Net Primary Productivity of <Emphasis Type="Italic">Spartina densiflora</Emphasis> Brong in an SW Atlantic Coastal Salt Marsh     

Gabriela González Trilla  Silvia De Marco  Jorge Marcovecchio  Ricardo Vicari  Patricia Kandus 《Estuaries and Coasts》2010,33(4):953-962

Coastal marshes are known as organic matter producers. The goal of this work is to study tiller demography, standing biomass, and net aerial primary productivity (NAPP) in a Spartina densiflora coastal wetland, using a method applied to permanent sample plots located at two sites differing in topographic location, a regularly flooded zone [relative low marsh (LM)] and an irregularly flooded one [relative high marsh (HM)]. Measurements were made every 2 months during the 2005–2007 period. The annual NAPP was estimated to be 2,599?±?705 gDW m^?2?year^?1 for the HM and 2,181?±?605 gDW m^?2?year^?1 and 602?±?154 gDW m^?2?year^?1 for the first and second period of the LM populations, respectively, showing a seasonal pattern reaching maximum values in summer. The reduced NAPP values of the LM sites in the second year was associated with an extremely high precipitation period related to the 2007–2008 El Niño event.  相似文献   

Integrated stratigraphy (cyclostratigraphy and biochronology) of late Middle Miocene deposits in the Mediterranean area and comparison with the North and Equatorial Atlantic Oceans: synthesis of the major results     

Fabrizio Lirer  Silvia Iaccarino 《地学学报》2005,17(4):338-349

The stratigraphic correlation of North and Equatorial Atlantic Ocean records with Mediterranean astronomically tuned sections reveals the diachrony of several planktonic foraminiferal bioevents, but shows the possibility to adopt the Mediterranean biostratigraphy in North Atlantic records. These data provide new tools for biostratigraphic correlation, mainly between the Mediterranean and the North Atlantic areas. Quantitative analyses carried out on planktonic foraminifera reveal the occurrence at Site 982-HoleB (ODP Leg 162) of some bioevents in the same order as those recorded in Mediterranean sequences. In addition, Neogloboquadrina atlantica praeatlantica first occurrence (FO) [within the short range of Paragloborotalia mayeri, sensuRiv. Ital. Paleontol. Stratigr. 108 (2002) 257] occurs in levels older than its FO in the Mediterranean area where it first appears at the same level as N. acostaensis s.s. coinciding with the last occurrence of P. partimlabiata. In agreement with the findings of Poore [Init. Rep. Deep Sea Drilling Proj. 49 (1979) 447] and the hypothesis of Zachariasse and Aubry [Paleobios 16 (1994) 68], the first representative of the neogloboquadrinids originated north of Iceland and migrated towards the southern latitudes at different times, first in the Mediterranean and mid-latitude Atlantic Ocean, then in low-latitudes (Site 397).  相似文献   

Structural and geochemical alterations in the Mg calcite bryozoan Myriapora truncata under elevated seawater pCO2 simulating ocean acidification     

Silvia Cocito  Maria Cristina Gambi  Paul David Taylor 《Marine Ecology》2011,32(2):211-221

The possible effects of ocean acidification on the calcareous skeleton of the Mediterranean bryozoan Myriapora truncata (Pallas, 1766) were studied by transplanting live and dead colonies into an area of natural volcanic CO₂ vents at Ischia (Gulf of Naples, Tyrrhenian Sea), Italy. Morphology and geochemistry were compared between colonies from normal (mean pH = 8.07, min. pH 7.95), below‐normal (mean pH 7.66, min. pH 7.32) and acidic (mean pH 7.43, min. pH 6.83) conditions after colonies had been exposed in situ for 45 and 128 days. Both distal (juvenile) and proximal (adult) parts of the branches were investigated. Skeletons of live colonies in acidic pH site after 45 days of exposure were less corroded than those of dead colonies, suggesting that the organic tissues enveloping the skeleton play a protective role. Colonies remained alive at the below‐normal and acidic pH sites during the 45‐day experiment but corrosion was very striking after 128 days, with colonies from the acidic site showing significant loss of skeleton. Compared to the control, these colonies also had lower levels of Mg (mean 8 versus 9.5 wt% Mg) within their skeletons. Electron microprobe mapping showed Mg to be higher in the outer layers of the skeletal walls in colonies from the normal pH site. Corrosion of outer layers of the walls probably explains the lower Mg level found in colonies exposed to acidic conditions. As solubility of calcite increases with Mg content, the enrichment of Mg in outer layers of the skeleton should enhance the vulnerability of Myriapora truncata to dissolution. These findings raise concerns over the survival of bryozoans with Mg calcite skeletons in the face of predicted decreases in oceanic pH levels.  相似文献   

