Journal
AGRICULTURAL AND FOREST METEOROLOGY
Volume 263, Issue -, Pages 346-361Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.agrformet.2018.09.005
Keywords
Evapotranspiration partitioning; Stable isotope; Two-source mixing model; Craig-Gordon model; Keeling plot approach; Kinetic fractionation factor
Categories
Funding
- National Key R&D Program of China [2017YFC0503904]
- National Natural Science Foundation of China [41475141, 41505005]
- U.S. National Science Foundation [1520684]
- Ministry of Education of China [PCSIRT]
- Priority Academic Program Development of Jiangsu Higher Education Institutions [PAPD]
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Terrestrial evapotranspiration (ET) consists of evaporation (E) from canopy-intercepted water, evaporation from soil and open water, and transpiration (T) from plants. Determining the contribution of T to ET (hereafter T/ET) is challenging but necessary for improving water resource management and understanding the response of ecosystem water/energy budgets to climate change. Water stable isotopes provide unique information on ecosystem processes and can be used to partition evapotranspiration at the ecosystem scale. In this paper, the aim is to review the state of the science on the isotope method for ecosystem ET partitioning, with a focus on uncertainties related to estimating the three isotopic end members (isotopic compositions of ET, T and E). The published results show larger T/ET variations during the growing season in croplands due to water management and rapid leaf area index (LAI) changes compared to in other natural ecosystems. Another robust result is that on average, grasslands have lower T/ET than woodlands. The isotopic composition of ET is provided by measurements, while the isotopic compositions of T and E are generally obtained using the Craig-Gordon model with appropriate modifications. Significant advances have been made in the techniques for estimating the isotopic composition of ET, largely due to the availability of fast-responding instruments for in situ measurements of water vapor isotopic composition. The largest source of uncertainty in the T/ET estimation comes from uncertainties in the isotopic composition of ET. Based on published results of the uncertainties in the three end members, we estimate that a typical uncertainty range for T/ET is +/- 21% (one standard deviation). This review provides background information and theoretical references for studies on isotopic hydrology, ecosystem processes and climate change.
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