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Deciphering the Role of Water Column Redoxclines on Methylmercury Cycling Using Speciation Modeling and Observations From the Baltic Sea
Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden.
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge MA, USA.
Department of Chemistry, Umeå University, Umeå, Sweden.
Now at D-USYS Department, ETH Zürich, Zürich, Switzerland; Institut des Sciences Analytiques et de Physico-chimie pour l ’ Environnement et les Materiaux, CNRS/UNIV PAU & PAYS ADOUR, Pau, France.
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2018 (English)In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 32, no 10, p. 1498-1513Article in journal (Refereed) Published
Abstract [en]

Oxygen-depleted areas are spreading in coastal and offshore waters worldwide, but the implication for production and bioaccumulation of neurotoxic methylmercury (MeHg) is uncertain. We combined observations from six cruises in the Baltic Sea with speciation modeling and incubation experiments to gain insights into mercury (Hg) dynamics in oxygen depleted systems. We then developed a conceptual model describing the main drivers of Hg speciation, fluxes, and transformations in water columns with steep redox gradients. MeHg concentrations were 2-6 and 30-55 times higher in hypoxic and anoxic than in normoxic water, respectively, while only 1-3 and 1-2 times higher for total Hg (THg). We systematically detected divalent inorganic Hg (Hg-II) methylation in anoxic water but rarely in other waters. In anoxic water, high concentrations of dissolved sulfide cause formation of dissolved species of Hg-II: HgS2H(aq)- and Hg (SH)(2)(0)((aq)). This prolongs the lifetime and increases the reservoir of Hg-II readily available for methylation, driving the high MeHg concentrations in anoxic zones. In the hypoxic zone and at the hypoxic-anoxic interface, Hg concentrations, partitioning, and speciation are all highly dynamic due to processes linked to the iron and sulfur cycles. This causes a large variability in bioavailability of Hg, and thereby MeHg concentrations, in these zones. We find that zooplankton in the summertime are exposed to 2-6 times higher MeHg concentrations in hypoxic than in normoxic water. The current spread of hypoxic zones in coastal systems worldwide could thus cause an increase in the MeHg exposure of food webs.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2018. Vol. 32, no 10, p. 1498-1513
Keywords [en]
mercury, methylmercury, anoxia, hypoxia, methylation, redoxcline
National Category
Environmental Sciences Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:oru:diva-70373DOI: 10.1029/2018GB005942ISI: 000450063500006Scopus ID: 2-s2.0-85055251568OAI: oai:DiVA.org:oru-70373DiVA, id: diva2:1266711
Funder
Swedish Research Council Formas, 2014-1088 2016-00875The Kempe Foundations, SMK-1243Swedish Environmental Protection Agency
Note

Funding Agency:

Danish Council for Independent Research  1323-00745

Available from: 2018-11-29 Created: 2018-11-29 Last updated: 2018-11-29Bibliographically approved

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Liem-Nguyen, Van

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