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Breathing of the Terrestrial Biosphere
Lessons Learned from a Global Network of Carbon
Dioxide and Water Vapor Flux Measurement Systems
and Applications towards studying Methane
Dennis Baldocchi University of California,
Berkeley
Workshop on ON THE RELEVANCE OF SURFACE AND
BOUNDARY LAYER PROCESSES FOR THE EXCHANGES OF
REACTIVE- AND GREENHOUSE GASES", Wageningen, The
Netherlands 9-12th of October 2007.
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Outline

• Background
• Coupled Carbon, Water and N Cycles
• Eddy Covariance
• Long-Term Carbon Fluxes
• Trends and Inter-annual Variability
• Flux Partitioning
• Disturbance
• Long-Term Water Vapor Fluxes
• Mechanisms
• Annual Fluxes
• Long-term Methane Fluxes
• New Methane Measurements

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Coupled Carbon, Water, Methane and Energy Fluxes
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Eddy Covariance

• Direct measure of the flux density between the
  atmosphere and biosphere
• In situ
• Quasi-continuous
• Integrative of broad area
• Introduces no artifacts, like chambers

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Eddy Covariance Technique
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The Flux Density is defined by the integral of
the CoSpectrum
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Conservation Budget, Advection and Flux Divergence
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Must Consider Storage in Air Layer, as at night
or with Plume Impaction
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Probability Distribution of Published NEE
Measurements, Integrated Annually
Baldocchi, Austral J Botany, submitted
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Does pdf change with time and/or as the Network
Grows?
FLUXNET Database n 300 in 2003 n 430 in 2005
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Does Net Ecosystem Carbon Exchange Scale with
Photosynthesis?
Baldocchi, Austral J Botany, submitted
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Net Ecosystem Carbon Exchange Scales with Length
of Growing Season
Baldocchi, Austral J Botany, submitted
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Ecosystem Respiration Scales with Ecosystem
Photosynthesis, with Offset by Disturbance
Baldocchi, Austral J Botany, submitted
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Time Since Disturbance Affects Net Ecosystem
Carbon Exchange
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Interannual Variation and Long Term Trends in
Net Ecosystem Carbon Exchange, Photosynthesis and
Respiration
Urbanski et al 2007 JGR
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Interannual Variations in Photosynthesis and
Respiration are Coupled
Baldocchi, Austral J Botany, submitted
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Soil Temperature An Objective Indicator of
Phenology??
Data of Pilegaard et al. Baldocchi et al. Int J.
Biomet, 2005
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Canopy Photosynthesis Starts when Soil
Temperature Matches Mean Annual Air Temperature
Baldocchi et al 2005 Int J Biomet
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Spatialize Phenology with Flux-Based
Transformation Climate Map
White, Baldocchi, Schwartz, JGR, submitted
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Flux Based Phenology Patterns with Match well
with data from Independent Phenology Network
White, Baldocchi and Schwartz, JGR, submitted
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Penman Monteith Equation

• Function of
• Available Energy (Rn-S)
• Vapor Pressure Deficit (D)
• Aerodynamic Conductance (Gh)
• Surface Conductance (Gs)

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Effects of Functional Types and Rsfc on
Normalized Evaporation
Rc is a f(LAI, N, soil moisture, Ps Pathway)
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Stomatal Conductance Scales with N, via
Photosynthesis
Photosynthetic Capacity Scales with Nitrogen
Stomatal Conductance scales with Nitrogen
Stomatal Conductance Scales with Photosynthesis
Wilson et al. 2001, Tree Physiology Schulze et al
1994. Annual Rev Ecology
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Effects of Leaf Area and Photosynthetic Capacity
on Normalized EvaporationWatered-Deficits
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Eco-hydrologyET, Functional Type, Physiological
Capacity and Drought
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Use Appropriate and Root-Weighted Soil Moisture
Soil Moisture, arthimetic average
Soil Moisture, root-weighted
Chen, Baldocchi et al, in prep.
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Interannual Variation ET
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Landscape Differences On Short Time Scales, Grass
ET gt Forest ET
Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, submitted
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Role of Land Use on ET On Annual Time Scale,
Forest ET gt Grass ET
Ryu, Baldocchi et al, JGR-Atmos, submitted
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• Savanna Uses More Water than Grassland
• Savanna Soil holds about 78 mm more Water
• Annual ET Decreases with Rg
• Rg is negatively correlated with Rain and Clouds
• System is Water not Radiation Limited

Ryu, Baldocchi, Ma, Hehn, JGR-Atmos, submitted
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Methane Efflux Scales with NEP
Rice in Ca
McMillan et al 2007 JGR
Whiting and Chanton, 1993 Nature
Shurpali and Verma, 1998
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Methane Fluxes Experience Much Seasonality and
transcend several Orders of Magnitude
McMillan et al 2007 JGR
Whalen 2005 Env Eng Sci
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Role of Landscape in Holland
Hendricks et al 2007 Biogeoscience
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Interannual Variation in Methane Fluxes due to
Water Table
Shurpali and Verma, 1998
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Methane Emission and Water Table
Roulet et al, 1992 Tellus
Bubier and Moore, TREE, 1994
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Measuring Methane with Off-Axis Laser Spectrometer
Los Gatos Research
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Flux detection limit
rwc 0.5 sw 0.125 m s-1 sc 0.84 ppb
minimum methane flux density on the order of 4.68
nmol m-2 s-1 (0.27 mg CH4 m-2 h-1),
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Methane Fluxes over a Peatland
Detto and Baldocchi, unpublished
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Methane Fetch Daytime, Ideal
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Methane Fetch at Night, Patchy and Complex
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Day and Night Footprints over Peatland
Detto and Baldocchi, unpublished
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Conclusions

• Net Ecosystem Carbon Exchange is a result of
  close coupling between photosynthesis and
  respiration
• Disturbance produces an additional respiratory
  source
• Long-term measurements are showing trends in CO2
  exchange due to ecosystem dynamics
• Methane Fluxes transcend several orders of
  magnitude and experience much seasonality due to
  modulation in water table and net primary
  productivity
• New opportunities to measure other traces gases,
  like methane, with new generation of tunable
  diode laser spectrometers
• Fluxes of trace gases is more complicated due to
  plume impaction, over small background signal,
  and patchy sources

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2 difference or 15 gC m-2 y-1
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Filtering Functions

• High pass filtering
• Low pass filtering
• Digital sampling
• Sensor response time
• Attenuation of signal via sampling
• Line or volume averaging
• Sensor separation

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Many sensors dont measure mixing ratio, they
measure molar density
1st order assumption, Boussinesq Approximation
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correction for moist air
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Closed Path TDL
After Detto and Baldocchi
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Ideal, steady-state, infinite fetch, no advection
Integrate and Define Constant Flux Layer
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Advective conditions