Summary:

Trace gas fluxes of carbon dioxide, methane, nitrous oxide, and nitric oxide (CO2, CH4, N2O, and NO) from surface soil were measured manually in an undisturbed forest at the Tapajos National Forest Seca-Floresta Site, which is within the footprint of the km 67 eddy flux tower. Measurements were made in January 2000 through April 2004, approximately twice per month. On each sampling date, up to four sets of 30-m lines were established off the existing transects at the Seca-Floresta site. Along each line eight chambers were installed for gas collection. In addition soil samples were collected for analysis of soil moisture as water-filled pore space (WFPS). There is one comma-delimited ASCII file with this data set.

Data Citation:

Cite this data set as follows:

Varner, R.K. and M. Keller. 2011. LBA-ECO TG-07 Soil Trace Gas Fluxes km 67 Seca-Floresta Site, Tapajos National Forest. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/ORNLDAAC/1026

Implementation of the LBA Data and Publication Policy by Data Users:

The LBA Data and Publication Policy [http://daac.ornl.gov/LBA/lba_data_policy.html] is in effect for a period of five (5) years from the date of archiving and should be followed by data users who have obtained LBA data sets from the ORNL DAAC. Users who download LBA data in the five years after data have been archived must contact the investigators who collected the data, per provisions 6 and 7 in the Policy.

This data set was archived in August of 2011. Users who download the data between August 2011 and July 2016 must comply with the LBA Data and Publication Policy.

Data users should use the Investigator contact information in this document to communicate with the data provider. Alternatively, the LBA Web Site [http://lba.inpa.gov.br/lba/] in Brazil will have current contact information.

Data users should use the Data Set Citation and other applicable references provided in this document to acknowledge use of the data.

Table of Contents:

• 1 Data Set Overview
• 2 Data Characteristics
• 3 Applications and Derivation
• 4 Quality Assessment
• 5 Acquisition Materials and Methods
• 6 Data Access
• 7 References

1. Data Set Overview:

Project: LBA (Large-Scale Biosphere-Atmosphere Experiment in the Amazon)

Activity: LBA-ECO

LBA Science Component: Trace Gas and Aerosol Fluxes

Team ID: TG-07 (Keller / de Mello)

The investigators were Keller, Michael M.; Crill, Patrick Michael; Oliveira Jr., Raimundo Cosme de; Silva, Hudson S.; Dias, Jadson Dezincourt; and Varner, Ruth K. You may contact Varner, Ruth K. (ruth.varner@unh.edu)

LBA Data Set Inventory ID: TG07_Manual_Flux_Km67

Trace gas fluxes of carbon dioxide, methane, nitrous oxide, and nitric oxide (CO2, CH4, N2O, and NO) from surface soil were measured manually in an undisturbed forest at the Tapajos National Forest Seca-Floresta Site, which is within the footprint of the km 67 eddy flux tower. Measurements were made in January 2000 through April 2004, approximately twice per month. On each sampling date, up to four sets of 30-m lines were established off the existing transects at the Seca-Floresta site. Along each line eight chambers were installed for gas collection. In addition soil samples were collected for analysis of soil moisture as water-filled pore space (WFPS).

Related Data Sets

• LBA-ECO TG-07 Trace Gas Fluxes, Undisturbed and Logged Sites, Para, Brazil: 2000-2002 (Similar measurements at a nearby site that was selectively logged)
• LBA-ECO TG-07 Soil CO2 Flux by Automated Chamber, Para, Brazil: 2001-2003 (CO2 fluxes from the soil measured using an automated system at the same site and during an overlapping time period)

2. Data Characteristics:

Data are provided in one comma-delimited ASCII file: Trace_gas_fluxes_Km_67_Flona_Tapajos_Para.csv

Example data records:

Site boundaries: (All latitude and longitude given in decimal degrees)

Time period:

• The data set covers the period 2000/01/12 to 2004/04/28
• Temporal Resolution: approximately twice per month

Platform/Sensor/Parameters measured include:

