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| Titel |
The patterns and implications of diurnal variations in the d-excess of plant water, shallow soil water and air moisture |
| VerfasserIn |
L. Zhao, L. Wang, X. Liu, H. Xiao, Y. Ruan, M. Zhou |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 10 ; Nr. 18, no. 10 (2014-10-17), S.4129-4151 |
| Datensatznummer |
250120501
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| Publikation (Nr.) |
 copernicus.org/hess-18-4129-2014.pdf |
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| Zusammenfassung |
| Deuterium excess (d-excess) of air
moisture is traditionally considered a conservative tracer of oceanic
evaporation conditions. Recent studies challenge this view and emphasize the
importance of vegetation activity in controlling the dynamics of air moisture
d-excess. However, direct field observations supporting the role of
vegetation in d-excess variations are not well documented. In this study, we
quantified the d-excess of air moisture, shallow soil water (5 and 10 cm)
and plant water (leaf, root and xylem) of multiple dominant species at hourly
intervals during three extensive field campaigns at two climatically
different locations within the Heihe River basin, northwestern China. The
ecosystems at the two locations range from forest to desert. The results
showed that with the increase in temperature (T) and the decrease in
relative humidity (RH), the δD–δ18O regression lines of
leaf water, xylem water and shallow soil water deviated gradually from their
corresponding local meteoric water line. There were significant differences
in d-excess values between different water pools at all the study sites. The
most positive d-excess values were found in air moisture (9.3‰) and
the most negative d-excess values were found in leaf water
(−85.6‰). The d-excess values of air moisture
(dmoisture) and leaf water (dleaf) during the sunny
days, and shallow soil water (dsoil) during the first sunny day
after a rain event, showed strong diurnal patterns. There were significantly
positive relationships between dleaf and RH and negative
relationships between dmoisture and RH. The correlations of
dleaf and dmoisture with T were opposite to their
relationships with RH. In addition, we found opposite diurnal variations for
dleaf and dmoisture during the sunny days, and for
dsoil and dmoisture during the first sunny day after
the rain event. The steady-state Craig–Gordon model captured the diurnal
variations in
dleaf, with small discrepancies in the magnitude. Overall, this
study provides a comprehensive and high-resolution data set of d-excess of
air moisture, leaf, root, xylem and soil water. Our results provide direct
evidence that dmoisture of the surface air at continental
locations can be significantly altered by local processes, especially plant
transpiration during sunny days. The influence of shallow soil water on
dmoisture is generally much smaller compared with that of plant
transpiration, but the influence could be large on a sunny day right after
rainfall events. |
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