Methodical approach to distribution of epilithic and drifting algae communities in a French subalpine river: Inferences on water quality assessment   总被引：2，自引：0，他引：2  

Thierry Rolland  Stéphanie Fayolle  Arlette Cazaubon  Stéphane Pagnetti 《Aquatic Sciences - Research Across Boundaries》1997,59(1):57-73

In a sub-alpine river, the Asse, with an unpredictable discharge regime, chlorophyll, density and taxonomic diversity of both drifting and periphytic communities were studied from a methodical approach. The investigations based on stamping two close cross-sections to know their spatial distributions in a heterogeneous bed substrate showed a heterogeneous pattern of colonization mainly influenced by hydrological variables as the current velocity, the size of the substrata (gravel-pebble-boulder). For the drifting algae, mainly composed with benthic species temporarily unhooked to the substrata, the heterogeneity of the distribution was reduced in fast flow which induced a mixing of the whole mass of water. For the periphyton, some results indicated that the greatest diversity and the highest chlorophyll concentration were found on pebble substratum where the current velocity was moderate. These results have also shown that the classical methods used to day for investigations were inadequate for most Mediterranean rivers. It was really difficult to estimate the water quality from classical index created for use in regular large plain rivers.  相似文献   

Thallium diagenesis in lacustrine sediments   总被引：1，自引：0，他引：1  

Lucie Laforte  André Tessier  Charles Gobeil 《Geochimica et cosmochimica acta》2005,69(22):5295-5306

Dated sediment cores and porewaters from two Canadian Shield lakes, located 40 km from Québec City (L. Tantaré) and 25 km downwind from an important smelter in northwestern Québec (L. Vose), were analyzed for thallium and other geochemical variables. Atmospheric deposition is the only source of anthropogenic Tl to these lakes. The porewater Tl concentration profiles in L. Tantaré display a peak below the sediment-water interface that suggests post-depositional Tl remobilization and transport to the overlying water and deeper sediments; such a dissolved Tl peak occurs just above the sediment-water interface in L. Vose. Modeling the porewater Tl profiles with a diagenetic reaction-transport equation reveals a zone of dissolved Tl production lying above a zone of Tl consumption in L. Tantaré sediments. In contrast, in L. Vose, Tl diffuses across the sediment-water interface from the anoxic hypolimnion and is fixed to the surficial sediments. The localization of the consumption zones, the shape of the dissolved Tl, sulfide and iron profiles, as well as calculations of saturation states are all consistent with the removal of Tl from porewater by co-precipitation with and/or adsorption to Fe sulfides. The concentrations of Tl removed from or added to sediments after their deposition (i.e., diagenetic Tl) amount to up to 36% of measured sediment Tl concentrations. Comparison of the reconstructed historical Tl records with those of polycyclic aromatic hydrocarbons (PAHs) and of Pb originating from coal burning or from smelting activities indicate that coal combustion is the major source of atmospheric Tl to L. Tantaré and that an additional important Tl source to L. Vose is the nearby smelter.  相似文献   

Paleoseismology: evidence of earth activity     

Lucie Nováková 《International Journal of Earth Sciences》2016,105(5):1467-1469

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Impoverishment of recent floodplain forest mollusc fauna in the lower Ohře River (Czech Republic) as a result of prehistoric human impact     

Lucie Juřičková  Jitka Horáčková  Vojen Ložek  Michal Horsák 《Boreas: An International Journal of Quaternary Research》2013,42(4):932-946

Analyses of fossil mollusc successions have rarely been used to study the development of floodplain forests during the Holocene. The Oh?e River, located in a prehistorically settled chernozem area in the Czech Republic, is partly situated in Cretaceous marlstones, yielding sediments suitable for fossilization directly in floodplain deposits. We analysed five fossil mollusc successions situated in the lower stretch of the Oh?e River and compared the results with recent mollusc assemblages studied along the entire 256 km of the river. Fossil samples were composed mostly of open‐country species throughout the Holocene or the whole preserved succession. Only some samples also contained woodland assemblages, but these were always greatly impoverished, with a very low frequency of strictly woodland species. Although the natural‐looking appearance of the present‐day floodplain forests of the lower river stretch has resulted in its being declared a nature reserve, modern floodplain forest mollusc assemblages there are also impoverished. This reduction in the distribution of strictly woodland species compared with modern assemblages in the upper stretch of the river seems to be the result of an ancient human settlement and continuous disturbances of the floodplain forest development since the Neolithic. Thus, fully developed floodplain forest assemblages occur recently only in the upper non‐impacted stretch of the river. Based on the studied fossil successions we can conclude that the lower Oh?e River floodplain was probably a mosaic of open and disturbed forest habitats throughout the Holocene. This area is part of a central European landscape island, where forests probably never fully developed and open patches from the early Holocene continually developed into an agricultural landscape.  相似文献   

