Organic complexation of rare earth elements in natural waters: Evaluating model calculations from ultrafiltration data     

Olivier Pourret  Mélanie Davranche  Gérard Gruau  Aline Dia 《Geochimica et cosmochimica acta》2007,71(11):2718-2735

The Stockholm Humic Model (SHM) and Humic Ion-Binding Models V and VI were compared for their ability to predict the role of dissolved organic matter (DOM) in the speciation of rare earth elements (REE) in natural waters. Unlike Models V and VI, SHM is part of a speciation code that also allows us to consider dissolution/precipitation, sorption/desorption and oxidation/reduction reactions. In this context, it is particularly interesting to test the performance of SHM. The REE specific equilibrium constants required by the speciation models were estimated using linear free-energy relationships (LFER) between the first hydrolysis constants and the stability constants for REE complexation with lactic and acetic acid. Three datasets were used for the purpose of comparison: (i) World Average River Water (Dissolved Organic Carbon (DOC) = 5 mg L⁻¹), previously investigated using Model V, was reinvestigated using SHM and Model VI; (ii) two natural organic-rich waters (DOC = 18-24 mg L⁻¹), whose REE speciation has already been determined with both Model V and ultrafiltration studies, were also reinvestigated using SHM and Model VI; finally, (iii) new ultrafiltration experiments were carried out on samples of circumneutral-pH (pH 6.2-7.1), organic-rich (DOC = 7-20 mg L⁻¹) groundwaters from the Kervidy-Naizin and Petit-Hermitage catchments, western France. The results were then compared with speciation predictions provided by Model VI and SHM, successively. When applied to World Average River Water, both Model VI and SHM yield comparable results, confirming the earlier finding that a large fraction of the dissolved REE in rivers occurs as organic complexes This implies that the two models are equally valid for calculating REE speciation in low-DOC waters at circumneutral-pH. The two models also successfully reproduced ultrafiltration results obtained for DOC-rich acidic groundwaters and river waters. By contrast, the two models yielded different results when compared to newly obtained ultrafiltration results for DOC-rich (DOC > 7 mg L⁻¹) groundwaters at circumneutral-pH, with Model VI predictions being closer to the ultrafiltration data than SHM. Sensitivity analysis indicates that the “active DOM parameter” (i.e., the proportion of DOC that can effectively complex with REE) is a key parameter for both Model VI and SHM. However, a survey of ultrafiltration results allows the “active DOM parameter” to be precisely determined for the newly ultrafiltered waters studied here. Thus, the observed discrepancy between SHM predictions and ultrafiltration results cannot be explained by the use of inappropriate “active DOM parameter” values in this model. Save this unexplained discrepancy, the results presented in this study demonstrate that both Model VI and SHM can provide reliable estimates of REE speciation in organic-rich waters. However, it is essential to know the proportion of DOM that can actively complex REE before running these two speciation models.  相似文献   

Solar and anthropogenic imprints on Lake Masoko (southern Tanzania) during the last 500 years   总被引：1，自引：0，他引：1  

Yannick Garcin  David Williamson  Laurent Bergonzini  Olivier Radakovitch  Annie Vincens  Guillaume Buchet  Joël Guiot  Simon Brewer  Pierre-Etienne Mathé  Amos Majule 《Journal of Paleolimnology》2007,37(4):475-490

The Masoko crater-lake in southern Tanzania provides a continuous record of environmental changes covering the last 500 years. Multi-proxy studies were performed on a 52 cm sediment core retrieved from the deepest part of the lake. Magnetic, organic carbon, geochemical proxies and pollen assemblages indicate a dry climate during the ‘Little Ice Age’ (AD 1550–1850), confirming that the LIA in eastern Africa resulted in marked and synchronous hydrological changes. However, the direction of response varies between different African lakes (low versus high lake-levels), indicating strong regional contrasts that prevent the clear identification of climate trends over eastern Africa at this time. Inferred changes in Masoko lake-levels closely resemble the record of solar activity cycles, indicating a possible control of solar activity on the climate in this area. This observation supports previous results from East African lakes, and extends this relationship southward. Finally, anthropogenic impact is observed in the Masoko sediments during the last 60 years, suggesting that human disturbance significantly affected this remote basin during colonial and post-colonial times.  相似文献   

The coupling of optimal economic growth and climate dynamics   总被引：1，自引：0，他引：1  

Olivier Bahn  Laurent Drouet  Neil R. Edwards  Alain Haurie  Reto Knutti  Socrates Kypreos  Thomas F. Stocker  Jean-Philippe Vial 《Climatic change》2006,79(1-2):103-119

