Adventures In Pollen
Dispersion Modeling
Craig Clark
February 3, 2005
Outline
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Introduction to the problem
Boundary layer torture and dispersion modeling
Summer 2003 example
The next phase: modeling of windbreak
The Problem
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Growth of GM crops has led to concern that
GM maize will outcross with nearby fields
Several studies have observed deposition, but
results cannot be with generalized to all field
and weather conditions
Numerical simulations can predict pollen
dispersal in a variety of field and weather
conditions
Maize Pollen Dispersion Basics
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Maize Pollen has a large terminal velocity (~20
cm/s)
Typically shed over several days – morning to
afternoon peak
Most pollen is deposited in or very near the
source field, but a significant amount of pollen
travels a much greater distance
Numerical Modeling
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Simulated flow profiles can be generated by scaling
relationships in the atmospheric surface layer (using
vegetation characteristics and local wind observations)
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Mean and turbulent flow characteristics are provided
for the Lagrangian Particle Dispersion Model
u ik' (t t)  u' ik (t) R ik (t)  u ik'' (t),
k  1,2,3
Lagrangian Particle Model
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Frame of reference is along the pollen particle
path
Particle accelerations follow a stochastic, autoregressive “random flight” approach
u ik' (t t)  u' ik (t) R ik (t)  u ik'' (t),
k  1,2,3
August 2003
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Pollen collected August 6th to 12th at Knapp
farm near Ames, IA
Peak pollen shed and deposition from August
9 to 11
WIND ROSE PLOT
Station #14848 - Knapp S, IA
10th
August
2003 Wind
Rose
NORTH
30%
24%
18%
12%
6%
WEST
EAST
Light SW wind
Wind just strong enough that
deposition will not be
symmetric about the field
SOUTH
MODELER
Wind Speed (m/s)
DATE
COMPANY NAME
10/20/03
> 2.50
DISPLAY
UNIT
2.00 - 2.50
Wind Speed
m/s
1.50 - 2.00
AVG. WIND SPEED
CALM WINDS
1.00 - 1.50
1.39 m/s
0.00%
0.50 - 1.00
ORIENTATION
PLOT YEAR-DATE-TIME
0.01 - 0.50
Direction
(blowing from)
2003
Aug 10 - Aug 10
Midnight - 11 PM
WRPLOT View 3.5 by Lakes Environmental Software - www.lakes-environmental.com
COMMENTS
PROJECT/PLOT NO.
August 10th 2003 Knapp Field Data
Knapp Log Pollen 08/10/03
Dispersive Tail
•
After 50m, there doesn’t
appear to be any relation
between log pollen
concentration and
distance from the field
2003 Knapp
Farm Model
Results
Comparison of Model and
Observations
Log Pollen Dispersion and Model Results
August 10 2003
2.5
2
1.5
1
0.5
0
0
50
100
150
Distance From Field
Pollen Deposition
Model Results
200
250
Comparison of Model and Observations
August 10 2003 Pollen Deposition and Model
Results
y = 0.6536x - 0.0073
Pollen Deposition
R2 = 0.8088
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0.2
0.4
0.6
Model Results
0.8
1
The Next Phase
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Windbreak around will reduce wind speed over
much of field and alter pollen dispersal
Use Takle and Wang shelterbelt model to
simulate effect of windbreak and canopy
Effect of Wind Break on Wind Speed and Turbulence
Effect of
Windbreak and
Canopy on
Dispersion
Effect of Bow Echo on Wind Break
Conclusions
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Model captures majority of observed variance in
August 2003 Knapp data
Modeled windbreak has substantial impact on
dispersal
Roughness changes at field edges generate a
natural shelter effect when upwind vegetation is
shorter
Future work: 3D shelterbelt model
Acknowledgements
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Ray Arritt, Mark Westgate, Susana Goggi
Cory Heilmann, Petrutza Caragea, James Correia
Jr., Chris Anderson
The wind break building crew!
Boulevard Wheat
Effect of Wind
Break on Vertical
Velocity
Effect of
windbreak and
canopy on
dispersion