Impact of trace metals on denitrification in estuarine sediments of the Douro River estuary,Portugal

Denitrification influences the nitrogen budget in estuaries by removing fixed nitrogen from the inorganic pool; rates are dependent on both geological and geographic conditions as well as increasing anthropogenic impacts. In this study the effects of copper (Cu), chromium (Cr), zinc (Zn), cadmium (Cd) and lead (Pb), on the denitrification pathway were evaluated in subtidal and intertidal sediments of the Douro River estuary. Dinitrogen, N₂O and NO₂⁻ production rates were measured in triplicate slurries of field samples under different treatments of metal concentrations. Results demonstrated that similar metal amendments led to different site responses for denitrification, suggesting that variations in sediment properties (metal concentrations, grain size, organic matter content, etc.) and/or differences in denitrifying community tolerance modulate the level of metal toxicity. Denitrifying communities in subtidal muddy sediments were not affected by increasing concentrations of metals. In contrast, intertidal sandy sites revealed high sensitivity to almost all trace metals tested; almost complete inhibition by Cr (95%) and Cu (85%) was observed for 98 and 79 μg per gram of wet sediment respectively, and by Zn (92%) at the highest concentration added (490 μg per gram of wet sediment). Moreover, the addition of trace metals stimulated N₂O and NO₂⁻ accumulation in intertidal sandy (Zn, Cu, Cr and Cd) and muddy sediments (Cu and Zn), demonstrating a pronounced inhibitory effect on specific steps within the denitrification enzymatic system. In summary, the results obtained suggest that, according to the type of estuarine sediment, trace metals cannot only reduce total N removal from an estuary via denitrification but also can enhance the release of N₂O, a powerful greenhouse gas.     

Relationship between physical and chemical soil attributes and plant species diversity in tropical mountain ecosystems from Brazil

Although the high diversity of plant species in the rupestrian fields has been primarily attributed to the existence of a set of distinct habitats, few studies support this assertion. The present study aimed to further investigate the relationship between physical and chemical attributes of soils with the diversity of plant species in this unique ecosystem. The rupestrian field is a unique vegetation formation that covers some of the southeastern Brazilian mountains in the transition of the Atlantic rain forest and the Cerrado （savanna）. Different habitats occur according to soil characteristics （e.g., presence of rocks, sand, fertility, hydrology, etc.）. These attributes ultimately influence the vegetation that is highly adapted to the harsh edaphic and climatic mountain conditions. Five distinct habitats were studied by us： rocky outcrops, peat bogs, sandy bogs, quartz gravelfields, and ＂cerrado＂ （savanna）. A floristic survey indicated that four families are found at greater frequency： Poaceae, Asteraceae, Cyperaceae, and Leguminosae. The greatest diversity of plant species was found in the rocky outcrops habitat, followed by cerrado, peat bog, quartz gravel grassland, and sandy bogs, respectively. The main difference in the floristic composition among these habitats was related to the dominant species. Trachypogon spicatus （Poaceae） was the most dominant species in the rocky outcrops, Axonopus siccus （Poaceae） in the peat bogs, Lagenocarpus rigidus （Cyperaceae） in the sandy bogs, Schizachyrium tenerum （Poaceae） in the cerrado, while Vellozia sp. 8 （Velloziaceae） dominated the vegetation in the quartz gravel grassland. This study demonstrated that physical and chemical soil properties strongly related the diversity of plant species occurring in the different habitats of rupestrian fields.     

Asymmetric Atlantic continental margins

We analyze the gross crustal structure of the Atlantic Ocean passive continental margins from north to the south, comparing eleven sections of the conjugate margins. As a general result, the western margins show a sharper continental-ocean transition with respect to the eastern margins that rather show a wider stretched and thinner margin. The Moho is in average about 5.7°±1° dipping toward the interior of the continent on the western side, whereas it is about 2.7°±1° in the eastern margins. Moreover, the stretched continental crust is on average 244 km wide on the western side, whereas it is up to about 439 km on the eastern side of the Atlantic. This systematic asymmetry reflects the early stages of the diachronous Mesozoic to Cenozoic continental rifting, which is inferred as the result of a polarized westward motion of both western and eastern plates, being Greenland, Northern and Southern Americas plates moving westward faster with respect to Scandinavia, Europe and Africa, relative to the underlying mantle.     

