Workshop Report:
SF6 tracer technique guidelines
9-10 March 2011
Palmerston North, New Zealand
Draft Report June 2011
Keith Lassey
NIWA Client report WLG2011-29
GLOBAL RESEARCH ALLIANCE
International Workshop
9-10 March 2011
Palmerston North, New Zealand
Compiled by Keith Lassey1
1
NIWA, P.O. Box 14-901, Kilbirnie, Wellington, New Zealand. Phone +64-4-386 0300
Fax +64-4-386 0574
Funding sources
New Zealand Government to support the goals and objectives of the Global Research
Alliance on Agricultural Greenhouse Gases
Disclaimer
This report has been commissioned by the New Zealand Government to support the
goals and objectives of the Global Research Alliance on Agricultural Greenhouse Gases.
While every effort has been made to ensure the information in this publication is
accurate, the Global Research Alliance does not accept any responsibility or liability for
error of fact, omission, interpretation or opinion that may be present, nor for the
consequences of any decisions based on this information. Any view or opinion
expressed does not necessarily represent the view of the Global Research Alliance.
Contents
Background
6
Workshop participants
6
Workshop Agenda
7
Outcomes
10
Table of contents for the Guidelines
Proposed content/outline for each chapter in the guidelines
10
11
1. Introduction
11
2. Purpose of Manual
11
3. Overview of the SF6 tracer technique and its evolution
12
4. Pre-experimental planning: how many animals are needed?
12
5. Permeation tubes: the source of SF6
13
6. Breath sampling systems
13
7. Special considerations for fistulated animals
14
8. Background–air sampling
14
9. Analyses of breath samples
15
10.
Animal management and feed intake
16
11.
Data quality assurance and quality control
18
12.
What SF6 detail should be reported?
18
13.
Future issues and potential improvements
18
14.
Unresolved puzzles [aka Enigmas]
18
15.
Information available on web
18
16.
Acknowledgements
19
17.
References
19
18.
Annex
19
Next steps
19
Acknowledgements
19
Glossary of abbreviations and terms
20
References
20
Appendix 1.
Workshop presentations
22
Workshop discussion
22
SF6 permeation tubes
22
Breath sampling apparatus
23
Background air sampling
24
Sample handling and gas analysis
24
Gas analysis
25
Animal management, diet and feed intake
25
Estimation of CH4 emission rates, yields, and emission factors
26
Other considerations
26
Statistical considerations for pre-experimental planning and data analysis
26
Acceptance and inclusion in guidelines
27
What SF6 tracer technique detail should be reported?
27
Future issues and potential improvements
27
Enigmas
27
Information available on the internet
28
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Background
The SF6 tracer technique pioneered by Johnson et al. (1994) has been used widely for
determining methane (CH4) emission rates by individual ruminant animals. It is a
technique available for robustly and accurately determining CH4 emissions by
individual grazing animals. The New Zealand Government in support of the goals of the
Global Research Alliance for Agricultural Greenhouse Gases funded a workshop held in
Palmerston North, 8–10 March 2011 to bring together key researchers and
organisations to discuss the diverse and innovative deployments of the SF6 tracer
technique, various technical aspects of the technique and the technique’s strengths
and weaknesses.
The goals of the workshop were to:
1. Discuss and detail the content of the proposed guidelines for the measurement
of CH4 emissions by individual animals using the SF6 tracer technique.
2. Allocate responsibilities to the authors of each section of the guidelines
3. To commence drafting key sections of the guidelines, focussing on those
sections that benefit from face-to-face consultation or where participants have
individual critical expertise
4. Develop an agreed timeframe that would assure completion of draft guidelines
by the end of June 2011.
This report details the draft outline of the chapters and their content as it was
developed at the workshop and identifies the authors for each chapter. Next steps are
to build on the chapter outline proposed in the workshop report after consideration of
the objectives of the guidelines, their target audience and how the writing process will
ensure that the final guidelines will be relevant and accessible to the target audience.
Workshop participants
Personal invites to attend the workshop were sent to all scientists currently known to
work in this area of science; of particular importance when selecting the participants
was their experience applying innovative approaches to the SF6 tracer technique. In
total 17 participants attended the workshop from 7 countries (Argentina, Australia,
Brazil, Canada, France, Ireland, and NZ), each brought considerable individual
experience with the technique and interpretation of results.
Table 1 lists workshop participants, alphabetically by country. One ‘participant’ (Alan
Iwaasa) was unable to participate in person, but supplied presentations and expressed
a keenness to be involved in the overall project.
Table 1:
Workshop participants, with contact details updated where necessary.
Participant
Host institution
José Gere
Grupo
de
Fisicoquímica
IFAS-UNCPBA, Tandil, ARGENTINA
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Email address
Ambiental,
[email protected]
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Chris Grainger
Roger Hegarty
Peter Moate
Richard Williams
Alexandre Berndt
Alan
(absent)
Iwaasa
Cécile Martin
Tommy Boland
Matthew Deighton
Keith Lassey
Ross Martin
German Molano
Cesar
Pinares-Patiño
Natasha Swainson
Ben Vlaming
Garry Waghorn
(formerly) Dept Primary Industry, Ellinbank, Vic.,
AUSTRALIA
Dept Animal Nutrition, Environmental and Rural
Sciences, University of New England, Armidale,
NSW, AUSTRALIA
Dept Primary Industry, Ellinbank, Vic.,
AUSTRALIA
Dept Primary Industry, Ellinbank, Vic.,
AUSTRALIA
Brazilian Agricultural Research Corporation,
Embrapa, São Carlos, São Paulo, BRAZIL
Semiarid Prairie Agricultural Research Centre,
Agriculture and Agri-Food, Swift Current, SAS,
CANADA
INRA, Unité de Recherches sur les Herbivores,
Saint-Genès-Champelle, FRANCE
School of Agriculture, Food Science and
Veterinary Medicine, University College Dublin,
IRELAND
Dept Animal and Bioscience Research, Animal &
Grassland Research and Innovation Centre,
Teagasc Moorepark, Fermoy, Co. Cork, IRELAND
NIWA Ltd, Wellington, NZ
NIWA Ltd, Wellington, NZ
AgResearch Ltd, Palmerston North, NZ
AgResearch Ltd, Palmerston North, NZ
[email protected]
AgResearch Ltd, Palmerston North, NZ
(formerly) AgResearch Ltd, Lincoln, NZ
Dairy NZ, Hamilton, NZ
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Workshop Agenda
Tuesday 8 March
9:15 – 10:00.
