166 research outputs found
Paraglacial evolution of Conway glacier complex foreland, Northwestern Spitsbergen, Svalbard
International audienceThis study aims to provide information concerning paraglacial evolution of landforms and sediments in a proglacial area in the Kongsfjorden area. Several subjects are emphasized:1- chronology of deglaciation2 - morphology of landforms3 - sedimentology of deposits4 - disintegration of the moraine complex by contemporary processe
Study of the dissolved organic matter (DOM) of the Auzon cut-off meander (Allier River, France) by spectral and photoreactivity approaches
International audienceWetlands are recognized for the importance of their hydrological function and biodiversity, and there is now a consensus to protect and restore them as well as to complete the knowledge on their functioning. Here, we studied the dissolved organic matter (DOM) of a wetland composed of the Auzon cutoff meander, the Allier River, the alluvial fluvial flow, and watershed aquifer. Water was sampled at different locations, in spring, summer, and autumn. For each sample, DOM was characterized for its chemical and optical properties and its photooxidant capacity through its ability to generate DOM triplet excited states (3 DOM*) and singlet oxygen upon simulated solar light exposure. UV-visible and fluorescence indices revealed that DOM was mainly microbial-derived whatever the sampling sites with spatial and temporal variations in terms of aromaticity (5.5-22%), specific UV absorbance at 254 nm (0.28-2.82 L m â1 mgC â1), ratio of the absorbance at 254 and 365 nm (4.6-10.8), fluorescence index (1.35-166), and biological index (0.812-2.25). All the samples generated 3 DOM* and singlet oxygen, rates of formation of which showed parallel variations. Using principal component analysis (PCA), we found positive correlations between the sensitizing properties of DOM samples and parameters associated to the abundance of low molecular weight and low absorbing chromophores. Moreover, the parameter variation across the wetland reinforced the hydrological movements observed in a previous study, suggesting that these parameters could be used as water connection tracers
Fluorescence analysis allows to predict the oxidative capacity of humic quinones in dissolved organic matter: implication for pollutant degradation
AbstractDissolved organic matter (DOM) controls the degradation and sequestration of aquatic pollutants and, in turn, water quality. In particular, pollutant degradation is performed by oxidant species that are generated by exposure of DOM to solar light, yet, since DOM is a very complex mixture of poorly known substances, the relationships between potential oxidant precursors in DOM and their oxydative capacity is poorly known. Here, we hypothesized that production of oxidant species could be predicted using fluorescence analysis. We analysed water samples from an alluvial plain by fluorescence spectroscopy; the three-dimensional spectra were then decomposed into seven individual components using a multi-way algorithm. Components include a protein-like fluorophore, e.g. tryptophan-like and tyrosine-like, three humic fluorophores, 2-naphthoxyacetic acid, and a by-product. We compared component levels with the ability of water samples to generate reactive species under solar light. The results show a strong correlation between reactive species production and the intensity of two humic-like fluorophores assigned to reduced quinones. Monitoring these fluorophores should thus allow to predict the ability of DOM degradation of pollutants in surface waters
pKa tuning in quadrupolar-type two-photon ratiometric fluorescent membrane probes
