Celi, L.

Lerda, C.

Magnacca, G.

Martin, M.

Nistic&#242

Said-Pullicino, D.

Sodano, M.

English

Nisticò, R.

Institutional Research Information System University of Turin

Geophysical Research AbstractsVol. 20, EGU2018-3906, 2018EGU General Assembly 2018© Author(s) 2018. CC Attribution 4.0 license.Dissolved organic carbon retention by coprecipitation during theoxidation of ferrous ironMarcella Sodano (1), Maria Martin (1), Cristina Lerda (1), Roberto Nisticò (2), Giuliana Magnacca (3), LuisellaCeli (1), and Daniel Said-Pullicino (1)(1) University of Torino, Dept. of Agricultural, Forest and Food Sciences, Grugliasco, Italy, (2) Politecnico di Torino, Dept. ofApplied Science and Technology, Torino, Italy , (3) University of Torino, Dept. of Chemistry, Torino, ItalyAlthough the importance of Fe (hydr)oxides for soil organic matter (OM) stabilization and C retention by surfaceadsorption is well known, only recently has coprecipitation been recognized as an important process responsiblefor C storage in hydromorphic soils, such as rice paddy soils. Under periodic fluctuations in redox conditions theinteraction between dissolved organic carbon (DOC) and Fe (hydr)oxides may not only involve organic coatingson mineral surfaces, but also Fe-DOC coprecipitates that form during the oxidation of soil solutions containingimportant amounts of DOC and Fe2+.The aim of this work was to provide new insights into the mechanisms involved, and the amount and selectivityof C retained during the coprecipitation process. A series of Fe-OM associations with increasing C loading wassynthesized at pH 6 by surface adsorption or coprecipitation (oxidation of ferrous iron) utilizing rice-straw deriveddissolved organic matter. The kinetics of Fe2+ oxidation and complexation, and the total and selective retentionof DOC during the coprecipitation process were evaluated. Moreover, synthesized associations, as well as a fieldcoprecipitate collected in situ from a paddy soil, were studied by X-ray diffraction, N2 gas adsorption-desorptionisotherms, electrophoretic mobility measurements and thermogravimetric analyses.Coprecipitation resulted in higher organic C contents (49-213 mg g−1) with respect to adsorbed systems (18-47mg g−1), and favoured the inclusion of OM within highly aggregated associations having particularly low BETspecific surface areas. Coprecipitates sampled in situ also showed a similar retention of organic C confirming thatthis process may contribute significantly to the OM stabilization in paddy topsoils. The mechanisms involved inthe retention of straw-derived DOM during coprecipitation were shown to be strongly dependent on C/Fe ratioof the solution. Although the overall coprecipitation process was highly selective for aromatic constituents, ini-tial complexation of Fe2+ and precipitation as C-rich metal salts involved the selective interaction with aliphaticcarboxylic constituents. The contribution of the latter mechanism to total C retention during coprecipitation wasshown to increase with increasing solution C/Fe ratios. These aliphatic complexes formed during coprecipitationmay play an important, though often underestimated, role in C stabilization in hydromorphic. The process-relatedselectivity of specific constituents of DOM during coprecipitation highlights the involvement of specific mecha-nisms, i.e. complexation, adsorption, salt precipitation, while ruling out non-selective, physical occlusion of OMwithin the forming coprecipitate.

Dissolved organic carbon retention by coprecipitation during the oxidation of ferrous iron

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Dissolved organic carbon retention by coprecipitation during the oxidation of ferrous iron

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