Welcome and Introduction
10:00 – 10:20.
Morning tea
10:20 – 10:40.
Overview of the SF6 technique [Keith]
Principles of a tracer, and choice of SF6
10:40 – 12:00.
SF6 PERMEATION TUBES
[Keith]
Permeation tubes in NZ: their fabrication, charging with SF6, and performance
monitoring
[Peter]
Permeation tubes at DPI, Vic, and SF6 release kinetics
[Tommy,Matthew]Permeation tubes in Ireland
[Cécile]
Permeation tubes in France
[Alexandre]
Permeation tubes in Brazil, esp. effect of washer size
[Roger]
Permeation tubes with very high release rates
[others?]
Permeation tubes as developed at home research institution
12:00 – 12:50.
LUNCH
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12:50 – 15:00.
[Keith]
[Richard]
[José?]
[others?]
[Ross/Keith]
[Cécile]
[Peter]
[others?]
BREATH SAMPLING APPARATUS
Halter with capillary-based flow limiter, inlet design to maximise breath
interception efficiency
Variations on capillary systems, such as crimped capillary; cleaning and
maintenance of sampling equipment
The Argentine ball-and-socket system for limiting flow rate
Any further variations on passive breath collection apparatus?
Pumped system to deliver sample into a bag, canister (evacuated), or even direct
to an analyzer
Sampling from fistulated animals
Rumen headspace gas composition, from fistulated and non-fistulated cows
Any special considerations for sampling from a fistulated animal, whether
problems with gas loss at fistula or opportunities to sample directly from rumen
headspace
15:00 – 15:20.
15:20 – 16:00.
[Keith]
AFTERNOON TEA
BACKGROUND AIR SAMPLING
Introduce the issues: selecting background site(s), and how to cope with spatial
gradients in background
[Richard]
Experiences with spatially variable indoor backgrounds
[others?]
Other experiences with background siting caused by spatially variable
backgrounds
16:00 – 17:00.
GAS ANALYSIS: SAMPLE HANDLING
[Keith]
The Johnson et al. approach: over-pressure by dilution
[Ross]
Extracting an under-pressured sample: a double-ended piston approach
developed by NIWA
[Ross]
Pumping a sample from a bag
[Richard, others?] Using vials for intermediate storage
Wednesday 9 March
9:00 – 9:10.
9:10 – 10:00.
[Ross]
[Ross/Keith]
10:00 – 10:20.
10:20 – 11:10.
[Keith]
[others?]
11:10 – 12:00.
[Roger?]
SYNOPSIS OF DAY 1
GAS ANALYSIS: GAS CHROMATOGRAPHY
Plumbing configurations of GC, examples of chromatograms
Detector (FID, ECD) responses to CH4, SF6, choice of gas standards in NZ
MORNING TEA
GAS ANALYSIS: GAS CHROMATOGRAPHY (CONTINUED)
Inferring CH4, SF6 mixing ratios from chromatograms: the NIWA procedure
other experiences with GC analyses
GAS ANALYSIS: OTHER TECHNOLOGIES
Gas analysis other than by GC — eg, IR or FTIR spectroscopy
12:00 – 12:50.
12:50 – 15:00.
[Garry et al.]
LUNCH
ANIMAL MANAGEMENT AND FEED INTAKE
Determination of feed intake under grazing and indoor situations, and of feed
properties (eg, NIR techniques)
Management of animals and feed under grazing and indoor situations, including
insertion of permeation tubes
Management of animals and analyses
AFTERNOON TEA
TOUR OF AGRESEARCH RUMINANT METHANE FACILITY
Will lead a tour of AgResearch facility; transport will be provided to AgResearch
and return
[César et al.]
[Cécile]
15:00 – 15:20.
15:20 – 17:00.
[César et al.]
Thursday 10 March
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9:00 – 9:10.
9:10 – 10:00.
[Keith]
[Keith]
[anyone?]
10:00 – 10:20.
10:20 – 12:00.
[Keith]
[all]
12:00 – 12:50.
12:50 – 15:00.
15:00 – 15:20.
15:20 – 16:30.
16:30 – 17:00.
SYNOPSIS OF WORKSHOP TO DATE
ESTIMATION OF CH4 EMISSION RATES, CH4 YIELDS, EFS
Equations linking CH4 and SF6 mixing ratios, in both sample and background, in
combination with SF6 permeation rate with estimated CH4 emission rate.
Definition of ‘CH4 yield’ both in units such as g(CH4)/kg(DM) and in energy terms,
% of GEI (IPCC definition).
Any other perspectives
MORNING TEA
DRAFTING OF MANUAL
How to proceed from here
Participants to please share key papers with others (with scanning facilities
available if necessary), and make available photo-files intended for manual.
LUNCH
DRAFTING OF MANUAL, CONTINUED
AFTERNOON TEA
DRAFTING OF MANUAL, CONTINUED
WRAP-UP
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Outcomes
Table of contents for the Guidelines
A draft outline of the proposed guidelines was prepared and supplied in advance of the
workshop to the participants. The workshop sessions were set-up to allow participants
to give scientific presentations that focused on the topics proposed to be included in
the guideline. Each participant summarised the current understanding of the topic and
in-depth discussions followed each session where participants considered i) agreed
minimum requirements, ii) site specific requirements or iii) ‘evolving’ requirements, for
each topic. The proposed outline of the guidelines and key issues to be covered was
revised as a result of the workshop and authors/co authors were nominated and
agreed.
Following these presentations and discussions, the participants agreed on a revised
Table of Contents and the authors for the Guidelines (see below). The participants also
agreed that the Guidelines should be as succinct and clear as possible, so that they
would be of use to a wide audience.
Agreed table of contents:
Chapter Title
Lead author
Author (s)
Introduction
Purpose of the manual
Overview of the SF6 tracer
technique and its evolution
Pre-experimental planning:
how many animals are
needed?
Keith Lassey
Keith Lassey
Keith Lassey
Roger Hegarty
Chris Grainger
Ben Vlaming, Natasha Swainson,
Peter Moate, Tommy Boland,
Cesar Pinares
Permeation tubes: the source
of SF6
Keith Lassey
Breath sampling systems
Mathew Deighton
Peter Moate, Richard Williams,
Matthew
Deighton,
Cécile
Martin, Roger Hegarty, Alex
Berndt, Alan Iwassa
Peter, Richard, José, Cécile,
Cesar, Ross, Alan
Special considerations
fistulated animals
for
Tommy Boland
Cécile Martin, Alan Iwassa, Garry
Waghorn, Alex Berndt
Background air sampling
Analysis of breath samples
Animal management and
feed intake
Peter Moate, Richard Williams
Keith Lassey and Ross Martin
Garry Waghorn
Mathew Deighton
Estimation
of
methane
emission rates and methane
yield
Acceptance and inclusion
guidelines
Peter Moate
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Cesar Pinares
Cesar Pinares, German Molano,
Cécile Martin, Tommy Boland,
Alex Berndt, Roger Hegarty
Keith Lassey, Mathew Deighton,
Ben Vlaming
Richard Hegarty, Cécile Martin,
Garry
Waghorn,
Natasha
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What SF6 detail should be
reported?
