ESEEM of industrial quartz powders: insights into crystal chemistry of Al defects

A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H⁺, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H⁺ (h_Al) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested. As a consequence, the h_Al centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes.     

Laboratory tests with interferometric optical fibre sensors to monitor shallow landslides triggered by rainfalls

Optical fibre–based sensors have now established their place in the field of geohazard monitoring due to their sensitivity to strain and temperature changes. Progressive development in the technology leads to the availability of novel, accurate and durable sensors at a relatively limited cost. This creates room for original monitoring applications that have been, so far, impeded by the shortcomings of conventional monitoring tools. In this work, we explore the applicability of an interferometric optical fibre sensor as a vibration sensing tool at laboratory scale. We tested the ability of the sensor to identify precursors of instability in a downscaled model of a rainfall-induced landslide composed of granular material. We carried out four experimental tests which involved different sensor deployments and soil mixtures. The recorded signals were processed by means of a time–frequency analysis and we identified two frequency-domain parameters—the spectral centroid and band power—that could provide information on the development of instability. Their ratio yielded a unique parameter through which a precursory stage could be outlined by defining a threshold value based on the data collected at the beginning of the experiment. In our lab tests, precursors of instability were detected 2–3 min before a crack was observed at the surface. This may upscale to a lead time of about 20–30 min or more in the field, classifying our monitoring approach in between an alarm and a warning system. The work presented here can be considered a first promising step towards an innovative monitoring system and shows the potential of optical fibre sensing as a shallow landslide monitoring technique, encouraging further testing, especially in real-case studies.

     

Estimating groundwater evapotranspiration rates using diurnal water-table fluctuations in a semi-arid riparian zone

In semi-arid climates, phreatophytes draw on shallow aquifers, and groundwater evapotranspiration (ET_G) is a principal component of groundwater budgets. Diurnal water table fluctuations, which often are a product of ET_G, were monitored in the riparian zone of Red Canyon Creek, Wyoming, USA. These fluctuations were higher in a riparian wetland (2–36 mm) than a grass-covered meadow (1–6 mm). The onset and cessation of water-table fluctuations correspond to daily temperatures relative to freezing. Spatial differences were due to vegetation type and specific yield, while temporal changes were due to vegetation dormancy. Ratios of ET_G to potential evapotranspiration (PET), K _c,GW, were similar to ratios of actual evapotranspiration (ET) to PET, K _c, in semi-arid rangelands. Before vegetation senescence, K _c,GW increased between precipitation events, suggesting phreatophytes pull more water from the saturated zone as soil moisture decreases. In contrast, K _c decreases with soil moisture following precipitation events as ET becomes increasingly water-limited. Error in ET_G is primarily from estimates of specific yield (S _y), which is difficult to quantify in heterogeneous sediments. ET_G values may be more reliable because the range of acceptable S _y is smaller than K _c and S _y does not change with vegetation type or soil moisture.     

Effects of common reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>) expansions on nitrogen dynamics of tidal marshes of the northeastern U.S.

Several recent studies indicate that the replacement of extant species withPhragmites australis can alter the size of nitrogen (N) pools and fluxes within tidal marshes. Some common effects ofP. australis expansion are increased standing stocks of N, greater differentiation of N concentrations between plant tissues (high N leaves and low N stems), and slower whole-plant decay rates than competing species (e.g.,Spartina, Typha spp.). Some of the greater differences between marsh types involveP. australis effects on extractable and porewater pools of dissolved inorganic nitrogen (DIN) and N mineralization rates. Brackish and salt marshes show higher concentrations of DIN in porewater beneathSpartina spp. relative toP. australis, but this is not observed in freshwater tidal marshes whenP. australis is compared withTypha spp. or mixed plant assemblages. With few studies of concurrent N fluxes, the net effect ofP. australis on marsh N budgets is difficult to quantify for single sites and even more so between sites. The magnitude and direction of impacts ofP. australis on N cycles appears to be system-specific, driven more by the system and species being invaded than byP. australis itself. WhereP. australis is found to affect N pools and fluxes, we suggest these alterations result from increased biomass (both aboveground and belowground) and increased allocation of that biomass to recalcitrant stems. Because N pools are commonly greater inP. australis than in most other communities (due to plant and litter uptake), one of the most critical questions remaining is “From where is the extra N inP. australis communities coming?” It is important to determine if the source of the new N is imported (e.g., anthropogenic) or internallyproduced (e.g., fixed, remineralized organic matter). In order to estimate net impacts ofP. australis on marsh N budgets, we suggest that further research be focused on the N source that supports high standing stocks of N inP. australis biomass (external input versus internal cycling) and the relative rates of N loss from different marshes (burial versus subsurface flow versus denitrification).     

Eclogite relics in the Variscan orogenic belt of Bulgaria (SE Europe)

Eclogitic rocks were sampled from two zones in the basement of the Sredna Gora terrane (central western Bulgaria): (1) partially retrogressed eclogites and amphibolites embedded in sillimanite-bearing garnet-micaschists with kyanite relics and migmatites and (2) banded amphibolites associated with muscovite-bearing metagranites within two-mica paragneisses. Rutile relics and oligoclase + green hornblende + epidote ± biotite pseudomorphs after garnet suggest an eclogite facies event. A tholeiitic, transitional affinity was determined for the protoliths, suggesting a continental rift environment, consistent with several eclogite-bearing complexes in the eastern segments of the Variscan belt that arose from the Cambro-Ordovician Gondwana break-up. Decreasing pressure after the eclogite overprint was demonstrated by (a) diopside-albite symplectite, and (b) plagioclase + red–brown to green amphibole kelyphite. The early static re-equilibration, dated to 398 ± 5.2 Ma by ⁴⁰Ar–³⁹Ar technique, was followed by an amphibolite facies foliation, which was pervasive in amphibolites, gneisses and micaschists, and poorly developed in eclogites. The lithospheric PT paths corresponding to higher and lower metamorphic gradients reflect the juxtaposition of crustal and lithospheric mantle units, respectively. In the build-up of the basement of the Balkan orogen, the physical properties of the lithological complexes might have influenced the collisional pattern of involved microplates.     

