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排序方式: 共有225条查询结果,搜索用时 31 毫秒
141.
Clémentine Perstrimaux Séverine Le Faucheur Monika Mortimer Serge Stoll Fabrizio Bernardi Aubry Margherita Botter Roberto Zonta Vera I. Slaveykova 《Aquatic Geochemistry》2015,21(2-4):343-362
The present study explores the effect of salinity and dissolved organic carbon (DOC) gradients on the stability and reactivity of titanium dioxide nanoparticle (TiO2-NP) agglomerates in ambient water from the Lagoon of Venice and their possible effect on nauplii sampled at the same locations. In all ambient water samples, TiO2-NPs formed rapidly micrometre-sized agglomerates. The increase in the salinity and concomitant decrease in DOC content induced the formation of larger agglomerates, with z-average hydrodynamic diameter increasing with TiO2-NP concentration and exposure duration. Under the studied conditions, ζ-potential exhibited negative values. In line with agglomeration results, enhancement of the salinity and lower DOC resulted in less negative ζ-potential with close to 0 values in the dispersions of 100 mg L?1 TiO2-NPs in sea water. Two-hour exposure to micrometre-sized agglomerates of TiO2-NPs resulted in an increase in the fluorescence of propidium iodide (PI) stained nauplii in comparison with unexposed controls, but had no effect at 24-h exposure. The increase in nauplii-associated PI fluorescence was more noticeable in dispersions containing 100 mg L?1 than those containing 10 mg L?1 TiO2-NPs, suggesting membrane permeability alteration in a concentration-dependent manner. However, the PI staining results have to be interpreted with caution because of the possible dye binding to the nauplii surface without penetration of cellular membrane. The effect of TiO2-NPs on nauplii was more pronounced at higher salinity and decreased with increasing DOC concentrations at 2 h, while no trends were found at 24-h exposure, as well as exposure to 100 mg L?1 TiO2-NPs. 相似文献
142.
The Mediterranean fin whale population, Balaenoptera physalus, is resident, with almost no exchanges with the Atlantic population. The entire population was estimated at 1300 or 13,300 individuals by a recent project depending on the platform used. This disparity shows the importance of long-term monitoring with a unique protocol of survey. Capture-recapture approaches using dorsal photographs and genetic identity collections over a 10 years period were used to estimate the abundance of the north-western Mediterranean fin whale. We identified 332 individuals using photographs and 470 using genotypes, with a total of 546 individuals identified between 2008 and 2019, when some whales were double-marked. The inter-annual percentage of recapture varied between 15% and 17% respectively for genotypes and photographs methods. Using Cormack-Jolly-Seber models, the abundance of fin whales in the north-western Mediterranean is estimated at 1295 individuals (95% CI: 1116–1474) with a survival probability of 0.945 (95% CI: 0.690–0.993) from genotypes. Abundance estimates from combined collections (photographs and genotypes) and corrected photograph estimates were similar to the genetic ones. Future studies might prioritize the genetic approach which is the least biased and with a narrower confidence interval. The genetic abundance estimates show relative stability over time, when compared to 1990 estimates, and should be included in future conservation actions. 相似文献
143.
Théophile Tchakoua Mama Pamboundom Berthelot Said Duvalier Ramlina Vamhindi Serge Guy Nana Engo Ousmanou Motapon Mama Nsangou 《Astrophysics and Space Science》2018,363(3):48
The potential energy surface (PES) for the \(\mathrm{CP}(\mathrm{X}^{2}\varSigma^{+})\)-\(\mathrm{He}(^{1}S)\) complex has been calculated at the RCCSD(T)-F12/VTZ-F12 level of theory. The analytic fit of the PES was obtained by using global analytical method. The fitted PES was used subsequently in the close-coupling approach for the computation of the state-to-state collisional excitation cross sections of the fine-structure levels of the CP-He complex. Collision energies were taken up to 1500 cm?1 and they yield after thermal averaging, state-to-state rate coefficients up to 200 K. The propensity rules between the lowest fine-structure levels were studied. These rules show, on one hand, a strong propensity in favour of even \(\Delta N\) transitions, and the other hand, that cross sections and collisional rate coefficients for \(\Delta j =\Delta N\) transitions are larger than those for \(\Delta j\neq \Delta N\) transitions. 相似文献
144.
