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Investigation:

TG-07 (Keller / Oliveira)

LBA Dataset ID:

LBA_TG07_STGFARM

Originator(s):

1. VARNER, R.K.
      2. KELLER, M.M.

Point(s) of Contact:

ORNL DAAC User Services Office Oak Ridge National Laboratory Oak Ridge, Tennessee 37 (ornldaac@ornl.gov)

Dataset Abstract:

This data set reports the results of an experiment that tested the short-term effects of root mortality on the soil-atmosphere fluxes of nitrous oxide, nitric oxide, methane, and carbon dioxide in a tropical evergreen forest.
Weekly trace gas fluxes are provided for treatment and control plots on sand and clay tropical forest soils in two comma separated ASCII files. The study site in the Tapajos National Forest (TNF) is near km 83 on the Santarem-Cuiaba Highway south of Santarem, Para, Brazil. Root mortality was induced by isolating blocks of land to 1 m depth using trenching and root exclusion screening. Gas fluxes were measured weekly for ten weeks following the trenching treatment and monthly for the remainder of the year. Monthly data are not included at this time.

Beginning Date:

2000-06-04

Ending Date:

2001-05-15

Metadata Last Updated on:

2009-04-30

Data Status:

Archived

Access Constraints:

PUBLIC

Data Center URL:

http://daac.ornl.gov/

Distribution Contact(s):

ORNL DAAC User Services Office Oak Ridge National Laboratory Oak Ridge, Tennessee 37 (ornldaac@ornl.gov)

Access Instructions:

PUBLIC

Data Access:

IMPORTANT: The LBA-ECO Project website is no longer being supported. Links to external websites may be inactive. Final data products from the LBA project can be found at the ORNL DAAC. Please follow the fair use guidelines found in the dataset documentation when using or citing LBA data.
Datafile(s):

LBA-ECO TG-07 Soil Trace Gas Flux and Root Mortality, Tapajos National Forest:  http://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=924

Documentation/Other Supporting Documents:

LBA-ECO TG-07 Soil Trace Gas Flux and Root Mortality, Tapajos National Forest:  http://daac.ornl.gov/LBA/guides/TG07_Root_Mortality_Experiment.html

Citation Information - Other Details:

Varner, R.K. and M.M. Keller. 2009. LBA-ECO TG-07 Soil Trace Gas Flux and Root Mortality, 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. doi:10.3334/ORNLDAAC/924

Keywords - Theme:

Parameter Topic Term Source Sensor
AIR TEMPERATURE ATMOSPHERE ATMOSPHERIC TEMPERATURE FIELD INVESTIGATION THERMOMETER
CARBON DIOXIDE BIOSPHERE SOILS FIELD INVESTIGATION IRGA (INFRARED GAS ANALYZER)
METHANE BIOSPHERE SOILS LABORATORY GC-FID (GAS CHROMATOGRAPH/FLAME IONIZATION DETECTOR)
NITROGEN OXIDES BIOSPHERE SOILS FIELD INVESTIGATION CHEMILUMINESCENCE
NITROUS OXIDE BIOSPHERE SOILS LABORATORY GAS CHROMATOGRAPHS
SOIL MOISTURE/WATER CONTENT LAND SURFACE SOILS FIELD INVESTIGATION WEIGHING BALANCE
SOIL MOISTURE/WATER CONTENT LAND SURFACE SOILS LABORATORY WEIGHING BALANCE
SOIL TEMPERATURE LAND SURFACE SOILS FIELD INVESTIGATION TEMPERATURE PROBE

Uncontrolled Theme Keyword(s):  CARBON DIOXIDE, GC-ECD, METHANE, NITRIC OXIDE, NITROUS OXIDE, ROOT MORTALITY, SOIL, SOIL MOISTURE, TRACE GAS EXCHANGE

Keywords - Place (with associated coordinates):

Region
(click to view profile)
Site
(click to view profile)
North South East West
Pará Western (Santarém) km 83 Logged Forest Tower Site -3.01700 -3.01700 -54.97070 -54.97070

Related Publication(s):

Varner, R. K., M. Keller, J. R. Robertson, J. D. Dias, H. Silva, P. M. Crill, M. McGroddy, and W. L. Silver, Experimentally induced root mortality increased nitrous oxide emission from tropical forest soils. Geophysical Research Letters 30(3):10.1029/2002GL016164, 2003.

Data Characteristics (Entity and Attribute Overview):

Data Characteristics:

Trace gas flux data are provided for treatment and control plots on sand and clay tropical forest soils in two comma separated ASCII files.



Values of -9999 in the ASCII file indicate missing values.