Issues
and
potential
improvements
Information available on the
web
Richard Williams
Swainson, Alan Iwassa, Alex
Berndt, German Molano
Peter Moate
All is this a separate section or a
part of all chapters
Peter Moate
Proposed content/outline for each chapter in
the guidelines
The participants agreed that because of the need for reliability of information about
the SF6 tracer technology, the development of the guidelines requires more than a
literature review and summary of currently adopted approaches. Instead, a critical
analysis and thorough discussion of all the issues involved with the methodology is
required in each relevant chapter to ensure the guidelines are credible, pass the
scrutiny of the wider science community, and when adopted, provide the best possible
emissions estimates. Consideration will be given to grey literature, unpublished
material and peer reviewed publications during the analysis.
1.
Introduction
[Lead: Keith Lassey: NIWA] [est. 2pp]
Short introduction to the topic: why measure ruminant methane; what is the SF 6 tracer
technique; and under what circumstances is it implemented in preference to (say)
enclosure techniques?
Mention that this manual was the product of an international workshop (place and
date) with authorship comprising active participants. The manual supplies a composite
of the varied proven implementations of the technique that the participants of the
workshop are prepared to share for inclusion in this manual.
2.
Purpose of Manual
[Lead: Keith Lassey: NIWA] [est. 2pp]
What does this manual seek to achieve? What readership does it try to reach? Basically
everything to do with the SF6 technique that will help get new converts to this
technique up and running, including photographs as well as text.
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3.
Overview of the SF6 tracer technique and its evolution
[Lead: Keith Lassey: NIWA, supported by Roger] [est. 3pp]
Summarise here the main facets of the technique summarised under headings that
comprise subsequent chapters. This introduction should give users confidence that
irrespective of known limitations and problems with SF6, there are currently no viable
alternatives for high-precision measurements from individual animals, so we need to
make the best of the method. In particular, cover the following:
the principles for operation, ‘constant’ SF6 emissions over time
a short history of the technique citing articles that have been pivotal to the
development of the technique; cross-reference Appendix 1 which comprises a
list of papers identified in a search of papers relating to the SF 6 technique.
report exit points of CH4 from ruminants, and that nose/mouth dominates
SF6 physical properties, molecular weight and other characteristics; industrial
uses and properties (insulator), increasing atmospheric concentrations.
Why is SF6 used for ruminal methane measurements; non toxic, low
atmospheric background concentrations, behaviour that makes it a useful
marker gas? What is the fate of rumen–sourced SF6? Why is SF6 better than
ethane, for example?
Finally, the importance of a system for measuring methane in grazing animals.
What deployments of SF6 have been done relative to global SF6 emissions
inventory (about
12kg released over 17 yrs from ruminant tracer
measurements vs 6800t released annually from all sources worldwide: Williams
et al., submitted) and especially its place in the future; especially farmlet trials,
and application in regions where use of chambers, tents or laser technology is
not possible. This could include hilly or arid regions, and might involve
collections over 5–10 days. The technique is relatively inexpensive and can be
applied to more animals than some other measurements.
Consideration of other techniques available, cost of technique vs other
methods, ease of use versatility, staff capabilities in using technique.
4.
Pre-experimental planning: how many animals are
needed?
[Lead: Chris Grainger, supported by Ben, Natasha, Peter, Tommy, Cesar] [est. 5pp]
Required animal numbers are affected by the required precision of measurement
across a herd being sought and the expected variation associated with different
treatments and measurement techniques. Ben Vlaming has tabulated data that
summarise animal number requirements and there are comparisons that show
variance associated with both the SF6 and chamber measurement techniques.
This aspect of the report will be useful for researchers trying to plan experiments,
because they will be forced to think about the magnitude of the difference they are
trying to detect, and make an appropriate choice of animal numbers, and whether to
use SF6 or chambers. May need some statistician input here. Will it cover animal
welfare, ethics approval, types of animals, age of animals, etc?
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5.
Permeation tubes: the source of SF6
[Lead: Keith Lassey: NIWA, supported by Peter, Richard, Matthew, Cécile, Roger,
Alex, Alan] [est. 9pp]
This chapter covers all aspects of permeation tubes, including:
Tube design and properties
Describe the various design details (diagrams where possible) and how to charge with
SF6. How to determine payload. Include description of designs by NIWA (Lassey et al.,
2001), Teagasc (role of washer dimension in controlling permeation rate, large capacity
tubes); INRA design, NSW high flow–rate tubes. Special care should be given to design
details, especially washers, Teflon thickness, and the importance of these variables.
Refining and standardising permeation tube construction/washer squashing, Teflon
thickness
Tube calibration
Considerations of calibration (oven temperature, use of gloves, scale calibration).
Estimation of release rate and ‘use–by–date’. There seems to be a range in preferred
release rates. Make it clear that when approaching ‘use–by date’, the issues
surrounding the accuracy of release rate extrapolation might outweigh the value of the
data.
Tube performance
How do tubes perform over time (eg, Lassey et al., 2001)? A quantitative
understanding of how permeation rates change over time could help reduce
uncertainty in CH4 emission estimates for serial experiments (eg, using MM kinetics of
Moate et al.).
Consider supplying details about places of manufacture, and the issues of shipping.
Suppliers of the components could be a worthwhile inclusion.
Insertion of Tubes
How tubes are inserted, consideration of tried and tested methods?
6.
Breath sampling systems
[Lead: Matthew Deighton: Teagasc, supported by Peter, Richard, José, Cécile, Cesar,
Ross, Alan] [est. 6pp]
This covers all systems used to sample “breath” (respired + eructed) from grazing or
housed animals, and to collect those samples for off–line or on–line analysis. These can
be divided into breath samples ‘sucked passively’ into pre–evacuated canisters, and
active pumping to bags or directly to the analyzer, the latter being a rare approach.
