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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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Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015
www.hydrol-earth-syst-sci.net/19/4229/2015/
doi:10.5194/hess-19-4229-2015
© Author(s) 2015. CC Attribution 3.0 License.
Groundwater-dependent ecosystems: recent insights
from satellite and field-based studies
D. Eamus1,2, S. Zolfaghar1,2, R. Villalobos-Vega1,2, J. Cleverly2, and A. Huete2
1National Centre for Groundwater Research and Training, University of Technology Sydney, P.O. Box 123,
Sydney, NSW 2007, Australia
2School of Life Sciences, University of Technology Sydney, P.O. Box 123, Sydney, NSW 2007, Australia
Correspondence to: D. Eamus (derek.eamus@uts.edu.au)
Received: 9 March 2015 – Published in Hydrol. Earth Syst. Sci. Discuss.: 4 May 2015
Revised: 30 September 2015 – Accepted: 30 September 2015 – Published: 21 October 2015
Abstract. 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 ecohydrol-
ogy 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 regula-
tions on groundwater extraction to avoid negative impacts on
GDEs.
We discuss three methods for identifying GDEs: (1) tech-
niques relying on remotely sensed information; (2) fluctua-
tions in depth-to-groundwater that are associated with diur-
nal 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 in-
dex within a Budyko framework, spatial distribution of evap-
otranspiration (ET) using remote sensing, groundwater mod-
elling and stable isotopes. Remote sensing methods often
rely on direct measurements to calibrate the relationship be-
tween 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 con-
clude with a discussion of a depth-to-groundwater thresh-
old in this mesic GDE. Beyond this threshold, significant
changes occur in ecosystem structure and function.
1 Introduction
Water stored below ground in the saturated zone (groundwa-
ter) is the largest global store of liquid freshwater, accounting
for about 96% of all liquid freshwater (Shiklomanov, 2008).
Whilst readily accessed by humans for millennia at naturally
occurring springs/oases and as baseflow discharge into rivers,
it has only been during the past 100 years that exploitation of
groundwater resources has become of global concern (Gleick
and Palaniappan, 2010). The rate of groundwater use of three
(Pakistan, Iran and Saudi Arabia) of the seven largest users
of groundwater (India, the USA, Pakistan, China, Iran, Mex-
ico and Saudi Arabia) use groundwater at an annual rate that
exceeds the renewable resource volume (Giordano, 2009).
Only three of the top 10 users are OECD members, reflecting
Published by Copernicus Publications on behalf of the European Geosciences Union.
4230 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
the large reliance on groundwater of less developed nations,
which are often located in arid and semi-arid climates where
surface water stores are generally low.
About two-fifths of the world’s terrestrial surface area is
arid or semi-arid and more than 38% of the world’s popu-
lation lives there. Managing groundwater resources sustain-
ably is therefore a major global social and economic prior-
ity (Glazer and Likens, 2012). Whilst about 40% of global
groundwater abstraction occurs in these regions, the scarcity
of rain means that only 2% of groundwater recharge occurs
there (Wada et al., 2010). Water is increasingly becoming a
geopolitical and strategic resource. Disputes between neigh-
bouring states are increasing as demands for groundwater in-
crease. Because of the close relationship between crop yield
and water supply, diminishing availability of groundwater in
arid and semi-arid regions has immediate and severe impacts
on food supplies, food prices and concomitant social unrest.
Recent estimates suggest that between 10 and 25% of the
food produced in China and India (home to 2.5billion peo-
ple) is at risk because of groundwater depletion (Seckler et
al., 1999; Brown, 2007).
Over-extraction of groundwater stores can create several
problems. These include loss of discharge from groundwater
to wetlands, springs and streams/rivers, which results in loss
of ecosystem structure and function and the associated loss
of ecosystem services (Eamus et al., 2006a; Murray et al.,
2006); increased depth of groundwater, thereby reducing its
availability within the root zone of terrestrial groundwater-
dependent vegetation; reduced availability of groundwater
for direct human consumption; and reduced availability of
groundwater for commercial use, including irrigation, stock
watering and other industrial applications.
In a recent wide-ranging review of groundwater-dependent
ecosystems (GDEs), Orellana et al. (2012) identified quan-
tification of the water used by GDEs and an understand-
ing of the physiology of GDEs as major unresolved prob-
lems. Naumburg et al. (2005) provide a review of the im-
pact of both declining and increasing depth to the water table
on phreatophytic vegetation in arid zones and provide two
conceptual models describing ecosystem responses to these
changes in depth. They note that information on root depth
and the impact this may have on responses to changes in
depth-to-groundwater as a key knowledge gap. In this current
review we discuss application of remote sensing techniques
to quantify rates of water use of GDEs. We present ecophys-
iological responses of vegetation to differences in ground-
water availability in two case studies plus the results of a 4-
year ecophysiological study of eucalypt woodlands across a
natural gradient in depth-to-groundwater in a mesic environ-
ment. From this last study we produce an integrated response
metric for the response of these woodlands to differences in
groundwater depth.
Whilst Hatton and Evans (1998) recognised five classes of
ecosystem dependency on groundwater, we use the simpli-
fied classification system proposed by Eamus et al. (2006b):
1. Aquifer and cave ecosystems where stygofauna reside.
This class also includes the hyporheic zones of rivers
and floodplains.
2. Ecosystems reliant on the surface expression of ground-
water. This includes springs, estuarine seagrasses, and
base-flow rivers, streams and wetlands.
3. Ecosystems reliant on sub-surface presence of ground-
water within the rooting depth of the ecosystem (usually
via the capillary fringe).
Application of this simple classification scheme assists man-
agers in identifying the correct techniques for assessing GDE
structure, function and management regime (Eamus et al.,
2006b), and this classification scheme was recently adopted
in the Australian National Atlas of Groundwater-Dependent
Ecosystems.
In this review, we focus on the ecohydrology of
groundwater-dependent ecosystems rather than on ground-
water resources per se. This is because we feel that environ-
mental allocations of groundwater have generally received
less attention than allocations to human demands and be-
cause we identify three important knowledge gaps in the sus-
tainable management of groundwater for environmental allo-
cations. These are the following:
1. How do we know where a groundwater-dependent
ecosystem (GDE) is in the landscape? If we do not know
where they are, we cannot manage them and allocate
groundwater resources appropriately.
2. How much groundwater is used by a GDE? If we do
not know how much groundwater is used, we cannot
allocate an appropriate quantity of the resource.
3. What are the likely responses of GDEs to over-
extraction of groundwater? Without knowing what to
measure, we cannot regulate groundwater extraction in
ways that do not negatively impact on GDEs.
2 Identifying groundwater-dependent vegetation
Identifying the location of GDEs is the first requisite step to
managing them. However, identifying their location across
a landscape is difficult, time-consuming, expensive and re-
quires a high level of technical expertise. In this section, a
range of new techniques that can be used to assist in this are
discussed.
2.1 Methods to identify GDEs: indirect inference
Early assessments of groundwater dependency generally
relied on inference (Eamus et al., 2006a; Clifton and
Evans, 2001). Recent applications of inferential techniques
to springs, wetland, rivers and lakes can be found in Brown
et al. (2010) and to springs, wetlands and streams reliant on
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4231
baseflow in Howard and Merrifield (2010) and are not further
discussed here.
2.2 Direct methods
2.2.1 Satellite-based approaches
In recent years remote sensing (RS) of land surfaces and veg-
etation structure (e.g. phenology, LAI) and function (e.g. ET,
gross primary productivity) has become increasingly sophis-
ticated (Glenn et al., 2010; Yuan et al., 2010; Jung et al.,
2011; Rossini et al., 2012; Kanniah et al., 2013; Ma et al.,
2013; Nagler et al., 2013) and increasingly applied to real-
world applications of water resources management (Scott et
al., 2008; Glenn et al., 2010; Barron et al., 2014; Doody et
al., 2014). Remote sensing (RS) provides a robust and spa-
tially explicit means to assess not only vegetation structure
and function but also relationships amongst these and climate
variables.
A key concept in the development of RS applications for
identifying the location of GDEs is that of “green islands”
(Everitt and DeLoach, 1990; Everitt et al., 1996; Neale, 1997;
Akasheh et al., 2008), which began with the airborne obser-
vations of desert oases and riparian corridors. In this model
the structure or function of one pixel in an RS image is com-
pared to that of another pixel located nearby. If one pixel
contains a GDE but the other does not, the hypothesis that the
structure and function of vegetation in the two pixels will di-
verge during extended dry periods can be tested. The under-
lying assumption is that vegetation with access to groundwa-
ter will not be subject to the same degree of soil water deficit
as vegetation that does not have access to groundwater; thus,
the spectral signature of the two pixels will diverge over time.
By comparing vegetation structure or function across con-
trasting periods (e.g. comparisons across “wet” and “dry”
periods) or across landscapes (e.g. comparisons from river-
side to upland pixels), green islands within a sea of browning
vegetation can be identified (Contreras et al., 2011).
Münch and Conrad (2007) used Landsat imagery to iden-
tify the presence/absence of wetlands across three catch-
ments in South Africa. They combined this with GIS terrain
modelling to determine whether GDEs could be identified us-
ing a landscape “wetness potential” for class II GDEs (those
reliant on a surface expression of groundwater). They con-
cluded that RS data could be used to classify landscapes by
comparing the attributes of potential GDEs to the attributes
of surrounding land covers during three periods: in July when
rains started at the end of a dry year; in August during the
winter of a wet year; and at the end of a dry summer. When
this was combined with a GIS model using landscape char-
acteristics, they were able to produce a regional-scale map of
the distributions of GDEs.
Plant density is often correlated with water availability,
especially in arid and semi-arid regions. Thus, plant den-
sity tends to be larger when groundwater is available than
-100
-80
-60
-40
-20
0
0 0.2 0.4 0.6 0.8
Depth of the water
table (m)
NDVI
Figure 1. The relationship between NDVI and depth to the water
table for the Hailiutu River catchment in northern China. Redrawn
from Lv et al. (2012).
in nearby vegetation that does not have access to groundwa-
ter. Lv et al. (2012) used a remotely sensed vegetation index
(normalised difference vegetation index; NDVI; 300m reso-
lution) to examine changes in depth-to-groundwater within a
small region in northern China. NDVI is a reliable measure
of the chlorophyll content (“greenness”) in leaves and vege-
tation cover (Gamon et al., 1995; Carlson and Ripley, 1997;
Huete et al., 2002). Using a 25m resolution digital eleva-
tion model and groundwater bore data, the resultant relation-
ship between NDVI and depth-to-groundwater was obtained
(Fig. 1).
Similar in shape to the relationship between LAI and
NDVI, the largest values of NDVI occurred at sites with
shallow groundwater and declined curvi-linearly as depth-
to-groundwater increased. In that study, a cut-off of ap-
proximately 10m depth-to-groundwater was identified be-
low which vegetation cover was relatively insensitive to fur-
ther increase in groundwater depth. In contrast, the thresh-
old was about 4.4m depth-to-groundwater in the Ejina area
of north-western China (Jin et al., 2011). In their study,
which included part of the Gobi desert where annual rainfall
was about 40mm, vegetation was absent in regions where
groundwater depth exceeded 5.5m. They also used NDVI
and 13 groundwater bores, from which relationships between
NDVI and groundwater depth for three vegetation classes
(grassland, woodland and scrubland) were established. Maxi-
mal values of NDVI occurred at sites with intermediate (2.5–
3.5m) depth-to-groundwater rather than at sites with shal-
lower groundwater, a result often ascribed to the effect of
anoxia arising from root flooding when the water table is too
shallow (Naumburg et al., 2005).
Geological, hydrological and ecological data can be used
to define areas that have common physical and climatic pro-
files. These regions are expected to have similar vegeta-
tion cover (assuming no management has induced significant
changes); thus, such areas are expected to have a similar RS
signature. Dresel et al. (2010) applied this approach for in-
dividual regions in South Australia by developing a correla-
tion analysis using Landsat summer NDVI and the MODIS
enhanced vegetation index (EVI) as surrogate measures of
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4232 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
productivity. EVI is effective for scaling productivity across
the range of global ecosystem types (Campos et al., 2013).
MODIS EVI images were used to identify regions display-
ing a consistent photosynthetic activity throughout the year.
Landsat NDVI images were then used to locate areas dis-
playing large inter-annual variation in photosynthetic activ-
ity across wet and dry years, which were identified by arid-
ity thresholds that were calculated from the Thornthwaite
index. Finally, they used an unsupervised classification of
Landsat spectral data to locate pixels with similar spectral
signatures of areas corresponding to known groundwater-
dependent ecosystems. Species-specific differences in spec-
tral signatures have been identified previously (Nagler et al.,
2004). By combining all three sources of information (geo-
logical, hydrological and ecological) within a GIS, Dresel et
al. (2010) identified all pixels across a catchment that had a
very high probability of being a GDE. Critical for provid-
ing assurance of accurate mapping, ground reconnaissance
(“truthing”) was used to validate these findings.
Mapping of groundwater discharge zones (that is, dis-
charge through transpiration and to the ground surface) pro-
vides an alternative approach to finding GDEs. Discharge of
groundwater has a large effect on local ecology. To define
the spatial extent of discharge, information is required about
the geology, hydrology, ecology and climate of a site (Tweed
et al., 2007). By using thermal, Landsat optical and MODIS
NDVI data coupled to digital elevation models and depth-to-
groundwater data, Leblanc et al. (2003a, b) located discharge
areas in the semi-arid Lake Chad basin in Africa. Similarly,
Tweed et al. (2007) examined discharge (and recharge) of the
Glenelg–Hopkins catchment in south-eastern Australia. Dis-
charge occurred through direct evaporation from the water
table (i.e. groundwater evaporation); groundwater transpira-
tion; and discharge to the ground surface at landscape de-
pressions, rivers, wetlands and break-of-slope localities. Im-
portantly, they observed low variability of vegetation activ-
ity across wet and dry periods (seasons or years) using the
NDVI as a measure of vegetation. In this case, the variability
in NDVI was correlated with locations where groundwater
was supporting vegetation activity. One possible limitation
to this method is that it tends to be most accurate in more
xeric locations, where rainfall is more likely to limit veg-
etation function, except during extended droughts in mesic
environments.
2.2.2 Fluctuations in groundwater depth
When rooting depth is sufficient, vegetation can directly ac-
cess the water table via the capillary zone of shallow un-
confined aquifers. In some circumstances groundwater up-
take by vegetation can be seen as a diel fluctuation in the
depth-to-groundwater (Miller et al., 2010), as first identified
in groundwater hydrographs by White (1932). These daily
fluctuations in depth-to-groundwater cease when the water
table falls below the rooting zone (Butler et al., 2007) or
when vegetation is dormant (Lautz, 2008; Martinet et al.,
2009; Miller et al., 2010). However, changes in the den-
sity of water with temperature can cause expansion and con-
traction of an aquifer (Post and von Asmuth, 2013), leading
to the erroneous conclusion that the vegetation is accessing
groundwater. Additionally, when the water table is very shal-
low, direct evaporation from groundwater via bare soil can be
substantial (1–10 mmday1) (Thorburn et al., 1992) and this
may also be misinterpreted. Thus, groundwater dependency
generally requires supporting confirmation from multiple in-
dicators and cannot be identified definitively from the White
method alone. Further elaboration of the White method is
given in Sect. 3.5.1 and described in detail in Orellana et
al. (2012).
2.2.3 Stable isotope analysis
Direct evidence that vegetation is using groundwater can
be obtained by comparing the stable isotope composition
of groundwater, soil water, surface water (if relevant) and
xylem water (Thorburn et al., 1993; Zencich et al., 2002;
Lamontagne et al., 2005; O’Grady et al., 2006a, b; Kray et
al., 2012; Busch et al., 1992; Ehleringer and Dawson, 1992;
Smith et al., 1998). This method is very effective in semi-arid
regions where groundwater is derived from snowmelt or win-
ter precipitation (which is isotopically lighter than summer
precipitation) (Ehleringer and Dawson, 1992; Smith et al.,
1998; Jobbagy et al., 2011). When sufficient differences in
isotopic composition exist among sources of water, the dom-
inant source used by different species at different times of
year can be identified (Zencich et al., 2002).
An example of deuterium isotope analysis of water col-
lected from xylem, soil, river and groundwater is shown in
Table 1. Species growing close to groundwater (Melaleuca
argentea) have xylem isotope compositions close to that of
groundwater but species growing further upslope away from
the river had xylem isotope compositions close to that of
soil water isotope. Further examples include (a) identifica-
tion of soil and surface water use by juvenile riparian plants,
in contrast to groundwater use by mature trees (Dawson and
Ehleringer, 1991); and (b) determination of the mountainous
source of groundwater and opportunistic use of that ground-
water by riparian trees (Chimner and Cooper, 2004).
Mixed-member models (i.e. “Keeling plots”) can be ap-
plied to allow estimation of the relative contribution of mul-
tiple sources of water to the water absorbed by roots (Phillips
and Greg, 2003). While it is possible for a linear mixing
model to distinguish more than two potential sources of wa-
ter, such an application requires the fractionation of 2H or
18O to be independent of each other, which is often not the
case. At a minimum, the use of stable isotopes can provide
information about spatial and temporal variation in ground-
water dependency across species and ecosystems. Applica-
tion of stable isotope analyses to quantify the rate of water
use is discussed later (Sect. 3.5.2).
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4233
Table 1. Deuterium analysis of xylem, soil, river water and groundwater in a study of three species growing in the Northern Territory of
Australia. The δ2H values (‰) of soil became more negative as distance from groundwater increased due to enrichment during surface
evaporation. At shallow sites (Melaleuca argentea) the groundwater is near the surface and xylem water δ2H values match soil water
and groundwater. As depth-to-groundwater increased (because of local topography: the site slopes up from the river) xylem water isotope
composition was increasingly more negative than groundwater because groundwater was unavailable to the roots. From Lamontagne et
al. (2005).
Depth-to- River Soil Xylem Groundwater
groundwater water water water
(m)
Daly River 0 44
M. argentea <0.25 44 43 to 48 43
B. acutangula 380 46 to 40 45
C. bella >15 56 to 91 59 to 71 Not available to roots
3 Application of remote sensing to the study of GDEs
3.1 A primer on remote sensing derived values of rates
of water flux
Before discussing the application of RS techniques to esti-
mate rates of groundwater use by vegetation, we will provide
a simple summary of the principles of using RS to estimate
ET more broadly. For a detailed and comprehensive evalua-
tion of these methods, refer to Glenn et al. (2007). Table 2
provides examples of recent studies that have used RS in the
study of GDEs.
The energy balance equation for land surfaces is
LE+H=RnG, (1)
where LE is latent energy flux (that is, ET), and His sensi-
ble heat flux. Rnis net radiation and Gis soil heat flux. Dif-
ferences in temperature between air temperature and canopy
temperature have been used to estimate sensible heat flux
(Glenn et al., 2010). Using the reasonable assumption that
Gaverages out to zero over any single 24 h period and Rn
is either measured or derived from remote sensing data, then
LE (that is, ET) can be calculated by difference.
Li and Lyons (1999) compared three methods that use sur-
face temperatures to estimate ET. In two methods, differ-
ences in surface and air temperature were used to estimate
ET, although the two methods differed in the details of the
aerodynamic resistance functions. The third model combined
NDVI, surface temperature and a soil-adjusted vegetation in-
dex that required the four extreme values of surface tempera-
ture and NDVI to be located simultaneously within the study
area (i.e. patches of dry bare soils; wet bare soil; wet, fully
vegetated patches; and dry, water stressed, fully vegetated
surfaces). This can make its application problematic. Two
methods used the energy balance equation to estimate ET,
whereas ET was estimated in a third by using RS data to esti-
mate the Priestley–Taylor factor that scales between ET and
potential ET (ETp). They concluded that the simplest first
and second models produced better estimates of ET and that
inclusion of the soil index improved the estimates of ET from
native (i.e. non-agricultural) vegetation. Likewise, Nagler et
al. (2005a, b) found that estimates of ET from riparian corri-
dors using RS were improved with the incorporation of a soil
index.
3.2 Estimating groundwater use by remote sensing
Quantifying the water balance of arid and semi-arid land-
scapes and aquifers is important to sustainably manage wa-
ter resources. Accurate and spatially distributed estimates of
discharge through vegetation are difficult to obtain through
field measurements. Recently, RS methods have been cali-
brated against Penman–Monteith estimates of ET (Glenn et
al., 2010; Nagler et al., 2013; Doody et al., 2014), which re-
quires only standard weather data (net radiation, wind speed
and vapour pressure deficit) and thus increases the coverage
of calibration sites. Because ET in GDEs is generally not lim-
ited by soil moisture when groundwater is of high quality
(i.e. not saline), it is assumed that actual ET rates are equiv-
alent to the ET of a reference grass crop (i.e. reference ET,
ET0), as computed following FAO-56 (Allen et al., 1998).
Then, normalised VIs, either EVIor NDVI, can be used
like crop coefficients to estimate the spatial distribution of
ETafrom ET0on a per-pixel basis. Nagler et al. (2013) used
an exponential scaling function of EVIto estimate ETa:
ETa=ET0ah1ebEVIic.(2)
Similarly, Groeneveld and Baugh (2007) found that this
methodology is particularly applicable to arid and semi-arid
vegetation underlain by a shallow water table. In arid and
semi-arid regions, annual rainfall is low and often erratic.
Consequently, the presence of a shallow water table results in
a relatively consistent supply of water to roots. NDVIwas
calculated from summer peak season NDVI (Groeneveld and
Baugh, 2007):
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4234 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
Table 2. Some examples of the application of remote sensing to the study of groundwater-dependent ecosystems.
