Species richness of the genus Molgolaimus (Nematoda) from local to ocean scale along continental slopes     

Gustavo Fonseca  Agnes W. Muthumbi  & Ann Vanreusel 《Marine Ecology》2007,28(4):446-459

This study investigated the distribution of Molgolaimus species (Nematoda) at different hierarchical spatial scales and observed the turnover of species along bathymetrical transects and among transects in two separate geographical regions. Samples from six transects (200–2000 m) from the Southern Oceans (SO) and four bathymetric transects (50–2000 m) from the Western Indian Ocean (WIO) were compared. Of the 30 species recorded, only one was common to both regions. WIO had higher local species richness than the SO. In both regions, the local scale was the greatest contributor to the total species richness. In the SO, there was no difference between species turnover at the different spatial scales, however, in the WIO, the turnover along bathymetrical transects was higher than among separated transects. For the particular genus studied, the evidence suggests that the study area in WIO has more widespread species and was better sampled, while the SO has many restricted species and it is most probably characterized by different biogeographical provinces. At the ocean scale (i.e. WIO versus SO), evolutionary histories may have strongly influenced nematodes species composition, while at local and regional scales, ecological processes are probably promoting species co‐existence and speciation. The high co‐existence of certain species at local scale is partially explained by species preference for different sediment layers.  相似文献   

Tintinnids (Ciliophora) and Other Net Microzooplankton (> 30 µm) in Southwestern Atlantic Shelf Break Waters     

Gustavo A. Thompson  Viviana A. Alder    & Demetrio Boltovskoy   《Marine Ecology》2001,22(4):343-355

Abstract. Proportions of foraminifers, tintinnids, polycystine radiolarians, pteropods and crustacean larval stages were estimated in a collection of 76 vertically stratified (0 – 100 m) 30 µm net microplankton samples from 16 stations along the Argentine shelf-slope (around 200 m isobath – between 40 and 56° S), covered on 13 – 18 November 1996. Tintinnids were identified to species. Relative abundances of the microzooplankton assessed and chlorophyll a values allow to define two contrasting groups of stations: 'deep' and 'shallow'. The former, located in pelagic, purely subantarctic Malvinas Current waters, hosted higher proportions of foraminifers and lower proportions of tintinnids, as well as less chlorophyll a (all differences were significant at the 0.1 % level). 'Shallow' stations were located in the area of the thermohaline front where the Patagonian Current comes in contact with the Malvinas Current, and were generally characterized by higher chlorophyll a levels (up to 3.7 µg Chl a  · l^–1). The distribution of tintinnid species, on the other hand, allowed no discrimination between these two areas, although some of the dominant forms showed much higher relative abundances in one of the two groups of stations. Twenty-six tintinnid taxa were recorded, yet only 6 accounted for 95 % of the specimens identified. Tintinnid taxocoenoses were characterized by a few abundant species and many rare ones. Numbers of tintinnid species and specific diversity did not differ noticeably with depth and latitude. Cape Horn Current waters were detected in the area by the presence of expatriated organisms presumably originating at mid-latitudes in the South Pacific Ocean.  相似文献   

Quantifying the impact of no-till on runoff in southern Brazil at hillslope and catchment scales     

Ana L. Londero  Jean P. G. Minella  Fabio J. A. Schneider  Dinis Deuschle  Danrlei Menezes  Olivier Evrard  Madalena Boeni  Gustavo H. Merten 《水文研究》2021,35(3):e14094

No-till (NT) is a conservation system that improves the hydrological regime of agricultural slopes by providing greater surface protection and benefits to the physical and hydrological properties of soils. However, the isolated use of NT is not enough to control runoff and its associated degradation processes. Therefore, this study aimed to evaluate the runoff of agricultural slopes under NT under different runoff control conditions by monitoring 63 rainfall events in two 2.4-ha zero-order catchments and 27 rainfall events in four 0.6-ha macroplots. The catchments are paired and similar in terms of the type of soil and relief, but different regarding the presence of terraces. The macroplots have different soil and crop management systems. By using monitoring techniques, the hyetographs and hydrographs revealed the influence of the different types of management on the catchments and macroplots and allowed rainfall characteristics, runoff volume, runoff coefficients, water infiltration, peak runoff, response times, and curve number to be analysed. The terraces positively affected the NT and controlled runoff and related variables, in addition to infiltration significantly increasing and runoff reducing in the terraced catchment. All the hydrological information assessed pointed to the positive effects provided by the presence of the terraces. The results in the macroplots showed that high amounts of phytomass and/or chiselling do not control runoff and its correlated variables in medium and high magnitude events. The study concludes by underlining the need for additional measures to control runoff (terraces), even in areas under NT and with high phytomass production. Additionally, the study emphasizes the importance of monitoring at the catchment scale to better understand the hydrological behaviour of agricultural areas and provide the necessary parameters to effectively control runoff.  相似文献   

