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The Role of Vegetation in The Role of Vegetation in Minimising GW Recharge – Minimising GW Recharge –
application to mining and waste application to mining and waste management industriesmanagement industries
Derek EamusDerek Eamus,,
C Macinnis-Ng, I Yunusa, M ZeppelC Macinnis-Ng, I Yunusa, M Zeppel
Terrestrial Ecohydrology Research GroupTerrestrial Ecohydrology Research Group
University of Technology, SydneyUniversity of Technology, Sydney
Outline of the talkOutline of the talk
• Why do we need to minimise GW recharge?Why do we need to minimise GW recharge?
• How can we minimise it?How can we minimise it?
• Design of store-release caps requires Design of store-release caps requires knowledge of rate of water use by knowledge of rate of water use by vegetationvegetation
• How might we model veg water use?How might we model veg water use?
Outline of the talkOutline of the talk
• A modified Jarvis-Stewart modelA modified Jarvis-Stewart model
• Using a Soil-Plant Atmosphere modelUsing a Soil-Plant Atmosphere model
• A case study of a site in NSWA case study of a site in NSW
Minimising GW recharge is Minimising GW recharge is important for:important for:
• Minimising development of dryland salinity Minimising development of dryland salinity
• Preventing leachates from waste storage Preventing leachates from waste storage dumps poisoning an aquiferdumps poisoning an aquifer
• Preventing acid drainage from mine-site Preventing acid drainage from mine-site rock dumpsrock dumps
How can we minimise How can we minimise GW recharge?GW recharge?
• Use vegetation to transpire rain back to the Use vegetation to transpire rain back to the atmosphere before it percolates beyond the atmosphere before it percolates beyond the root zoneroot zone
• Therefore need to design a “cap” on the siteTherefore need to design a “cap” on the site
• This raises many questions of design, eg: This raises many questions of design, eg: • How deep should the soil be on the clay cap? How deep should the soil be on the clay cap? • How do we know how much water the vegetation How do we know how much water the vegetation
will transpire on a daily/seasonal/annual basis? will transpire on a daily/seasonal/annual basis?
Water use by vegetation – Water use by vegetation – a remindera reminder
• Water use by vegetation is determined by:Water use by vegetation is determined by:• Solar radiation inputSolar radiation input• Soil moisture contentSoil moisture content• Atmospheric water content (humidity or Atmospheric water content (humidity or
vapour pressure deficit)vapour pressure deficit)• Leaf area index of the vegetationLeaf area index of the vegetation
• Current models require parameterisation Current models require parameterisation for each site individually – eg SPA, for each site individually – eg SPA, VADOSE, Penman-MonteithVADOSE, Penman-Monteith
• Models have a large number of input Models have a large number of input variables – SPA has about 15, VADOSE variables – SPA has about 15, VADOSE has far too many, the P-M has 6has far too many, the P-M has 6
We can model veg water useWe can model veg water use
• Parameterising models for every site and Parameterising models for every site and vegetation type is too slow and expensivevegetation type is too slow and expensive
• We have developed a modified Jarvis-We have developed a modified Jarvis-Stewart model that can be used for any Stewart model that can be used for any ecosystem dominated by woody ecosystem dominated by woody vegetationvegetation
We can model veg water useWe can model veg water use
Modelling tree water use – Modelling tree water use – the original JS approachthe original JS approach
)/1( ca
apnc GG
DGCRE
)()()( 321 fDfRfGG SMaxcc
)()(ˆ)( 321 fDfRfEE SMaxcc
Penman-Monteith Equation and Jarvis-Stewart Model1. Needs measurements of Gc
2. Circular, Complex and Time Consuming
A modified Jarvis-Stewart Model1. Measurements in Ec
2. Retains Mechanistic understanding of processes
Model Functional DependenciesModel Functional Dependencies
)exp()(ˆ 232 DkDkDf
)exp()( 22 DkDf
f1(RS )RS1000
1000 k1RS k1
f3()0
wC w1
, W,W C, C
Dependence of Gc and Ec onchanging solar radiation
Dependence of Gc on changingvapour pressure deficit
Dependence of Gc and Ec onchanging soil moisture content
Dependence of Ec on changingvapour pressure deficit
Veg Veg water use water use varies as varies as a function a function
of light, of light, VPD and VPD and
soil soil moisturemoisture
0 200 400 600 800 1000 1200 1400
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 1 2 3 4 5 6 7 8 8 9 10 11 12 13
0 200 400 600 800 1000 1200 1400
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0 1 2 3 4 5 6 7 8 8 9 10 11 12 13
0.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Summer Winter
f)e)d)
b)a)
Solar Radiation (W m-2)
Stan
d Tr
ansp
irat
ion
(mm
hr
-1)
c)
Vapour Pressure Deficit (kPa)
Soil Moisture Content (mm3 mm-3)
Solar Radiation (W m-2)
Can
opy
Con
duct
ance
(m
m h
r-1
)
Vapour Pressure Deficit (kPa)
Soil Moisture Content (mm3 mm-3)
Ec/
Ec m
ax G
c/G
c m
ax
How well does the modified How well does the modified Jarvis-Stewart model perform?Jarvis-Stewart model perform?
