Accumulation of methylmercury in the high-altitude lake uru uru (3686 m a.s.l, bolivia) controlled by sediment efflux and photodegradation

Stéphane Guédron, Dario Achá, Sylvain Bouchet, David Point, Emmanuel Tessier, Carlos Heredia, Stéfany Rocha-Lupa, Pablo Fernandez-Saavedra, Marizol Flores, Sarah Bureau, Israel Quino-Lima, David Amouroux

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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.

Original languageEnglish
Article number7936
Pages (from-to)1-14
Number of pages14
JournalApplied Sciences (Switzerland)
Issue number21
StatePublished - 1 Nov 2020

Bibliographical note

Funding Information:
Funding: This research was funded by Agence National pour la Recherche, as a contribution to the LA PACHÁMAMA project (ANR CESA program, No ANR-13-CESA-0015-01, PI: D. Amouroux:, COMIBOL project (INSU CNRS/IRD EC2CO Program, PI: D. Point:, EUTITICACA project (founded by the Impuestos Directos a los Hidrocarburos IDH administrated by the Universidad Mayor de San Andrés, PI: D. Achá: darioAchá and TRACISOMER supported by a grant from Labex OSUG@2020 (PI: S. Guédron: S. Guédron and S. Bureau (ISTerre/IRD/UGA) are part of Labex OSUG@2020 (Investissements d’avenir—ANR10 LABX56).

Publisher Copyright:
© 2020 by the authors. Licensee MDPI, Basel, Switzerland.


  • Diel and seasonal cycles
  • Monomethylmercury
  • Photodegradation
  • Water–sediment interface


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