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Tropical estuarine deltas generally present poorly buffered waters in their freshwaters. Carbonate chemistry predicts that mixture of such warm freshwater with seawater will create rapid consumption of the freshwater carbon dioxide (CO2) by the carbonate buffering capacity of the seawater. In this study, we used the Paraiba do Sul River as a laboratory to investigate how thermodynamics compare with biological processes, gas exchange, and tidal advection from mangrove. We conducted three spatial surveys covering the salinity gradient of the main channel and surrounding mangrove waters and one 24-h mooring in a mangrove creek. In the main channel, dissolved inorganic carbon (DIC) and total alkalinity (TA) showed closely conservative distribution along the salinity gradient, increasing seaward. The partial pressure of CO2 (pCO(2)) followed a bell-shaped curve predicted by carbonate chemistry for conservative mixing of river and ocean endmembers. During high river flow, pCO(2) sharply decreased between salinities 0 and 5 (1800 to 390 ppmv), a pCO(2) drawdown attributed to riverine outgassing and thermodynamics. Indeed, the mixing of TA-poor freshwater (363 +/- 16 mu mol kg(-1)) with TA-rich seawater creates a deficit of dissolved CO2 not related to biotic processes. During low river flow, the entire mixing zone was undersaturated in pCO(2) with an increasing trend seaward. However, observed pCO(2) values were slightly above those predicted by conservativity. Approximately half of this deviation was attributed to biological activity (net heterotrophy), and remaining deviation was assigned to the effects of gas exchange (18%) and water heating (36%). The effect of gas exchange was higher in fresh and low salinity waters, reflecting the higher outgassing/ingassing of CO2, and lower buffering capacity. Water heating was more important in mid- to high-salinities as a result of diel patterns of solar irradiance. Heterotrophy was slight and not able to outcompete thermodynamics and generate outgassing during estuarine mixing. Consistently, stable isotopic signatures of DIC (delta C-13-DIC) presented slight deviations below the conservative mixing, corroborating net heterotrophy in the main channel. Areas of CO2 uptake due to phytoplankton activity were identified but restricted to the freshwater endmember during low river flow, with lowest pCO(2) (up to 41 ppmv) and the highest chlorophyll a (up to 21.3 mu g L-1). The estuary was a CO2 sink during low river flow ( - 1.34 to -5.26 mmolC m(-2) d(-1)) and a source during high river flow (5.71 to 19.37 mmolC m(-2) d(-1)). In the mangrove creek, the pCO(2), DIC, delta C-13-DIC and TA presented deviations from the conservativity, with slopes between TA and DIC demonstrating organic carbon degradation mediated by aerobic respiration and sulphate reduction. Mangrove creek waters were a CO2 source (average of 134.81 mmolC m(-2) d(-1)), exhibiting high values of pCO(2) (up to 21,720 ppmv). The results reveal that the low buffering capacity in the main channel of tropical estuarine deltas can be the predominant driver of pCO(2), generating CO2 undersaturation along the mixing zone, a process overlooked in estuarine systems. Moreover, air-water CO2 exchange, thermal variability, and biological activities contribute to deviation of the carbonate system from conservative mixing in specific estuarine areas, also modulating pCO(2) variability.

A adição de substâncias húmicas é um recurso viável tanto para melhoria de características físicas e químicas de solos pobres ou degradados, quanto para fixação de carbono, sendo estratégia recomendada para solos do semi-árido brasileiro. O presente trabalho teve como objetivo caracterizar ácidos húmicos (AH), produzidos a partir de carvão vegetal de Mimosa tenuiflora (jurema-preta) e Aspidosperma pyrifolium (pereiro), duas espécies florestais que estão entre as três de maior ocorrência no semi-árido nordestino. Foram produzidos carvões em diferentes temperaturas finais de carbonização (250, 300, 350, 400, 450, 500 e 550 °C). Os carvões em pó após peneiramento foram oxidados com HNO3 25% (p/p). Os AH foram extraídos a partir dos produtos de reação, segundo a técnica padrão adotada pela Sociedade Internacional de Substâncias Húmicas (IHSS), com modificações. Os AH obtidos foram caracterizados por análise elementar, termogravimetria, espectrofotometria no infra-vermelho (IV), espectrofotometria no UV-Visível e fluorescência, o que possibilitou a identificação e a classificação da estrutura química e dos grupos funcionais dos AH, além da composição elementar, grau de aromaticidade das moléculas e grau de humificação. A análise elementar mostrou baixas porcentagens de hidrogênio, indicando alta aromaticidade dos AH obtidas dos diferentes carvões vegetais. As análises termogravimétricas mostraram que os AH são resistentes à termodegradação, sugerindo a existência de estruturas aromáticas fortemente condensadas, para os AH obtidos das duas espécies. As demais análises mostraram resultados que estão em acordo com a literatura, permitindo concluir que a metodologia adotada para extrair e caracterizar os AH a partir dos carvões vegetais foi eficiente e que os compostos produzidos a partir do carvão são similares aos AH encontrados em solos e ao AH padrão da IHSS (International Humic Substances Society). Made available in DSpace on 2019-09-20T00:37:10Z (GMT). No. of bitstreams: 1 CARACTERIZACAODEACIDOSHUMICOS.pdf: 235381 bytes, checksum: c0a565f53036a7327ff9c4236dededf2 (MD5) Previous issue date: 2009

