Seasonal and inter-annual zooplankton dynamics in temporary pools with different hydroperiods   总被引：1，自引：0，他引：1  

Silvia Tavernini   《Limnologica》2008,38(1):63-75

The results of a research carried out in 2001 on nine temporary mountain pools (Northern Apennines, Italy) underlined a major role of hydroperiod in shaping zooplankton communities of temporary habitats. In 2002, the same pools were studied to assess inter-annual differences in zooplankton seasonal patterns. Data on precipitations (both snow and rainfalls) were collected to evaluate the influence of precipitation regimes on hydroperiod and concurrently on hydrochemical features and zooplankton dynamics.Mean annual snow and rainfall abundances were highly similar in both years but precipitation patterns were different. Moreover, different air temperatures were measured in the 2 years of study. These factors influenced water persistence and dry and wet cycles in the pools: in 2001, three pools dried out in summer and remained dry until autumn rainfalls (type A pools), in five pools (type B pools) the summer dry period was interrupted by re-filling due to storms in July and only in one pool water did remain for the entire research period (C1). In 2002, type A and B pools underwent only one dry phase (June–July) while C1 showed a hydroperiod similar to the one that occurred in the previous year. Overall, type A and B pools can be classified as ‘seasonal’ and C1 as ‘near-permanent or permanent’.Principal component analysis and paired t-tests did not show significant differences between years in the hydrochemical features of the pools. However, the seasonal pools showed a wide range of variation in their hydrochemical parameters while water features of the permanent pool presented less variability.Within the pools, divergences in the number and in the type of zooplankton taxa between the 2 years were limited. Rotifer and copepod density of the seasonal pools were comparable over years and only cladocerans exhibited distinct density dynamics. Cladoceran appeared to be associated with ionic content and influenced by the occurrence of ice-melting and by the wet phase length of the pools.On the contrary, the permanent pool showed diverse zooplankton seasonal patterns in 2001 compared to 2002. Over years, different pH values were measured; pH and conductivity varied with changing water volume, which in turn explained a significant amount of the observed variation in zooplankton densities in 2002.  相似文献   

Sonoran Desert productivity and the effect of trap size on litterfall estimates in dryland vegetation     

Alberto Búrquez  Angelina Martínez-Yrízar  Silvia Núez 《Journal of Arid Environments》1999,43(4):459

We describe the temporal and spatial litterfall and test the accuracy of different litter collection devices in a Sonoran Desert community. Two low-lying PVC litter trap designs were tested and compared against a standard IBP trap. The test traps collected significantly more plant litter than the IBP traps, which failed to capture most of the litter of ephemerals and low shrubs. The largest differences between the traps appeared after the pulses of growth of ephemeral plants. Data collection for a period of almost 2 years showed an annual total litterfall of 3·43 Mg ha⁻¹for the test traps and 2·77 Mg ha⁻¹for the IBP traps. These values are well above the average for deserts and fit better into the lower range of tropical dry forests. The test PVC traps are inexpensive, economical in collecting and sorting effort, and less prone to vandalism. Also, they can be laid in higher numbers than IBP traps, thus providing a better representation of the highly heterogeneous desert environment.  相似文献   

A contribution to the reconstruction of Miocene seepage from authigenic carbonates of the northern Apennines (Italy)     

Stefano Conti  Daniela Fontana  Silvia Mecozzi 《Geo-Marine Letters》2010,30(3-4):449-460

Authigenic carbonates from outcrops of the northern Apennines consist of small and irregular lenses and exhibit numerous features indicative of cold-seep settings. Detailed petrographic, mineralogical and geochemical studies from two Miocene deposits are presented. The first carbonate outcrop, named Fosso Riconi, is located in the foredeep basin of the Apenninic chain, whereas the second deposit represents a satellite basin called Sarsetta. The stable isotope data from specific carbonate minerals show a wide range of values well known from other palaeoseeps of the Apennine Mountains. The majority of seep carbonates are formed by low-Mg calcite and ankerite. Those minerals have δ¹³C values between ?7 and ?23‰ V-PDB, suggesting variable amounts of carbonate derived from oxidized methane, seawater (dissolved inorganic carbon) and sedimentary organic matter. Dolomite samples have the lowest δ¹³C values (?30.8 to ?39.0‰ V-PDB), indicating methane as the main carbon source. The findings suggest an evolutionary formation of the seeps and development of authigenic carbonates influenced by the activity of chemosynthetic organisms, of which large lucinid clams are preserved. Bioirrigation by the clams controlled the sediment–water exchange, and is here considered as an explanation for the anomalous Mg content of the calcite. We hypothesize that the seep carbonates were formed during periods of active methane-rich seepage, whereas during periods of slow seepage carbonate formation was reduced. Despite different geological settings, the two examined deposits of Sarsetta and Fosso Riconi show similar features, suggesting that a common pattern of fluid circulation played a major role in carbonate formation at both seep sites.  相似文献   