In this paper, we study optimal economic growth programs coupled with climate change dynamics. The study is based on models derived from MERGE, a well established integrated assessment model (IAM). We discuss first the introduction in MERGE of a set of “tolerable window” constraints which limit both the temperature change and the rate of temperature change. These constraints, obtained from ensemble simulations performed with the Bern 2.5-D climate model, allow us to identity a domain intended to preserve the Atlantic thermohaline circulation. Next, we report on experiments where a two-way coupling is realized between the economic module of MERGE and an intermediate complexity “3-D-” climate model (C-GOLDSTEIN) which computes the changes in climate and mean temperature. The coupling is achieved through the implementation of an advanced “oracle based optimization technique” which permits the integration of information coming from the climate model during the search for the optimal economic growth path. Both cost-effectiveness and cost-benefit analysis modes are explored with this combined “meta-model” which we refer to as GOLDMERGE. Some perspectives on future implementations of these approaches in the context of “collaborative” or “community” integrated assessment modules are derived from the comparison of the different approaches.  相似文献   

Influence of observed and RCM-simulated precipitation on the water discharge over the Sirba basin, Burkina Faso/Niger     

Christophe Messager  Hubert Gallée  Olivier Brasseur  Bernard Cappelaere  Christophe Peugeot  Luc Séguis  Michel Vauclin  Romain Ramel  Gilles Grasseau  Laurent Léger  Denis Girou 《Climate Dynamics》2006,27(2-3):199-214

The forcing of a hydrologic model (ABC) by both observed and simulated precipitation from a regional climate model (MAR) has been performed over the Sirba watershed (39,000 km²) located in the Sahelian region. Two aspects have been more specifically examined: the spatial and temporal representations of precipitation. The comparison between simulated and observed discharges—using observed rainfall datasets as forcing of the hydrologic model—has shown that the representation of daily precipitation (which is mainly convective in the Sahelian region) was not sufficiently accurate to correctly simulate the hydrologic response of the watershed. Since this response drives the soil water budget and consequently the amount of evaporation in forthcoming coupling experiments, it is thus necessary to develop more realistic infra-daily precipitation associated with convective events. A new temporal disaggregation scheme has been then developed. Considering observed as well as simulated precipitation fields, this method has significantly improved the simulated discharge at the catchment outlet. The major role played by the temporal component compared to spatial component of the precipitation has been then underlined. In addition, the present study shows the unsuitability of the simulated precipitation from the RCM to directly force a hydrologic model at infra daily timescale even if the cumulative amount and the main features of the precipitation seasonal cycle are well simulated.  相似文献   

Soil surface characteristics influence on infiltration in black marls: application to the Super‐Sauze earthflow (southern Alps,France)     

Jean‐Philippe Malet  Anne‐Veronique Auzet  Olivier Maquaire  Bruno Ambroise  Luc Descroix  Michel Esteves  Jean‐Pierre Vandervaere  Emmanuel Truchet 《地球表面变化过程与地形》2003,28(5):547-564

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Mapping upper mantle anisotropy beneath SE France by SKS splitting indicates Neogene asthenospheric flow induced by Apenninic slab roll-back and deflected by the deep Alpine roots     

Guilhem Barruol  Anne Deschamps  Olivier Coutant   《Tectonophysics》2004,394(1-2):125-138

The presence of two regional seismic networks in southeastern France provides us high-quality data to investigate upper mantle flow by measuring the splitting of teleseismic shear waves induced by seismic anisotropy. The 10 three-component and broadband stations installed in Corsica, Provence, and western Alps efficiently complete the geographic coverage of anisotropy measurements performed in southern France using temporary experiments deployed on geodynamic targets such as the Pyrenees and the Massif Central. Teleseismic shear waves (mainly SKS and SKKS) are used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 1.0 and 1.5 s have been observed at most sites, but some larger delay times, above 2.0 s, have been observed at some stations, such as in northern Alps or Corsica, suggesting the presence of high strain zones in the upper mantle. The azimuths of the fast split shear waves define a simple and smooth pattern, trending homogeneously WNW–ESE in the Nice area and progressively rotating to NW–SE and to NS for stations located further North in the Alps. This pattern is in continuity with the measurements performed in the southern Massif Central and could be related to a large asthenospheric flow induced by the rotation of the Corsica–Sardinia lithospheric block and the retreat of the Apenninic slab. We show that seismic anisotropy nicely maps the route of the slab from the initial rifting phase along the Gulf of Lion (30–22 Ma) to the drifting of the Corsica–Sardinia lithospheric block accompanied by the creation of new oceanic lithosphere in the Liguro–Provençal basin (22–17 Ma). In the external and internal Alps, the pattern of the azimuth of the fast split waves follows the bend of the alpine arc. We propose that the mantle flow beneath this area could be influenced or perhaps controlled by the Alpine deep penetrative structures and that the Alpine lithospheric roots may have deflected part of the horizontal asthenospheric flow around its southernmost tip.  相似文献   

Fog harvesting: An alternative source of water supply on the West Coast of South Africa   总被引：1，自引：0，他引：1  

