BOREAS TF-11 CO2 and CH4 Concentration data from the SSA-Fen Summary: The BOREAS TF-11 team collected several data sets in their efforts to fully describe the flux and site characteristics at the SSA-Fen site. This data set contains temperature, pH, and concentration profiles of methane and carbon dioxide within the surface 50 cm of peat. The measurements were conducted as part of a 2x2 factorial experiment in which we added carbon (300 g m-2 as wheat straw) and nitrogen (6 g m-2 as urea) to four replicate locations in the vicinity of the TF-11 tower. The data set covers the period from the first week of June 1994 through the second week of September, 1994. 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 CO2 and CH4 Concentration data from the SSA-Fen 1.2 Data Set Introduction This data set contains temperature, pH, and concentration profiles of methane and carbon dioxide within the surface 50 cm of peat. The measurements were conducted as part of a 2x2 factorial experiment in which we added carbon (300 g m-2 as wheat straw) and nitrogen (6 g m-2 as urea) to four replicate locations in the vicinity of the TF-11 tower. In addition to siting and treatment variables, it reports air temperature and water table height relative to the average peat surface during each measurement. The data set covers the period from the first week of June 1994 through the second week of September, 1994. 1.3 Objective/Purpose Much of the area within the boreal forest biome is comprised of wetlands, in which large carbon stores and high water tables drive fundamentally different atmospheric interactions than occur under the other forest types studied by BOREAS. One key difference is in the form carbon is emitted following soil microbial respiration--in wetlands, much of it is emitted as methane. Wetlands are the dominant influence of boreal forests on atmospheric methane. This study was undertaken in order to assess responses of methane emissions in northern wetlands to potential changes in plant productivity, nitrogen availability or both. Whiting and Chanton (1993) recently observed that methane emissions from wetlands across the globe are well related to net primary productivity. This may be for a variety of reasons, including enhanced plant transport, increased methanogenic substrates from root exudates, increased litter input cascading to enhanced substrate availability for methanogenesis, or enhanced C and N mineralization of decomposing residues. Previous work by us (Valentine et al. 1994) and others has shown that substrate availability is a key constraint on methane production in wetlands. The present study was an effort to test whether substrate manipulation results from laboratory studies could be mirrored under field conditions. 1.4 Summary of Parameters We measured concentrations of methane and carbon dioxide dissolved in the porewater of the surface 50 cm of peat using probes integrating a series of "swampsuckers" similar to the device described by Burton and Beauchamp (1994). Measurements are reported for 0 (surface), 5, 10, 20, 30, 40, and 50 cm depths. One profile probe was established per platform * treatment combination, yielding 16 probes. Measurements were made weekly coincident with the flux measurements. Temperature profiles of the surface 50 cm of peat were obtained using thermocouples integrated with the swampsucker probe. Measurements are reported for 0 (surface), 5, 10, 20, 30, 40, and 50 cm depths. Measurements were made weekly to coincide with the flux measurements in dataset one. 1.5 Discussion These data were collected from a set of small locations within the fen, and therefore no one location represented the entire study site. In fact, the fen in which this work was conducted was characterized by a large scale gradient of vegetation, microtopography, and hydrology such that the study site itself is only representative of the portion of the fen in which it was located (i.e. the lower 1/3). These data were collected at the same site and over the same time period as Shashi Verma and his team measured methane and carbon dioxide fluxes using eddy correlation. Measurements made using micrometeorological and chamber techniques comprised the two major components of the TF-ll effort. 1.6 Related Data Sets BOREAS TE-05 CO2 Concentration and stable isotope composition. BOREAS TF-11 Biomass Data over the SSA-Fen BOREAS TF-11 CO2 and CH4 Flux data from the SSA-Fen BOREAS TGB-01/TGB-03 CH4 Chamber flux data over the NSA Fen BOREAS TGB-01/TGB-03 Water Table and Peat Temperature Data over the NSA BOREAS TGB-03 Plant Species Composition Data over the NSA Fen BOREAS TGB-01/TGB-03 NEE Data over the NSA Fen BOREAS TGB-03 CH4 and CO2 Chamber Flux Data over NSA Upland Sites 2. Investigator(s) 2.1 Investigator(s) Name and Title Name: David Valentine Title: Research Associate (through 16 Aug 1996) Assistant Professor (since 01 Sep 1996) Affiliations: Until 16 Aug 1996: Natural Resource Ecology Laboratory Colorado State University Fort Collins, CO Since 01 Sep 1996: Department of Forest Sciences University of Alaska Fairbanks, AK 2.2 Title of Investigation Influence of substrate characteristics and other environmental