HR: 10:50h
AN: B12C-03    [Abstracts]
TI: MIBA-US: Temporal and Spatial Variation of Water Isotopes in Terrestrial Ecosystems Across the United States
AU: * Knohl, A
EM: alexander.knohl@ipw.agrl.ethz.ch
AF: ETH Zurich, Institute of Plant Sciences, Universitatsstr. 3, Zurich, 8092, Switzerland
AU: Tu, K P
EM: kevintu@berkeley.edu
AF: University of California, Berkeley, 4007 Valley Life Sciences Building, Berkeley, CA 94720, United States
AU: Boukili, V
EM: vschmidt@berkeley.edu
AF: University of California, Berkeley, 4007 Valley Life Sciences Building, Berkeley, CA 94720, United States
AU: Brooks, P D
EM: isotopes@uclink.berkeley.edu
AF: University of California, Berkeley, 4007 Valley Life Sciences Building, Berkeley, CA 94720, United States
AU: Mambelli, S
EM: mambelli@berkeley.edu
AF: University of California, Berkeley, 4007 Valley Life Sciences Building, Berkeley, CA 94720, United States
AU: Riley, W J
EM: wjriley@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States
AU: Dawson, T E
EM: tdawson@berkeley.edu
AF: University of California, Berkeley, 4007 Valley Life Sciences Building, Berkeley, CA 94720, United States
AU: MIBA-US site participants, a
AB: The oxygen and hydrogen isotope ratios of water in plants and soils are powerful tools for identifying the water sources in terrestrial ecosystems, partitioning evapotranspiration fluxes between evaporation and transpiration, and validating global climate models. To date, water isotope samples have only been collected at very few sites for any particular region or continent and often these collections are not made in coordination with important complementary observations such as eddy covariance measurements of latent and sensible heat fluxes and carbon dioxide exchange. We present data from 2005 and 2006 on the seasonal and interannual variation in the oxygen and hydrogen isotope ratios of leaf, stem and soil water across 12 eddy covariance flux sites comprising the MIBA (Moisture Isotopes in the Biosphere and Atmosphere) network within the continental United States. Values of δ¹⁸O in leaf, stem and soil water ranged from -10 to +30°, -16 to -2°, and -16 to 0°, respectively, reflecting the large variation across the major climatic and vegetation zones in the U.S. Stems were often more depleted than soils, but both approached the isotope ratios of local precipitation. As expected leaves were always more enriched than soil or stems and exhibited the greatest seasonal variation. Within each site, variation in δD and δ¹⁸O were strongly related, yet there were different "evaporation lines" for leaves, stems and soil. Differences in the slopes and intercepts of these evaporation lines appeared to be most strongly related to climatic differences among the sites. We demonstrate the utility of the MIBA data for constraining process-based models by comparing against response functions and spatial and temporal patters predicted by ISOLSM for the continental U.S. We also compare measurements against predictions by the widely used Craig-Gordon model of fractionation during evaporation.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0476 Plant ecology (1851)
DE: 0495 Water/energy interactions (1878)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting