A mechanistic model of H218O and C18OO fluxes between ecosystems and the atmosphere: Model description and sensitivity analyses
Tóm tắt
The concentration of 18O in atmospheric CO2 and H2O 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 18O content of canopy water vapor, leaf water, and vertically resolved soil water; leaf photosynthetic 18OC16O (hereinafter C18OO) fluxes; CO2 oxygen isotope exchanges with soil and leaf water; soil CO2 and C18OO diffusive fluxes (including abiotic soil exchange); and ecosystem exchange of H218O and C18OO 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 C18OO soil‐surface flux; (2) the impacts on the C18OO soil‐surface flux of the soil‐gas diffusion coefficient formulation, soil CO2 source distribution, and rooting distribution; (3) the impacts on the C18OO fluxes of carbonic anhydrase (CA) activity in soil and leaves; and (4) the sensitivity of model predictions to the δ18O value of atmospheric water vapor and CO2. Previously published simplified models are unable to capture the seasonal and diurnal variations in the C18OO soil‐surface fluxes simulated by ISOLSM. Differences in the assumed soil CO2 production and rooting depth profiles, carbonic anhydrase activity in soil and leaves, and the δ18O value of atmospheric water vapor have substantial impacts on the ecosystem CO2 flux isotopic composition. We conclude that accurate prediction of C18OO ecosystem fluxes requires careful representation of H218O and C18OO exchanges and transport in soils and plants.
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Tài liệu tham khảo
Bonan G. A land surface model (LSM version 1.0) for ecological hydrological and atmospheric studies: Technical description and user's guide TN‐417+STR Natl. Cent. for Atmos. Res. Boulder Colo. 1996.
Brenninkmeier C., 1983, Oxygen isotope fractionation between CO2 and H2O, Isot. Geosci., 1, 181
Craig H., 1965, Stable Isotopes in Oceanographic Studies and Paleotemperatures, 9
Dickinson R. E. A.Henderson‐Sellers P. J.Kennedy andM. F.Wilson Biosphere/atmosphere transfer scheme (BATS) for the NCAR community climate model NCAR Tech. Note TN275 Natl. Cent. for Atmos. Res. Boulder Colo. 1986.
Hesterburg R., 1991, Production and stable isotopic composition of CO2 in soil near Bern, Switzerland. Tellus, Ser. B, 43, 197, 10.3402/tellusb.v43i2.15264
Noone D. C. C. J.Still andW. J.Riley Diagnosing impacts of changes in the biosphere by modeling 18O of atmospheric CO2 with a general circulation model paper presented at Sixth International CO2 Conference Cent. of Atmos. and Oceanic Stud. Grad. School of Sci. Tohoku Univ. Sendai Japan 2001.
Press W., 1989, Numerical Recipes (FORTRAN)
Skirrow G., 1975, Chemical Oceanography, 1
Tans P. P., Oxygen isotopic equilibrium between carbon dioxide and water in soils, Tellus, Ser. B, 50, 163, 10.3402/tellusb.v50i2.16094
Warrick A. W., 2002, Soil Physics Companion