Mercury, copper and zinc contamination in soils and fluvial sediments from an abandoned gold mining area in southern Minas Gerais State, Brazil     

Ricardo Cesar  Silvia Egler  Helena Polivanov  Zuleica Castilhos  Ana Paula Rodrigues 《Environmental Earth Sciences》2011,64(1):211-222

Mercury, zinc and copper contamination was evaluated in soils and fluvial sediments from an abandoned gold mining site at Descoberto Municipality (southern Minas Gerais State, Brazil). Metals bioavailability and potential mobility were studied through physical, chemical and mineralogical characterization, geoaccumulation indexes calculations, mercury speciation and determination of potentially bioavailable contents of zinc and copper. Values of pH were in the neutral range, while organic matter concentrations were very low. Mineralogical characterization, in the total samples, indicated the presence of quartz, kaolinite and gibbsite for all samples. Total mercury, zinc and cooper concentrations were higher than the limits recommended by Brazilian documents. Geoaccumulations indexes revealed that most of the sediment samples were low to moderately polluted by zinc and copper, while just one sample was very strongly polluted by mercury. Mercury speciation revealed the predominance of the elementary form for all samples, and low concentrations for exchangeable, strongly bound and residual fractions. Zinc and copper behavior was strongly controlled by iron and aluminum concentrations, while their bioavailable contents were very low in comparison with the total concentrations.  相似文献   

Origin of rare earth element anomalies in mangrove sediments,Sepetiba Bay,SE Brazil: used as geochemical tracers of sediment sources     

Emmanoel V. Silva-Filho  Christian J. Sanders  Michel Bernat  Ana M. G. Figueiredo  Silvia M. Sella  Julio Wasserman 《Environmental Earth Sciences》2011,64(5):1257-1267

Elemental contents were determined in two mangrove habitats along Sepetiba Bay, SE Brazil, an area impacted by local industrial activities, as well as hinterland water diversion networks. This study demonstrates how specific REEs (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) may be used as a sediment source tracer to mangrove-dominated coastlines. From the two stations studied, a pair of cores was collected, one in the mangrove forest and the other in the tidal flat. Station 1 results show a general enrichment in most of the fractioned patterns of the REEs normalised by Post-Archean Australian Shale. The relatively light rare earth elements are similarly enriched in the generally more polluted Station 1. Despite the probable difference in background sediment characteristics, a common sharp increase in mud contents patterns in the upper part of the mangrove sediment core was related to a lower REE content as well as Eu anomalies. With existing knowledge of clockwise water circulation in the bay, these patterns can be explained by man-made water diversion from the São Francisco and Guandu rivers, initiated more than 30 years ago, whereby suspended matter with relatively large contents of REEs and material originating from industrial sources accumulate in the eastern sector of the bay. This is the first comprehensive assessment of REEs as sedimentary tracers in a mangrove ecosystem in Brazil.  相似文献   

Assessment of benthic trophic status of marine coastal ecosystems: Significance of meiofaunal rare taxa     

Antonio Pusceddu  Silvia BianchelliCristina Gambi  Roberto Danovaro 《Estuarine, Coastal and Shelf Science》2011

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XMM–Newton EPIC observations of Her X-1     

Gavin Ramsay  Silvia Zane  Mario A. Jimenez-Garate  Jan-Willem den Herder  C. J. Hailey 《Monthly notices of the Royal Astronomical Society》2002,337(4):1185-1192

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The discovery of clumpy structure in the diffuse gas towards Cyg OB2 No. 12     

Flavio Scappini  Silvia Casu  Cesare Cecchi-Pestellini  Michael Olberg 《Monthly notices of the Royal Astronomical Society》2002,337(2):495-498

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Unveiling the thermal and magnetic map of neutron star surfaces though their X-ray emission: method and light-curve analysis     

Silvia Zane  Roberto Turolla 《Monthly notices of the Royal Astronomical Society》2006,366(3):727-738

Recent Chandra and XMM–Newton observations of a number of X-ray 'dim' pulsating neutron stars have revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ∼12–35 per cent), the pulse shape is often non-sinusoidal, and the hard X-ray colour appears to be anticorrelated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4−3125, has been found to undergo rather sensible changes in both its spectral and timing properties over a time-scale of a few years. All these new findings seem difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field, at least if surface emission is produced in an atmosphere on top of the crust. In this paper we explore how a dipolar+quadrupolar star-centred field influences the properties of the observed light curves. The phase-resolved spectrum has been evaluated accounting for both radiative transfer in a magnetized atmosphere and general relativistic ray-bending. We computed over 78 000 light curves, varying the quadrupolar components and the viewing geometry. A comparison of the data with our model indicates that higher-order multipoles are required to reproduce the observations.  相似文献   

