BOREAS TF-11 SSA Fen Leaf Gas Exchange Data Summary The BOREAS TF-11 team gathered a variety of data to complement their tower flux measurements collected at the SSA Fen site. This data set contains single-leaf gas exchange data from the SSA Fen site during 1994 and 1995. These leaf gas exchange properties were measured for the dominant vascular plants using portable gas exchange systems. The data are stored in tabular ASCII files. Table of Contents: 1 Data Set Overview 2 Investigator(s) 3 Theory of Measurements 4 Equipment 5 Data Acquisition Methods 6 Observations 7 Data Description 8 Data Organization 9 Data Manipulations 10 Errors 11 Notes 12 Application of the Data Set 13 Future Modifications and Plans 14 Software 15 Data Access 16 Output Products and Availability 17 References 18 Glossary of Terms 19 List of Acronyms 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS TF-11 SSA Fen Leaf Gas Exchange Data 1.2 Data Set Introduction The BOReal Ecosystem-Atmosphere Study (BOREAS) Tower Flux-11 (TF-11) team collected single-leaf gas exchange data at the Southern Study Area (SSA) Fen site in 1994 and 1995. These leaf gas exchange properties were measured for the dominant vascular plants using portable gas exchange systems. The variables that were measured include leaf species, leaf area, boundary layer conductance, leaf temperature, net CO2 assimilation rate, stomatal conductance, internal CO2 concentration, photosynthetic photon flux density (PPFD), air temperature, CO2 concentration, relative humidity, and air vapor pressure. 1.3 Objectives/Purpose The objectives of this study were to quantify the response of leaf gas exchange properties (e.g., net CO2 assimilation rate, stomatal conductance) to environmental conditions in the field and to determine diurnal and seasonal changes in leaf gas exchange properties. 1.4 Summary of Parameters Each data record includes the date and time of measurements, leaf properties (species, leaf area, boundary layer conductance, leaf temperature, net CO2 assimilation rate, stomatal conductance, internal CO2 concentration), and environmental conditions (PPFD, air temperature, CO2 concentration, relative humidity, air vapor pressure). 1.5 Discussion Our overall project goal was to investigate the surface-atmosphere exchange of carbon dioxide and methane, and the associated energy fluxes, at the SSA Fen site. Leaf-level gas exchange measurements were made in the field on the dominant vascular plant species growing at the SSA Fen site. Our primary focus was on Betula pumila (bog birch) and Menyanthes trifoliata (buckbean) based on the relative abundance (as reflected in, e.g., leaf area index (LAI)) of these species in the fen. A limited set of measurements was also made on Carex (sedge) species, mostly Carex diandra. 1.6 Related Data Sets BOREAS TF-11 SSA Fen Tower Flux and Meteorological Data BOREAS TF-11 SSA Fen 1996 Water Surface Film Capping Data BOREAS TF-11 SSA Fen Soil Surface CO2 Flux Data BOREAS TF-11 SSA Fen 1995 Leaf Area Index Data 2. Investigator(s) 2.1 Investigator(s) Names and Titles Dr. Timothy J. Arkebauer, Associate Professor Department of Agronomy University of Nebraska-Lincoln Dr. Shashi B. Verma, Professor Department of Agricultural Meteorology University of Nebraska-Lincoln 2.2 Title of Investigation Field Micrometeorological Measurements, Process-Level Studies and Modeling of Methane and Carbon Dioxide Fluxes in a Boreal Wetland Ecosystem 2.3 Contact Information Contact 1 ----------- Dr. Timothy J. Arkebauer Department of Agronomy University of Nebraska Lincoln, NE (402) 472-2847 (402) 472-3654 (fax) tja@unlinfo.unl.edu Contact 2 ----------- David Knapp Raytheon ITSS NASA GSFC Greenbelt, MD (301) 286-1424 (301) 286-0239 (fax) David.Knapp@gsfc.nasa.gov 3. Theory of Measurements Most gas exchange measurements were made by using an LI-6200 system in the closed-circuit mode. The net CO2 assimilation rate is calculated via the change in CO2 concentration in the sample chamber with time. Stomatal conductance is calculated from the rate of change of water vapor concentration with time, the fraction of the total system flow through the desiccant, and the (previously determined) boundary layer conductance of the leaf. Further details can be found in the LI-6200 Technical Reference Manual (LI-COR, Inc., 1990). Measurements were also made with an LI-6400 system operated in the open mode. Here, the net CO2 assimilation rate is calculated via the difference between the CO2 concentration entering and exiting the sample chamber. Similarly, the stomatal conductance is a function of the water vapor concentrations entering and exiting the sample chamber, in conjunction with the boundary layer conductance of the leaf. Further details can be found in the LI-6400 Technical Reference Manual (LI-COR, Inc., 1995). In all cases, the internal CO2 concentrations of the leaves were calculated based on the measured net CO2 assimilation rates and leaf conductances. Additional information on the theory related to leaf gas exchange measurements can be found in Ball (1987). 