Role of particle sorption properties in the behavior and speciation of trace metals in macrotidal estuaries: The cadmium example Auteur(s) : Gonzalez, Jean-louis Thouvenin, Benedicte Dange, Catherine Chiffoleau, Jean-francois Boutier, Bernard Éditeur(s) : Springer Berlin / Heidelberg Résumé : The role of particles in the fate and speciation of trace metals in macrotidal estuaries was studied using a surface complexation model (MOCO). Cadmium was selected as the target metal contaminant due to its reactivity in estuaries: cadmium behavior is mainly controlled by heterogeneous processes (sorption/desorption) related to salinity and suspended matter gradients. Various scenarios of suspended matter distribution according to salinity were simulated. The impact of surface properties (specific surface area, density of surface sites, acido-basic properties, and complexation constant) was evaluated using data collected on particles from the Gironde, Loire, and Seine estuaries. Our results show that particle surface properties, evaluated on the basis of various parameters, are instrumental in "non-conservative" contaminant speciation in the estuarine environment. Their evaluation enables us to understand and simulate, to a large extent, the fate of "Cd-type" contaminants (whose behavior is controlled by competition between sorption and desorption processes). The natural variations of these properties can be responsible for significant modifications of the Cd speciation in the macrotidal estuaries where salinity and SM gradients are very strong. The Handbook of Environmental Chemistry (1433-6839) (Springer Berlin / Heidelberg), 2006 , Vol. 5H , P. 265-301 Droits : 2006 Springer http://archimer.ifremer.fr/doc/2006/publication-2005.pdf DOI:10.1007/b89479 http://archimer.ifremer.fr/doc/00000/2005/ | Partager |
Distribution et évolution saisonnière du cuivre dissous dans un écosystème estuarien macrotidal d'Europe occidentale (estuaire de l'Aule, France) Auteur(s) : Bordin, G Éditeur(s) : Gauthier-Villars Résumé : The seasonal variations of total dissolved copper were surveyed during one year (1983/1984) in the Aulne estuary (Western Brittany, France), an ecosystem with a high rate of water renewal. Copper in filtered water samples (after and without acidification) was determined after preconcentration on Chelex 100, and the eluates were analyzed by graphite furnace atomic absorption spectroscopy. The concentrations of free and complexed copper were then plotted versus chlorosity. Globally, the total dissolved copper concentrations tend to decrease with salinity. The role of physicochemical parameters such as pH and suspended matter (adsorption-desorption mechanisms) on dissolved copper content is shown to be significant. With a variable intensity, desorption (release) takes place in summer and in autumn, while adsorption is observed at very low chlorosity in winter. The dissolved copper concentrations in the Aulne estuary (0.26 to 2.52-mu-g.l-1, with the highest values in autumn) are similar to most estuarine copper values. The proportion of complexed species ranges from 4 to 69% (average of 27%). Les variations saisonnières des concentrations en cuivre dissous dans l'estuaire de l'Aulne (Bretagne occidentale) ont été mesurées au cours d'un cycle annuel (1983/1984). Les concentrations en cuivre libre et celles en cuivre complexé ont été suivies séparément en fonction de la chlorosité, un paramètre conservatif. Les profils obtenus pour le cuivre total dissous montrent généralement une décroissance des teneurs en métal des eaux douces aux eaux marines, tout en restant supérieures à celles de la droite théorique de mélange. On montre le rôle fondamental de la variation du pH concomitante de celle de la matière en suspension (mécanisme d'adsorption-désorption) dans l'évolution des teneurs en cuivre dissous. Ce processus agit plus ou moins intensément dans le sens de la désorption (été, automne) ou de l'adsorption (hiver aux faibles chlorosités). Dans l'ensemble, les teneurs en cuivre total dissous (de 0,26 à 2,52 J.lg.l- 1 , les valeurs automnales étant les plus élevées) sont comparables à celles de nombreux autres écosystèmes estuariens, avec un taux de complexation compris entre 4 et 69% (moyenne de 27% ). Oceanologica Acta (0399-1784) (Gauthier-Villars), 1991 , Vol. 14 , N. 5 , P. 445-457 Droits : Gauthier-Villars http://archimer.ifremer.fr/doc/00103/21377/18977.pdf http://archimer.ifremer.fr/doc/00103/21377/43066.pdf http://archimer.ifremer.fr/doc/00103/21377/ | Partager |
Spatio-temporal variability in benthic silica cycling in two macrotidal estuaries: Causes and consequences for local to global studies Auteur(s) : Raimonet, Melanie Ragueneau, Olivier Andrieux Loyer, Francoise Philippon, Xavier Kerouel, Roger Le Goff, Manon Memery, Laurent Éditeur(s) : Academic Press Ltd- Elsevier Science Ltd Résumé : The high heterogeneity of silica cycling in coastal margins and the lack of silica data (compared to nitrogen and phosphorus) prevent the estimation of global silica retention in estuaries. In this study, the spatial and temporal variability of porewater silicic acid (Si(OH)4) profiles e that integrate benthic transport and reaction processes e was investigated at different spatial (metre, longitudinal and crosssection, intra-estuary) and temporal (tidal, seasonal) scales in two macrotidal estuaries, very close geographically but essentially differing in their shape. Studying the spatial and temporal variability of Si(OH)4 concentrations in porewaters provided evidence for the importance of transport processes, e.g. bio-irrigation, tidal pumping, resuspension and any combination of these processes, in affecting Si(OH)4 concentrations and fluxes and therefore temporary or permanent retention along the landeocean continuum. We confirm that aSiO2 (amorphous silicate) transported by rivers and estuaries clearly needs to be better characterized as it provides an important source of reactive aSiO2 to sediments. This study allows us to: (1) interrogate spatial and temporal scales, although both are most often in complete interaction; (2) design the most appropriate sampling schemes to be representative of any given system and to extrapolate at the scale of the whole estuary; (3) quantify uncertainty associated to the estimations of Si(OH)4 stocks and fluxes in this type of ecosystem, essential for budget calculations. We showed that two adjacent small macrotidal estuaries, may exhibit different behaviours regarding Si retention. Temporary retention has been observed in the meanders of the Aulne Estuary and not along the more linear Elorn Estuary, demonstrating the importance of the morphology and hydrodynamic components of the estuarine filter. Research is needed in other systems and climatic zones, but our study suggests that the typology should not only account for the different types of landeocean continuum (fjord, delta, mangrove.), but also incorporate the physical or biological attributes of the estuarine filter. Estuarine Coastal And Shelf Science (0272-7714) (Academic Press Ltd- Elsevier Science Ltd), 2013-03 , Vol. 119 , P. 31-43 Droits : 2013 Elsevier Ltd. All rights reserved. http://archimer.ifremer.fr/doc/00124/23529/22370.pdf DOI:10.1016/j.ecss.2012.12.008 http://archimer.ifremer.fr/doc/00124/23529/ | Partager |
Strong gradient of benthic biogeochemical processes along a macrotidal temperate estuary: focus on P and Si cycles Auteur(s) : Raimonet, Melanie Andrieux, Francoise Ragueneau, Olivier Michaud, Emma Kerouel, Roger Philippon, Xavier Nonent, Michel Memery, Laurent Éditeur(s) : Springer Biogeochemistry (0168-2563) (Springer), 2013-10 , Vol. 115 , N. 1-3 , P. 399-417 Droits : Springer Science+Business Media Dordrecht 2013 http://archimer.ifremer.fr/doc/00130/24115/22493.pdf DOI:10.1007/s10533-013-9843-3 http://archimer.ifremer.fr/doc/00130/24115/ | Partager |