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排序方式: 共有182条查询结果,搜索用时 156 毫秒
121.
122.
R. Herrero B. Cordero P. Lodeiro C. Rey-Castro M.E. Sastre de Vicente 《Marine Chemistry》2006,99(1-4):106
Samples of dead biomass from the marine brown algae Fucus ceranoides, Fucus vesiculosus and Fucus serratus were studied for their ability to remove cadmium from aqueous solutions. The metal sorption process is rapid, with 90% of the metal uptake completed within the first 25 min of contact. The kinetic data was described successfully by a pseudo second order chemical sorption process with rate constants of ca. 0.6 g mmol− 1 min− 1. At pH 4.5, the raw biomass of the three species exhibited equilibrium uptake capacities for Cd as high as 0.8 mmol g− 1 (90 mg g− 1), on a dry weight basis, without chemical pretreatment. These sorption capacities are much higher than those reported for activated carbon and chitin. The sorption of Cd was found to increase as pH increases, reaching a plateau at pH 5.Batch sorption experiments and continuous potentiometric titrations of acid-treated biomass samples in 0.05 M NaNO3 were used to derive thermodynamic binding parameters according to the NICCA model. The total amount of acid sites was 2.4–2.9 mmol g− 1, with median values of the affinity distribution for protons and cadmium ions, log K˜H and log K˜Cd, of 3.7 and 2.69, respectively (conditional values). The apparent heterogeneity of the sorbent was successfully taken into account by the empirical NICCA isotherm, which described very well the competition between protons and metal ions, in contrast with a simpler discrete competitive Langmuir model.The experimental results demonstrate that these seaweeds constitute a promising, efficient, cheap and biodegradable sorbent biomaterial for cadmium removal from wastewaters. This use would represent an example of exploitation of a renewable marine resource in water treatment technologies for the prevention of heavy metal pollution in the environment. 相似文献
123.
Vicente Fernndez David E. Dietrich Robert L. Haney Joaquín Tintor 《Progress in Oceanography》2005,66(2-4):321
In this paper, we present the results from a 1/8° horizontal resolution numerical simulation of the Mediterranean Sea using an ocean model (DieCAST) that is stable with low general dissipation and that uses accurate control volume fourth-order numerics with reduced numerical dispersion. The ocean model is forced using climatological monthly mean winds and relaxation towards monthly climatological surface temperature and salinity. The variability of the circulation obtained is assessed by computing the volume transport through certain sections and straits where comparison with observations is possible. The seasonal variability of certain currents is reproduced in the model simulations. More important, an interannual variability, manifested by changes in currents and water mass properties, is also found in the results. This may indicate that the oceanic internal variability (not depending on external atmospheric forcing), is an important component of the total variability of the Mediterranean circulation; variability that seems to be very significant and well documented by in situ and satellite data recovered in the Mediterranean Sea during the last decade. 相似文献
124.
Vance P. Vicente 《Marine Ecology》1989,10(2):179-191
Abstract. Long-term changes in the distributional patterns of commercial sponges ( Spongia spp. and Hippospongia spp.) within the West Indian Region indicates that: 1) commercial sponges had a widespread distribution throughout the whole West Indian Region and were ubiquitous in very shallow water until about the first half of the present century; 2) they were fished commercially not only in the traditional northern Caribbean sites (Florida, Gulf of Mexico, Bahamas) but also in the Greater ( e. g. , Hispaniola, Jamaica) and Lesser Antilles; and 3) they became extinct throughout most of the Lesser Antilles ( e. g. , Puerto Rico, Vieques, St. Thomas) sometime during the first half of this century. Mortalities of spongiids within the Antilles were found to differ from other marine mortalities in that: 1) species disappeared from a large region; 2) species vanished from different habitats and depths; and 3) natural populations never recovered. Species richness patterns suggest that commercial sponge genera ( Spongia and Hippospongia ) evolved under slightly cooler elimatic conditions than those found at present, and that these extinctions occurred as a direct or indirect effect of positive thermal anomalies in sea surface and atmospheric temperatures between 1900–1950. The concept that species diversity is stable on a regional scale is questioned. 相似文献
125.
