HR: 15:25h
AN: B53D-07 [Abstracts]
TI: The Biogeochemistry of Soil Fe-Redox Cycling: Is Mottling the Visible End Member of Series of
Ubiquitous Organo-Fe Reactions?
AU: * Richter, D d
EM: drichter@duke.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Durham, NC 27708
United States
AU: Fimmen, R
EM: rlf@duke.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Durham, NC 27708
United States
AU: Vasudevan, D
EM: dvasudev@bowdoin.edu
AF: Bowdoin College, Chemistry Department, Brunzwick, ME 04011
United States
AB:
The redox cycling of iron is well studied in aquatic systems and in soils that are consistently or frequently anaerobic.
Such studies describe a prominent redox cycling of Fe, complete with root-associated Fe-oxidizing bacteria, development of
"iron plac" surrounding roots, and the production of enormous amounts of acidity that can weather minerals in a process known
as ferrolysis. The objective of our research was to investigate the biogeochemical details of a Fe-redox cycle in a
generally well oxygenated, upland soil which has prominent mottles at 1.2 to 1.5-m depth. Within the B horizon of this
Kanhapludult soil, we found gray (5Y 8/2) microsites proliferated with roots and mycorrhizal hyphae, enriched in kaolinite
(0.73g clay/g soil) and organic carbon with relatively modern 14C age, but relatively low in Fe oxides (5mg DCB-Fe/g soil).
These gray microsites contrasted with those that were orange (2.5 YR), which had virtually no roots or fungal hyphae,
relatively low clay (0.27g clay/g soil) and organic carbon (which had relatively old 14C age), but remarkably high contents
of crystalline Fe oxides (37mg DCB-Fe/g soil). Quinoid compounds were present in both microsites suggesting the possibility
of redox reactions with polyphenols. This chemical system is suggested to be biogenically initiated by Rhizosphere additions
of organic reductants apparently initiates the Fe-redox cycle, which mobilizes enormous quantities of Fe, which upon
oxidation generates significant fluxes of protons that are potentially available for mineral weathering. Such systems may be
much more common and significant than we appreciate.
DE: 1045 Low-temperature geochemistry
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting