A mesocosm study of oxygen and trace metal dynamics in sediment microniches of reactive organic material

Niklas Letho, Morten Larsen, Hao Zhang, Ronnie N. Glud, William Davison

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Abstract

Deposition of particulate organic matter (POM) induces diagenetic hot spots at the sediment-Water interface (SWI). Here we explore the effects of intensive POM degradation for metal mobilization at the SWI. By using a combined planar optode-DGT (diffusive gradient in thin-films) sensor we obtained simultaneous measurements of dissolved O2 and trace metal dynamics around an aggregate of reactive organic matter placed on the SWI of a sediment mesocosm. The aggregate induced a rapid, highly localized, decrease in O2 concentration, resulting in an anoxic feature at the SWI. Co-located with this feature, we observed intense Fe and Mn mobilization, removal of Co, Ni and Zn and found evidence for the concurrent release and precipitation of Pb within a small confined volume. We also identified two small microniches in the anoxic sediment below the SWI, defined by elevated trace metal mobilization.
Differences between the metal release rates in these two microniches indicate that they were formed by the mineralisation of different types of organic matter buried in the sediment. Our results provide direct empirical evidence for the potential importance of POM-induced reactive microniches when considering
the fluxes of metals from and within aquatic sediments, and suggest that other elements’ cycles may also be affected.Deposition of particulate organic matter (POM) induces diagenetic hot spots at the sediment-Water interface (SWI). Here we explore the effects of intensive POM degradation for metal mobilization at
the SWI. By using a combined planar optode-DGT (diffusive gradient in thin-films) sensor we obtained simultaneous measurements of dissolved O2 and trace metal dynamics around an aggregate of reactive organic matter placed on the SWI of a sediment mesocosm. The aggregate induced a rapid, highly localized, decrease in O2 concentration, resulting in an anoxic feature at the SWI. Co-located with this feature, we observed intense Fe and Mn mobilization, removal of Co, Ni and Zn and found evidence for the concurrent release and precipitation of Pb within a small confined volume. We also identified two
small microniches in the anoxic sediment below the SWI, defined by elevated trace metal mobilization. Differences between the metal release rates in these two microniches indicate that they were formed by the mineralisation of different types of organic matter buried in the sediment. Our results provide direct empirical evidence for the potential importance of POM-induced reactive microniches when considering the fluxes of metals from and within aquatic sediments, and suggest that other elements’ cycles may also be affected.
OriginalsprogEngelsk
Artikelnummer11369
TidsskriftScientific Reports
Vol/bind7
Udgave nummer1
Sider (fra-til)11369
Antal sider12
ISSN2045-2322
DOI
StatusUdgivet - 2017

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