factors on methane emissions from the BOREAS Southern Study Area fen site. 2.3 Contact Information Contact 1 --------- David Valentine Department of Forest Sciences University of Alaska Fairbanks, AK (907) 474-7614 (907) 474-6184 (fax) ffdwv@aurora.alaska.edu Contact 2 --------- Sara Conrad NASA/GSFC Greenbelt, MD (301) 286-2624 (301) 286-0239 (fax) Sara.Conrad@gsfc.nasa.gov 3. Theory of Measurements Concentration profiles of methane (CH4) and carbon dioxide (CO2) were measured by collecting porewater samples at 0, 5, 10, 20, 30, 40, and 50 cm using a probe integrating a series of swampsluckers, similar in design to the one described by Burton and Beauchamp (1994). Porewater CH4 concentration was determined by first stripping the porewater by adding an equal amount of air and shaking the syringe for 5 minutes, then measuring the CH4 concentration in the equilibrated air using a gas chromatograph equipped with a flame ionization detector, and finally back-calculating the porewater CH4 concentration based on Henry's law partitioning. Carbon dioxide concentrations in the headspace were measured by passing the chromatographically separated headspace sample through a Shimadzu methanizer just upstream of the flame ionization detector. Porewater concentrations were calculated using Henry's law partitioning and accounting for pH of the porewater. The porewater pH was measured after headspace equilibration with a Beckman pH meter and a combination pH probe with a Ag/AgCl reference electrode. Temperatures at each porewater sampling depth were measured using twisted wire thermocouples in the gas profile sampling probe. 4. Equipment: 4.1 Sensor/Instrument Description 4.1.1 Collection Environment Data were collected near mid-day (+/- 2 h) at weekly intervals for each platform. Flooding at the site at the end of July 1994 prevented data collection for one week. 4.1.2 Source/Platform The porewater profile samplers were placed, four per platform, at the beginning of the season and remained in place throughout the summer. 4.1.3 Source/Platform Mission Objectives NA 4.1.4 Key Variables Name Unit Description ----- ------ ------------ PWCH4 µmol/L Dissolved methane PWCO2 µmol/L Dissolved carbon dioxide SOILT C Peat temperature pH pH unit Porewater pH after equilibration with headspace 4.1.5 Principles of Operation A probe combining sampling tubes and twisted wire thermocouples at several depths is used to measure temperatures and to obtain porewater samples for analysis of pH and concentrations of CH4 and CO2. 4.1.6 Sensor/Instrument Measurement Geometry None given. 4.1.7 Manufacturer of Sensor/Instrument The profile samplers were built by investigator. They were made of series of teflon (PTFE) or stainless steel tubing (1/8 OD) embedded in epoxy resin within 3/4" PVC pipe. All tubing elements pass through the upper end of the pipe and terminate in a stopcock used for sampling. Each tubing element terminates at a specific point along the side of the pipe corresponding to the depth to be sampled. Opposite each side opening was a twisted wire thermocouple (Copper- Constantine), with lead wires also exiting through the upper end of the pipe and terminating with plugs. Gas chromatograph: GC-8A gas chromatograph equipped with 1 mL sample injection loop, flame ionization detector, and methanizer, manufactured by Shimadzu Scientific Instruments, Inc. 7102 Riverwood Drive Columbia, Maryland 21046 USA (410) 381-1227 (410) 381-1222 (fax) (800) 477-1227 The electronic thermometer: Omega microprocessor thermometer model HH21, was manufactured by OMEGA Engineering, Inc One Omega Drive Stamford, CT 06907-0047 P.O. Box 4047 (800) 826-6342 (203) 359-1660 (203) 359-7700 (fax) The pH meter: Beckman 11 portable pH meter with automatic temperature compensation with Beckman combination pH probe (Ag/AgCl reference electrode), manufactured by Beckman Instruments Inc. 2500 Harbor Boulevard Box 3100 Fullerton, CA 92634-3100 Telephone: (800) 742-2345 FAX: (800) 643-4366 4.2 Calibration 4.2.1 Specifications Profile samplers: Air bubbles drawn into the syringe from the sampler reflect gas bubbles in the profile, and are typically very concentrated in CH4 (often 40% by volume). Our interest in the concentration profile centered on how dissolved gases were distributed, and therefore we decided to expell any sampled bubbles immediately. Based on comparisons of the electronic thermometer with a laboratory mercury thermometer at typical soil temperature ranges, all temperatures obtained from the thermocouples were adjusted upward by 0.5 °C. The pH meter was calibrated using commercially available pH buffers at pH 4 and 7. The gas chromatograph column oven was operated at 70°C, FID temperature was 180 °C, N2 carrier gas flowed at 35 mL per minute. 4.2.1.1 Tolerance None given. 