Fractionnement isotopique dans l'eau de cristallisation du sulfate de calcium     

J. C. Fontes 《International Journal of Earth Sciences》1966,55(1):172-178

Résumé Le fractionnement isotopique (¹⁸O) entre l'eau de solubilisation et l'eau de cristallisation du gypse a été déterminé expérimentalement. La différence de l'ordre de 4 semble indépendante de la température. La connaissance de la composition isotopique de l'eau de solubilisation donne des indications paléoclimatiques et paléogéographiques.

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The¹⁸O fractionation between mother water and crystallisation water of the gypsum was determined by experiments. The difference, about 4 seems independent of temperature. The knowledge of the isotopic composition of mother water gives paleoclimatic and paleogeographic informations.

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Zusammenfassung Der¹⁸O-Gehalt im Porenwasser und Konstitutionswasser im Gips wurden experimentell bestimmt. Der Unterschied von 4 scheint unabhängig von der Temperatur zu sein. Die Kenntnis der Isotopenzusammensetzung des Porenwassers gibt paläoklimatische und paläogeographische Informationen.

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Effect of solar radiation and the subsequent dark periods on two newly isolated and characterized Antarctic marine bacteria     

Edgardo A. Hernández  Gustavo A. Ferreyra  Walter P. Mac Cormack 《Polar research》2004,23(1):67-77

Two strains of psychrotolerant Antarctic marine bacteria were isolated and characterized using biochemical and molecular techniques. Sequencing of 16S rRNA gene showed that UVvi strain belongs to the genus Arthrobacter whereas UVps strain is related to the Flexibacter-Cytophaga-Bacteroides (FCB) group. Response of the strains to solar radiation was studied during the summer of 1999 in Potter Cove, near Jubany station (South Shetland Island, Antarctica). The effect of photosynthetically available radiation (PAR, 400-700 nm), ultraviolet-A (UV-A, 320-400 nm) and ultraviolet-B radiation (UV-B, 280-320 nm) on cell viability was studied using mixed cultures in quartz bottles covered with interferential filters and exposed to solar radiation. In all experiments, four treatments were used: dark (with light screened out), PAR (with UV radiation screened out), PAR+UV-A (UV-B screened out) and PAR+UV-A+UV-B. Under the assayed conditions, PAR+UV-A and PAR+UV-A+UV-B radiation showed similar negative effects on the viability of the studied strains. However, at the end of the exposure time, mortality values in PAR+UV-A+UV-B treatments were higher than those observed under PAR+UV-A treatments. In both PAR+UV-A and PAR+UV-A+UV-B treatments we observed high levels of hydrogen peroxide compared with the dark control. The Arthrobacter UVvi strain showed significant recovery in dark conditions after exposure to the PAR+UV-A but not after the PAR+UV-A+UV-B treatment. This strain proved to be more resistant to UV radiation than the FCB group-related UVps strain. The results showed that UV radiation has a deleterious effect on these Antarctic marine bacteria and also revealed that the analysed components of the Antarctic bacterioplankton may have different responses when they are exposed to the same irradiance conditions.  相似文献   

The usefulness of UV–visible and fluorescence spectroscopies to study the chemical nature of humic substances from soils and composts   总被引：1，自引：1，他引：1  

Marta Fuentes  Gustavo Gonzlez-Gaitano  Jos Ma García-Mina 《Organic Geochemistry》2006,37(12):1949

