Protocols

KBS013: CH4, N2O, CO2 Fluxes

In use from sometime

Field Gas Sampling Protocol

Field Sampling: Usually April to November

Equipment:

Preparation:

  1. Place metal frames in ground, bottom edge approximately 1in below surface. The frames must be level to
    hold water in and maintain a proper air-tight seal at sampling. (On badly sloping sites, this can be achieved
    by carefully hammering a wooden 2 × 4 placed over the top [the channel is on the top] of the base; use a
    level to check anle). Frames should be set into ground at least 1 day before sampling; they remain in the
    soil until winter, and are not removed between sampling times except for plowing treatments.

  2. Plant growth within the box frames needs to be clipped without disturbing the soil prior to sampling

  3. Vials need to be crimped prior to sampling date. Number of boxes * 4sampling times(T0-T3) = number of
    vials needed. All vials are numbered with the set ID, then vials #’s 1-210 (for a full campaign, excluding
    fertilizer sites; 1-136 for treatments 1-8 only), for gas sample identification.

  4. It is a good idea to check the boxes (frames and lids) for plant growth and damage, and to level the frames
    the day before sampling.

  5. The box lids need maintenance work on occasion. The epoxyseals lining the edges of the box lid should be
    checked by filling the boxes with water – look for leaks. We’ve also been sealing the bottom channel on the
    gas box frames to prevent leaking.

Sampling:

  1. Record T0 soil temperature on data sheet.

  2. Record gas box lid type- it will be marked on the top (A,B, or C)

  3. Check the frames for obvious cracks. Fill the frame troughs with water without spilling water onto the
    soil (added water may stimulate biological activity).

  4. Check septa (venoject) on the box lids and replace if needed; they get dirty and gooey as they weather.

  5. Place PVC lid on frame and check to see if a proper seal has formed; if lid has been laying flat on the
    ground, make sure you’re not just moving the air that’s been trapped inside for weeks directly onto the frame.
    Gently pull lid up and feel for suction or check water level

  6. Flush the sample vial with air from the chamber using a vent neele. Remove the vent needle and inject
    sample. We usually flush with 10ml and inject as much as of an additional 10ml as possible (The over pressure
    gaurds against sample contamination, and provides an easy means for removing known volumes from the vial
    during gas analysis).

  7. Start timer as the first sample is injected into the vial; record vial number and time on data sheet.

Helpful hints: It is easiest to keep track of where you are in the vial sequence by placing the vent needle
in the next vial to be used and turning the "used" vials upside down in the tray. Some of the
septa/vials may leak – this shouls be fairly obvious, listen for the leak. If rain is expected, data sheets
can be photocopied onto rainproof paper.

In the lab, analyze vials for CH4 (using the GC-FID), N2O (GC-FID), and CO2 (IRGA). Analyze prior N2O,
because the ECD carrier gas contains 10% CH4- you will contaminate CH4 samples with carryover from the ECD
injection port. Samples should be analyzed within a

Abstract

Sampling Frequency: Weekly and/or Precipitation-Event Basis

CO2 and N2O fluxes are estimated using in situ closed-cover flux chambers. Bases of the chambers (28 cm x 28 cm x 10 cm high) are permanently installed in all plots of 4 replicate blocks (removed only for farming activities). Chamber bases are constructed from aluminum sheeting with a channel on the top outside rim to fit a plexiglass cover (29 cm x 29 cm x 14 cm high) fitted with a rubber septa. Base channels are filled with water during sampling to provide a gas-tight seal.

Gas fluxes are measured at 40 minute sampling intervals over a 3 hour period. Samples are taken from gas traps by inserting a 10 mL syringe into the rubber septa and drawing 10mL which is used to flush a vented 3 mL glass vial. Glass vials are sealed with butyl septa and crimped with a standard crimp seal. Another 10 mL gas sample is taken from the trap and placed in the glass vial, giving the vial a gas overpressure of 7 mL. CH4and N2O are determined by gas chromatography. CH4is analyzed with aflame ionization detector (300 degrees C), while N2O is analyzed with a 63Ni electron capture detector (350 degrees C). CO2 is analyzed using an infrared gas analyzer. Gases for both CH4 and N2O are separated on a Poropak Q column (1.8 m, 80/100 mesh) at 80 degrees C. Carrier gas for CH4 is nitrogen, while carrier gas for N2O is argon/methane (90/10).

Protocol

Author: Tim Bergsma

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