El estudio de la radiactividad ambiental es un tema que no suele incluirse en los cursos de física de nivel secundario o incluso universitario. En consecuencia, los estudiantes no son capaces de discutir correctamente los efectos de la exposición a la radiación gamma terrestre. Este trabajo propone acercar el tema de la interacción de las radiaciones ionizantes con nuestro medio ambiente; en el cual se mide la tasa de exposición a la radiación gamma natural utilizando un monitor de tipo Geiger-Müller. La medición se realiza en distintos ambientes de trabajo, urbano y turístico, de la provincia de San Luis. En particular, en las Salinas del Bebedero y en la antigua mina de oro de La Carolina y sus zonas aledañas. Por lo tanto, nuestro objetivo es, además del desarrollo de nuevas técnicas para la enseñanza de la física, despertar el interés científico de los estudiantes en las aplicaciones de la física nuclear a las ciencias del medio ambiente The study of environmental radioactivity is a topic not usually included in physics courses at the secondary and even university levels. Consequently, students are not able to properly discuss the effects of exposure to terrestrial gamma radiation. This paper proposes to approach the issue of ionizing radiation interaction with our environment, in which measurements of gamma exposure rates using a Geiger-Müller type gauge are evaluated. The experimental activity is performed in different working environments, urban and touristic, of San Luis province in Argentina. Particularly, the Bebedero salt mine and the La Carolina old gold mine and surrounding areas. Therefore, our aim is also to develop new techniques for teaching physics, awaking the scientific interest of students in nuclear physics applications to environmental sciences Fil: Rizzotto, M. G.. Universidad Nacional de San Luis - CONICET. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi" (IMASL). San Luis. Argentina Fil: Anjos, R. M.. Universidade Federal Fluminense. Instituto de Física. Río de Janeiro. Brasil Fil: Estellita, Leticia. Universidade Federal Fluminense. Instituto de Física. Río de Janeiro. Brasil Fil: Sosa Flores, C.. Universidad Nacional de San Luis (UNSL). Facultad de Ciencias Físico-Matemáticas y Naturales (UNSL-FCFMYN). Departamento de Física. San Luis. Argentina Fil: Debans, Jorge Matías. Universidad Nacional de San Luis (UNSL). Facultad de Ciencias Físico-Matemáticas y Naturales (UNSL-FCFMYN). Departamento de Minería Fil: Gutierrez, G. A.. Universidad Nacional de San Luis (UNSL). Facultad de Ciencias Físico-Matemáticas y Naturales (UNSL-FCFMYN). Departamento de Minería Fil: Claros Figueroa, A.. Instituto Aleluya. San Luis. Argentina

The inelastic, two-neutron and α transfer and quasielastic cross sections for the 18O+110Pd system have been measured in the near barrier region (40 MeV Elab 58 MeV). The experiments were performed in the S˜ao Paulo Pelletron laboratory. Coupled-channel analysis of the experimental data was performed using the S˜ao Paulo potential as a microscopic bare interaction. In the calculations, low-lying inelastic excitations, one- and two-neutron and α transfers to the target were considered as the main couplings, with no extra surface absorption. The agreement between the theoretical results and the experimental data is good. The role played by the coupled channels is very different in comparison with similar data analyses for the closed-shell region around 58Ni.

We present results on radiocarbon dating of foraminifera shell samples, collected on the upper slope of Campos Basin, in Southern Brazil. This is the first time that the sedimentation rate of this area is measured with a fine scale (cm) stratigraphy. C-14 ages vary from (2560 +/- 80) years. BP at the top to (7260 +/- 80) years. BP at the bottom of the sediment column. The mean accumulation ratio for the whole column is (6.2 +/- 0.7) cm/kyears. (C) 2004 Elsevier B.V. All rights reserved.