International audienceTwo bolaamphiphilic quadrupoles built from a fluorene core conjugated with azine endgroups were designed and successfully used to stain GUV membranes. Their quadrupolar character induces both a shift of the pKa values close to the physiological pH and large two-photon absorption responses (i.e. over 1000 GM for acidic forms). As such they hold promise as ratiometric two-photon pH probes for monitoring slight variations of pH near cell membranes using two-photon excitation in the NIR regio
Un Paradis perdu. Restaurer ou les effets de l'intervention humaine sur le cours du temps â Ă propos de quelques rĂ©alitĂ©s monumentales (France, Cambodge)
Les interventions sur les monuments anciens en milieu rural gagneront Ă ĂȘtre plus « lĂ©gĂšres » quâen milieu urbain, dĂšs lors que la part du temps est prise en considĂ©ration. En France comme au Cambodge, toute restauration complĂšte appelle dâautres travaux Ă un rythme plus rapprochĂ©, plus difficiles dâexĂ©cution, plus importants en moyens et plus impactants sur les architectures et sculptures. Entre le XIIe et le XIXe siĂšcle, les maçonneries des Ă©glises romanes dâAuvergne ont Ă©tĂ© peu entretenues, mais lâĂ©piderme des matĂ©riaux de construction a globalement bien tenu. Un siĂšcle aprĂšs les restaurations du XIXe siĂšcle, du fait de lâutilisation des ciments durs et de matĂ©riaux exogĂšnes, la dĂ©gradation des parties restaurĂ©es et non restaurĂ©es impose de nouvelles interventions rapprochĂ©es dans le temps, alors que la premiĂšre pĂ©riode nâavait connu aucune grande phase de restauration, lâentretien seul ayant suffi.La dĂ©forestation est quant Ă elle la principale cause de la dĂ©gradation accĂ©lĂ©rĂ©e des maçonneries assemblĂ©es Ă sec des temples khmers, mais on tirera une leçon utile de lâexemple du temple de Ta Prohm Ă Angkor qui conserve son couvert forestier protecteur. DĂšs lors que lâexubĂ©rance de la vĂ©gĂ©tation est contrĂŽlĂ©e, au Cambodge comme en France, un Ă©difice ancien supporte aisĂ©ment la prĂ©sence de mousses, lichens et cyanobactĂ©ries, voire de graminĂ©es, qui enveloppent le site dans un biofilm protecteur. Ă lâinverse, chaque restauration ou nettoyage dĂ©clenche lâinstallation rapide dâorganismes jeunes plus agressifs que les organismes ĂągĂ©s vivant au ralenti et finissant par former une « biopatine » protectrice. Face aux bouleversements industriels, le XIXe siĂšcle a restaurĂ© ses Ă©difices emblĂ©matiques. Notre siĂšcle doit probablement conserver de maniĂšre raisonnĂ©e des rĂ©fĂ©rences monumentales synonymes dâune lente disparition. Pourtant un Ă©difice ayant subi de multiples interventions se corrigeant les unes les autres, produit dâune Ă©conomie de loisirs, ne produira jamais lâĂ©motion dâune ruine discrĂštement entretenue dans laquelle il est possible de se perdre, en dehors de tout itinĂ©raire balisĂ© et de toute proposition pĂ©dagogique. Le « rĂ©ensauvagement » de sites ruraux est donc un enjeu qui dĂ©passe « lâabsolue nĂ©cessité », en rĂ©alitĂ© toute relative des restaurations.Interventions on ancient monuments in rural areas will benefit from being "lighter" than in urban areas, as long as the time issue is taken into account. In France as in Cambodia, any complete restoration calls for other works at a closer pace, more difficult to carry out, more important in terms of resources and more impacting on architectures and sculptures. Between the 12th and the 19th century, the masonry of Romanesque churches in Auvergne was poorly maintained, but the building materials epidermis has generally held up quite well. A century and a half after the 19th century restorations, due to using hard cements and exogenous materials, degradation of the restored and unrestored parts requires new close in time interventions, whereas the first period had not seen any major restoration phase, maintenance alone did suffice.Deforestation is the main cause of the accelerated degradation of dry-assembled masonry of Khmer temples, but