Jana Olivier 《GeoJournal》2004,61(2):203-214

Experiments conducted during the 1990s investigated the feasibility of using fog water to supplement existing water supplies in the arid west coast region of South Africa. Based on these results, a project was initiated aimed at implementing an operational fog water collection system to provide potable water to a small, water-poor rural community. A 70 m² fog water collector was subsequently erected on the crest of the hill located next to the mission station called Lepelfontein. The volume of water collected was measured by means of a water flow meter and a tipping bucket. An automatic weather station recorded rainfall, wind speed and direction. The data record spans the period September 1999–August 2001. This paper gives a brief overview of the methods used to select the experimental site and describes the design of the fog water collection system. This is followed by a detailed account of the water yields, the contribution of fog and rainfall to the total yield, the characteristics of wet events, the factors associated with water collection and water quality. On average, yields of around 4.6 l of water were collected per square metre of collecting surface per day with maximum daily yields approaching 4000 l. The quality of the water was excellent. It thus appears that fog water collection may have considerable potential as an alternative water source at many other locations on the west coast of South Africa. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The deficient T waves of tsunami earthquakes   总被引：4，自引：0，他引：4  

Emile A. Okal  Pierre-Jean Alasset  Olivier Hyvernaud  François Schindelé 《Geophysical Journal International》2003,152(2):416-432

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The role of physical-biological coupling in the benthic boundary layer under megatidal conditions: The case of the dominant species of theAbra alba community in the Eastern Baie de Seine (English Channel)     

Frédéric Olivier  Christian Retière 《Estuaries and Coasts》1998,21(4):571-584

Recent evidence has shown that postlarvae and juveniles of the most dominant species of theAbra alba community of the eastern Baie de Seine are able to re-enter the water column after larval settlement and undergo active and/or passive redistribution. However, few subtidal studies have been conducted to investigate and quantify the processes controlling the abundance of drifting postlarvae and juveniles. The purpose of this study was to verify the reproducibility or the variability of this phenomenon and to assess coupling between the intensity of drifting and that of bed shear stress, which is dependent on tidal currents, wave characteristics, and sediment features. This study was conducted in June and July 1995 at two sites in the bay, one located at the center of the muddy fine-sediment community and the other at its external border with the fine clean sands of theOphelia borealis community. At each site, suprabenthic sledge samples were taken during specific tidal conditions (low tide, slack water, and flood and ebb peaks) during a neap and a spring tide. Physical data (current velocity, turbidity, and suspended matter content) and meiobenthic samples were taken at the same time. Under megatidal conditions, drifting was a quantitatively important dispersal mechanism for at least 15 of the fine-sediment dominant species belonging to various groups such as polychaetes, molluscs (gastropods and bivalves), and echinoderms. The fluctuation in abundance of drifters was related to tidal range, tidal period, location of the site, and the recruitment dynamics. However, species differed strongly in theri response to hydrodynamical parameters. Three types of drifting species were observed: species that were only present in the water column (‘undet. cardiids’ and Mytilidae); species that were both drifting and present at the seaded (Abra alba, Phaxas pellucidus, Eteone picta, Mysella bidentata, Ophiura texturata, Owenia fusiformis, Pholoe minuta, Phyllodoce lineata, Pectinaria koreni, andSpisula subtruncata); species that were present at the seabed but did not drift during the sampling period (Acrocnida brachiata, Eteone longa, Eumida sanguinea, Glycinde normanni, Magelona mirabilis, Nemertean sp1,Nephtys sp.,Spiophanes bombyx, andTubulanus polymorphus). Each drifting pattern is related to eco-ethological species characteristics and may have very different consequences on population dynamics.  相似文献   

Determination of cirrus radiative parameters from combination between active and passive remote sensing measurements during FRENCH/DIRAC 2001     

Grard Brogniez  Frdric Parol  Laurianne Bcu  Jacques Pelon  Olivier Jourdan  Jean-Franois Gayet  Frdrique Auriol  Christian Verwaerde  Jean-Yves Balois  Bahaiddin Damiri 《Atmospheric Research》2004,72(1-4):425

In the context of the next AQUA Train satellite experiment, airborne measurements were carried out to simulate satellite measurements. They were conducted between September 25 and October 12, 2001, off the coast of southern France over the Atlantic Ocean and over the Mediterranean Sea, respectively. During the intensive Field Radiation Experiment on Natural Cirrus and High-level clouds (FRENCH/DIRAC 2001), natural ice clouds were sampled from in situ and remote sensing measurements. On October 5 and 7, 2001, cirrus cloud decks were described by a complete data set acquired by: (i) in situ microphysical instruments onboard the TBM-700 aircraft: PMS probe, and Polar Nephelometer (ii) and downward-looking radiative instruments onboard the Mystère 20 aircraft: an infrared radiometer, a lidar, a visible imager with polarisation capabilities, and a middle infrared radiometer. Moreover, classical thermodynamical measurements were carried out onboard the Mystère 20. Mean microphysical characteristics of cirrus deck are derived from interpretation of remote sensing measurements. These properties are compared with those derived from in situ microphysical measurements in order to evaluate the radiative impact of natural cirrus clouds.  相似文献