Notes on methods Application Reference
eVI (MODIS) +MODISland Calibrated, empirical model of Scott et al.,
surface temp +water balance riparian ET; groundwater use (2008)
equation quantified from ETg=ET(P1S)
eVI (MODIS) +empirical Calibrated, empirical model of Tillman et al.
(2012)
relationship of ET, eVI and EToriparian ET; groundwater use
quantified
“Green island method”: Identifying location of GDEs by Tweed et al.
calculate standard deviation in determining where veg activity (2007)
NDVI across 14-year pixel shows minimal seasonal variation
by pixel
“Green island method”: Identifying location of GDEs by Dresel et al.
calculate standard deviation in determining where veg activity (2010)
eVI across years and seasonally shows minimal seasonal/inter
annual variation
“Green island method”: Identifying location of GDEs by Colvin et al.
calculate LAI for adjacent determining larger LAI (2007)
pixels; find regions with larger
LAI with GW access
NDVI (MODIS)+groundwater Relationship between GW depth Jin et al.
depth from bore data and vegetation cover (2011)
NDVI (MODIS)+groundwater Relationship between GW depth Lv et al.
depth from bore data and vegetation cover (2012)
Surface energy balance Estimating ET from GDEs at pixel- Yang et al.
(2008, 2011)
(SEBAL)+Landsat surface by-pixel resolution
temp; LAI derived from MODIS
SEBAL+NDVI (MODIS) Estimating ET at 90 m resolution Bindhu et al.
(2013)
SEBAL+MODIS Estimating ET Tang et al.
(2013)
SEBAL+SWAT model Estimating groundwater recharge Githui et al.
(hydrology) (2012)
SEBAL+LANDSAT images Estimating arid zone shallow Matic et al.
aquifer discharge (2011)
Penman–Monteith equation with km-scale estimates of ET Cleugh et al.
RS estimates of LAI, NDVI and (2007)
used to estimate land surface
conductance
EVI+surface temperature +Partitions ET into vegetation and Mu et al.
canopy fractional cover soil components (2007)
ET
a=ETarainfall)/(EToEstimated GW use (ETg) rather Groeneveld
rainfall) than ETa(2008)
ETalinearly correlated with
NDVI
ETg=ET0rainfall)NDVI
MODIS veg indices compared; Estimate ETaand GcYebra et al.
PM equation used to find Gc(2013)
and regress Gcagainst MODIS veg
indices
MODIS reflectance +residual Estimate ET at 1 km spatial Guerschman
moisture index (from eVI)+resolution et al. (2009)
global veg moisture index
Actual ET calculated from
PET·crop factor and crop factor
is derived from EVI
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4235
NDVI=(NDVI NDVIz)/(NDVImNDVIz),(3)
where NDVIzand NDVImare the NDVI values for zero veg-
etation cover and NDVI at saturation, respectively. Although
selection of the values for NDVIzand NDVImcan introduce
uncertainty, Groeneveld and Baugh (2007) found significant
convergence in the NDVI by removal of non-systematic scat-
ter in the data. Calibration of ET in the field is not required
to apply this method, but it is necessary to define NDVIm.
This requires highly verdant pixels in the RS images, aris-
ing either from irrigation or the presence of, for example, ri-
parian vegetation that maintains a large LAI. At mesic sites,
defining NDVIzmay also be difficult. Despite these prob-
lems, Groeneveld and Baugh (2007) were able to disaggre-
gate the influence of groundwater supply from that of recent
rainfall.
Groeneveld et al. (2007) applied this NDVImethodology
to three arid sites in the US where annual ETavalues were
available through the availability of Bowen ratio or eddy
covariance measurements. A significant linear relationship
(R2=0.94) was found between measured annual ETaand
mid-summer NDVI, despite very different vegetation com-
position and structure across those sites. However, the regres-
sion of ETa/ET0versus NDVIdid not pass through the ori-
gin and would introduce an offset error if NDVIwere used
to estimate ETa. To overcome this, Groeneveld et al. (2007)
transformed ETato ET
a:
ET
a=(ETarainfall)/(ET0rainfall).(4)
The resulting regression of ET
aversus NDVIyielded a
slope of 0.97, an intercept of zero and an R2of 0.96. They
concluded that NDVIwas a reliable indicator of ET
a. Re-
arranging the equation above and substituting NDVIfor
ET
a, they demonstrated that
ETa(estimated)=(ET0rainfall)NDVI+rainfall.(5)
They estimated the amount of groundwater transpired (ETg)
by deducting annual rainfall from annual ETa. That is,
ETg=(ET0rainfall) NDVI. The average error in ETgwas
estimated to be about 12%, which in the absence of field
measurements is a very valuable estimate of rates of ground-
water use. Further application of the Groeneveld et al. (2007)
method can be found in Groeneveld (2008).
Up-scaling from point to larger-scale estimates of ET
Riparian vegetation is often reliant on groundwater (either
through bank recharge or direct access to the shallow water
table), especially in arid and semi-arid regions. Rates of ET
are enhanced by groundwater use in dry environments (Clev-
erly, 2013), where riparian ET is a large component of the
water balance (Dahm et al., 2002; Scott et al., 2008). How-
ever, measurement of the riparian ET component depends
upon the physical characteristics of the riparian corridor. If
a riparian corridor is sufficiently wide, eddy covariance can
be used to directly measure ET (Cleverly, 2013). Where the
corridor is insufficiently wide, tree-scale sap flow techniques
can be used (O’Grady et al., 2006; Goodrich et al., 2000b).
Combinations of both methods (Moore et al., 2008; Oishi et
al., 2008) can be used to partition transpiration from evapo-
transpiration (Scott et al., 2006a), thereby estimating the pro-
portion of ET due to transpiration from groundwater with the
condition that groundwater evaporation is negligible.
RS methods are used to expand from measurements of ET
at discrete locations to the large scale that is required by re-
source managers. In two studies (Nagler et al., 2005a, b),
MODIS EVI and maximum daily air temperatures (from
MODIS land surface temperature LST) were used to derive
an empirical estimate of riparian ET for the San Pedro River
and middle Rio Grande of the USA (Nagler et al., 2005a, b).
Their equations for daily ET were
ET =a1ebEVIc/ h1+e−{Tad/e}i
+f (middle Rio Grande)and (6)
ET =a1ebEVI(LSTc) +d(both rivers)(7)
where a,b,c,d,eand fare regression constants derived
by regression analysis, Tais air temperature derived from
MODIS LST retrievals, and EVI was normalised to obtain
EVI. Strong correlations between EVI,Taand ET were
observed and used to provide scaled estimates for larger ar-
eas of vegetation. Despite this being an empirically derived
equation from a single study, the form of the equation ap-
pears to be relatively robust across catchments (Nagler et al.,
2005b). Similarly, Scott et al. (2008) and Nagler et al. (2009)
applied these equations (Nagler et al., 2005a, b) in which
they used MODIS-derived nocturnal surface temperature and
daily maximal air temperature, respectively. In the regression
between ET derived from RS and EC methods, the coeffi-
cient of determination (R2) was larger than 0.93 during all
three years of study and across three vegetation types (grass-
land, shrubland and woodland), thereby indicating the broad
applicability of this method. Thus, this method has the abil-
ity to (a) scale from point measurements using individual EC
towers to much larger areas; and (b) estimate the difference
between annual rainfall and ET and, where ET>rainfall, es-
timate vegetation groundwater use.
3.3 Gravity Recovery and Climate
Experiment (GRACE) for detecting changes in
total terrestrial water storage
In addition to remote sensing measures of ET anomalies or
NDVI green islands, there are also new satellite sensors and
techniques that provide estimates of groundwater fluctua-
tions and soil moisture storage changes that are of value to
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4236 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
the study of GDEs (Brunner et al., 2007). The twin satel-
lites known as the Gravity Recovery and Climate Experi-
ment (GRACE) were launched in 2002 for the purpose of
making detailed measurements of Earth’s gravity field (Ta-
pley et al., 2004). Although Earth’s gravity variations tend
to be relatively constant over long time intervals, more dy-
namic, time-variable gravity fields can be detected and these
have been related to land surface moisture, groundwater fluc-
tuations, sea ice, sea level rise, and deep ocean currents.
GRACE’s ability to monitor changes in such “unseen water
reserves” from space are a significant new addition to hy-
drological studies that can substantially improve our knowl-
edge of below- and above-ground water resources and associ-
ated changes to vegetation functioning and GDEs. However,
GRACE is not able to estimate rates of actual groundwater
use by GDEs.
Technically, the GRACE satellites detect changes in the
Earth’s gravity field by monitoring the changes in distance
between the two spacecraft as they orbit the Earth. The rel-
ative distance will change in response to variations in the
Earth’s mass, including changes in mass of both above- and
below-ground water reservoirs (groundwater, soil moisture,
snow, ice, and surface waters). The GRACE satellite data di-
rectly measure changes in total water storage (TWS) and not
changes in the individual hydrologic components (e.g. sur-
face water, soil moisture, and groundwater). Groundwater
storage changes from GRACE are thus inferred by isolat-
ing and removing the contributions of all other TWS compo-
nents, using either independent hydrologic data sets and/or
land surface models.
In most cases, soil moisture becomes the sole compo-
nent that must be removed from the gravity data to estimate
groundwater changes, since variability of snow and surface
water is relatively insignificant to total water storage vari-
ability. By subtracting the soil moisture contribution, the re-
maining time-variable change in GRACE’s measure of total
water storage will be due to changes in groundwater. Thus,
1TWS =1SW+1SM+1GW,(8)
where 1TWS, 1SW, 1SM and 1GW are changes in total
water store, surface water, soil moisture, and groundwater
respectively.
Many studies have compared changes in groundwater stor-
age obtained from GRACE data with in situ data for validat-
ing the accuracy of GRACE data at either regional or conti-
nental scales (Henry et al., 2011; Leblanc et al., 2009; Rodell
et al., 2009, 2007; Scanlon et al., 2012a, b; Syed et al., 2009).
GRACE is not a way to measure exact water storage
amounts from space and cannot be used to measure how
much water is stored in a river basin at a particular instant
in time. Instead, gravity information is used to assess relative
changes in water storage over large areas at monthly, sea-
sonal or annual time steps. Seasonal changes in water stor-
age may be the easiest to detect using the GRACE technique
because such changes tend to be large.
In general, GRACE data are more accurate for large ar-
eas over long time intervals. For example, GRACE can de-
tect seasonal and annual changes in water storage over large
areas and can detect month-to-month changes over entire
river basins (of the order of millions of square kilome-
tres). Presently, GRACE can confidently detect water storage
changes in areas larger than 200000 km2.
Rodell and Famiglietti (2001) showed that GRACE data
can estimate annual groundwater change over the High
Plains, USA, within about 8.7mm of their actual value. This
level of accuracy may not always be an improvement for
well-sampled and instrumented aquifers, but for most places
in the world, estimates of water levels within a centimetre or
less are extremely valuable and will help reveal groundwater
depletion in areas of the world where such measurements are
not systematically recorded.
Despite these coarse scales, such information can be ex-
tremely useful for water resources managers, especially as
GRACE data continue to be refined to provide improved es-
timates of groundwater fluctuations and depletion. Regional
monitoring of groundwater levels is limited by the lack of
ground-based measurements and the lack of a sufficiently ex-
tensive network of monitoring wells. Thereby, the GRACE
technique offers an objective, unbiased method for monitor-
ing water storage changes at large scales.
Although many advances in TWS monitoring have been
made using GRACE data, the practical application of
GRACE data for local water resources management has been
limited by the low spatial (>150000 km2) and temporal
(>10 days) resolution of GRACE measurements and by
difficulties in disaggregating the various TWS components
(Rodell et al., 2007). There is a trade-off between coarse spa-
tial resolution and accuracy, and it remains to be determined
whether better spatial resolutions can be achieved without
degrading or increasing the uncertainties. However, Houborg
et al. (2012) show the potential value of GRACE data to sig-
nificantly improve drought prediction capacity through as-
similation of these data into the Catchment Land Surface
Model using ensemble Kalman smoother and forcing data
from North American and Global Land Data Assimilation
Systems Phase 2 (NLDAS-2). Similarly, Sun et al. (2013) im-
posed GRACE observations as constraints when recalibrat-
ing a regional-scale groundwater model, further highlighting
the value of GRACE data to the study of groundwater and
GDEs.
3.3.1 Downscaling of GRACE
To fully realize the potential of GRACE data for hydrological
applications, downscaling both in space and time is required.
This will enable better predictions of changes in groundwa-
ter level (Houborg et al., 2012). Sun et al. (2013) explored
various downscaling techniques for GRACE data for use-
ful predictions of changes in water level. They developed
artificial neural network (ANN) model schemes to predict
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4237
Figure 2. Change in (a) total water storage anomalies; (b) groundwater anomalies; (c) soil moisture storage anomalies; and (d) surface water
anomalies relative to the mean of the Murray–Darling Basin during the multiyear drought. Redrawn from Leblanc et al. (2009).
such changes directly by using a gridded GRACE product
and other publicly available hydrometeorological data sets.
Their statistical downscaling approach can be readily inte-
grated into local water resources planning activities, espe-
cially in the absence of continuous in situ groundwater ob-
servations. They noted that downscaled GRACE data could
potentially fill the gap created by the declining coverage of
in situ groundwater monitoring networks and “index” wells
used to gauge the wellbeing of aquifers.
3.3.2 Groundwater depletion studies and GRACE
GRACE satellite data have been used to estimate ground-
water depletion associated with severe droughts in Europe,
the US, China, and India (Leblanc et al., 2009; Rodell et al.,
2009). Groundwater pumping of aquifers often increases dur-
ing severe droughts for urban, agriculture, livestock, and in-
dustry needs. This results in the decline of groundwater levels
and the decrease in groundwater discharge to springs, surface
water bodies and riparian zones (Peters et al., 2003). Leblanc
et al. (2009) attempted to attribute groundwater loss dur-
ing the recent drought in the Murray–Darling Basin in Aus-
tralia to groundwater pumping. However, they found that the
pumping rate represented only less than 10% of the decline
rate in groundwater storage as observed by GRACE from
2003 to 2008 (Fig. 2). They concluded that the observed de-
cline can mostly be explained by reductions of groundwater
recharge and the vast amount of groundwater transpired dur-
ing the drought by the widespread presence of deep rooted
trees (GDEs) as well as capillary rise from the saturated to
the unsaturated zone.
3.4 Remote sensing limitations and challenges in
studies of GDEs
Remote sensing applications in studies of GDEs vary greatly,
from basic detection, mapping, and monitoring of GDEs to
more complex and quantitative measurements of ET, func-
tioning, and energy and water balance. In most cases, map-
ping of GDE locations at appropriate management scales is
prerequisite to more detailed studies, such as groundwater
assessments that may require accurate estimates of ET (Gou
et al., 2015).
Regardless of the application, there will be certain lim-
itations in the use of remote sensing that need to be con-
sidered. Other geospatial data sources will often need to be
integrated to make the best use of remote sensing, includ-
ing climate, soils, landscape morphology, and ecologic data
layers that will enable potential areas for GDEs to be de-
lineated (Bertand et al., 2012). Multiple sensors and image
data sets are best suited for studies of GDEs because of the
inherent spectral–spatial–temporal limitations of single sen-
sor systems. For example, the use of fine spatial resolution
Landsat (30m) and high temporal frequency MODIS data
(1–2 day) allows us to identify potential GDE vegetation
patches (Landsat) and track changes in their seasonal and
inter-annual dynamics (MODIS spectral vegetation indices,
VIs). Thus, vegetated areas that maintain high VI “green-
ness” values during extended dry periods can be flagged as
“high GDE potential”, under the premise that GDEs exhibit
low seasonality in greenness and ET between dry and wet
seasons and low inter-annual variability across years.
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4238 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
However, many ecosystems may contain trees and shrubs
that are non-GDE yet also exhibit weak seasonality and inter-
annual variation due to their evergreen phenologies. In these
mixed tree–grass landscapes, seasonal variability follows the
very dynamic herbaceous grass layer that is strongly coupled
to rainfall rather than groundwater availability. The stronger
seasonality present in the grass layer can readily mask GDE
signals from the tree layer and confuse GDE detection. This
“mixed-pixel” problem restricts many remote sensing ap-
plications, particularly when the matrix background of an
area with GDEs has insufficient thermal or greenness con-
trast to enable GDE detection. The detection of “cool” ther-
mal patches (transpiring GDE trees) from relatively warmer
backgrounds (soil) will be a function of the size and magni-
tude of the cold patch relative to the pixel area. The “greener”
and “cooler” signals from a groundwater-dependent tree may
be averaged out by the non-GDE plants present in the same
pixel and a stressed GDE tree can gradually fade into the
warmer soil background matrix. Spatial heterogeneity may
overwhelm detection. Finer resolution imagery will improve
detection capabilities, but temporal information is then made
poorer, due to inherent sensor resolution trade-offs.
It should be noted that although remote sensing is a use-
ful diagnostic tool and proxy for the detection and sensing
of GDEs, most detection and mapping is done by inference
and careful user interpretation. Remote sensing often can-
not directly ascertain causes and mechanisms of GDEs, and
much remains to be done to assess GDE influences on the
water balance, their sensitivity to changing water availabil-
ity, and responses to stress conditions. Future sensor systems
planned for launch in the next few years include follow-
on GRACE twin satellite missions with improved sensing
capabilities allowing more detailed analyses of groundwa-
ter, soil moisture, and surface water distributions and trends.
The soil moisture active passive (SMAP) mission, launched
in 2014, provides improved soil moisture retrievals which
will improve upon the detection and differentiation of soil-
moisture-induced vegetation dynamics from those associated
with groundwater use.
4 Hydrological modelling of water use by GDEs
4.1 Conceptual water balance approaches
A spreadsheet tool
O’Grady and co-workers have developed a simple but
useful first-order approximation to estimate ground-
water use of vegetation in an Excel spreadsheet tool
(Leaney et al., 2011; http://www.csiro.au/products/
recharge-discharge-estimation-suite). This toolbox in-
cludes three methods to estimate rates of groundwater
discharge by vegetation:
1. Groundwater Risk Model,
0
0.2
0.4
0.6
0.8
1
1.2
01234
ETa/ETp
P/ETp
Figure 3. A representation of the Budyko formulation using the
Choudhury–Yang formulation with three different values of n
(from 1.5 to 2.0). Redrawn from Leaney et al. (2011).
2. Ecological Optimality Model, and
3. Groundwater Discharge Salinity Model (not described
here).
The groundwater risk model uses historical monthly rain-
fall and evaporation data for a site to produce a water balance.
Soil texture is used to estimate soil moisture characteristics
in each layer of the model, and groundwater uptake by veg-
etation is assumed to occur when ET exceeds rainfall, when
also accounting for soil water storage for each month. ET
is estimated from total evaporation using the Budyko frame-
work (Budyko, 1974; Donohue et al., 2007; Yang et al., 2008;
Roderick and Farquhar, 2009). The risk model in Leaney
et al. (2011) uses the Choudhury–Yang formulation of the
Budyko equation:
ETa=PETp/Pn+ETpn1/n ,(9)
where Pis rainfall and nis a fitting parameter that deter-
mines the shape of the curve. Determining the value of nis
difficult, but a close approximation can be derived from the
climate wetness index (CWI=P /ETp). When CWI >0.3,
nis approximately equal to CWI and when CWI<0.3, nis
approximately 1.8 (Leaney et al., 2011). The influence of
variation in nand the Budyko formulation is shown in Fig. 3.
The model is run using historical monthly rainfall and esti-
mated ET. Pan evaporation rates can be used instead of ETp,
in which case ETp=0.75Epan. Modest agreement between
modelled and observed rates of groundwater discharge was
found in two Australian studies where ET exceeded rain-
fall in the Wattle Range by 2 to 440 mm yr1(Benyon and
Doody, 2004), although the range of estimated groundwater
discharge rates was large: 107 to 671mm yr1(Benyon and
Doody, 2004) and 380 to 730mm yr1(Benyon et al., 2006).
As an alternative method to the risk assessment just de-
scribed, Leaney et al. (2011) applied Eagleson’s theory of
ecological optimality (Eagleson, 1978). This proposes that
the LAI of a site is maximised according to long-term rain-
fall and soil water holding capacity such that productivity
is maximised whilst minimising the development of water
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4239
stress. In this hypothesis, native vegetation is assumed to be
at equilibrium with the local hydrological regime (Nemani
and Running, 1989). Ellis and Hatton (2008) have shown
that the LAI of a site is proportional to a climate wetness
index (CWI=P /ETp), whilst Eamus et al. (2001) used the
Baldocchi–Meyers index (foliar [N]×P /Eeq, where foliar
[N] is the concentration of nitrogen in leaves and Eeq is equi-
librium evapotranspiration) and found a strong (R2=0.95
for 16 sites globally) curvilinear relationship with LAI, sup-
porting the essentials of Eagleson’s optimality theory. Sim-
ilarly, Zeppel (2013) examined multiple species across sites
in Australia and found strong convergence in daily rates of
tree water use and leaf area across five evergreen sclerophyl-
lous genera. In the Eagleson optimality method of Leaney et
al. (2011), the relationship between LAI and the CWI of Ellis
and Hatton (2008) is used:
LAI =(3.31×CWI)0.04.(10)
In GDEs, groundwater discharge combines with precipita-
tion to supply ET (O’Grady et al., 2011); thus,
CWIg=(P +GW)/ETp,(11)
where CWIgis the climate wetness index that includes the
groundwater component (GW). Likewise, the Budyko curve
can be modified to include the contribution of groundwater
discharge to ET:
ET/ETp=1+P /ETp1+P /ETpw1/w
(Zhang et al., 2004)and (12)
ET/ETpg=1+[P+GW]/ETp
1+{P+GW}/ETpw1/w
(O’Grady et al., 2011). (13)
Within zones of the same CWI, sites with access to shallow
groundwater maintain a larger LAI than sites without access
to groundwater (O’Grady et al., 2011). To determine GW, the
pairs of equations (CWI, CWIg; ET/ETp, [ET/ETp]g) were
optimised by obtaining the difference in rainfall required to
attain a given LAI with a known CWI value (O’Grady et al.,
2011).
