Browsing by Autor "Carlos Heredia"

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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.
Anthropogenic Eutrophication of Lake Titicaca (Bolivia) Revealed by Carbon and Nitrogen Stable Isotopes Fingerprinting
(RELX Group (Netherlands), 2022) Carlos Heredia; Stéphane Guédron; David Point; Vincent Perrot; Sylvain Campillo; Claire Vérin; Maria Elena Espinoza; Pablo Fernandez; Céline Duwig; Darío Achá
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
Holocene variations in Lake Titicaca water level and their implications for sociopolitical developments in the central Andes
(National Academy of Sciences, 2023) Stéphane Guédron; Christophe Delaere; Sherilyn C. Fritz; Julie Tolu; Pierre Sabatier; Anne-Lise Devel; Carlos Heredia; Claire Vérin; Eduardo Queiroz Alves; Paul A. Baker
Holocene climate in the high tropical Andes was characterized by both gradual and abrupt changes, which disrupted the hydrological cycle and impacted landscapes and societies. High-resolution paleoenvironmental records are essential to contextualize archaeological data and to evaluate the sociopolitical response of ancient societies to environmental variability. Middle-to-Late Holocene water levels in Lake Titicaca were reevaluated through a transfer function model based on measurements of organic carbon stable isotopes, combined with high-resolution profiles of other geochemical variables and paleoshoreline indicators. Our reconstruction indicates that following a prolonged low stand during the Middle Holocene (4000 to 2400 BCE), lake level rose rapidly ~15 m by 1800 BCE, and then increased another 3 to 6 m in a series of steps, attaining the highest values after ~1600 CE. The largest lake-level increases coincided with major sociopolitical changes reported by archaeologists. In particular, at the end of the Formative Period (500 CE), a major lake-level rise inundated large shoreline areas and forced populations to migrate to higher elevation, likely contributing to the emergence of the Tiwanaku culture.
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<sup>-1</sup> or μmol L<sup>-1</sup> 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.
Provenance of lead ores used for water pipes production in the ancient Roman Gaul (Vienne, France)
(Elsevier BV, 2025) Carlos Heredia; Stéphane Guédron; Alexandra T. Gourlan; Bruno Helly; Hugo Delile; Laura Calzolari; Sylvain Campillo; S. Santenac; Laurence Audin; Philippe Télouk
Reconstructing two millennia of copper and silver metallurgy in the Lake Titicaca region (Bolivia/Peru) using trace metals and lead isotopic composition
(Elsevier BV, 2021) Stéphane Guédron; Julie Tolu; Christophe Delaere; Pierre Sabatier; Julien Barré; Carlos Heredia; Élodie Brisset; Sylvain Campillo; Richard Bindler; Sherilyn C. Fritz