Sub–headings might be as follows:
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Halter, canister and plumbing design
This involves design of systems to deliver breath samples into pre–evacuated canisters,
including halter design, from the inlet and its position relative to the nostrils, to the
tubing, protection from damage, crimping capillary tubing or alternative flow limiters
(Argentine system), presence or absence of inline filter and of valves on yokes. Good
designs are available, and points such as minimising the number of joints, use of
stainless steel vs. brass, material used for halter construction are all important.
Of equal importance are the collection canisters. Some recommendation to use either
PVC, stainless steel or aluminium is relevant, and also positioning on the neck or back
of the animal is important. Harness construction (Matt Deighton) is very important to
ensure happy animals, happy ethics and reasonably content researchers.
Information should apply to sheep and cattle, with comments about other species
(goats, deer, camelids). Also, consider the importance of design for young (small) and
mature individuals, and the impact on data.
Active (pumped) sample delivery
This delivery can be used for penned animals or otherwise when a uniform delivery
rate needs to be assured, or for an automated system that analyzes bags sequentially
(eg, NIWA ‘Lung’ system: Lassey et al. (GGAA2010 special issue in AFST)).
7.
Special considerations for fistulated animals
[Lead Tommy Boland: Teagasc, supported by Cécile, Alan, Garry, Alex] [est. 3pp]
Fistulated animals provide both a problem and an opportunity, which may also be
influenced by cannula design.
The problem relates to the potential for gas leakage at non–uniform rate
around the cannula. This should be addressed by any participants who have
compared fistulated and non–fistulated animals (Canadian group?).
A useful opportunity relates to the potential for gas sampling directly from the
rumen headspace. (eg,, INRA). Talk about the merits and demerits of this.
Another opportunity relates to being able to remove permeation tubes and
replace them with newly–calibrated tubes (could be the same tubes,
recalibrated).
If rumen fistulation does not affect methanogenesis, why is there an over estimate of
methane. One suggestion was that both SF6 and methane could escape from the
fistula, so less SF6 came out in the breath, and the methane from hind gut
fermentation that is excreted via the lungs, in conjunction with low SF 6 concentrations,
resulted in the overestimate. This could be modelled.
8.
Background–air sampling
[Lead: Peter Moate or Richard Williams, supported by Matthew] [est. 2pp]
This section discusses both the apparatus used to collect background samples (usually
identical or similar to that used for breath sampling), and the strategy for selecting
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sites for backgrounds. The latter is especially important when animals are housed
indoors or in incompletely ventilated areas where there can be appreciable
concentration gradients of CH4 and/or SF6.
Need guidance on where to sample background air; height, proximity to an animal,
number of samples in a paddock, in an enclosed environment. Also, some information
on how to make these decisions. Also, indicate the importance of background gas
concentrations on the accuracy of methane estimations, cross–referencing Chapter 11.
Should there be canisters dedicated to backgrounds? Recommend if you need
dedicated canisters for background collections.
9.
Analyses of breath samples
[Lead: Keith Lassey: NIWA and Ross, supported by Richard, Alex, Alan, Roger]
[est. 10pp]
This is really getting gas out of a canister into a GC, and GC operation (or alternative
analyzer). Information in this section will apply equally for SF6 and methane.
Sample extraction
How to extract the sample from the canister at sub–ambient pressure or the partially–
inflated bag. This will traverse the two main options:
dilute the canister with gas that is free of CH4 and SF6 (usually N2) to provide
super–ambient pressure; this allows the diluted sample to be either bled
directly to the analyzer (the usual approach as advocated by Johnson et al.) or
injected into a vial suitable for interim storage and/or transportation to the
analytical laboratory
pump the sample directly from the canister or bag to the analyzer (NIWA’s
‘piston system’ (being prepared for publication) or ‘Lung’ system (latter
reported by Lassey et al. in AFST/GGAA2010 special issue)).
Analysis by gas chromatography
This is the pre–dominant means of analysis, using flame ionisation detection (FID) and
electron capture detection (ECD) for CH4 and SF6 respectively.
Discuss the merits of GC and potential configurations, including:
specifications concerning columns, detectors, software
columns and detectors in series or parallel
GC plumbing such as sample loops and multi–port valves
what can go wrong? eg, dirty samples; excessive SF6 concentrations, power
failure, etc.
examples of ‘chromatograms’
linearity and curvi–linearity of FID and ECD respectively
availability and choice of gas standards (CH4 and SF6) and their inclusion
frequency during analytical runs
how to infer CH4 and SF6 mixing ratios from chromatograms
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calibration - gas sources
Analysis by other technologies
Have non–GC technologies to measure CH4 and/or SF6 mixing ratios proven feasible?
Note lessons learned by Roger’s group.
Intermediate sample storage
Discuss special considerations for intermediate storage devices such as vials (eg, Alan,
Alex) or bags (Richard). These could be motivated by need for long–distance transport
of (sub–)samples from field site to lab, by limited availability of canisters, and/or by
capability for automated analysis of vial–stored samples. Do gas ratios change if
samples are stored for a week or a month? Settle on recommended methods for
transporting gases.
10. Animal management and feed intake
[Lead: Garry Waghorn, supported by Cesar, German, Cécile, Tommy, Alex, Roger]
[est. 10pp]
Discuss aspects of animal and feed management that are germane to the SF 6
technique. This includes considerations when the animals concerned will be grazing
(preparation of both animals and pasture), and for animals that will be housed or
penned (preparation of animals and feeding regime). Discuss also the insertion of
permeation tubes (per os, per fistula).
Just what should be measured relates to objectives of the research, which need to be
clearly defined in advance.
This chapter has three components: managing animals, assessing the rate of feed
consumption (DMI), and analysing samples of feed. The latter produces feed
composition, including in particular the DM content and gross energy (GE) content
which are usually closely related. Botanical or chemical properties of the feed are of
peripheral interest to the estimation of CH4 yield, but will often be tested for their
possible influence on CH4 yield, depending on the research objective.
Animal preparation
Discuss the handling of animals, including the need to acclimatize the animals to
wearing breath collection gear, and considerations relating to dosing with permeation
tubes.
Determining intake
Measurement of feed intake is inessential to the determination of CH4 emission rates
using the SF6 tracer technique. However, CH4 emission rates by themselves are not
amenable to extrapolation across a herd or flock to assess enteric emissions on a farm
to country level. For this purpose, the CH4 yield is much more robust, but it does
require knowledge of the intake of feed from which the CH4 is derived. Thus, in many
situations intake will be an important component of research, because it will aid
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interpretation. This section will cover (in brief) the opportunities provided by
measuring intake – i.e. better interpretation of findings, opportunities for improved
comparisons between diets, or feeding systems etc. A brief overview should be given
of benefits and negative aspects of indoor feeding, the risks associated with estimating
intakes from feeding tables, and the challenges (and uncertainties) associated with
measuring intakes at grazing. Some mention needs to be made of rates of eating,
meals per day and the rates of methanogenesis during (and immediately after) eating,
compared to other times, because this may affect overall methane production.
