HR: 11:05h
AN: B52A-03 INVITED     [Abstracts]
TI: The Stable Soil Organic Carbon Pool: Small Molecules In Small Pores?
AU: * Guggenberger, G
EM: guggenberger@landw.uni-halle.de
AF: Martin Luther University Halle-Wittenberg, Institute of Soil Science and Plant Nutrition, Halle, 06099 Germany
AB: For a long-term sequestration of carbon in soil the stable soil organic carbon pool is most important. Sorption to mineral phases is considered as a key process in the formation of this pool. This paper aims at presenting evidence on the location where stable carbon is found in soil, the type of bonding by which organic matter is stabilized, and the possible source of the stabilized organic matter. To approach this a combination of 14C AMS measurements, microspectroscopic techniques, BET surface measurements, stable isotope analysis, and molecular techniques was employed. Analyses were carried out on the mineral-associated heavy fraction of the soil, and soil and mineral samples used for dissolved organic matter sorption/desorption experiments and treatment with sodium hypochloride. The results suggest that parts of the mineral-associated organic matter is located on plain mineral surfaces while others can be found associated with meso- and micropores of minerals, in particular of high-porosity Fe- and Al-oxi/hydroxides. In these pore mouths, the organic matter is stabilized by strong chemisorptive bondings (ligand exchange) which may act three dimensionally. The mean turnover time of this type of organic carbon is in the range of several thousand years. There is evidence that (dissolved) organic matter sorbed into these pore mouths soon after formation of these pedogenic minerals will be barely accessible for microbial decomposition during the life time of the minerals themselves. This intimate association of organic matter with minerals may be responsible for the slow turnover times. But likewise this complicates extremely the characterization of the type of organic matter sorbed. So results obtained from the structural characterization of the dissolv ed organic matter being sorbed using IR, NMR, AFM, and degradative techniques are often not in concordance with the structure of the organic matter sorbed into the pore mouths of the minerals. However, results gave rise to the concept that small, flexible and highly charged molecules are primarily involved in this type of stabilization.
DE: 1694 Instruments and techniques
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting