Sources, Transport, and accumulation of Mercury in the northwestern Mediterranean margin sediments during the Industrial Era and influence of turbiditic events

Cossa, Daniel; Buscail, Roselyne; Dennielou, Bernard; Radakovitch, Olivier; Puig, Pere; Khripounoff, Alexis; Boutier, Bernard; Berné, Serge

doi:10.1016/j.pocean.2023.103186

Cited by 1 publication

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“…ME are shown in Figure 2b. Mercury concentrations ranged from 142 to 216 ng g −1 ; these values are relatively low for sediments accumulated within the second half of the twentieth century in the Rhône prodelta (Cossa et al, 2024), where Hg concentrations have reached up to 700 ng g −1 (Augier et al, 1980) and confirm the decrease of the Hg contamination of the RR inputs observed in the last decades (Cossa et al, 2018;Poulier et al, 2019). There was little change in Hg concentrations over the 30 cm of the cores, only a slight decrease with depth below a homogeneous layer of 10 cm thick (Figure 2b).…”

Section: Solid Phasementioning

confidence: 97%

Mercury Mobility in Epibenthic Waters of a Deltaic Environment

Cossa,

Dang,

Thomas

2024

JGR Biogeosciences

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Mercury (Hg) cycling at the sediment‐water interfaces (SWI) encompasses multiple homogeneous and heterogeneous biogeochemical reactions whose result is not yet elucidated. Estuarine SWIs, where the organic matter mineralization is active, constitute experimental sites particularly suitable for scrutinizing Hg speciation and mobilization. Here, we present high‐resolution vertical concentration profiles of Hg species, including inorganic divalent Hg () and monomethyl Hg (MMHg) in solid and dissolved (<0.22 μm) phases, on both sides of the SWI of the proximal part of the Rhône prodelta (northwestern Mediterranean Sea) using sediment cores and dialyzers implemented for a 67‐day‐long period. Concentrations of the dissolved species were <0.10 nM in the sediment pore waters but reached up to 0.58 nM in the epibenthic water zone, a concentration level that is ∼200 times higher than that of the water column. Conversely, MMHg concentrations were low (<0.5 pM) above the SWI and increased to up to 4.6 pM in the sulfate‐reducing zones of the sediment. The dynamic of the Hg species interconversions was explored using one‐dimensional transport‐reaction equations. This model allowed us to constrain the depth intervals where various species are produced or consumed and to approximate the reaction rates. We conclude that the epibenthic zone of the Rhône prodelta is a location of intense mobilization of inorganic HgII associated with organic matter mineralization and MMHg distribution in pore water is controlled by microbiological in situ reactions, but sedimentary MMHg does not diffuse in the overlying water column.

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