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A mechanistic model of H 2 18 O and C 18 OO fluxes between ecosystems and the atmosphere: Model description and sensitivity analyses
Author(s) -
Riley W. J.,
Still C. J.,
Torn M. S.,
Berry J. A.
Publication year - 2002
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2002gb001878
Subject(s) - soil water , flux (metallurgy) , atmosphere (unit) , environmental science , environmental chemistry , water vapor , atmospheric sciences , eddy covariance , carbon dioxide , surface water , chemistry , soil science , ecosystem , hydrology (agriculture) , ecology , geology , environmental engineering , physics , geotechnical engineering , organic chemistry , biology , thermodynamics
The concentration of 18 O in atmospheric CO 2 and H 2 O is a potentially powerful tracer of ecosystem carbon and water fluxes. In this paper we describe the development of an isotope model (ISOLSM) that simulates the 18 O content of canopy water vapor, leaf water, and vertically resolved soil water; leaf photosynthetic 18 OC 16 O (hereinafter C 18 OO) fluxes; CO 2 oxygen isotope exchanges with soil and leaf water; soil CO 2 and C 18 OO diffusive fluxes (including abiotic soil exchange); and ecosystem exchange of H 2 18 O and C 18 OO with the atmosphere. The isotope model is integrated into the land surface model LSM, but coupling with other models should be straightforward. We describe ISOLSM and apply it to evaluate (1) simplified methods of predicting the C 18 OO soil‐surface flux; (2) the impacts on the C 18 OO soil‐surface flux of the soil‐gas diffusion coefficient formulation, soil CO 2 source distribution, and rooting distribution; (3) the impacts on the C 18 OO fluxes of carbonic anhydrase (CA) activity in soil and leaves; and (4) the sensitivity of model predictions to the δ 18 O value of atmospheric water vapor and CO 2 . Previously published simplified models are unable to capture the seasonal and diurnal variations in the C 18 OO soil‐surface fluxes simulated by ISOLSM. Differences in the assumed soil CO 2 production and rooting depth profiles, carbonic anhydrase activity in soil and leaves, and the δ 18 O value of atmospheric water vapor have substantial impacts on the ecosystem CO 2 flux isotopic composition. We conclude that accurate prediction of C 18 OO ecosystem fluxes requires careful representation of H 2 18 O and C 18 OO exchanges and transport in soils and plants.