145.
Chemical weathering studies in relation to geomorphological research in southeastern Canada 总被引:1,自引:0,他引:1
Although chemical weathering provides fundamental information relevant to geomorphology, the subject has been overlooked during the 20th century in Canada. This paper provides an overview of the current state of Canadian research on chemical weathering in southeastern Canada and takes into account three spatial and temporal contexts: (1) the formation of bedrock morphology by chemical weathering, (2) occurrences, characteristics and age of saprolites and (3) contemporary chemical denudation rates. Long-term geomorphological evolution of southeastern Canadian landscapes shows that chemical weathering has played an important role. An example is taken from the Laurentide region of the Canadian Shield north of Montréal (Québec). The present topography resulted from the stripping of the former weathering mantle and from the probable subsequent modification of the weathering front, first by the action of hillslope processes and rivers and then by glaciers, before and during Plio-Pleistocene times. The present landscape reflects the timing of the formation of erosion surfaces, and of the stripping of the Paleozoic cover rocks and exposure of the Shield. Since the late seventies, several isolated occurrences of saprolite-soil profiles have been discovered in eastern Canada and prompted a renewal of the study of these materials about the Cenozoic evolution of these regions. One of the problems in this field of research is the dating of saprolites and their inclusion in a chronostratigraphic framework, along with the other Cenozoic surficial deposits and landforms. Because of the multiple factors involved in the development of secondary minerals in saprolites during the course of weathering, it is preferable to distinguish the dating of saprolites from the study of their mineralogical and geochemical evolution. Fortunately, several new techniques are becoming available for the absolute dating of surficial deposits and saprolites, including the use of cosmogenic radionuclides. Saprolites provide a strong potential field of research for our understanding of the geological evolution of eastern Canada during the Cenozoic. Contemporary weathering and erosion rates are fields of research that have gained increasing interest recently, since modeling landscape geochemical response can be applied to various environmental stress situations, such as acidification by rain and forest harvesting. Rock-type may be the main factor explaining the large differences between watersheds. In fact, variability of cation removal in the temperate zone is probably most closely related to flow-paths of water. Investigations, at different scales, from entire watersheds to slopes to individual pedons, highlight the problem. In the Catamaran Brook watershed (New Brunswick), water chemistry is explained by a mix of groundwater and soil solution from the horizons at the base of the floodplain soils. Geochemical mass-balances based on net outputs give little information on the weathering reactions of primary minerals, the weathering products or on the nature of the weathering processes that provide the dissolved load of streams. Mineralogic and petrographic analysis of selected soil pedons are necessary to determine weathering reactions and their role as sources or sinks for bases, silica, aluminum and iron in the various compartments through which water percolates before it reaches the stream. 相似文献
146.
Planning the use of fish for food security in the Pacific 总被引:1,自引:0,他引:1
Johann D. Bell Mecki Kronen Aliti Vunisea Warwick J. Nash Gregory Keeble Andreas Demmke Scott Pontifex Serge Andréfouët 《Marine Policy》2009
Fish is a mainstay of food security for Pacific island countries and territories (PICTs). Recent household income and expenditure surveys, and socio-economic surveys, demonstrate that subsistence fishing still provides the great majority of dietary animal protein in the region. Forecasts of the fish required in 2030 to meet recommended per capita fish consumption, or to maintain current consumption, indicate that even well-managed coastal fisheries will only be able to meet the demand in 6 of 22 PICTs. Governments of many PICTs will need to increase local access to tuna, and develop small-pond aquaculture, to provide food security. Diversifying the supply of fish will also make rural households in the Pacific more resilient to natural disasters, social and political instability, and the uncertainty of climate change. 相似文献
147.