Late Tertiary and Quaternary volcanism of southeastern Spain can be fitted in a platetectonics model, taking into account the post-Paleozoic evolution of the stable and semimobile Iberian areas and the new orogenic belts bordering the Mediterranean between Africa and the Iberian Peninsula.The occurrence and distribution of calc-alkaline and potassic volcanism suggest an oceanic crust sinking downwards from the Iberian plate. This active margin is causally related to the convergence and collision of Iberia and Africa during Late Cretaceous—Early Miocene time span.A pre-collision distensive phase is inferred from the stratigraphie and tectonic record between the Triassic and Late Cretaceous, while since the Late Miocene another distensive phase is related to the actualistic features. 相似文献
126.
127.
Claus Fröhlich José Romero Hansjörg Roth Christoph Wehrli Bo N. Andersen Thierry Appourchaux Vicente Domingo Udo Telljohann Gabrielle Berthomieu Philippe Delache Janine Provost Thierry Toutain Dominique A. Crommelynck André Chevalier Alain Fichot Werner Däppen Douglas Gough Todd Hoeksema Antonio Jiménez Maria F. Gómez José M. Herreros Teodoro Roca Cortés Andrew R. Jones Judit M. Pap Richard C. Willson 《Solar physics》1995,162(1-2):101-128
The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar constant, two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given.died 13 October 1994 相似文献
128.
José A. M. Demattê Julianne de Castro Oliveira Tiago Rodrigues Tavares Leonardo Ramirez Lopez Fabrício da Silva Terra Suzana Romeiro Araújo Caio Troula Fongaro Stoécio Malta Ferreira Maia Francisco Fujita de Castro Mello Rodnei Rizzo Simone Vicente Marco Antonio de Melo Bortolleto Pedro Henrique Ramos Cerqueira 《Environmental Earth Sciences》2016,75(18):1277
129.
Lidia Romero Antonio Camacho Eduardo Vicente Maria R. Miracle 《Journal of Paleolimnology》2006,35(1):167-177
Sedimentation fluxes of photosynthetic pigments and their derivatives, focused on the anoxygenic bacteria populations, were
determined in meromictic Lake La Cruz over a three-year period using sediment traps. Bacterial settling occurs in pulses in
response to lake dynamics. Two main annual events affect particle settling in Lake La Cruz: (1) Following an event of massive
calcium precipitation in summer that caused water whiting, a maximum flux of chlorophyll a and derivatives towards the sediment was registered. Although whiting is accompanied by massive phytoplankton biomass sinking,
it was not followed by concomitant photosynthetic bacterial sinking. (2) In contrast, the disruption of the chemocline and
the contact of bacterial populations with oxygenated waters during autumn overturn provoked a destruction of the sulfur bacterial
plate, causing mass mortality, registered in the settling material as photosynthetic pigments and their derivatives from phototrophic
bacteria. Among the bacteriochlorophyll a oxidation products, bacterioviridin (bvir) was detected in high relative abundance in the settled material collected by sediment
traps. The much increased flux of bvir after thermal overturn, associated with mass mortality of the purple sulfur bacterium,
Amoebobacter purpureus, confirms the suitability of this molecule as a useful paleoindicator of the degree of oxygen exposure experienced by the
purple sulfur bacteria population. 相似文献
130.
I. de Vicente K. Cattaneo L. Cruz-Pizarro A. Brauer P. Guilizzoni 《Journal of Paleolimnology》2006,35(1):55-64
P-fractional composition has been studied in a 64-cm long sediment core collected in an eutrophic hardwater lake (Lake Alserio,
northern Italy) in an attempt to identify the main mechanisms (chemical or biologic) controlling CaCO3 precipitation in the water column. The results of the sedimentary phosphate fractionation showed that the most important
P fraction was an organic fraction extracted with hot NaOH: org-Palkali (26% of Psed). A digestion of the supernatant of the P-fraction bound to CaCO3 allowed the detection of a large pool of org-P (19% of Psed). Although the nature of this fraction is unclear, we suggest that it may be involved in the biologically mediated precipitation
of CaCO3. The high CaCO3 concentration in the entire vertical sediment profile, as well as the presence of inorg- and org-P bound to Ca in both laminated
and non-laminated zones, suggest that the CaCO3 precipitation is not a recent process but is a process that has been occurring in the lake for some time. Accordingly, the
change from a homogeneous sediment to a laminated sequence might be caused by the eutrophication process of Lake Alserio occurring
since the 1960s, which has allowed the preservation of the varved sediment as a consequence of the drastic reduction in bioturbation. 相似文献