File: Trench_10weeks_NO_CO2_Final.csv



Column Label Description

1 Date YYYY/MM/DD

2 Site_ID Trench Description: Clay_NoTrench, Clay_Trench, Sand_NoTrench, Sand_Trench

3 Chamber Chamber Number: 1-5

4 Rep Replicates for each chamber (A and B)

5 Time hh:mm (local standard time, UTC-4 hours)

6 Air_T degrees Celsius

7 Soil_T degrees Celsius

8 NO_flux ng-N cm-2 hr-1

9 CO2_Flux umoles m-2 s-1



Example Data Records

Header records omitted

...

Date, Site_ID, Chamber, Rep, Time, Air_ T, Soil_ T, NO_ Flux, CO2_ Flux

2000/06/04,Clay_NoTrench,1,A,12:41,26.7,25,0.7,3.43

2000/06/04,Clay_NoTrench,1,B,12:46,26.9,25.2,1.21,6.18

2000/06/04,Clay_NoTrench,2,A,10:27,26.5,24.7,8.42,3.85

2000/06/04,Clay_NoTrench,2,B,10:33,26.4,25,10.44,3.28

...

2000/08/03,Sand_Trench,4,B,08:48,23.8,23.4,5.94,1.58

2000/08/03,Sand_Trench,5,A,07:57,23.3,23.4,7.56,0.78

2000/08/03,Sand_Trench,5,B,08:04,23.1,23.5,5.19,1.4



File: Trench_10weeks_N2O_CH4_Final.csv



Values of -9999 in the ASCII file indicate missing values.

Column Label Description

1 Date YYYY/MM/DD

2 Site_ID Trench Description: Clay_NoTrench, Clay_Trench, Sand_NoTrench, Sand_Trench

3 Chamber Chamber Number: 1-5

4 Rep Replicates for each chamber (A and B)

5 N2O_Flux Flux ng-N cm-2 hr-1

6 CH4_Flux Flux mg CH4 m-2 d-1



Example Data Records



Header records omitted

...



Date, Site_ID, Chamber, Rep, N2O_ flux, CH4_ flux

2000/06/04,Clay_NoTrench,1,A,28.03,2.8

2000/06/04,Clay_NoTrench,1,B,13.28,-0.49

2000/06/04,Clay_NoTrench,2,A,9.4,-0.43

2000/06/04,Clay_NoTrench,2,B,4.18,-0.78

2000/06/04,Clay_NoTrench,3,A,1.58,-9999

2000/06/04,Clay_NoTrench,3,B,12.95,-0.97

...

2000/08/14,Sand_Trench,4,B,3.92,-1.07

2000/08/14,Sand_Trench,5,A,-3.39,-1.43

2000/08/14,Sand_Trench,5,B,-1.32,1.15















Data Application and Derivation:

Root mortality was induced by isolating blocks of land to 1 m using trenching and root exclusion screening. Gas fluxes were measured weekly for ten weeks following the trenching treatment. For nitrous oxide there was a highly significant increase in soil-atmosphere flux over the ten weeks following treatment for trenched plots compared to control plots. N2O flux averaged 37.5 and 18.5 ng N cm-2 h-1 from clay trenched and control plots and 4.7 and 1.5 ng N cm-2 h-1 from sand trenched and control plots. In contrast, there was no effect for soil-atmosphere flux of nitric oxide, carbon dioxide, or methane. These fluxes can be obtained from the data files.



Root biomass in the trenched plots averaged 222 (+/-25) g m-2 in the clays and 260 (+/-25) g m-2 in the sands. Root biomass decreased slightly over the first four weeks following trenching in the clay soils to 173 (+/-21) gm-2. In contrast, root biomass increased slightly in the sand trench plots following root mortality to 277 (+/-30) gm-2, possibly resulting from colonization by decomposers.

Quality Assessment (Data Quality Attribute Accuracy Report):

Quality Assessment:

NO standards were run in the field at the beginning and end of 8 enclosure flux samples or approximately every hour. NO standard response calculated using a linear fit of the two standards encompassing the measurement period was compared to the frequent (generally hourly) standardization. A given hourly standard run varied by as much as 60% from the standard response calculated from the linear fit. On two dates of eight tested, at least 50% of the standards fall outside of the predicted standard response based on the starting and ending standards by at least 20%. On two other dates at least 10% of the standard runs fall outside of this +/-20% window. For additional QA, please see flux measurement section.

Process Description:

Data Acquisition Materials and Methods:

Site Description



The region receives approximately 2000 mm of precipitation per year and has an annual mean temperature of 25 C. Vegetation at the site is evergreen, mature tropical forest with a total biomass of about 372 Mg ha-1. Experimental plots were located on contrasting soils, a clay textured Oxisol (80% clay, 18% sand, 2% silt) and a sand textured Ultisol (60% sand, 38% clay, 2% silt).





