Importance of Sampling Frequency in Reducing Uncertainty
Louise Barton1, Benjamin Wolf2, David Rowlings3, Clemens Scheer3, Ralf Kiese2, Peter Grace3, Katia Stefanova1, and Klaus Butterbach-Bahl2,4
1The University of Western Australia2Institute for Meteorology and Climate Research, Germany 3Queensland University of Technology, Australia 4International Livestock Research Institute, Kenya
Presenter’s travel costs were funded by OECD-Cooperative Research Program.
The various research projects have funded by the
• Australian Government’s Climate Change Research Program,
• Australian Research Council (DP0559791)
• Department of Agriculture & Food Western Australia.
• Grains & Research Development Corporation
• German Science Foundation
ACKNOWLEDGEMENTS
Jun-09 Aug-09 Oct-09 Dec-09 Feb-10 Apr-10 Jun-10
Dai
ly fl
ux (g
N h
a-1)
0
20
40
60
80
100
Source: Scheer et. al. 2013. Nutrient Cycling in Agroecosystems 95: 43–56.
Irrigated cropping, subtropical climate, Australia
NITROUS OXIDE FLUXES AND TEMPORAL VARIABILITY
“How often do I need to sample using manual chambers?”
Rain-fed cropping, Wongan Hills, south-western Australia
Investigate the effect of sample frequency on estimates of annual N2O fluxes by using data collected:
• On a sub-daily basis using automated chamber systems
• From a variety of climates and land-uses
OVERALL OBJECTIVE
Semi-arid
Sub-tropical
Tropical
LOCATION DATASETS
(Yrs,Treat)
CLIMATE LANDUSE ANNUAL N2O FLUX
(kg N ha-1)
Bellenden Kerr, Australia
One (1, 1) Tropical Forest 1.16
Cunderdin, Australia
Eight (4, 2) Semi-arid Cereal cropping
0.08–0.16
Höglwald, Germany
Two (1, 1) Temperate Plantation forest
0.58–2.46
Kingsthorpe, Australia
Three (1, 3) Sub-tropical Irrigated cereal-cottoncropping
2.61–2.93
Mooloolah Valley, Australia
Five (3, 2) Sub-tropical Forest, Pasture,Orchard
0.48–8.12
Wongan Hills, Australia
Eight (2, 4) Semi-arid Cereal cropping
0.03–0.07
Xilin, Inner Mongolia
One (1) Semi-arid Steppegrassland
0.21
TWENTY EIGHT DATASETS: RANGE IN ANNUAL FLUXES
LOCATION DATASETS
(Yrs,Treat)
CLIMATE LANDUSE ANNUAL N2O FLUX
(kg N ha-1)
DAILY FLUX CV(%)
EPISODICITY
Bellenden Kerr, Australia
One (1, 1) Tropical Forest 1.16 98 Moderate
Cunderdin, Australia
Eight (4, 2) Semi-arid Cereal cropping
0.08–0.16 173–428 High to Extreme
Höglwald, Germany
Two (1, 1) Temperate Plantation forest
0.58–2.46 169–179 High
Kingsthorpe, Australia
Three (1, 3) Sub-tropical Irrigated cereal-cottoncropping
2.61–2.93 181–235 High to Extreme
Mooloolah Valley, Australia
Five (3, 2) Sub-tropical Forest, Pasture,Orchard
0.48–8.12 78–172 Moderate to High
Wongan Hills, Australia
Eight (2, 4) Semi-arid Cereal cropping
0.03–0.07 380–913 Extreme
Xilin, Inner Mongolia
One (1) Semi-arid Steppegrassland
0.21 260 Extreme
TWENTY EIGHT DATASETS: RANGE IN ‘EPISODICITY’
CV, coefficient of variation
APPROACH
Daily fluxes by averaging sub-daily fluxes (removed diurnal variation)
Annual fluxes calculated for different sampling frequencies (5 intervals) using ‘Jack-Knife’ analysis
For each sampling frequency, annual flux compared with ‘best’ estimate (daily) Result expressed as % of ‘daily’ annual flux
For each data set, we calculated:
Frequency (day) Permutations Example
Daily (0) 1 All sample days
3-days/week (2) 7 Sun-Tue-Thu; Mon-Wed-Fri; Tue-Thu-Sat etc
Weekly (7) 7 Sun, Mon, Tue, Wed, Thu, Fri, Sat
Every 2nd week (14) 14 Sun (Week 1, 2), Mon (Week 1, 2) etc
Every 4th week (28) 28 Sun (Weeks 1–4), Mon (Week 1–4) etc
Jun-09 Aug-09 Oct-09 Dec-09 Feb-10 Apr-10 Jun-10
Dai
ly fl
ux (g
N h
a-1)
0
5
10
15
20 Plus limeNo lime
12%
9%
8%
Source: Barton et. al. 2013. Agriculture, Ecosystems and Environment 167: 23–32.
