Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

Shim, J. H.; Powers, Heath; Meyer, Clifton W.; Knohl, Alexander; Dawson, Todd E.; Riley, William J.; Pockman, William T.; McDowell, Nate G.

doi:10.5194/bg-10-4937-2013

Cited by 7 publications

(7 citation statements)

References 86 publications

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“…In summer and over land, recent rainfall can lead to a temporal reduction of transpiration and stronger contribution of soil evaporation (Yepez et al, 2005;Shim et al, 2013). This aspect is confirmed by the analysis of the characteristics of the HLA events.…”

Section: Differences Between Anticorrelation and No-anticorrelation Esupporting

confidence: 55%

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Deuterium excess as a proxy for continental moisture recycling and plant transpiration

et al. 2014

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Abstract. Studying the evaporation process and its link to the atmospheric circulation is central for a better understanding of the feedbacks between the surface water components and the atmosphere. In this study, we use 5 months of deuterium excess (d) measurements at the hourly to daily timescale from a cavity ring-down laser spectrometer to characterise the evaporation source of low-level continental water vapour at the long-term hydrometeorological monitoring site Rietholzbach in northeastern Switzerland. To reconstruct the phase change history of the air masses in which we measure the d signature and to diagnose its area of surface evaporation we apply a Lagrangian moisture source diagnostic. With the help of a correlation analysis we investigate the strength of the relation between d measurements and the moisture source conditions. Temporal episodes with a duration of a few days of strong anticorrelation between d and relative humidity as well as temperature are identified. The role of plant transpiration, the large-scale advection of remotely evaporated moisture, the local boundary layer dynamics at the measurement site and recent precipitation at the site of evaporation are discussed as reasons for the existence of these modes of strong anticorrelation between d and moisture source conditions. We show that the importance of continental moisture recycling and the contribution of plant transpiration to the continental evaporation flux may be deduced from the d-relative humidity relation at the seasonal timescale as well as for individual events. The methodology and uncertainties associated with these estimates of the transpiration fraction of evapotranspiration are presented and the proposed novel framework is applied to individual events from our data set. Over the whole analysis period (August to December 2011) a transpiration fraction of the evapotranspiration flux over the continental part of the moisture source region of 62 % is found albeit with a large event-to-event variability (0 % to 89 %) for continental Europe. During days of strong local moisture recycling a higher overall transpiration fraction of 76 % (varying between 65 % and 86 %) is found. These estimates are affected by uncertainties in the assumptions involved in our method as well as by parameter uncertainties. An average uncertainty of 11 % results from the strong dependency of the transpiration estimates on the choice of the non-equilibrium fractionation factor. Other uncertainty sources like the influence of boundary layer dynamics are probably large but more difficult to quantify. Nevertheless, such Lagrangian estimates of the transpiration part of continental evaporation could potentially be useful for the verification of model estimates of this important landatmosphere coupling parameter.

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Section: Differences Between Anticorrelation and No-anticorrelation Esupporting

confidence: 55%

“…The occurrence of precipitation may play an important role for HRA and HLA events in summer as mentioned above in the discussion of Table 4a and b, due to its momentary effect of reducing transpiration (Yepez et al, 2005;Shim et al, 2013).…”

Section: Differences Between Anticorrelation and No-anticorrelation Ementioning

confidence: 99%

Deuterium excess as a proxy for continental moisture recycling and plant transpiration

et al. 2014

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“…Specific humidity at the evaporation site (Table 4a) indicates wetter conditions during uptake for HRA periods than during NRA periods. In summer and over land, recent rainfall can lead to a temporal reduction of transpiration and stronger contribution of soil evaporation (Yepez et al, 2005;Shim et al, 2013). This aspect is confirmed by the analysis of the characteristics of the HLA events.…”

Section: Differences Between Anticorrelation and No-anticorrelation Esupporting

confidence: 55%

“…tant role for HRA and HLA events in summer as mentioned above in the discussion of Table 4a and b, due to its momentary effect of reducing transpiration (Yepez et al, 2005;Shim et al, 2013).…”

Section: The Occurrence Of Precipitation May Play An Impor-mentioning

confidence: 89%

Deuterium excess as a proxy for continental moisture recycling and plant transpiration