a useful lesson will be learned from the example of Ta Prohm temple in Angkor which retains its protective forest cover. As soon as the vegetation exuberance is controlled, in Cambodia as in France, an old building easily supports the presence of mosses, lichens and cyanobacteria, even grasses, which envelop the site in a protective biofilm. Conversely, each restoration or cleaning triggers the rapid installation of young organisms that are more aggressive than older organisms living in slow motion and eventually forming a protective âbiopatinâ. Faced with industrial upheavals, the 19th century restored its iconic monuments. Our century must probably preserve in a reasoned way monumental references reflecting a slow disappearance. However, a building that has undergone multiple interventions correcting each other, in a leisure economy, will never produce the emotion of a discreetly maintained ruin in which on can get lost, apart from any marked route and any educational proposal. Rural sites âgoing back to the wildâ is therefore an issue that goes beyond the restorations âabsolute â actually all relative â necessityâ
Comparaison lasergrammétrie/photogrammetrie pour la mesure de l'érosion de pierres de façade (abbatiale de Manglieu, Puy-de-DÎme)
In close cooperation with two research programs on historical monuments deterioration, short range LIDAR and numerical photogrammetry methods are applied to the quantitative analysis and mapping of stone decay. Used equipment, implementation on the field and precision levels are analysed and compared. Their respective fields of application are finally discussed and estimated.Dans le cadre de deux programmes de recherche portant sur la dégradation des monuments historiques, des méthodes de laser-grammétrie courte portée et de photogrammétrie numérique sont appliquées à la quantification et à la spatialisation de l'érosion de la pierre. Le matériel utilisé, la mise en oeuvre sur le terrain et les niveaux de précision atteints par les différentes méthodes sont analysés et comparés. Leurs champs d'application respectifs sont ensuite évalués et discutés.Vautier Franck, Voldoire Olivier. Comparaison lasergrammétrie/photogrammetrie pour la mesure de l'érosion de pierres de façade (abbatiale de Manglieu, Puy-de-DÎme). In: Collection EDYTEM. Cahiers de géographie, numéro 12, 2011. Images et modÚles 3D en milieux naturels. pp. 199-205
Temporal scales and deglaciation rhytms in a polar glacier margin, baronbreen, Svalbard
International audiencePolar regions are very sensitive to climate variability. Glacial environments, such as Spitsbergen, respond drastically to climate warming by the disintegration of ice masses, release of huge amounts of free water and rapid evolution of terrestrial landforms. Paraglacial studies have shown that sediment yield decreases with time following a relaxation curve. The study examines the effects of scaling on rythms of deglaciation and sediment fluxes in a small catchment. The study site was located on the Kongsfjorden area, northwest Spistbergen, Svalbard, in the front of Baron and Conway glaciers (79°N, 12°20'E). The area consists of a patchwork of glacial and fluvioglacial deposits that are reworked or built by paraglacial processes, and was investigated for field geomorphological mapping. To reconstruct the kinematics of deglaciation since the end of the Little Ice Age, several photographics sources (from 1907 to 2004) have been collected and analysed. Sedimentological analyses were made of samples collected in the field. Grain-size deposits were analysed using wet- and dry- mechanical- sieving techniques to isolate the gravel and sand fractions. Fine fraction was measured using a Coulter LS230 laser granulometer. This study provides several insights into the relationship between temporal scales, climatic