Aquatic humic and fulvic acids from nine mainstem and seven major tributary sites in the Amazon River Basin are characterized by their elemental and lignin phenol compositions. Combined humic ...substances represent 60% of the riverine dissolved organic carbon (DOC), with fulvic to humic acid (FA : HA) ratios in the mainstem averaging 4.7 plus or minus 1.0. All dissolved humic and fulvic acids have clearly recognizable lignin components at levels (8 and 3% of the carbon) suggesting a predominantly allochthonous source. Lignin compositional characteristics are dominated by diagenetic transformations, which include preferential loss of methoxylated structural units and oxidative degradation of lignin side chains. Fulvic acids have consistently lower lignin levels, lower lignin phenol methoxylation, higher acid : aldehyde ratios, and higher C: N ratios than coexisting humic acids, all indicative of greater aerobic degradation of the fulvic acid fraction. An extreme example of lignin degradation is seen in the Rio Negro humic and fulvic acids, which differ significantly in lignin and elemental compositions from other blackwater tributary and mainstem samples. Over most of the mainstem humic and fulvic acids behave conservatively. However, downstream of the Rio Negro confluence, humic acids appear to be selectively adsorbed onto fine suspended particles. Approximately 25 and 40% of the total fluxes of lignin and of carbon are represented in the dissolved humic substances. The annual flux of dissolved, chemically recognizable lignin in the Amazon River at Obidos is calculated to be 1.2 10 super(11) g yr super(-1).
A methodology providing access to dumbbell-tipped, metal-semiconductor and metal oxide-semiconductor heterostructured nanorods has been developed. The synthesis and characterization of CdSedS ...nanorods incorporating ferromagnetic cobalt nanoinclusions at both nanorod termini (i.e., dumbbell morphology) are presented. The key step in the synthesis of these heterostructured nanorods was the decoration of CdSedS nanorods with platinum nanoparticle tips, which promoted the deposition of metallic CoNPs onto Pt-tipped CdSedS nanorods. Cobalt nanoparticle tips were then selectively oxidized to afford CdSedS nanorods with cobalt oxide domains at both termini. In the case of longer cobalt-tipped nanorods, heterostructured nanorods were observed to self-organize into complex dipolar assemblies, which formed as a consequence of magnetic associations of terminal CoNP tips. Colloidal polymerization of these cobalt-tipped nanorods afforded fused nanorod assemblies from the oxidation of cobalt nanoparticle tips at the ends of nanorods via the nanoscale Kirkendall effect. Wurtzite CdS nanorods survived both the deposition of metallic CoNP tips and conversion into cobalt oxide phases, as confirmed by both XRD and HRTEM analysis. A series of CdSedS nanorods of four different lengths ranging from 40 to 174 nm and comparable diameters (6-7 nm) were prepared and modified with both cobalt and cobalt oxide tips. The total synthesis of these heterostructured nanorods required five steps from commercially available reagents. Key synthetic considerations are discussed, with particular emphasis on reporting isolated yields of all intermediates and products from scale up of intermediate precursors.
The synthesis of a ferromagnetic heterostructured material consisting of a CdSe@CdS nanorod attached to a single dipolar cobalt nanoparticle (CoNP) into a "matchstick" morphology is reported. ...CdSe@CdS nanorods were modified by an activation reaction with Pt(acac)
2
which enabled selective one-sided deposition of a dipolar metallic CoNP-tip
via
the thermolysis of Co
2
(CO)
8
in the presence of polystyrene ligands. Small (<2 nm) PtNP-tips on CdSe@CdS nanorods were found to be responsible for the selective deposition of CoNP-tips onto one terminus per nanorod. The influence of the Pt-activation step for cobalt tipping was investigated by examination of numerous conditions and characterization of intermediates and materials using transmission electron microscopy and synchrotron X-ray diffraction.
Activation of CdSe@CdS nanorods by a platinum deposition reaction enables selective deposition of a single dipolar cobalt nanoparticle tip per nanorod.
