Diatom taxonomic and morphological changes as indicators of metal pollution and recovery in Lac Dufault (Québec, Canada)

We studied diatom taxonomic composition and the presence of morphological alterations (size and deformations) along a sediment core collected in Lac Dufault, Abitibi, whose watershed has a long history of mining pollution presently undergoing mitigation. According to sediment dating with ²¹⁰Pb and metal profiles along the core, we could identify four periods in the contamination history of the lake, which were characterized by different diatoms. Tabellaria flocculosa was dominant in the pre-mining period but was drastically reduced at the onset of pollution when Fragilaria cf. tenera became important. This diatom, together with other Fragilaria species and cysts of Chaetoceros muelleri, typified the transition period in which Cu reached its maximum value and other metals started to increase. During the period of maximum contamination with Zn, Cd, and Fe accompanied by acid mine drainage, Achnanthes minutissima and Brachysira vitrea were dominant. These taxa started to wane in the most recent sediments representing a partial chemical recovery. Asterionella formosa, which almost vanished at mining onset, reappeared with high abundance in these superficial sections. Beside these taxonomical shifts, we observed during the contamination period significant reduction in valve length together with increased percentages of valve deformations. Because available data on water chemistry and a diatom-based pH reconstruction suggest that Lac Dufault escaped severe acidification, diatom patterns observed in the core can be mostly ascribed to metal contamination. Individual diatom abundance and valve length had strong statistical relationships with the different metals identified in the core. Diatom changes both taxonomic and morphological can be excellent specific indicator of metal contamination and early recovery.     

Seasonal changes of microbial populations in the sediments of the basins of Lugano and Agno

This research was carried out with the aim to explore the heterotrophic microbial population of two sediments in different oxic conditions of the Lake of Lugano (Lago di Lugano). The values of the viable bacterial counts found in our sediment samples were typical for an eutrophic lake.The increase in the proportion of anaerobic to aerobic bacteria at 30 °C observed in the sediment samples of Agno may reflect the depletion of oxygen concentrations in the water column.The generaAeromonas, Pseudomonas, Bacillus andClostridium, as well as strains belonging to the Coryneform-group, represented the major taxonomic groups of heterotrophic bacterial communities in the water-sediment interface.     

Sources and chronology of fifteen elements in the sediments of lakes affected by metal deposition in a mining area

Sources and chronologies of metal contamination were studied in sediment cores of three lakes of the Rouyn-Noranda mining area (Québec, Canada) affected by atmospheric deposition of anthropogenic contaminants. One of the three lakes also received acid mine drainage. The sediments were dated using ²¹⁰Pb and ¹³⁷Cs and analysed for stable Pb isotope ratios and for total concentrations of 15 elements (Ag, Al, Au, Ca, Cu, Cd, Fe, Hg, Mn, Ni, P, Pb, S, Ti, Zn). Stable lead isotopic signatures helped to determine the quantitative contributions of different industrial Pb sources to our sampling sites. This source apportionment showed the dominant influence of the Rouyn-Noranda copper smelter in airborne Pb emissions for the decades following 1926, when industrialization began in the region. The smelter source had a low ratio of ²⁰⁶Pb/²⁰⁷Pb ranging between 0.90 and 1.05, as typical of the Abitibi Archean sulphides. The relationships between element (metal) sedimentary fluxes and anthropogenic Pb fluxes allowed us to infer the origin of the anthropogenic source. These relationships strongly suggest that the copper smelter was (and may still be) an atmospheric source of Cd, Cu, Pb, Zn, Ag and Hg to the surrounding lakes. Our study indicates that the efforts made by the Rouyn-Noranda copper smelter to reduce airborne emissions of metals have been translated in reduced atmospheric metal loadings to the surrounding lakes.     