This section mustn’t become a book, sticking to issues pertinent to use of the SF6
tracer technique for measuring methane. Provide references to literature that
discusses feed intake measurement and monitoring in a broader sense without
repeating here.
The combination of DM (or GE) content plus the assessed rate of feed consumption
allows estimation of DMI or GEI. In cases of grazing where feed intakes are notoriously
difficult to measure, a third approach would be to apply an energy requirements
model to asses GEI directly. All of these options will be addressed:
available options to measure intake in penned/housed animals, and to estimate
intake by grazing animals
measurement of DM and GE content of diet
assessment of GEI using energy requirement modelling
Diet
If intake is measured, it is equally important to measure the composition of what is
eaten (say why); Routine analysis will be appropriate in some circumstances, but in
other situations more detailed analyses may be appropriate; pectin, lipids nitrate etc,
but also measures of digestibility, degradation rate etc.
Duration of measurement
Impact on accuracy.
11. Estimation of methane emission rates and methane yield
[Lead: Peter Moate, supported by Keith, Matthew, Ben] [est. 5pp]
Present the formula for CH4 emission rate as a function of CH4 and SF6 mixing ratios in
breath samples and in backgrounds. Discuss the underlying assumptions, the
implications of variable or uncertain backgrounds, and the choice of period over which
the breath samples are integrated (usually 24 hours, also multi–day) and the number
of replicate periods. Cite relevance of CH4 per unit liveweight or LW gain.
Discuss CH4 yield and its major sources and appropriate means of quantification of
uncertainty, and how it becomes a useful basis for estimating EFs, noting that IPCC Tier
1 EFs for cattle are computed this way.
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12. Data quality assurance and quality control
[Lead: Cesar Pinares, supported by Richard, Cécile, Garry, Natasha, Alan, Alex,
German] [est. 4pp]
QA/QC of SF6 data: how to recognise crook data (criteria?). Distinguish “methane
emissions” and “estimated methane emissions”. Use IPCC standards here.
13. What SF6 detail should be reported?
[Lead: Richard Williams, supported by Peter] [est. 2pp]
Make recommendations about what should be reported in publications and reports.
These include following properties of permeation tube used in study: age since
charged with SF6, SF6 payload, SF6 release rate, how tubes were calibrated and for how
long, location of background collections and background magnitudes (CH4 and SF6).
14. Future issues and potential improvements
[Lead: all leads of other chapters] [est. 2pp]
Ensure these are addressed in headings above where appropriate:
Could recalculate old data based on Peter’s Michaelis–Menton kinetics,
enabling retrospective fine–tuning of permeation rates. This may lessen the
variance within data sets and remedy over–estimates of emissions.
Figure out if changes to flow rates over time are proportionately greatest for
tubes with high permeation rates
Intra–ruminal temperature: does it matter?
15. Unresolved puzzles [aka Enigmas]
[Lead: all] [est. 1pp]
Relationships between SF6 release rate and CH4 emission estimates (Ben, Cesar
in peer–reviewed papers) that is not seen by Matthew (but was Matthew’s
experiment designed to detect it or capable of detecting it?)
Much lower methane yields from sheep fed chicory or white clover measured
by SF6 (12–16 and 16.7 g/kg DMI) compared to chambers (21–25 g/kg DMI).
What is the reference to this (Garry)?
How to explain much greater variation between animals when yield (with
measured intakes) is measured by SF6 with 4 days of measurements, than
chambers. Peter mentioned ‘couching distribution’.
Matt’s use of better, stainless steel, connections to prevent leakage around
capillary tubes reduced estimates of methane production and he doesn’t know
why.
16. Information available on web
[Lead: Peter Moate] [est. 1pp]
Include cross–references to various SOPs, Codes of Practice.
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17. Acknowledgements
18. References
These are references cited in this document. Use the AFST reference style. They will
likely all be merged by the editor into a single alphabetised list rather than by chapter.
It would be helpful if all authors could use Endnote in their individual contributions, or
export their final reference list into an Endnote-compatible format.
19. Annex
This annex will be a list of citations of all known papers in the literature that report on
the SF6 tracer technique. The list has been made available to workshop participants as
a separate file, inviting participants to add to the list. As of 30 June 2011, the list
comprises 94 references.
Next steps
The workshop participants agreed that the development of standardised guidelines is
urgently needed to provide consistency, transparency and, probably most importantly,
reliability of the measured emissions. Comprehensive guidelines will provide potential
users of the SF6 tracer technique with a set of best practice guidelines drawn from the
experiences of research groups around the world who have deployed the technique in
diverse and innovative ways. The guidelines will help facilitate greater international
uptake of this low cost method for obtaining CH4 emissions data from grazing
ruminants, which in turn will provide greater confidence in CH4 emissions factors,
national inventory estimates and the efficacy of mitigation approaches.
The next step is for those experts who have indicated their interest in this project,
whether it is as an author, lead author or editor, to seek appropriate resources from
their national institution to enable them to participate. New Zealand agreed in
principle to take the role of scientific coordinator and editor of the guidelines subject
to necessary resources being made available.
The guidelines should build on the chapter outline proposed in the workshop report
after consideration of the objectives of the guidelines, their target audience and how
the writing process will ensure that the final guidelines will be relevant and accessible
to the target audience.
Acknowledgements
NZAGRC personnel did a great job in organising the workshop logistics, including travel
arrangements for all participants, and with their hospitality. Harry Clark (Director
NZAGRC) and Victoria Bradley (NZAGRC Operations Manager) personally attended
some workshop sessions or checked that all was running smoothly which was much
appreciated. Host institutions of all participants kindly permitted their respective
participations.
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Glossary of abbreviations and terms
CH4
methane
GC
gas chromatography, or gas chromatograph
GL
guidelines and protocols for the measurement of methane emissions
by individual animals using the SF6 tracer technique
GRA
Global Research Alliance (http://www.globalresearchalliance.org/)
LA
lead author of a GL chapter
MAF
NZ Ministry of Agriculture and Forestry (http://www.maf.govt.nz)
NZAGRC
NZ
Agricultural
Greenhouse
(http://www.nzagrc.org.nz/)
PT
permeation tube, with SF6 as the permeant
SA
supporting author (also known as contributing author) of a GL chapter
SF6
sulphur hexafluoride
Gas
Research
Centre
References
Gere, J.I., Gratton, R., 2010. Simple, low-cost flow controllers for time averaged
atmospheric sampling and other applications. Lat. Am. Appl. Res. 40, 367–376.
