Mobility and fluxes of trace elements and nutrients at the sediment–water interface of a lagoon under contrasting water column oxygenation conditions

• Published in: Applied geochemistry 2013-04, Vol.31 (35-51), p.35-51
• Main Authors: Rigaud, Sylvain, Radakovitch, Olivier, Couture, Raoul-Marie, Deflandre, Bruno, Cossa, Daniel, Garnier, Cédric, Garnier, Jean-Marie
• Format: Article
• Language: English
• Subjects: adsorption; ammonium compounds; anaerobic conditions; arsenic; benthic organisms; chromium; cobalt; coprecipitation; data collection; desorption; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Sciences; Exact sciences and technology; Geochemistry; iron; manganese; manganese dioxide; mercury; minerals; nickel; nutrients; oxidants; Pollution, environment geology; redox reactions; Sciences of the Universe; sediment contamination; sediments; sulfides; thermodynamics
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2012.12.003

► Main constituents and trace elements concentration profiles in contaminated sediments. ► Contrasting oxygen concentrations in the overlying water column. ► Combination of thermodynamic calculations and inverse transport-reactions modelling. ► Identification and quantification of diagenetic reactions controlling trace elements mobility. ► Assessment of trace elements and nutrients fluxes at the sediment–water interface. The early diagenesis of the major carrier phases (Fe and Mn minerals), trace elements (As, Co, Cr, Hg, MeHg, Ni) and nutrients (ΣNO3, NH4+, ΣPO4) and their exchange at the sediment water/interface were studied in the Berre Lagoon, a Mediterranean lagoon in France, at one site under two contrasting oxygenation conditions (strictly anoxic and slightly oxic) and at an adjacent site with perennially well-oxygenated water. From the concentration profiles of the primary biogeochemical constituents and trace elements of the pore and bottom waters, as well as the total and reactive particulate phases, it was possible to locate and identify the diagenetic reactions controlling the mobility of trace elements in the sediments and quantify their rates by coupling one-dimensional steady-state transport-reaction modelling and thermodynamic speciation calculations. Under oxic conditions and in the absence of benthic organisms, the main redox reactions were well identified vertically in the surface sediments and followed the theoretical sequence of oxidant consumption: O2>ΣNO3/MnO2>Fe(OH)3>SO42-. However, under anoxic conditions, only MnO2, Fe(OH)3 and SO42- reduction were present, and they all occurred at the interface. The main biogeochemical controls on the mobility of As, Cr, Hg, MeHg and Ni in the surface sediments were identified as the adsorption/desorption on and/or coprecipitation/codissolution with Fe oxy-hydroxides. In contrast, Co mobility was primarily controlled by its reactivity towards Mn oxy-hydroxides. In sulphidic sediments, As, Hg and MeHg were sequestered along with Fe sulphides, whereas Co and Ni precipitated directly as metallic sulphides and Cr mobility was enhanced by complexation with dissolved organic ligands. The fluxes of trace elements at the sediment–water interface are essentially dependent on the localisation of their remobilisation and immobilisation reactions under the interface, which in turn is governed by the benthic water oxygenation conditions and kinetic competition among those reaction and diffusion processes. Und