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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-296
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-296
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Sep 2020

14 Sep 2020

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A revised version of this preprint is currently under review for the journal BG.

The effect of organic matter (OM) quality on the redox stability of OM-Fe association in freshwater sediments

Nana O.-A. Osafo1,2, Jiří Jan1,3, Petr Porcal1,2,3, Daniel A. Petrash1,4, and Jakub Borovec1,2,3 Nana O.-A. Osafo et al.
  • 1Soil and Water Research Infrastructure, Biology Centre CAS, České Budějovice, Czech Republic
  • 2Faculty of Science, University of South Bohemia, České Budějovice, 370 05, Czech Republic
  • 3Institute of Hydrobiology, Biology Centre CAS, České Budějovice, 370 05, Czech Republic
  • 4Department of Environmental Geochemistry andBiogeochemistry, Czech Geological Survey, Prague, 152 00, Czech Republic

Abstract. Redox sensitive iron (Fe) oxyhydroxides participate in the biogeochemical cycling of nutrients and trace metals. Their co-precipitation with organic matter (OM) leads to environmentally relevant OM-Fe associations. The stability of OM in such associations is still uncertain. It has been proposed that OM either increases the stability of the complex against reductive dissolution or enhance the dissolution (both abiotic and biotically) of Fe oxyhydroxides. The OM character, in terms of specific functional groups binding to Fe, could be a critical factor determining the fate and stability of OM-Fe. Here, sediment samples from a vertical profile of a mesotrophic freshwater reservoir were treated using a sequential extraction scheme designed to distinguish Fe oxyhydroxides of different redox reactivity based on dissolution kinetics. To assess the reactivity and stability of the complexes, special attention was payed to the determination of redox active vs. stable fractions of Fe and the corresponding dissolved organic matter (DOM) components sequentially extracted. The quality of the extracted DOM was evaluated using UV-VIS and fluorescence spectroscopy together with the PARAFAC model. A selectivity model was used to ascertain the quality of OM preferentially associated with the different redox stable Fe oxyhydroxides. Accordingly, we found that humic-like substances render the OM-Fe associations redox labile, while non-humic substances enhance the stability of the associations. These findings improve the understanding required for predicting the fate of OM-Fe associations in freshwater sediments with different organic matter sources and characters.

Nana O.-A. Osafo et al.

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Nana O.-A. Osafo et al.

Nana O.-A. Osafo et al.

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Short summary
We investigated the role that OM quality plays in the stability of the OM-Fe association in freshwater sediments. It was found that non-humic components enhance OM-Fe stability, while humic components enhance the reductive dissolution of OM-Fe. This information is useful for predicting the fate of OM-Fe in freshwater systems with discrete sources of OM. Stable OM-Fe complexes improve aqueous environments by reducing the release of greenhouse gases, heavy metals and excess nutrients, such as P.
We investigated the role that OM quality plays in the stability of the OM-Fe association in...
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