Browsing by Autor "Pablo Fernandez"

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Algal Bloom Exacerbates Hydrogen Sulfide and Methylmercury Contamination in the Emblematic High-Altitude Lake Titicaca
(Multidisciplinary Digital Publishing Institute, 2018) Darío Achá; Stéphane Guédron; David Amouroux; David Point; Xavier Lazzaro; Pablo Fernandez; Géraldine Sarret
Algal blooms occurrence is increasing around the globe. However, algal blooms are uncommon in dominantly oligotrophic high-altitude lakes. Lake Titicaca, the largest freshwater lake in South America, located at 3809 m above the sea level, experienced its first recorded algal bloom covering a large fraction of its southern shallow basin in March–April 2015. The dominant algae involved in the bloom was Carteria sp. Water geochemistry changed during the bloom with a simultaneous alkalinization in heterotrophic parts of the lake and acidification in eutrophic shallow areas. A decrease in oxygen saturation (from 105 to 51%), and a dramatic increase in hydrogen sulfide (H2S) concentrations (from <0.02 to up to 155 µg∙L−1) resulted in the massive death of pelagic organisms. Such changes were brought by the exacerbated activity of sulfate-reducing bacteria (SRB) in this sulfate-rich lake. Although levels in total mercury remained stable during the event, MMHg % rose, highlighting higher conservation of produced MMHg in the water. Such an increase on MMHg % has the potential to produce exponential changes on MMHg concentrations at the end food web due to the biomagnification process. Our physicochemical and climatological data suggest that unusually intense rain events released large amounts of nutrients from the watershed and triggered the bloom. The observed bloom offers a hint for possible scenarios for the lake if pollution and climate change continue to follow the same trend. Such a scenario may have significant impacts on the most valuable fish source in the Andean region and the largest freshwater Lake in South America. Furthermore, the event illustrates a possible fate of high altitude environments subjected to eutrophication.
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
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.