4.2 Groundwater flow and variable saturation models:
MODFLOW and HYDRUS
Two models, MODFLOW and HYDRUS, are commonly
used to investigate the hydrologic state of the coupled sur-
face water–groundwater–soil–vegetation system (McDonald
and Harbaugh, 1988; Doble et al., 2006; Shah et al., 2007;
Lowry and Loheide, 2010; Loheide and Booth, 2011; Ajami
et al., 2012). HYDRUS applies Richard’s equation to simu-
late water, heat and solute movements in soil, whereas MOD-
FLOW is a fully distributed and coupled hydrologic model of
groundwater flow (Orellana et al., 2012). Hydrologic models
that apply Richard’s equation in a soil medium of variable
saturation are important for evaluating the mechanisms that
generate groundwater hydrographs and flow. MODFLOW
can also perform spatial scaling of ET as a function of depth-
to-groundwater, although the form of ET depends upon pa-
rameterisation of the model. Often, ET is determined as ETp
or ET0, but measurements of ETafrom eddy covariance can
also be used. In one example, Wilcox et al. (2007) estimated
ET from Cleverly et al. (2002) to evaluate the interaction be-
tween riparian ET and surface water–groundwater interac-
tions.
Variable saturation models have improved our understand-
ing of the interactions between groundwater and soil mois-
ture in the vadose zone. Root water uptake (RWU) creates
soil moisture deficits in the vadose zone and the capillary
fringe, thereby causing vadose zone water content to fluctu-
ate with depth-to-groundwater (Nachabe et al., 2005; Shah
et al., 2007; Logsdon et al., 2010). Using HYDRUS 1-D,
Lowry and Loheide (2010) integrated ETgand RWU from
the vadose zone by estimating the groundwater subsidy as
the difference between RWU from the shallow groundwater
and RWU from free drainage. Further complicating the re-
lationship between groundwater and soil moisture, hydraulic
redistribution of moisture from deep in the soil column to
the surface (i.e. hydraulic lift) can reduce the amplitude of
fluctuations in depth-to-groundwater, increase the amount of
ETgthat is lost to groundwater evaporation, and decrease the
nocturnal recovery in depth-to-groundwater (Orellana et al.,
2012).
One of the goals of ecohydrological modelling in GDEs
is the prediction of vegetation state based upon groundwater
regime (Loheide and Booth, 2011). Likewise, the principle
drivers of water use by vegetation in GDEs were aquifer at-
tributes (Sy, regional groundwater flow), meteorology (solar
radiation, vapour pressure deficit), environmental stress, and
vegetation attributes (LAI, species composition) (Cleverly et
al., 1997; Perkins and Sophocleous, 1999; Dahm et al., 2002;
Cleverly et al., 2006; Butler et al., 2007; Lautz, 2008; Abudu
et al., 2010). In general, these controls are observed in the
wider literature on the controls of vegetation water use (Ea-
mus et al., 2006b; Whitley et al., 2009). As the meteorolog-
ical, environmental and vegetation effects on ET have been
thoroughly described, we will focus on the regional aquifer
effects on ETghere.
One geomorphologic attribute of the aquifer that controls
the flow of groundwater and thereby affects the distribution
of groundwater-dependent vegetation depends upon whether
the aquifer is gaining (i.e. water flows into the aquifer from
its surroundings) or losing (i.e. an area where groundwa-
ter is lost to adjacent unsaturated soils) (Cleverly, 2013). A
larger ETgcan lead to contrasting effects on seepage from
streams to aquifers, depending upon whether along a los-
ing or gaining reach (Ajami et al., 2011). Similarly, fluctu-
ations in depth-to-groundwater can differ between gaining
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4240 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
and losing reaches, of which the occurrence of the latter is
where groundwater inflow might be insufficient to support
large recovery rates in depth-to-groundwater (Schilling and
Zhang, 2012). The relationships between plant water use,
aquifer dynamics, and seasonality (e.g. Logsdon et al., 2010;
Ajami et al., 2011) are influenced by the rooting patterns and
groundwater depth–ETgrelationships of the specific plant
functional types that inhabit the GDE (Baird and Maddock,
2005).
5 Field-based measurements of water use by GDEs
5.1 Sub-daily fluctuation in groundwater depth
An idealised representation of the White method in a shallow
unconfined aquifer is shown in Fig. 4.
In Fig. 4 the oscillating curve represents the cycle of
groundwater drawdown arising from evapotranspiration (ET)
during the day followed by a “rebound” of the water table
when ET returns to zero at night. The dashed straight line
(with slope=r) provides an estimate of the recovery rate,
which is how fast the water table rises in the absence of
groundwater use (Butler et al., 2007). After accounting for
recovery, the daily drawdown of the water table is scaled
by the effective specific yield (Sy), or the volume of water
(per unit surface area of an unconfined aquifer) released from
the soil pores with a given change in depth-to-groundwater
(White, 1932):
ETg=Sy(24r+s), (14)
where sis the change in aquifer storage and is deter-
mined from the 24h change in depth-to-groundwater. This
approach has been successfully applied in the Okavango
Delta in Botswana (Bauer et al., 2004), an upland grass-
land catchment in central Argentina (Engel et al., 2005), an
oak/grassland site on the Great Hungarian Plain of eastern
Hungary (Nosetto et al., 2007), the Sopron Hills of western
Hungary (Gribovszki et al., 2008), the Gobi desert of north-
western China (Wang et al., 2014), and various sites in the
USA (Butler et al., 2007; Lautz et al., 2008; Martinet et al.,
2009).
The White method tends to over-estimate ETg(Loheide et
al., 2005; Martinet et al., 2009). A major source of error is
estimation of Sy, to which this method is very sensitive (Lo-
heide et al., 2005; Gribovszki et al., 2008; Lautz, 2008; Logs-
don et al., 2010; Miller et al., 2010). Furthermore, represen-
tative measurements of the readily available Syare difficult to
make and are complicated by capillary flux, trapped air, hys-
teresis, and departure of the soil–water ecosystem from an
equilibrium (Logsdon et al., 2010). The value of Syis depen-
dent upon soil texture (Loheide et al., 2005); thus, Martinet
et al. (2009) applied a value of Sythat varied with the soil
texture in contact with the capillary fringe of the water ta-
ble. With a measure of ETg(e.g. from eddy covariance), the
1.9
1.95
2
2.05
2.1
2.15
2.2
2.25
0:00 12:00 0:00 12:00 0:00 12:00
Groundwater depth (m)
Time of day
Figure 4. An idealised representation of changes in depth-to-
groundwater over a 48h period. The water table declines (depth
increases) during the day because of transpiration by vegetation but
increases (depth decreases) at night when transpiration tends to zero
and recharge exceeds loss. The dashed line represents the trajectory
of overnight recharge in the absence of transpiration on the follow-
ing day. See text for further discussion of this.
White equation can be inverted to investigate the variation
in Sy(Miller et al., 2010). Using an inversion of the White
method, estimates of Syaccount for spatial heterogeneity in
soil texture and scaling effects on Sy, but further studies are
required before comprehensive predictions of Sycan be ob-
tained without independent measurements of ETg. Alterna-
tively, Nachabe et al. (2005) used a more direct estimate of
Syin the soil column by combining measured fluctuations
of depth-to-groundwater and soil moisture across the vadose
(i.e. unsaturated) zone. In either case, additional instrumen-
tation to measure ETgor soil moisture profiles improved the
estimation of Sy.
Several modifications to the White method were evaluated
in a study by Fahle and Dietrich (2014), in which they com-
pared errors in estimation of Sy, recovery and ETg. No model
outperformed the others in each of these error benchmarks,
thus illustrating that errors in the estimation of Syare com-
pensated by errors in the estimation of recovery (Fahle and
Dietrich, 2014). The methods that provided the best estimates
for recovery of the groundwater used approaches to estimate
sub-daily rates of ETgand recovery (Gribovszki et al., 2008;
Loheide, 2008). In both methods, recovery was estimated
from the previous and following nights, although application
to other methods might require site-specific parameterisation
of the time period that is most representative for their study
conditions (e.g. 18:00–06:00; Fahle and Dietrich, 2014). In
the method of Gribovszki et al. (2008), recovery was esti-
mated from the time rate of change in depth-to-groundwater,
and this important upgrade reduced the error of recovery es-
timates (Gribovszki et al., 2010; Fahle and Dietrich, 2014).
Groundwater hydrographs include the impact of regional
fluctuations in the aquifer that are not associated with local
changes arising from ET of vegetation (Engel et al., 2005).
A regional effect that can cause problems with the White
method occurs when tides from nearby water bodies gener-
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4241
ate two daily peaks in the groundwater hydrograph (Miller et
al., 2010), thereby requiring measurements of the water body
that is causing the effect. After accounting for the regional
hydrograph, soil moisture content in the vadose zone can
still affect the correlation between sap flow measurements
of ETgand groundwater fluctuations (Engel et al., 2005).
This was consistent with the modelling results of Loheide et
al. (2005), who found that daily fluctuations were dampened
by root water uptake from the vadose zone alone. Spectral
methods (e.g. windowed Fourier decomposition) are effec-
tive at identifying break points in the daily signal like those
associated with regional groundwater and soil moisture ef-
fects, although variations in ETgcan result in loss of am-
plitude, consequently rendering spectral analysis unsuitable
for quantitative analysis without an adequate scaling factor
(Schilling and Zhang, 2012; Soylu et al., 2012).
5.2 Using stable isotopes to estimate rates of
groundwater use
Estimates of the proportion of total vegetation water use de-
rived from groundwater can be determined from stable iso-
tope analyses (Querejeta et al., 2007; Maguas et al., 2011;
Feikema et al., 2010; Kray et al., 2012; McLendon et al.,
2008). Two types of information are required to quantita-
tively partition ETgfrom ET. The first is an independent es-
timate of ET0or ETaas derived from eddy covariance (Kel-
liher et al., 1992; Baldocchi and Vogel, 1996; Baldocchi and
Ryu, 2011), sap flow (Cook and O’Grady, 2006; O’Grady et
al., 2006a, b; Zeppel, 2013) or RS techniques (Nagler et al.,
2009, 2013). The second is the stable isotope composition of
water in soil, groundwater and xylem. Upon determination
of the proportion of ET that is due to ETg(Sect. 3.2), the
amount of ETg, for example in mmday1, is the product of
that proportion and ET.
Three generalities can be identified in the results of sta-
ble isotope studies of GDEs. First, multi-species compar-
isons at a common site generally confirm niche separation
(spatially or temporally) in patterns of water uptake, thereby
minimising competition for water (Lamontagne et al., 2005;
Querejeta et al., 2007; Kray et al., 2012). Second, increased
depth-to-groundwater results in a declining proportion of
groundwater use (O’Grady et al., 2006), although this can
vary amongst different vegetation communities (McLendon
et al., 2008). Finally, as time since last rain increases, the
proportion of groundwater used by vegetation usually in-
creases (McLendon et al., 2008), but not always (Kray et al.,
2012). Consequently, seasonality of groundwater use may
occur when rainfall is highly seasonal and groundwater avail-
ability is maintained throughout the dry season (O’Grady et
al., 2006).
Stable isotope composition varies with depth (Table 1;
Querejeta et al., 2007). Consequently, taking an average
value to represent the entire rooting depth can lead to errors.
Whilst use of two independent isotopes allows the relative
contribution of three sources to be determined, obtaining in-
dependence of both isotopes is very difficult. As an alterna-
tive, Cook and O’Grady (2006) developed a model that esti-
mates the relative water uptake by vegetation from different
soil depths. This model is based upon the following axioms:
the rate of water uptake is determined by (a) the gradient in
water potential between bulk soil and leaves; (b) root distri-
bution through the soil profile; and (c) a lumped hydraulic
conductance parameter. Soil isotopic composition as a func-
tion of depth and of xylem water is used to constrain root dis-
tributions within the model. This has the advantage over end-
member analyses (an analytic tool to determine the relative
contributions of soil water and groundwater to transpiration;
Phillips and Gregg, 2003) because (i) it produces a quanti-
tative estimation of the proportion of water extracted from
multiple depths (including groundwater); (ii) it does not re-
quire distinct values of isotope composition for end-member
analyses and therefore can deal with the more typical grading
of isotope composition observed through the soil profile; and
(iii) it is based on simple ecophysiological principles. Cook
and O’Grady (2006) applied this model and demonstrated
that two co-occurring species obtained 7–15% of their tran-
spirational water from the water table, a third species ac-
cessed 100% from the water table, and a fourth species de-
rived 53–77% from groundwater.
6 Functional responses of GDEs to changes in GW
depth
Effects of groundwater on growth and
dendrochronological traits
A reduced growth rate in response to declining water avail-
ability is a universally observed plant response (Kelliher et
al., 1980; Osmond et al., 1987; Oberhuber et al., 1998; Sarris
et al., 2007). In most GDEs rainfall and groundwater pro-
vide important supplies of water, and the ratio of rainfall-
to-groundwater uptake varies spatially and temporally. Con-
sequently, increases in groundwater depth may be expected
a priori to have the potential to affect plant growth. Den-
drochronology (the study of growth in tree rings) has a long
history in ecological research spanning many decades (Drew
and Downes, 2009; McCarroll and Loader, 2004). However,
its application to the study of GDEs is much more recent
(e.g. Giantomasi et al., 2012). Similarly, recording point
dendrometers, which are sensitive stem gauges that monitor
growth increment at hourly timescales, recently have been
used for expanding applications. In this section we briefly
review some of the insights gained form dendrochronology
and dendrometry in the study of GDEs.
Tree rings represent the history of past growth events,
which are often but not always annual (Prior et al., 2012).
Quantification of growth rates from tree rings can be used
to reconstruct fluctuations in the supply water from precip-
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4242 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
itation and groundwater (Oberhuber et al., 1998; Bogino
and Jobbagy, 2011; Perez-Valdivia and Sauchyn, 2011; Xiao
et al., 2014). In mountainous regions where the regional
water supply is derived from snowmelt, tree growth and
groundwater depth are correlated with precipitation during
the year prior to growth because much of the snow re-
ceived in the winter melts in the year after it fell (Oberhuber
et al., 1998; Perez-Valdivia and Sauchyn, 2011). Likewise,
tree ring growth and groundwater fluctuations are correlated
to the dominant climate driver in an area (e.g. the Pacific
decadal oscillation and El Niño–Southern Oscillation in Cal-
ifornia, USA) (Hanson et al., 2006). In some circumstances,
the effect of groundwater can be disentangled from climate
through the use of spectral analysis (Bogino and Jobbagy,
2011), but in other cases depth-to-groundwater was not found
to be a significant factor in explaining differences in either
ring width of basal area increment (Stock et al., 2012).
The timing of groundwater dependence can influence the
presence of a climate signal in tree rings: climate signals can
be weaker during formation of late wood, when growth rates
are small (Oberhuber et al., 1998), or during the dry season,
when precipitation rates are negligible and growth is sup-
ported by groundwater (Drake and Franks, 2003). Thus, anal-
ysis of tree ring chronologies can provide an insight into the
importance of access to groundwater for plant growth. Indi-
vidual events can be identified in the tree ring growth record
(Hultine et al., 2010), as can long-term trends in depth-to-
groundwater (Bogino and Jobbagy, 2011). In riparian cotton-
wood trees and willows, Hultine et al. (2010) identified rapid,
large and reversible responses of tree ring width to draining
and refilling of a reservoir (Fig. 5).
Longer-term trends in depth-to-groundwater have im-
pacted dendrochronologies in both directions, toward lower
growth rates with groundwater extraction (Lageard and
Drew, 2008) and toward increasing growth rates with
decreasing depth-to-groundwater, except in response to
root anoxia arising from flooding (Bogino and Jobbagy,
2011). However, specific responses depend upon depth-to-
groundwater and individual differences amongst functional
types; for example, riparian cottonwood trees (P. fremontii)
responded to rewetting with growth that was larger and faster
than the response of co-occurring willow (S. exigua), a small-
stature, thicket-forming shrub that is restricted to stream-
side areas with very shallow groundwater (Scurlock, 1998;
Rood et al., 2011). From an understanding of the relation-
ships between tree growth and depth-to-groundwater, histor-
ical periods of sensitivity to hydrological drought (i.e. af-
fecting groundwater levels) versus meteorological drought
(i.e. below-average precipitation) can be identified (Potts and
Williams, 2004; Adams and Kolb, 2005; Cocozza et al.,
2011). Such insights have value in developing a long-term
understanding of the relationships amongst GDEs, climate
and groundwater depth.
Wood formed during drought is enriched in 13C, reflecting
decreases in stomatal conductance relative to photosynthesis
0
2
4
6
8
10
12
14
2003 2004 2005 2006 2007
Tree ring width (mm)
Year
Figure 5. Change in tree ring width of cottonwood (solid line, di-
amonds) and willow (dashed line, squares) before (2004), during
(2005–2006) and after draining the reservoir (early 2005) and refill-
ing (mid 2006). Redrawn from Hultine et al. (2010).
and the consequential ratio of [CO2] within and outside of
the leaf (Ci/Ca) (McCarroll and Loader, 2004; Cocozza et
al., 2011; Horton et al., 2001; Maguas et al., 2011). Interpre-
tation of δ13C in tree rings can be complicated by the effects
of phloem loading (Gessler et al., 2009) and by photosyn-
thetic re-fixation in the bark (Cernusak et al., 2001), although
with independent confirmation, xylem δ13C can explain dif-
ferences in groundwater use and water stress in groundwater-
dependent trees. In one such comparison, δ13C was constant
across xylem from Populus along a perennial stream (thereby
implying access to groundwater), but changed with mois-
ture conditions in an intermittent reach (Potts and Williams,
2004). Likewise, changes in ring width over time were re-
flected by δ13C from leaves (Hultine et al., 2010), such that
less negative values of δ13C indicated increased water-use
efficiency when the supply of water was reduced.
On small timescales (hourly to daily), incremental stem
growth (and shrinkage) is measured using precision den-
drometers that contain linear-variable-displacement trans-
ducers (Zweifel et al., 2005; Drew et al., 2008; Drew and
Downes, 2009). Changes in maximum daily trunk shrink-
age arising from reduced water availability occur earlier and
stronger than changes in stomatal conductance, stem wa-
ter potential or transpiration (Ortuno et al., 2006; Cone-
jero et al., 2007, 2011; Galindo et al., 2013). Nonetheless,
rates of sap flow declined with maximum daily stem shrink-
age, both of which responded exponentially to changes in
depth-to-groundwater (Ma et al., 2013). Similarly, Febru-
ary et al. (2007) and Drake et al. (2013) found that in-
creased groundwater supply (actual or simulated) resulted in
increased stem increment, sap flow and xylem water poten-
tial.
7 Two case studies
Two case studies are now presented, one from Australia and
one from the USA. These case studies serve several purposes.
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4243
First, they provide examples of the multiple approaches re-
quired in the study of GDEs (physiological, remote sensing,
ecological). Second, they provide a valuable bridge between
Sects. 2–6 (water use, remote sensing, modelling) and Sect. 8
(vegetation response trajectories to changes in groundwater
depth). Finally, they integrate the results of many years of
concentrated study into two diverse ecosystems.
7.1 The Gnangara Mound
The Gnangara Mound is a shallow unconfined aquifer of the
Swan Coastal Plain in Western Australia. Increased depth-to-
groundwater has occurred over the past several decades as the
result of long-term declines in annual rainfall, increased hu-
man abstraction and increased discharge arising from the de-
velopment of a plantation industry in the region (Elmahdi and
McFarlane, 2012). The impacts of groundwater abstraction
on woodlands have been documented in this region (Groom
et al., 2000; Canham et al., 2009, 2012; Stock et al., 2012). In
1985 large rates of summer abstraction in this Mediterranean
climate were associated with increased and widespread mor-
tality of native woodlands (up to 80% mortality close to ab-
straction bores; Mattiske and Associated, 1988).
To determine long-term floristic changes associated with
groundwater abstraction, a series of transect studies were
initiated in 1988. A 2.2m increase in depth-to-groundwater
coupled to higher-than-normal summer temperatures re-
sulted in further adult mortality of overstorey species by as
much as 80%; additionally, 64% mortality was recorded in
understory species 2 years after the start of groundwater ab-
straction (Groom et al., 2000). Increased rates of mortality
were not observed at control sites that were not subject to
groundwater pumping.
Large inter-specific differences in rates of mortality were
observed in these Gnangara studies. Consequently, a fur-
ther study examined the vulnerability of individual species
to increased depth-to-groundwater (Froend and Drake, 2006;
Canham et al., 2009). Using xylem embolism vulnerability
curves as a measure of sensitivity to water stress, Froend and
Drake (2006) compared three Banksia and one Melaleuca
species. They found that xylem vulnerability reflected the
broad ecohydrological distribution of species across a topo-
graphic gradient, and they identified a threshold leaf water
potential below which increased mortality was likely. Simi-
larly, Canham et al. (2009) examined Huber values (the ratio
of sapwood to leaf area), leaf-specific hydraulic conductivity
(kl) and xylem vulnerability of two obligate phreatophytes
and two facultative phreatophytes. At sites where depth-to-
groundwater was shallow, there were no inter-specific dif-
ferences in vulnerability to water stress. However, by com-
paring across a topographic gradient, Canham et al. (2009)
showed that two facultative phreatophytes (but not the obli-
gate phreatophytes) were more resistant to xylem embolism
at the upper slope (larger depth-to-groundwater) than the
lower slope.
