Ecosystem-level Carbon dioxide fluxes in two long-term experimental wet sedge tundra sites near Toolik Lake, AK, ARC LTER 1994.


Ecosystem-level Carbon dioxide fluxes were measured in two long-term experimental wet sedge tundra sites near Toolik Lake, AK. Experimental treatments at each site included factorial NxP, greenhouse and shade house and were begun in 1985 (Sag site) or in 1988 (Toolik sites). Fluxes were measured on quadrats that were later sampled for biomass and leaf area.

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Shaver, G. 2000. Ecosystem-level Carbon dioxide fluxes in two long-term experimental wet sedge tundra sites near Toolik Lake, AK, ARC LTER 1994. Environmental Data Initiative.



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Associated Researcher

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Sunday, July 24, 1994 to Wednesday, July 27, 1994

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Plots were setup as indicated below, with annual fertilization treatments of 10 g/m2 Nitrogen (as NH4NO3) and 5 g/m2 Phosphorous (as triple superphosphate). Greenhouses and shadehouses were annually set up in late May or early June and removed in the end of August or early September.
Sites: Block 1 - Toolik Inlet (CT, N, P, NP, GH, GHNP, and Shade treatment codes)
Indicated as "Block 1"
Treatments began summer of 1989; one 5x10m
Block 2 - Toolik Outlet (Same treatments)
"Block 2"
Treatments began summer of 1989; one 5x10m

Calculations: Units: Tissue mass data are expressed in g/quadrat (400 cm2). Multiply by 25 to get g/m2. Leaf blade area is in cm2/quadrat. Multiply by .0025 to get m2 leaf/m2 ground.

Sampling Description.

Biomass quadrats, size 20x20 cm, were randomly located along line transects within plots. There were 4 quadrats/plot (treatment) collected in Blocks 1 and 2. All aboveground biomass plus belowground stems and rhizomes were clipped in 20x20 cm quadrats. Ecosystem-level CO2 fluxes were measured on 3 of the 4 quadrats using a LiCor 6200 Portable Photosynthesis System. A custom-made clear Plexiglas cuvette (30x30 cm surface area x 30 cm high) was placed directly over the quadrat to be sampled using the standing surface water as a seal. A standard depth was used to keep the chamber volume constant. After allowing the LiCor system to stabilize for a few seconds, 10 consecutive observations of the average CO2 flux over 20 second intervals were made. The last 6 of the 10 observations were then averaged for use as the flux measurement. Air temperature, photosynthetically active photon flux, and CO2 concentration inside the cuvette were also recorded with each observation. All flux measurements were made on a warm sunny day (26 July 1994) between 11:00 AM and 3 PM Alaska Daylight time. The cuvette was then removed briefly to allow air temperatures and CO2 concentrations to recover before being shaded with an opaque blanket for ecosystem respriation. During the unshaded measurements photon flux inside the cuvette varied from 600-2000 microE m-2 sec-1, but most measurements were made between 950-1200 micro E m-2 sec-1. Photon flux during the unshaded measurements were always less than 10 micro E m-2 sec-1, usually zero. Air temperatures were between 18o and 28o C, with most measurements made between 20o and 24o C. Concentration of CO2 inside the cuvette was 330-440 ppm, with most measurements made at 340-350 ppm.
In presenting our results, we use the unshaded (full sunlight) CO2 flux measurement as our measure of Net Ecosystem Production, or NEP. Ecosystem Respiration, or RE, is the measurement made in the darkened cuvette. Gross Ecosystem Production (=Gross Ecosystem Photosynthesis), or GEP, is the difference between NEP and RE. In this presentation, negative values represent CO2 losses to the atmosphere (RE is always negative), and positive values represent CO2 inputs (GEP is always positive).
See 1994gswsbm.txt for information on the biomass collection.

Version Changes: 

15Mar95 Separated comma delimited data from Excel file. JL
28Oct2004 Added units and precision to variable description section. JL
Version2: Created Excel metadata form. Changed title and added attribut table. 10Jan06 JimL
Version 3: Added LTERNET Data Access server proxy for Excel and comma delimited data files.
Version 4: Update LTERNET Data Access server proxy link for Excel and comma delimited data files. Changed from knb to das in url.
Version 5: Updated the metadata form to new version and eml to 2.1.0 JimL 9Jul2012
Version 6: Updated metadata to newer form (with sites sheet). Ch March 2013.
Version 7: Checked keywords against the LTER network preferred list and replaced non-preferred terms. Jim L 27Jan14
Version 8: Changed Distribution URL since the LTER network DAS system is being discontinued. JimL 9Apr2015

Sites sampled.

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