Reconciling optical and X-ray mass estimates: the case of the elliptical galaxy NGC 3379     

Silvia Pellegrini  Luca Ciotti 《Monthly notices of the Royal Astronomical Society》2006,370(4):1797-1803

NGC 3379 is a well-studied nearby elliptical for which optical investigations have claimed a little dark matter content, or even no dark matter. Recently, its total mass profile M ( r ) has been derived by exploiting Chandra observations of its extended and X-ray emitting interstellar medium, based on the hypothesis of hydrostatic equilibrium for the hot gas. The resulting total mass within the effective radius R _e has been claimed to be a few times larger than that found by optical studies. Here, we show that part of the discrepancy can be due to an underestimate of the optically derived mass, and the remaining discrepancy of a factor of ∼2 can be explained by deviations from hydrostatic equilibrium of the hot gas. By using hydrodynamical simulations tailored to reproduce the observed hot gas properties of NGC 3379, and by assuming as input for the simulations the total mass profile derived optically, we show that (i) the hot gas at the present time has X-ray properties consistent with those observed only if it is outflowing over most of the galactic body, and (ii) an overestimate of M of the same size found in the recent X-ray analysis is recovered when assuming hydrostatic equilibrium. We also show that the hot gas is outflowing even for a dark matter fraction within R _e as large as derived with the standard X-ray procedure based on the hydrostatic equilibrium assumption, which shows the unapplicability of the method for this galaxy. Finally, we find that the whole range of dark mass amount and distribution allowed for by optical studies is compatible with a hot gas flow with the observed X-ray properties.  相似文献   

On the use of X-rays to determine dynamical properties of elliptical galaxies     

Luca Ciotti  Silvia Pellegrini 《Monthly notices of the Royal Astronomical Society》2004,350(2):609-614

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Carbon mass-balance modelling and carbon isotope exchange processes in dynamic caves   总被引：3，自引：0，他引：3  

Silvia Frisia  Ian J. Fairchild  Renza Miorandi  Andrea Borsato 《Geochimica et cosmochimica acta》2011,75(2):380-400

Diverse interpretations have been made of carbon isotope time series in speleothems, reflecting multiple potential controls. Here we study the dynamics of ¹³C and ¹²C cycling in a particularly well-constrained site to improve our understanding of processes affecting speleothem δ¹³C values. The small, tubular Grotta di Ernesto cave (NE Italy) hosts annually-laminated speleothem archives of climatic and environmental changes. Temperature, air pressure, pCO₂, dissolved inorganic carbon (DIC) and their C isotopic compositions were monitored for up to five years in soil water and gas, cave dripwater and cave air. Mass-balance models were constructed for CO₂ concentrations and tested against the carbon isotope data. Air advection forces winter pCO₂ to drop in the cave air to ca. 500 ppm from a summer peak of ca. 1500 ppm, with a rate of air exchange between cave and free atmosphere of approximately 0.4 days. The process of cave ventilation forces degassing of CO₂ from the dripwater, prior to any calcite precipitation onto the stalagmites. This phase of degassing causes kinetic isotope fractionation, i.e. ¹³C-enrichment of dripwater whose δ¹³C_DIC values are already higher (by about 1‰) than those of soil water due to dissolution of the carbonate rock. A subsequent systematic shift to even higher δ¹³C values, from −11.5‰ in the cave drips to about −8‰ calculated for the solution film on top of stalagmites, is related to degassing on the stalagmite top and equilibration with the cave air. Mass-balance modelling of C fluxes reveals that a very small percentage of isotopically depleted cave air CO₂ evolves from the first phase of dripwater degassing, and shifts the winter cave air composition toward slightly more depleted values than those calculated for equilibrium. The systematic ¹³C-enrichment from the soil to the stalagmites at Grotta di Ernesto is independent of drip rate, and forced by the difference in pCO₂ between cave water and cave air. This implies that speleothem δ¹³C values may not be simply interpreted either in terms of hydrology or soil processes.  相似文献   

