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Paulo Pereira Xavier Úbeda Deborah Martin Jorge Mataix‐Solera Artemi Cerdà Maria Burguet 《水文研究》2014,28(11):3681-3690
The aim of this work is to study the effects of a wildfire on water‐extractable elements in ash from a Pinus pinaster forest located in Portugal. The pH, electrical conductivity (EC), calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), sodium and potassium adsorption ratio (SPAR), aluminium (Al3+), manganese (Mn2+), iron (Fe2+), zinc (Zn2+), sulphur (S), silica (Si) and phosphorous (P) were analysed in ash sampled from a sloped area burned in a wildfire and from litter from a contiguous unburned area, with similar morphological conditions. The results showed that ash leachates had higher pH and EC, and were significantly richer in water‐extractable Ca2+, Mg2+, Na+, K+, SPAR, S and Si and significantly poorer in water‐extractable Al3+, Fe2+, Mn2+ and Zn2+ than litter solutions. No significant differences were observed in water‐extractable P. The fire changed the ash solute chemistry compared with the unburned litter and increased the sample variability of nutrient distribution with potential implications for plant recovery. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Ricardo Hirata Ana Gesicki Ondra Sracek Reginaldo Bertolo Paulo César Giannini Ramón Aravena 《Journal of South American Earth Sciences》2011,31(4):444-456
This paper presents the results of a new investigation of the Guarani Aquifer System (SAG) in São Paulo state. New data were acquired about sedimentary framework, flow pattern, and hydrogeochemistry. The flow direction in the north of the state is towards the southwest and not towards the west as expected previously. This is linked to the absence of SAG outcrop in the northeast of São Paulo state. Both the underlying Pirambóia Formation and the overlying Botucatu Formation possess high porosity (18.9% and 19.5%, respectively), which was not modified significantly by diagenetic changes. Investigation of sediments confirmed a zone of chalcedony cement close to the SAG outcrop and a zone of calcite cement in the deep confined zone. The main events in the SAG post-sedimentary history were: (1) adhesion of ferrugineous coatings on grains, (2) infiltration of clays in eodiagenetic stage, (3) regeneration of coatings with formation of smectites, (4) authigenic overgrowth of quartz and K-feldspar in advanced eodiagenetic stage, (5) bitumen cementation of Pirambóia Formation in mesodiagenetic stage, (6) cementation by calcite in mesodiagenetic and telodiagenetic stages in Pirambóia Formation, (7) formation of secondary porosity by dissolution of unstable minerals after appearance of hydraulic gradient and penetration of the meteoric water caused by the uplift of the Serra do Mar coastal range in the Late Cretaceous, (8) authigenesis of kaolinite and amorphous silica in unconfined zone of the SAG and cation exchange coupled with the dissolution of calcite at the transition between unconfined and confined zone, and (9) authigenesis of analcime in the confined SAG zone. The last two processes are still under operation. The deep zone of the SAG comprises an alkaline pH, Na–HCO3 groundwater type with old water and enriched δ13C values (<?3.9), which evolved from a neutral pH, Ca–HCO3 groundwater type with young water and depleted δ13C values (>?18.8) close to the SAG outcrop. This is consistent with a conceptual geochemical model of the SAG, suggesting dissolution of calcite driven by cation exchange, which occurs at a relatively narrow front recently moving downgradient at much slower rate compared to groundwater flow. More depleted values of δ18O in the deep confined zone close to the Paraná River compared to values of relative recent recharged water indicate recharge occur during a period of cold climate. The SAG is a “storage-dominated” type of aquifer which has to be managed properly to avoid its overexploitation. 相似文献
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Origin of silicic volcanism in the Panamanian arc: evidence for a two-stage fractionation process at El Valle volcano 总被引:1,自引:1,他引:0
Paulo J. Hidalgo Thomas A. Vogel Tyrone O. Rooney Ryan M. Currier Paul W. Layer 《Contributions to Mineralogy and Petrology》2011,162(6):1115-1138
In the Central American Volcanic Arc, adakite-like volcanism has often been described as volumetrically insignificant. However,
extensive silicic adakitic volcanism does occur in the Panamanian arc and provides an opportunity to evaluate the origin of
this magma-type as well as to contrast its origin with other Central American silicic magmas. The Quaternary volcanic deposits
of El Valle volcano are characterized by pronounced depletions in the heavy rare earth elements, low Y, high Sr, high Sr/Y,
relatively high MgO, and low K2O/Na2O, when compared with other Quaternary Central American volcanics at similar SiO2. These chemical features are also diagnostic of adakitic signatures. Our new 40Ar/39Ar ages of lava flows and ash flows that compose the volcanic edifice of El Valle volcano illustrate that the eruptive volume
