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

NASA GSFC

Greenbelt, MD

\(301\) 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