Cropping, semi-arid climate, Australia
Annual flux: 0.05–0.06 kg N ha-1
DAILY NITROUS OXIDE FLUX PROFILE: ‘Extremely’ episodic
Sampling interval (days)0 5 10 15 20 25 30
% D
evia
tion
of a
nnua
l flu
x
0
200
400
600
800
1000 No limePlus lime
Sampling interval (days)0 5 10 15 20 25 30
% D
evia
tion
of a
nnua
l flu
x
0
200
400
600
800
1000 No limePlus lime
12%
9%
SAMPLING FREQUENCY & ANNUAL FLUX : ‘Extremely’ episodic
Cropping, semi-arid climate, Australia %
of ‘
daily
’ ann
ual f
lux
Sampling interval (days)0 5 10 15 20 25 30
% D
evia
tion
of a
nnua
l flu
x
0
200
400
600
800
1000 No limePlus lime
12%
9%
8%
0 (Daily) 2 7 14 28% Best estimate 100 61–141 21–251 10–464 3–893
Annual Flux(kg N ha-1) 0.05–0.06 0.03–0.08 0.01–0.14 0.01–0.5 0–0.5
SAMPLING FREQUENCY & ANNUAL FLUX : ‘Extremely’ episodic
Sampling interval (days)0 5 10 15 20 25 30
% D
evia
tion
of a
nnua
l flu
x
0
200
400
600
800
1000 No limePlus lime
Cropping, semi-arid climate, Australia %
of ‘
daily
’ ann
ual f
lux
01-Jan 01-Mar 01-May 01-Jul 01-Sep 01-Nov 01-Jan
Dai
ly fl
ux (g
N h
a-1)
-20
0
20
40
60
80
100
12%
9%
8%
Source: Butterbach-Bahl et. al. 2002. Plant and Soil 240: 117–123.
Plantation forest, temperate climate, Germany
Annual flux: 2.46 kg N ha-1
DAILY NITROUS OXIDE FLUX PROFILE: ‘Highly’ episodic
9%
Sampling interval (days)0 5 10 15 20 25 30
% D
evia
tion
of a
nnua
l flu
x
40
60
80
100
120
140
160
180
SAMPLING FREQUENCY & ANNUAL FLUX : ‘Highly’ episodic
Plantation forest, temperate climate, Germany%
of ‘
daily
’ ann
ual f
lux
0 (Daily) 2 7 14 28% Best estimate 100 97–105 88–118 78–120 60–156
Annual Flux(kg N ha-1) 2.46 2.40–2.58 2.16–2.90 1.93–2.97 1.49–3.85
01-Apr 01-Jun 01-Aug 01-Oct 01-Dec 01-Feb 01-Apr
Daily
flux
(g N
ha-1
)
02468
1012141618
12%
9%
8%
Source: Kiese et. al. 2003. Global Biogeochemical Cycles 17: 1043
Annual flux: 1.2 kg N ha-1
DAILY NITROUS OXIDE FLUX PROFILE: ‘Moderately’ episodic
Rainforest, tropical climate, Australia
Sampling interval (days)0 5 10 15 20 25 30
% D
evia
tion
of a
nnua
l flu
x
50
60
70
80
90
100
110
120
130
9%
8%
SAMPLING FREQUENCY & ANNUAL FLUX: ‘Moderately’ episodic
Rainforest, tropical climate, Australia
0 (Daily) 2 7 14 28% Best estimate 100 100–102 98–103 72–107 57–123
Annual Flux(kg N ha-1) 1.2 1.1–1.2 1.1–1.2 0.8–1.2 0.7–1.4
% o
f ‘da
ily’ a
nnua
l flu
x
8%
RECOMMENDED SAMPLING FREQUENCY
Sampling interval (d)0 7 14 21 28
Num
ber o
f dat
aset
s
0
5
10
15
20
25Within 10% Within 20% Within 30% Within 40% Within 50%
Source: Barton et. al. 2015. Sci. Rep. 5:15912 | DOI: 10.1038/srep15912
• 71% of data sets = daily measurements• 25% of data sets = 3 daily measurements per week
8%
Source: Barton et. al. 2015. Sci. Rep. 5:15912 | DOI: 10.1038/srep15912
RECOMMENDED SAMPLING FREQUENCY
Sampling interval (d)0 7 14 21 28
Num
ber o
f dat
aset
s
0
5
10
15
20