Grainger, C., Clarke, T., McGinn, S.M., Auldist, M.J., Beauchemin, K.A., Hannah,
M.C., Waghorn, G.C., Clark, H., Eckard, R.J., 2007. Methane emissions from dairy cows
measured using the sulfur hexafluoride (SF6) tracer and chamber techniques. J. Dairy
Sci. 90, 2755–2766.
Johnson, K., Huyler, M., Westberg, H., Lamb, B., Zimmerman, P., 1994.
Measurement of methane emissions from ruminant livestock using a SF 6 tracer
technique. Environ. Sci. Tech. 28, 359–362.
Lassey, K.R., Walker, C.F., McMillan, A.M.S., Ulyatt, M.J., 2001. On the
performance of SF6 permeation tubes used in determining methane emission rates
from grazing livestock. Chemosphere: Global Change Sci. 3, 377–381.
Lassey, K.R., Pinares-Patiño, C.S., Martin, R.J., Molano, G., McMillan, A.M.S., 2011.
Enteric methane emission rates determined by the SF6 tracer technique: temporal
patterns and averaging periods. Anim. Feed Sci. Technol. 166–167, 183–191.
McGinn, S.M., Beauchemin, K.A., Iwaasa, A.D., McAllister, T.A., 2006. Assessment
of the sulfur hexafluoride (SF6) tracer technique for measuring enteric methane
emissions from cattle. J. Environ. Qual. 35, 1686–1691.
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Martin, R.J., Bromley, A.M., Harvey, M.J., Moss, R.C., Pattey, E., Dow, D., 2011. The
“Lung”: a software-controlled air accumulator for quasi-continuous multi-point
measurement of agricultural greenhouse gases. Atmos. Meas. Tech. Discuss. 4, 1935–
2011.
Pinares-Patiño, C.S., Machmüller, A., Molano, G., Smith, A., Vlaming, J.B., Clark, H.,
2008. The SF6 tracer technique for measurements of methane emission from cattle —
effect of tracer permeation rate. Can. J. Anim. Sci. 88, 309–320.
Pinares-Patiño, C.S., Lassey, K.R., Martin, R.J., Molano, G., Fernandez, M.,
MacLean, S., Sandoval, E., Luo, D., Clark, H., 2011. Assessment of the sulfur
hexafluoride (SF6) tracer technique using respiratory chambers for estimation of
methane emissions from sheep. Anim. Feed Sci. Technol. 166–167, 201–209.
Vlaming, J.B., Brookes, I.M., Hoskin, S.O., Pinares-Patiño, C.S., Clark, H., 2007. The
possible influence of intra-ruminal sulphur hexafluoride release rates on calculated
methane emissions from cattle. Can. J. Anim. Sci. 87, 269–275.
Woodward, S.L., Waghorn, G.C., Ulyatt, M.J., Lassey, K.R., 2001. Early indications
that feeding Lotus will reduce methane emissions from ruminants. Proc. N.Z. Soc.
Animal Prod. 61, 23–26.
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Appendix 1.
Workshop presentations
Workshop discussion
The section presents workshop deliberations (presentations plus some discussion)
under the headings of the workshop programme (Appendix 1) together with extra
headings that were decided upon at the workshop to incorporate new and
unanticipated material into the GL. Individual presentations are available as annexes to
this report. More detail on the discussion points that are to be traversed in the GL
chapters are relegated to Appendix 2.
The remainder of this section presents workshop material and its relevance to the GL.
Wherever a topic is mentioned, or portrayed as raised by a workshop participant, it
should be taken as a recommendation that that topic be traversed in the GL. Thus in
traversing the main content of presentations and the discussion stimulated by those
presentations, the subject material of the GL is being defined and traversed.
Accordingly, the major workshop presenters under each heading are also on the
authorship of the corresponding chapter of the GL. More detail on the intended
coverage of each chapter is provided in Appendix 2.
SF6 permeation tubes
Presentations were given by Keith, Peter, Matthew, Cécile, Alexandre and Richard, on
various aspects of permeation tubes (PTs). Topics covered included tube fabrication,
charging, calibrating and deployment. In addition, an investigation of a possible effect
of tube orientation was reported by Richard (no effect detected). Presentations by
Cécile, Alexandre, Ben and Alan each covered various aspects of the SF 6 tracer
technique that included a component on PTs.
Roger overviewed his experiences with high-emission PTs (and of infrared analysers,
relevant to ‘Gas analysis’ below), and also with tracers alternative to SF 6. The highemission PTs were motivated by the need for higher SF6 concentrations for detection
by IR analysers. It is not a direction that Roger would recommend.
A particularly novel approach to analysing PT performance was described by Peter: the
application of Michaelis-Menten kinetics to describe SF6 interaction with the
permeable membrane, as a possible refinement to determining SF 6 permeation rates
by linear regression. In effect it furthers the revelation by Lassey et al. (2001) that SF 6
permeation rates gradually decline over time by offering a means to quantify that
decline with sufficient ease and surety to retrospectively correct for tube performance.
If this promise is fulfilled, it will greatly enhance the utility of the SF 6 tracer technique
by permitting serial experiments on animals with unrecoverable permeation tubes in
their rumens. This work is under preparation for publication.
Peter raised the spectre that when retaining PTs for calibration in an oven or incubator
with set-point at 39°C, there should be an independent check of oven fidelity such as
by using a simple mercury thermometer (such as designed for human body
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temperature) or temperature logger. Peter had found that the set temperature on
their incubator was 2°C out! No other workshop participant reported precautionary
checks on set temperatures, and there was some alarm at the possibility of a 2°C error
because of the sensitivity of permeation rate to temperature of between 3 and 10%
per °C.
All the above considerations will receive mention in the GL as part of ‘best practice’
procedures, under sub-headings such as those in Appendix 2 (Section 5 therein). In the
case of applying Michaelis-Menten kinetics, permission from Peter will be required if
that development has not been published.
Breath sampling apparatus
Presentations were given by Keith, Ross, Richard, Peter, José and Cesar, on systems for
sampling breath from grazing or housed animals. Topics covered include: the
‘plumbing’ configuration between inlet and canister and its mounting on the facial
halter, different means to restrict sample flow rates, bags as gas collection vessels,
multi-day sampling, and any special considerations for fistulated animals.