Neutron star surface emission: Beyond the dipole model     

Silvia Zane 《Astrophysics and Space Science》2007,308(1-4):259-265

Recent Chandra and XMM-Newton observations of a number of X-ray “dim” pulsating neutron stars revealed quite unexpected features in the emission from these sources. Their soft thermal spectrum, believed to originate directly from the star surface, shows evidence for a phase-varying absorption line at some hundred eVs. The pulse modulation is relatively large (pulsed fractions in the range ～8–35% in amplitude), the pulse shape is often non-sinusoidal, and the hard X-ray color appears to be anti-correlated in phase with the total emission. Moreover, the prototype of this class, RX J0720.4-3125, has been found to undergo rather sensible changes both in its spectral and timing properties over a timescale of a few years. By modeling the light curves of two sources, RBS 1223 and RX J0720.4-3125, it has been found evidence for two hot regions located at a slightly non antipodal direction. All these new findings are difficult to reconcile with the standard picture of a cooling neutron star endowed with a purely dipolar magnetic field. Here we present more realistic models of surface emission, where the effects of different neutron star thermal and magnetic surface distributions are accounted for. We show how a star-centered field made of a dipolar and a quadrupolar component can influence the properties of the observed light curves and we present results that account self-consistently for toroidal and poloidal crustal field configurations.  相似文献   

New estimations of precipitation and surface sublimation in East Antarctica from snow accumulation measurements     

Massimo Frezzotti  Michel Pourchet  Onelio Flora  Stefano Gandolfi  Michel Gay  Stefano Urbini  Christian Vincent  Silvia Becagli  Roberto Gragnani  Marco Proposito  Mirko Severi  Rita Traversi  Roberto Udisti  Michel Fily 《Climate Dynamics》2004,23(7-8):803-813

Surface mass balance (SMB) distribution and its temporal and spatial variability is an essential input parameter in mass balance studies. Different methods were used, compared and integrated (stake farms, ice cores, snow radar, surface morphology, remote sensing) at eight sites along a transect from Terra Nova Bay (TNB) to Dome C (DC) (East Antarctica), to provide detailed information on the SMB. Spatial variability measurements show that the measured maximum snow accumulation (SA) in a 15 km area is well correlated to firn temperature. Wind-driven sublimation processes, controlled by the surface slope in the wind direction, have a huge impact (up to 85% of snow precipitation) on SMB and are significant in terms of past, present and future SMB evaluations. The snow redistribution process is local and has a strong impact on the annual variability of accumulation. The spatial variability of SMB at the kilometre scale is one order of magnitude higher than its temporal variability (20–30%) at the centennial time scale. This high spatial variability is due to wind-driven sublimation. Compared with our SMB calculations, previous compilations generally over-estimate SMB, up to 65% in some areas.  相似文献   

Development of agroclimatic zoning model to delimit the potential growing areas for macaw palm (Acrocomia aculeata)     

Falasca  Silvia  Ulberich  Ana  Pitta-Alvarez  Sandra 《Theoretical and Applied Climatology》2017,129(3-4):1321-1333

Theoretical and Applied Climatology - The growing biodiesel production requires the use of new technologies and alternative feedstocks to maintain the growing demand of this biofuel. The macaw...  相似文献   

Age and geotectonic setting of Late Neoproterozoic juvenile mafic gneisses and associated paragneisses from the Ribeira belt (SE Brazil) based on geochemistry and Sm–Nd data — Implications on Gondwana assembly     

Renata da Silva Schmitt  Rudolph Allard Johannes Trouw  Silvia Regina Medeiros  Elton Luiz Dantas   《Gondwana Research》2008,13(4):502-515