Hydrochemical constraints between the karst Tabular Middle Atlas Causses and the Saïs basin (Morocco): implications of groundwater circulation

The karst Tabular Middle Atlas Causses reservoir is the main drinking-water supply of Fez-Meknes region (Saïs Basin) in Morocco. Recent analyses showed a decline in associated groundwater chemical quality and increased turbidity. To understand this hydrosystem, four surveys were undertaken during fall and spring, 2009–2011. Hydrogeochemical studies coupled with isotopic analyses (δ¹⁸O, δD and ²²²Rn) showed that the aquifers between the causses (mountains) and the Saïs Basin are of Liassic origin and at the southern extremities are of Triassic origin. Five recharge zones of different altitudes have been defined, including two main mixing zones in the south. Deuterium excess results suggest local recharge, while a plot of δ¹⁸O versus δD characterizes a confined aquifer in the eastern sector. ²²²Rn results reveal areas of rapid exchanges with an upwelling time of less than 2 weeks. A schematic conceptual model is presented to explain the groundwater circulation system and the behavior of this karst system.     

Hypothesis on a possible role of El Ni?o in the occurrence of influenza pandemics

The El Ni?o phenomenon is the Earth??s strongest climatic fluctuation on an interannual timescale and has a quasi-global impact, although originating in the tropical Pacific Ocean. A very strong El Ni?o is recognized to cause extreme dryness and wetness in different parts of the world. We show that all the eight well-documented influenza pandemics, starting from the first certain one documented in ad 1580, originated in China and in Russia, a few years after the occurrence of a very strong or after a prolonged strong/moderate El Ni?o event. At present, the next El Ni?o will probably occur at the beginning of 2013 (Mazzarella et al. Theor Appl Climatol 100:23?C27, 2010), and this forecast may suggest to be well prepared to take appropriate precautionary epidemiological measures.     

Enhanced pumping test using physicochemical tracers to determine surface-water/groundwater interactions in an alluvial island aquifer,river Rhône,France

Groundwater extracted from the Barthelasse Island aquifer, surrounded by the river Rhône (southeastern France), contributes to the drinking water supplies of 180,000 inhabitants. Owing to its location close to the river and the presence of two backwaters (oxbow lakes), the pumped groundwater is highly vulnerable to river pollution. A pumping test was conducted over 24 h to analyse and quantify the water exchange processes between the river, backwaters and groundwater. During the pumping test, isotopic (δ¹⁸O, δ²H and ²²²Rn), hydrochemical and hydrophysical monitoring of the groundwater was undertaken. Hydraulic heads were measured in pumping wells and at a piezometer located between the wells. Discrete water samples were collected at several observation points in the field, including the backwater and river. The results show mixing between three end-members, as defined by the deuterium excess and silica concentration, led by river Rhône water which had been affected by water–rock interactions over time and mixing with surface evaporated waters. The pumped water resulted from mixing between three end-members, all of which depended on the river Rhône but differed in terms of residence time in the system. Although the groundwater pumping wells are close to each other (<70 m) and have similar depths, the changes in the contributions from end-member waters at each well were different during the pumping test. Comparing isotopic tracers and geochemistry made it possible to quantify the different hydrological compartments that contribute to the groundwater pumped from the boreholes, which is critical in constructing a conceptual flow model.

     

Three-dimensional hydrodynamical simulations of the large-scale structure of W50−SS433

We present 3D hydrodynamical simulations of a precessing jet propagating inside a supernova remnant (SNR) shell, particularly applied to the W50−SS433 system in a search for the origin of its peculiar elongated morphology. Several runs were carried out with different values for the mass-loss rate of the jet, the initial radius of the SNR, and the opening angle of the precession cone. We found that our models successfully reproduce the scale and morphology of W50 when the opening angle of the jets is set to 10° or if this angle linearly varies with time. For these models, more realistic runs were made considering that the remnant is expanding into an interstellar medium with an exponential density profile (as H  i observations suggest). Taking into account all these ingredients, the large-scale morphology of the W50−SS433 system, including the asymmetry between the lobes (formed by the jet–SNR interaction), is well reproduced.     

Mineralogical and chemical characterization of historical mortars from military fortifications in Lisbon harbour (Portugal)

Historical mortars from sixteenth to seventeenth century military forts located at the mouth of the Tagus River in Lisbon have been characterized by polarized light microscopy (PLM), thermal analysis (TG/DTA), X-ray diffractometry (XRD) and scanning electron microscopy + energy dispersive spectroscopy (SEM + EDS). The results indicate that the mortars used were all hydraulic lime-based. The presence of well-rounded lime lumps indicates a limited use of water during the lime hydration process. The detection of hydrated calcium chloroaluminate and carboaluminate compounds mostly at binder-aggregate interfaces provides evidence for the onset of pozzolanic reactions during mortar production as further confirmed by the presence of ceramic fragments in the aggregate fractions intentionally added by the fort builders to increase the hydraulic properties of the mortars. The higher mechanical strength and greater resistance to degradation processes imparted by these pozzolanic compounds could explain why, despite the extreme proximity of the investigated sites to the sea, salt weathering processes do not appear to have significantly affected the studied mortars.