Spectroscopic Investigation on Hydrophobic and Hydrophilic Fractions of Dissolved Organic Matter Extracted from Soils at Different Salinities

Organic matter can be considered one of the most important indicators of the extent of soil desertification processes. Among the causes of desertification, salinization induced by different factors is raising the greatest concern in the Mediterranean area. In the present research, hydrophilic (HI) and hydrophobic (HO) fractions of dissolved organic matter (DOM) extracted from soils at different degrees of salinization have been investigated by means of spectroscopic techniques such as tridimensional fluorescence spectroscopy in the mode of emission excitation matrix (EEM) and Fourier transform infrared spectroscopy (FT‐IR). The FT‐IR spectra were distinctive in differentiating HI from HO fractions and each DOM fraction as a function of soil salinity. The EEM spectra of HO fractions exhibited a shift toward longer emission wavelengths and higher fluorescence intensity (FI) values as compared to that of the HI fractions. These results could be ascribed to the different molecular complexities of HI and HO fractions. Further, a marked quenching effect was observed in the FI of both the DOM fractions with increasing soil salinity, which allowed to obtain immediate information on the soil salinity degree by comparing the fluorescence intensity.     

Complex dynamics of small-moderate volcanic events: the example of the 2011 rhyolitic Cordón Caulle eruption,Chile

After decades of repose, Puyehue-Cordón Caulle Volcano (Chile) erupted in June 2011 following a month of continuously increasing seismic activity. The eruption dispersed a large volume of rhyolitic tephra over a wide area and was characterized by complex dynamics. During the initial climactic phase of the eruption (24–30 h on 4–5 June), 11–14-km-high plumes dispersed most of the erupted tephra eastward towards Argentina, reaching as far as the Atlantic Ocean. This first eruptive phase was followed by activity of lower intensity, leading to the development of a complex stratigraphic sequence, mainly due to rapid shifts in wind direction and eruptive style. The resulting tephra deposits consist of 13 main layers grouped into four units. Each layer was characterized based on its dispersal direction, sedimentological features, and on the main characteristics of the juvenile fraction (texture, density, petrography, chemistry). The lowest part of the eruptive sequence (Unit I), corresponding to the tephra emitted between 4 and 5 June, is composed of alternating lapilli layers with a total estimated volume of ca. 0.75 km³; these layers record the highest intensity phase, during which a bent-over plume dispersed tephra towards the southeast-east, with negligible up-wind sedimentation. Products emitted during 5–6 June (Unit II) signaled an abrupt shift in wind direction towards the north, leading to the deposition of a coarse ash deposit in the northern sector (ca. 0.21 km³ in volume), followed by a resumption of easterly directed winds. A third phase (Unit III) began on 7 June and resulted in tephra deposits in the eastern sector and ballistic bombs around the vent area. A final phase (Unit IV) started after 15 June and was characterized by the emission of fine-grained white tephra from ash-charged plumes during low-level activity and the extrusion of a viscous lava flow. Timing and duration of the first eruptive phases were constrained based on comparison of the dispersal of the main tephra layers with satellite images, showing that most of the tephra was emitted during the first 72 h of the event. The analyzed juvenile material tightly clusters within the rhyolitic field, with negligible chemical variations through the eruptive sequence. Textural observations reveal that changes in eruption intensity (and consequently in magma ascent velocity within the conduit) and complex interactions between gas-rich and gas-depleted magma portions during ascent resulted in vesicular clasts with variable degrees of shear localization, and possibly in the large heterogeneity of the juvenile material.     

Italian accelerometric archive: geological, geophysical and geotechnical investigations at strong-motion stations

Geological, geophysical and geotechnical investigations, for the characterization of the strong-motion recording sites managed by the Italian Civil Protection, have been carried out in the framework of the project “Italian strong-motion database in the period 1972–2004”. The project aimed at creating an updated database of strong-motion data acquired in Italy by different institutions in the time span 1972–2004, and at improving the quality of disseminated data. This article illustrates the state of the recording site characterization before the beginning of the project, explains the criteria adopted to select the sites where geophysical/geotechnical investigation have been performed and describes the results of the promoted field surveys.     

Multivariate analysis to investigate Cl distribution in rocks from different settings

Chlorine concentration has been determined by chemical methods in 97 samples of basic rocks collected at Etna volcano (Sicily, Southern Italy), Sao Miguel (Azores Islands), and Lanzarote (Canary Islands). The samples have been processed together with data related to specific magmatic and tectonic conditions, drawn from the literature. Thus, the contents of SiO₂, K₂O, and P₂O₅ of 228 samples have been used to investigate Cl distribution in the considered environments, using principal component analysis. The log-centered variance-covariance matrix has been processed in order to overcome the closure constraints. The results indicate that a clear distinction between continental and oceanic regions can be obtained in the components space. A preliminary discriminant diagram involving chlorine thus can be proposed.