variability and geomorphological responses. Glacier response to climate variations is non-linear and not immediate and depends of the catchment size and induced differential geomorphological responses. In a source-to-sink-fluxes and sediment budget perspective, this example illustrates the different stages of the paraglacial sediment cascade. It appears that the paraglacial sequence, known as a morphogenic crisis, could be affected by internal small threshold events, which are able to mobilize large quantities of sediment. It means that, at small scale, the curve profile is more irregular than suggested by large-scale models.Les rĂ©gions polaires sont trĂšs sensibles Ă la variabilitĂ© climatique. Les environnements glaciaires, comme le Spitsberg, rĂ©pondent au rĂ©chauffement climatique par la dĂ©sintĂ©gration de masses de glace, l'Ă©vacuation de grandes quantitĂ©s d'eau sous forme liquide et par des Ă©volutions rapides des modelĂ©s sur les marges glaciaires. Des Ă©tudes paraglaciaires antĂ©rieures ont montrĂ© que le taux de production sĂ©dimentaire diminue avec le temps selon une courbe de relaxation exponentielle nĂ©gative. L'Ă©tude prĂ©sentĂ©e dans cet article examine les effets de changements d'Ă©chelles sur les rythmes de la dĂ©glaciation et sur les flux sĂ©dimentaires dans un petit bassin versant. Le site de l'Ă©tude correspond aux fronts des glaciers Baron et Conway dans la rĂ©gion du Kongsfjorden, au nord-ouest du Spitsberg (Svalbard, 79°N, 12°20'E). Cet espace prĂ©sente un patchwork de dĂ©pĂŽts sĂ©dimentaires glaciaires et fluvio-glaciaires et a Ă©tĂ© analysĂ© sur le terrain pour Ă©tablir une cartographie gĂ©omorphologique. DiffĂ©rentes sources photographiques, de 1907 Ă 2004, ont Ă©tĂ© sĂ©lectionnĂ©es et analysĂ©es afin de reconstituer la cinĂ©matique de la dĂ©glaciation depuis la fin du Petit Ăge glaciaire. Les analyses sĂ©dimentologiques ont Ă©tĂ© rĂ©alisĂ©es Ă partir d'un Ă©chantillonnage rĂ©alisĂ© sur le terrain. La granulomĂ©trie des dĂ©pĂŽts a Ă©tĂ© analysĂ©e par tamisage mĂ©canique pour isoler les fractions sableuses et grossiĂšres. La fraction fine a Ă©tĂ© mesurĂ©e en utilisant un granulomĂštre laser Coulter LS230. Cette Ă©tude apporte des Ă©lĂ©ments de rĂ©ponse dans la relation entre Ă©chelles temporelles, variabilitĂ© climatique et les rĂ©ponses gĂ©omorphologiques. La rĂ©ponse des glaciers aux variations climatiques est non-linĂ©aire, non immĂ©diate et dĂ©pend de la taille du bassin-versant ce qui induit des rĂ©ponses gĂ©omorphologiques diffĂ©rentielles. Dans une perspective de transferts sĂ©dimentaires en cascade, de la source aux dĂ©pĂŽts, et de budgets sĂ©dimentaires, cette Ă©tude montre les diffĂ©rentes Ă©tapes de la dynamique paraglaciaire. Il apparaĂźt que la sĂ©quence paraglaciaire, connue comme une crise morphogĂ©nique, peut ĂȘtre affectĂ©e par de petits Ă©vĂ©nements internes, capables de mobiliser de grandes quantitĂ©s de sĂ©diments. Cela signifie que, sur une Ă©chelle temporelle infĂ©rieure au siĂšcle, le profil de la courbe de relaxation est plus irrĂ©gulier, que celui suggĂ©rĂ© par les modĂšles Ă grande Ă©chelle
Temporal scales and deglaciation rhytms in a polar glacier margin, baronbreen, Svalbard
International audiencePolar regions are very sensitive to climate variability. Glacial environments, such as Spitsbergen, respond drastically to climate warming by the disintegration of ice masses, release of huge amounts of free water and rapid evolution of terrestrial landforms. Paraglacial studies have shown that sediment yield decreases with time following a relaxation curve. The study examines the effects of scaling on rythms of deglaciation and sediment fluxes in a small catchment. The study site was located on the Kongsfjorden area, northwest Spistbergen, Svalbard, in the front of Baron and Conway glaciers (79°N, 12°20'E). The area consists