The synthesis of a ferromagnetic heterostructured material consisting of a CdSedS nanorod attached to a single dipolar cobalt nanoparticle (CoNP) into a "matchstick" morphology is reported. CdSedS ...nanorods were modified by an activation reaction with Pt(acac) sub(2) which enabled selective one-sided deposition of a dipolar metallic CoNP-tip via the thermolysis of Co sub(2)(CO) sub(8) in the presence of polystyrene ligands. Small (<2 nm) PtNP-tips on CdSedS nanorods were found to be responsible for the selective deposition of CoNP-tips onto one terminus per nanorod. The influence of the Pt-activation step for cobalt tipping was investigated by examination of numerous conditions and characterization of intermediates and materials using transmission electron microscopy and synchrotron X-ray diffraction.
Microvascular disease, reflected by retinal vascular changes, has been shown to predict clinical coronary heart disease. Whether retinal vascular changes are associated with subclinical coronary ...artery disease is unclear and was examined in this study. The authors conducted a multiethnic, population-based study of 6,147 persons aged 45–84 years, sampled from six US communities in 2002–2004, who were free of clinical cardiovascular disease. Coronary artery calcification (CAC), a noninvasive measure of subclinical coronary artery disease, was assessed by cardiac computed tomography scanning and categorized into three groups of increasing severity: none (average CAC score = 0), mild (1–100), and moderate-to-severe (>100). Retinopathy signs and retinal vascular caliber were graded from retinal photographs following standardized protocols. After adjustment for age, gender, race/ethnicity, blood pressure, diabetes, lipid profile, smoking, and other risk factors, retinopathy was associated with having a moderate-to-severe CAC score (odds ratio = 1.43, 95% confidence interval: 1.18, 1.75). This association remained significant in both men and women and in persons with and without diabetes or hypertension. Variations in retinal vascular caliber were not significantly associated with CAC score. This study shows that retinopathy signs are independently associated with CAC, supporting the concept that common pathophysiologic processes may underlie both micro- and macrovascular disease.
La contribution andine à la biogéochimie de l'Amazone
Les fleuves andins ont vraisemblablement un rôle déterminant sur la biogéochimie de l'Amazone au Brésil. Les données disponibles sur le C ...organique, le NO3-, et le PO43- des fleuves andins montrent des concentrations très variables et ne révèlent aucune relation avec leur altitude ou leur position dans le bassin. En général, les concentrations des fleuves andins sont semblables à celles du chenal principal et de ses principaux affluents. L'explication des phénomènes d'altération du matériel provenant des Andes ne peut être que spéculative. Cependant, l'atténuation du signal andin est liée à la décomposition et à l'ajout de matériel en aval des Andes. Les analyses de 13C sur la matière organique particulaire ou soluble du chenal principal de l'Amazone mettent en évidence qu'une fraction andine persiste dans le système fluvial qui se jette dans l'océan Atlantique. En 1994, un nouveau programme international de recherche a commencé pour mieux caractériser la biogéochimie des fleuves andins.
Contributions from Andean rivers may play a significant role in determining the basin-wide biogeochemistry integrated into the mainstem Amazon River of Brazil. Concentration data for organic C, NO3-, and PO43- in Andean rivers are highly variable and reveal no clear spatial or altitudinal patterns. Concentrations measured in Andean rivers are similar to those reported in the mainstem Amazon river and its major tributaries. Explanations of processes which alter Andean-derived particulates and solutes as they exit the Cordillera are only speculative at this time, but their net effect is to diminish Andean signals through decomposition and dilution by lowland inputs. The 13C of particulate and dissolved organic matter in the mainstem Amazon provides evidence that some fraction of Andean derived material persists within the river system, ultimately to be discharged to the Atlantic Ocean. In 1994 a new collaborative research program was launched to further characterize the biogeochemistry of Andean rivers.