• FIELD INVESTIGATION / IRGA (INFRARED GAS ANALYZER) / CARBON DIOXIDE
• LABORATORY / GC-ECD (GAS CHROMATOGRAPH/ELECTRON CAPTURE DETECTOR) / NITROUS OXIDE
• LABORATORY / GC-FID (GAS CHROMATOGRAPH/FLAME IONIZATION DETECTOR) / METHANE
• FIELD INVESTIGATION / NO2 CHEMILUMINESCENT DETECTOR / NITRIC OXIDE
• FIELD INVESTIGATION / THERMOMETER / AIR TEMPERATURE
• FIELD INVESTIGATION / TEMPERATURE PROBE / SOIL TEMPERATURE

3. Data Application and Derivation:

Trace gas fluxes from undisturbed tropical forests are important components of the global carbon and nitrogen budgets. These time series of soil-atmosphere gas exchange of NO, N2O, CH4 and CO2 reveal important seasonal and inter-annual variations in flux and provide insight to the environmental and biological controls in this ecosystem.

4. Quality Assessment:

The quality of trace gas flux measurements have been discussed by Keller and Reiners (1994). We did not directly measure any pressure differentials that could exist in our chamber system, although according to the source of our dynamic chamber design, Rayment and Jarvis (1997) indicated that the pressure differential between the chamber and the outside air was less than 0.004 Pa in laboratory tests.

For NO measurements, frequent standardization in the field was necessary. The LMA-3 is relatively unstable under the changing temperature, humidity, and background contaminant levels found in the field (Keller et al., 2005). Varner et al. (2003) found that intra-day variation in standard NO gas concentrations could be as great as 60% even after accounting for linear drift between the beginning and the end of a measurement day. We also compared the concentration of the field NO standard periodically with laboratory standards to assure that they did not drift (Veldkamp and Keller, 1997).

5. Data Acquisition Materials and Methods:

Field sampling of soil gas flux

The Seca Floresta site is located in the Flona Tapajos approximately 8 km from the km 67 eddy flux tower site. On each sampling date up to four 30 meter sampling lines were established off existing transects at the site. Along each line eight chambers were installed at randomly selected points and fluxes for all four gases were measured. After gas flux sampling was completed, soil samples were collected for determination of soil moisture content.

We sampled gas fluxes using enclosures consisting of a section of polyvinylchloride pipe (0.25 m diameter) that served as a base and an acrylonitrile-butadiene-styrene cap that fit snugly on the base. The combination of base plus cap was nearly cylindrical with a height of about 20 cm when inserted into the soil. Bases were inserted at most 30 min prior to flux measurements and they were removed immediately after completion of flux measurements in order to avoid artifacts related to root mortality from chamber insertion (Keller et al., 2000; Varner et al., 2003). Dynamic open chambers were used for measurement of NO and CO2 (Varner et al., 2003), and static vented chambers were used for measurements of N2O and CH4 (Keller and Reiners, 1994). The measurement of these two pairs of gases was sequential, in a haphazard order, after lifting the chamber top to equilibrate the head space with ambient air.

Field analytical system for NO and CO2

We used an integrated flow system to measure NO and CO2. The chamber flow rate was regulated to about 300 cm3 min-1. Air entered the chamber through a chimney-like air gap that was specifically designed to minimize exchange with the outside air and to avoid pressure fluctuations within the chamber (Rayment and Jarvis, 1997). Using this design, the pressure differential between the chamber and the outside air was less than 0.004 Pa in laboratory tests. The chamber base was capped for 3 to 10 min. Air flowed from the soil enclosure through a Teflon-lined polyethylene sample line 30 m in length and then it entered an infrared gas analyzer (Li-Cor 6262) for CO2 measurement. From the Li-6262, the sampled air then passed through a flow control manifold where it was mixed with a makeup airflow of about 1,200 cm3 min-1 and a flow of NO (1 ppm) in oxygen-free nitrogen standard gas that varied from 3 to 10 cm3 min-1 as measured on an electronic mass flowmeter (Sierra Top-Trak). The flowmeter was checked occasionally against a NIST-traceable electronic bubble flowmeter (Gilibrator). The makeup air and standard additions maintained optimum and linear performance of the NO2 chemiluminescent analyzer (Scintrex LMA-3) according to the manufacturer's recommendations. The mixed sample stream passed through a Cr2O3 catalyst for conversion of NO to NO2 (Levaggi et al., 1974). The NO2 chemiluminescent analyzer was standardized by a two-point calibration approximately hourly. Frequent standardization in the field was necessary because the LMA-3 was relatively unstable under the changing temperature, humidity, and background contaminant levels found in the field. Varner et al. (2003) found that intraday variation in standards could be as great as 60 percent even after accounting for linear drift between the beginning and the end of a measurement day. We also compared the concentration of the field NO standard periodically with laboratory standards to assure that they did not drift (Veldkamp and Keller, 1997). Signals from the CO2 and NO2 analyzers and the mass flowmeter for the NO standard gas were recorded on a datalogger (Campbell CR10). Fluxes were calculated from the linear increase of concentration versus time adjusted for the ratio of chamber volume to area and the air density within the chamber.