Temperature and precipitation trends in Canada during the 20th century     

Xuebin Zhang  Lucie A. Vincent  W.D. Hogg  Ain Niitsoo 《大气与海洋》2013,51(3):395-429

Abstract

Trends in Canadian temperature and precipitation during the 20th century are analyzed using recently updated and adjusted station data. Six elements, maximum, minimum and mean temperatures along with diurnal temperature range (DTR), precipitation totals and ratio of snowfall to total precipitation are investigated. Anomalies from the 1961–1990 reference period were first obtained at individual stations, and were then used to generate gridded datasets for subsequent trend analyses. Trends were computed for 1900–1998 for southern Canada (south of 60°N), and separately for 1950–1998 for the entire country, due to insufficient data in the high arctic prior to the 1950s.

From 1900–1998, the annual mean temperature has increased between 0.5 and 1.5°C in the south. The warming is greater in minimum temperature than in maximum temperature in the first half of the century, resulting in a decrease of DTR. The greatest warming occurred in the west, with statistically significant increases mostly seen during spring and summer periods. Annual precipitation has also increased from 5% to 35% in southern Canada over the same period. In general, the ratio of snowfall to total precipitation has been increasing due mostly to the increase in winter precipitation which generally falls as snow and an increase of ratio in autumn. Negative trends were identified in some southern regions during spring. From 1950–1998, the pattern of temperature change is distinct: warming in the south and west and cooling in the northeast, with similar magnitudes in both maximum and minimum temperatures. This pattern is mostly evident in winter and spring. Across Canada, precipitation has increased by 5% to 35%, with significant negative trends found in southern regions during winter. Overall, the ratio of snowfall to total precipitation has increased, with significant negative trends occurring mostly in southern Canada during spring.

Indices of abnormal climate conditions are also examined. These indices were defined as areas of Canada for 1950–1998, or southern Canada for 1900–1998, with temperature or precipitation anomalies above the 66th or below the 34th percentiles in their relevant time series. These confirmed the above findings and showed that climate has been becoming gradually wetter and warmer in southern Canada throughout the entire century, and in all of Canada during the latter half of the century.  相似文献   

Reaching out through the heliosphere     

Lucie Green 《Astronomy& Geophysics》2007,48(4):4.24-4.24

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Study of the air-sea interactions at the mesoscale: the SEMAPHORE experiment     

L. Eymard  S. Planton  P. Durand  C. Le Visage  P. Y. Le Traon  L. Prieur  A. Weill  D. Hauser  J. Rolland  J. Pelon  F. Baudin  B. Bénech  J. L. Brenguier  G. Caniaux  P. De Mey  E. Dombrowski  A. Druilhet  H. Dupuis  B. Ferret  C. Flamant  P. Flamant  F. Hernandez  D. Jourdan  K. Katsaros  D. Lambert  J. M. Lefèvre  P. Le Borgne  B. Le Squere  A. Marsoin  H. Roquet  J. Tournadre  V. Trouillet  A. Tychensky  B. Zakardjian 《Annales Geophysicae》1996,14(9):986-1015

