1
  
Water, Energy and Carbon Fluxes From Tower and
Aircraft Measurements During SMACEX   J. H.
Prueger, W. P. Kustas, J. L. Hatfield, L.E.
Hipps, F. Li, C.M.U. Neale, J.I. MacPherson, M.C.
Anderson, T.B. Parkin 
2
Motivation

• Estimated 124 Pg C (Peta grams 1012 kg) added to
  the atmosphere 1850-1990.
• 13 from the conversion of mid-latitude
  grasslands to cultivated cropland.
• Houghton, R.A. 1999. The annual net flux of
  carbon to the atmosphere from changes in land use
  1850-1990. Tellus.

3
Objectives

• Quantify water use and CO2 uptake in space and
  time over corn and soybeans.
• Compare tower E.C. measurements with an aircraft
  E.C. system.

4
(No Transcript)
5
Corn for Harvest
6
(No Transcript)
7
(No Transcript)
8
(No Transcript)
9
July 04 02 Rainfall (mm)
10
Total Rainfall (6/1/02-8/19/02) (cm)
11
Study Site

• Walnut Creek Watershed, Ames Iowa
• 5100 ha typical corn/soy rotation
• Privately owned production fields

12
Instrumentation - EC

• 12 EC 3-D sonic anemometer (CSAT3)
• 10 Open path CO2/H2O IRGA (LI7500)
• 2 KH20
• Time series and flux averages

13
Instrumentation - Ancillary

• Net radiation (Kipp Zonen, REBS)
• Soil heat flux plates w/soil TC (REBS)
• Vitel ?v sensors
• Temperature/humidity (Vaisala)
• Radiometric temps (soil canopysoil)
• Wind speed and rain gauge

14
(No Transcript)
15

• Twin Otter
• Instrumentation
• SMEX02 Flights
• Twin Otter FLUX measurements
• Latent Heat (LE)
• Sensible Heat (H)
• CO2

16
CO2 Gradient in Corn Canopy
DOY 202 Nighttime
DOY 202 Daytime
17
Soil CO2 flux Measurements

• For soil CO2 flux spatial variability
• 3 types of soil chambers
• Non-portable continuous hourly fluxes
• Portable chamber but not continuous
• Hybrid-

18
Data Quality/Conditioning

• Data screening
• Diurnal trends
• Suspect data removed
• Gap filling Falge et al. Ag For. Met.
  (107,2001)
• 2-D Coordinate rotation
• Density effects (Webb, Pearman and Leuning)

19
(No Transcript)
20
Exploratory Equivalence Analysis(are the EC
equivalent)
Variable June 06 Sept. 17 CV
CO2 Yes Yes lt09
H Yes Yes lt11
LE Yes Yes lt10

21
(No Transcript)
22

23

24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
Observations

• Transition (grass to corn/soy) results in
  considerable variation in the way Rn-G is part.
• More variation in H for soy than corn more LE for
  corn than soy, variations decrease after full
  canopy
• Differences in CO2 fluxes significant (corngtgtsoy)
  and consistent with phenotype differences.
• Strong correlation between LAI, LE and CO2

30
Observations

• Tower network fluxes were representative of
  regional values obtained from aircraft.
• Single corn and soy tower meas. based on remotely
  sensed LAI provided similar regional flux values
  from the tower network.

31
Conclusions

• Results indicate highly dynamic system
• Variability observed across spatial/temporal
  scales
• Results represent only one component of a complex
  system (veg.atmos.)
• Integration with soil and within canopy processes
  need to be considered
• Further detailed analysis forthcoming