of a patchwork of glacial and fluvioglacial deposits that are reworked or built by paraglacial processes, and was investigated for field geomorphological mapping. To reconstruct the kinematics of deglaciation since the end of the Little Ice Age, several photographics sources (from 1907 to 2004) have been collected and analysed. Sedimentological analyses were made of samples collected in the field. Grain-size deposits were analysed using wet- and dry- mechanical- sieving techniques to isolate the gravel and sand fractions. Fine fraction was measured using a Coulter LS230 laser granulometer. This study provides several insights into the relationship between temporal scales, climatic variability and geomorphological responses. Glacier response to climate variations is non-linear and not immediate and depends of the catchment size and induced differential geomorphological responses. In a source-to-sink-fluxes and sediment budget perspective, this example illustrates the different stages of the paraglacial sediment cascade. It appears that the paraglacial sequence, known as a morphogenic crisis, could be affected by internal small threshold events, which are able to mobilize large quantities of sediment. It means that, at small scale, the curve profile is more irregular than suggested by large-scale models.Les rĂ©gions polaires sont trĂšs sensibles Ă la variabilitĂ© climatique. Les environnements glaciaires, comme le Spitsberg, rĂ©pondent au rĂ©chauffement climatique par la dĂ©sintĂ©gration de masses de glace, l'Ă©vacuation de grandes quantitĂ©s d'eau sous forme liquide et par des Ă©volutions rapides des modelĂ©s sur les marges glaciaires. Des Ă©tudes paraglaciaires antĂ©rieures ont montrĂ© que le taux de production sĂ©dimentaire diminue avec le temps selon une courbe de relaxation exponentielle nĂ©gative. L'Ă©tude prĂ©sentĂ©e dans cet article examine les effets de changements d'Ă©chelles sur les rythmes de la dĂ©glaciation et sur les flux sĂ©dimentaires dans un petit bassin versant. Le site de l'Ă©tude correspond aux fronts des glaciers Baron et Conway dans la rĂ©gion du Kongsfjorden, au nord-ouest du Spitsberg (Svalbard, 79°N, 12°20'E). Cet espace prĂ©sente un patchwork de dĂ©pĂŽts sĂ©dimentaires glaciaires et fluvio-glaciaires et a Ă©tĂ© analysĂ© sur le terrain pour Ă©tablir une cartographie gĂ©omorphologique. DiffĂ©rentes sources photographiques, de 1907 Ă 2004, ont Ă©tĂ© sĂ©lectionnĂ©es et analysĂ©es afin de reconstituer la cinĂ©matique de la dĂ©glaciation depuis la fin du Petit Ăge glaciaire. Les analyses sĂ©dimentologiques ont Ă©tĂ© rĂ©alisĂ©es Ă partir d'un Ă©chantillonnage rĂ©alisĂ© sur le terrain. La granulomĂ©trie des dĂ©pĂŽts a Ă©tĂ© analysĂ©e par tamisage mĂ©canique pour isoler les fractions sableuses et grossiĂšres. La fraction fine a Ă©tĂ© mesurĂ©e en utilisant un granulomĂštre laser Coulter LS230. Cette Ă©tude apporte des Ă©lĂ©ments de rĂ©ponse dans la relation entre Ă©chelles temporelles, variabilitĂ© climatique et les rĂ©ponses gĂ©omorphologiques. La rĂ©ponse des glaciers aux variations climatiques est non-linĂ©aire, non immĂ©diate et dĂ©pend de la taille du bassin-versant ce qui induit des rĂ©ponses gĂ©omorphologiques diffĂ©rentielles. Dans une perspective de transferts sĂ©dimentaires en cascade, de la source aux dĂ©pĂŽts, et de budgets sĂ©dimentaires, cette Ă©tude montre les diffĂ©rentes Ă©tapes de la dynamique paraglaciaire. Il apparaĂźt que la sĂ©quence paraglaciaire, connue comme une crise morphogĂ©nique, peut ĂȘtre affectĂ©e par de petits Ă©vĂ©nements internes, capables de mobiliser de grandes quantitĂ©s de sĂ©diments. Cela signifie que, sur une Ă©chelle temporelle infĂ©rieure au siĂšcle, le profil de la courbe de relaxation est plus irrĂ©gulier, que celui suggĂ©rĂ© par les modĂšles Ă grande Ă©chelle
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