Determining the Oxygen Isotope Composition of Evapotranspiration Using Eddy Covariance

Timothy J Griffis; S. D. Sargent; X. Lee; J. M. Baker; J. Greene; M. Erickson; X. Zhang; K. Billmark; N. Schultz; W. Xiao; N. Hu

doi:10.1007/s10546-010-9529-5

Determining the Oxygen Isotope Composition of Evapotranspiration Using Eddy Covariance

Timothy J Griffis, S. D. Sargent, X. Lee, J. M. Baker, J. Greene, M. Erickson, X. Zhang, K. Billmark, N. Schultz, W. Xiao, N. Hu

Soil, Water, and Climate

Research output: Contribution to journal › Article › peer-review

48 Scopus citations

Abstract

The oxygen isotope composition of evapotranspiration (δ_F) represents an important tracer in the study of biosphere-atmosphere interactions, hydrology, paleoclimate, and carbon cycling. Here, we demonstrate direct measurement of δ_F based on the eddy-covariance and tunable diode laser spectroscopy (EC-TDL) techniques. Results are presented from laboratory experiments and field measurements in agricultural ecosystems. The field measurements were obtained during the growing seasons of 2008 and 2009. Water vapour mixing ratios (χ_w) and fluxes (F) were compared using EC-TDL and traditional eddy-covariance and infrared gas analyser techniques over a soybean canopy in 2008. The results indicate that χ_w and F agreed to within 1 and 6%, respectively. Measurements of δ_F above a corn canopy in 2009 revealed a diurnal pattern with an expected progressive ¹⁸O enrichment through the day ranging from about -20‰ before sunrise to about -5‰ in late afternoon. The isotopic composition of evapotranspiration was similar to the xylem water isotope composition (δ_x = -7.2‰) for short periods of time during 1400-1800 LST, indicating near steady-state conditions. Finally, the isotopic forcing values (I_F) revealed a diurnal pattern with mean maximum values of 0.09ms^-1‰ at midday. The I_F values could be described as an exponential relation of relative humidity confirming previous model calculations and measurements over a soybean canopy in 2006. These patterns and comparisons indicate that long-term continuous isotopic water vapour flux measurements based on the eddy-covariance technique are feasible and can provide new insights related to the oxygen isotope fractionation processes at the canopy scale.

Original language	English (US)
Pages (from-to)	307-326
Number of pages	20
Journal	Boundary-Layer Meteorology
Volume	137
Issue number	2
DOIs	https://doi.org/10.1007/s10546-010-9529-5
State	Published - 2010

Bibliographical note

Funding Information:
Acknowledgements This work is dedicated to the memory of Bert Tanner who helped pioneer tunable diode laser spectroscopy techniques for micrometeorological research. We express our sincere thanks to Jeremy Smith and Bill Breiter for their technical assistance in the lab and at the field site. Funding for this research has been provided by the National Science Foundation, ATM-0546476 (TG), ATM-0914473 (XL), DEB-0514908 (XL and TG), the Office of Science (BER) U.S. Department of Energy, DE-FG02-06ER64316 (TG and JB) and the College of Food, Agricultural and Natural Resource Sciences, at the University of Minnesota.

Keywords

Eddy covariance
Evapotranspiration
Isotopic discrimination
Isotopic forcing
Oxygen isotopes
Tunable diode laser spectroscopy
Water vapour

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@article{a1949420d9074e07a86070569d7486e1,

title = "Determining the Oxygen Isotope Composition of Evapotranspiration Using Eddy Covariance",

abstract = "The oxygen isotope composition of evapotranspiration (δF) represents an important tracer in the study of biosphere-atmosphere interactions, hydrology, paleoclimate, and carbon cycling. Here, we demonstrate direct measurement of δF based on the eddy-covariance and tunable diode laser spectroscopy (EC-TDL) techniques. Results are presented from laboratory experiments and field measurements in agricultural ecosystems. The field measurements were obtained during the growing seasons of 2008 and 2009. Water vapour mixing ratios (χw) and fluxes (F) were compared using EC-TDL and traditional eddy-covariance and infrared gas analyser techniques over a soybean canopy in 2008. The results indicate that χw and F agreed to within 1 and 6%, respectively. Measurements of δF above a corn canopy in 2009 revealed a diurnal pattern with an expected progressive 18O enrichment through the day ranging from about -20‰ before sunrise to about -5‰ in late afternoon. The isotopic composition of evapotranspiration was similar to the xylem water isotope composition (δx = -7.2‰) for short periods of time during 1400-1800 LST, indicating near steady-state conditions. Finally, the isotopic forcing values (IF) revealed a diurnal pattern with mean maximum values of 0.09ms-1‰ at midday. The IF values could be described as an exponential relation of relative humidity confirming previous model calculations and measurements over a soybean canopy in 2006. These patterns and comparisons indicate that long-term continuous isotopic water vapour flux measurements based on the eddy-covariance technique are feasible and can provide new insights related to the oxygen isotope fractionation processes at the canopy scale.",

keywords = "Eddy covariance, Evapotranspiration, Isotopic discrimination, Isotopic forcing, Oxygen isotopes, Tunable diode laser spectroscopy, Water vapour",

author = "Griffis, {Timothy J} and Sargent, {S. D.} and X. Lee and Baker, {J. M.} and J. Greene and M. Erickson and X. Zhang and K. Billmark and N. Schultz and W. Xiao and N. Hu",

