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| Titel |
Stable oxygen isotope analysis reveal vegetation influence on soil water movement and ecosystem water fluxes in a semi-arid oak woodland |
| VerfasserIn |
Arndt Piayda, Maren Dubbert, Christiane Werner, Matthias Cuntz |
| 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 |
250114527
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| Publikation (Nr.) |
 EGU/EGU2015-15316.pdf |
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| Zusammenfassung |
| Mechanistically disentangling the role and function of vegetation within the hydrological
cycle is one of the key questions in the interdisciplinary field of ecohydrology. The presence
of vegetation can have various impacts on soil water relations: transpiration of active
vegetation causes great water losses, rainfall is intercepted, soil evaporation can be reduced
and infiltration, hydraulic redistribution and translatory flow might be altered. In
drylands, covering around 40% of the global land surface, the carbon cycle is closely
coupled to water availability due to (seasonal) droughts. Specifically savannah type
ecosystems, which cover large areas worldwide, are, due to their bi-layered structure, very
suitable to study the effects of distinct vegetation types on the ecosystem water
cycle.
Oxygen isotope signatures (δ18O) have been used to partition ecosystem
evapotranspiration (ET ) because of the distinct isotopic compositions of water
transpired by leaves relative to soil evaporated vapor. Recent developments in laser
spectroscopy enable measurements of δ18O in the vapor phase with high temporal
resolution in the field and bear a novel opportunity to trace water movement within the
ecosystem.
In the present study, the effects of distinct vegetation layers (i.e. trees and herbaceous
vegetation) on soil water infiltration and redistribution as well as ecosystem water fluxes in a
Mediterranean cork-oak woodland are disentangled. An irrigation experiment was carried out
using δ18O labeled water to quantify the distinct effects of trees and herbaceous vegetation on
1) infiltration and redistribution of water in the soil profile and 2) to disentangle the effects of
tree cover on the contribution of unproductive soil evaporation and understory transpiration to
total ET .
First results proof that stable δ18O isotopes measured onsite with laser spectroscopy is a
valuable tool to trace water movement in the soil showing a much higher sensitivity than
common TDR-type probes. It was possible to track soil water redistribution even beyond zero
net water flux measured with TDR probes. Under shaded conditions beneath tree crowns,
infiltration of precipitation reaches much deeper depths due to the limited radiation energy
input and thus, reduced evaporative losses, compared to open areas between crowns. As a
consequence, the isotopic enrichment back to initial conditions (as observed before the
artificial precipitation event) was strongly delayed. Despite the higher water availability
beneath tree crowns, transpiration of understory plants and soil evaporation rates were
reduced compared to the open area due to the lack of energy. However, transpiration could be
maintained much longer and at higher rates after the precipitation event then soil
evaporation. These first results support previous findings at this site where a clear
difference in understory plant community structure was observed. Beneath tree crowns,
favorable water conditions enables a higher occurrence of grasses and nitrogen
fixing forbs, whereas in between tree crowns drought adapted native species became
dominant. |
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