1. Adventures In Pollen Dispersion Modeling
Craig Clark
February 3, 2005

2. Outline Introduction to the problem
Boundary layer torture and dispersion modeling
Summer 2003 example
The next phase: modeling of windbreak

3. The Problem
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

4. Maize Pollen Dispersion Basics
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

5. Numerical Modeling
Simulated flow profiles can be generated by scaling relationships in the atmospheric surface layer (using vegetation characteristics and local wind observations)
Mean and turbulent flow characteristics are provided for the Lagrangian Particle Dispersion Model

6. Lagrangian Particle Model
Frame of reference is along the pollen particle path
Particle accelerations follow a stochastic, auto-regressive “random flight” approach

7. August 2003
Pollen collected August 6th to 12th at Knapp farm near Ames, IA
Peak pollen shed and deposition from August 9 to 11

8. August 10th 2003 Wind Rose Light SW wind
Wind just strong enough that deposition will not be
symmetric about the field

9. August 10th 2003 Knapp Field Data
Knapp Log Pollen 08/10/03

10. Dispersive Tail
After 50m, there doesn’t appear to be any relation between log pollen concentration and distance from the field

11. 2003 Knapp Farm Model Results

12. Comparison of Model and Observations

13. Comparison of Model and Observations

14. The Next Phase
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

15. Effect of Wind Break on Wind Speed and Turbulence

16. Effect of Windbreak and Canopy on Dispersion

17. Effect of Bow Echo on Wind Break

18. Conclusions
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

19. Acknowledgements Ray Arritt, Mark Westgate, Susana Goggi
Cory Heilmann, Petrutza Caragea, James Correia Jr., Chris Anderson
The wind break building crew!
Boulevard Wheat

20. Effect of Wind Break on Vertical Velocity

21. Effect of windbreak and canopy on dispersion