspended sediment shows mainly kaolinite, gibbsite and quartz, which indicate monosialitization process from rocks. Hydrogeochemistry is dominated by 1) Silica (H 4 SiO 4 ) from weathering, 2) Chloride (Cl -) from rainfall and sewage sources and 3) Sodium (Na + ) from all three sources. Na + /H 4 SiO 4 ratio proved to be a very good pollution indicator in gneiss granitic watersheds as Paquequer watershed. Wastewater comes to Paquequer river downstream Serra dos Orgãos National Park. The polluted points are mainly inside the city, along the main stream and the affluent (Fisher) that drains the landfill.
Soils and Rocks
A simple and low cost field experiment is described. The aim is to investigate the natural flow p... more A simple and low cost field experiment is described. The aim is to investigate the natural flow pathways developed upon rainfall infiltration in an unsaturated soil profile. Chloride was used as tracer species and the traced solution was applied on a tropical rainforest soil in the city of Rio de Janeiro. One dimensional infiltration was simulated in two experimental plots of a small catchment area (3.5 km2). Pore pressure was monitored with electronic tensiometers at diffenrent depths (20cm, 40cm, 80cm, 120cm and 200cm) and samples of soil solution were collected periodically for chemical analysis using suction samplers at the same depths. The technique proved to be efficient when combined with the analysis of the monitored physical and chemical parameters. The experiment showed the occurrence of preferential flow through a clayey soil control layer upon rainfall infiltration, at one dimensional condition. These preferential flow pathways are related to biotic processes and vegetat...
Anuário do Instituto de Geociências UFRJ, 2014
A bacia de drenagem do rio Paquequer (269 km²) faz parte da região hidrográfica do rio Paraíba do... more A bacia de drenagem do rio Paquequer (269 km²) faz parte da região hidrográfica do rio Paraíba do Sul e situa-se no município de Teresópolis no estado do Rio de Janeiro. A sua litologia é representativa dos granitos e gnaisses da Região Sudeste do Brasil. Objetiva-se avaliar o processo de intemperismo destas rochas e a mobilidade dos elementos químicos através da hidrogeoquímica fluvial. Foram amostrados 15 pontos fluviais (com medição de vazão e parâmetros físico-químicos) sendo 9 no canal principal e 6 nos principais afluentes. As amostras foram analisadas por ICP-MS para Si, Fe, Mn, Al, Cu, Ni, Cr, Zn, Ba, Rb, Sr, Pb, Cd e Co e por cromatografia de íons para Na + , K + , Mg 2+ e Ca 2+. Dados da literatura referentes à composição elementar destas rochas foram utilizados. A hidrogeoquímica fluvial é dominada por Na, Ca e Si. Os metais Pb, Cd, Co e Cr apresentaram valores muito baixos refletindo a baixa abundância nas rochas e a inexistência de fontes antrópicas industriais. As concentrações encontradas para os elementos Ni, Zn e Cu foram baixas e relacionadas ao núcleo urbano. A análise estatística multivariada mostrou 4 grupos principais, sendo utilizado o grupo 2 (pontos do médio e baixo curso do canal principal) para a estimativa de intemperismo. A composição geoquímica da Unidade Rio Negro (migmatito) influenciou a hidrogeoquímica através da razão Mg/Fe, maior no afluente que drena esta litologia. A carga fluvial indicou a fonte principal litológica para Si, Mg, Na, K, Ca, Sr, Ba e Rb. A estimativa de taxa de intemperismo indicou 3 grupos de elementos: i) os muito móveis (Ca e Sr); ii) os pouco móveis (Mg, K, Mn, Rb, Ba e Si) e iii) os imóveis (Fe e Al). Desta forma sugere-se que o plagioclásio (com Ca e Sr na sua estrutura) é o primeiro mineral a ser dissolvido e lixiviado na água percolante no perfil de intemperismo, seguido pelo K-feldspato e biotita. Parte do Si é retida para a cristalização de minerais secundários como os argilominerais. Os elementos Fe e Al têm tendência a formação de óxidos e hidróxidos que permanecem no perfil de intemperismo, justificando a baixa mobilidade.
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Papers by Carla Semiramis Silveira