Detecting the stepwise propagation of the Eastern Sicily thrust belt (Italy): insight from thermal and thermochronological constraints

An extensive dataset of vitrinite reflectance, FTIR parameters on organic matter, illite content in mixed layers illite‐smectite, apatite fission tracks and U‐Th/He dating has been used to reconstruct the stepwise propagation of the Eastern Sicily fold‐and‐thrust belt during Late Palaeogene and Neogene times. The results indicate that the fold‐and‐thrust belt is divisible into two levels of thermal maturity. These levels consist of a less evolved level of thermal maturity that records limited sedimentary burial and minor heating, and a more evolved level of thermal maturity that indicates tectonic burial and exhumation at different times. Deformation and exhumation of shallowly buried units are linked to wedge forward propagation by low‐angle thrusts, whereas the evolution of deeply buried units is associated with tectonic imbrications by duplex formation and steep thrusts. The two tectonic styles alternate during evolution of the fold‐and‐thrust belt under low erosion rates.     

Water quality and relationship between superficial and ground water in Rome (Aniene River basin,central Italy)

Chemical, physical, and biological features of streams and ground water of the North-Eastern area of Rome are jointly analyzed in order to assess the status of water resources. Ground water was investigated with classical survey methods (pH, temperature, and electric conductivity). Microbiological pollution, faunal composition, and stream surrounding area conditions of surface waters were studied, in order to quantify the residual value of these ecosystems from both a human and an environmental point of view. Results show a general impairment of the system and the comparison between superficial waters and shallow ground waters makes it possible to detect the presence of a connection between the two levels. This relationship occurs as an exchange from superficial waters (streams and rivers) to the shallow aquifers. Where superficial waters are contaminated, as in the Tor Sapienza stream, pollutants move to the shallow aquifers too, due to the decreased pressure of the over-exploited aquifer. Moreover, uncontrolled drilling activity, diffused in urban areas, makes it possible the connection between shallow and deep ground water. Notwithstanding this, the mixing between superficial and deep ground water system in Rome is not very widespread and, apparently, limited to restricted areas.     

Deep-sea coral aragonite as a recorder for the neodymium isotopic composition of seawater

Deep-sea corals have been shown to be useful archives of rapid changes in ocean chemistry during the last glacial cycle. Their aragonitic skeleton can be absolutely dated by U-Th data, freeing radiocarbon to be used as a water-mass proxy. For certain species of deep-sea corals, the growth rate allows time resolution that is comparable to ice cores. An additional proxy is needed to exploit this opportunity and turn radiocarbon data into rates of ocean overturning in the past.Neodymium isotopes in seawater can serve as a quasi-conservative water-mass tracer and initial results indicate that deep-sea corals may be reliable archives of seawater Nd isotopes. Here we present a systematic study exploring Nd isotopes as a water-mass proxy in deep-sea coral aragonite. We investigated five different genera of modern deep-sea corals (Caryophyllia, Desmophyllum, Enallopsamia, Flabellum, Lophelia), from global locations covering a large potential range of Nd isotopic compositions. Comparison with ambient seawater measurements yields excellent agreement and suggests that deep-sea corals are reliable archives for seawater Nd isotopes.A parallel study of Nd concentrations in these corals yields distribution coefficients for Nd between seawater and coral aragonite of 1-10, omitting one particular genus (Enallopsamia). The corals and seawater did however not come from exactly the same location, and further investigations are needed to reach robust conclusions on the incorporation of Nd into deep-sea coral aragonite.Lastly, we studied the viability of extracting the Nd isotope signal from fossil deep-sea corals by carrying out stepwise cleaning experiments. Our results show that physical removal of the ferromanganese coating and chemical pre-cleaning have the highest impact on Nd concentrations, but that oxidative/reductive cleaning is also needed to acquire a seawater Nd isotope signal.     

Adsorption of Copper, Nickel, and Cadmium on Goethite in the Presence of Organic Ligands

Adsorption of copper, cadmium and nickel at low concentrations on goethite was studied in the presence of the simple organic ligands oxalate, salicylate, and pyromellitate. The experimental metal adsorption behavior was compared to calculations with a surface complexation model to evaluate the most important interactions. Oxalate mostly decreased Cu and Ni adsorption at high pH-values by competition between solution and surface complexation but had no effect on Cd adsorption. Cu adsorption in the presence of oxalate below pH 6 could best be described by defining a ternary complex of type A (surface-metal-ligand). Salicylate had only minor effects on metal adsorption. The adsorption of Cu in the presence of salicylate above pH 5 could be explained by a ternary complex of type A. Pyromellitate increased the adsorption of Cu and Cd in the acidic pH-range, likely by formation of ternary surface complexes of type B (surface-ligand-metal).