HR: 1330h
AN: B42A-0945    [PDF]
TI: Process Based Belowground Carbon Dioxide Modeling in a Desert Ecosystem
AU: * Zobitz, J M
EM: zobitz@math.utah.edu
AF: University of Utah, Department of Mathematics, 155 South 1400 East, Salt Lake City, UT 84112-0090 United States
AU: Bowling, D R
EM: bowling@biology.utah.edu
AF: University of Utah, Department of Biology, 257 South 1400 E, Salt Lake City, UT 84112-0840 United States
AB: We describe a study to integrate and assess biological and physical processes that govern belowground carbon dioxide levels at a semi-arid grassland near Canyonlands National Park. Carbon dioxide concentrations were measured every 30 minutes at 5 and 15 cm depth within the rooting zones of the two dominant grass species, Stipa hymenoides and Hilaria jamesii, as well as the interspace between the two. For Stipa hymenoides at 5 cm, a rain event caused belowground carbon dioxide levels to rise from 600 ppm to 2000 ppm with a response time of 8 hours, with a gradual return to quasi-steady state levels in subsequent days. A similar response was observed for H. jamesii. We developed and simulated a one-dimensional diffusion model with a production term for various types of CO$_{2}$ production from the literature (either constant with increasing depth or a process based source). The process based production considered microbial and root respiration as well as the temperature dependence of soil respiration. Model inputs included volumetric soil water content, temperature and bulk density. Incorporating a process based production term led to high correlation between measured and modeled CO$_{2}$ concentrations (r$^{2}$ as high as 0.92). Our results indicate that carbon dioxide levels increased during rain events due to physical (not biological) processes as the soil saturated with water, and CO$_{2}$ molecules diffused more slowly from the soil.
DE: 3200 MATHEMATICAL GEOPHYSICS (New field)
DE: 3210 Modeling
DE: 3230 Numerical solutions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting