Geochemical signatures and mechanisms of trace elements dispersion in the area of the Vale das Gatas mine (Northern Portugal)

A geochemical survey involving the collection and analysis of 170 stream sediment samples was carried out in Vale das Gatas area in order to delineate geochemical signatures and to detect pollution hazards due to mining.Factor analysis applied to the data showed that the most important variables accounting for the first factor are Ag, Pb, Bi, As, W, Cd, Zn and Cu. These variables represent the most significant metalliferous elements of the original paragenesis, which still maintain a close relationship in the secondary geological environment. The spatial distribution of the factor scores referred to factor 1 indicates that positive scores occur predominantly in the Vale das Gatas and Sabrosa streams and in the main Pinhão river. The results also show that the Vale das Gatas mine is the most important contamination source in the Vale das Gatas district.In order to study the dispersion, transfer and uptake mechanisms of trace elements from the Vale das Gatas mine, additional sample media were collected, i.e., stream sediments, tailings, coatings, waters (surficial and mine waters) and specific biological species. Four sample stations were selected, namely two in connection with abandoned adits of the Vale das Gatas mine, one located in the Vale das Gatas stream and one located in the Pinhão River. The results show that chemical reactions of leaching and precipitation took place controlling the heavy metals in areas near the Vale das Gatas mine.At the same time, positive anomalous patterns are visible along the Pinhão river for about 20 km. The mineralogical composition of the stream sediments suggests that processes of mechanical dispersion also interfere in the secondary distribution of the metalliferous elements in that media.     

The microscopic structure of the oxygen–aluminium hole center in natural and neutron irradiated blue topaz

The dominant O⁻ hole center in natural and neutron irradiated blue topaz with general formula Al₂SiO₄(F,OH)₂ has been investigated with electron paramagnetic resonance (EPR) and optical absorption. The analysis of the EPR spectra of the O⁻ center yielded superhyperfine interactions with two equivalent Al neighbors in four magnetically inequivalent positions. From the g-factors it is found that the O⁻ hole center is located in (8d) Wyckoff positions on fluoride sites that were substituted by hydroxyl molecules prior to the irradiation. The spin Hamiltonian parameters were successfully interpreted with the model of transferred hyperfine interaction by exchange polarization supporting the localization of O⁻ in (F,OH)⁻ sites. The O⁻ center has the same thermal stability as the absorption band centered at 620 nm, which is responsible for the blue color. The intensity of the absorption band correlates linearly with the O⁻ concentration. Its correlation with the blue color is discussed.     

Evidence from olivine/melt element partitioning that nonbridging oxygen in silicate melts are not equivalent

Partitioning of Ca, Mn, Mg, and Fe²⁺ between olivine and melt has been used to examine the influence of energetically nonequivalent nonbridging oxygen in silicate melts. Partitioning experiments were conducted at ambient pressure in air and 1400°C with melts in equilibrium with forsterite-rich olivine (Fo >95 mol%). The main compositional variables of the melts were NBO/T and Na/(Na+Ca). In all melts, the main structural units were of Q⁴, Q³, and Q² type with nonbridging oxygen, therefore, in the Q³ and Q² units.For melts with high Q³/Q²-abundance ratio (corresponding to NBO/T near 1), increasing Na/(Na+Ca) [and Na/(Na+Ca+Mn+Mg+Fe²⁺)] results in a systematic decrease of the partition coefficients, K_Ca^ol/melt, K_Mn^ol/melt, K_Mg^ol/melt, and K_Fe2+^ol/melt, because of ordering of the network-modifying Ca, Mn, Mg, and Fe²⁺ among nonbridging oxygen in Q³ and Q² structural units. This decrease is more pronounced the smaller the ionic radius of the cation. With decreasing Q³/Q² abundance ratio (less-polymerized melts) this effect becomes less pronounced.Activity-composition relations among network-modifying cations in silicate melts are, therefore, governed by availability of energetically nonequivalent nonbridging oxygen in individual Qⁿ-species in the melt. As a result, any composition change that enhances abundance of highly depolymerized Qⁿ-species will cause partition coefficients to decrease.     

Effects of Amazonian deforestation on climate: a numerical experiment with a coupled biosphere-atmosphere model with soil hydrology

Summary A coupled biosphere-atmosphere statistical-dynamical model (SDM) is used to study the climatic effects of Amazonian deforestation. A soil moisture model based on BATS has been incorporated into the SDM in order to study the biogeophysical feedback of change in surface characteristics to regional climate due to the deforestation. In the control experiment, the mean annual and mean seasonal climate is well simulated by the model when compared with NCEP/NCAR reanalysis data. In the deforestation experiment, the evergreen broadleaf trees in the Amazonian region are substituted by short grass. The effects of Amazonian deforestation on regional climate are analysed taking into account the model simulations for the land portion of the latitude belts comprising the tropical region. Amazonian deforestation results in regional climate changes such as a decrease in evaporation, precipitation, available surface net radiation and soil moisture content, and an increase in temperatures and sensible heat flux. The reduction in transpiration was responsible for the most part of the decrease in total evapotranspiration. The reduction in precipitation was larger than the decrease in evapotranspiration so that runoff was reduced. The simulation of the diurnal cycle of the surface temperature shows an increase in temperature during the day and a decrease at night, which is in agreement with observations, whereas earlier GCM experiments showed an increase both during the day and night. In general, the changes in temperature and energy fluxes are in good agreement with GCM experiments, showing that the SDM is able to simulate the characteristics of the tropical climate that are associated with the substitution of forest by pasture areas.     