Impact of recent climate change on the hydrology of coastal Mediterranean rivers in Southern France 总被引:2,自引:1,他引:1
The purpose of this paper is to analyse the regional impact of recent climate change on the water resources in southern France. We produced spatial reconstructions of the monthly evolutions of temperature, precipitation and water discharge in 15 watersheds of six coastal river basins and examined the major changes based on trend analysis for the last 40 years. In this part of the Mediterranean, the general warming trend was strongly enhanced by changes in the atmospheric circulation patterns, characterized by a northward extension of the subtropical high pressure domain during spring and summer. During these seasons, monthly warming rates could achieve almost twice the mean annual warming rates. Although annual precipitation did not follow clear trends, water discharge significantly decreased in one third of the watersheds and accounted for an estimated 20% reduction of the water resources in this region. This concerns both the highest and lowest watersheds. In the former, the reduction is likely the result of a temperature induced switch of snowfall to rainfall at high altitudes. In the latter, the reduction of discharge seems to come from lower groundwater levels, which may be related to the temperature increase too, but also have other origins. The recent climatic evolution is consistent with most modelling simulations for the future, indicating that the reduction of the water resources will hold on, probably still enhanced by decreases in precipitation. 相似文献
148.
Serge Janicot 《Comptes Rendus Geoscience》2009,341(8-9):575-590
A review is given of the summer monsoon systems in Africa and India, and of their comparison at different time scales. Features of the circulation are described first, including the main respective meteorological centres of action controlling the annual cycle of the rain bands over these two regions. The main elements of the atmospheric intraseasonal variability are then presented, which controls in particular the onset of these two monsoon systems. Then the sensitivity of these two monsoon systems to oceanic and continental surface conditions in the context of interannual variability is discussed and compared. Consequences in term of predictability are commented. Finally, the Intergovernmental Panel on Climate Change (IPCC4) scenarios of the future climate over these two regions are presented. 相似文献
149.
Louis Arbez Aurelien Royer Danielle Schreve Remi Laffont Serge David Sophie Montuire 《第四纪科学杂志》2021,36(2):224-238
Lemmus and Myopus are two lemming species with distinct habitat requirements but which show very similar dental morphologies. They are thus extremely difficult to distinguish from one another in the fossil record on the basis of their dental remains, leading to poor understanding of the palaeobiogeographical evolution of Myopus as well as inaccurate palaeoenvrionmental reconstructions. Currently, the presence of Myopus in the fossil register from the Pleistocene is still debated and no firm occurrence of this lemming in western Europe has yet been confirmed for the Late Pleistocene. In this paper, we used geometric morphometrics on modern material to establish morphological differences between Lemmus and Myopus teeth (first lower and third upper molars). Morphological data were then used to build a robust linear discriminant model able to confidently classify isolated teeth of these two genera, and finally, linear discriminant models were used on fossil remains of Lemmus/Myopus from two Late Pleistocene archaeological/palaeontological sites (Grotte des Gorges and Gully Cave). This study demonstrates, for the first time, the presence of Myopus schisticolor in west European Late Pleistocene sites between the end of Marine Isotope Stage 3 and the beginning of the Holocene, during climatic events that favoured the development of taiga forest of birch and pine in these regions. 相似文献
150.
Regional climate modelling of the 2006 West African monsoon: sensitivity to convection and planetary boundary layer parameterisation using WRF 总被引:3,自引:3,他引:0
Regional climate model (RCM) is a valuable scientific tool to address the mechanisms of regional atmospheric systems such as the West African monsoon (WAM). This study aims to improve our understanding of the impact of some physical schemes of RCM on the WAM representation. The weather research and forecasting model has been used by performing six simulations of the 2006 summer WAM season. These simulations use all combinations of three convective parameterization schemes (CPSs) and two planetary boundary layer schemes (PBLSs). By comparing the simulations to a large set of observations and analysis products, we have evaluated the ability of these RCM parameterizations to reproduce different aspects of the regional atmospheric circulation of the WAM. This study focuses in particular on the WAM onset and the rainfall variability simulated over this domain. According to the different parameterizations tested, the PBLSs seem to have the strongest effect on temperature, humidity vertical distribution and rainfall amount. On the other hand, dynamics and precipitation variability are strongly influenced by CPSs. In particular, the Mellor?CYamada?CJanjic PBLS attributes more realistic values of humidity and temperature. Combined with the Kain?CFritsch CPS, the WAM onset is well represented. The different schemes combination tested also reveal the role of different regional climate features on WAM dynamics, namely the low level circulation, the land?Catmosphere interactions and the meridional temperature gradient between the Guinean coast and the Sahel. 相似文献