Aemisegger¹,

Sodemann²,

Lehner³

et al. 2013

Preprint

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Abstract. Studying the evaporation process and its link to the atmospheric circulation is central for a better understanding of the feedbacks between the surface water components and the atmosphere. Stable water isotopes are ideal tools to investigate surface evaporation as they are naturally available tracers of water phase changes in the atmosphere. The strength of isotope fractionation processes depends on environmental conditions such as relative humidity and temperature. In this study, we use five months of deuterium excess (d) measurements at the hourly to daily timescale from a cavity ring-down laser spectrometer to characterise the evaporation source of low-level continental water vapour at the long-term hydrometeorological monitoring site Rietholzbach in northeastern Switzerland. To reconstruct the phase change history of the air masses in which we measure the d signature and to diagnose its area of surface evaporation we apply an established Lagrangian moisture source diagnostic. With the help of a correlation analysis we investigate the strength of the relation between d measurements and the moisture source conditions. Temporal episodes with a duration of a few days of strong anticorrelation between d and relative humidity as well as temperature are identified. The role of plant transpiration, the large-scale advection of remotely evaporated moisture, the local boundary layer dynamics at the measurement site and recent precipitation at the site of evaporation are discussed as reasons for the existence of these modes of strong anticorrelation between d and moisture source conditions. The relation between d in atmospheric water vapour at the measurement site and the relative humidity conditions at the location of evaporation exhibits distinct characteristics for land surface evaporation and ocean evaporation. We show that the importance of continental moisture recycling and the contribution of plant transpiration to the continental evaporation flux can be deduced from the d-relative humidity relation at the seasonal timescale as well as for individual events. The slope of the relation between d and the diagnosed moisture source relative humidity provides a novel framework to estimate the transpiration fraction of land evapotranspiration at the local to continental scale. Over the whole analysis period (August to December 2011) a transpiration fraction of the evapotranspiration flux over the continental part of the moisture source region of 63% is found albeit with a large event-to-event variability (0% to 99%) for continental Europe. During days of strong local moisture recycling a higher overall transpiration fraction of 82% (varying between 65% and 94%) is found. Such Lagrangian estimates of the transpiration part of continental evaporation could potentially be useful for the verification of model estimates of this important land-atmosphere coupling parameter.

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“…This station was selected from the Global Network of Isotopes in Precipitation as it was the closest station that included monthly measurements for several years (2009–2013), and relative humidity and atmospheric temperatures were representative of the conditions at our experimental site. To ensure correct representation, point measurements of isotopic values of precipitation obtained close to our study site were compared with the data from the Boulder station and yielded very similar patterns (Earman et al ., ; Shim et al ., ) (Fig. S5).…”

Section: Methodsmentioning

confidence: 99%

Warming combined with more extreme precipitation regimes modifies the water sources used by trees

et al. 2016

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The persistence of vegetation under climate change will depend on a plant's capacity to exploit water resources. We analyzed water source dynamics in piñon pine and juniper trees subjected to precipitation reduction, atmospheric warming, and to both simultaneously. Piñon and juniper exhibited different and opposite shifts in water uptake depth in response to experimental stress and background climate over 3 yr. During a dry summer, juniper responded to warming with a shift to shallow water sources, whereas piñon pine responded to precipitation reduction with a shift to deeper sources in autumn. In normal and wet summers, both species responded to precipitation reduction, but juniper increased deep water uptake and piñon increased shallow water uptake. Shifts in the utilization of water sources were associated with reduced stomatal conductance and photosynthesis, suggesting that belowground compensation in response to warming and water reduction did not alleviate stress impacts for gas exchange. We have demonstrated that predicted climate change could modify water sources of trees. Warming impairs juniper uptake of deep sources during extended dry periods. Precipitation reduction alters the uptake of shallow sources following extended droughts for piñon. Shifts in water sources may not compensate for climate change impacts on tree physiology.

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Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

Cited by 7 publications

References 86 publications

Deuterium excess as a proxy for continental moisture recycling and plant transpiration

Deuterium excess as a proxy for continental moisture recycling and plant transpiration

Deuterium excess as a proxy for continental moisture recycling and plant transpiration

Warming combined with more extreme precipitation regimes modifies the water sources used by trees

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