Geotechnical properties and behavior of high-porosity, organic-rich sediments in Eckernförde Bay, Germany

The organically rich, fine-grained, very soft, high porosity sediments in the inner portion of Eckernförde Bay, Germany have varying amounts of methane gas, with the horizon of gas fluctuating vertically on a seasonal cycle. The sharp vertical gradient in water content, with values exceeding 500% at the sediment–water interface, and corresponding gradient in density can be expected to cause a significant subbottom acoustic impedance contrast in these surficial sediments. Equations are presented to characterize geotechnical property variations of the upper 5 m. The upper 1.5 m exhibits appreciable ‘apparent’ overconsolidation with a trend toward a normally consolidated stress state at 2.5 m depth. The coefficient of permeability of the upper 40 cm is low (4×10^-6 cm s^-1) and the sediment is highly compressible with compression indices of 2.7–6.8. Triaxial compression test results indicate that the sediment behaves as a normally consolidated clay with a low friction angle (22°). The rheological behavior of the upper 20–30 cm, determined with a small vane device, is indicative of a shear-thinning material, implying that the resistance to penetration decreases with increasing velocity.     

Effect of monochloramine on isolated fulvic acid

Monochloramine is interesting both as a selective oxidant of fulvic acid and as a drinking water disinfectant. In this study, the controlled reaction of aquatic fulvic acid with monochloramine did not result in products detectable by ether extraction-gas chromatography-flame ionization detection techniques. Evidence of a reaction was shown by bleaching of the fulvic acid solution (decreased absorbance at 465 nm) and chlorine substitution. Chlorine-containing products were quantified by the total carbon adsorbable organic halide (TOX) parameter. Bleaching and organic chlorine formation were much less extensive than in the reaction of free chlorine with fulvic acid. Monochloramine was shown to produce an organic chlorine fraction more hydrophilic and with higher molecular size than that produced by chlorine and fulvic acid. Results suggest that monochloramine may be useful tool for the investigation of certain humic functionalities because it reacts rather selectively and to a small extent with aquatic fulvic acid.     

The kerogen type, depositional environment and maturity, of the Irati Shale, Upper Permian of Paraná Basin, Southern Brazil

Two samples from the upper and lower horizons of the Irati oil shale of the Paraná Basin, Brazil were sampled in a single borehole, and analysed using organic petrography and geochemistry. The results are interpreted in terms of the kerogen type, maturity and depositional environment of the two horizons.Organic petrography shows the oil-shales to be composed of a mineral groundmass, mainly clay minerals, carbonate and pyrite, associated, and sometimes impregnated, with fluorescing organic material and disseminated phytoclasts. Humic material is fairly rare and mostly present as very small particles. The liptinitic particles are mostly alginite (A and B), sporinite and more rarely resinite. Reflectance measurements (upper seam = 0.34% R₀; lower seam = 0.40% R₀) indicate an equivalent rank of lignite/sub-bituminous coal (ASTM), i.e. immature with respect to oil and gas generation. Different organic geochemical methods (Rock-Eval pyrolysis, solvent extraction, GC and GC-MS) demonstrate both samples to be immature, rich oil-shales (100–114 kg/ton) containing Type I kerogen, of a dominantly bacterially-degraded algal origin deposited in a lacustrine environment. The presence of Botryococcus suggests deposition under fresh/brackish water conditions.A tentative interpretation of the extract and vitrinite reflectance data suggests a maximum paleo-burial of between 1.3 and 2.8 km for the analysed section of the Irati Formation.     

Governing Metropolitan Lisbon: A tale of fragmented urban governance

This article is concerned with the nature of the present governance framework in the Lisbon metropolitan area and with the conditions responsible for the lack of any consistent intergovernmental and inter-tier co-ordination. It shows how Lisbon, where a form of metropolitan government was introduced only in 1991, is different from other European cities, but at the same time similar with regard to the limits associated with the associative or (polycentric) model adopted. The article concludes by discussing alternative scenarios for the reform of metropolitan government as well as the institutional and policy challenges facing the Lisbon metropolitan area. This revised version was published online in August 2006 with corrections to the Cover Date.