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| Titel |
Separating the contributions of vegetation and soil to evapotranspiration using stable isotopes |
| VerfasserIn |
Matthias Cuntz, Maren Dubbert, Arndt Piayda, Alexandra Correia, Filipe Costa e Silva, Olaf Kolle, Cristina Máguas, Alexander Mosena, João S. Pereira, Corinna Rebmann, Christiane Werner |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106242
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| Publikation (Nr.) |
 EGU/EGU2015-5902.pdf |
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| Zusammenfassung |
| Semi-arid ecosystems contribute about 40% to global net primary productivity,
although water-availability limits carbon uptake. Precipitation shows periodical
summer droughts and evapotranspiration accounts for up to 95% of water loss of the
ecosystem. Thus functional understanding of evapotranspiration and the contributions of
evaporation and transpiration from over- and understorey vegetation to water cycling in
semi-arid regions is key knowledge in forest management under future climate
change.
Water isotopes trace water through the compartments of an ecosystem from soil and the
vegetation to the atmosphere. They are used to partition evapotranspiration ET into its
components evaporation E and transpiration T . The method is, however, sensitive to the
knowledge of the isotopic composition of water at the evaporating sites. This led
to a discussion recently about the dominance of transpiration in water loss from
the terrestrial biosphere, and also how methodological problems could bias these
results.
Here we present observations from a Portuguese cork-oak woodland. It is a bi-layered
system of widely spaced cork-oak trees and a herbaceous layer dominated by native annual
forbs and grasses. Water fluxes and their isotopic compositions were measured on bare soil
and vegetated plots with a transparent through-flow chamber and a water isotope laser. Soil
moisture and temperature were measured in several depths and soil samples were taken for
soil water isotope analysis.
Based on these observations, we review current strategies of ET partitioning. We
highlight pitfalls in the presented strategies and show uncertainty analyses for the different
approaches. We show that the isotopic composition of evaporation is very sensitive to the
sampling strategy but is described well by a steady-state formulation (Dubbert et al., J
Hydrolo 2013). The isotopic composition of transpiration, on the other hand, is
not in steady state, most of the time (Dubbert et al., New Phytolo 2014). We will
demonstrate the consequences for the partitioning of ET of current simplifications in soil
moisture isotope descriptions and current steady-state assumption for transpiration
isotopes. |
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