‘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.

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

Coupled Carbon, Water, Methane and Energy Fluxes

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

Eddy Covariance Technique

The Flux Density is defined by the integral of the CoSpectrum

Conservation Budget, Advection and Flux Divergence

Must Consider Storage in Air Layer, as at night or with Plume Impaction

Baldocchi, Austral J Botany, submitted Probability Distribution of Published NEE Measurements, Integrated Annually

FLUXNET Database: n ~ 300 in 2003; n ~ 430 in 2005 Does pdf change with time and/or as the Network Grows?

Baldocchi, Austral J Botany, submitted Does Net Ecosystem Carbon Exchange Scale with Photosynthesis?

Baldocchi, Austral J Botany, submitted Net Ecosystem Carbon Exchange Scales with Length of Growing Season

Baldocchi, Austral J Botany, submitted Ecosystem Respiration Scales with Ecosystem Photosynthesis, with Offset by Disturbance

Time Since Disturbance Affects Net Ecosystem Carbon Exchange

Interannual Variation and Long Term Trends in Net Ecosystem Carbon Exchange, Photosynthesis and Respiration Urbanski et al 2007 JGR

Baldocchi, Austral J Botany, submitted Interannual Variations in Photosynthesis and Respiration are Coupled

Data of Pilegaard et al.; Baldocchi et al. Int J. Biomet, 2005 Soil Temperature: An Objective Indicator of Phenology??

Canopy Photosynthesis Starts when Soil Temperature Matches Mean Annual Air Temperature Baldocchi et al 2005 Int J Biomet

Spatialize Phenology with Flux-Based Transformation & Climate Map White, Baldocchi, Schwartz, JGR, submitted

White, Baldocchi and Schwartz, JGR, submitted Flux Based Phenology Patterns with Match well with data from Independent Phenology Network

Penman Monteith Equation Function of: Available Energy (Rn-S) Vapor Pressure Deficit (D) Aerodynamic Conductance (Gh) Surface Conductance (Gs)

Effects of Functional Types and R sfc on Normalized Evaporation R c is a f(LAI, N, soil moisture, Ps Pathway)

Stomatal Conductance Scales with Photosynthesis Wilson et al. 2001, Tree Physiology Schulze et al Annual Rev Ecology Photosynthetic Capacity Scales with Nitrogen Stomatal Conductance scales with Nitrogen Stomatal Conductance Scales with N, via Photosynthesis

Effects of Leaf Area and Photosynthetic Capacity on Normalized Evaporation: Watered-Deficits

Eco-hydrology: ET, Functional Type, Physiological Capacity and Drought

Use Appropriate and Root-Weighted Soil Moisture Soil Moisture, arthimetic average Chen, Baldocchi et al, in prep. Soil Moisture, root-weighted

Interannual Variation ET

Landscape Differences On Short Time Scales, Grass ET > Forest ET Ryu, Baldocchi, Ma and Hehn, JGR-Atmos, submitted

Role of Land Use on ET: On Annual Time Scale, Forest ET > Grass ET Ryu, Baldocchi et al, JGR-Atmos, submitted

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

Whiting and Chanton, 1993 Nature Methane Efflux Scales with NEP McMillan et al 2007 JGR Rice in Ca Shurpali and Verma, 1998

Whalen 2005 Env Eng Sci Methane Fluxes Experience Much Seasonality and transcend several Orders of Magnitude McMillan et al 2007 JGR

Hendricks et al 2007 Biogeoscience Role of Landscape in Holland

Interannual Variation in Methane Fluxes due to Water Table Shurpali and Verma, 1998

Methane Emission and Water Table Roulet et al, 1992 Tellus Bubier and Moore, TREE, 1994

Measuring Methane with Off-Axis Laser Spectrometer Los Gatos Research

Flux detection limit r wc ~ 0.5  w ~ m s -1  c ~ 0.84 ppb minimum methane flux density on the order of 4.68 nmol m -2 s -1 (0.27 mg CH 4 m -2 h -1 ),

Methane Fluxes over a Peatland Detto and Baldocchi, unpublished

Methane Fetch Daytime, Ideal

Methane Fetch at Night, Patchy and Complex

Day and Night Footprints over Peatland Detto and Baldocchi, unpublished

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

2% difference or 15 gC m-2 y-1

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

Many sensors don’t measure mixing ratio, they measure molar density 1 st order assumption, Boussinesq Approximation

‘correction’ for moist air

Closed Path TDL After Detto and Baldocchi

Ideal, steady-state, infinite fetch, no advection Integrate and Define Constant Flux Layer

Advective conditions