Evapotranspiration components determined by stable isotope, sap flow and eddy covariance techniques

Williams, David G.; Cable, William; Hultine, Kevin R.; Hoedjes, J.C.B.; Yépez, Enrico A.; Simonneaux, Vincent; Er‐Raki, Salah; Boulet, G.; Bruin, H.A.R. de; Chehbouni, Abdelghani; Hartogensis, Oscar; Timouk, Frank

doi:10.1016/j.agrformet.2004.04.008

Cited by 418 publications

(344 citation statements)

References 52 publications

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“…Bare-soil evaporation was not measured independently in this study owing to our lack of recording microlysimeters and the difficulties in obtaining a spatially-representative estimate for an entire growing season from small-scale micro-lysimeters. Nevertheless, it is a common practice to estimate a component flux as a residual (Barbour et al, 2005;Dugas et al, 1996;Scott et al, 2003;Williams et al, 2004), and we can check whether the independent estimates of T and ET are compatible. As the time from the last precipitation event increased in an interstorm period, it is reasonable to expect that T increasingly dominates an ET signal because surface soil rapidly dries, increasing the resistance to water flux from deeper layers despite a large demand from the atmosphere (Wythers et al, 1999).…”

Section: Transpiration and Evaporationmentioning

confidence: 99%

“…Ecosystem ET has been partitioned into bare-soil evaporation, interception reservoir evaporation, and transpiration from the overstory and understory vegetation (e.g. Barbour et al, 2005;Dugas et al, 1996;Ham et al, 1990;Scott et al, 2003;Williams et al, 2004;Yepez et al, 2003). Often, these studies have been over relatively short time periods (days to weeks) and data for woody plant encroached areas are sparse.…”

Section: Introductionmentioning

confidence: 99%

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Partitioning of evapotranspiration and its relation to carbon dioxide exchange in a Chihuahuan Desert shrubland

Scott

Huxman

Cable

et al. 2006

Hydrological Processes

189

154

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Key to evaluating the consequences of woody plant encroachment on water and carbon cycling in semiarid ecosystems is a mechanistic understanding of how biological and non-biological processes influence water loss to the atmosphere. To better understand how precipitation is partitioned into the components of evapotranspiration (bare-soil evaporation and plant transpiration) and their relationship to plant uptake of carbon dioxide (CO 2 ) as well as ecosystem respiratory efflux, we measured whole plant transpiration, evapotranspiration, and CO 2 fluxes over the course of a growing season at a semiarid Chihuahuan Desert shrubland site in south-eastern Arizona. Whole plant transpiration was measured using the heat balance sap-flow method, while evapotranspiration and net ecosystem exchange (NEE) of CO 2 were quantified using the Bowen ratio technique.Before the summer rainy season began, all water and CO 2 fluxes were small. At the onset of the rainy season, evapotranspiration was dominated by evaporation and CO 2 fluxes were dominated by respiration as it took approximately 10 days for the shrubs to respond to the higher soil moisture content. During the growing season, periods immediately following rain events (<2 days) were dominated by evaporation and respiration while transpiration and CO 2 uptake peaked during the interstorm periods. The surface of the coarse, well-drained soils dried quickly, rapidly reducing evaporation. Overall, the ratio of total transpiration to evapotranspiration was 58%, but it was around 70% during the months when the plants were active. Peak respiration responses following rain events generally lagged after the evaporation peak by a couple of days and were better correlated with transpiration. Transpiration and CO 2 uptake also decayed rather quickly during interstorm periods, indicating that optimal plant soil moisture conditions were rarely encountered. NEE of CO 2 was increasingly more negative as the growing season progressed, indicating a greater net uptake of CO 2 and greater water use efficiency due mainly to decreases in respiration.

