Benthic biogeochemical cycling of mercury in two contaminated northern Adriatic coastal lagoons

Previous research recognized most of the Northern Adriatic coastal lagoon environments as contaminated by mercury (Hg) from multiple anthropogenic sources. Among them, the Pialassa Baiona (P.B.) Lagoon, located near the city of Ravenna (Italy), received between 100 and 200 tons of Hg, generated by an acetaldehyde factory in the period 1957-1977. Further east, the Grado Lagoon has been mainly affected by a long-term Hg input from the Idrija mine (western Slovenia) through the Isonzo River since the 16th century. Hg cycling at the sediment-water interface (SWI) of the two lagoons was investigated and compared by means of an in situ benthic chamber, estimating diffusive Hg and Methyl-Hg fluxes in the summer season. Major chemical features in porewaters (Fe, Mn, H₂S, dissolved inorganic (DIC) and organic carbon (DOC), nutrients) and in the solid phase (C_org, N and S) were also explored to understand the general biogeochemical conditions of the system in response to benthic respiration. The daily integrated flux for the methylated Hg form was extremely low in P.B. Lagoon, accounting for only 7% of the corresponding flux calculated for the Grado Lagoon. Despite a higher sedimentary Hg content in the P.B. Lagoon (14.4-79.0 μg g⁻¹) compared to the Grado Lagoon (10.7-12.5 μg g⁻¹), the in situ fluxes of Hg in the two experimental sites appeared similar. A selective sequential extraction procedure was applied to the solid phase, showing that the stable crystalline mineral phase cinnabar (HgS) is the predominant Hg fraction (about 50%) in the Grado Lagoon surface sediments. Conversely, Hg mobilization and sequestration in the P.B. Lagoon is related to the extremely anoxic redox conditions of the system where the intense sulfate reduction, by the release of sulfur and the formation of sulfides, limits the metal recycling at the SWI and its availability for methylation processes. Thus, the environmental conditions at the SWI in the P.B. Lagoon seem to represent a natural “barrier” for the potential risk of Hg transfer to the aquatic trophic chain.     

Expanding pools morphology in live-bed conditions

Sediment load plays a fundamental role in natural river morphology evolution. Therefore, the correct assessment of the role of the sediment load on natural or anthropic pools morphology downstream of river grade control structures, such as rock chute or block ramps, is of fundamental interest for preserving the fish habitat and the river morphology. This work presents an experimental study on the sediment load influence on rectangular expanding pools downstream of block ramps in live-bed conditions. Several longitudinal and transversal expanding ratios have been tested. Ramp slopes were varied between 0.083 and 0.25. The effect of the pool geometry and the sediment load on hydraulic jump downstream of block ramp as well as scour morphologies and flow patterns have been analyzed. Equations were derived to evaluate the maximum scour hole depth, the longitudinal distance of the section in which it occurs, and the maximum water elevations both in the pool and in the downstream contraction.     

First <Superscript>13</Superscript>C/<Superscript>12</Superscript>C isotopic characterisation of volcanic plume CO<Subscript>2</Subscript>

We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO₂ in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ¹³C of volcanic CO₂ between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work highlights a temporal trend of systematic increase of δ¹³C values of Etna CO₂ from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ¹³C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO₂ emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.     

Water and other volatile systematics of olivine-hosted melt inclusions from the Yellowstone hotspot track

Major oxide, trace element and volatile (H₂O, CO₂, S, F, and Cl) compositions have been analyzed for olivine-hosted melt inclusions in eight basalt samples from Yellowstone National Park and the Snake River Plain (SRP) to identify the least differentiated melt compositions and assess the volatile budget of the Yellowstone hotspot. Melt-inclusion chemistry was evaluated to understand potential overprinting effects in the shallow mantle and crust of magmas derived from deeper levels. Maximum water concentrations of 3.3 wt% and CO₂ up to 1,677 ppm have been observed in olivine-hosted melt inclusions from the Gerritt Basalts at Mesa Falls, Idaho (SRP region), which is significantly higher than the maximum concentrations measured in lavas from other hotspots such as Hawaii (~0.8–0.9 wt%). Maximum water concentrations were generally observed in the least differentiated melt inclusions in terms of incompatible major oxide concentrations, indicating that high water concentrations are characteristic of the mantle or perhaps lower crust rather than resulting from differentiation enhancement within the shallow crust, even taking into account the fact that water behaves as an incompatible element during crystal fractionation. Enrichment in Ba coupled with depletion in Th in many of the melt inclusions and their host rocks is a characteristic of many arc lavas and may indicate that volatiles in Yellowstone-Snake River Plain basalts could have a subduction zone origin.     

