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Purpose <p>The stability of organic matter (OM) in freshwater sediments is largely determined by its interactions with iron (Fe) oxyhydroxides, which play a crucial role in carbon (C) and Fe cycling, and in regulating nutrient dynamics in soils and sediments. However, under anoxic conditions, different solubility patterns can be observed for reasons that are not yet fully understood. This study aims to elucidate the influence of OM source, concentration, pH, and association mechanisms (coprecipitation vs. sorption) on OM-Fe stability.</p> Methods <p>Four natural OM sources (NOM) were used to form OM-Fe associations. These sources were used for coprecipitation and sorption of dissolved OM (DOM) onto Fe oxyhydroxides at pH 5 and 7. The experiment was carried out with four different DOC: Fe molar ratios. The stability of the products was evaluated by monitoring the dissolution kinetics of sodium dithionite and the release of Fe<sup>2+</sup>, dissolved organic carbon (DOC), and changes in DOM composition.</p> Results <p>Coprecipitation was more efficient than sorption for DOC retention in Fe oxyhydroxides, especially at higher DOC: Fe ratios. Dissolution was about four times slower for coprecipitated OM-Fe compounds than for sorbed ones. For all NOM sources and mechanisms, amidic (proteinaceous) OM fractions were more stable, while aromatic, phenolic, and cellulosic OM were more soluble. <i>Typha</i> biomass showed the highest amidic fraction, while peat was the lowest.</p> Conclusion <p>These results highlight the role of OM composition in OM-Fe stability and its impact on the stabilization of Fe in freshwater sediments. The trophic level of the aquatic ecosystem and the proportion of the littoral zone can significantly affect the Fe cycle.</p>

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Factors affecting organic matter association with iron under reducing conditions

  • 期刊论文

  • 发表日期：

    2025年10月9日

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  • Nana O -A Osafo,
  • Jiří Jan,
  • Petr Porcal,
  • Jakub Borovec

摘要

Purpose

The stability of organic matter (OM) in freshwater sediments is largely determined by its interactions with iron (Fe) oxyhydroxides, which play a crucial role in carbon (C) and Fe cycling, and in regulating nutrient dynamics in soils and sediments. However, under anoxic conditions, different solubility patterns can be observed for reasons that are not yet fully understood. This study aims to elucidate the influence of OM source, concentration, pH, and association mechanisms (coprecipitation vs. sorption) on OM-Fe stability.

Methods

Four natural OM sources (NOM) were used to form OM-Fe associations. These sources were used for coprecipitation and sorption of dissolved OM (DOM) onto Fe oxyhydroxides at pH 5 and 7. The experiment was carried out with four different DOC: Fe molar ratios. The stability of the products was evaluated by monitoring the dissolution kinetics of sodium dithionite and the release of Fe2+, dissolved organic carbon (DOC), and changes in DOM composition.

Results

Coprecipitation was more efficient than sorption for DOC retention in Fe oxyhydroxides, especially at higher DOC: Fe ratios. Dissolution was about four times slower for coprecipitated OM-Fe compounds than for sorbed ones. For all NOM sources and mechanisms, amidic (proteinaceous) OM fractions were more stable, while aromatic, phenolic, and cellulosic OM were more soluble. Typha biomass showed the highest amidic fraction, while peat was the lowest.

Conclusion

These results highlight the role of OM composition in OM-Fe stability and its impact on the stabilization of Fe in freshwater sediments. The trophic level of the aquatic ecosystem and the proportion of the littoral zone can significantly affect the Fe cycle.