4.2.2 Frequency of Calibration The gas chromatograph was calibrated at the start of each day using one of two calibration standards, depending on anticipated concentration ranges. Headspace samples from equilibrating porewater gas profile samples had high concentrations of both methane and carbon dioxide, so we used a standard containing 10,000 ppmv (analysis±2%) of both these gases (Scotty IV Can mix 216, obtained from Scott Specialty Gases, Longmont, CO 80501, tel. 303/442-4700). For flux measurements entailing much lower concentrations of methane and carbon dioxide, we diluted the above-referenced Scotty standard 10:1 with ambient air. This was done by loading a stopcock-fitted, 60 mL polypropylene syringe with excess standard, expelling all but 6 mL, then immediately pulling in outside ambient air to make up 60 mL. Calculation of the diluted standard accounted for average concentrations of methane and carbon dioxide in ambient air. Analyses of diluted standards yielded reproducibility across dilutions of better than 3%. All standards were run on the GC until reproducibility was better than 1% over the course of three standard injections from a single syringe. Calibration was rechecked initially every 10 samples, but detector stability was so high that calibration was checked only at the end of the day for most of the season. End of day calibration checks were always within 5% of the starting calibration. The pH probe was subject to drift, so a 2-point calibration was performed after every 10 samples. 4.2.3 Other Calibration Information None given. 5. Data Acquisition Methods Profiles of peat temperature and concentrations of methane and carbon dioxide were measured concurrently with the flux measurements (submitted as dataset tf11chfl.txt). We sampled 20 mL of the surface water directly with a 60 mL polypropylene syringe, and for subsurface concentrations combined the syringe with a sampler similar to the one described by Burton and Beauchamp (1994) with ports at 5, 10, 20, 30, 40, and 50 cm. We added a twisted wire copper- constantine thermocouple at each depth, and measured temperature using an electronic thermometer. Any bubbles drawn into the syringe were expelled immediately after sampling, and the water samples were stored in a refrigerator at 4 C until analysis within four days. Analysis consisted first making a 1:1 headspace:water mixture in the syringe using ambient air, then shaking vigorously for five minutes. The equilibrated headspace was then injected into the GC and analyzed as above for CH4 and CO2. Original porewater concentrations were calculated based on Henry's Law partitioning corrected for temperature and, for CO2, the water pH after equilibration (after Shurpali et al. 1993). Temperature at each depth was measured simply by plugging each thermocouple lead into the electronic thermomter. The pH of each porewater sample was measured after headspace equilibration. The sample was stirred gently during the measurement, and the pH was recorded after the reading stabilized (generally after 2 min.). 6. Observations 6.1 Data Notes Profile and other data are sparse or missing for the end of July 1994 because heavy rains raised the water table above the tops of all chamber collars and of most platforms. 6.2 Field Notes None given. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage All measurements were made along two transects identified by their location relative to the TF-11 micrometeorology tower: a north transect (NA and NB platforms) and a south transect (SA and SB platforms). All measurements were made within 70 m of the TF-ll tower whose North American Datum of 1983 (NAD83) coordinates are 53.80206°N, 104.61798°W. 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution These data are point measurements at the given locations. 7.1.4 Projection Not applicable 7.1.5 Grid Description Not applicable 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Data for each platform were collected weekly from 08-Jun-1994 until 15-Sep-1994. 7.2.2 Temporal Coverage Map None. 7.2.3 Temporal Resolution Each profile was sampled approximately weekly. Concentration profile data were optimally collected at daily time intervals. 7.3 Data Characteristics Data characteristics are defined in the companion data definition file (tf11flux.def). 7.4 Sample Data Record Sample data format shown in the companion data definition file (tf11flux.def). 8.1 Data Granularity All of the CO2 and CH4 Concentration data from the SSA-Fen are contained in one dataset. 8.2 Data Format(s) The data files contain 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 are shown in the companion data definition file (tf11flux.def). 9. Data Manipulations 9.1 Formulae 9.1.1 Derivation Techniques and Algorithms None Given. 9.2 Data Processing Sequence 9.2.1 Processing Steps None Given. 9.2.2 Processing Changes None Given. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None Given 9.3.2 Calculated Variables Porewater CH4 concentration (PWCH4) was calculated as CH4hs * P/Po * Kh + Vhs/Vw * (CH4hs-CH4amb) * P/RT where CH4hs is the equilibrated headspace concentration of CH4 (ppm) P and Po are ambient and sea-level atmospheric pressures (101325 Pa) Kh is the Henry's law constant for CH4 at ambient temperature (298 K) Vhs and Vw are the volumes of headspace and water in the syringe CH4amb is the ambient CH4 concentration (1.8 ppmv) R is the universal gas constant (8314.4 [L Pa]/[K mol] T is the ambient temperature (298 K) Porewater CO2 concentration (PWCO2) was calculated as CO2hs * P/Po * Kh*(1+Ka1/10^pH * (1+Ka2/10^pH)) + Vhs/Vw*(CO2hs-CO2amb)*P/RT where CO2hs is the equilibrated headspace concentration of CO2 (ppm) P and Po are ambient and sea-level atmospheric pressures (101325 Pa) Kh is the Henry's law constant for CO2 at ambient temperature (298 K) Ka1 and Ka2 are the 1st and 2nd dissociation constants for aqueous CO2 pH is the pH of the porewater after stripping Vhs and Vw are the volumes of headspace and water in the syringe CO2amb is the ambient CO2 concentration (350 ppmv) R is the universal gas constant (8314.4 [L Pa]/[K mol]) T is the ambient temperature (298 K) 9.4 Graphs and Plots None Given. 