HR: 09:45h
AN: B51E-08    [Abstracts]
TI: Multi-Year Dynamics of Upland-Oak Forest Organic Horizons: Observations Based on a Unique 14C-Tracer and a Mechanistic Model
AU: * Hanson, P J
EM: hansonpj@ornl.gov
AF: Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, TN 37831-6422 United States
AU: Trumbore, S E
EM: setrumbo@uci.edu
AF: University of California, Irvine, 19172 Jamboree Rowland Hall 290, Irvine, CA 92697-3100 United States
AU: Swanston, C W
EM: swanston@llnl.gov
AF: Lawrence Livermore National Laboratory, Center for Accelerator Mass Spectrometry P.O. Box 808, L-397, Livermore, CA 94551 United States
AU: Garten, C T
EM: gartenctjr@ornl.gov
AF: Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, TN 37831-6422 United States
AU: Callaham, M A
EM: mcallaham@fs.fed.us
AF: USDA Forest Service, Southern Research Station 320 Green Street, Athens, GA 30602 United States
AU: Jardine, P
EM: jardinepm@ornl.gov
AF: Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, TN 37831-6422 United States
AU: Post, W M
EM: postwmiii@ornl.gov
AF: Oak Ridge National Laboratory, Bethel Valley Road, Oak Ridge, TN 37831-6422 United States
AB: The Enriched Background Isotope Study (EBIS) was initiated on the Oak Ridge Reservation (ORR) near Oak Ridge, Tennessee in the fall of 2000 to collect and utilize unique 14C-labeled leaf litter for a multi-year, litter-replacement experiment. The goal of EBIS is to understand key mechanisms driving soil carbon cycling and to develop robust models for describing the fate and accumulation of carbon within organic and mineral soils of oak-dominated forests. EBIS uses a combination of high-to-low gradients of 14C-signatures within the soils, roots, and leaf litter across the ORR together with manipulated 14C-litter enrichments or dilutions to track litter-layer C movement through the organic and mineral soil horizons. Through 3-years of defined 14C-litter-additions, we have no evidence that canopy leaf litter is a near-term source of mineral soil carbon. Rather, the downward migration of leaf-litter carbon is driven by annual layering and gravity-induced packing of organic matter to the surface of the mineral horizons. The well-drained, acid soils of these upland sites studies support only low earthworm populations and, therefore, bioturbation is an ineffective mechanism for C transport in this ecosystem. Standard multi-component isotopic mixing models were shown to be inadequate for the prediction of the observed 14C-distributions within the organic horizons following multiple year litter additions. Models containing expanded spatial and temporal details were needed to successfully capture organic-layer C turnover and transport through the organic layers of these soils. Critical details required to model 14C-dynamics in these soils include: the tracking of individual litter-layer cohorts over time, daily time-step simulations of intra-annual litter and humus decomposition as a function of temperature and water content, and the simulation of DOC leaching as a mass-loss and differential 14C-transport process. Within only a short time span (3 to 4 years), the EBIS is providing a robust means to quantify rates of soil carbon inputs, turnover and accumulation applicable to both short- (years) and long-term (decades to century) extrapolations.
UR: http://ebis.ornl.gov
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0466 Modeling
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005