4. Equipment 4.1 Instrument Description Most of the measurements were made with an LI-6200 Portable Photosynthesis System. Several measurements were made with a prototype LI-6400 Portable Photosynthesis System. 4.1.1 Collection Environment All measurements were made on intact plants in the field at the SSA Fen site under ambient environmental conditions. 4.1.2 Source/Platform Measurements were made from platforms or boardwalks raised approximately 0.2 m above the fen surface. 4.1.3 Source/Platform Mission Objectives None given. 4.1.4 Key Variables Leaf properties: net CO2 assimilation rate, stomatal conductance, internal CO2 concentration, leaf temperature. Environmental conditions: air temperature, air vapor pressure, incident PPFD, air CO2 concentration. 4.1.5 Principles of Operation The LI-6200 was operated in the closed mode. Net CO2 assimilation rate was determined from the time rate of change of CO2 concentration in the sample chamber. Stomatal conductance was determined from the time rate of change of water vapor concentration in the chamber, in conjunction with the fraction of the system flow diverted through the desiccant and the (previously determined) leaf boundary layer conductance. CO2 concentrations were measured with an infrared gas analyzer (IRGA). A pump circulated the air from the sample chamber, through the analyzer, and back into the sample chamber. Water vapor concentrations in the sample chamber were determined by a Vaisala humidity chip and a thermistor sensing the air temperature. Leaf temperatures were determined by a thermocouple pair that measured the temperature difference between the air thermistor and a thermocouple appressed to the leaf. The LI-6400 was operated in the open mode. Net CO2 assimilation rate was determined from the difference between the CO2 concentration entering and exiting the sample chamber. Stomatal conductance was determined by the difference between the water vapor concentrations entering and exiting the chamber. Both CO2 and water vapor concentrations were measured with a pair of IRGAs. Additional information can be found in the LI-COR LI-6200 and LI-6400 Technical Reference manuals. 4.1.6 Sensor/Instrument Measurement Geometry None given. 4.1.7 Manufacturer of Instrument LI-COR, Inc. P.O. Box 4425 4421 Superior Street Lincoln, NE 68504 USA (402) 467-3576 (402) 467-2819 (fax) 4.2 Calibration 4.2.1 Specifications The IRGAs, the humidity chips, the flow meters, and the quantum sensors were calibrated by the manufacturer prior to each field season. The zero and span of the LI-6200 CO2 analyzer and the zeros and spans of the LI-6400 CO2 and water vapor analyzers were calibrated against known standard gases in the field. 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration Annual calibrations of the IRGAs, the humidity chips, the flow meters and the quantum sensors was done by the manufacturer. Daily calibration of the zero and span of the IRGAs in the field. The CO2 zero and the flow meter zero were checked and adjusted several times daily. 4.2.3 Other Calibration Information Calibration gases for the IRGAs were obtained from Acklands, 1042 Quebec Ave., Saskatoon, Saskatchewan CANADA, S7K 1V5 (Primary supplier: Linde gas, Alberta, CANADA). These gases were calibrated against gases of known concentration traceable to the National Oceanic and Atmospheric Administration (NOAA), Boulder, CO. The LI-6400 water vapor analyzer span was calibrated using an LI-610 Dew Point Generator (LI-COR, Inc., Lincoln, NE 68504). 