Mafic gneisses and associated paragneisses from the Cabo Frio Tectonic Domain in the southeastern part of the Ribeira Belt, along the coast of Rio de Janeiro State in southeast Brazil, were subjected to a geochemical and Sm–Nd isotope study. Four lithotypes are distinguished: aluminous paragneisses (mainly sillimanite–kyanite–garnet–biotite gneiss), calcsilicate lenses, quartzo–feldspathic metasedimentary gneisses and mafic–ultramafic lenses. The whole-rock major and trace, including rare earth element distributions in the mafic–ultramafic intercalations indicate that derivation from subalkaline basalt/gabbro of tholeiitic affinity with E-MORB signature from a non-subduction environment. These mafic rocks have positive ε_Nd(t) and T_DM of 1.1 Ga. The metasedimentary rocks have negative ε_Nd(t) and T_DM of 1.7 Ga. A Sm–Nd whole rock isochron of mafic rocks yielded an age of 604 ± 38 Ma for the crystallization. This matches with the age of some detrital zircon grains from the paragneisses. The depositional basin, named Buzios–Palmital, was active at least until 620 Ma (age of the youngest detrital zircon) and was subsequently deformed and metamorphosed at ca. 525 Ma (age of metamorphic zircons) during the Buzios Orogeny. It is interpreted as a back arc basin with relation to the 630 Ma magmatic arc of the Oriental Terrane in the Ribeira Belt to the NW. However, after 600 Ma, the Buzios–Palmital basin changed to an active margin setting because the arc collided with the continental margin and the subduction shifted to the back arc environment. By 610 Ma, most of the Brasiliano belts registered collisional events related to multiple convergent blocks. The stress fields and paleocontinent shapes would have allowed the occurrence of extensional areas with not only sedimentary deposition but also ocean floor spreading. Its remnants are preserved in this Brazilian coastal region as an ancient suture, reworked intensively during the Mesozoic rifting events. The reconnaissance of Late Neoproterozoic basins in the Brasiliano–Pan-African belts is of major importance to partially unravel the final amalgamation events of SW Gondwana. Considering that the Buzios–Palmital basin rock units are mostly covered by the marginal Atlantic basins, it is possible that other evidence could be preserved in the coastal regions of SW-Africa and SE-South America.  相似文献   

Comparative assessment of spatiotemporal snow cover changes and hydrological behavior of the Gilgit,Astore and Hunza River basins (Hindukush–Karakoram–Himalaya region,Pakistan)     

Adnan Ahmad Tahir  Jan Franklin Adamowski  Pierre Chevallier  Ayaz Ul Haq  Silvia Terzago 《Meteorology and Atmospheric Physics》2016,128(6):793-811

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Electron Transfer Between Sulfide and Humic Acid: Electrochemical Evaluation of the Reactivity of Sigma-Aldrich Humic Acid Toward Sulfide     

Zhi-Guo Yu  Silvia Orsetti  Stefan B. Haderlein  Klaus-Holger Knorr 《Aquatic Geochemistry》2016,22(2):117-130

Little is known of potential reactivity and redox properties of reduced dissolved organic matter (DOM), although DOM in anoxic environments, e.g., groundwater, peat soils, or lake sediments, can be expected to differ from DOM of oxidized environments. We therefore investigated the impact of electrochemical and wet chemical [hydrogen (H₂)/Pd catalyst] reduction in Sigma-Aldrich humic acid (HA) as a model DOM for high salinity, high ionic strength, or iron-rich systems on its reactivity toward sulfide. Mediated electrochemical measurement showed that the reactivity of HA toward sulfide decreased in the order non-reduced HA > electrochemically reduced (?0.1 V) HA > H₂/Pd-reduced HA > electrochemically reduced (?0.4 V) HA. Results indicated that measured initial values of electron-accepting capacities of HA had a strongly positive correlation with the sulfide transformation, except for the H₂/Pd treatment of HA. This latter treatment obviously changed HA structures and lead to a different reactivity toward sulfide, limiting a direct comparison to electrochemically reduced organic matter. Our result confirmed that reduced HA was still reactive toward sulfide, although to a lower extent compared with oxidized HA. Compared to electrochemical reduction, H₂/Pd pre-treatment of HA alters redox properties and reactivity of organic matter and may therefore lead to results that cannot be transferred to natural systems.  相似文献   

Rainfall thresholds for the possible landslide occurrence in Sicily (Southern Italy) based on the automatic reconstruction of rainfall events   总被引：1，自引：1，他引：0  

Massimo Melillo  Maria Teresa Brunetti  Silvia Peruccacci  Stefano Luigi Gariano  Fausto Guzzetti 《Landslides》2016,13(1):165-172

Review of the literature on the reconstruction of the rainfall responsible for slope failures reveals that criteria for the identification of rainfall events are lacking or somewhat subjective. To overcome this problem, we developed an algorithm for the objective and reproducible reconstruction of rainfall events and of rainfall conditions responsible for landslides. The algorithm consists of three distinct modules for (i) the reconstruction of distinct rainfall events, in terms of duration (D, in h) and cumulated event rainfall (E, in mm), (ii) the identification of multiple ED rainfall conditions responsible for the documented landslides, and (iii) the definition of critical rainfall thresholds for possible landslide occurrences. The algorithm uses pre-defined parameters to account for different seasonal and climatic settings. We applied the algorithm in Sicily, southern Italy, using rainfall measurements obtained from a network of 169 rain gauges, and information on 229 rainfall-induced landslides occurred between July 2002 and December 2012. The algorithm identified 29,270 rainfall events and reconstructed 472 ED rainfall conditions as possible triggers of the observed landslides. The algorithm exploited the multiple rainfall conditions to define objective and reproducible empirical rainfall thresholds for the possible initiation of landslide in Sicily. The calculated thresholds may be implemented in an operational early warning system for shallow landslide forecasting.  相似文献