PARENT SESSION
Poster Session #42: Carbon Storage.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
86
Simulating 
18O of water and carbon dioxide at a tallgrass prairie in Oklahoma.
Riley, W.1, Still, C.2, Helliker, B.3, Ribas-Carbo, M.4, Burba, G.5, Verma, S.5, Torn, M.1, Berry, J.4, 1 2 3 4 5
ABSTRACT- The oxygen isotope composition (18O) of atmospheric CO2 is influenced by the 18O of various water pools that exchange oxygen with CO2. The most important of these pools, leaf and soil water, interact with photosynthetic and respiratory fluxes. We have developed a simulation framework that couples a soil transport model with a land surface model, and compared simulation results with isotopic measurements of water and CO2 gathered at a tallgrass prairie site in DOE's ARM Southern Great Plains region. Simulated soil moisture, temperature, and isotopic composition of plant and soil water compare well with measurements. Air samples collected on the night of May 9 show a depletion of 10‰ in the 18O of ecosystem (soil and plant) respiration over a 6-hour period. This pattern might be driven by a trend in the 18O of either plant or soil respiration or the relative contribution of these sources to the total flux. The model predictions of the 18O of soil-respired CO2 show variations of ~1-2‰ over this period and fairly constant flux partitioning, suggesting that the trend in isotopic composition of leaf-respired CO2 is due to replenishment of leaf water (which ends the day isotopically enriched by evaporation) with the source soil water.
KEY WORDS: modeling soil 18O