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341.
E. Martinez Carretero 《Journal of Arid Environments》1999,42(4):305
Four plant communities were determined through floristical and non-metric analysis: a Dolichlasium lagascae community in crevices on sunny rock outcrops; a Cercidium praecox ssp. glaucum community on sunny slopes; an Artemisia mendozana–Adesmia trijuga community on shady slopes; and a Eupatorium buniifolium community on dry riverbanks. The discriminant function analysis showed that the first group corresponds to the sunny rock outcrops discriminated by Na content (r=0·53, p<0·05), the second group is for sunny slopes discriminated by electric conductivity and the third for shady slopes–riparian discriminated by the (Ca+Mg) content (r=0·54, p<0·05). A pattern of primary succession on outcrop surfaces is proposed. 相似文献
342.
Rosa de la Torre Leopoldo G. Sancho Asunción de los Ríos Karen Olsson-Francis Petra Rettberg Jean-Pierre P. de Vera Jesus Martinez Frías Maria Mercedes Lucas Ana Pintado 《Icarus》2010,208(2):735-292
In the space experiments Lithopanspermia, experimental support was provided to the likelihood of the lithopanspermia concept that considers a viable transport of microorganisms between the terrestrial planets by means of meteorites. The rock colonising lichens Rhizocarpon geographicum and Xanthoria elegans, the vagrant lichen Aspicilia fruticulosa, and endolithic and endoevaporitic communities of cyanobacteria and bacteria with their natural rock substrate were exposed to space for 10 days onboard the Biopan facility of the European Space Agency (ESA). Biopan was closed during launch and re-entry. In addition, in the Stone facility, one sample of R. geographicum on its natural granitic substrate was attached at the outer surface of the re-entry capsule close to the stagnation point, only protected by a thin cover of glass textolite. Post-flight analysis, which included determination of the photosynthetic activity, LIVE/DEAD staining, and germination capacity of the ascospores, demonstrated that all three lichen were quite resistant to outer space conditions, which include the full spectrum of solar extraterrestrial electromagnetic radiation or selected wavelength ranges. This high resistance of the lichens to space appears to be due to their symbiotic nature and protection by their upper pigmented layer, the cortex. In contrast, the rock- or halite-inhabiting bacteria were severely damaged by the same exposure. After atmospheric re-entry, the granite of the Stone sample was transformed into a glassy, nearly homogenous material, with several friction striae. None of the lichen cells survived this re-entry process. The data suggest that lichens are suitable candidates for testing the concept of lithopanspermia, because they are extremely resistant to the harsh environment of outer space. The more critical event is the atmospheric re-entry after being captured by a planet. Experiments simulating the re-entry process of a microbe-carrying meteoroid did not show any survivors. 相似文献
343.
Jamaica Bay, NY, is a highly urbanized estuary within the boroughs of New York City conspicuously lacking published information
on dissolved trace metal concentrations. The current study examines the distribution and cycling of trace metals in that embayment
with data gathered during cruises in November 2004, April 2005, and June 2006. Most of the metal distributions (Fe, Zn, Co,
Ag, Cu, Pb, Ni) in the water column are explained by the input of substantial volumes of treated wastewater effluent. However,
several lines of evidence suggest that submarine groundwater discharge (SGD) is also an important source of dissolved Fe,
Zn, Co, Ni, and isotopically distinct stable Pb ratios (206Pb, 207Pb, 208Pb) in the Bay. Conversely, the recirculated seawater component of SGD is an apparent sink for dissolved Mo. This study provides
the first measurements of dissolved trace metals in the Jamaica Bay water column and subterranean estuary and provides evidence
for trace metal input due to SGD. 相似文献
344.
S. Toucanne S. Zaragosi J.F. Bourillet P.L. Gibbard F. Eynaud J. Giraudeau J.L. Turon M. Cremer E. Cortijo P. Martinez L. Rossignol 《Quaternary Science Reviews》2009,28(25-26):2974-2981
The correlation of continental sedimentary records with the marine isotope stratigraphy is a challenge of central importance in Quaternary stratigraphy, particularly in Western Europe where long records of glaciation on land areas are particularly rare. Here we demonstrate for the first time the interrelationship of events during the last 1.2 Ma in an ocean-sediment core from the Bay of Biscay (NE Atlantic), SW of the Channel. The identification of discharge variations from tributary river systems to the ‘Fleuve Manche’ palaeoriver during glacio-eustatic sea-level lowstands demonstrates the correlation of the marine sediment stratigraphy to the expansion and recession of the European ice-sheets. The amplitude and chronology of European ice-sheet oscillations since the late Early Pleistocene is discussed and our results demonstrate that the first coalescence of the Fennoscandian and British ice-sheets in the North Sea basin ca 450 ka ago caused a profound change in lowstand European drainage alignment. This change caused a rerouting of Fennoscandian and eastern British ice-sheets-derived meltwaters from northwards into the Nordic Seas to southwards into the eastern North Atlantic thereafter. Besides allowing a thorough synchronisation of the European ice-sheet palaeogeography with the well-dated records of palaeoceanographical changes, our results improve the stratigraphy of the English Channel palaeovalleys and will provide important constraints on paleoclimatic scenarios considering the impact that such rerouting and meltwater surges might have on the stability of the oceanic conveyor belt. 相似文献
345.
346.