The SEMAPHORE (Structure des Echanges Mer-Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale) experiment has been conducted from June to November 1993 in the Northeast Atlantic between the Azores and Madeira. It was centered on the study of the mesoscale ocean circulation and air-sea interactions. The experimental investigation was achieved at the mesoscale using moorings, floats, and ship hydrological survey, and at a smaller scale by one dedicated ship, two instrumented aircraft, and surface drifting buoys, for one and a half month in October-November (IOP: intense observing period). Observations from meteorological operational satellites as well as spaceborne microwave sensors were used in complement. The main studies undertaken concern the mesoscale ocean, the upper ocean, the atmospheric boundary layer, and the sea surface, and first results are presented for the various topics. From data analysis and model simulations, the main characteristics of the ocean circulation were deduced, showing the close relationship between the Azores front meander and the occurrence of Mediterranean water lenses (meddies), and the shift between the Azores current frontal signature at the surface and within the thermocline. Using drifting buoys and ship data in the upper ocean, the gap between the scales of the atmospheric forcing and the oceanic variability was made evident. A 2 °C decrease and a 40-m deepening of the mixed layer were measured within the IOP, associated with a heating loss of about 100 W m⁻². This evolution was shown to be strongly connected to the occurrence of storms at the beginning and the end of October. Above the surface, turbulent measurements from ship and aircraft were analyzed across the surface thermal front, showing a 30% difference in heat fluxes between both sides during a 4-day period, and the respective contributions of the wind and the surface temperature were evaluated. The classical momentum flux bulk parameterization was found to fail in low wind and unstable conditions. Finally, the sea surface was investigated using airborne and satellite radars and wave buoys. A wave model, operationally used, was found to get better results compared with radar and wave-buoy measurements, when initialized using an improved wind field, obtained by assimilating satellite and buoy wind data in a meteorological model. A detailed analysis of a 2-day period showed that the swell component, propagating from a far source area, is underestimated in the wave model. A data base has been created, containing all experimental measurements. It will allow us to pursue the interpretation of observations and to test model simulations in the ocean, at the surface and in the atmospheric boundary layer, and to investigate the ocean-atmosphere coupling at the local and mesoscales.  相似文献   

On the Integrability of Limited-Area Numerical Weather Prediction Model ALADIN over Extended Time Periods     

Huth  Radan  Mládek  Richard  Metelka  Ladislav  Sedlák  Pavel  Huthová  Zuzana  Kliegrová  Stanislava  Kyselý  Jan  Pokorná  Lucie  Halenka  Tomáš  Janoušek  Martin 《Studia Geophysica et Geodaetica》2003,47(4):863-873

This note summarizes results of the first integration of regional numerical weather prediction model ALADIN in a climate mode. The ALADIN model, developed in an international cooperation led by Météo France, is operationally used for weather prediction. The grid step of the model is 12 km; the integration domain covers a major part of Europe. A one-month-long run has been performed with this model on observed boundary conditions (represented by assimilations by the global model ARPEGE). It is demonstrated that no excessive error is generated and accumulated in the model during the integration; hence the model is integrable for extended time periods and may serve a basis for a development towards a regional climate model.  相似文献   

A GCM Simulation of Heat Waves, Dry Spells, and Their Relationships to Circulation     

Radan Huth  Jan Kyselý  Lucie Pokorná 《Climatic change》2000,46(1-2):29-60

Heat waves and dry spells are analyzed (i) at eightstations in south Moravia (Czech Republic), (ii) inthe control ECHAM3 GCM run at the gridpoint closest tothe study area, and (iii) in the ECHAM3 GCM run fordoubled CO₂ concentrations (scenario A) at thesame gridpoint (heat waves only). The GCM outputs arevalidated both against individual station data andareally representative values. In the control run, theheat waves are too long, appear later in the year,peak at higher temperatures and their numbers areunder- (over-) estimated in June and July (in August).The simulated dry spells are too long, and the annualcycle of their occurrence is distorted.Mid-tropospheric circulation, and heat waves and dryspells are linked much less tightly in the controlclimate than in the observed. Since mid-troposphericcirculation is simulated fairly successfully, wesuggest the hypothesis that either the air-masstransformation and local processes are too strong inthe model or the simulated advection is too weak. Inthe scenario A climate, the heat waves become a commonphenomenon: warming of 4.5 °C in summer(difference between scenario A and control climates)induces a five-fold increase in the frequency oftropical days and an immense enhancement of extremityof heat waves. The results of the study underline theneed for (i) a proper validation of the GCM outputbefore a climate impact study is conducted and (ii)translation of large-scale information from GCMs intolocal scales using downscaling and stochasticmodelling techniques in order to reduce GCMs' biases.  相似文献   

⁴⁰Ar/ ³⁹Ar dating of Penninic Front tectonic displacement (W Alps) during the Lower Oligocene (31–34 Ma)     

T. Simon-Labric  Y. Rolland  T. Dumont  T. Heymes  C. Authemayou  M. Corsini  M. Fornari 《地学学报》2009,21(2):127-136

Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the ⁴⁰Ar/³⁹Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite–phengite thermobarometry yields 10–15 km and T ∼280 °C, while ⁴⁰Ar/³⁹Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde ⁴⁰Ar/³⁹Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.  相似文献