We compared it to the standard We compared it to the standard P-M approach and to an P-M approach and to an artificial neural network artificial neural network
statistical modelstatistical model
1 Jan 2 Jan 3 Jan 4 Jan 5 Jan 6 Jan 7 Jan
0.00
0.05
0.10
0.15
0.20
5 Feb 6 Feb 7 Feb 8 Feb 9 Feb 10 Feb 11 Feb 12 Feb
0.00
0.05
0.10
0.15
0.20
0.25
14 Jul 15 Jul 16 Jul 17 Jul 18 Jul 19 Jul 20 Jul 21 Jul
0.00
0.05
0.10
0.15
0.20
9 Sep 10 Sep 11 Sep 12 Sep 13 Sep 14 Sep 15 Sep 16 Sep
0.00
0.05
0.10
0.15
0.20
0.25
Sta
nd
Tra
nsp
irat
ion
(m
m h
r-1)
Sapflow PM Jarvis ANN
Summer Winter
• With our modified JS model, the slope of With our modified JS model, the slope of the regression for observed and modelled the regression for observed and modelled is close to oneis close to one
A A comparison comparison
of three of three sites – all sites – all
three three behave behave similarlysimilarly
Do we need to parameterise Do we need to parameterise the model independently the model independently
for each site?for each site?
• If average parameter values work, this If average parameter values work, this would be a massive saving in effort.....would be a massive saving in effort.....
The The modified JS modified JS
using using average average
parameter parameter values values
does very does very well well
(Paringa data(Paringa data))
Using an Using an averaged set averaged set of parameter of parameter values allows values allows
us to us to generate daily generate daily rates of water rates of water use from just use from just a set of met a set of met
datadata
Applying a modelling approach to Applying a modelling approach to testing the mechanismtesting the mechanism
• We applied the Soil-Plant-Atmosphere We applied the Soil-Plant-Atmosphere model of Williams model of Williams et al.et al. 2001 to the problem 2001 to the problem
• The SPA model is a detailed mechanistic The SPA model is a detailed mechanistic model that calculates C fluxes, water fluxes, model that calculates C fluxes, water fluxes, leaf water potential and GPP of landscapesleaf water potential and GPP of landscapes
The The SPASPA models water flux from models water flux from SSoil, oil, through the through the PPlant to the lant to the AAtmospheretmosphere
Plant data
Soil data
Soil water uptake
Sap flow
Leaf water potential
Met data
Stomatal
conductance
Photosynthesis
GPP
Transpiration INPUTS
OUTPUTS
The SPA The SPA model model
does well does well in in
modelling modelling sap flow at sap flow at
our siteour site
(a) Spring
0.0 0.1 0.2 0.3
Mod
elle
d sa
p flo
w (
mm
3 w
ater
hr
-1 m
m-2
grou
nd a
rea)
0.0
0.1
0.2
0.3
Regression of measured & modelled sap flow1:1 line
(b) Summer
Measured sap flow (mm3 water hr-1 mm-2 ground area)
0.0 0.1 0.2 0.3
Mod
elle
d sa
p flo
w (
mm
3 wat
er h
r-1
mm
-2 gr
ound
are
a)
0.0
0.1
0.2
0.3
Regression of measured & modelled sap flow1:1 line
(b) Summer
Day of study period
85 90 95 100 105 110 115 120
Sap
flow
(mm
day
-1)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
ModelledMeasured
(a) Spring
Day of study period0 5 10 15 20 25 30Sa
p flo
w (m
m d
ay-1
)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
ModelledMeasured
Veg water use Veg water use was independent was independent
of the water of the water content of the content of the
upper 80 cm of upper 80 cm of soil – highlighting soil – highlighting the importance the importance of deep roots in of deep roots in the clay layerthe clay layer
Daily
Et (
mm da
y-1
)
0.0
0.5
1.0
1.5
2.0
day - spring vs measured sap flw - spring x column 1 vs y column 1
80 cm soil moisture storage (mm)
Day of study period
0 20 40 60 80 100 120
Soil m
oistur
e (mm
)
80
120
160
200
240
280
(a)
(b)
ConclusionsConclusions
• The modified JS model allows quantification of The modified JS model allows quantification of water use from basic met data and using average water use from basic met data and using average parameter valuesparameter values
• The SPA model is a detailed model that allows us to The SPA model is a detailed model that allows us to examine the mechanisms underlying observed examine the mechanisms underlying observed behaviourbehaviour
• Management of deep drainage through vegetation is Management of deep drainage through vegetation is a realistic option for the waste and mining industriesa realistic option for the waste and mining industries
Published by CSIRO 2006 ISBN 0 643 06834 1Published by CSIRO 2006 ISBN 0 643 06834 1