The aim of this work is to study the suitability of the use of fluorescence and UV–visible spectroscopies to evaluate the humification degree of different organic alkaline extracts obtained from diverse materials (humic substances, composted and non-composted materials). Our results indicate that the complementary utilization of the fluorescence index proposed by Milori et al. [Milori, D., Martin-Neto, L., Bayer, C., Mielniczuk, J., Vagnato, V., 2002. Humification degree of soil humic acids determined by fluorescence spectroscopy. Soil Science, 167, 739–749] (the total area of the emission spectra collected over a range of 460–650 nm using an excitation wavelength of 465 nm), the ratio between the electron-transfer band and benzenoid band of benzene UV light absorption, and the molar absorption coefficients at 600 nm and 280 nm proved capable of discriminating between extracts obtained from non-humified, partially humified and very humified materials.Likewise, our results suggest that humification is related to increments in the aromatic character of the molecules, which may be reflected in the presence of more aromatic rings and/or more condensed polyaromatic structures, and the degree of substitution in aromatic rings with polar functional groups, as well as to the possible increase in the conjugation degree in unsaturated aliphatic chains.  相似文献   

Oxygen,sulfur, and strontium isotope and fluid inclusion studies of barite deposits from the Iglesiente-Sulcis mining district,Southwestern Sardinia,Italy     

G. Cortecci  J. Ch. Fontes  A. Maiorani  G. Perna  E. Pintus  B. Turi 《Mineralium Deposita》1989,24(1):34-42

This paper deals with barite from stratiform, karst, and vein deposits hosted within Lower Paleozoic rocks of the Iglesiente-Sulcis mining district in southwestern Sardinia. For comparison sulfates from mine waters are studied. Stratiform barite displays ³⁴S=28.8–32.1, ¹⁸O=12.7–15.6, and ⁸⁷Sr/⁸⁶Sr=0.7087, in keeping with an essentially Cambrian marine origin of both sulfate and strontium. Epigenetic barite from post-Hercynian karst and vein deposits is indistinguishable for both sulfur and oxygen isotopes with ³⁴S=15.3–26.4 and ¹⁸O=6.6–12.5; ⁸⁷Sr/⁸⁶Sr ratios vary 0.7094–0.7140. These results and the microthermometric and salinity data from fluid inclusions concur in suggesting that barite formed at the site of mineralization by oxidation of reduced sulfur from Cambrian-Ordovician sulfide ores in warm, sometimes hot solutions consisting of dilute water and saline brine with different ¹⁸O values. The relative proportion of the two types of water may have largely varied within a given deposit during the mineralization. In the karst barite Sr was essentially provided by carbonate host rocks, whereas both carbonate and Lower Paleozoic shale host rocks should have been important sources for Sr of the vein barite. Finally, ³⁴S data of dissolved sulfate provide further support for the mixed seawater-meteoric water composition of mine waters from the Iglesiente area.  相似文献   

18O and 34S in the Upper Bartonian gypsum deposits of the Paris basin     

J.C. Fontes  R. Létolle 《Chemical Geology》1976,18(4):285-295

Isotopic analyses (¹⁸O and ³⁴S) of the Eocene gypsum from the Paris basin show a range beyond the normal Tertiary marine values. The possibility of a reduction process during diagenesis is discussed.A hypothesis of continental origin by leaching of Permotriassic deposits is proposed for this formation on the basis of a comparison of the isotopic contents recorded from Germany and eastern France.  相似文献   

Taxonomy, facies relationships and palaeobiology of bakevelliid bivalves from the Lower Cretaceous of west-central Argentina     

Darío Gustavo Lazo   《Cretaceous Research》2003,24(6):765

Cretaceous bakevelliids in Argentina are restricted to the Lower Cretaceous. They are recorded in shallow marine deposits in two Mesozoic basins located in the Andes foothills in Patagonia. In the Austral Basin (44°–55°S) there is only one genus, Gervillella, represented by a single specimen from the Barremian. In the Neuquén Basin (30°–40°S) two genera, Gervillaria and Gervillella, occur, ranging from the Berriasian to the Lower Barremian. In the Pilmatué Member of the Agrio Formation two species are identified: Gervillaria alatior (Imlay) and Gervillella aviculoides (J. Sowerby). The former is also recorded in Mexico while the latter is more widespread, occurring in Europe, Asia, and Africa. In the Bajada del Agrio section they come from eight tabular shell beds located near and on top of shallowing-upwards cycles. They were abundant only in four of these levels. These shell beds are interpreted as having been deposited in the mid-ramp (middle of cycles), and upper mid-ramp (top of cycles). A functional analysis of shells revealed two life habits: epibyssate and endobyssate.  相似文献   

The anticentre old open cluster NGC 1883: radial velocity and metallicity     

Sandro Villanova  Gustavo Baume  Giovanni Carraro 《Monthly notices of the Royal Astronomical Society》2007,379(3):1089-1096

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