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| Titel |
Influence of adsorption versus coprecipitation on the retention of rice
straw-derived dissolved organic carbon and subsequent reducibility of Fe-DOC
systems |
| VerfasserIn |
Marcella Sodano, Cristina Lerda, Maria Martin, Luisella Celi, Daniel Said-Pullicino |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127866
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| Publikation (Nr.) |
 EGU/EGU2016-7789.pdf |
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| Zusammenfassung |
| The dissimilatory reduction of Fe oxides is the main organic C-consuming process in paddy
soils under anoxic conditions. The contribution of Fe(III) reduction to anaerobic C
mineralization depends on many factors, but most importantly on the bioavailability of labile
organic matter and a reducible Fe pool as electron donors and acceptors, respectively. On the
other hand, the strong affinity of these minerals for organic matter and their capability of
protecting it against microbial decomposition is well known. Natural Fe oxides in these soils
may therefore play a key role in determining the C source/sink functions of these
agro-ecosystems.
Apart from contributing to C stabilization, the interaction between Fe oxides and
dissolved organic C (DOC) may influence the structure and reactivity of these natural oxides,
and selectively influence the chemical properties of DOC. Indeed, Fe-DOC associations may
not only reduce the availability of DOC, but may also limit the microbial reduction of Fe
oxides under anoxic conditions. In fact, the accessibility of these minerals to microorganisms,
extracellular enzymes, redox active shuttling compound or reducing agents may
be impeded by the presence of sorbed organic matter. In soils that are regularly
subjected to fluctuations in redox conditions the interaction between DOC and Fe
oxides may not only involve organic coatings on mineral surfaces, but also Fe-DOC
coprecipitates that form during the rapid oxidation of soil solutions containing important
amounts of DOC and Fe(II). However, little is known on how these processes influence
DOC retention, and the structure and subsequent reducibility of these Fe-DOC
associations.
We hypothesized that the nature and extent of the interaction between DOC and Fe oxides
may influence the accessibility of the bioavailable Fe pool and consequently its reducibility.
We tested this hypothesis by synthesizing a series of Fe-DOC systems with increasing C:Fe
ratios prepared by either surface adsorption or coprecipitation, DOC was obtained by
incubating a suspension of rice straw in water (straw-solution ratio of 1:30) under oxic
conditions at 25˚ C for 30 days to simulate the decomposition of rice straw in the field.
Increasing amounts of DOC were equilibrated (pH = 6) with a known mass of ferrihydrite
(initial molar C:Fe ratios of 1, 5 and 10) to obtain surface coated Fe-DOC systems with
increasing C loading. On the other hand, coprecipitates with similar initial C:Fe ratios were
obtained by oxidation of a Fe(II) solution in the presence of increasing amounts of DOC at
pH = 6. A natural Fe-DOC coprecipitate was also obtained by in situ sampling of a paddy soil
solution from the topsoil during a cropping season, and subsequent oxidation in the
laboratory. The surface and chemical properties of all substrates were subsequently
evaluated and compared. We hereby present the first results of the influence of
adsorption vs coprecipitation on the selective retention of DOC, structure and surface
charge, as well as their susceptibility to chemical reduction with ascorbic acid. |
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