Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation - Archive ouverte HAL Access content directly
Journal Articles Applied Sciences Year : 2020

Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation

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Stéphane Guedron
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  • PersonId : 847606
Dario C. Acha
  • Function : Author
Sylvain Bouchet
  • Function : Author
David E. Point
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Carlos Heredia
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Stéfany Rocha-Lupa
  • Function : Author
Pablo Fernandez-Saavedra
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Marizol Flores
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Sarah Bureau
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Israel Quino-Lima
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Abstract

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.
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hal-03006743 , version 1 (16-11-2020)

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Stéphane Guedron, Dario C. Acha, Sylvain Bouchet, David E. Point, Emmanuel Tessier, et al.. Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation. Applied Sciences, 2020, 10 (21), pp.7936. ⟨10.3390/app10217936⟩. ⟨hal-03006743⟩
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