10. Errors 10.1 Sources of Error During sampling, a leak in the syringe or elsewhere in the profile probe system could generate bubbles that would strip gases from the sample. As bubbles were expelled after sampling, this may have reduced the calculated porewater contents of CH4 and CO2. Samples could not be run immediately because the time involved in retuning the gas chromatograph normal flux measurement mode to lower sensitivity in order to run porewater samples was prohibitive. We stored the porewater samples in a refrigerator at ~4 C for up to four days in order to run all weekly porewater samples once per week. We do not know what error may have accrued from the storage, but microbial respiration may have boosted CO2 levels and decreased CH4 levels. 10.2 Quality Assessment 10.2.1 Data Validation by Source None given. 10.2.2 Confidence Level/Accuracy Judgement The degree to which CH4 and CO2 concentrations may have changed during sample storage is unknown and likely variable. Nevertheless, the existence of good correlations between CH4 flux (data set tf11chfl.txt) and concentration data suggest that these errors are likely small and do not dominate real patterns of gas concentrations in time or space. 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 Data were examined for general consistency and clarity. 11. Notes 11.1 Limitations of the Data See section 10.1 11.2 Known Problems with the Data See section 10.1 11.3 Usage Guidance None given. 11.4 Other Relevant Information None given. 12. Application of the Data Set Several avenues are being pursued in publications now being produced to answer the following questions. For this dataset, we are most interested in how and why do CH4 concentration profiles and flux measurements vary through time and across the landscape. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description We used only commercially available software, mostly Quattro Pro spreadsheet and the Statistical Analysis System (SAS) 14.2 Software Access None given. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREAS Data Manager Bldg. 22, Rm. G87 Code 923 NASA GSFC Greenbelt, MD 20771 (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See Section 15.1. 15.3 Procedures for Obtaining Data Users may place requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans These data are available from the Earth Observing System Data and Information System (EOSDIS) 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 16. Output Products and Availability 16.1 Tape Products None. 16.2 Film Products None. 16.3 Other Products Comma delimited ASCII text files. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation None given. 17.2 Journal Articles and Study Reports Burton DL, Beauchamp EG. 1994. Profile nitrous oxide and carbon dioxide concentrations in a soil subject to freezing. Soil Science Society of America Journal 58(1):115-22. 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. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). 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., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 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. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). 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. Shurpali NJ, Verma SB, Clement RJ, Billesbach DP. 1993. Seasonal Distribution of Methane Flux in a Minesota Peatland Measured by Eddy Correlation. Journal of Geophysical Research 98(D11):20,649-20,655. Valentine DW, Holland EA, Schimel DS. 1994. Ecosystem and physiological controls over methane production in northern wetlands. Journal of Geophysical Research 99(D1):1563-71. 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System DAAC - Distributed Active Archive Center EOS - Earth Observing System EOSDIS - EOS Data and Information System GSFC - Goddard Space Flight Center NASA - National Aeronautics and Space Administration ORNL - Oak Ridge National Laboratory URL - Uniform Resource Locator SSA - BOREAS Southern Study Area 20. Document Information 20.1 Document Revision Date Written: 29-Jan-1997 Last Updated: 06-Oct-1998 20.2 Document Review Date(s) BORIS Review: 06-Oct-1998 Science Review: 20.3 Document ID 20.4 Citation Valentine, D.W. 1996. Influence of substrate characteristics and other environmental factors on methane emissions from the BOREAS Southern Study Area fen site. II. Profiles of gas concentration, temperature, and pH in the surface peat. 20.5 Document Curator 20.6 Document URL Keywords Methane flux peat profile wetland TF11_CH4_CO2_Conc.doc 10/09/98