Mercury sources and transformations in a man-perturbed tidal estuary; the Sinnamary Estuary, French Guiana

Type Article
Date 2008-07
Language English
Author(s) Muresan B1, Cossa Daniel1, Coquery M2, Richard S3
Affiliation(s) 1 : Inst Francais Rech Exploitat Mer, F-83507 La Seyne Sur Mer, France.
2 : Ctr Natl Machinisme Agr Genie Rural & Eaux & Fore, F-69336 Lyon 9, France.
3 : Lab Rech Environm Barrage Petit Saut Hydreco, F-97388 Kourou, French Guiana.
Source Geochimica et Cosmochimica Acta (0016-7037) (Elsevier), 2008-07 , Vol. 72 , N. 22 , P. 5416-5430
DOI 10.1016/j.gca.2008.08.021
WOS© Times Cited 15
Keyword(s) Partitioning, Speciation, Redox, Mercury, Reservoir, Estuary
Abstract The distribution, partition and speciation of mercury (Hg) were studied along the redox gradient of an anthropogenically perturbed tropical estuary, the Sinnamary Estuary in French Guiana. This system is a partially mixed estuary characterized by an anoxic freshwater end-member, while the marine end member consists of the Amazon Plume. The set up of an artificial oxygenation system in the anoxic freshwater end-member generates sharp gradients of major chemical species (iron, sulfides, etc.) coupled with intense organic matter (OM) turnover. The coexistence of oxygenated waters and dissolved sulfides in an organic rich environment depicts the Upper Sinnamary Estuary (USE: part of Sinnamary Estuary under the tidal influence but upstream of the salt intrusion) as a potential site for Hg methylation. The concentrations of all mercurial species (HgT) in the unfiltered samples (HgTUNF), in the dissolved (HgTD) and particulate (HgTP) phases of the USE average 11 ± 3, 6 ± 2 and 5 ± 3 (i.e. 600 ± 200 pmol g-1) pmol L-1 respectively. Average concentrations of monomethylmercury (MMHg) in the unfiltered (MMHgUNF), dissolved (MMHgD) and particulate (MMHgP) phases were 3.7 ± 1.0, 2.0 ± 0.9 and 1.8 ± 1.2 (i.e. 220 ± 130 pmol g-1) pmol L-1 respectively. Water oxygenation and sulfides concentrations emerged to play a critical role in controlling MMHg levels. Additionally, iron cycling, acid-base mechanisms, and edoxdependent processes were involved in the MMHg partitioning between phases. Overall, the USE constitutes a biogeochemical reactor that gathers partitioning and methylation processes. Thepermanent MMHg inputs from the anoxic freshwater end-member combined with the intense endogenous Hg methylation ensures high MMHg levels in both dissolved and particulate phases. To illustrate, the USE exports 60 ± 20 % more MMHgUNF than it imports: 5.5 ± 0.7 vs. 3.5 ± 1.2 kg y-1.
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