It is not only above-ground tissues that adapt to changes
in groundwater depth. Differences in root growth also re-
spond to changes in depth-to-groundwater. Thus Canham et
al. (2012) found that root growth varied with depth within
the soil column: at the surface, root growth responded to sea-
sonality and microclimate; at depth, root growth occurred all
year and was dependent upon soil aeration (i.e. roots elon-
gated rapidly following a declining water table during the
summer and died back in the following winter as the ground-
water rebounded). These results are consistent with the in-
creases in ET following groundwater decline that were ob-
served by Cleverly et al. (2006). The ability to rapidly in-
crease root depth during the (dry) summer is a critical at-
tribute of phreatophytes occupying sites with seasonally dy-
namic depth-to-groundwater.
The development of ecosystem response trajectories for
the impact of groundwater abstraction is an important re-
source management imperative. Froend and Sommer (2010)
examined a rare, 40-year vegetation survey data set from
the Gnangara Mound. Whilst the long-term average (1976–
2008) rainfall was 850mm, the annual average for the re-
cent past was about 730mm and depth-to-groundwater has
increased by 1m in the past 50 years. Depth-to-groundwater
fluctuates about 0.5–3m seasonally, and maximal depth oc-
curs at the end of summer. Two transects were compared: a
“control” where gradual increases in depth-to-groundwater
(9cmyr1) have occurred as a result of the decline in annual
rainfall; and an “impacted” transect where large rates of in-
crease in depth-to-groundwater have occurred (50cm yr1).
Principal component analyses were used to identify three
vegetation communities: those associated with down-slope,
mid-slope and upper-slope positions. Species having a high
reliance on consistent water supplies (mesic species) were
dominant at the down-slope site, while xeric species domi-
nated the upper-slope sites.
On the control transect it was hypothesised that groundwa-
ter decline would result in a replacement of the mesic by the
xeric species. However, this hypothesis was not supported.
Indeed, most of the compositional and structural attributes
of the three communities remained unchanged. The principle
community-scale response was a change in the abundance of
mesic and xeric species rather than complete replacement of
one species for another. In contrast to the results of Shatfroth
et al. (2000), mesic species at sites with shallow groundwater
were not more sensitive to increases in depth-to-groundwater
than xeric species. By contrast, changes in composition on
the impacted transect were far more pronounced, and mass
mortality was observed across all classes (mesic to xeric)
species. This study emphasises the importance of the rate of
change in depth-to-groundwater as a determinant of the re-
sponse of species and communities.
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4244 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
7.2 Riparian forest vegetation in the south-western
USA
In the south-western USA, the majority of GDEs are riparian
or littoral, where a shallow aquifer is formed by runoff from
snowmelt in the mountainous headwaters. Much of the agri-
culture in the region is found along the rivers due to the large
amount of surface water that flows past. The focus of irriga-
tion to the riparian corridors has placed intense competition
between water resources for people versus the environmen-
tal flows that are required to maintain shallow aquifers and
associated GDEs. Of further risk to riparian GDEs and agri-
culture, groundwater extraction and land use change threaten
riparian ecosystems (Scott et al., 1999; Nippert et al., 2010;
Pert et al., 2010). Thus, many studies have been undertaken
over several decades to investigate the water use of GDEs
in south-western North America (van Hylckama, 1970; Gay
and Fritschen, 1979; Sala et al., 1996; Devitt et al., 1998;
Goodrich et al., 2000a; Cleverly et al., 2002; Scott et al.,
2004; Nagler et al., 2005b).
Sunlight is plentiful in the south-western USA; thus, ri-
parian GDEs are strong carbon sinks (Kochendorfer et al.,
2011). However, seasonal variability in surface water dis-
charge and aquifer recharge can create cycles of hypoxia
and drought stress (Lowry et al., 2011), both of which act
to reduce production (Shah and Dahm, 2008). Often existing
between these two states of stress, riparian vegetation can
transpire substantial amounts of water, reaching near the the-
oretical maximum (12mmday1) (Cleverly, 2013). This
general release from limitations due to energy, moisture and
stress results in rates of latent heat flux that exceed precipita-
tion (i.e. ET/P > 1) (Scott et al., 2000, 2006b; Cleverly et al.,
2006) and net radiation (Devitt et al., 1998). Even when lit-
tle or no groundwater use can be identified in the vegetation
(e.g. in Sporobolis), ET losses from the riparian corridor can
exceed precipitation inputs (Scott et al., 2000), implying that
soil moisture in the vadose zone can be recharged by ground-
water and that riparian GDEs need not use the groundwater
directly.
In south-western North America, vegetation in riparian
corridors and adjacent rangelands or shrublands is classified
by reliance upon access to groundwater (i.e. obligate or fac-
ultative phreatophyte; Smith et al., 1998) or plant functional
type (obligate wetland, shallow-rooted or deep-rooted ripar-
ian, transitional riparian, or upland; Pockman and Sperry,
2000; Baird and Maddock, 2005; Baird et al., 2005). The
result of groundwater depletion has distinct effects on the
vegetation in each functional type. Shallow-rooted, obligate
phreatophytes (e.g. cottonwood, Populus spp.) can be very
sensitive to groundwater decline, resulting in reductions of
ET, productivity and canopy conductance as a consequence
of increases in vapour pressure deficit that are correlated
with depth-to-groundwater (Gazal et al., 2006; Kochendor-
fer et al., 2011). Branch sacrifice, partial crown dieback and
mortality commonly occur in Populus following substantial
groundwater drawdown (Mahoney and Rood, 1991; Kran-
jcec et al., 1998; Scott et al., 1999; Rood et al., 2000, 2003;
Cooper et al., 2003). However, stomatal closure and crown
dieback in Populus can prevent total hydraulic failure, and
thereby minimise mortality rates, by maintaining favourable
xylem water potentials within the remainder of the crown
(Amlin and Rood, 2003).
Decreased baseflow and drawdown of groundwater lev-
els has been associated with a shift in dominance to xe-
rophytic species in the American Southwest at the ex-
pense of forbs and obligate phreatophytes (Stromberg et
al., 1996, 2006, 2007, 2010). Xerophytes in the riparian
corridors of the American Southwest include deep-rooted
phreatophytes (e.g. Proposis,Tamarix) and upland species
(e.g. Chrysothamnus), any of which may be opportunistic
users of groundwater or groundwater-independent. Stress tol-
erance, opportunistic use of groundwater and use of mul-
tiple water sources (e.g. soil moisture) have contributed to
the invasive success of Tamarix (Busch et al., 1992; Clev-
erly et al., 1997; Di Tomaso, 1998; Nippert et al., 2010).
Consequently, Tamarix inhabit sites with variable depth-to-
groundwater (Lite and Stromberg, 2005), which results in an
amount of ET that is equivalently variable in time and space
(Cleverly et al., 2002; Cleverly, 2013).
The effective area of riparian vegetation has historically
increased in the American Southwest due to expansion of
deep-rooted phreatophytes like Tamarix and Prosopis (Hul-
tine and Bush, 2011). The upland vegetation that previously
occupied riverine upper terraces and grasslands supported
small rates of ET (Shafroth et al., 2005; Hultine and Bush,
2011); thus, expansion of phreatophytes into these areas has
resulted in an increase in ET losses (Scott et al., 2006b;
Cleverly, 2013) and thereby has placed a potential strain on
groundwater resources. In the case of expansion by Tamarix,
groundwater extraction may result in enhancement of ET
(Cleverly et al., 2006), contrasting with post-extraction re-
ductions in ET by native, shallow-rooted phreatophytes such
as Populus (Cooper et al., 2006; Gazal et al., 2006) and thus
representing a shift in the ecohydrology of riparian corri-
dors throughout the semi-arid regions of south-western North
America.
8 Integrating multiple-scale responses
8.1 Multiple traits across leaf, branch, whole-tree and
stand
The responses of vegetation to differences in depth-to-
groundwater have been examined extensively at leaf, tree,
canopy and population scales. Rates of leaf-scale photosyn-
thesis, stomatal conductance, whole plant hydraulic conduc-
tance, tree- and canopy-scale transpiration and plant den-
sity are known to decline in response to reduced supply
of groundwater (Table 3). Similarly, increased Huber value,
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D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4245
Table 3. A summary of some of the recent literature documenting the response of vegetation, across multiple scales, to reduced availability
of groundwater.
Process/trait Response to reduced availability of References
groundwater and range of depths
Leaf-scale Decreased (zero to 9m DGW); Horton et al. (2001)
photosynthesis
Stomatal Decrease (zero to 9 m DGW); Horton et al. (2001)
conductance Decreased (zero to >1 m DGW increased); Cooper et al. (2003)
Stomatal resistance increased from 38.8 to 112.5 Zunzunegui et al. (2000)
(zero to >3 m DGW) Gries et al. (2003)
Decreased (7 to 23 m DGW) Kochendorfer et al.
Decreased (2 to 4 m DGW) (2011)
Canopy Decreased (1.5 to >5 m DGW) Carter and White (2009)
conductance Decreased (2 to 4 m DGW) Kochendorfer et al.
(2011)
Leaf and stem 9pd decrease from 0.5 to 1.7MPa (zero to 9m); Horton et al. (2001)
water 9pd decreased from 0.2–0.4 to 0.4 to 0.8MPa Cooper et al. (2003)
potential (zero to >1 m DGW increased); Froend and Drake (2006)
Decreased from 0.79 to 2.55 MPa (<2 to Zunzunegui et al. (2000)
20 m DGW); Gries et al. (2003)
Decreased from 1.85 to 3.99 (zero to
>3 m DGW)
9midday decreased (7 to 23 m DGW)
Transpiration Total Et decreased 32% (0.9 to 2.5 m DGW); Cooper et al. (2006)
Gazal et al. (2006)
Ford et al. (2008)
rate Et decreased (2 to 4 m DGW) Kochendorfer et al.
Edecreased from 966 to 484 mm (1.1 to (2011)
3.1 m DGW)
Annual Edecreased (zero to 8 m DGW)
Resistance to Increased (1.5 to 30m DGW); Canham et al. (2009)
xylem PLC50 decreased from 1.07 to 3.24 MPa (<2 to Froend and Drake (2006)
embolism >20 m DGW)
Growth rate Decreased (zero to >1m DGW increased); Scott et al. (1999)
Decreased (7 to 23 m DGW) Gries et al. (2003)
Leaf area Decreased from 3.5 to 1.0 (1.5 to >5 m DGW) Carter and White (2009)
index Decreased O’Grady et al. (2011)
Decreased from 2.5 to 0.66 (zero to >3 m DGW) Zunzunegui et al. (2000)
Decreased from 2.7 to 1.7 (1.1 to 3.1 m DGW) Gazal et al. (2006)
Huber value Increased from 3.3 to 4.7 (1.1 to 3.1 m DGW) Gazal et al. (2006)
(SWA/LA) No change (1.5 to 30 m DGW) Canham et al. (2009)
Increased from 3.4 to 4.3 ×104(1.5 to Carter and White (2009)
>5 m DGW)
Plant density Vascular species number decreased; Zinko et al. (2005)
Species composition changed (0.9 to Cooper et al. (2006)
2.5 m DGW); Merritt and Bateman
plant cover type changed (1.1 to 2.5m DGW); (2012)
vegetation cover and diversity decreased (1 to Lv et al. (2013)
110 m DGW)
NDVI Decreased (1 to 110 m DGW); Lv et al. (2013)
Decreased (zero to 1.5 m DGW increased) Aguilar et al. (2012)
Decreased (1.8 to 3.5 m DGW) Wang et al. (2011)
Crown Increased between <40 to >50 % (zero to 9m); Horton et al. (2001)
dieback Leaf loss 34 % (zero to >1 m DGW increased) Cooper et al. (2003)
Mortality Increased (>2.2 DGW increased) Groom et al. (2000)
Increased (zero to >1 m DGW increased) Scott et al. (1999)
Increased (0.4 to 5 m DGW) González et al. (2012)
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4246 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
crown dieback and mortality in response to reduced supply of
groundwater have been observed (Table 3). Consequently, re-
sponse functions for individual traits are readily apparent; ex-
amples include changes with depth-to-groundwater in rates
of photosynthesis (Horton et al., 2001), plant cover (Elmore
et al., 2006), NDVI (Lv et al., 2012) and crown dieback (Hor-
ton et al., 2001). However, few studies have examined mul-
tiple traits across multiple scales and then provided an in-
tegrated “ecosystem-scale” response function to differences
in groundwater availability. Integrated ecosystem-scale re-
sponses to changes in groundwater availability have been hy-
pothesised to be linear (Fig. 6), curvi-linear or a step func-
tion with which minimal damage occurs until a threshold is
reached (Leffler and Evans, 1999; Eamus et al., 2006).
Information on how vegetation adapts to differences in
water supply is critical for predicting vegetation survival,
growth and water use, which have important impacts on site
hydrology (McDowell et al., 2008; Carter and White, 2009).
The development of integrated response curves to reduced
groundwater availability would significantly enhance our un-
derstanding of water requirements and lead to the identifica-
tion of response thresholds. Such thresholds could be used to
identify the limits of reduction in water-source availability,
a useful parameter for characterising water requirements for
resource and conservation management (Froend and Drake,
2006).
In a recent comprehensive, 3-year study, Zolfaghar (2014)
examined leaf, branch, tree and stand-scale functional and
structural attributes of woodlands across a gradient of depth-
to-groundwater (2.4 to 37.5m) in mesic Australia. She ex-
amined eighteen traits, including stand-scale basal area and
tree height, leaf turgor loss point, sapwood hydraulic conduc-
tivity, sensitivity to xylem embolism and above ground net
primary productivity. An increase in depth-to-groundwater
across these sites was hypothesised to result in
1. reduced standing biomass;
2. adjustment of leaf-, tree- and plot-scale plant traits with
associated repercussions for plant water relations;
3. increased drought tolerance; and
4. increased water-use efficiency.
Figure 7 provides a summary of the observed responses
of each trait to increasing depth-to-groundwater. Refer to Ta-
ble 4 for the abbreviations used in Fig. 7.
It is clear from Fig. 7 that increased depth-to-groundwater
was associated with declines in basal area, tree height and
LAI, and hence light interception, of native woodlands.
As a consequence, above-ground net primary productivity
was reduced as groundwater availability declined. Increased
drought tolerance, as indicated by increased water-use effi-
ciency, an increased Huber value and reduced water poten-
tial at turgor loss and solute potential at full turgor, supported
Figure 6. Hypothetical response functions for ecosystem function
to differences in groundwater availability. From Eamus et al. (2006).
the principle over-arching hypothesis of increasing depth-to-
groundwater results in a suite of leaf-branch and tree-scale
adaptations that increase tree tolerance to reduced water sup-
ply.
A key aspect of this research was to develop an
ecosystem-scale response function for depth-to-groundwater.
Zolfaghar (2014) normalised the responses (0 to 1) such that
a response of 1 indicates no effect of differences in depth-
to-groundwater and 0.5 indicates a 50% decline/increase in
the maximal/minimum value of a particular trait. The nor-
malised response function is presented in Fig. 8. Despite the
large number of traits and species across the seven sites,
the standard error of the ecosystem-scale average for each
data point was remarkably small, indicating significant con-
vergence in normalised responses to differences in depth-to-
groundwater. Convergence of functional variations in traits
across sites and species is increasingly observed with respect
to rainfall or other climatic variables (Wright et al., 2004;
Kattge et al., 2011). Indeed, identification of plant functional
types (PFTs) is a practical means for models of land surface–
atmosphere interactions across biomes to integrate the phys-
iology of vegetation. Similarly, improved accuracy can be
obtained from dynamic global vegetation models (DGVMs)
through the construction of large data sets (cf. Wright et al.,
2004; Kattge et al., 2011) that include a representation of
groundwater-dependent ecosystems.
A second feature apparent in the response function of
Fig. 8 is the large R2of the sigmoidal regression, reflect-
ing the relatively high degree of confidence in this threshold
response. The response curve further suggests that extrac-
tion of groundwater beyond 7–9m depth is likely to result
in significant changes in ecosystem structure and function.
Although we cannot pinpoint the exact breakpoint with pre-
cision, it is clearly apparent that a breakpoint does occur in
the data. Furthermore, two recent reviews based on water bal-
ance concluded that groundwater uptake ceased when depths
exceeded 7.5m (Benyon et al., 2006) or 8–10 m (O’Grady
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4247
Table 4. The meaning of the abbreviations/traits used in Fig. 7.
Abbreviation Explanation/definition
9TLP The water potential of leaves at which turgor is zero
Q100 The solute potential at a relative water content of 100%
RWCTLP The relative water content at which leaf turgor is zero
SWD The saturated water content of wood
KsSapwood-specific hydraulic conductivity of branch xylem
KLLeaf-specific hydraulic conductivity of branch xylem
PLC50 The water potential at which 50% of the hydraulic conductivity is lost
PLC88 The water potential at which 88% of the hydraulic conductivity is lost
HvHuber value: the ratio of leaf area to sapwood area
BA Total basal area of trees within a plot
LAI Leaf area index of a stand of trees
AGB Above-ground biomass
ANPP Above-ground net primary productivity
WUE Water-use efficiency; calculated as the ratio of ANPP/stand water use
Height Average height of the trees in a plot
Water use Rates of stand water use; up-scaled from sap flow measurements
Stem density The number of trees per hectare
Litterfall Rates of annual litterfall within a plot
Figure 7. A summary of the traits examined and the general trend in response of those traits to increased depth-to-groundwater along a
natural topographic gradient. Upward/downward pointing arrows within a coloured text box indicate increasing/decreasing values of the
plant trait as depth-to-groundwater increases. Horizontal arrows indicate no change. Table 4 provides the definition of all abbreviations used
in this figure.
et al., 2010), whilst Cook et al. (1998) established a limit of
approximately 8m for a Eucalypt savanna. Finally, Kath et
al. (2014) identified thresholds of groundwater depth across
118 sites in south-eastern Australia for two tree species rang-
ing from 12.1 to 26.6m, further supporting our identifica-
tion of a breakpoint in the responses of trees to groundwa-
ter depth. Such a strong response, consistent across multiple
www.hydrol-earth-syst-sci.net/19/4229/2015/ Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015
4248 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
Figure 8. Ecosystem response to increase in depth-to-
groundwater, fitted with four-parameter sigmoidal function.
From Zolfaghar (2014).
traits, should provide a strong management signal to guide
future groundwater abstraction.
8.2 Co-ordination across traits
Some plant traits are a better indicator of plant sensitivity to
water stress than others. Leaf water potential at turgor loss
is recognised as a physiological measure of plant sensitivity
to water stress (McDowell et al., 2008). Similarly, measure-
ments of vulnerability to xylem cavitation and safety margins
are critical determinants of drought tolerance (Markesteijn et
al., 2011; Sperry et al., 2008). Safety margins are equal to
the difference between minimum daily branch water poten-
tial and PLC50 (Meinzer et al., 2008; Sperry et al., 2008). A
strong linear correlation between these two traits (Fig. 9) in
the Kangaloon study (Zolfaghar, 2014) reveals co-ordination
in the response of leaf (cell trait) and xylem (branch trait)
anatomy, as has been observed previously in a study of eight
tropical dry forest species (Brodribb et al., 2003). This re-
lationship indicates that as depth-to-groundwater increased,
sensitivity to drought at both leaf cell and branch scale de-
creased (lower leaf water potential is needed to reach the tur-
gor loss point, and PLC50 declined).
9 Concluding remarks
The existence of GDEs has been known for several centuries.
The ecological, social, cultural and economic importance of
GDEs, however, has only been understood more recently.
Whilst inferential methods were the main means for deter-
mining the presence/location of GDEs for many decades,
these have now been replaced by more direct methodolo-
gies which include the use of stable isotopes and hourly di-
rect measurements of fluctuations in shallow groundwater
depth. The most revolutionary recent development has, per-
Figure 9. Co-ordination in the response of a leaf-scale and branch-
scale trait and drought sensitivity. From Zolfaghar (2014).
haps, been the application of remote sensing techniques to
identify the location of GDEs but also to reveal key features
of their functional behaviour.
Increasing frequencies, spatial and temporal extent and
severity of drought and resulting drought-induced mortality
of forests have been recorded extensively (Dai, 2011; Eamus
et al., 2013) in the past two decades. Climate-change-
induced changes in rainfall distribution and amounts pose
a new stress to both groundwater resources and associated
GDEs. For the first time, remotely sensed information on
both the structure (e.g. LAI) and functioning (e.g. rates
of water use and primary productivity) of GDEs are now
available across several decades. The challenge now is to
use this long history of remotely sensed and meteorological
data as a unique natural experiment to determine response
functions of multiple GDEs to changes in climate (and
groundwater depth) globally to inform both the science of
ecology and the practical needs of water and land resource
managers into the future.
Edited by: P. Saco
References
Abudu, S., Bawazir, A. S., and King, J. P.: Infilling Missing Daily
Evapotranspiration Data Using Neural Networks, J. Irrig. Drain.
Eng., 136, 317–325, doi:10.1061/(asce)ir.1943-4774.0000197,
2010.
Adams, H. D. and Kolb, T. E.: Tree growth response to drought
and temperature in a mountain landscape in northern Ari-
zona, USA, J. Biogeogr., 32, 1629-1640, doi:10.1111/j.1365-
2699.2005.01292.x, 2005.