of adakitic-like volcanism is substantial during the Quaternary (~120 km3). Adakitic-like magmas dominate the stratigraphic record. Common to all models for the origin of an adakite geochemical signature
is the involvement of garnet, as a residual or fractionating phase. The stability of garnet in hydrous magmas has been recently
reevaluated with important consequences; garnet is a stable primary igneous phase at pressure and temperature conditions expected
for magma differentiation at the roots of a mature island arc. Moreover, adakite-like volcanism erupted at El Valle volcano
displays the middle rare earth element depletion observed in other Panamanian volcanic centers that has been attributed to
significant amphibole fractionation. Extensive amphibole fractionation may have occurred in two stages. The first stage of
fractionation, garnet + amphibole fractionation, occurs from hydrous basaltic–andesitic parental magmas that have ponded at
the base of an overthickened crust. The second stage occurs at mid-lower crustal levels where abundant amphibole + plagioclase
and minor sphene crystallized from water-rich magmas. These two stages combined may have resulted in an amphibole-rich cumulate
layer. This amphibole layer is likely the source of the abundant amphibole-rich cumulate enclaves and blobs found in volcanic
products across the Panamanian arc. Stalling of water-rich magmas during this two-stage fractionation process could drive
the interstitial liquids to the evolved compositions typical of continental crust, while leaving behind amphibole-rich cumulate
rocks that may eventually be returned to the asthenosphere. Differentiation of H2O-rich magmas under the conditions appropriate for the roots of island arcs may therefore be a key process in developing a
better understanding of the generation of continental crust in island arc environments. 相似文献
207.
Nicolai Mirlean Paulo Baisch Marcelo P. Travassos Cristina Nassar 《Geo-Marine Letters》2011,31(1):65-73
Arsenic levels (up to 130 mg kg−1) substantially exceeding the official threshold have recently been documented in beach and nearshore sediments along more
than 50 km of coastline in the Brazilian state of Espírito Santo between 19°50′ and 20°12′S. In an attempt to assess the sources
of this enrichment, we performed a study on arsenic distribution in the main mineral substances and living organisms in the
beach environment. Laboratory tests on arsenic retention by beach carbonate debris have also been carried out. The data suggest
that sedimentary arsenic occurs largely bound to particles of the calcareous red alga Corallina panizzoi, whereby live specimens contained much smaller amounts of this metalloid than was the case for nonliving material (2.4 and
20.3 mg kg−1, respectively). Experimental tests confirmed the ability of C. panizzoi detritus to retain arsenic at pH intervals and ionic strength characteristic of seawater. There are two potential sources
of that metalloid for calcareous debris in sediments: brown macroalgae, which were found to contain high levels of As (up
to 66.3 mg kg−1), and ferruginized sandstones (up to 23.0 mg kg−1). We argue that any contribution of brown algae to beach sediment enrichment by As would be minor, and consider the ferrous
sandstones from coastal sedimentary rocks of the Barreiras Group as the principal large-scale source of arsenic in the marine
environment of Espírito Santo. The experimental data, together with field studies, corroborate the interpretation that arsenic
anomalies in sediments with calcareous debris can form when weathered continental rocks even only slightly enriched in As
are leached by marine waters, and the As is at least partially retained by biogenic calcareous detritus in nearshore sediments.
Considering that rocks of the Barreiras Group are exposed to marine erosion far to the north of Espírito Santo, we estimate
that marine sediments containing calcareous material are “anomalously” enriched in As along approximately 2,000 km of the
Brazilian tropical coastline. 相似文献
208.
Darren O'Brien Paulo Garcia Jonathan Ferreira Sylvie Cabrit Luc Binette 《Astrophysics and Space Science》2003,287(1-4):129-134
Following the work of Garcia et al. (2001a) (GFCB), we compute the thermal properties and ionization structure of magnetically-driven disk winds. The original model's dominant heating function along the jet, ambipolar diffusion, is augmented by a mechanical heating term supposed to arise from weak shocks, as used by (Shang et al., 2002). We add this mechanical heating function to a cold disk wind model and calculate its effect on the jet as a whole. The temperature and ionization of the flow are calculated in the case of cold jet solutions consistent with the underlying accretion disk (Ferreira, 1997). These solutions are compared to those of (GFCB) in order to quantitatively determine the effect of the mechanical heating on the flow. We then use the computed thermal and ionization structures to calculate jet synthetic observations. We find that the addition of mechanical heating leads to higher electron fractions, in turn leading to increased line fluxes and line ratios approaching observed values. 相似文献
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