Browsing by Autor "Sylvain Bouchet"

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Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation
(Multidisciplinary Digital Publishing Institute, 2020) Stéphane Guédron; Darío Achá; Sylvain Bouchet; David Point; Emmanuel Tessier; Carlos Heredia; Stéfany Rocha-Lupa; Pablo Fernandez-Saavedra; Marizol Giovana Flores; Sarah Bureau
In shallow aquatic environments, sediment is a significant source of monomethylmercury (MMHg) for surface water (SW). High-altitude aquatic ecosystems are characterized by extreme hydro-climatic constraints (e.g., low oxygen and high UV radiation). We studied, during two seasons, the diel cycles of MMHg in SW and sediment porewaters (PW) of Lake Uru Uru (3686 m a.s.l, Bolivia) contaminated by urban and mining activities. Our results show that diel changes in SW MMHg concentrations (up to 1.8 ng L−1) overwhelm seasonal ones, with higher MMHg accumulation during the night-time and the dry season. The calculation of MMHg diffusive fluxes demonstrates that the sediment compartment was the primary source of MMHg to the SW. Most MMHg efflux occurred during the dry season (35.7 ± 17.4 ng m−2 day−1), when the lake was relatively shallow, more eutrophicated, and with the redoxcline located above the sediment–water interface (SWI). Changes in MMHg accumulation in the PWs were attributed to diel redox oscillations around the SWI driving both the bacterial sulfate reduction and bio-methylation. Finally, we highlight that although MMHg loading from the PW to the SW is large, MMHg photodegradation and demethylation by microorganisms control the net MMHg accumulation in the water column.
Diagenetic production, accumulation and sediment-water exchanges of methylmercury in contrasted sediment facies of Lake Titicaca (Bolivia)
(Elsevier BV, 2020) Stéphane Guédron; Stéphane Audry; Darío Achá; Sylvain Bouchet; David Point; Thomas Condom; Carlos Heredia; Sylvain Campillo; Pascale A. Baya; Alexis Groleau
In Situ Photochemical Transformation of Hg Species and Associated Isotopic Fractionation in the Water Column of High-Altitude Lakes from the Bolivian Altiplano
(American Chemical Society, 2022) Sylvain Bouchet; Emmanuel Tessier; Jérémy Masbou; David Point; Xavier Lazzaro; Mathilde Monperrus; Stéphane Guédron; Darío Achá; David Amouroux
Photochemical reactions are major pathways for the removal of Hg species from aquatic ecosystems, lowering the concentration of monomethylmercury (MMHg) and its bioaccumulation in foodwebs. Here, we investigated the rates and environmental drivers of MMHg photodegradation and inorganic Hg (IHg) photoreduction in waters of two high-altitude lakes from the Bolivian Altiplano representing meso- to eutrophic conditions. We incubated three contrasting waters in situ at two depths after adding Hg-enriched isotopic species to derive rate constants. We found that transformations mostly occurred in subsurface waters exposed to UV radiation and were mainly modulated by the dissolved organic matter (DOM) level. In parallel, we incubated the same waters after the addition of low concentrations of natural MMHg and followed the stable isotope composition of the remaining Hg species by compound-specific isotope analysis allowing the determination of enrichment factors and mass-independent fractionation (MIF) slopes (Δ199Hg/Δ201Hg) during in situ MMHg photodegradation in natural waters. We found that MIF enrichment factors potentially range from -11 to -19‰ and average -14.3 ± 0.6‰ (1 SE). The MIF slope diverged depending on the DOM level, ranging from 1.24 ± 0.03 to 1.34 ± 0.02 for the low and high DOM waters, respectively, and matched the MMHg MIF slope recorded in fish from the same lake. Our in situ results thus reveal (i) a relatively similar extent of Hg isotopic fractionation during MMHg photodegradation among contrasted natural waters and compared to previous laboratory experiments and (ii) that the MMHg MIF recorded in fish is characteristic for the MMHg bonding environment. They will enable a better assessment of the extent and conditions conducive to MMHg photodegradation in aquatic ecosystems.
Late Holocene volcanic and anthropogenic mercury deposition in the western Central Andes (Lake Chungará, Chile)
(Elsevier BV, 2019) Stéphane Guédron; Julie Tolu; Élodie Brisset; Pierre Sabatier; Vincent Perrot; Sylvain Bouchet; Anne‐Lise Develle; Richard Bindler; Daniel Cossa; S. C. Fritz
Late Hololocene mercury deposition history in Lake Chungara (4500 m. a.s.l., Chile): Influence of volcanic eruptions and changes in Paleolimnoecology
(2017) Stéphanie Guédron; Julie Tolu; Élodie Brisset; Pierre Sabatier; Anne‐Lise Develle; Sylvain Bouchet; Richard Bindler; A Dominic; Sherilyn C. Fritz; Paul A. Baker
International audience
Linking Microbial Activities and Low-Molecular-Weight Thiols to Hg Methylation in Biofilms and Periphyton from High-Altitude Tropical Lakes in the Bolivian Altiplano
(American Chemical Society, 2018) Sylvain Bouchet; Marisol Goñi‐Urriza; Mathilde Monperrus; Rémy Guyoneaud; Pablo Fernandez; Carlos Heredia; Emmanuel Tessier; Claire Gassie; David Point; Stéphane Guédron
The sources and factors controlling concentrations of monomethylmercury (MMHg) in aquatic ecosystems need to be better understood. Here, we investigated Hg transformations in sediments, periphyton associated with green algae's or aquatic plants, and benthic biofilms from the Lake Titicaca hydrosystem and compared them to the occurrence of active methylating microorganisms and extracellular Hg ligands. Intense Hg methylation was found in benthic biofilms and green algae's periphyton, while it remained low in sediments and aquatic plants' periphyton. Demethylation varied between compartments but remained overall in the same range. Hg methylation was mainly carried out by sulfate reducers, although methanogens also played a role. Its variability between compartments was first explained by the presence or absence of the hgcAB genes. Next, both benthic biofilm and green algae's periphyton exhibited a great diversity of extracellular low-molecular-weight (LMW) thiols (13 or 14 compounds) present at a range of a few nmol L-1 or μmol L-1 but clearly dominated by cysteine and 3-mercaptopropionic acid. Hg methylation was overall positively correlated to the total thiol concentrations, albeit to different extents according to the compartment and conditions. This work is the first examining the interplay between active methylating bacterial communities and extracellular ligands in heterotrophic biofilms and supports the involvement of LMW thiols in Hg methylation in real aquatic systems.
Mercury compound-specific stable isotope fractionation in high-altitude lake ecosystems of the Bolivian Altiplano
(Elsevier BV, 2025) Jérémy Masbou; David Point; Sylvain Bouchet; Jeroen E. Sonke; Carlos A. Molina; Carla Ibañez; Anne Lorrain; Julio Pinto; Darío Achá; David Amouroux
Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends
(Elsevier BV, 2017) Stéphane Guédron; David Point; Darío Achá; Sylvain Bouchet; Pascale A. Baya; Emmanuel Tessier; Mathilde Monperrus; Carlos I. Molina; Alexis Groleau; Laurent Chauvaud