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| Titel |
Groundwater-dependent ecosystems: recent insights from satellite and field-based studies |
| VerfasserIn |
D. Eamus, S. Zolfaghar, R. Villalobos-Vega, J. Cleverly, A. Huete |
| 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 ; 19, no. 10 ; Nr. 19, no. 10 (2015-10-21), S.4229-4256 |
| Datensatznummer |
250120830
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| Publikation (Nr.) |
 copernicus.org/hess-19-4229-2015.pdf |
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| Zusammenfassung |
Groundwater-dependent ecosystems (GDEs) are at risk globally due to
unsustainable levels of groundwater extraction, especially in arid and
semi-arid regions. In this review, we examine recent developments in the
ecohydrology of GDEs with a focus on three knowledge gaps: (1) how do we
locate GDEs, (2) how much water is transpired from shallow aquifers by GDEs
and (3) what are the responses of GDEs to excessive groundwater extraction?
The answers to these questions will determine water allocations that are
required to sustain functioning of GDEs and to guide regulations on
groundwater extraction to avoid negative impacts on GDEs.
We discuss three methods for identifying GDEs: (1) techniques relying on
remotely sensed information; (2) fluctuations in depth-to-groundwater that
are associated with diurnal variations in transpiration; and (3) stable
isotope analysis of water sources in the transpiration stream.
We then discuss several methods for estimating rates of GW use, including
direct measurement using sapflux or eddy covariance technologies, estimation
of a climate wetness index within a Budyko framework, spatial distribution of
evapotranspiration (ET) using remote sensing, groundwater modelling and
stable isotopes. Remote sensing methods often rely on direct measurements to
calibrate the relationship between vegetation indices and ET. ET from GDEs is
also determined using hydrologic models of varying complexity, from the White
method to fully coupled, variable saturation models. Combinations of methods
are typically employed to obtain clearer insight into the components of
groundwater discharge in GDEs, such as the proportional importance of
transpiration versus evaporation (e.g. using stable isotopes) or from
groundwater versus rainwater sources.
Groundwater extraction can have severe consequences for the structure and
function of GDEs. In the most extreme cases, phreatophytes experience crown
dieback and death following groundwater drawdown. We provide a brief review
of two case studies of the impacts of GW extraction and then provide an
ecosystem-scale, multiple trait, integrated metric of the impact of
differences in groundwater depth on the structure and function of eucalypt
forests growing along a natural gradient in depth-to-groundwater. We conclude
with a discussion of a depth-to-groundwater threshold in this mesic GDE.
Beyond this threshold, significant changes occur in ecosystem structure and
function. |
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