The DEM or Mt. Etna: geomorphological and structural implications

Abstract

A Digital Elevation Model (DEM) of Mt. Etna is presented; it has altimetric and planimetric resolution of 1 m and 5 m, respectively, and covers an area of about 120 km . This 3-D view of Mt. Etna allowed both recognition and location of the main morphostructural and volcano-tectonic features of the volcano. A slope map has been generated from the DEM; on the basis of slope distributions and surface textures, five acclivity domains have been recognized. The largest domain, south of the summit craters, reflects the occurrence of old plateau lavas, distinct from central volcanoes which built the present Etnean volcanic system. Interaction between the central volcanoes, with their summit calderas and failed slopes, produced the other recognised domains. Furthermore, newly identified relevant morphostructural lines are discussed. © Elsevier, Paris     

Architecture,structural and tectonic significance of the Seagap fault (offshore Tanzania) in the framework of the East African Rift

The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub-parallel Seagap fault zone in continental/transitional crust landward of the ocean-continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400-km-long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large-scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle-Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike-slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike-slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge-enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re-activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards.     

On the variability of concrete strength as a source of irregularity in elevation for existing RC buildings: a case study

A proper assumption of the concrete strength is essential to model existing RC structures; their seismic performance, in fact, can be affected by the poor quality of materials, both in terms of low strength and high variability. This paper considers the effects of the variability of concrete strength within buildings. Due to the high variability of concrete strength, in fact, buildings can experience irregular seismic responses, both in plan and in elevation. This research investigates the effects of irregularity in elevation due to the strength variability of concrete in a case study, namely a four-storey RC framed building, designed for vertical loads only. The variability of the concrete strength has been evaluated on the basis of an extensive survey carried out by the REGIONE TOSCANA (Tuscany Regional Government) on a large sample of RC framed buildings. Special attention has been paid to the adequacy of current codes provisions (Eurocodes, FEMA) on how to quantify concrete strength.     

Effect of the variability in plan of concrete mechanical properties on the seismic response of existing RC framed structures

A proper characterization of concrete strength is essential to correctly model existing RC structures, whose seismic performance is affected by the poor quality of materials. The purpose of this work is to evaluate the effect of incorrect assumptions for concrete strength and the adequacy of current Codes provisions (Eurocodes, FEMA). Even the effects of the non homogeneity of concrete strength within the building is considered due to its high variability; in fact, buildings can experience an irregular seismic response, both in plan and in elevation. In this work the effects of irregularity in plan due to the strength variability of concrete is analyzed on a case study, a four storey RC framed building, designed for vertical loads only. The variability of concrete strength has been evaluated using the data of an extensive investigation developed by REGIONE TOSCANA on a large sample of RC framed buildings.     

SERS investigation of possible extraterrestrial life traces: Experimental adsorption of adenine on a Martian meteorite

Abstract– The identification of adenine by surface enhanced Raman scattering (SERS) on different mineral phases of a Martian meteorite Dar al Gani (DaG) 670 has been adopted as a test to verify the capability of this technique to detect trace amounts of organic or biological substances deposited over, or contained in, extraterrestrial materials. Raman spectra of different phases of meteorite (olivine, pyroxene, and ilmenite), representative of Martian basaltic rocks, have been measured by three laser sources with wavelengths at 785, 632.8, and 514.5 nm, coupled to a confocal micro‐Raman apparatus. Adenine deposited on the Martian meteorite cannot be observed in the normal Raman spectra; when, instead, meteorite is treated with silver colloidal nanoparticles, the SERS bands of adenine are strongly enhanced, allowing an easy and simple identification of this nucleobase at subpicogram level.