5. Data Acquisition Methods A positive net CO2 assimilation rate (e.g., photosynthesis) means that the net flux of CO2 is into the leaf. A negative net CO2 assimilation rate (e.g., respiration) indicates the net flux of CO2 is out of the leaf. Measurements of Betula and Menyanthes were made on single leaves (or portions of single leaves). For Carex measurements, several (typically 10 to 12) leaves were taped together, and the resulting rectangular area was placed in the sample chamber. The LI-6200 measurements were made with a 0.25-liter sample chamber. Most measurements were made on plants growing adjacent to either the main (eddy correlation) boardwalk or raised platforms located approximately 200 m north and south of the main boardwalk. Most measurements were made under natural illumination (sunlight); however, a limited number of measurements were made with a red light emitting diode (LED) light source in conjunction with a LI-6400 gas exchange system. Leaves to be measured were placed in the sample chamber without altering their original orientation. The sample chamber was held with a tripod standing on the fen surface. Light response curves were usually made by attenuating natural illumination with neutral density filters. Respiration rates were determined after enclosing leaves in an opaque film-changing bag. Assimilation rates versus internal CO2 concentration responses were determined using a transient technique with an LI-6200 gas exchange system. The net CO2 assimilation rate and the internal CO2 concentrations for these studies were corrected for chamber leaks, and an external fan was used to moderate chamber temperatures (for details see McDermitt et al., 1989). Leaf areas for irregularly shaped leaves (e.g., most of the Betula samples) were determined by tracing the leaf outline on ruled graph paper. 6. Observations 6.1 Data notes None given. 6.2 Field Notes A limited set of field notes and observations is available by request from T.J. Arkebauer. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage Most measurements were made on plants growing adjacent to either the main (eddy correlation) boardwalk or raised platforms located approximately 200 m from the eddy correlation instrumentation, north and south of the main boardwalk. The North American Datum 1983 (NAD83) corner coordinates of the SSA Fen site are: Site Longitude Latitude BOREAS X BOREAS Y -------------------------------------------------------------- SSA-Fen 104.61798° W 53.80206° N 419.527 330.991 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution Not applicable. 7.1.4 Projection These data were collected at point locations. 7.1.5 Grid Description None. 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Measurements were made from 8 June - 7 September, 1994 and 30 June - 6 August, 1995. 7.2.2 Temporal Coverage Map None. 7.2.3 Temporal Resolution None given. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (tf11leaf.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (tf11leaf.def). 8. Data Organization 8.1 Data Granularity All of the SSA Fen Leaf Gas Exchange Data are contained in one data set. 8.2 Data Format The data file contains numerical and character fields of varying length separated by commas. The character fields are enclosed with single apostrophe marks. There are no spaces between the fields. Sample data records shown in the companion data definition file (tf11leaf.def). 9. Data Manipulations 9.1 Formulae Formulae for calculating the net CO2 assimilation rates, stomatal conductances and internal CO2 concentrations are given in the LI-6200 and LI-6400 Technical Reference Manuals. 9.1.1 Derivation Techniques/Algorithms None given. 9.2 Data Processing Sequence 9.2.1 Processing Steps 1. Data were received by BORIS from TF-11. 2. BORIS standardized the units and loaded data into the data base. 3. BORIS extracted data from database into ASCII files. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Correction/Adjustments None. 9.3.2 Calculated Variables None. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error Calibration drift: The flow meter zero and IRGA CO2 zero exhibited occasional drifts. The zeros were set periodically throughout the day. Dew/wetness: When leaves were wet, the stomatal conductance and internal CO2 values may not be correct. Examples of spurious data include conductances less than zero and CO2 concentrations in the thousands. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgment None given. 10.2.3 Measurement Error for Parameters None given. 10.2.4 Additional Quality Assessments None given. 10.2.5 Data Verification by Data Center BORIS loaded the data into the data base and checked for any inconsistencies during loading. Certain data records were found to have unrealistic values in some of the columns. In cases were these large values prevented these records from being loaded (i.e., they did not fit in the data base column) the values were changed to -999. Only 36 records were found to have this kind of problem. None given. 11. Notes 11.1 Limitations of the Data None given. 