Analysis of CH4 and N2O

We made static enclosure measurements for CH4 and N2O fluxes using the same bases and vented caps (Keller and Reiners, 1994). Four enclosure headspace samples were taken over a 30-min sampling period with 20 ml nylon syringes. Analysis of grab samples for CH4 and N2O were completed within 36 h by FID and ECD gas chromatography. Gas concentrations were calculated by comparing peak areas for samples to those for commercially prepared standards (Scott-Marin) that had been calibrated against the LBA-ECO (a component of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia) standards prepared by the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostic Laboratory (NOAA/CMDL). Fluxes were calculated similarly to those for CO2 and NO.

Determination of soil water-filled pore space (WFPS)

Soil samples were taken to 10 cm depth in each chamber location on each date for determination of soil moisture (oven dried at 105 degrees C). Soil moisture was expressed as WFPS (the mean from the chambers) using soil bulk densities of 1.25 and 1.02 for Ultisol and Oxisol soils, respectively, at the undisturbed forest sites (Silver et al., 2000).  We recorded air and soil (2 cm depth) temperature using thermistor probes to accompany each soil enclosure measurement.

6. Data Access:

This data is available through the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Data Archive Center:

Contact for Data Center Access Information:

E-mail: uso@daac.ornl.gov
Telephone: +1 (865) 241-3952

7. References:

Keller, M., and W. A. Reiners (1994), Soil-atmosphere exchange of nitrous oxide, nitric oxide, and methane under secondary succession of pasture to forest in the Atlantic lowlands of Costa Rica. Global Biogeochem. Cycles, 8, 399-410.

Keller, M., A. M. Weitz, B. Bryan, M. M. Rivera, and W. L. Silver (2000), Soil-atmosphere nitrogen oxide fluxes: Effects of root disturbance. J. Geophys. Res., 105, 17 693-698.

Keller, M., R. K. Varner, J. D. Dias, H. Silva, P. Crill, R. C. de Oliveira, Jr. and G. P. Asner (2005), Soil-Atmosphere Exchange of Nitrous Oxide, Nitric Oxide, Methane, and Carbon Dioxide in Logged and Undisturbed Forest in the Tapajos National Forest, Brazil. Earth Interactions 9(23):1-28.

Levaggi, D., E. L. Kothny, T. Belsky, E. de Vera, and P. K. Mueller (1974), Quantitative analysis of nitric oxide in the presence of nitrogen dioxide at atmospheric concentrations. Environ. Sci. Technol., 8, 348-350.

Rayment, M. B., and P. G. Jarvis (1997), An improved open chamber system for measuring soil CO2 effluxes in the field. J. Geophys. Res., 102, 28 779-784.

Silver, W. L., J. Neff, M. McGroddy, E. Veldkamp, M. Keller, and R. Cosme, (2000), Effects of soil texture on belowground carbon and nutrient storage in a lowland Amazonian forest ecosystem. Ecosystems, 3, 193-209.

Varner, R. K., M. Keller, J. R. Robertson, J. D. Dias, H. Silva, P. M. Crill, M. McGroddy, and W. L. Silver (2003), Experimentally induced root mortality increased nitrous oxide emissions from tropical forest soils. Geophys. Res. Lett., 30, 1144, doi:10.1029/2002GL016164.

Xu, L., M. D. Furtaw, R. A. Madsen, R. L. Garcia, D. L. Anderson and D. K. McDermitt (2006), On maintaining pressure equilibrium between a soil CO2 flux chamber and the ambient air, J. Geophy. Res., 111, D08S10; doi:10.1029/2005JD006435.