Experimental Design



The experiment was a randomized complete block design. For each soil type, 5 pairs of 2.5 x 2.5 m plots were located so that there were no trees greater than 10 cm diameter at breast height (DBH; 1.3 m) on the plots. One plot in each pair was randomly selected for trenching. In the trenched plots, trenches were dug to 1-m depth and were lined with a fine stainless steel mesh (<0.5 mm) to prevent the penetration of roots while allowing the movement of water and gases. All vegetation was clipped from the trenched plots at the time of trenching and every two weeks thereafter to prevent colonization of the plot by live roots. The trenching operations were completed in the period from Julian day 147 through 156 in 2000 (May 27 through June 4). For all plots, measurements were made in an interior square region, 2 x 2 m that was surrounded by a 0.5-m wide buffer strip.



Trace Gas Flux Measurements



The soil-atmosphere fluxes of CO2, NO, N2O and CH4 were measured weekly for approximately 10 weeks following the trenching treatment. Two chamber bases were inserted approximately 2 cm depth in the soil at randomly selected points in the sampled plots within 30 minutes of the weekly flux measurement. These chamber bases were removed immediately after flux measurements were completed. Dynamic flow-through chambers were used for measurement of NO and CO2 and static vented chambers were used for measurements of N2O and CH4. The measurement of these two pairs of gases was sequential after lifting the chamber top to equilibrate the headspace with ambient air.



An integrated backpack system was used to measure NO and CO2 over 3 to 10 minutes from enclosures. The flow through the chamber 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.



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 make-up air flow of about 1200 cm3 min-1 and a flow of NO (1 ppm) standard gas that varied from 3 to 10 cm3 min-1 as measured on an electronic mass flowmeter (Sierra Top-Trak). The make-up air and standard addition maintain optimum and linear performance of the NO2 chemiluminescent analyzer (Scintrex LMA-3). The mixed sample stream passed through a Cr2O3 catalyst for conversion of NO to NO2. The NO2 chemiluminescent analyzer was standardized by a two-point calibration approximately hourly. The intra-day stability of the calibration on each sampling date was checked by comparison of each standard run to a linear interpolation between the standards runs at the beginning and end of the daily measurement period. The concentration of the field NO standard was compared periodically with laboratory standards to assure that they did not drift. Signals from the CO2 and NO2 analyzers and the mass flow meter for the NO standard gas were recorded on a datalogger (Campbell CR10). Fluxes were calculated from the linear increase of concentration versus time.



Static enclosure measurements were made for CH4 and N2O fluxes using the same bases and vented caps. Four enclosure headspace samples were taken over a 30-minute sampling period with 20-ml nylon syringes. Analysis of grab samples for CH4 and N2O were completed within 36 hours by FID and ECD gas chromatography. Gas concentrations were calculated by comparing peak areas for samples to those for standards.



Roots were sampled using a root corer with a 6-cm internal diameter. Cores were removed to 10 cm depth on 2 dates (June 4 (day 156) and 30 (day 182)) following trenching. Roots were sorted and dried at 65 degree C and weighed.

References:

Keller, M., et al., (2001) Biomass in the Tapajos National Forest, Brazil: Examination of sampling and allometric uncertainties, Forest Ecol. Manage., 154, 371-382. doi:10.1016/S0378-1127(01)00509-6



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. doi:10.1029/94GB01660



Levaggi, D., et al., (1974). Quantitative analysis of nitric oxide in presence of nitrogen dioxide at atmospheric concentrations, Environ. Sci. Tech., 8, 348-350. doi:10.1021/es60089a003





Silver, W. L., et al., (2000). Effects of soil texture on belowground carbon and nutrient storage in a lowland Amazonian forest ecosystem, Ecosystems, 3, 193-209. doi:10.1007/s100210000019



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 emission from tropical forest soils, Geophys. Res. Letts., 30, 10.1029/2002GL016164.



Veldkamp, E., and M. Keller, (1997) Nitrogen oxide emissions from a banana plantation in the humid tropics, J. Geophy. Res., 102, 15,889-15,898. doi:10.1029/97JD00767



Verchot, L. V., et al., (1999). Land use change and biogeochemical controls of nitrogen oxide emissions from soil in eastern Amazonia, Global Biogeochem. Cycles, 13, 31-46. doi:10.1029/1998GB900019



Vogt, K. A., and H. Persson, (1991). Measuring growth and development of roots, in Techniques and approaches in forest tree ecophysiology, edited by J. P. Lassoie and T. M. Hinkley, 447-502, CRC Press, Boca Raton, Fl.

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