Presentations by Ben, Alan, and Cécile on their respective research covered some
aspects of sampling, with Cécile specifically covering sampling from fistulated cattle,
including use of a cannula to enable sampling directly from the rumen headspace.
Richard described the approach at DPI Victoria for limiting sample flow rates by
crimping capillary tubing as an alternative to requiring a long length of (expensive)
capillary tubing that the original protocol called for (Johnson et al. 1994). José
described the novel approach (described also by Cesar) of using a ‘ball and socket’ to
restrict flows to very low levels appropriate for multi-day sampling (Gere & Gratton
2010).
Richard also described fabricating and using bags, each with a septum, as inexpensive
yet reliable (but usually single-use) collection vessels. Without a ‘sucking’ capacity, preevacuated bags require pumps for active sample collection, and a hand syringe was
used for sample extraction.
Keith described a variation of the tracer technique that automated the collection of
successive breath samples (20-min accumulations every 20 mins for 6 days from each
of 3 housed animals) by pumping into individual Tedlar bags from which samples are
drawn, again by pump, directly into the analyser (gas chromatograph): Lassey et al.
(2011). This is a particular application of a more general ‘Lung’ system used to collect
up to three samples in parallel and analyse them for trace gas content (Martin et al.
2011). The Lung system operates unattended, with automated valves diverting airflows
to and from different bags under software control within the laboratory, avoiding
disturbance of the ‘plumbing’ on the animal halter.
All of the different strategies to control sample flow rates and sample containment
discussed above will be traversed in the GL under headings and with content such as in
Section 6 of Appendix 2.
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Background air sampling
A presentation by Richard, on considerations for background sampling for both grazing
and housed animals, included the siting of background samplers and the association
between individual housed animals and individual background sites. In a presentation
below (‘Estimation of CH4 emission rates, yields, and emission factors’), Keith discussed
some criteria for sample versus background mixing ratios.
Richard showed a slide of the atmospheric growth in CH4 and in SF6 at Australia’s clean
air station at Cape Grim, NW Tasmania, showing current ‘clean-air’ atmospheric mixing
ratios at 1.8 ppm and 6.7 ppt, respectively. (Those of us in atmospheric sciences are
well acquainted with such time series, but graphs of such time series are still worth
reiterating in the GL as many GL readers would know little about global background
levels). In agricultural regions, local CH4 mixing ratios can be higher than clean-air
backgrounds. Within a feeding environment for cattle hosting intra-ruminal SF6
permeation tubes, mixing ratios of both CH4 and SF6 can exceed double the ‘clean-air’
values, and inside a feeding bin can be higher by more than an order of magnitude.
Few, if any, of the workshop participants had investigated local gradients in
background CH4 and SF6 as thoroughly as Richard and DPI-Vic colleagues. Keith
reported some investigations of such gradients done in an experiment with housed
cows at Dexcel (now Dairy NZ) in Hamilton with Sharon Woodward in 2000. The latter
work was published in short form without mention of such investigations (Woodward
et al. 2001). Recommendations about siting and elevation of background samplers,
and about the ventilation of indoor areas will be made in the GL (see Section 8 of
Appendix 2).
Sample handling and gas analysis
Ross demonstrated a ‘piston system’, co-designed by Ross and NIWA colleagues, which
enables gas samples to be withdrawn from a canister without the need to dilute with
nitrogen to super-ambient pressure as was proposed by the originators of the
technique (Johnson et al. 1994). Super-ambient pressure simplified sample transfer to
the GC by bleeding off part of the over-pressure. Using a piston system to extract an
undiluted sample has two major advantages: (1) it avoids diluting the signal and so
effectively decreases the low detection limit for measurements; and (2) it allows a
smaller sample to be drawn into a pre-evacuated canister, avoiding concern that the
collection rate falls off as sample pressure rises, and makes the entire sample available
to the GC (instead of just the over-pressured portion). There was a lot of interest
expressed in this system, which has been used for about 10 years in NZ experiments. It
also lends itself to automation. A paper describing the piston system is presently under
preparation for publication.
Alan’s presentation covered sample storage in vials (exetainers) with transfer via
syringe, necessitating placement of a septum near the valve of the canister. Such
transfer is one of several manual transfers that become necessary (eg, syringe to GC),
implying multiple handing, increasing the cost (and risk of handling error) of gas
analysis.
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Discussion arose around sample containers for intermediate storage, such as to
facilitate transportation to a distant laboratory for analysis, or to free up ‘yokes’ when
gas analysis cannot proceed imminently. An important property of such storage
containers would be their retention of gas integrity. The candidates here were vials
(eg, exetainers), or bags (see ‘Breath sampling apparatus’ above).
Both of the above methods of sample extraction together with the ‘traditional’ overpressuring with nitrogen will be traversed in the GL (see ‘Sample extraction’, Section 9
of Appendix 2), as will recommendations about storage containers (see ‘Intermediate
sample storage’, Section 9 of Appendix 2).
Gas analysis
A presentation by Keith covered aspects of gas chromatography (GC), including
inference of SF6 mixing ratio from non-linear electron-capture detection (ECD) and the
choice and application of gas standards.
Roger’s presentation covered infrared detection techniques (for which much higher
concentrations of SF6 are needed than for GC detection), and detection techniques
suited to alternative tracers. Roger has moved away from this approach, and appears
to regard it as an investigation that didn’t bear fruit.
A view held in some of the community of SF6 tracer technique researchers is that little
error is made in taking GC/ECD response to be linear (and in some cases linear through
the origin). I am aware of some groups not represented at the workshop that use a
single SF6 gas standard which leaves little choice but to presume linearity. So this
section in the GL will cover aspects of GC pertinent to applying the SF 6 tracer
technique, which will include typical detector response and the need for, and choice
of, gas standards. For more detail, see ‘Analysis by gas chromatography’, Section 9 of
Appendix 2.
Animal management, diet and feed intake
A presentation by Garry covered aspects of animal and feed management and
estimation of feed intakes that are particularly pertinent when applying the SF 6 tracer
technique to either grazing or housed animals. Input came from others including those
whose broader presentations had also covered these topics (eg, Cécile, Alexandre,
Ben, Cesar, Natasha, Chris).
