Sedimentary processes in the Thau Lagoon (France): From seasonal to century time scales

As a part of the MICROBENT programme, an investigation of the sedimentation framework was carried out at the water-sediment interface in the Thau Lagoon (French Mediterranean coast). Two main sites, C4 in the middle of the lagoon and C5 near oyster farms, were visited six times between December 2001 and May 2003. Interface sediments were studied using classical sedimentology parameters (radiography RX, grain size distribution) and analysis of selected radionuclides (234Th, 7Be, 210Pb, 226Ra). On a century time scale, excess 210Pb (210Pbxs) presents classical profiles with an upper mixed layer, followed by an exponential decrease of activities to undetectable levels below 20 – 30 cm. At the central site, C4, cores seem to register episodic changes in mean grain size, presenting recurrently peaks. The upper 10 cm of 210Pbxs profiles at site C5 exhibit a mixed layer associated with coarser sediments: this could be related to biological activity. Sedimentation rates derived from 210Pbxs varied from 0.15 cm y−1 at the edge of the basin, to 0.25 cm y−1 at the central site. On a seasonal time scale, 234Th and 7Be both show significant variations in activities and in penetration within the sediment. Bioturbation rates derived from both radionuclides agree well and range between 1–10 cm2 y−1 at site C4 and 1–31 cm2 y−1 at site C5. 234Th and 7Be fluxes at the water-sediment interface show too seasonal variations, more pronounced for site C5. This latter site presents especially a higher variability that is well marked with season, probably in relation with its position near oyster farms

Interactions between trace elements and dissolved organic matter in the stagnant anoxic deep layer of a meromictic lake

About 80% and more than 90% of the dissolved organic carbon (DOC) in the bottom water of Lake Pavin were isolated, respectively, on Amberlite XAD and Spherodex DEAE resins. Trace element concentrations in the fractions isolated were analyzed by using ICP-MS. Uranium, molybdenum, and antimony were found to be about 40% associated with fulvic and hydrophilic acids adsorbed on XAD resins at pH 2, the metal-organic association being not dissociated. Much higher percentages of the same elements, plus vanadium, were adsorbed on the DEAE resin at the pH of natural water, possibly because of the better preservation of acid labile organic complexes or of the supplementary adsorption of inorganic compounds. Ultrafiltration and dialysis made it possible to exclude colloidal fractions together with much U (78%), Mo (80%), V (55%), and DOC (65%). These elements and many others (including barium) were previously found to be quite reactive at the bottom of the lake, (apparently being scavenged by settling particles, which are mostly diatoms, then dissolved at the sediment-water interface). Conversely, trace elements with a conservative behavior in the bottom layer (such as lithium and cesium) were not found associated with dissolved organic mater (DOM). Barium was not strongly associated with the extractable DOM, which may argue for a direct interaction with inorganic particles or the existence of very labile complexes. Our work suggests the existence of relatively stable (nonacid labile) U and Mo-DOM colloidal associations in the anoxic bottom waters of the lake and their importance in the scavenging of those metals

MTL and Umlaut NG - Engine and Framework for Model Transformation

Model Tranformation Language (MTL) is an open-source object- and view-oriented imperative language dedicated to model transformations, developed in the context of the OMG Query/View/Transformation (QVT) proposal. MTL is the stepping stone towards defining a transformation framework that we call Umlaut NG. It enables a variety of advanced model transformations, such as application of design patterns, weaving aspects at design level, synthesis test cases from UML models and derivation of products in product lines

Ingénierie Dirigée par les Modèles : des concepts à la pratique...

National audienceL'Ingénierie Dirigée par les Modèles (IDM), ou Model Driven Engineering (MDE) en anglais, s'inscrit dans l'évolution des techniques pour le développement de systèmes informatiques afin d'en maîtriser leurs complexités en se concentrant sur une préoccupation plus abstraite que la programmation classique. En s'appuyant sur des approches génératives, il s'agit d'engendrer tout ou partie d'une application à partir de modèles. Un modèle est une abstraction, une simplification d'un système qui est nécessaire et suffisante pour comprendre un aspect particulier du système modélisé et répondre aux questions que soulève cet aspect du système. Un système peut être décrit par différents modèles liés les uns aux autres, et exprimé chacun à l'aide d'un langage de modélisation dédié (Domain Specific Modeling Languages - DSML). Le principe est d'utiliser autant de langages de modélisation différents que les aspects chronologiques ou technologiques du développement du système le nécessitent. L'activité consistant à définir ces DSML (la syntaxe et la sémantique), appelée métamodélisation, est donc une problématique clé de l'IDM. En outre, les autres problématiques clés de l'IDM consistent à rendre les modèles construits opérationnels (pour la simulation, la génération de code, de documentation ou de test, la validation, la vérification, l'exécution, etc.) à l'aide de composition et de transformation de modèle. A la fois un cours et un tutoriel, cet ouvrage offre une approche didactique et pragmatique d'apprentissage de l'IDM. Nous présentons dans la première partie les principes clés de cette nouvelle ingénierie. Nous introduisons une description précise de l'état des connaissances de manière à aborder les concepts avancés de l'IDM, ainsi que les motivations et l'étendue du bouleversement attendu dans l'ingénierie du logiciel. La deuxième partie aborde ensuite les différentes étapes d'un développement dirigé par les modèles en les illustrant au travers d'un exemple concret. Chaque étape est décrite de manière à présenter l'état de la pratique et introduire certains des outils actuellement disponible