Waste rock dump investigation at Roşia Montană gold mine (Romania): a geostatistical approach   总被引：1，自引：1，他引：0  

Diego Servida  Sara Comero  Mara Dal Santo  Luisa de Capitani  Giovanni Grieco  Pietro Marescotti  Silvia Porro  Ferenc Lázár Forray  Ágnes Gál  Alexandru Szakács 《Environmental Earth Sciences》2013,70(1):13-31

Ro?ia Montan?, the largest European gold mine, could be re-opened. Environmental problems led to severe pollution of the Ro?ia and Abrud Rivers. The two main potentially toxic element (PTE) sources in mine sites are, in general, the abandoned underground workings and the piles of waste rock. Since the composition of waste rocks is often heterogeneous, this study faces the problem of estimating their mineralogical and chemical features starting from a set of sampling point. Twenty-five samples were collected on the main waste dump of the Ro?ia Montan? mine following a virtual squared grid (knots distance about 25 m). Grain size, color, bulk chemistry, mineralogy, acid mine drainage potential and a set of selected PTE (Ag, As, Cu, Ni, Pb and Zn) concentrations were determined on each sample. In a first approximation two main waste rock groups were identified: WR1 bulk composition is dacite-dominated, while WR2 is andesite-dominated. In both of them the concentrations of PTEs are below the regulatory limits for soils, with the exception of As. In terms of acid mine drainage, WR1 has a net acid-producing potential, while WR2 has a net neutralizing potential. The anisotropy of WR properties were analysed by means of semi-variograms and displayed with contour maps. Application of positive matrix factorization for the analysis of all the data relative to waste rocks allowed defining, in a semi-quantitative way, the factors controlling pollution and their spatial distribution. The processing of score matrix G factor associated with the geostatistical elaboration promises to be a powerful tool to discern the composition of mine dumps and support the exploitation and remediation phases.  相似文献   

The Place Names of the Middle East Before and After Ptolemaic Cartography: An Emblematic Selection from Ancient Maps     

Silvia Siniscalchi  Cosimo Palagiano 《The Cartographic journal》2013,50(3):205-216

The cultural gap between Europe and Asia (at first political and then religious) saw an increase with the spread of Islam, which, to the European imagination, was synonymous with ‘foreign’. This separation grew after the discovery of America (1492) with the loss of the central commercial position of the Mediterranean reducing the level of contact between the countries of its basin. Traces of these changes can be recognized on historic Western maps in the transformation of their toponyms (place names). Through a comparative cartographic analysis, this paper examines some of the key changes and phases that occurred during the era.  相似文献   

Macrobenthos and multi-molecular markers as indicators of environmental contamination in a South American port (Mar del Plata,Southwest Atlantic)     

Mariano J. Albano  Paulo da Cunha Lana  Claudia Bremec  Rodolfo Elías  César C. Martins  Natalia Venturini  Pablo Muniz  Silvia Rivero  Eduardo A. Vallarino  Sandra Obenat 《Marine pollution bulletin》2013

We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites.  相似文献   

Characterization of ground motions using recurrence plots     

Silvia R. García  Miguel P. Romo  Jesús Figueroa-Nazuno 《Geofísica Internacional》2013,52(3):209-227

The current analysis of earthquakes is typically based on linear mathematical models that may fail to describe and forecast particular behaviors, because in many cases the data complexity may induce a highly non linear behavior. In this paper the implementation of an alternative method for seismic time series analysis is presented. The RPs (Recurrence Plots) enables recognition and treatment of measured accelerations. An RP obtained from seismic data allows a more efficient interpretation of the ground motions and this explanation contributes to characterize materials and responses. The nonlinear attributes from RPs analysis can be used as filters to reveal patterns or be combined to predict a seismic property. Automated seismic data characterization, based on nonlinear seismic attributes, could rewrite the rules of earthquake phenomena interpretation. The objective of this work is to establish a new methodology for practical application of nonlinear dynamics in seismic pattern/attributes recognition, an evolving and challenging engineering field.  相似文献