Synthesis of cordierite using industrial waste fly ash

Fly ash is a product arising from coal combustion in thermal power plants. It represents a major source of environmental pollution. It is well known by its chemical composition rich of SiO₂ and Al₂O₃. With the aim of preserving the environment against this contamination, fly ash was used along with the starting materials for producing glass cordierite (2MgO, 2Al₂O₃, 5SiO₂). Four formulations were developed by mixing the silica gel, magnesium chloride (MgCl₂.6H₂O) and fly ash in the percentages enclosing the stoichiometry of cordierite (2MgO, 2Al₂O₃, 5SiO₂). Different experimental techniques (DTA/TGA, X-ray diffraction, FTIR and SEM) were used to characterise the prepared formulations. The results shown that for all formulations, a cordierite phase was obtained at 1200 °C along with several secondary phases such as mullite, cristobalite, silicon oxide, enstatite and spinel. At 1300 °C, pure indialite (α-cordierite) was obtained along with a small amount of spinel. The four formulations sintered at 1200 °C exhibit a homogenous morphology and high porosity. The acicular-shaped indialite grains were observed in both formulations with excess of alumina and excess of magnesia.     

Stable isotopic and elemental characteristics of recent tufa from a karstic Krka River (south‐east Slovenia): useful environmental proxies?

Tufa samples from 16 consecutive barrages along a 13 km section of the groundwater‐fed Krka River (Slovenia) were analysed for their petrographical, mineralogical, elemental and stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope composition, to establish their relation to current climatic and hydrological conditions. Waters constantly oversaturated with calcite and the steep morphology of the Krka riverbed stimulate rapid CO₂ degassing and subsequent tufa precipitation. The carbon isotope fractionation (Δ¹³C) between dissolved inorganic carbon and tufa in the Krka River evolves towards isotopic equilibrium being controlled by continuous CO₂ degassing and tufa precipitation rate downstream. The Δ¹³C increased from 1·9 to 2·5‰ (VPDB); however, since tufa precipitation rates remain similar downstream, the major controlling factor of carbon isotope exchange is most probably related to the continuous ¹²CO₂ degassing downstream leaving the carbon pool enriched in ¹³C. In the case of oxygen, the isotope fractionation (Δ¹⁸O) was found to be from 1·0 to 2·3‰ (VSMOW) smaller than reported in the literature. The observed discrepancies are due to different precipitation rates of calcite deposits because Krka tufas on cascades grow relatively faster compared to slowly precipitated calcite deposits in cave or stream pools. Due to non‐equilibrium oxygen isotope exchange between Krka tufa and water, the δ¹⁸O proxy showed from 1·2 to 8·2°C higher calculated water temperatures compared to measured water temperatures, demonstrating that δ¹⁸O proxy‐based temperature equations are not reliable for water temperature calculations of fast‐growing tufa on cascades. Because Mg is bound to the terrigenous dolomite fraction in the Krka tufa samples, the Mg/Ca was also found to be an unreliable temperature proxy yielding over up to 20°C higher calculated water temperatures.     

Dissolved metal contamination in the East River-Long Island sound system: potential biological effects

A suite of dissolved trace metals (Ag, Cd, Cu and Pb), inorganic nutrients (NO(3), PO(4)), and chlorophyll a was measured along a 55 mile transect from the East River into western and central Long Island Sound. The main objectives of this study were to determine the relative levels of contamination from sewage, and to assess its possible biological impact on local waters. The East River-Long Island Sound system receives large volumes of treated sewage and industrial effluent as a result of the heavy urbanization of the area. Despite these strong environmental pressures, this study is among the first to report dissolved metal levels from that region. Consistent with the locations of anthropogenic sources, a strong east-west concentration gradient was observed for Ag, Pb, NO(3) and PO(4) with the highest levels found in the East River. In contrast, dissolved Cd and Cu were relatively constant throughout the area of study, suggesting that sewage sources have a more limited influence on the levels of those metals. Remobilization from contaminated sediments may represent the primary source of Cd and Cu to the Long Island Sound under low-runoff conditions in summer. Chlorophyll a concentrations, used as an indicator of total biomass, were also low in the East River. These low chlorophyll concentrations could not be explained by nutrient or light limitation, water column stratification, or to advection of phytoplankton out of the river during tidal flushing. These preliminary results suggest a potential toxic effect of sewage on the biological communities of the East River.     

