title: Diurnal variability and biogeochemical reactivity of mercury species in an extreme high-altitude lake ecosystem of the Bolivian Altiplano.
abstract: Methylation and demethylation represent major transformation pathways regulating the net production of methylmercury (MMHg). Very few studies have documented Hg reactivity and transformation in extreme high-altitude lake ecosystems. Mercury (Hg) species concentrations (IHg, MMHg, Hg°, and DMHg) and in situ Hg methylation (M) and MMHg demethylation (D) potentials were determined in water, sediment, floating organic aggregates, and periphyton compartments of a shallow productive Lake of the Bolivian Altiplano (Uru Uru Lake, 3686 m). Samples were collected during late dry season (October 2010) and late wet season (May 2011) at a north (NS) and a south (SS) site of the lake, respectively. Mercury species concentrations exhibited significant diurnal variability as influenced by the strong diurnal biogeochemical gradients. Particularly high methylated mercury concentrations (0.2 to 4.5 ng L(-1) for MMHgT) were determined in the water column evidencing important Hg methylation in this ecosystem. Methylation and D potentials range were, respectively, <0.1-16.5 and <0.2-68.3 % day(-1) and were highly variable among compartments of the lake, but always higher during the dry season. Net Hg M indicates that the influence of urban and mining effluent (NS) promotes MMHg production in both water (up to 0.45 ng MMHg L(-1) day(-1)) and sediment compartments (2.0 to 19.7 ng MMHg g(-1) day(-1)). While the sediment compartment appears to represent a major source of MMHg in this shallow ecosystem, floating organic aggregates (dry season, SS) and Totora's periphyton (wet season, NS) were found to act as a significant source (5.8 ng MMHg g(-1) day(-1)) and a sink (-2.1 ng MMHg g(-1) day(-1)) of MMHg, respectively. This work demonstrates that high-altitude productive lake ecosystems can promote MMHg formation in various compartments supporting recent observations of high Hg contents in fish and water birds.
authors.affiliation: Géosciences Environnement Toulouse, UMR 5563-IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400, Toulouse, France.
authors.forename: L
authors.initials: L
authors.lastname: Alanoca
authors.affiliation: Géosciences Environnement Toulouse, UMR 5563-IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400, Toulouse, France. david.amouroux@univ-pau.fr.|Laboratoire de Chimie Analytique Bio-inorganique et Environnement, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053, Pau cedex 9, France. david.amouroux@univ-pau.fr.
authors.forename: D
authors.initials: D
authors.lastname: Amouroux
authors.affiliation: Laboratoire de Chimie Analytique Bio-inorganique et Environnement, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053, Pau cedex 9, France.
authors.forename: M
authors.initials: M
authors.lastname: Monperrus
authors.affiliation: Laboratoire de Chimie Analytique Bio-inorganique et Environnement, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053, Pau cedex 9, France.
authors.forename: E
authors.initials: E
authors.lastname: Tessier
authors.affiliation: Equipe Environnement et Microbiologie, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Goni
authors.affiliation: Equipe Environnement et Microbiologie, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France.
authors.forename: R
authors.initials: R
authors.lastname: Guyoneaud
authors.affiliation: Laboratorio de Calidad Ambiental, Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, casilla 3161, La Paz, Bolivia.
authors.forename: D
authors.initials: D
authors.lastname: Acha
authors.affiliation: Equipe Environnement et Microbiologie, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Bâtiment IBEAS, BP1153, 64013, Pau Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Gassie
authors.affiliation: Géosciences Environnement Toulouse, UMR 5563-IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400, Toulouse, France.
authors.forename: S
authors.initials: S
authors.lastname: Audry
authors.affiliation: Laboratorio de Hidroquímica, Instituto de Investigaciones Químicas, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, casilla 3161, La Paz, Bolivia.
authors.forename: M E
authors.initials: ME
authors.lastname: Garcia
authors.affiliation: Laboratorio de Hidroquímica, Instituto de Investigaciones Químicas, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, casilla 3161, La Paz, Bolivia.
authors.forename: J
authors.initials: J
authors.lastname: Quintanilla
authors.affiliation: Géosciences Environnement Toulouse, UMR 5563-IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400, Toulouse, France.|Laboratorio de Calidad Ambiental, Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, casilla 3161, La Paz, Bolivia.
authors.forename: D
authors.initials: D
authors.lastname: Point
mesh_terms: D000531:Altitude; D000818:Animals; D001838:Bolivia; D017753:Ecosystem; D004777:Environment; D004784:Environmental Monitoring; D005399:Fishes / Q000378:metabolism; D060106:Lakes / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D008767:Methylmercury Compounds / Q000737:chemistry; D008906:Mining; D012621:Seasons; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008767:Methylmercury Compounds; D014874:Water Pollutants, Chemical; D008628:Mercury
keywords: Altiplano; Biogeochemistry; Bolivia; Demethylation; Lake; Mercury; Methylation