Supplementary information to
MMHg production and export from intertidal sediments to the water column of a tidal lagoon (Arcachon Bay, France).
S. Bouchet1*, D. Amouroux1, P. Rodriguez-Gonzalez1, E. Tessier1, M. Monperrus1, G Thouzeau2, J. Clavier2, E. Amice2, J. Deborde3, S. Bujan3, J. Grall4, and P. Anschutz3
1. Laboratoire de Chimie Analytique Bio-inorganique et Environnement, Institut Pluridisciplinaire de Recherche sur l’Environnement et les Matériaux, UMR 5254 CNRS - Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053 Pau cedex 9, France
2. Laboratoire des Sciences de l’Environnement Marin, UMR 6539 CNRS/UBO/IRD, IUEM, Technopôle Brest-Iroise, 4 rue Dumont d’Urville, 29280 Plouzané, France
3. Laboratoire Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), UMR 5805 CNRS -Université de Bordeaux I, 33405 Talence, France
4. OSU IUEM, Technopôle Brest-Iroise, 4 rue Dumont d’Urville, 29280 Plouzané, France
* Corresponding author. Tel.: +33-5-59-40-77-56; fax: +33-5-59-40-77-81
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Materials and methods
Trace elements analyses
Concentrations of some trace elements were analyzed by ICP-MS (X7 II Thermo Elemental) by a conventional nebulization method and with standard addition methods to calculate their benthic fluxes, as for Hg species. The instrument was operated in the collision cell mode with a mixed gas (8 % H2 in a N5 grade He, Linde gas) to remove polyatomic interferences (Leonhard et al., 2002). Prior to analyses, the samples were precisely diluted ten times with ultra-pure water in order to decrease the salt content and minimize the matrix interferences. The results have been validated by the analyses of CASS-4 and NASS-5 (NRCC) certified marine waters (Pinel-Raffaitin et al., 2008).
Macrofaunal abundance and biomass in benthic chambers
In the field, macrofaunal samples were gently washed on a 1-mm sieve and preserved in 4% formaldehyde solution. At the laboratory, individuals were sorted, counted and identified to the species level under a dissecting or a compound microscope. For macrofauna biomass determination, samples were dried at 60°C for 48 h and the ash-free dry weight (AFDW) was calculated after 4h ignition at 450°C.
Ancillary data measurements
Sediment was freeze-dried and the weight loss was used to calculate water content. The dried solid was homogenized for solid-phase analysis. An ascorbate reagent was used to remove from the sediment the most reactive Fe (III) phases (Fe-asc), all Mn (III,IV) oxides and oxyhydroxides (Mn-asc), reducible by heterotrophic bacteria and associated phosphorus (P-asc; Kostka et Luther III, 1994; Anschutz et al., 1998, 2005; Deborde et al., 2007). Particulate organic carbon (C-org), total carbon (C-tot), and total sulphur (S-tot) were measured on freeze-dried samples by infrared spectroscopy using a LECO C-S 125. Particulate organic carbon was measured after removal of carbonates with 2 M HCl during 24 h from 50 mg of powdered sample. The precision of these analyses was ± 0.02 wt%. Dissolved Fe (II) was determined by the ferrozine method (Stookey, 1970) and dissolved Mn2+ by atomic absorption spectrometry. PO43- was measured with the spectrophotometric method described by Murphy and Riley (1970). The precision estimated from replicates was ±5% for Mn and P, and ±7% for Fe. DOC was measured with a high-temperature catalytic oxidation analyzer (Shimadzu TOC 5000). Dissolved sulfides were measured by a methylene blue method adapted from Cline (1969).
Table SI-1. Mean (± SD) benthic fluxes of oxygen and selected trace metals measured in the benthic chambers in March 2005, May 2006 and October 2007 in Arcachon Bay.
Fig. SI-1. Example of a typical sediment pore-water profile for dissolved inorganic phosphorus, ammonium, SCO2, Fe2+, Mn2+ and H2S, recorded at St.2 in May 2006.
Fig SI-2. Box-and-whisker plots representing the individual Hg species concentrations in the bottom waters (n = 45, lower and upper limits of the box represent the percentiles 25 and 75).
Fig SI-3. Box-and-whisker plots representing the distribution of the individual benthic fluxes values over the three periods studied (n = 39, 6 values discarded, lower and upper limits of the box represent the percentiles 25 and 75).
Fig Si-4. Relationships between IHg benthic fluxes and PO43- and Mn benthic fluxes for the three seasons considered.
References
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