Horizontal sighting range and Secchi depth as estimators of underwater PAR attenuation in a coastal lagoon

Attenuation of photosynthetically available radiation (PAR) measured using a light meter, was related to Secchi disk, horizontal black disk and horizontal sighting ranges observed in a coastal lagoon of the Southern California Current System. Vertical attenuation coefficient (K_PAR) was calculated from radiometric PAR profiles. Vertical (Z_D) and horizontal (HS) sighting ranges were measured with white (Secchi depth or Z_SD, HS _W ) and black (Z _BD, HS _B ) targets. Empirical power models for the K_PAR-Z_SD (K_PAR=1.47 Z_SD ^−1.13), K_PAR-Z _BD (K_PAR=0.98 Z _BD ^−1.26), K_PAR-HS _W (K_PAR=1.22 HS _W ^−1.14) and K_PAR-HS _B (K_PAR=0.73 HS _B ^−1.07) relationships were developed. The parameters of these models may not apply to other water bodies because their values depend on the range of water reflectance in each case, as reported in the literature. This is the first contribution reporting K_PAR-HS empirical relations in an estuarine environment but their application may be limited to this coastal lagoon. While this approach may be universal, more data are needed to explore the variability of the parameters between different water bodies.     

Influence des perturbations thermiques de l'atmosphère sur la qualité des images solaires

Résumé Le Pic du Midi de Bigorre étant pris comme site expérimental, l'influence sur la qualité des images solaires de deux types de perturbations thermiques de l'atmosphère est examinée, celles-ci étant dues respectivement au sol local et à la convection au sein de l'écoulement incident. Une méthode pyrhéliométrique permettant la détection de la convection en ciel clair est exposée.

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A parameter characterizing the quality of photospheric images has been defined through a three class distribution; it has been estimated over various samples taken during 230 hours of observing time at the Pic du Midi Observatory.Its occurrence is compared to that of two types of atmospheric thermal disturbances, one being created by the local ground and the other brought along by the incident flow and due mainly to convection.The time-derivation of the temperature, which is, under some conditions, well related to the nearby thermal field, may be taken as a characteristic atmospheric parameter, and it is shown that the best quality for solar images occurs only - and then with a fairly good frequency - when its value is slightly positive.A method is described which aims at the detection of convection in the clear atmosphere; as the upward motions are bringing aerosols from the lower layers, a less transparent volume is ascending during the first part of the day and then, its top may intercept the optical axis of the telescope. The diurnal variation of the atmospheric transparency, as observed with a pyrheliometer, shows clearly this occurrence, which may be quite different from one day to another.

     

Calc-Alkaline Magmatism at the Archean Proterozoic Transition: the Caico Complex Basement (NE Brazil)

The Paleoproterozoic metaplutonic rocks of the CaicóComplex Basement (Seridó region, NE Brazil) provide importantand crucial insights into the petrogenetic processes governingcrustal growth and may potentially be a proxy for understandingthe Archean–Proterozoic transition. These rocks consistof high-K calc-alkaline diorite to granite, with Rb–Sr,U–Pb, Pb–Pb and Sm–Nd ages of c. 2·25–2·15Ga. They are metaluminous, with high Yb_N, K₂O/Na₂O and Rb/Sr,low I_Sr ratios, and are large ion lithophile elements (LILE)enriched. Petrographic and geochemical data demonstrate thatthey belong to differentiated series that evolved by low-pressurefractionation, thus resulting in granodioritic liquids. We proposea model in which the petrogenesis of the Caicó Complexorthogneisses begins with partial melting of a metasomaticallyenriched spinel- to garnet-bearing lherzolite (with high-silicaadakite melt as the metasomatic agent), generating a basic magmathat subsequently evolved at depth through fractional crystallizationof olivine, followed by low-pressure intracrustal fractionation.A subduction zone setting is proposed for this magmatism, toaccount for both negative anomalies in high field strength elements(HFSE) and LILE enrichment. Mantle-derived juvenile magmatismwith the same age is also known in the São Franciscoand West Africa cratons, as well as in French Guyana, and thusthe Archean–Proterozoic transition marks a very importantcontinental accretion event. It also represents a transitionfrom slab-dominated (in the Archean) to wedge-dominated post-Archeanmagmatism. KEY WORDS: calc-alkaline; magmatism; NE Brazil; Paleoproterozoic; petrogenesis     

Isotopic and Chemical Constraints on the Biogeochemistry of Dissolved Inorganic Carbon and Chemical Weathering in the Karst Watershed of Krka River (Slovenia)

