The Speciation and Mobility of Mn and Fe in Estuarine Sediments

Véronique E. Oldham, Matthew G. Siebecker, Matthew R. Jones, Alfonso Mucci, Bradley M. Tebo, George W. Luther

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

Dissolved and solid-phase speciation of Mn and Fe was measured in the porewaters of sediments recovered from three sites in the Greater St. Lawrence Estuary: the Saguenay Fjord, the Lower St. Lawrence Estuary (LSLE) and the Gulf of St. Lawrence (GSL). At all sites and most depths, metal organic ligand complexes (Mn(III)–L and Fe(III)–L) dominated the sedimentary porewater speciation, making up to 100% of the total dissolved Mn or Fe. We propose that these complexes play a previously underestimated role in maintaining oxidized soluble metal species in sedimentary systems and in stabilizing organic matter in the form of soluble metal–organic complexes. In the fjord porewaters, strong (log KCOND > 13.2) and weak (log KCOND < 13.2) Mn(III)–L complexes were detected, whereas only weak Mn(III)–L complexes were detected at the pelagic and hemipelagic sites of the GSL and LSLE, respectively. At the fjord site, Mn(III)–L complexes were kinetically stabilized against reduction by Fe(II), even when Fe(II) concentrations were as high as 57 μM. Only dissolved Mn(II) was released from the sediments to overlying waters, suggesting that Mn(III) may be preferentially oxidized by sedimentary microbes at or near the sediment–water interface. We calculated the dissolved Mn(II) fluxes from the sediments to the overlying waters to be 0.24 µmol cm−2 year−1 at the pelagic site (GSL), 11 µmol cm−2 year−1 at the hemipelagic site (LSLE) and 2.0 µmol cm−2 year−1 in the fjord. The higher benthic flux in the LSLE reflects the lower oxygen concentrations (dO2) of the bottom waters and sediments at this site, which favor the reductive dissolution of Mn oxides as well as the decrease in the oxidation rate of dissolved Mn(II) diffusing through the oxic layer of the sediment and its release to the overlying water.

Original languageEnglish
Pages (from-to)3-26
Number of pages24
JournalAquatic Geochemistry
Volume25
Issue number1-2
DOIs
StatePublished - Apr 1 2019

Keywords

  • Diagenesis
  • Fe(III)–L
  • Flux
  • Iron
  • Manganese
  • Mn(III)–L
  • Organic complexation
  • Oxygen
  • Porewaters
  • Redox chemistry
  • Sediment
  • St. Lawrence Estuary

Fingerprint Dive into the research topics of 'The Speciation and Mobility of Mn and Fe in Estuarine Sediments'. Together they form a unique fingerprint.

  • Cite this

    Oldham, V. E., Siebecker, M. G., Jones, M. R., Mucci, A., Tebo, B. M., & Luther, G. W. (2019). The Speciation and Mobility of Mn and Fe in Estuarine Sediments. Aquatic Geochemistry, 25(1-2), 3-26. https://doi.org/10.1007/s10498-019-09351-0