Garry’s talk had some usefully-provocative points that generated discussion around:
preparation of both animals and feed
determining feed intake by grazing animals
the merits of a small number of ‘meals’ to housed animals versus more
protracted feed delivery (ie, role of rate of feed consumption)
determining feed composition and digestibility: what to measure and how
to measure it (eg use of near-infrared reflectance spectroscopy)
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Garry stressed the importance of clearly defining in advance the objectives of the
research, because this will determine experimental protocols and measurements.
The above points are given more detail in Section 10 of Appendix 2 which summarises
coverage of the relevant chapter of the GL.
Estimation of CH4 emission rates, yields, and emission factors
A presentation by Keith covered all topics in this heading, including the equations
concerned, and criteria for mixing ratios in ‘breath’ samples relative to those in
background samples that would yield useful results.
Keith’s presentation raised a novel query about data analysis: estimating CH4 emission
rate based on N consecutive days of sampling conventionally proceeds as an average
(over N days) of quotients (of CH4 mixing ratio divided by SF6 mixing ratio, with each
mixing ratio itself a daily average, and background corrected). An equally valid
estimator is the quotient of 2 averages (the average CH4 mixing ratios over all N days
divided by the counterpart average SF6). The latter is in principle the same as
estimating CH4 emissions based on an N-day sample collection. Keith raised the query
which estimator is the better? It was apparent that most workshop participants had
not considered such alternative estimators. Note that this query has recently been
traversed by Lassey et al. (2011). It will also be traversed in the GL.
A useful oral contribution came from Peter, emphasising the need to properly scope
backgrounds. He noted the dearth in published experiments of information on
background collections — their number and location(s), and representative CH4 and
SF6 mixing ratios — or in some cases a failure to report a background correction in the
equation that estimates CH4 emission rate, including in the seminal paper by Johnson
et al. (1994). Peter also reminded the workshop that underlying the estimation of CH 4
emission rate was the ideal gas law, PV = nRT, and that the data analyst should be
mindful of applying consistent units.
Caveats were noted for estimates of CH4 yield for grazing animals for which feed
intakes are inferred and poorly quantified.
Other considerations
In general discussion, various other sub-topics not explicitly covered under the above
headings were deemed worthy of explicit consideration. Accordingly, the GL will
include short chapters or sections that explicitly address the following topics.
Statistical considerations for pre-experimental planning and
data analysis
The intent is to establish the number of animals required if an experiment is to have
sufficient power to detect the anticipated differences in CH4 yield between treatments.
Such considerations are not novel to the SF6 tracer technique, but their consideration
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should take account of the inter-animal and inter-day variability that seems to be
associated with the technique itself.
Discussion of these considerations pointed to Ben’s PhD thesis which addressed this
topic in some detail. This will be a fairly short but focused chapter, led by Chris, a keen
proponent of the chapter (see Section 4 of Appendix 2).
Acceptance and inclusion in guidelines
It was felt that the GL should recommend criteria for identification of ‘crook data’ and
for data acceptance — ie, should offer some QA/QC criteria or guidelines. Cesar
offered to lead this chapter, through wide consultation with workshop participants
(see Section 12 of Appendix 2).
What SF6 tracer technique detail should be reported?
Peter and Richard had compiled the results of a literature search of papers applying
the SF6 tracer technique, which they shared with participants. They noted a large range
in the type and level of detail reported in those papers on how the technique was
applied. For example, some failed to report: how the PTs were calibrated or over what
duration; the time between calibration and the experiment; the range of SF6
permeation rates; the delivery rate of breath sample; the siting of background
samplers and the background mixing ratios encountered. Some supplied little or no
detail on the gas chromatography (configuration, gas standards, etc), or crossreferenced other papers that supplied little detail. The GL will include a chapter led by
Richard and Peter that recommends a minimum level of detail that should be
reported, which would include addressing the particular examples above.
The afore-mentioned list of references from a literature search is a useful resource
that will be included as an annex to the GL, with all participants invited to add further
publications. Additions to date have significantly lengthened the list, which as of 30
June 2011, contains 94 references.
Future issues and potential improvements
This would anticipate issues that could potentially arise, such as standardization of PT
structure and fabrication, possible retrospective improvement to data interpretation
(eg, in the light of applying Michaelis-Menten kinetics to recalculate SF6 permeation
rates); whether temporal variation in intra-ruminal temperature matters. These and
other considerations that will be traversed are proposed in Section 14 of Appendix 2.
Enigmas
Acknowledge that some puzzles about the SF6 tracer technique persist as unexplained.
These include the following:
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1. Indications that CH4 emission estimates may depend upon SF6 release rate have
been reported by the AgResearch group (Vlaming et al. 2007, Pinares-Patiño et
al. 2008), but apparently not confirmed in Ireland (Matthew, communicated at
workshop). No mechanistic explanation has been forthcoming for such
dependence.
2. Much lower estimates of methane yields from sheep fed chicory or white
clover when measured using the SF6 tracer technique than when measured
using chambers (Garry, communicated at workshop).
3. Why does variation in CH4 yield between animals appear greater when using
the SF6 tracer technique over several days with measured intakes, than when
measured using chambers (eg, McGinn et al. 2006, Grainger et al. 2007,
Pinares-Patiño et al. 2011)? Is this at least partially explained by Lassey et al.
(2011) who demonstrate that SF6 is not emitted by a sheep at a uniform rate?
4. If rumen fistulation does not affect methanogenesis, why can it lead to an overestimated CH4 emission? For example, is it to do with escape of SF6 and CH4 at
the fistula plus some hind-gut CH4 excreted via the lungs, with the result that
proportionately more of the internally-sourced SF6 escapes at the fistula than
of CH4?
5. Is the use of stainless steel componentry in the breath-collection ‘plumbing’
better than brass? Matthew had found that the former (at least at the capillary
junctions) had led to lower estimates of methane production, but no-one else
could corroborate this.
6. Matthew reported that intramuscular injections of antibiotic reduced CH4
yields two weeks after injection. Why? Could other drugs have similar effects?
For how long is this prolonged?
Some or all of these ‘puzzles’, also addressed in Section 15 of Appendix 2, may be
addressed in the GL, according to the editor’s discretion following finalization of the
Chapters 1–14. Criteria to be applied for inclusion include whether it is important to
the efficacy of the SF6 tracer technique, whether it no longer appears to be the enigma
that it appeared to be at the workshop, and whether or not it is better addressed—or
is already addressed—elsewhere in the GL.
Information available on the internet
It was felt appropriate to include under separate heading cross-references to any other
‘manuals’ on the SF6 tracer technique, such as standard operating procedures or codes
of practice. Peter would take the lead on seeking out and reporting such websites.
This section is important.
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