Aguilar, C., Zinnert, J. C., Jose Polo, M., and Yound, D. R.: NDVI
as an indicator for changes in water availability to woody vege-
tation, Ecol. Appl., 23, 290–300, 2012.
Ajami, H., Meixner, T., Maddock, T., Hogan, J. F., and Guertin,
P.: Impact of land-surface elevation and riparian evapotranspira-
tion seasonality on groundwater budget in MODFLOW models,
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4249
Hydrogeol. J., 19, 1181–1188, doi:10.1007/s10040-011-0743-0,
2011.
Ajami, H., Maddock, T., Meixner, T., Hogan, J. F., and Guertin,
D. P.: RIPGIS-NET: A GIS tool for riparian groundwater evap-
otranspiration in MODFLOW, Ground Water, 50, 154–158,
doi:10.1111/j.1745-6584.2011.00809.x, 2012.
Akasheh, O. Z., Neale, C. M. U., and Jayanthi, H.: Detailed map-
ping of riparian vegetation in the middle Rio Grande River using
high resolution multi-spectral airborne remote sensing, J. Arid
Environ., 72, 1734–1744, 2008.
Allen, R. G., Pereira, L. S., Raes, D., and Smith, M.: Crop evapo-
transpiration: Guidelines for computing crop requirements, Irri-
gation and Drainage Paper No. 56, FAO, Rome, Italy, 1998.
Amlin, N. and Rood, S.: Drought stress and recovery of riparian
cottonwoods due to water table alteration along Willow Creek,
Alberta, Trees Struct. Funct., 17, 351–358, 2003.
Baird, K. J. and Maddock, T.: Simulating riparian evapotranspira-
tion: A new methodology and application for groundwater mod-
els, J. Hydrol., 312, 176–190, 2005.
Baird, K. J., Stromberg, J. C., and Maddock, T.: Linking riparian
dynamics and groundwater: An ecohydrologic approach to mod-
eling groundwater and riparian vegetation, Environ. Manage., 36,
551–564, 2005.
Baldocchi, D. D. and Ryu, Y.: A synthesis of forest evaporation
fluxes – from days to years – as measured with eddy covariance,
in: Forest Hydrology and Biogeochemistry: Synthesis of Past Re-
search and Future Directions, edited by: Levia, D. F., Carlyle-
Moses, D., and Tanaka, T., Springer Sciences+Business Media
B. V., Dordrecht, the Netherlands, 101–116, 2011.
Baldocchi, D. D. and Vogel, C. A.: Energy and CO2flux densities
above and below a temperate broad-leaved forest and a boreal
pine forest, Tree Physiol., 16, 5–16, 1996.
Barron, O. V., Emelyanova, I., van Niel, T. G., Pollock, D., and
Hodgson, G.: Mapping groundwater dependent ecosystems using
remote sensing measures of vegetation and moisture dynamics,
Hydrol. Process., 28, 372–385, 2014.
Bauer, P., Thabeng, G., Stauffer, F., and Kinzelbach, W.: Estima-
tion of the evapotranspiration rate from diurnal groundwater level
fluctuations in the Okavango Delta, Botswana, J. Hydrol., 288,
344–355, 2004.
Benyon, R. G. and Doody, T. M.: Water Use by Tree Plantations
in South East South Australia. CSIRO Forestry and Forest Prod-
ucts Technical Report Number 148, CSIRO, Mount Gambier SA,
2004.
Benyon, R. G., Theiveyanathan, S., and Doody, T. M.: Impacts of
tree plantations on groundwater in south-eastern Australia, Aust.
J. Bot., 54, 181–192, doi:10.1071/bt05046, 2006.
Bogino, S. M. and Jobbagy, E. G.: Climate and groundwater ef-
fects on the establishment, growth and death of Prosopis calde-
nia trees in the Pampas (Argentina), Forest Ecol. Manage., 262,
1766–1774, doi:10.1016/j.foreco.2011.07.032, 2011.
Brodribb, T. J., Holbrook, N. M., Edwards, E. J., and Gutierrez, M.
V.: Relations between stomatal closure, leaf turgor and xylem
vulnerability in eight tropical dry forest trees, Plant Cell Envi-
ron., 26, 443–450, 2003.
Brown, J., Bach, L., Aldous, A., Wyers, A., and DeGagne, J.:
Groundwater-dependent ecosystems in Oregon: an assessment of
their distribution and associated threats, Front. Ecol. Environ., 9,
97–102, 2010.
Brown, L.: Water tables falling and rivers running dry: international
situation, Int. J. Environ., 3, 1–5, 2007.
Brunner, P., Franssen, H.-J. H., Kgotlhang, L., Bauer-Gottwein,
P., and Kinzelbach, W.: How can remote sensing contribute in
groundwater modeling?, Hydrogeol. J., 15, 5–18, 2007.
Budyko, M. I.: Climate and life, Academic Press, San Diego, CA,
508 pp., 1974.
Busch, D. E., Ingraham, N. L., and Smith, S. D.: Water uptake in
woody riparian phreatophytes of the Southwestern United States:
a stable isotope study, Ecol. Appl., 2, 450–459, 1992.
Butler, J. J., Kluitenberg, G. J., Whittemore, D. O., Loheide, S. P.,
Jin, W., Billinger, M. A., and Zhan, X. Y.: A field investigation
of phreatophyte-induced fluctuations in the water table, Water
Resour. Res., 43, W02404, doi:10.1029/2005WR004627, 2007.
Campos, G. E. P., Moran, M. S., Huete, A., Zhang, Y., Bresloff,
C., Huxman, T. E., Eamus, D., Bosch, D. D., Buda, A. R., and
Gunter, S. A.: Ecosystem resilience despite large-scale altered
hydroclimatic conditions, Nature, 494, 349–352, 2013.
Canham, C. A., Froend, R. H., and Stock, W. D.: Water stress vul-
nerability of four Banksia species in contrasting ecohydrological
habitats on the Gnangara Mound, Western Australia, Plant Cell
Environ., 32, 64–72, 2009.
Canham, C. A., Froend, R. H., Stock, W. D., and Davies, M.: Dy-
namics of phreatophyte root growth relative to a seasonally fluc-
tuating water table in a Mediterranean-type environment, Oe-
cologia, 170, 909–916, 2012.
Carlson, T. N. and Ripley, D. A.: On the relation between NDVI,
fractional vegetation cover, and leaf area index, Remote Sens.
Environ., 62, 241–252, doi:10.1016/s0034-4257(97)00104-1,
1997.
Carter, J. L. and White, D. A.: Plasticity in the Huber value con-
tributes to homeostasis in leaf water relations of a mallee Eu-
calypt with variation to groundwater depth, Tree Physiol., 29,
1407–1418, doi:10.1093/treephys/tpp076, 2009.
Cernusak, L. A., Marshall, J. D., Comstock, J. P., and Balster, N. J.:
Carbon isotope discrimination in photosynthetic bark, Oecolo-
gia, 128, 24–35, doi:10.1007/s004420100629, 2001.
Chimner, R. A. and Cooper, D. J.: Using stable oxygen isotopes to
quantify the water source used for transpiration by native shrubs
in the San Luis Valley, Colorado USA, Plant Soil, 260, 225–236,
doi:10.1023/B:PLSO.0000030190.70085.e9, 2004.
Cleverly, J. R.: Water use by Tamarix, in: Tamarix. A Case Study of
Ecological Change in the American West, Sher, A. and Quigley,
M. F., Oxford University Press, New York, NY, 85–98, 2013.
Cleverly, J. R., Smith, S. D., Sala, A., and Devitt, D. A.: Invasive
capacity of Tamarix ramosissima in a Mojave Desert floodplain:
the role of drought, Oecologia, 111, 12–18, 1997.
Cleverly, J. R., Dahm, C. N., Thibault, J. R., Gilroy, D. J.,
and Coonrod, J. E. A.: Seasonal estimates of actual evapo-
transpiration from Tamarix ramosissima stands using three-
dimensional eddy covariance, J. Arid Environ., 52, 181–197,
doi:10.1006/jare.2002.0972, 2002.
Cleverly, J. R., Dahm, C. N., Thibault, J. R., McDonnell, D. E.,
and Coonrod, J. E. A.: Riparian ecohydrology: Regulation of wa-
ter flux from the ground to the atmosphere in the Middle Rio
Grande, New Mexico, Hydrol. Process., 20, 3207–3225, 2006.
Clifton, C. A. and Evans, R.: Environmental water requirements
to maintain groundwater dependent ecosystems, Environmental
www.hydrol-earth-syst-sci.net/19/4229/2015/ Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015
4250 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
Flows Initiative Technical Report Number 2, Commonwealth of
Australia, Canberra, 2001.
Cocozza, C., Giovannelli, A., Traversi, M. L., Castro, G., Cheru-
bini, P., and Tognetti, R.: Do tree-ring traits reflect different water
deficit responses in young poplar clones (Populus×canadensis
Monch ’I-214’ and P. deltoides ’Dvina’)?, Trees Struct. Funct.,
25, 975–985, doi:10.1007/s00468-011-0572-8, 2011.
Conejero, W., Alarcón, J. J., García-Orellana, Y., Abrisqueta, J.
M., and Torrecillas, A.: Daily sapflow and maximum daily trunk
shrinkage measurements for diagnosing water stress in early ma-
turing peach trees during the post harvest period, Tree Physiol.,
27, 81–88, 2007.
Conejero, W., Mellisho, C. D., Ortuno, M. F.: Using trunk diame-
ter sensors for regulated irrigation scheduling in early maturing
peach trees, Environ. Exp. Bot., 71, 409–415, 2011.
Contreras, S., Jobbagy, E. G., Villagra, P. E., Nosetto, M. D., and
Puigdefabregas, J.: Remote sensing estimates of supplementary
water consumption by arid ecosystems of central Argentina, J.
Hydrol., 397, 10–22, 2011.
Cook, P. G. and O’Grady, A. P.: Determining soil and ground wa-
ter use of vegetation from heat pulse, water potential and stable
isotope data, Oecologia, 148, 97–107, doi:10.1007/s00442-005-
0353-4, 2006.
Cook, P. G., Hatton, T. J., Pidsley, D., Herczeg, A. L., Held,
A., O’Grady, A., and Eamus, D: Water balance of a trop-
ical woodland ecosystem, northern Australia: a combination
of micro-meteorological, soil physical and groundwater chem-
ical approaches, J. Hydrol., 210, 161–177, doi:10.1016/S0022-
1694(98)00181-4, 1998.
Cooper, D. J., D’Amico, D., and Scott, M.: Physiological and mor-
phological response patterns of Populus deltoides to alluvial
groundwater pumping, Environ. Manage., 31, 215–226, 2003.
Cooper, D. J., Sanderson, J. S., Stannard, D. I., and Groeneveld, D.
P.: Effects of long-term water table drawdown on evapotranspi-
ration and vegetation in an arid region phreatophyte community,
J. Hydrol., 325, 21–34, 2006.
Dahm, C. N., Cleverly, J. R., Coonrod, J. E. A., Thibault, J. R.,
McDonnell, D. E., and Gilroy, D. F.: Evapotranspiration at the
land/water interface in a semi-arid drainage basin, Freshwater
Biol., 47, 831–843, 2002.
Dai, A.: Drought under global warming: a review, Wiley Interdisci-
plinary Reviews – Climate Change, 2, 45–65, 2011.
Dawson, T. E. and Ehleringer, J. R.: Streamside trees that do not
use stream water, Nature, 350, 335–337, doi:10.1038/350335a0,
1991.
Devitt, D. A., Sala, A., Smith, S. D., Cleverly, J. R., Shaulis, L. K.,
and Hammett, R.: Bowen ratio estimates of evapotranspiration
for Tamarix ramosissima stands on the Virgin River in southern
Nevada, Water Resour. Res., 34, 2407–2414, 1998.
Di Tomaso, J. M.: Impact, biology, and ecology of saltcedar
(Tamarix spp.) in the southwestern United States, Weed Tech-
nol., 12, 326–336, 1998.
Doble, R., Simmons, C., Jolly, I., and Walker, G.: Spatial relation-
ships between vegetation cover and irrigation-induced ground-
water discharge on a semi-arid floodplain, Australia, J. Hydrol.,
329, 75–97, doi:10.1016/j.jhydrol.2006.02.007, 2006.
Donohue, R. J., Roderick, M. L., and McVicar, T. R.: On the impor-
tance of including vegetation dynamics in Budyko’s hydrological
model, Hydrol. Earth Syst. Sci., 11, 983–995, doi:10.5194/hess-
11-983-2007, 2007.
Doody T. M., Benyon, R. G., Theiveyanathan, S., Koul, V., and
Stewart, L.: Development of pan coefficients for estimating evap-
otranspiration from riparian woody vegetation, Hydrol. Process.,
28, 2129–2149, doi:10.1002/hyp.9753, 2014.
Drake, P. L. and Franks, P. J.: Water resource partitioning, stem
xylem hydraulic properties, and plant water use strategies in a
seasonally dry riparian tropical rainforest, Oecologia, 137, 321–
329, doi:10.1007/s00442-003-1352-y, 2003.
Drake, P. L., Coleman, B. F., and Vogwill, R.: The response of semi-
arid ephemeral wetland plants to flooding: linking water use to
Hydrol. Proc., Ecohydrology, 6, 852–862, 2013.
Dresel, P. E., Clark, R., Cheng, X., Reid, M., Terry, A., Fawcett,
J., and Cochrane, D.: Mapping Terrestrial GDEs: Method devel-
opment and example output. Victoria Department of Primary In-
dustries, Melbourne, VIC., 66 pp., 2010.
Drew, D. M. and Downes, G. M.: The use of precision dendrometers
in research on daily stem size and wood property variation: A
review, Dendrochronologia, 27, 169–172, 2009.
Drew, D. M., O’Grady, A. P., Downes, G. M., Read, J., and
Worledge, D.: Daily patterns of stem size variation in irrigated
and unirrigated Eucalyptus globulus, Tree Physiol., 28, 1573–
1581, 2008.
Eagleson, P. S.: Climate, soil and vegetation: 1. Introduction to wa-
ter balance dynamics, Water Resour. Res., 14, 705–712, 1978.
Eamus, D., Hutley, L. B., and O’Grady, A. P.: Daily and seasonal
patterns of carbon and water fluxes above a north Australian sa-
vanna, Tree Physiol., 21, 977–988, 2001.
Eamus, D., Haton, T., Cook, P., and Colvin, C.: Ecohydrology: veg-
etation function, water and resource manangement, CSIRO, Mel-
bourne, 2006a.
Eamus, D., Froend, R., Loomes, R., Hose, G., and Murray, B.: A
functional methodology for determining the groundwater regime
needed to maintain the health of groundwater-dependent vegeta-
tion, Aust. J. Bot., 54, 97–114, 2006b.
Eamus, D., Boulain, N., Cleverly, J., and Breshears, D. D.: Global
change-type drought induced tree mortality: vaour pressure
deficit is more important than temperature per se in causing de-
cline in tree health, Ecol. Evol., 3, 2711–2729, 2013.
Ehleringer, J. R. and Dawson, T. E.: Water uptake by plants: per-
spectives from stable isotope composition, Plant Cell Environ.,
15, 1073–1082, 1992.
Ellis, T. W. and Hatton, T. J.: Relating leaf area index of natural
eucalypt vegetation to climate variables in southern Australia,
Agr. Water Manage., 95, 743–747, 2008.
Elmahdi, A. and McFarlane, D.: Integrated multi-agency frame-
work: sustainable water management, Proc. Inst. Civ. Eng. Water
Manage., 165, 313–326, doi:10.1680/wama.11.00003, 2012.
Elmore, A. J., Manning, S. J., Mustard, J. F., and Craine, J. M.:
Decline in alkali meadow vegetation cover in California: the ef-
fects of groundwater extraction and drought, J. Appl. Ecol., 43,
770–779, 2006.
Engel, V., Jobbagy, E. G., Stieglitz, M., Williams, M., and Jack-
son, R. B.: Hydrological consequences of eucalyptus afforesta-
tion in the argentine pampas, Water Resour. Res., 41, W10409,
doi:10.1029/2004wr003761, 2005.
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4251
Everitt, J. H. and DeLoach, C. J.: Remote sensing of Chinese
Tamarisk (Tamarix chinensis) and associated vegetation, Weed
Science, 38, 273–278, 1990.
Everitt, J. H., Judd, F. W., Escobar, D. E., Alaniz, M. A., Davis, M.
R., and MacWhorter, W.: Using remote sensing and spatial infor-
mation technologies to map sabal palm in the lower Rio Grande
Valley of Texas, Southw. Natural., 41, 218–226, 1996.
Fahle, M. and Dietrich, O.: Estimation of evapotranspiration using
diurnal groundwater level fluctuations: Comparison of different
approaches with groundwater lysimeter data, Water Resour. Res.,
50, 273–286, doi:10.1002/2013wr014472, 2014.
February, E. C., Higgins, S. I., Newton, R., and West, A. G.: Tree
distribution on a steep environmental gradient in an arid savanna,
J. Biogeogr., 34, 270–278, 2007.
Feikema, P. M., Morris, J. D., and Connell, L. D.: The water balance
and water sources of a Eucalyptus plantation over shallow saline
groundwater, Plant Soil, 332, 429–449, 2010.
Ford, C. R., Mitchell, R. J., and Teskey, R. O.: Water table depth
affects productivity, water use and the response to nitrogen ad-
dition in a savvan system, Can. J. Forest Res., 38, 2118–2127,
2008.
Froend, R. H. and Drake, P. L.: Defining phreatophyte response to
reduced water availability: preliminary investigations on the use
of xylem cavitation vulnerability in Banksia woodland species,
Aust. J. Bot., 54, 173–179, 2006.
Froend, R. H. and Sommer, B.: Phreatophytic vegetation response
to climatic and abstraction-induced GW drawdown: examples
of long-term spatial and temporal variability in community re-
sponse, Ecol. Eng., 36, 1191–1200, 2010.
Galindo, A., Rodrigues, P., Mellisho, C. D., Torrecillas, E., Mori-
ana, A., Cruz, Z. N., Conejero, W., Moreno, F., and Terrecillas,
A.: Assessment of discreetly measured indicators and maximum
daily trunk shrinkage for detecting water stress in pomegranate
trees, Agr. Forest Meteorol., 180, 58–65, 2013.
Gamon, J., Field, C., Goulden, M., Griffin, K., Hartley, A., Joel,
G., Penuelas, J., and Valentini, R.: Relationships between NDVI,
canopy structure, and photosynthesis in 3 Californian vegetation
types, Ecol. Appl., 5, 28–41, 1995.
Gay, L. W. and Fritschen, L. J.: An energy budget analysis of water
use by saltcedar, Water Resour. Res., 15, 1589–1592, 1979.
Gazal, R. M., Scott, R. L., Goodrich, D. C., and Williams, D. G.:
Controls on transpiration in a semiarid riparian cottonwood for-
est, Ag. Forest Meterol., 137, 56–67, 2006.
Gessler, A., Brandes, E., Buchmann, N., Helle, G., Rennenberg,
H., and Barnard, R. L.: Tracing carbon and oxygen isotope sig-
nals from newly assimilated sugars in the leaves to the tree-ring
archive, Plant Cell Environ., 32, 780–795, doi:10.1111/j.1365-
3040.2009.01957.x, 2009.
Giantomasi, M. A., Roig-Juñent, F. A., and Villagra, P. E.: Use of
differential water sources by Prosopis flexuosa DC: a dendroeco-
logical study, Plant Ecol., 214, 11–27, doi:10.1007/s11258-012-
0141-2, 2012.
Giordano, M.: Global groundwater? Issue and solutions, Ann. Rev.
Environ. Res. 34, 153–178.2009.
Glazer, A. N. and Likens, G. E.: The water table: the shifting foun-
dation of life on land, Ambio, 41, 657–669, 2012.
Gleick, P. and Palaniappan, M.: Peak water limits to freshwater
withdrawal and use, P. Natl. Acad. Sci., 107, 11155–11162,
2010.
Glenn, E. P., Huete, A. R., Nagler, P. L., Hirschboeck, K. K., and
Brown, P.: Integrating remote sensing and ground methods to
estimate evapotranspiration, Crit. Rev. Pl. Sci., 26, 139–168,
doi:10.1080/07352680701402503, 2007.
Glenn, E. P., Nagler, P. L., and Huete, A. R.: Vegetation Index Meth-
ods for Estimating Evapotranspiration by Remote Sensing, Surv.
Geophys., 31, 531–555, doi:10.1007/s10712-010-9102-2, 2010.
Gonzalez, E., Gonzalex-Sanchis, M., Comin, F. A., and Muller, E.:
Hydrologic thresholds for riparian forest conservation in a reg-
ulated large Mediterranean river, River Res. Appl., 28, 81–80,
2012.
Goodrich, D. C., Chehbouni, A., Goff, B., MacNish, B., Maddock,
T., Moran, S., Shuttleworth, W. J., Williams, D. G., Watts, C.,
Hipps, L. H., Cooper, D. I., Schieldge, J., Kerr, Y. H., Arias,
H., Kirkland, M., Carlos, R., Cayrol, P., Kepner, W., Jones, B.,
Avissar, R., Begue, A., Bonnefond, J. M., Boulet, G., Branan,
B., Brunel, J. P., Chen, L. C., Clarke, T., Davis, M. R., De-
Bruin, H., Dedieu, G., Elguero, E., Eichinger, W. E., Everitt, J.,
Garatuza-Payan, J., Gempko, V. L., Gupta, H., Harlow, C., Har-
togensis, O., Helfert, M., Holifield, C., Hymer, D., Kahle, A.,
Keefer, T., Krishnamoorthy, S., Lhomme, J. P., Lagouarde, J. P.,
Lo Seen, D., Luquet, D., Marsett, R., Monteny, B., Ni, W., Nou-
vellon, Y., Pinker, R., Peters, C., Pool, D., Qi, J., Rambal, S.,
Rodriguez, J., Santiago, F., Sano, E., Schaeffer, S. M., Schulte,
M., Scott, R., Shao, X., Snyder, K. A., Sorooshian, S., Unkrich,
C. L., Whitaker, M., and Yucel, I.: Preface paper to the Semi-Arid
Land-Surface-Atmosphere (SALSA) Program special issue, Agr.
