Transcript PPT

Evapotranspiration in a lotic wetland
ecosystem
G. Milton Ward
Department of Biological Sciences and
Center for Freshwater Studies
University of Alabama
Tuscaloosa, Alabama, USA
Water Budget
Evapotranspiration
Surface
Precipitation
Storage
Outflow
Groundwater Flow
Alnus
serrulata
Juncus
effusus
Talladega Wetland
in October
Beaver Dam
Nymphaea
odorata
Talladega Wetland
hydrologic installation
mm of Precipitation
or Evaporation
TWE Precipitation and Pan Evaporation
Precipitation
1600
1400
1200
1000
800
600
400
200
0
Evaporation
93
94 95
96
97
98 99
Years
00
01 02
03
Preliminary Water Budget for Talladega Wetland
Evapotranspiration (mm)
879 64 %
1367
Storage
= -3
301 Surface
22% Outflow
Precipitation
286 21%
Groundwater Flow
EvapotranspirationThe E-T component of this
budget was a spatially
integrated average calculated
from a modified
Penman-Monteith equation.
Spatial Mean = 75% of Pan
estimate
Because of the inherent
uncertainty of such
calculations, and the need to
refine our ET estimate, we
installed an eddy covariance
system in the wetland.
Measurement of E-T using eddy covariance techniques
Krypton Hygrometer
Surface Energy Budget
Rn= LE + H ± G
Net Radiometer
3-D Anemometer
Campbell Scientific, Inc.
Equipment is deployed on a tower that rises
above the canopy
Equipment is deployed on a tower that rises
above the canopy
•10 m tower in a stand of alder, Alnus serrulata
•Surface energy budget data collected 10x per
second and averaged over 30 min
•ET (mm) calculated from effluxes of latent energy
•Daily ET was calculated as the sum of daytime
(Rn>0) 30 min ET
•When necessary, data were corrected for closure
of energy balance using the Bowen Ratio
W/m
2
Surface energy budget for 25 Jul 03
900
800
700
600
500
400
300
200
100
0
-100
ET = 3.38 mm H2O
Rn
LE
H
G
Time of Day
Surface Energy Budget Closure Is Needed !!!
Advection can be a source of error
ET (mm)
ET (mm)
Daily Variation ranged between 0.46 to 4.4 mm/d in
2003 and 0.40 to 6.0 mm/d in 2002. The slightly
higher rate in 2002 was attributed to a somewhat
warmer and less humid growing season.
6.0
4.5
3.0
1.5
0.0
6.0
4.5
3.0
1.5
0.0
2002
A
M
J
J
A
S
O
M
J
J
A
S
O
2003
A
Month
Monthly E-T fluxes from Talladega Wetland
2003_ET
2002_Temp
2003_Temp
6
30
5
25
4
20
3
15
2
10
1
5
0
0
April
May
June
July
August
September
October
Mean Daily Air Temp (C)
Daily Daytime E-T (mm/d)
2002_ET
Can ET be indexed to PET?
Our longer term measurement of evaporation is that of
potential ET, using a class-A evaporation pan. A comparison of
actual ET versus PET in 2002 revealed that pan evaporation
measurements tended to capture only 84% of AET as
measured by Eddy Covariance.
Daily ET (mm)
6
5
4
3
2
y = 0.8379x + 1.1661
R2 = 0.7337
1
0
0
1
2
3
4
5
Daily Pan Evaporation (mm)
6
E- T at Talladega Wetland in comparison
with similar habitats in the SE US
Habitat
State
ET (mm/d)
Citation
Method
Wetland
FL
4.16
Jacobs et al
‘02
Eddy
Covariance
Wetland
FL
0.5 (Feb)
10.0 (Sep)
Dolan et al ’84
Water Table
Vegetate
d Lake
FL
0.2 (Feb)
5.0 (Jul)
Sumner ’96
Eddy
Covariance
Wetland
AL
3.81 (May-Oct ‘02)
2.38 (Apr-Oct ’03)
This Study
Eddy
Covariance
RiparianSaltcedar
NM
5.4 (Flooded site)
3.4 (Non-Flooded)
Cleverly et al
‘02
Eddy
Covariance
Beaver pond exposed!!!!
Where are those beaver when you really need them?
Research support by funding from NSF EPSCoR and NSF IGERT programs