11.2 Known Problems With The Data Other than the few times measurements were made on moist leaves (as discussed above) there are no known problems with the data set. 11.3 Usage Guidance The normal caveat of 'use at your own risk' applies. Correspondence with T.J. Arkebauer is encouraged when questions arise. A positive net CO2 assimilation rate (e.g., photosynthesis) means that the net flux of CO2 is into the leaf. A negative net CO2 assimilation rate (e.g., respiration) indicates the net flux of CO2 is out of the leaf. 11.4 Other Relevant Information Dr. Evan C. Jolitz was responsible for most of the day to day coordination of the field measurements. His assistance is greatly appreciated. We also thank LI-COR, Inc., for their generous contribution of the prototype LI-6400 gas exchange system. 12. Application of the Data Set This data can be used to better understand the leaf carbon dioxide flux at a typical fen in the boreal forest. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description None given. 14.2 Software Access None given. 15. Data Access 15.1 Contact for Data Center/Data Access Information These BOREAS data are available from the Earth Observing System Data and Information System (EOS-DIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: ORNL DAAC User Services Oak Ridge National Laboratory (865) 241-3952 ornldaac@ornl.gov ornl@eos.nasa.gov 15.2 Procedures for Obtaining Data BOREAS data may be obtained through the ORNL DAAC World Wide Web site at http://www-eosdis.ornl.gov/ or users may place requests for data by telephone, electronic mail, or fax. 15.3 Output Products and Availability Requested data can be provided electronically on the ORNL DAAC's anonymous FTP site or on various media including, CD-ROMs, 8-MM tapes, or diskettes. The complete set of BOREAS data CD-ROMs, entitled "Collected Data of the Boreal Ecosystem-Atmosphere Study", edited by Newcomer, J., et al., NASA, 1999, are also available. 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products These data are available on the BOREAS CD-ROM series. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation LI-6200 Technical Reference Manual. March 1990. LI-COR, Inc., Lincoln, NE, USA. LI-6400 Technical Reference Manual. August 1995. LI-COR, Inc., Lincoln, NE, USA. 17.2 Journal Articles and Study Reports Ball, J.T. 1987. Calculations related to gas exchange. In: Stomatal Function. E. Zeiger, G.D. Farquhar and I.R. Cowan (eds.). Stanford University Press, Stanford, CA, pp. 446-475. McDermitt, D.K., J.M. Norman, J.T. Davis, T.M. Ball, T.J. Arkebauer, J.M. Welles, and S.R. Roemer. 1989. CO2 response curves can be measured with a field-portable closed-loop photosynthesis system. Ann. Sci. For. 46:416s-420s. Sellers, P. and F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN-94). Sellers, P. and F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN-96). Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society, 76(9):1549-1577. Sellers, P.J., F.G. Hall, R.D. Kelly, A. Black, D. Baldocchi, J. Berry, M. Ryan, K.J. Ranson, P.M. Crill, D.P. Lettenmaier, H. Margolis, J. Cihlar, J. Newcomer, D. Fitzjarrald, P.G. Jarvis, S.T. Gower, D. Halliwell, D. Williams, B. Goodison, D.E. Wickland, and F.E. Guertin. 1997. BOREAS in 1997: Experiment Overview, Scientific Results and Future Directions. Journal of Geophysical Research, 102 (D24): 28,731-28,770. Suyker, A.E., S.B. Verma, and T.J. Arkebauer. 1997. Season-long measurement of carbon dioxide exchange in a boreal fen. Journal of Geophysical Research, 102 (D24): 29,021-29,028. 17.3 Archive/DBMS Usage Documentation 18. Glossary of Terms None. 19 List of Acronyms ASCII - American Standard Code for Information Interchange BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System CD-ROM - Compact Disk-Read-Only-Memory DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GMT - Greenwich Mean Time GSFC - Goddard Space Flight Center IFC - Intensive Field Campaign IRGA - Infrared Gas Analyzer LAI - Leaf Area Index LED - Light Emitting Diode NASA - National Aeronautics and Space Administration NOAA - National Oceanic and Atmospheric Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park PPFD - Photosynthetic Photon Flux Density SSA - Southern Study Area TF - Tower Flux URL - Uniform Resource Locator 20. Document Information 20.1 Document Revision Date Written: 30-Jun-1997 Last Revised: 10-May-1999 20.2 Document Review Date(s) BORIS Review: 27-Apr-1999 Science Review: 20.3 Document ID 20.4 Citation T.J. Arkebauer and E.C. Jolitz_ 20.5 Document Curator 20.6 Document URL Keywords: LEAF GAS EXCHANGE TF11_Leaf_Gas_Exchange.doc 06/09/99