The hydrogeochemical and carbon isotope characteristics of the Krka River, Slovenia, were investigated to estimate the carbon transfer from the land ecosystem in the watershed. During the 3-year sampling period (2008–2010), temperature, pH, electrical conductivity, major ion content, dissolved inorganic carbon (DIC) and dissolved organic carbon content, and the isotopic composition of DIC (δ¹³C_DIC) were monitored in the main stream of the Krka River and its tributaries. The major solute composition of analysed waters is dominated by an input of HCO₃ ^?, Ca²⁺ and Mg²⁺ originating from carbonate dissolution. The Mg²⁺/Ca²⁺ and Mg²⁺/HCO₃ ^? molar ratio values ranging from 0.24 to 0.71 and 0.05 to 0.30, respectively, indicate a high degree of dolomite dissolution relative to calcite. Dissolved CO₂ concentrations in the river were up to tenfold supersaturated relative to the atmosphere, resulting in supersaturation with respect to calcite and degassing of CO₂ downstream. The δ¹³C values in river water range from ?15.6 to ?9.4 ‰ and are controlled by the input of tributaries, exchange with atmospheric CO₂, degradation of organic matter, and dissolution of carbonates. The mass balance calculations for riverine DIC suggest that the contribution from carbonate dissolution and degradation of organic matter have major influence, whereas the exchange with atmospheric CO₂ has minor influence on the inorganic carbon pool in the Krka River.     

GIS-based analysis of the Stream Length-Gradient Index for evaluating effects of active tectonics: a case study of Enfidha (North-East of Tunisia)

Our study aims at calculating morphometric indices through the recourse to the Digital Elevation Model (DEM) and its attributes (hydrographic networks, watersheds, and reliefs). This quantitative measurement is used for the morphotectonical analysis of the Enfidha area (North-East of Tunisia) in the GIS environment and statistical platform. The Enfidha area is selected to analyze and identify neotectonic morphostructures on basis of the morphological evolution of the landscape. The coastal Enfidha plain is part of the Tunisian Sahel that is marked by its instability and frequent earthquakes that prove the presence of the recent deformation and active subsurface faults. This morphometric modeling in the geological investigation area reflects the morphotectonic spatial evolution in the Quaternary basins areas. Stream length (SL) proposed by Hack (1973) and denominated by Etchebehere et al. (2004) Revista do Instituto de Geociências USP, Série Científica, São Paulo 4(2):43–56 as the RDE index (Relation Declivity Extension) was used for application in the studies of neotectonic approach. RDE index is one of the morphotectonical indices that designates the tectonics anomalies in rivers. The variability in (RDE) values can indicate both a lithology resistance towards erosion and major active subsurface faults or low slope. Our geostatistical method is required to obtain RDE index maps based on lithological filtrations and value interpolations which are calculated in a drainage line network. This method calculates, measures, and validates spatial distribution of hack RDE index through a high statistical accuracy in a quantitative anomalies study. The RDE anomaly maps of the study area mirror the concurrence between anomaly zones, major active subsurface E-W faults, and local geological discontinuities related to neotectonical activities that affect the hydrographic network. This study proves that the RDE index can be especially used to detect the influence of active large-scale faults on the landscape evolution.     

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Résumé

Les observations tensiométriques et piézométriques au voisinage du ruisseau des Maurets, dans le bassin du Réal Collobrier, fournissent des informations intéressantes sur les mécanismes hydrologiques en cas de crue. Des mesures au pas de temps hebdomadaire montrent une bonne corrélation entre le débit dans la rivière et le niveau piézométrique au voisinage de celle-ci. D'autre part, on observe que ce niveau ne peut monter que si la pression d'eau dans le sol avant la crue est voisines de zéro. D'autres observations tensiométriques plus détaillées ont été effectuées au pas de temps de la demi-heure. Elles montrent que seules les pluies de fortes intensités peuvent provoquer une montée rapide de la pression positive d'eau du sol (saturation), à condition que cette pression soit très voisine de zéro avant la pluie. Dans ce cas, le gradient vertical de la charge hydraulique est quasi-nul, et des zones saturées contributives apparaissent et se développent, accompagnées de forts débits de crue dans la rivière. Ainsi, même dans des conditions méditerranéennes, les crues peuvent être provoquées par le développement des surfaces saturées contributives au voisinage des rivières. Dans ce cas, sur le bassin étudié, ces surfaces saturées ont une durée de vie très courte.