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Section: Transpiration and Evaporationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Partitioning of evapotranspiration and its relation to carbon dioxide exchange in a Chihuahuan Desert shrubland

Scott

Huxman

Cable

et al. 2006

Hydrological Processes

189

154

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“…Although calibration focused on the wound width, it will also account for possible uncertainties in sapwood moisture content, sapwood density and the upscaling from individual trees to orchard scale. Similar sap flow calibrations have been performed by Williams et al (2004) in an olive orchard assuming evaporation from the soil is negligible and by using a combination (Köstner et al 1992). The advantage of this method of calibration is that it can be performed in field without the use of weighing lysimeters, which although ideal, are expensive to install and require a number of years for the tree planted in the lysimeter to reach an adequate size for measurement.…”

Section: Sap Flow and Transpirationmentioning

confidence: 95%

Crop coefficient approaches based on fixed estimates of leaf resistance are not appropriate for estimating water use of citrus

et al. 2014

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The estimation of crop water use is critical for accurate irrigation scheduling and water licenses. However, the direct measurement of crop water use is too expensive and time consuming to be performed under all possible conditions, which necessitates the use of water use models. The FAO-56 procedure is a simple, convenient and reproducible method, but as canopy cover and height vary greatly among different orchards, crop coefficients may not be readily transferrable from one orchard to another. Allen and Pereira (2009) therefore incorporated a procedure into the FAO-56 approach which estimates crop coefficients based on a physical description of the vegetation and an adjustment for relative crop stomatal control over transpiration. Transpiration crop coefficients derived using this procedure and fixed values for citrus, did not provide good estimates of water use in three citrus orchards. However, when mean monthly leaf resistance was taken into account, 1 good agreement was found with measured values. A relationship between monthly reference evapotranspiration and mean leaf resistance provided a means of estimating mean leaf resistance which estimated transpiration crop coefficients with a reasonable degree of accuracy. The use of a dynamic estimate of mean leaf resistance therefore provided reasonable estimates of transpiration in citrus.

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“…Although such information provides a powerful constraint on model construction and water management, our ability to quantify the T from ET remains limited, since it is difficult to measure independently at the ecosystem scale 2) . Historically, eddy covariance based technique approaches have been used to partition ET fluxes, however, it is always derived by incorporating measurements of a single reference height above the vegetation and some empirical formulas, T and E is often not independently verified with measurements.…”

Section: Introductionmentioning

confidence: 99%

“…Historically, eddy covariance based technique approaches have been used to partition ET fluxes, however, it is always derived by incorporating measurements of a single reference height above the vegetation and some empirical formulas, T and E is often not independently verified with measurements. Although recently the transpiration measurement by sap flux sensor, evaporation measurement by soil chamber have been combined into the eddy covariance, a complicating issue is the mismatch in footprints between the landscape-scale fluxes derived by eddy covariance and the more localized fluxes obtained by these instruments 1), 2) . Not long ago, measurements of the stable isotope have been utilized for the purpose of ET partitioning.…”

Section: Introductionmentioning

confidence: 99%

Investigating Vegetation-Atmosphere Water Exchange by Using High Frequency Spectroscopy Vapor Isotope Observations

et al. 2014

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In this study, we first time test the feasibility of partitioning evapotranspiration using high frequency in-situ measurements of water vapor isotopes in a paddy field, Mase, Japan. By combining isotope measurements with Keeling plot method and Craig-Gordon model, transpiration is found representing more than 90% of the total evapotranspiration flux at the daily scale. However, the errors in this method could not be neglected. The primary cause of these errors is demonstrated to be the underestimate of water evaporation estimated by Craig-Gordon model. The variation of measured water vapor d-excess is significantly affected by the dominant components of evapotranspiration on diurnal time scale, it is suggested that the vegetation play a significant role in land surface water exchange process.

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Evapotranspiration components determined by stable isotope, sap flow and eddy covariance techniques

Cited by 418 publications

References 52 publications

Partitioning of evapotranspiration and its relation to carbon dioxide exchange in a Chihuahuan Desert shrubland

Partitioning of evapotranspiration and its relation to carbon dioxide exchange in a Chihuahuan Desert shrubland

Crop coefficient approaches based on fixed estimates of leaf resistance are not appropriate for estimating water use of citrus

Investigating Vegetation-Atmosphere Water Exchange by Using High Frequency Spectroscopy Vapor Isotope Observations

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