Forest Meteorol., 105, 3–20, 2000a.
Goodrich, D. C., Scott, R., Qi, J., Goff, B., Unkrich, C. L., Moran,
M. S., Williams, D., Schaeffer, S., Snyder, K., MacNish, R.,
Maddock, T., Pool, D., Chehbouni, A., Cooper, D. I., Eichinger,
W. E., Shuttleworth, W. J., Kerr, Y., Marsett, R., and Ni, W.:
Seasonal estimates of riparian evapotranspiration using remote
and in situ measurements, Agr. Forest Meterol., 105, 281–309,
2000b.
Gou, S., Gonzales, S., and Miller, G.: Mapping potential
groundwater-dependent ecosystems for sustainable management,
Ground Water, 53, 99–110, 2015.
Gribovszki, Z., Kalicz, P., Szilagyi, J., and Kucsara, M.: Ripar-
ian zone evapotranspiration estimation from diurnal groundwater
level fluctuations, J. Hydrol., 349, 6–17, 2008.
Gribovszki, Z., Szilagyi, J., and Kalicz, P.: Diurnal fluctua-
tions in shallow groundwater levels and streamflow rates and
their interpretation – A review, J. Hydrol., 385, 371–383,
doi:10.1016/j.jhydrol.2010.02.001, 2010.
Gries, D., Zeng, F., Foetzki, A., Arndt, S. K., Bruelheide, H.,
Thomas, F. M., Zhang, X., and Runge, M.: Growth and water re-
lations of Tamarix ramosissima and Populus euphratica on Tak-
lamakan desert dunes in relation to depth to a permanent water
table, Plant Cell Environ., 26, 725–736, 2003.
Groeneveld, D. P.: Remotely-sensed groundwater evapotranspira-
tion from alkali scrub affected by declining water table, J. Hy-
drol., 358, 294–303, 2008.
Groeneveld, D. P. and Baugh, W. M.: Correcting satellite data to
detect vegetation signal for eco-hydrologic analyses, J. Hydrol.,
344, 135–145, 2007.
Groeneveld, D. P., Baugh, W. M., Sanderson, J. S., and Cooper, D.
J.: Annual groundwater evapotranspiration mapped from single
satellite scenes, J. Hydrol., 344, 146–156, 2007.
www.hydrol-earth-syst-sci.net/19/4229/2015/ Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015
4252 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
Groom, B. P., Froend, R. H., and Mattiske, E. M.: Impact of ground-
water abstraction on Banksia woodland, Swan Coastal Plain,
Western Australia, Ecol. Manage. Restor., 1, 117–124, 2000.
Hanson, R. T., Dettinger, M. D., and Newhouse, M. W.: Relations
between climatic variability and hydrologic time series from four
alluvial basins across the southwestern United States, Hydrogeol.
J., 14, 1122–1146, doi:10.1007/s10040-006-0067-7, 2006.
Hatton, T. and Evans, R.: Dependence of ecosystems on groundwa-
ter and its significance to Australia, Occasional Paper No. 12/98,
Land and Water Res. Res. and Dewvelopment Corporation,
CSIRO, Australia, 1998.
Henry, C. M., Allen, D. M., and Huang, J.: Groundwater stor-
age variability and annual recharge using well-hydrograph and
GRACE satellite data, Hydrogeol. J., 19, 741–755, 2011.
Horton, J. L., Kolb, T. E., and Hart, S. C.: Responses of riparian
trees to inter-annual variation in groundwater depth in a semi-
arid river basin, Plant Cell Environ., 24, 293–304, 2001.
Houborg, R., Rodell, M., Li, B., Reichle, R., and Zaitchik, B. F.:
Drought indicators based on model assimilated GRACE terres-
trial water storage observations, Water Resour Res., 48, W07525,
doi:10.1029/2011WR011291, 2012.
Howard, J. and Merrifield, M.: Mapping groundwater de-
pendent ecosystems in California, PLoS ONE, 5, e11249,
doi:10.1371/journal.pone.0011249, 2010.
Huete, A., Didan, K., Miura, T., Rodriguez, E. P., Gao, X., and Fer-
reira, L. G.: Overview of the radiometric and biophysical perfor-
mance of the MODIS vegetation indices, Remote Sens. Environ.,
83, 195–213, doi:10.1016/s0034-4257(02)00096-2, 2002.
Hultine, K. R. and Bush, S. E.: Ecohydrological consequences of
non-native riparian vegetation in the southwestern United States:
A review from an ecophysiological perspective, Water Resour
Res., 47, W07542, doi:10.1029/2010wr010317, 2011.
Hultine, K. R., Bush, S. E., and Ehleringer, J. R.: Ecophysiol-
ogy of riparian cottonwood and willow before, during, and af-
ter two years of soil water removal, Ecol. Appl., 20, 347–361,
doi:10.1890/09-0492.1, 2010
Jin, X. M., Schaepman, M. E., Clevers, J. G., Su, Z. B., and Hu, G.:
Groundwater depth and vegetation in the Ejina area, China, Arid
Land Res. Manage., 25, 194–199, 2011.
Jobbagy, E. G., Nosetto, M. D., Villagra, P. E., and Jackson, R. B.:
Water subsidies from montains to deserts:their roile in sustain-
ing groundwater fed oases in a sandy landscape, Ecol. Appl., 21,
678–694, 2011.
Jung, M., Reichstein, M., Margolis, H. A., Cescatti, A., Richard-
son, A. D., Arain, M. A., Arneth, A., Bernhofer, C., Bonal, D.,
Chen, J. Q., Gianelle, D., Gobron, N., Kiely, G., Kutsch, W.,
Lasslop, G., Law, B. E., Lindroth, A., Merbold, L., Montagnani,
L., Moors, E. J., Papale, D., Sottocornola, M., Vaccari, F., and
Williams, C.: Global patterns of land-atmosphere fluxes of car-
bon dioxide, latent heat, and sensible heat derived from eddy co-
variance, satellite, and meteorological observations, J. Geophys.
Res., 116, G00J07, doi:10.1029/2010jg001566, 2011.
Kanniah, K. D., Beringer, J., and Hutley, L. B.: Response of savanna
gross primary productivity to interannual variability in rainfall:
Results of a remote sensing based light use efficiency model,
Prog. Phys. Geogr., 37, 642–663, 2013.
Kath, J., Reardon-Smith, K., Le Brocque, A. F., Dyer, F. J., Dafny,
E., Fritz, L., and Batterham, M.: Groundwater decline and tree
change in floodplain landscapes: Identifying non-linear threshold
responses in canopy condition, Global Ecol. Conserv., 2, 148–
160, 2014.
Kattge, J., Diaz, S., Laborel, S., et al.: TRY – a global database of
plant traints, Global Change Biol., 17, 2905–2935, 2011.
Kelliher, F. M., Kirkham, M. B., and Tauer, C. G.: Stomatal resis-
tance, transpiration and growth of drought-stressed eastern cot-
tonwood, Can. J. Forest Res. 10, 447–451, 1980.
Kelliher, F. M., Kostner, B. M. M., Hollinger, D. Y., Byers, J. N.,
Hunt, J. E., McSeveny, T. M., Meserth, R., Weir, P. L., and
Schulze, E. D.: Evaporation, xylem sapflow and tree transpira-
tion in a New Zealand broad-leaved forest, Agr. Forest Meteorol.,
62, 53–73, doi:10.1016/0168-1923(92)90005-o, 1992.
Kochendorfer, J., Castillo, E. G., Haas, E., Oechel, W. C., and
Paw U, K. T.: Net ecosystem exchange, evapotranspiration and
canopy conductance in a riparian forest, Agr. Forest Meteorol.,
151, 544–553, 2011.
Kranjcec, J., Mahoney, J. M., and Rood, S. B.: The responses of
three riparian cottonwood species to water table decline, Forest
Ecol. Manage., 110, 77–87, 1998.
Kray, J. Cooper, D., and Sanderson, J.: Groundwater use by native
plants in response to changes in precipitation in an intermountain
basin, J. Arid Environ.,83, 25–34, 2012.
Lageard, J. G. A. and Drew, I. B.: Hydrogeomorphic con-
trol on tree growth responses in the Elton area of the
Cheshire Saltfield, UK, Geomorphology, 95, 158–171,
doi:10.1016/j.geomorph.2007.05.017, 2008.
Lamontagne, S., Cook, P. G., O’Grady, A., and Eamus, D.: Ground-
water use by vegetation in a tropical savanna riparian zone (Daly
River, Australia), J. Hydrol., 310, 280–293, 2005.
Lautz, L. K.: Estimating groundwater evapotranspiration rates us-
ing diurnal water-table fluctuations in a semi-arid riparian zone,
Hydrogeol. J., 16, 483–497, 2008.
Leblanc, M. J., Leduc, C., Razack, M., Lemoalle, J., Dagorne,
D., and Mofor, L.: Application of remote sensing and GIS
for groundwater modelling of large semiarid areas: example of
the Lake Chad Basin, Africa. Hydrology of Mediterranean and
Semiarid Regions Conference, Montpieller, France, April 2003,
IAHS (Red Books Series), Wallingford, UK, 186–192, 2003a.
Leblanc, M. J., Razack, M., Dagorne, D., Mofor, L., and Jones, C.:
Application of Meteosat thermal data to map soil infiltrability in
the central part of the Lake Chad basin, Africa, Geophys. Res.
Lett., 30, 1998, doi:10.1029/2003gl018094, 2003b.
Leblanc, M. J., Tregoning, P., Ramillien, G., Tweed, S. O., and
Fakes, A.: Basin-scale, integrated observations of the early
21st century multiyear drought in southeast Australia, Water Re-
sour. Res., 45, W04408, doi:10.1029/2008WR007333, 2009.
Leffler, A. J. and Evans, A. S.: Variation in carbon isotope composi-
tion among years in the riparian tree Populus fremontii, Oecolo-
gia, 119, 311–319, 1999.
Li, F. and Lyons, T.: Estimation of regional evapotranspiration
through remote sensing, J. Appl. Meteorol., 38, 1644–1654,
1999.
Lite, S. J. and Stromberg, J. C.: Surface water and ground-water
thresholds for maintaining Populus-Salix forests, San Pedro
River, Arizona, Biol. Conserv., 125, 153–167, 2005.
Logsdon, S. D., Schilling, K. E., Hernandez-Ramirez, G., Prueger,
J. H., Hatfield, J. L., and Sauer, T. J.: Field estimation of specific
yield in a central Iowa crop field, Hydrol. Process., 24, 1369–
1377, doi:10.1002/hyp.7600, 2010.
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4253
Loheide, S. P.: A method for estimating subdaily evapotranspiration
of shallow groundwater using diurnal water table fluctuations,
Ecohydrology, 1, 59–66, 2008.
Loheide, S. P. and Booth, E. G.: Effects of changing channel mor-
phology on vegetation, groundwater, and soil moisture regimes in
groundwater-dependent ecosystems, Geomorphology, 126, 364–
376, 2011.
Loheide, S. P., Butler, J. J., and Gorelick, S. M.: Estimation of
groundwater consumption by phreatophytes using diurnal wa-
ter table fluctuations: A saturated-unsaturated flow assessment,
Water Resour. Res., 41, W07030, doi:10.1029/2005wr003942,
2005.
Lowry, C. S. and Loheide, S. P.: Groundwater-dependent vegeta-
tion: Quantifying the groundwater subsidy, Water Resour. Res.,
46, W06202, doi:10.1029/2009wr008874, 2010.
Lowry, C. S., Loheide, S. P., Moore, C. E., and Lundquist, J. D.:
Groundwater controls on vegetation composition and pattern-
ing in mountain meadows, Water Resour. Res., 47, W00J11,
doi:10.1029/2010wr010086, 2011.
Lv, J., Wang, X. S., Zhou, Y., Qian, K., Wan, L., Eamus, D., and Tao,
Z.: Groundwater-dependent distribution of vegetation in Hailiutu
River catchment, a semi-arid region in China, Ecohydrology, 6,
142–149, 2012.
Ma, X., Huete, A., Yu, Q., Coupe, N. R., Davies, K., Broich, M.,
Ratana, P., Beringer, J., Hutley, L. B., Cleverly, J., Boulain,
N., and Eamus, D.: Spatial patterns and temporal dynam-
ics in savanna vegetation phenology across the North Aus-
tralian Tropical Transect, Remote Sens. Environ., 139, 97–115,
doi:10.1016/j.rse.2013.07.030, 2013.
Máguas, C., Rascher, K. G., Martins-Loução, A., Carvalho, P.,
Pinho, P., Ramos, M., Correia, O., and Werner, C.: Responses
of woody species to spatial and temporal ground water changes
in coastal sand dune systems, Biogeosciences, 8, 3823–3832,
doi:10.5194/bg-8-3823-2011, 2011.
Mahoney, J. M. and Rood, S. B.: A device for studying the influ-
ence of declining water table on poplar growth and survival, Tree
Physiol., 8, 305–314, 1991.
Markesteijn, L., Poorter, L., Paz„ H., Sack, L., and Bongers, F.: Eco-
logical differentiation in xylem cavitation resistance is associated
with stem and leaf structural traits, Plant Cell Environ., 34, 137–
148, 2011.
Martinet, M. C., Vivoni, E. R., Cleverly, J. R., Thibault, J. R.,
Schuetz, J. F., and Dahm, C. N.: On groundwater fluctuations,
evapotranspiration, and understory removal in riparian corridors,
Water Resour. Res., 45, W05425, doi:10.1029/2008WR007152,
2009.
McCarroll, D. and Loader, N. J.: Stable isotopes
in tree rings, Quaternary Sci. Rev., 23, 771–801,
doi:10.1016/j.quascirev.2003.06.017, 2004.
McDonald, M. G. and Harbaugh, A. W.: A modular three-
dimensional finite-difference ground-water flow model, Depart-
ment of Interior, US Geological Survey, Washington, D.C., 1988.
McDowell, N., Pockman, W. T., Allen, C. D., Breshears, D. D.,
Cobb, N., Kolb, T., Plaut, J., Sperry, J., West, A., Williams,
D. G., and Yepez, E. A.: Mechanisms of plant survival and
mortality during drought: why do some plants survive while
others succumb to drought?, New Phytol., 178, 719–739,
doi:10.1111/j.1469-8137.2008.02436.x, 2008.
McLendon, T., Hubbard, P. J., and Martin, D. W.: Partitioning the
use of precipitation-and groundwater-derived moisture by vege-
tation in an arid ecosystem in California, J. Arid Environ., 72,
986–1001, 2008.
Meinzer, F. C., Campanello, P. I., Domec, J.-C., Gatti, M. G., Gold-
stein, G., Villalobos-Vega, R., and Woodruff, D. R.: Constraints
on physiological function associated with branch architecture
and wood density in tropical forest trees, Tree Physiol., 28, 1609–
1617, 2008.
Merritt, D. M. and Bateman, H. L.: Linking stream flow and ground-
water to avian habitat in a desert riparian system, Ecol. Appl., 22,
1973–1988, 2012.
Miller, G. R., Chen, X., Rubin, Y., Ma, S., and Baldoc-
chi, D. D.: Groundwater uptake by woody vegetation in
a semiarid oak savanna, Water Resour. Res., 46, W10503,
doi:10.1029/2009wr008902, 2010.
Moore, G. W., Cleverly, J. R., and Owens, M. K.: Nocturnal transpi-
ration in riparian Tamarix thickets authenticated by sap flux, eddy
covariance and leaf gas exchange measurements, Tree Physiol.,
28, 521–528, 2008.
Münch, Z, and Conrad, J.: Remote sensing and GIS based deter-
mination of groundwater dependent ecosystems in the Western
Cape, South Africa, Hydrogeol. J., 15, 19–28, 2007.
Murray, B. R., Hose, G. C., Eamus, D., and Licari, D.: Valuation
of groundwater-dependent ecosystems: a functional methodol-
ogy incorporating ecosystem services, Aust. J. Bot., 54, 221–
229, 2006.
Nachabe, M., Shah, N., Ross, M., and Vomacka, J.: Evapotranspi-
ration of two vegetation covers in a shallow water table environ-
ment, Soil Sci. Soc. Am. J., 69, 492–499, 2005.
Nagler, P. L., Glenn, E., Thompson, T., and Huete, A.: Leaf area
index and NDVI as predictors of canopy characteristics and light
interception by riparian species on the Lower Colarado River,
Agr. Forest Meteorol., 116, 103–112, 2004.
Nagler, P. L., Cleverly, J., Glenn, E., Lampkin, D., Huete, A., and
Wan, Z. M.: Predicting riparian evapotranspiration from MODIS
vegetation indices and meteorological data, Remote Sens. Envi-
ron., 94, 17–30, 2005a.
Nagler, P. L., Scott, R. L., Westenburg, C., Cleverly, J. R., Glenn, E.
P., and Huete, A. R.: Evapotranspiration on western US rivers es-
timated using the Enhanced Vegetation Index from MODIS and
data from eddy covariance and Bowen ratio flux towers, Remote
Sens. Environ., 97, 337–351, doi:10.1016/j.rse.2005.05.011,
2005b.
Nagler, P. L., Morino, K., Didan, K., Erker, J., Osterberg, J., Hul-
tine, K. R., and Glenn, E. P.: Wide-area estimates of saltcedar
(Tamarix spp.) evapotranspiration on the lower Colorado River
measured by heat balance and remote sensing methods, Ecohy-
drology, 2, 18–33, doi:10.1002/eco.35, 2009.
Nagler, P. L., Glenn, E., Nguyen, U., Scott, R., and Doody, T.: Esti-
mating riparian and agricultural actual evapotranspiration by ref-
erence evapotranspiration and MODIS enhanced vegetation in-
dex, Remote Sensing, 5, 3849–3871, 2013.
Naumburg, E., Mata-Gonzalez, R., Hunter, R. G., McLendon,
T., and Martin, D. W.: Phreatophytic vegetation and ground-
water fluctuations: a review of current research and appli-
cation of ecosystem response modeling with an emphasis
on great basin vegetation, Environ. Manage., 35, 726–740,
doi:10.1007/s00267-004-0194-7, 2005.
www.hydrol-earth-syst-sci.net/19/4229/2015/ Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015
4254 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
Neale, C. M. U.: Classification and mapping of riparian systems
using airborne multispectral videography, Restor. Ecol., 5, 103–
112, 1997.
Nemani, R. R. and Running, S. W.: Testing a theoretical climate soil
leaf-area hydrological equilibrium of forests using satellite data
and ecosystem simulation, Agr. Forest Meteorol., 44, 245–260,
1989.
Nippert, J. B., Butler, J. J., Kluitenberg, G. J., Whittemore, D. O.,
Arnold, D., Spal, S. E., and Ward, J. K.: Patterns of Tamarix
water use during a record drought, Oecologia, 162, 283–292,
doi:10.1007/s00442-009-1455-1, 2010.
Nosetto, M. D., Jobbagy, E. G., Toth, T., and Bella, C. M. D.: The
effects of tree establishment on water and salt dynamics in natu-
rally salt-affected grasslands, Oecologia, 152, 695–705, 2007.
Oberhuber, W., Stumbock, M., and Kofler, W.: Climate tree-growth
relationships of Scots pine stands (Pinus sylvestris L.) exposed
to soil dryness., Trees Struct. Funct., 13, 19–27, 1998.
O’Grady, A. P., Cook, P. G., Howe, P., and Werren, G.: Groundwa-
ter use by dominant tree species in tropical remnant vegetation
communities, Aust. J. Bot., 54, 155–171, doi:10.1071/bt04179,
2006a.
O’Grady, A. P., Eamus, D., Cook, P. G., and Lamontagne, S.:
Groundwater use by riparian vegetation in the wet–dry tropics
of northern Australia, Aust. J. Bot., 54, 145–154, 2006b.
O’Grady, A. P., Carter, J. L., and Holland, K.: Review of Australian
groundwater discharge studies of terrestrial systems, in: Water
for a Healthy Country National Research Flagship, CSIRO, Mel-
bourne, 2010.
O’Grady, A. P., Carter, J. L., and Bruce, J.: Can we predict ground-
water discharge from terrestrial ecosystems using existing eco-
hydrological concepts?, Hydrol. Earth Syst. Sci., 15, 3731–3739,
doi:10.5194/hess-15-3731-2011, 2011.
Oishi, A. C., Oren, R., and Stoy, P. C.: Estimating components
of forest evapotranspiration: A footprint approach for scaling
sap flux measurements, Agr. Forest Meteorol., 148, 1719–1732,
doi:10.1016/j.agrformet.2008.06.013, 2008.
Orellana, F., Verma, P., Loheide, S. P., and Daly, E.: Mon-
itoring and modelling water-vegetation interactions in
groundwater-dependent ecosystems, Rev. Geophys., 50,
Rg3003, doi:10.1029/2011rg000383, 2012.
Ortuno, M. F. and Garcia-Orellana, Y.: Stem and leaf water poten-
tials, gas exchange, sapflow and trunk diameter fluctuation for
detecting water stress in lemon trees, Trees, 20, 1–8, 2006.