25Within 10% Within 20% Within 30% Within 40% Within 50%
Corn-soybean, Iowa, USA“At relatively frequent sampling intensities (i.e., once every 3d) N2O–N flux estimates were within ±10% of the expected value”
Parkin (2008)Cotton, Shanxi Province, China“Sampling daily (at 9am) to every two days caused a deviation of up to 7.3% from annual flux estimated from sub-daily measurements.”
Lui et al. (2010)Pasture, Otago, New Zealand“… gas samples collected three times a week between 10:00-12:00h provided zero bias in calculating cumulative emissions when compared with those based on frequent, 2-hourly, flux measurements.”
Van der Weeden et al. 2013Sugar Cane, Queensland, Australia“Weekly sampling with biweekly sampling for one week after >20 mm of rainfall was the recommended sampling regime. It resulted in no extreme (>20%) deviations from the ‘actuals’, had a high probability of estimating the annual cumulative emissions within 10% precision …”
Reeves et al. (2016)
OTHER STUDIES
8%
RECOMMENDED SAMPLING STRATEGY:‘Jackknife’ and ‘Informed’
LOCATION DATASETS
(Yrs,Treat)
CLIMATE LANDUSE ANNUAL N2O FLUX(kg N ha-1)
EPISODICITY JACKNIFE(sampling days)
INFORMED(sampling days)
Bellenden Kerr, Australia
One (1, 1) Tropical Forest 1.16 Moderate 52 156
Mooloolah Valley, Australia
Five (3, 2) Sub-tropical Forest, Pasture,Orchard
0.48–8.12 Moderate to High
156–365 Not determined
Höglwald, Germany
Two (1, 1) Temperate Plantation forest
0.58–2.46 High 156 83
Xilin, Inner Mongolia
One (1) Semi-arid Steppegrassland
0.21 Extreme 156 Not determined
Cunderdin, Australia
Eight (4, 2) Semi-arid Cereal cropping
0.08–0.16 High to Extreme
156–365 Not determined
Kingsthorpe, Australia
Three (1, 3) Sub-tropical Irrigated cereal-cottoncropping
2.61–2.93 High to Extreme
365 Not determined
Wongan Hills, Australia
Eight (2, 4) Semi-arid Cereal cropping
0.03–0.07 Extreme 365 60
æ Nitrous oxide emissions generally need to be measured daily to accurately estimate (within 10%) annual fluxes in a variety of land-uses and climates• 71% of data sets = daily measurements• 25% of data sets = 3 daily measurements per week
æ For study sites where temporal variability has not previously been characterised (or when variability is expected to change from year-to-year) recommend daily sampling with manual chambers
æ Recommended sampling frequency increases with increasing “episodicity”
æ Data from automated chambers should be continuously used to develop guidelines for manual chamber sampling frequency
CONCLUSIONS
0 5 10 15 20 25 30
% D
evia
tion
of E
F
-500
0
500
1000 Year 1Year 2 Year 3 12%
9%
Emission Factor: 0.01-0.06%
SAMPLING FREQUENCY & EMISSION FACTOR
Cropping, semi-arid climate, Australia
12%
9%
Relationship between coefficient of variation of the daily N2O flux and the deviation (range) from the ‘best estimate’ annual N2O flux: 4-weekly sampling interval