Biogeochemical modelling of anaerobic vs. aerobic methane oxidation in a meromictic crater lake (Lake Pavin, France)

International audienceMethane is a powerful greenhouse gas and its concentration in the atmosphere has increased over the past decades. Methane produced by methanogenic Archae can be consumed through aerobic and anaerobic oxidation pathways. In anoxic conditions found in freshwater environments such as meromictic lakes, CH4 oxidation pathways involving different terminal electron acceptors such as NO 3 , SO2 4 , and oxides of Fe and Mn are thermodynamically possible. In this study, a reactive transport model was developed to assess the relative significance of the different pathways of CH4 consumption in the water column of Lake Pavin. In most cases, the model reproduced experimental data collected from the field from June 2006 to June 2007. Although the model and the field measurements suggest that anaerobic CH4 oxidation may contribute to CH4 consumption in the water column of Lake Pavin, aerobic oxidation remains the major sink of CH4 in this lake

Impact of the seismo-volcanic crisis offshore Mayotte on the Dziani Dzaha Lake

Since May 2018, an unexpected long and intense seismic crisis started offshore Mayotte (Indian Ocean, France). This ongoing seismic sequence is associated with the birth of a newly discovered submarine volcano 50 km east of Petite Terre. Here, we investigate the indirect impact of this crisis on the stability of an atypical ecosystem located in Mayotte, the Dziani Dzaha Lake. This lacustrine system presented physical, chemical and biogeochemical characteristics that were distinct from those classically observed in modern lakes or seawater, e.g. high salinity (up to 70 psu), lack of nitrate, sulfate content below 3 mM, and permanent water column anoxia below ca. 1.5 m depth (2012–2017 period). Based on three surveys conducted in 2020 and 2021, we documented an episode of water column oxygenation, a significant pH decrease and an impressive change in the carbon isotope signatures. These preliminary data suggest that the functioning of biogeochemical cycles in the Dziani Dzaha Lake is impacted by increased CO2 inputs and the changes in the lake mixing dynamics, which is an indirect consequence of the ongoing seismo-volcanic crisis

Biogeochemical Dynamics of Molybdenum in a Crater Lake: Seasonal Impact and Long-Term Removal

International audienceDespite a large variety of processes that can control Mo and its potential to become an environmental tracer of euxinic environment, this element is not often studied in lakes. The aim of this paper is to identify main seasonal biogeochemical processes that involve Mo in a well constrained freshwater system (Lake Pavin water-column) in order to evaluate their respective importance. In Lake Pavin, 4 main processes have been identified: 1) the transitional process represented by Mo assimilation of by phytoplankton in the epilimnion (nitrogen biological fixation and nitrate assimilation); 2) transient process represented by dissolved Mo adsorption onto Fe and Mn metal oxides at oxic/anoxic interface (depth 50 - 60 m); 3) Mo precipitation where apparent sulfide production rate is maximum, and from 80 m depths; 4) release of dissolved Mo due to Mo benthic flux or input from a deep source

A Demonstration for Building Modular and Efficient DSLs: The Kermeta v2 Experience

National audienceThis demonstration presents the new version (v2) of the Kermeta workbench that uses one domain-specific meta-language per language implementation concern. We show that the usage and combination of those meta-languages is simple and intuitive enough to deserve the term mashup and implemented as an original modular compilation scheme in the new version of Kermeta. This demonstration illustrates the use of the new version of Kermeta by presenting its use to design and implement two DSLs: Kompren, a DSL for designing and implementing model slicers; KCVL, the Commun Variability Language dedicated to variability management in software design models

Very Low Phytoplankton Diversity in a Tropical Saline-Alkaline Lake, with Co-dominance of Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta)

International audienceLake Dziani Dzaha (Mayotte Island, Indian Ocean) is a tropical thalassohaline lake which geochemical and biological conditions make it a unique aquatic ecosystem considered as a modern analogue of Precambrian environments. In the present study, we focused on the diversity of phytoplanktonic communities, which produce very high and stable biomass (mean 2014-2015 = 652 ± 179 μg chlorophyll a L −1). As predicted by classical community ecology paradigms, and as observed in similar environments, a single species is expected to dominate the phytoplanktonic communities. To test this hypothesis, we sampled water column in the deepest part of the lake (18 m) during rainy and dry seasons for two consecutive years. Phytoplanktonic communities were characterized using a combination of metagenomic, microscopy-based and flow cytometry approaches, and we used statistical modeling to identify the environmental factors determining the abundance of dominant organisms. As hypothesized, the overall diversity of the phytoplanktonic communities was very low (15 OTUs), but we observed a co-dominance of two, and not only one, OTUs, viz., Arthrospira fusiformis (Cyanobacteria) and Picocystis salinarum (Chlorophyta). We observed a decrease in the abundance of these co-dominant taxa along the depth profile and identified the adverse environmental factors driving this decline. The functional traits measured on isolated strains of these two taxa (i.e., size, pigment composition, and concentration) are then compared and discussed to explain their capacity to cope with the extreme environmental conditions encountered in the aphotic, anoxic, and sulfidic layers of the water column of Lake Dziani Dzaha