Osmond, C. B., Austin, M. P., Berry, J. A., Billings, W. D., Boyer,
J. S., Dacey, J. W. H., Nobel, P. S., Smith, S. D., and Winner, W.
E.: Stress physiology and the distribution of plants, Bioscience,
37, 38–47, 1987.
Perez-Valdivia, C. and Sauchyn, D.: Tree-ring reconstruc-
tion of groundwater levels in Alberta, Canada: Long term
hydroclimatic variability, Dendrochronologia, 29, 41–47,
doi:10.1016/j.dendro.2010.09.001, 2011.
Perkins, S. P. and Sophocleous, M.: Development of a compre-
hensive watershed model applied to study stream yield under
drought conditions, Ground Water, 37, 418–426, 1999.
Pert, P. L., Butler, J. R. A., Brodie, J. E., Bruce, C., Hon-
zak, M., Kroon, F. J., Metcalfe, D., Mitchell, D., and Wong,
G.: A catchment-based approach to mapping hydrological
ecosystem services using riparian habitat: A case study from
the Wet Tropics, Australia, Ecolog. Complex., 7, 378–388,
doi:10.1016/j.ecocom.2010.05.002, 2010.
Peters, E., Torfs, P. J., Van Lanen, H. A., and Bier, G.: Propa-
gation of drought through groundwater – A new approach us-
ing linear reservoir theory, Hydrol. Process., 17, 3023–3040,
doi:10.1002/hyp.1274, 2003.
Phillips, D. L. and Gregg, J. W.: Source partitioning using stable
isotopes: coping with too many sources, Oecologia, 136, 261–
269, 2003.
Pockman, W. and Sperry, J.: Vulnerability to xylem cavitation and
the distribution of Sonoran desert vegetation, Am. J. Bot., 87,
1287–1299, 2000.
Post, V. E. A. and von Asmuth, J. R.: Review: Hydraulic head
measurements-new technologies, classic pitfalls, Hydrogeol. J.,
21, 737–750, doi:10.1007/s10040-013-0969-0, 2013.
Potts, D. L. and Williams, D. G.: Response of tree ring holocellulose
δ13C to moisture availability in Populus fremontii at perennial
and intermittent stream reaches, W. N. Am. Natural., 64, 27–37,
2004.
Prior, L. D., Grierson, P. F., McCaw, W. L., Tng, D. Y. P., Nichols,
S. C., and Bowman, D.: Variation in stem radial growth of the
Australian conifer, Callitris columellaris, across the world’s dri-
est and least fertile vegetated continent, Trees Struct. Funct., 26,
1169–1179, doi:10.1007/s00468-012-0693-8, 2012.
Querejeta, J. I., Estrada-Medina, H., Allen, M. F., and Jiménez-
Osornio, J. J.: Water source partitioning among trees growing on
shallow karst soils in a seasonally dry tropical climate, Oecolo-
gia, 152, 26–36, 2007.
Rodell, M. and Famiglietti, J. S.: Terrestrial water storage varia-
tions over Illinois : Analysis of observations and implications for
Gravity Recovery and Climate Experiment (GRACE), Water Re-
sour. Res., 37, 1327–1340, 2001.
Rodell, M., Chen, J. L., Kato, H., Famiglietti, J. S., Nigro, J., and
Wilson, C. R.: Estimating groundwater storage changes in the
Mississippi River basin (USA) using GRACE, Hydrogeol. J., 15,
159–166, 2007.
Rodell, M., Velicogna, I., and Famiglietti, J. S.: Satellite-based esti-
mates of groundwater depletion in India, Nature, 460, 999–1002,
2009.
Roderick, M. L. and Farquhar, G. D.: Water availability and evap-
otranspiration in the Murray Darling Basin: A look at the past
and a glimpse into the future, Murray-Darling Basin Authority,
Canberra, 2009.
Rood, S. B., Patino, S., Coombs, K., and Tyree, M.: Branch sacri-
fice: cavitation-associated drought adaptation of riparian cotton-
woods, Trees Struct. Funct., 14, 248–257, 2000.
Rood, S. B., Braatne, J., and Hughes, F.: Ecophysiology of ripar-
ian cottonwoods: stream flow dependency, water relations and
restoration, Tree Physiol., 23, 1113–1124, 2003.
Rood, S. B., Goater, L. A., Gill, K. M., Braatne, J. H.: Sand and
sandbar willow: A feedback loop amplifies environmental sensi-
tivity at the riparian interface, Oecologia, 165, 31–40, 2011.
Rossini, M., Cogliati, S., Meroni, M., Migliavacca, M., Galvagno,
M., Busetto, L., Cremonese, E., Julitta, T., Siniscalco, C., Morra
di Cella, U., and Colombo, R.: Remote sensing-based estimation
of gross primary production in a subalpine grassland, Biogeo-
sciences, 9, 2565–2584, doi:10.5194/bg-9-2565-2012, 2012.
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies 4255
Sala, A., Devitt, D. A., and Smith, S. D.: Water use by Tamarix
ramosissima and associated phreatophytes in a Mojave Desert
floodplain, Ecol. Appl., 6, 888–898, 1996.
Sarris, D., Christodoulakis, D., and Korner, C.: Recent decline
in precipitation and tree growth in the eastern Mediterranean,
Global Change Biol., 13, 1187–1200, doi:10.1111/j.1365-
2486.2007.01348.x, 2007.
Scanlon, B. R., Longuevergne, L., and Long, D.: Ground referenc-
ing GRACE satellite estimates of groundwater storage changes
in the California Central Valley, USA, Water Resour. Res., 48,
W04520, doi:10.1029/2011WR011312, 2012a.
Scanlon, B. R., Faunt, C. C., Longuevergne, L., Reedy, R. C., Alley,
W. M., McGuire, V. L., and McMahon, P. B.: Groundwater de-
pletion and sustainability of irrigation in the US High Plains and
Central Valley, P. Natl. Acad. Sci., 109, 9320–9325, 2012b.
Schilling, K. E. and Zhang, Y. K.: Temporal scaling of groundwa-
ter level fluctuations near a stream, Ground Water, 50, 59–67,
doi:10.1111/j.1745-6584.2011.00804.x, 2012.
Scott, M. L., Shafroth, P. B., and Auble, G. T.: Responses of riparian
cottonwoods to alluvial water table declines, Environ. Manage.,
23, 347–358, 1999.
Scott, R. L., Shuttleworth, W. J., Goodrich, D. C., and Maddock,
T.: The water use of two dominant vegetation communities in a
semiarid riparian ecosystem, Agr. Forest Meteorol., 105, 241–
256, 2000.
Scott, R. L., Edwards, E., Shuttleworth, W., Huxman, T., Watts, C.,
and Goodrich, D.: Interannual and seasonal variation in fluxes of
water and carbon dioxide from a riparian woodland ecosystem,
Agr. Forest Meteorol., 122, 65–84, 2004.
Scott, R. L., Huxman, T. E., Cable, W. L., and Emmerich, W. E.:
Partitioning of evapotranspiration and its relation to carbon diox-
ide exchange in a Chihuahuan Desert shrubland, Hydrol. Pro-
cess., 20, 3227–3243, 2006a.
Scott, R. L., Huxman, T. E., Williams, D. G., and Goodrich, D.
C.: Ecohydrological impacts of woody-plant encroachment: sea-
sonal patterns of water and carbon dioxide exchange within a
semiarid riparian environment, Global Change Biol., 12, 311–
324, doi:10.1111/j.1365-2486.2005.01093.x, 2006b.
Scott, R. L., Cable, W. L., Huxman, T. E., Nagler, P. L., Hernandez,
M., and Goodrich, D. C.: Multiyear riparian evapotranspiration
and groundwater use for a semiarid watershed, J. Arid Environ.,
72, 1232–1246, 2008.
Scurlock, D.: From the Rio to the Sierra: An Environmental His-
tory of the Middle Rio Grande Basin, General Technical Re-
port RMRS-GTR-5, USDA Forest Service, Rocky Mountain Re-
search Station, Fort Collins, CO, 1998.
Seckler, D., Barker, R., and Amarasinghe, U.: Water scarcity in the
twenty-first century, Int. J. Water Res. Dev., 15, 29–42, 1999.
Shafroth, P. B., Cleverly, J. R.,Dudley, T. L., Taylor, J. P., Van Riper,
C., Weeks, E. P., and Stuart, J. N.: Control of Tamarix in the
Western United States: Implications for water salvage, wildlife
use, and riparian restoration, Environ. Manage., 35, 231–246,
2005.
Shah, J. J. F. and Dahm, C. N.: Flood regime and leaf fall determine
soil inorganic nitrogen dynamics in semiarid riparian forests,
Ecol. Appl., 18, 771–788, 2008.
Shah, N., Nachabe, M., and Ross, M.: Extinction depth and evap-
otranspiration from ground water under selected land covers.
Ground Water, 45, 329–338, 2007.
Shiklomanov, I. A.: World water resources: A new appraisal and as-
sessment for the 21st century, United Nations Educational, Sci-
entific and Cultural Organisation, St. Petersburg, Russia, 2008.
Smith, S. D., Devitt, D. A., Sala, A., Cleverly, J. R., and Busch, D.
E.: Water relations of riparian plants from warm desert regions,
Wetlands, 18, 687–696, 1998.
Soylu, M. E., Lenters, J. D., Istanbulluoglu, E., and Loheide II, S. P.:
On evapotranspiration and shallow groundwater fluctuations: A
Fourier-based improvement to the White method, Water Resour.
Res., 48, W06506, doi:10.1029/2011wr010964, 2012.
Sperry, J. S., Meinzer, F. C., and McCulloh, K. A.: Safety and effi-
ciency conflicts in hydraulic architecture: scaling from tissues to
trees, Plant Cell Environ., 31, 632–645, 2008.
Stock, W. D., Bourke, L., and Froend, R. H.: Dendroecological indi-
cators of historical responses of pines to water and nutrient avail-
ability on a superficial aquifer in south-western Australia, Forest
Ecol. Manage., 264, 108–114, 2012.
Stromberg, J. C., Tiller, R., and Richter, B.: Effects of groundwa-
ter decline on riparian vegetation of semiarid regions: The San
Pedro, Arizona, Ecol. Appl., 6, 113–131, 1996.
Stromberg, J. C., Lite, S. J., Rychener, T. J., Levick, L. R., Dixon,
M. D., and Watts, J. M.: Status of the riparian ecosystem in the
upper San Pedro River, Arizona: Application of an assessment
model, Environ. Monit. Assess., 115, 145–173, 2006.
Stromberg, J. C., Beauchamp, V. B., Dixon, M. D., Lite, S. J., and
Paradzick, C.: Importance of low-flow and high-flow characteris-
tics to restoration of riparian vegetation along rivers in and south-
western United States, Freshwater Biol., 52, 651–679, 2007.
Stromberg, J. C., Lite, S. J., and Dixon, M. D.: Effects of stream
flow patterns on riparian vegetation of a semiarid river: impli-
cations for a changing climate, River Res. Appl., 26, 712–729,
doi:10.1002/rra.1272, 2010.
Sun, A. Y.: Predicting groundwater level changes us-
ing GRACE data, Water Resour. Res., 49, 5900–5912,
doi:10.1002/wrcr.20421, 2013.
Syed, T. H., Famiglietti, J. S., and Chambers, D. P.: GRACE-
based estimates of terrestrial freshwater discharge from
basin to continental scales, J. Hydrometeorol., 10, 22–40,
doi:10.1175/2008JHM993.1, 2009.
Tapley, B. D., Bettadpur, S., Watkins, M., and Reigber,
C.: The gravity recovery and climate experiment: Mission
overview and early results, Geophys. Res. Lett., 31, L09607,
doi:10.1029/2004GL019920, 2004.
Thorburn, P. J., Walker, G. R., and Woods, P. H.: Comparison of
diffuse discharge from shallow-water tables in soils and salt flats,
J. Hydrol., 136, 253–274, 1992.
Thorburn, P. J., Hatton, T., and Walker, G. R.: Combining measure-
ments of transpiration and stable isotopes to determine ground-
water discharge from forests, J. Hydrol., 150, 563–587, 1993.
Tweed, S. O., LeBlanc, M., Webb, J. A., and Lubczynski, M. W.:
Remote sensing and GIS for mapping groundwater recharge and
discharge areas in salinity prone catchments, southeastern Aus-
tralia, Hydrogeol. J., 15, 75–96, 2007.
van Hylckama, T. E. A.: Water use by salt cedar, Water Resour. Res.,
6, 728–735, 1970.
Wada, Y., Van Beek, L. P. H., Van Kempen, C. M., Reckman,
J. W. T. M., Vasak, S., and Bierkens, M. F. P.: Global deple-
tion of groundwater resources, Geophys. Res. Lett., 37, L20402,
doi:10.1029/2010gl044571, 2010.
www.hydrol-earth-syst-sci.net/19/4229/2015/ Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015
4256 D. Eamus et al.: Groundwater-dependent ecosystems: recent insights from satellite and field-based studies
Wang, P., Zhang, Y. C., Yu, J. J., Fu, G. B., and Ao, F.: Vegeta-
tion dynamics induced by groundwater flucturations in the lower
Heihe River Basin northwestern China, J. Plant Ecol., 4, 77–90,
2011.
Wang, P., Yu, J. J., Pozdniakov, S. P., Grinevsky, S. O., and
Liu, C. M.: Shallow groundwater dynamics and its driving
forces in extremely arid areas: a case study of the lower Heihe
River in northwestern China, Hydrol. Process., 28, 1539–1553,
doi:10.1002/hyp.9682, 2014.
White, W. N.: A method of estimating ground-water supplies based
on discharge by plants and evaporation from soil: Results of in-
vestigations in Escalante Valley, Utah, in: Interior, US Geological
Survey, Washington, D.C., p. 105, 1932.
Whitley, R. and Eamus, D.: How much water does a woodland
or plantation use: a review of some measurement methods,
Land &Water Australia, Canberra, 2009.
Wilcox, L. J., Bowman, R. S., and Shafike, N. G.: Evaluation of Rio
Grande management alternatives using a surface-water/ground-
water model, J. Am. Water Resour. As., 43, 1595–1603, 2007.
Wright, I. J., Groom, P. K., Lamont, B. B., Poot, P., Prior, L. D.,
Reich, P. B., Schulze, E. D., Veneklaas, E. J., and Westoby, M.:
Leaf trait relationships in Australian plant species, Funct. Plant.
Biol., 31, 551–558, 2004.
Xiao, S. C., Xiao, H. L., Peng, X. M., and Tian, Q. Y.: Intra-annual
stem diameter growth of Tamarix ramosissima and association
with hydroclimatic factors in the lower reaches of China’s Heihe
River, J. Arid Land, 6, 498–510, doi:10.1007/s40333-013-0248-
x, 2014.
Yang, H., Yang, D., Lie, Z., and Sun, F.: New analytical derivation
of the mean annual water energy balance equation, Water Resour.
Res., 44, W03410, doi:10.1029/2007WR006135, 2008.
Yang, X., Smith, P. L., Yu, T., and Gao, H.: Estimating ET from
terrestrial GDEs using Landsat images, Int. J. Dig. Earth., 4, 154–
170, 2011.
Yuan, W. P, Liu, S. G., Yu, G. R., Bonnefond, J. M., Chen, J. Q.,
Davis, K., Desai, A. R., Goldstein, A. H., Gianelle, D., Rossi,
F., Suyker, A. E., and Verma, S. B.: Global estimates of evap-
otranspiration and gross primary production based on MODIS
and global meteorology data, Remote Sens. Environ., 114, 1416–
1431, doi:10.1016/j.rse.2010.01.022, 2010.
Zencich, S. J., Froend, R. H., Turner, J. V., and Gailitis, V.: Influence
of groundwater depth on the seasonal sources of water accessed
by Banksia tree species on a shallow, sandy coastal aquifer, Oe-
cologia, 131, 8–19, 2002.
Zeppel, M.: Convergence of tree water use and hydraulic architec-
ture in water-limited regions: a review and synthesis, Ecohydrol-
ogy, 6, 889–900, 2013.
Zhang, L., Hickel, K., Dawes, W. R., Cheiw, F. H. S., Western,
A. W., and Briggs, P. R.: A rational function approach for esti-
mating mean annual evapotranspiration, Water Resour. Res., 40,
W02502, doi:10.1029/2003WR002710, 2004.
Zinko, U., Seibert, J., Merritt, D. M., Dynesius, M., and Nilsson, C.:
Plant species numbers predicted by a topography-based ground-
water flow index, Ecosystems, 8, 430–441, 2005.
Zolfaghar, S.: Comparative ecophysiology of Eucalyptus wood-
lands along a depth-to-groundwater gradient, PhD thesis, Uni-
versity of Technology, Sydney, 228 pp., 2014.
Zunzunegui, M., Barradas, M. C. D., and Novo, F. G.: Different
phenotypic responses of Halimium halimifolium in relation to
groundwater availability, Plant Ecol., 148, 165–174, 2000.
Zweifel, R., Zimmermann, L., and Newbery, D. M.: Modelling
tree water deficit from microclimate: an approach to quantifying
drought stress, Tree Physiol., 25, 147–156, 2005.
Hydrol. Earth Syst. Sci., 19, 4229–4256, 2015 www.hydrol-earth-syst-sci.net/19/4229/2015/
... Groundwater is an important water resource (Moosdorf andOehler, 2017, Liggett andTalwar, 2009) and the existence of most coastal, aquatic and terrestrial ecosystems depends on its availability (Liggett and Talwar, 2009, Murray et al., 2003, Eamus et al., 2015. Terrestrial vegetation (e.g. ...
... hydrogeological settings), namely, the evapotranspiration rate, precipitation, and temperature (Huang et al., 2020b). For instance, most ecosystems in tropical and boreal biomes are independent of the groundwater because of the surplus surface water from preceding precipitation (Eamus et al., 2015). However, given the low precipitation and limited surface water resources in arid environments (e.g. ...
... climate change, groundwater draw-down, droughts, pollution and wildfires) (Lv et al., 2013, Alaibakhsh et al., 2017, Coletti et al., 2017, Stella and Bendix, 2018. The methods used for monitoring ecosystem health in GDEs also include hydrogeological approaches (e.g. using environmental tracers or piezometers), which involves the collection of specific space-and-time data to understand ecosystem health from the interaction of the groundwater with Groundwater-Dependent Vegetation (GDV) (Eamus et al., 2015). However, it may be impossible to monitor the entire GDE by using hydrogeological approaches; therefore, indicators of an ecosystem's health are used instead (Eamus et al., 2015, Caldwell et al., 1998. ...
Thesis
Full-text available
There have been increasing calls to monitor Groundwater-Dependent Ecosystems (GDEs) more effectively, since they are biodiversity hotspots that provide several ecosystem services. The accurate monitoring of GDEs is an indispensable under Sustainable Development Goal (SDG) 15, because it promotes the existence of phreatophytes. It is imperative to monitoring GDEs, since their ecological significance (e.g., as biodiversity hotspots) is not well understood in most environments they exist. For example, vegetation diversity in GDEs requires routine monitoring, to conserve their biodiversity status and to preserve the ecosystem services in these environments. Such monitoring requires robust measures and techniques, particularly in arid environments threatened by groundwater over-abstraction, landcover and climate change. Although in-situ methods are reliable, they are challenging to use in extensive transboundary groundwater resources such as the Khakea-Bray Transboundary Aquifer. To avoid these setbacks, remote sensing technologies have spatially explicit landscape-scale capabilities for characterising vegetation diversity in GDEs. Remotely-sensed data and the Spectral Variation Hypothesis (SVH) have the inherent capability to provide a unique opportunity to monitor the vegetation diversity of GDEs, and their response to seasonal or intra-annual environmental stressors. Therefore, this research seeks to review the trends and milestones in using remote sensing for characterising vegetation diversity in GDEs, and use satellite remote sensing data (i.e., Sentinel-2 MSI and Landsat 8 OLI) to characterise the vegetation diversity in the Khakea-Bray Transboundary Aquifer. In addition, this thesis aims to monitor the spatio-temporal variations of vegetation diversity in the Khakea-Bray Transboundary Aquifer. Overall, the remote sensing data demonstrated the potential of characterising vegetation diversity in the Khakea-Bray Transboundary Aquifer (R 2 = 0.61 and p = 0.0003). It was observed that the vegetation diversity in the Khakea-Bray Transboundary Aquifer was concentrated more around natural pans and along roads, fence lines and rivers, and that the changes in vegetation diversity within these areas was driven mainly by land conversion and climate variability. These findings are imperative for natural resource managers seeking to conserve the Khakea-Bray Transboundary Aquifer and to achieve the national or regional biodiversity targets. More importantly, this work provides a spatially explicit framework on how GDEs can be monitored in semi-arid environments, to achieve the SDGs.
... GDEs require access to groundwater on a permanent or intermittent basis to meet their water requirements (Eamus et al., 2006), and limitations exist in identifying and mapping GDEs and determining their water needs. Groundwater extraction from unconfined aquifers with shallow water tables poses substantial risks to GDEs and can lead to ecosystem degradation, loss of ecosystem services and environmental damage (Tomlinson and Boulton, 2008;Eamus et al., 2015). ...
... While intensive field techniques are valuable, they are mostly restricted to research studies and are considered too costly for widespread application. Over the last decade, advances in technology and requirements to detect and monitor GDEs across broader spatial scales has seen an emphasis placed on developing and applying remote sensing methods (Eamus et al., 2015;Castellazzi et al., 2019). For example, in regions with distinct dry periods, GDEs can be mapped by identifying vegetation which remains green through dry seasons or drought episodes. ...