Amado LL da Rosa CE Leite AM Moraes L Pires WV Pinho GL Martins CM Robaldo RB Nery LE Monserrat JM Bianchini A Martinez PE Geracitano LA 《Marine pollution bulletin》2006,52(2):199-206
Biomarkers of exposure and effect of pollutants were analyzed in croakers Micropogonias furnieri (Teleostei: Sciaenidae) captured in winter and summer in a polluted and in a non-polluted site at the Patos Lagoon estuary (Southern Brazil). Catalase and glutathione S-transferase activities (exposure biomarkers) and lipid peroxidation (effect biomarker) were analyzed in liver samples. Other two effect biomarkers were also studied: blood cells DNA damage (through comet assay and micronucleus test) and respiratory burst measurements. In a broad view, results point to an important seasonal variation of the biochemical biomarkers analyzed. However, data obtained clearly indicate that croakers collected in winter at the polluted site were subjected to a level of clastogenic agents sufficient to generate irreversible genetic damages (mutations) and impair the fish immune system. 相似文献
347.
Review of solutions for 3D hydrodynamic modeling applied to aquaculture in South Pacific atoll lagoons 总被引:1,自引:0,他引:1
Andréfouët S Ouillon S Brinkman R Falter J Douillet P Wolk F Smith R Garen P Martinez E Laurent V Lo C Remoissenet G Scourzic B Gilbert A Deleersnijder E Steinberg C Choukroun S Buestel D 《Marine pollution bulletin》2006,52(10):1138-1155
A workshop organized in French Polynesia in November 2004 allowed reviewing the current methods to model the three-dimensional hydrodynamic circulation in semi-enclosed atoll lagoons for aquaculture applications. Mollusk (e.g. pearl oyster, clam) aquaculture is a major source of income for South Pacific countries such as French Polynesia or Cook Islands. This aquaculture now requires a better understanding of circulation patterns to improve the spatial use of the lagoons, especially to define the best area to set larvae collectors. The pelagic larval duration of the relevant species (<20 days) and the size of the semi-closed lagoons (few hundreds of km2) drive the specifications of the model in terms of the spatial and temporal scale. It is considered that, in contrast with fish, mollusk larvae movements are limited and that their cycle occurs completely in the lagoon, without an oceanic stage. Atolls where aquaculture is productive are generally well-bounded, or semi-closed, without significant large and deep openings to the ocean. Nevertheless part of the lagoon circulation is driven by oceanic water inputs through the rim, ocean swells, tides and winds. Therefore, boundary conditions of the lagoon system are defined by the spatial structure of a very shallow rim (exposition and number of hoas), the deep ocean swell climate, tides and wind regimes. To obtain a realistic 3D numerical model of lagoon circulation with adequate forcing, it is thus necessary to connect in an interdisciplinary way a variety of methods (models, remote sensing and in situ data collection) to accurately represent the different components of the lagoon system and its specific boundary conditions. We review here the current methods and tools used to address these different components for a hypothetical atoll of the Tuamotu Archipelago (French Polynesia), representative of the semi-closed lagoons of the South Pacific Ocean. We hope this paper will serve as a guide for similar studies elsewhere and we provide guidelines in terms of costs for all the different stages involved. 相似文献
348.
Analysis of Urban Atmosphere Plume Concentration Fluctuations 总被引:1,自引:1,他引:0
Dennis Finn Kirk L. Clawson Roger G. Carter Jason D. Rich Chris Biltoft Martin Leach 《Boundary-Layer Meteorology》2010,136(3):431-456
Concentration variability in the fast-response tracer dataset for continuous, near-surface, point source releases in the urban
core from the Joint Urban 2003 field study is analyzed. Concentration variability for conditionally and unconditionally sampled
time series is characterized by probability densities, concentration fluctuation intensity, skewness, and kurtosis. Significant
day-night differences in plume dispersion are observed. Relative to daytime, nighttime plumes were more likely to have reduced
concentration fluctuation intensities, higher normalized surface concentrations, suppressed vertical mixing, and a greater
prevalence of Gaussian-like distributions rather than log-normal or mixed mode distributions. This was in spite of the similar
stability and turbulence conditions in the urban core for day and night. The potential roles of flow meander and thermal stability
in explaining these differences are examined. Probability densities of concentration are found to be a strong function of
fluctuation intensity. There are few differences in probability densities between day and night when classified by fluctuation
intensity. There are no appreciable differences between conditional and unconditional probability densities and only small
differences between conditional and unconditional sampling statistics relative to the larger differences usually observed
in more homogeneous settings. Fluctuation intensity, skewness, and kurtosis are higher for the daytime experiments, and closer
to the source, but show little difference between conditional and unconditional results over most of their range of values.
The log-normal distribution provides a better overall fit to a broader range of the dataset than the exponential or clipped-normal
distributions. 相似文献
349.
Two kinds of objective functions for parameter optimisation in simplified general circulation models (SGCMs) are introduced
and tested with an SGCM employing linear parameterisations for diabatic heating, surface friction and horizontal diffusion.
(a) A set of circulation indices is introduced to characterise the zonal mean primary and secondary circulation and the global
energetics. The objective function is then given by the distance between the modelled and a reference (e.g. observed) circulation
in a state space spanned by these indices. (b) The global and time mean entropy production and kinetic energy dissipation
are introduced as additional objective functions, following the maximum entropy production principle. It is found that both
methods lead to optimal parameter values close to the standard configuration of the model, though the method of the second
kind is restricted to those model parameters associated with internal processes such as heat and momentum fluxes. 相似文献
350.
Modeling the mechanical behavior of coarse-grained soil using additive manufactured particle analogs
Acta Geotechnica - Systematic investigation of the effects of individual particle properties, such as shape, size, surface roughness, and constituent materials stiffness, on the behavior of... 相似文献