Late glacial and Holocene Ostracoda from the Melilla cold-water coral mound field     

Claudius M. Pirkenseer  Silvia Spezzaferri  Claudio Stalder 《Swiss Journal of Geoscience》2018,111(3):549-560

The ostracod assemblages from sediment core TTR17-401G recovered from the Melilla cold-water coral mound field in the eastern Alboran Sea spanning the last 13 ka are analysed quantitatively, taxonomically and palaeoecologically. The core can be subdivided in three distinct assemblages linked to environmental shifts during the Younger Dryas and the Bølling–Allerød interstadial. A total of 9 ostracod species is recorded, Paracypris polita is dominant throughout the core. Common accessory taxa Cytherella robusta, Echinocythereis vidua and Macromckenziea ligustica characterize the well-oxygenated ostracod assemblage 2 affected by the Younger Dryas. Favourable growth conditions for ostracods during the latter are indicated by large-sized Krithe praetexta specimens.  相似文献   

Distribution of benthic foraminiferal assemblages in the transitional environment of the Djerba lagoon (Tunisia)     

Akram El Kateb  Claudio Stalder  Christoph Neururer  Robin Fentimen  Jorge E. Spangenberg  Silvia Spezzaferri 《Swiss Journal of Geoscience》2018,111(3):589-606

The eastern edge of the Djerba Island represents an important tourist pole. However, studies describing the environmental processes affecting this Island are scarce. Although never studied before, the peculiar Djerba lagoon is well known by the local population and by tourists. In July 2014, surface sediment and seawater samples were collected in this lagoon to measure grain size, organic matter content and living foraminiferal assemblages to describe environmental conditions. Seawater samples were also collected and the concentration of 17 chemical elements were measured by ICP-OES. The results show that a salinity gradient along the studied transect clearly impacts seagrass distribution, creating different environmental conditions inside the Djerba lagoon. Biotic and abiotic parameters reflect a transitional environment from hypersaline to normal marine conditions. Living benthic foraminifera show an adaptation to changing conditions within the different parts of the lagoon. In particular, the presence of Ammonia spp. and Haynesina depressula correlates with hypersaline waters, whilst Brizalina striatula characterizes the parts of the lagoon colonized by seagrass. Epifaunal species, such as Rosalina vilardeboana and Amphistegina spp. colonize hard substrata present at the transition between the lagoon and the open sea.  相似文献   

Using topographical attributes to evaluate gully erosion proneness (susceptibility) in two mediterranean basins: advantages and limitations   总被引：2，自引：0，他引：2  

G&#;mez-Guti&#;rrez  &#;lvaro  Conoscenti  Christian  Angileri  Silvia Eleonora  Rotigliano  Edoardo  Schnabel  Susanne 《Natural Hazards》2015,79(1):291-316

Empirical multivariate predictive models represent an important tool to estimate gully erosion susceptibility. Topography, lithology, climate, land use and vegetation cover are commonly used as input for these approaches. In this paper, two multivariate predictive models were generated for two gully erosion processes in San Giorgio basin (Italy) and Mula River basin (Spain) using only topographical attributes as independent variables. Initially, nine models (five for San Giorgio and four for Mula) with pixel sizes ranging from 2 to 50 m were generated, and validation statistics were calculated to estimate the optimal pixel size. The best models were selected based on model performance using the area under the receiver operating characteristic (AUC) curve and the generalized cross-validation. The best pixel size was 4 m in the San Giorgio basin and 20 m in the Mula basin. The finest resolution was not necessarily the best; rather, the relationship between digital elevation model resolution and size of the landform was important. The two selected models showed an excellent performance with AUC values of 0.859 and 0.826 for San Giorgio and Mula, respectively. The Topographic Wetness Index and the general curvature were identified as key topographical attributes in San Giorgio and Mula basins, respectively. Both attributes were related to the processes observed in the field and described in the literature. Finally, maps of gully erosion susceptibility were produced for each basin. These maps showed that 22 and 20 % of San Giorgio and Mula basins, respectively, present favourable conditions for the development of gullies.  相似文献   

On the Effect of a Low-level Jet on Atmospheric Pollutant Dispersion: A Case Study Over a Coastal Complex Domain,Employing High-Resolution Modelling     

Haikin  Nitsa  Castelli  Silvia Trini 《Boundary-Layer Meteorology》2022,182(3):471-495

Boundary-Layer Meteorology - A low-level-jet (LLJ) event that occurred over a coastal area in complex terrain is analyzed to investigate its effect on the dispersion of potential air pollutants...  相似文献