Article
Study region Australia Study focus Our incomplete knowledge of groundwater systems and processes imposes barriers in attempting to manage groundwater sustainably. Challenges also arise through complex institutional arrangements and decision-making processes, and the difficulty in involving stakeholders. In some areas, these difficulties have led to water table decline and impacts on groundwater users and groundwater-dependent ecosystems. However, there is potential to improve the sustainable use of groundwater resources through improvements in management practices. We discuss some of the challenges, and present survey results of research, government, and industry professionals across the groundwater sector in Australia. New hydrological insights for the region The highest-ranked challenge identified in the survey was the difficulty in determining regional-scale volumetric water extraction limits. This is surprising given the criticism in the international literature of volumetric based approaches for groundwater management, and the decreased reliance on this approach in Australia and elsewhere in recent years. Other major challenges are the difficulty in determining and implementing maximum drawdown criteria for groundwater levels, determining water needs of ecosystems, and managing groundwater impacts on surface water. Notwithstanding these gaps in technical understanding and tools and a lack of resources for groundwater studies, improvements in stakeholder communication should enable more effective decision-making and improve compliance with regulations designed to protect groundwater and dependent ecosystems.
... Figure 8c also confirms this, but this aspect is not the focus of our study. The relationship between groundwater and ecological vegetation has always been an important issue for research [58,59]. In particular, the relationship between vegetation and groundwater is very complex in arid and semi-arid areas, where plant roots have a strong response to changes in groundwater [60]. ...
... This can be explained by the limited root systems of herbs. The relationship between groundwater and ecological vegetation has always been an important issue for research [58,59]. In particular, the relationship between vegetation and groundwater is very complex in arid and semi-arid areas, where plant roots have a strong response to changes in groundwater [60]. ...
Article
Full-text available
In aeolian sandy grass shoal catchment areas that rely heavily on groundwater, mining-induced geological deformation and aquifer drainage are likely to cause irreversible damage to natural groundwater systems and affect the original circulation of groundwater, thus threatening the ecological environment. This study aimed to predict the impact of groundwater level decline on vegetation growth in the Hailiutu River Basin (HRB), which is a coal-field area. Based on remote-sensing data, the land use/cover change was interpreted and analyzed, and the central areas of greensward land in the basin were determined. Subsequently, the correlation between groundwater depth and grassland distribution was analyzed. Then, the groundwater system under natural conditions was modeled using MODFLOW, and the groundwater flow field in 2029 was predicted by loading the generalized treatment of coal mine drainage water to the model. The change in groundwater depth caused by coal mining and its influence on the grassland were obtained. The results show that coal mining will decrease the groundwater depth, which would induce degradation risks in 4 of the original 34 aggregation centers of greensward land that originally depended on groundwater for growth in HRB because they exceeded the groundwater threshold. The prediction results show that the maximum settlement of groundwater level can reach 5 m in the northern (Yinpanhao), 6 m in the eastern (Dahaize), and 10 m in the southern (Balasu) region of HRB. Attention should be paid to vegetation degradation in areas where groundwater depth exceeds the minimum threshold for plant growth.
... Previous studies on groundwater-dependent ecosystems support the suggestion that certain species are reliant on this deeper groundwater (so called phreatophytes) (Naumburg et al 2005, Eamus et al 2015 especially in drier intervals (Gou and Miller 2014). However, the hypothesis of deeper roots mediating plant sensitivity to hydroclimate variability via groundwater access has not yet been widely demonstrated. ...
Article
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With predicted climate change, drylands are set to get warmer and drier, increasing water stress for the vegetation in these regions. Plant sensitivity to drier periods and drought events will largely depend on trait strategies to access and store water, often linked to the root system. However, understanding the role of below-ground traits in enhancing ecological resilience to these climate changes remains poorly understood. We present the results of a study in southern Africa where we analysed the relationship between root depth and the Vegetation Sensitivity Index (VSI) (after Seddon, Macias-Fauria et al. (2016)). VSI demonstrates remotely-sensed aboveground vegetation responses to climate variability; thus our study compares aboveground vegetation responses to belowground root traits. Results showed a significant negative relationship between root depth and vegetation sensitivity. Deeper roots provided greater resistance to climate variability as shown by lower sensitivity and higher temporal autocorrelation in vegetation greenness (as measured by the Enhanced Vegetation Index, EVI). Additionally, we demonstrated a link between deeper roots and depth to groundwater, further suggesting that it is the ability of deeper roots to enable access to groundwater that provides ecological resistance to climate variability. Our results therefore provide important empirical evidence that the ability to access deeper water resources during times of lower water availability through deeper roots, is a key trait for dryland vegetation in the face of future climate change. We also show that belowground traits in drylands leave a fingerprint on aboveground, remotely-sensed plant-climate interactions, an important finding to aid in scaling up data-scarce belowground research.
... One landscape class that has had an increasing body of work over recent decades are groundwater-dependent ecosystems (GDEs). Most existing remote sensing methods of classifying GDEs in the landscape describe the form rather than the function of groundwater-dependent vegetation (Eamus et al., 2015;Orellana et al., 2012;Pérez Hoyos et al., 2016). For example, the form of a GDE can be investigated from its height and structure using Light Detection and Ranging (LiDAR) (Lefsky et al., 2002) or Inferometric Synthetic Aperature Radar (InSAR) (Castellazzi et al., 2019), or through its relative greenness dynamics using Normalised Difference Vegetation Index (NDVI) (Fu and Burgher, 2015;Alaibakhsh et al., 2017;Barron et al., 2014;Jarchow et al., 2020). ...
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Rivers in arid regions often rely on flow generated from wetter regions upstream, leading to high transmission losses of downstream flows. These transmission losses support a range of ecosystems but partitioning the volume of the transmission losses across the floodplain, riparian zone and in‐channel is difficult. This study presents a methodology relying primarily on multi‐decade satellite remotely sensed actual evapotranspiration estimates to partition these losses. The method was applied to the ~40,000 km2 floodplain of Cooper Creek in the central Australian arid zone, where first the alluvial landscape was classified based on actual evapotranspiration rates, and second both regional‐ (i.e., for the entire floodplain) and local‐scale (i.e., for each waterhole) water balances were calculated to partition these losses. Regional‐scale results estimated 82% of transmission losses occurred on the floodplain, 13% in the riparian zone and 5% from open water in the river channel and waterholes. These results showed that a refinement of the conceptual model of recharge from the waterholes is necessary as vast areas of the riparian zone are likely to be accessing a shallow freshwater lens rather than a discrete freshwater lens below the permanent waterholes. This method can be used in other data‐poor arid river systems as it uses globally accessible data sources.
... Central Asia comprises a large fraction of the world's drylands and more than 80 % of the global temperate deserts are located in here (Zhang et al., 2016), is one of the most sensitive areas to climate change and human activities (Huang et al., 2017;Yin et al., 2021). Existing widely in arid endorheic basins of Central Asia, groundwater-dependent ecosystems (GDEs), i.e., aquatic and terrestrial regions whose ecological components rely on groundwater for at least some period of time during their life history, are considered fragile and prone to regime shifts (Orellana et al., 2012;Eamus et al., 2015;Liu et al., 2021). Importantly, ecological drought has profound effects on the resilience and stability of such ecosystems (Ridolfi et al., 2006;Qin et al., 2021), alongside negative ecohydrological and environmental consequences (Wu et al., 2019a;Yin et al., 2022), and potentially diminish the resources and services these ecosystems provide to human societies (Munson et al., 2021). ...
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Drought has become a major threat to regional sustainable development in drylands. Ecological drought, emphasizing the process of drought impacts on ecosystems in coupled human-natural systems, has been posing large risks to the stability of groundwater-dependent ecosystems (GDEs) in drylands. Yet, the interconnected avenues via which ecological drought drives vegetation transition, ecological resilience and ecosystem services in GDEs with species-specific traits remain elusive, especially in arid endorheic basins. Here, we combine comprehensive field measurements derived from representative groundwater depth transects in Central Asia and simulations obtained from the stochastic eco-hydrological models and the Langevin approach, we find that two groundwater-dependent species, the salt-tolerant Haloxylon ammodendron and salt-sensitive Haloxylon persicum, exhibit contrasting water use strategies being driven by variations in eco-physiological traits and environmental regimes. Nonetheless, both the low-resilient H. ammodendron and high-resilient H. persicum vegetation tend to show bistable transition corresponding to vegetated and bare soils under drought stress with stochastic noises and time delays. Alarmingly, ecological drought is accelerating catastrophic transitions in both Haloxylon ecosystems induced by diminishing ecological flows, depleting soil moisture, and aggravating salinization, together with climate forcing. In particular, exacerbated drought stress reduces ecological resilience, enhances the likelihood of catastrophic shifts, and reduces ecosystem services of GDEs in arid endorheic basins. Our results highlight that ecological drought adaptation strategies must account for resilience maintenance by balancing water scarcity, water overuse, and water/soil quality to avoid accelerating regime shifts in dryland ecosystems.
... In recent years, some approaches to the identification of GDE have been published in the national and international technical-scientific literature, at different scales, from the adoption of automatic GIS mapping criteria of hydrogeological and ecological variables [31][32][33], to the development of groundwater flow models [34] or remote sensing techniques [35,36]. ...
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Groundwater contributes to the maintenance of the functioning of ecosystems, through aspects related to hydrodynamics and chemical composition. Groundwater-dependent ecosystems (GDE) also offer a wide spectrum of ecosystem services to populations; therefore, their identification and mapping, which is the focus of the present paper, is of high value to environmental policies; for example, WFD envisages protecting both water bodies and GDE. An ecosystem dependence index was applied to proceed with this task in the Azores archipelago, being estimated by adding the values of three partial variables (spring density; wetlands/lakes; river baseflow) over a 10 by 10 m2 grid; with this methodology avoiding pitfalls due to lack of data. The results enabled the identification and mapping of five GDE, in Flores and São Miguel islands, supported by only three of the 28 groundwater bodies delimited in the Azores RBD. Those groundwater bodies are considered to have a good status according to the WFD requirements; thus, GDE, regardless of their typology, are not at risk of deterioration as a result of the interaction with groundwater. Nevertheless, other studies have shown that some GDE are in conflicting ecological areas and require specific management and protection measures, coupling land use and water resource planning.
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Desertification and salinization are both threats to the ecosystem services in inland river oases of arid regions. Previous studies focus on either desertification or salinization, and there is a lack of joint studies on the two issues. The essential cause of desertification in a transition zone is usually concentrated irrigation water use, which leads to shrink of the subsurface flow field of groundwater, decline of the groundwater level, and loss of groundwater supply to the vegetation. The salinization problem in an oasis area is mainly caused by the local excess groundwater in the oasis, referring to secondary salinization, which leads to salt migration with the groundwater level rise to form salt crystallization at the land surface. Thus, the processes of desertification and secondary salinization are connected, and the solutions to the two problems can be complementary, i.e., by transporting the excess groundwater in the local secondary salinization area to the transition zone area where water is scarce. This paper, taking Luocheng Irrigation District in the Heihe River Basin of northwestern China as an example, estimates 1.76–4.70 million m³ of excess groundwater that can be extracted in the salinized area. Using this amount of water through engineering regulation, it is estimated that the transition zone nearby the irrigation district, which is under desertification threat, can be restored with an area of 23–212 km². An engineering system is designed for coordinated groundwater regulation and the implementation with an experimental farm in the irrigation district is demonstrated.
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Intense anthropogenic activities in arid areas have great impacts on groundwater process by causing river dried-up and phreatic decline. Groundwater recharge and discharge have become hot spot in the dried-up river oases of arid regions, but are not well known, challenging water and ecological security. This study applied a stable isotope and end-member mixing analysis method to quantify shallow groundwater sources and interpret groundwater processes using data from 186 water samples in the Wei-Ku Oasis of central Asia. Results showed that shallow groundwater (well depth < 20 m) was mainly supplied by surface water and lateral groundwater flow from upstream, accounting for 88 and 12%, respectively, implying surface water was the dominant source. Stable isotopes and TDS showed obviously spatiotemporal dynamic. Shallow groundwater TDS increased from northwest to southeast, while the spatial variation trend of groundwater δ18O was not obvious. Surface water and groundwater in non-flood season had higher values of stable isotopes and TDS than those in flood season. Anthropogenic activities greatly affect groundwater dynamics, where land-cover change and groundwater overexploitation are the main driving factors. The findings would be useful for further understanding groundwater sources and cycling, and help restore groundwater level and desert ecosystem in the arid region. HIGHLIGHTS The sources of shallow groundwater in the dried-up river oasis of central Asia were quantified.; Surface water was the dominant source of shallow groundwater.; Anthropogenic activities greatly affect groundwater dynamic and cycle.;
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Identifying and mapping of potential Groundwater-dependent ecosystems (pGDEs) are pivotal to well understanding of the interaction between groundwater and ecosystem as well as rational allocation of regional water resources. As the largest tributary of the Yellow River with complex landscape types, the Weihe River basin is an essential region for both water and sediment management in the Yellow River basin. However, either the distribution of pGDEs or the role of groundwater in ecosystems of the Weihe River basin has been largely unexplored. In this study, focused on the Weihe River basin, the framework for identifying and mapping of pGDEs was suggested to perform hierarchical grade based on the coupling of NDVI classification method and Groundwater-dependent Ecosystem Mapping (GEM) method. Moreover, the identification and mapping of pGDEs were validated based on statistical analyses among Normalized Difference Vegetation Index (NDVI), water table depth (WTD), previous month’s precipitation (Ppm), evapotranspiration (ET), and precipitation (P). The spatial patterns of pGDEs obtained from mapping are generally consistent with those from validation, and the differences of pGDEs in the Weihe River distributed largely. The pGDEs group of “Likely” and “Very Likely” accounted for 22.5% of the basin, and mainly distributed in Ziwuling Mountains, Qinling Mountains, Liupan Mountains, and Huanglong Mountains, and the “Neutral” group was scattered in the loess area of the northwestern basin, accounting for 13%. The finding of this study promotes the development of the GDEs identification and provides references for water and ecosystem regulation and protection of the Weihe River basin as well as other similar basins.
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In spite of the relative importance of groundwater in costal dune systems, studies concerning the responses of vegetation to ground water (GW) availability variations, particularly in Mediterranean regions, are scarce. Thus, the main purpose of this study is to compare the responses of co-occurring species possessing different functional traits, to changes in GW levels (i.e. the lowering of GW levels) in a sand dune ecosystem. For that, five sites were established within a 1 km<sup>2</sup> area in a meso-mediterranean sand dune ecosystem dominated by a Pinus pinaster forest. Due to natural topographic variability and anthropogenic GW exploitation, substantial variability in depth to GW between sites was found. Under these conditions it was possible to identify the degree of usage and dependence on GW of different plant species (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader) and how GW dependence varied seasonally and between the heterogeneous sites. Results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy). Species comparison revealed that variability in pre-dawn water potential (Ψ<sub>pre</sub>) and bulk leaf δ<sup>13</sup>C was related to site differences in GW use in the deep-rooted ( Pinus pinaster, Myrica faya ) and phreatophyte ( Salix repens ) species. However, such variation was more evident during spring than during summer drought. The exotic invader, Acacia longifolia , which does not possess a very deep root system, presented the largest seasonal variability in Ψ<sub>pre</sub> and bulk leaf δ<sup>13</sup>C. In contrast, the response of Corema album , an endemic understory drought-adapted shrub, seemed to be independent of water availability across seasons and sites. Thus, the susceptibility to lowering of GW due to anthropogenic exploitation, in plant species from sand dunes, is variable, being particularly relevant for deep rooted species and phreatophytes, which seem to depend heavily on access to GW.
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There is increasing recognition of the role that groundwater plays in the maintenance of ecosystem structure and function. As a result, water resources planners need to develop an understanding of the water requirements for these ecosystems. In this study we reviewed estimates of groundwater discharge from terrestrial vegetation communities around Australia and explored this data set for empirical relationships that could be used to predict groundwater discharge in data poor areas. In particular we explored how leaf area index and the water balance of groundwater systems conformed to two existing ecohydrological frameworks; the Budyko framework, which describes the partitioning of rainfall into evapotranspiration and runoff within a simple supply and demand framework, and Eagleson's theory of ecological optimality. We demonstrate strong convergence with the predictions of both frameworks. Terrestrial groundwater systems discharging groundwater lie above the water limit line as defined in the Budyko framework. However, when climate wetness was recalculated to include groundwater discharge there was remarkable convergence of these sites along this water limit line. Thus, we found that there was a strong correlation between estimates of evapotranspiration derived from the Budyko's relationship with observed estimates of evapotranspiration. Similarly, the LAI of ecosystems with access to groundwater have higher LAI than those without access to groundwater, for a given climatic regime. However, again when discharge was included in the calculation of climate wetness index there was again strong convergence between the two systems, providing support for ecological optimality frameworks that maximize LAI under given water availability regimes. The simplicity and utility of these simple ecohydrological insights potentially provide a valuable tool for predicting groundwater discharge from terrestrial ecosystems, especially in data poor areas.
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Groundwater plays a major, if often unrecognized, role in both hydrologic and human systems. The majority of the world's drinking water probably comes from groundwater, and in the last half century, there has been an amazing, if largely ignored, boom in agricultural groundwater use that has provided improved livelihoods and food security to billions of farmers and consumers. However, increased use of groundwater has also created problems, and there are fears — sometimes challenged — that the boom may soon turn to bust. This article reviews the recent literature on the geographic and temporal dimensions of groundwater use and the range of technological and institutional approaches that have been applied in attempts at its management. It then examines the key reasons the resource has proven so difficult to manage and concludes that, in many cases, the most promising solutions may lie outside the groundwater sector and within a broader approach to resource systems.
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Ecohydrology: Vegetation Function, Water and Resource Management describes and provides a synthesis of the different disciplines required to understand the sustainable management of water in the environment in order to tackle issues such as dryland salinity and environmental water allocation. It provides in the one volume the fundamentals of plant ecophysiology, hydrology and ecohydrology as they relate to this topic. Both conceptual foundations and field methods for the study of ecohydrology are provided, including chapters on groundwater dependent ecosystems, salinity and practical case studies of ecohydrology. The importance of ecologically sustainable development and environmental allocations of water are explained in a chapter devoted to policy and principles underpinning water resource management and their application to water and vegetation management. A chapter on modelling brings together the ecophysiological and hydrological domains and compares a number of models that are used in ecohydrology. For the sustainable management of water in Australia and elsewhere, this important reference work will assist land managers, industry, policy makers, students and scientists achieve the required understanding of water in landscapes.
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The role of groundwater in controlling ecosystems in Australia is poorly understood. The findings of a report prepared for the Land and Water Resources Research and Development Corporation (LWRRDC) entitled 'Dependence of Australian Ecosystems on Groundwater' are summarized. Four ecosystems were considered: terrestrial vegetation, river base flow systems, aquifer and cave ecosystems and wetlands. Criteria used to assess dependence on groundwater are outlined. The ecosystems were classified according to their dependence on groundwater. Case studies illustrating the complexities in evaluating the significance of ecosystem dependence on groundwater are presented.
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Various human groups have greatly affected the processes and evolution of Middle Rio Grande Basin ecosystems, especially riparian zones, from A.D. 1540 to the present. Overgrazing, clear-cutting, irrigation farming, fire suppression, intensive hunting, and introduction of exotic plants have combined with droughts and floods to bring about environmental and associated cultural changes in the Basin. As a result of these changes, public laws were passed and agencies created to rectify or mitigate various environmental problems in the region. Although restoration and remedial programs have improved the overall "health" of Basin ecosystems, most old and new environmental problems persist.
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Chinese tamarisk is an invader of riparian sites in the southwestern United States and northern Mexico. Plant canopy light reflectance measurements showed that Chinese tamarisk had higher visible (0.55- and 0.65-μm wavelengths and 0.63- to 0.69-μm waveband) reflectance than did associated woody and herbaceous plant species in the late fall-early winter period when its foliage turned a yellow-orange to orange-brown color prior to leaf drop. Chinese tamarisk had a yellow-orange color on conventional color (0.40- to 0.70-μm) aerial photographs during this phenological stage that made it distinguishable from other plant species. Computer analyses of conventional color film positive transparencies showed that Chinese tamarisk populations could be quantified from associated vegetation. This technique can permit area estimates of Chinese tamarisk infestations on wildland areas.
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Eight species of Tamarix were first brought to North America in the 1800s from southern Europe or the eastern Mediterranean region. Many of the species escaped cultivation and by the 1920s invaded about 4,000 ha of riparian habitat in the southwestern United States. By 1987, it was estimated to have increased to at least 600,000 ha. The success of saltcedar in the southwest can be attributed to several factors related to its growth habit, reproduction, water usage, ability to tolerate highly saline conditions, and redistribution of salt from deep in the soil profile to the soil surface. The flowers produce small, numerous, and tufted seeds that can be carried long distances by wind or water. The seeds, however, have a short period of viability, and must come in contact with suitable moisture within a few weeks of dispersal. Unlike obligate phreatophytes, such as willows and cottonwoods, saltcedar is a facultative phreatophyte and is often able to survive under conditions where groundwater is inaccessible. The high evapotranspiration rates of saltcedar can lower the water table and alter the floristic composition in heavily infested areas. Mature plants are tolerant to a variety of stress conditions, including heat, cold, drought, flooding, and high salinity. Saltcedar is not an obligate halophyte but survives in areas where groundwater concentrations of dissolved solids can average 8,000 ppm or higher. In addition, the leaves of saltcedar excrete salts that are deposited on the soil surface under the plant, inhibiting germination and growth of competing species.