note = "Funding Information: Acknowledgements This work is dedicated to the memory of Bert Tanner who helped pioneer tunable diode laser spectroscopy techniques for micrometeorological research. We express our sincere thanks to Jeremy Smith and Bill Breiter for their technical assistance in the lab and at the field site. Funding for this research has been provided by the National Science Foundation, ATM-0546476 (TG), ATM-0914473 (XL), DEB-0514908 (XL and TG), the Office of Science (BER) U.S. Department of Energy, DE-FG02-06ER64316 (TG and JB) and the College of Food, Agricultural and Natural Resource Sciences, at the University of Minnesota.",

year = "2010",

doi = "10.1007/s10546-010-9529-5",

language = "English (US)",

volume = "137",

pages = "307--326",

journal = "Boundary-Layer Meteorology",

issn = "0006-8314",

publisher = "Springer Netherlands",

number = "2",

}

TY - JOUR

T1 - Determining the Oxygen Isotope Composition of Evapotranspiration Using Eddy Covariance

AU - Griffis, Timothy J

AU - Sargent, S. D.

AU - Lee, X.

AU - Baker, J. M.

AU - Greene, J.

AU - Erickson, M.

AU - Zhang, X.

AU - Billmark, K.

AU - Schultz, N.

AU - Xiao, W.

AU - Hu, N.

N1 - Funding Information: Acknowledgements This work is dedicated to the memory of Bert Tanner who helped pioneer tunable diode laser spectroscopy techniques for micrometeorological research. We express our sincere thanks to Jeremy Smith and Bill Breiter for their technical assistance in the lab and at the field site. Funding for this research has been provided by the National Science Foundation, ATM-0546476 (TG), ATM-0914473 (XL), DEB-0514908 (XL and TG), the Office of Science (BER) U.S. Department of Energy, DE-FG02-06ER64316 (TG and JB) and the College of Food, Agricultural and Natural Resource Sciences, at the University of Minnesota.

PY - 2010

Y1 - 2010

N2 - The oxygen isotope composition of evapotranspiration (δF) represents an important tracer in the study of biosphere-atmosphere interactions, hydrology, paleoclimate, and carbon cycling. Here, we demonstrate direct measurement of δF based on the eddy-covariance and tunable diode laser spectroscopy (EC-TDL) techniques. Results are presented from laboratory experiments and field measurements in agricultural ecosystems. The field measurements were obtained during the growing seasons of 2008 and 2009. Water vapour mixing ratios (χw) and fluxes (F) were compared using EC-TDL and traditional eddy-covariance and infrared gas analyser techniques over a soybean canopy in 2008. The results indicate that χw and F agreed to within 1 and 6%, respectively. Measurements of δF above a corn canopy in 2009 revealed a diurnal pattern with an expected progressive 18O enrichment through the day ranging from about -20‰ before sunrise to about -5‰ in late afternoon. The isotopic composition of evapotranspiration was similar to the xylem water isotope composition (δx = -7.2‰) for short periods of time during 1400-1800 LST, indicating near steady-state conditions. Finally, the isotopic forcing values (IF) revealed a diurnal pattern with mean maximum values of 0.09ms-1‰ at midday. The IF values could be described as an exponential relation of relative humidity confirming previous model calculations and measurements over a soybean canopy in 2006. These patterns and comparisons indicate that long-term continuous isotopic water vapour flux measurements based on the eddy-covariance technique are feasible and can provide new insights related to the oxygen isotope fractionation processes at the canopy scale.

AB - The oxygen isotope composition of evapotranspiration (δF) represents an important tracer in the study of biosphere-atmosphere interactions, hydrology, paleoclimate, and carbon cycling. Here, we demonstrate direct measurement of δF based on the eddy-covariance and tunable diode laser spectroscopy (EC-TDL) techniques. Results are presented from laboratory experiments and field measurements in agricultural ecosystems. The field measurements were obtained during the growing seasons of 2008 and 2009. Water vapour mixing ratios (χw) and fluxes (F) were compared using EC-TDL and traditional eddy-covariance and infrared gas analyser techniques over a soybean canopy in 2008. The results indicate that χw and F agreed to within 1 and 6%, respectively. Measurements of δF above a corn canopy in 2009 revealed a diurnal pattern with an expected progressive 18O enrichment through the day ranging from about -20‰ before sunrise to about -5‰ in late afternoon. The isotopic composition of evapotranspiration was similar to the xylem water isotope composition (δx = -7.2‰) for short periods of time during 1400-1800 LST, indicating near steady-state conditions. Finally, the isotopic forcing values (IF) revealed a diurnal pattern with mean maximum values of 0.09ms-1‰ at midday. The IF values could be described as an exponential relation of relative humidity confirming previous model calculations and measurements over a soybean canopy in 2006. These patterns and comparisons indicate that long-term continuous isotopic water vapour flux measurements based on the eddy-covariance technique are feasible and can provide new insights related to the oxygen isotope fractionation processes at the canopy scale.

KW - Eddy covariance

KW - Evapotranspiration

KW - Isotopic discrimination

KW - Isotopic forcing

KW - Oxygen isotopes

KW - Tunable diode laser spectroscopy

KW - Water vapour

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