Contribución andina a la biogeoquímica del Río Amazonas.
Los ríos andinos podrían ejercer una influencia significativa sobre la biogeoquímica del Río Amazonas. Las concentraciones en C orgánico, NO3-, and PO43- de los ríos andinos son altamente variables y no presentan claros patrones geográficos o altitudinos. En general, las concentraciones presentan valores similares a aquéllos observados en el Río Amazonas. Actualmente sólo existen explicaciones especulativas de los procesos que modifican el material de origen andino ; sin embargo, la atenuación de la señal andina es una consecuencia del proceso de descomposición y de la añadidura de materiales provenientes de las planicies bajas. El contenido de 13C en el material orgánico del Río Amazonas constituye una evidencia concreta de que cierta fracción del material andino persiste y es transportado hacia el Atlántico. Un nuevo programa colaborativo de investigación se inició en 1994 con el propósito de caracterizar de una manera más completa la biogeoquímica de los ríos andinos.
Este trabalho discute os efeitos das mudanças do uso do solo na biogequímica dos rios da bacia de drenagem do rio Ji-Paraná (Rondônia). Nesta região, a distribuição espacial do desmatamento e das ...propriedades do solo resultam em sinais diferentes, possibilitando a divisão dos sistemas fluviais em três grupos: rios com águas pobres em íons e baixo impacto; rios com conteúdo iônico intermediário e impacto médio e rios com elevados conteúdo iônico e impacto antropogênico. As características biogeoquímicas dos rios têm relação significativa com a área de pasto, melhor parâmetro para prever a condutividade elétrica (r² = 0,87) e as concentrações de sódio (r² = 0,75), cloreto (r² = 0,69), potássio (r² = 0,63), fosfato (r² = 0.78), nitrogênio inorgânico (r² = 0.52), carbono inorgânico (r² = 0.81) e carbono orgânico (rain ² = 0.51) dissolvidos. Cálcio e magnésio tiveram sua variância explicada pelas características do solo e pastagem. Nossos resultados indicam que as mudanças observadas na micro-escala constituem "sinais biogeoquímicos" gerados pelo processamento do material nas margens dos rios. A medida em que os rios evoluem para ordens superiores, os sinais persistentes nos canais fluviais estão mais associdados às características da bacia de drenagem (solos e uso da terra). Apesar dos efeitos das mudanças observadas no uso do solo não serem ainda detectáveis na macro-escala (bacia amazônica), a disrupção da estrutura e funcionamento dos ecossistemas é detectável nas micro e meso escalas, com alterações significativas na ciclagem de nutrientes nos ecossistemas fluviais.
In this article we present the results of the effects of land use change on the river biogeochemistry of the Ji-Paraná basin (Rondônia). In this region, the spatial distribution of deforestation and soil properties result in different biogeochemical signals, allowing the division of the fluvial systems into three groups: rivers with low ionic concentration and low impact; rivers with intermediate ionic content and medium impact; and rivers with high ionic content and anthropogenic impact. River biogeochemical characteristics present a significant correlation with pasture area, the best predictor for electric conductivity (r² = 0,87), sodium (r² = 0,75), chloride (r² = 0,69), potassium (r² = 0,63), phosphate (r² = 0,78), and dissolved inorganic nitrogen (r² = 0,52), inorganic carbon (r² = 0,81) and organic carbon (r² = 0,51). For calcium and magnesium, both soil properties and pasture explained most of the observed variability. Our results indicate that the changes observed at the micro-scale constitute "biogeochemical signals" generated by the material processing at the riparian zones. As the rivers evolve to higher orders, the persistent signals in the fluvial channels are very closely related to the drainage basin characteristics (soils and land use), which, in turn, become the determinant of these systems dynamics. While at the macro-scale (the whole basin) the effects of land use changes are not yet detectable in the Amazon, the disruption of the structure and functioning is occuring at the micro and meso scales, with significant alterations of nutrient cycling in fluvial ecosystems
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