HR: 09:15h
AN: B51E-06    [Abstracts]
TI: Geomorphic controls on the amount and quality of organic matter associated with mineral surfaces
AU: * Berhe, A
EM: aaberhe@nature.berkeley.edu
AF: Ecosystem Sciences Division, University of California at Berkeley, 151 Hilgard Hall # 3110, Berkeley, CA 94720-3110 United States
AU: Harden, J W
EM: jharden@usgs.gov
AF: Geological Division, US Geological Survey, 345 Middlefield Rd ms 962, Menlo Park, CA 94025 United States
AU: Torn, M S
EM: mstorn@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Rd., MS 90-1116, Berkeley, CA 94720 United States
AU: Burton, S D
EM: sarah.burton@pnl.gov
AF: EMSL user facilty, Pacific Northwest National Laboratory, P.O. Box 999, K8-98, Richland, WA 99352 United States
AU: Kleber, M
EM: mkleber@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, One Cyclotron Rd., MS 90-1116, Berkeley, CA 94720 United States
AU: Harte, J
EM: jharte@berkeley.edu
AF: Ecosystem Sciences Division, University of California at Berkeley, 151 Hilgard Hall # 3110, Berkeley, CA 94720-3110 United States
AB: Soil minerals play a critical role in stabilization of organic matter. In eroding slopes and depositional settings, the question of whether and to what extent the processes of soil erosion and deposition constitute a carbon dioxide sink is closely associated with stability of the mineral-organic matter associations. Here we use (a) density fractionation to determine the amount of soil organic carbon (SOC) that is associated with the mineral or heavy fraction (HF); (b) solid state 13C-NMR of bulk vs. mineral associated fraction to determine chemical composition of the organic constituents and (c) amount of crystalline primary, non-crystalline and organically complexed Fe and Al to estimate the soil's overall chemical protective capacity. We found that although around 99% of the soil is composed of HF, the SOC matter associated with it was less than 50% of bulk SOC and this amount increases with decreasing slope (higher in depositional basins). The soil organic matter associated with the HF was found to be more decomposed - as evidenced by the higher Alkyl:O-Alkyl ratio and aromaticity. Moreover, the average inventory of metal ions that promote stabilization of SOC through stable or meta-stable associations of SOC with the HF was found to be at least twice as much in the depositional basins compared to the eroding slopes. This study shows that the amount and quality of organic matter associated with HF changes significantly with topography and associated geomorphic processes such as erosion and deposition.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005