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Annual carbon balance of a raised peat bog in New Zealand
Dave Campbell
Jordan Goodrich
Catherine Sturgeon
Wetland restoration programme
• Six year Ministry for Science and Innovation programme Wetland Restoration 2010-16
– Subcontract to Landcare Research
• Fits into “ecosystem functioning” objective
– Carbon fluxes and balanceof an intact peatland
– Informs restoration targets for restored peatlands
Presentation objectives
• Annual net ecosystem carbon balance (NECB) at NZ’s largest true raised peat bog (year 1)
• Sensitivity of NECB components to environmental drivers
Outline
• Peatlands and carbon
– Northern hemisphere analogues
• Site description and methods
• Results
– CO2 exchange
– CH4 exchange
– Dissolved organic C export
– One-year NECB
Mean annual precipitation = 1262 mm Mean annual temperature = 14.6°C
Area >90 km2
Elevation 2 – 5 m a.s.l. Kopuatai bog
Peatlands and carbon
• Globally large stores of carbon
– E.g. northern peatlands contain C equivalent to around 1/3 of global soil C store
• Long-term C balance gains over thousands of years
– Uptakes of CO2 partially offset by respired CO2, methane emissions and leached C in runoff
– Net cooling effect on climate?
Mean annual precipitation = 1262 mm Mean annual temperature = 14.6°C
Area >90 km2
Elevation 2 – 5 m a.s.l. Kopuatai bog
Kopuatai bog, NZ
DOC export
NECB = FCO2-C + FCH4-C + FDOC-C (+ fire-C)
Net ecosystem carbon budget
DOC in rain
• Flux calculations using EddyPro v4.0
• Gap-filling and CO2 flux partitioning
– Fitting Lloyd & Taylor function to night-time NEE (ER)
– Fitting light response of daytime NEE
– Partitioning via NEE = (GPP ER)
• Preliminary gap-filling FCH4 via daily means of filtered data
Peatland CO2 exchange (NEE)
Kopuatai bog, 37S M.A.T. = 14.6 C
Mer Bleue bog, Ottawa, 45N M.A.T. = 6 C
Peat formation via vascular plants - Mainly wire rush (Empodisma robustum)
Peat formation via mosses
Annual courses of NEE at Mer Bleue bog, Canada
Data from A. Prof. Elyn Humphreys, Carleton University, Ottawa
Mean annual sum NEE –74 gC m–2 yr–2 (1999-2009) (range –10 to –138 gC m–2)
Winter loss Growing season gain
CO2 exchange at Kopuatai
D J F M A M J J A S O N D J F M A M J J-10
-5
0
5
NE
E (
mo
l m
-2s
-1)
Date (2011-2013)
Two contrasting summer seasons
D J F M A M J J A S O N D J F M A M J J-300
-250
-200
-150
-100
-50
0
Wa
ter
tab
le d
ep
th (
mm
)
Date (2011-2013)
Seasonal variation in diel CO2 exchange
0 3 6 9 12 15 18 21
-7
-6
-5
-4
-3
-2
-1
0
1
2
3
NE
E (
mo
l m
-2s
-1)
Time of day
Summer
Autumn
Winter
Spring
NEE daily mean totals (2012) Summer : 1.44 gC m-2day-1
Autumn : 0.51 gC m-2day-1
Winter : 0.00 gC m-2day-1
Spring: 0.92 gC m-2day-1
Growing season 9–10 months (cf. Mer Bleue 5 -6 months)
Monthly sums of NEE
CO2 source CO2 sink
1 2 3 4 5 6 7 8 9 10 11 12-60
-50
-40
-30
-20
-10
0
10
Month
NE
E (
gC
m-2
mo
nth
-1)
2012
2013
Jan – April total NEE 2012: –131 gC m–2
2013: –66 gC m–2
Total NEE 2012 264 gC m2 year1 (vs. Mer Bleue range –10 to –138 gC m–2)
Importance of the water table
50 100 150 200 250 300 350-2
-1
0
1
NE
E (
gC
m-2
day
-1)
2012
2013
50 100 150 200 250 300 3500
2
4
6
GP
P (
gC
m-2
day
-1)
50 100 150 200 250 300 3500
1
2
3
ER
(gC
m-2
day
-1)
50 100 150 200 250 300 350-300
-200
-100
0
WT
depth
(m
m)
Day of Year
15-day running means NEE
GPP
ER
Water table
Methane flux, FCH4
Little diurnal variation in FCH4
0 3 6 9 12 15 18 210
20
40
60
80
100
120
140
Time of day
FC
H4 (
nm
ol m
-2s
-1)
01-Mar-2012 - 30-Apr-2012
0 3 6 9 12 15 18 210
20
40
60
80
100
120
140
Time of day
FC
H4 (
nm
ol m
-2s
-1)
01-Feb-2013 - 31-Mar-2013
But…
0 3 6 9 12 15 18 210
20
40
60
80
100
120
140
Time of day
FC
H4 (
nm
ol m
-2s
-1)
01-Nov-2012 - 31-Dec-2012
Evidence for plant-mediated CH4 transport?
Controls on FCH4
-300 -200 -100 00
20
40
60
80
100
120
Water table depth (mm)
FC
H4 (
nm
ol m
-2s
-1)
5 10 15 200
20
40
60
80
100
120
Peat temperature (C)
FC
H4 (
nm
ol m
-2s
-1)
-300 -200 -100 00
20
40
60
80
100
120
Water table depth (mm)
FC
H4 (
nm
ol m
-2s
-1)
5 10 15 200
20
40
60
80
100
120
Peat temperature (C)
FC
H4 (
nm
ol m
-2s
-1)
-300 -200 -100 00
20
40
60
80
100
120
Water table depth (mm)
FC
H4 (
nm
ol m
-2s
-1)
5 10 15 200
20
40
60
80
100
120
Peat temperature (C)
FC
H4 (
nm
ol m
-2s
-1)
F M A M J J A S O N D J F M A M J J0
20
40
60
80
100
120
FC
H4 (
nm
ol m
-2s
-1)
F M A M J J A S O N D J F M A M J J-300
-200
-100
0
WT
de
pth
(m
m)
F M A M J J A S O N D J F M A M J J5
10
15
20
Tp
ea
t ( C
)
Daily means
Estimated annual FCH4
Daily mean 59.4 mg C m-2 day-1
Annual total 21.7 g C m-2 year-1
F M A M J J A S O N D0
20
40
60
80
100
120
Date (2012)
FC
H4 (
mg
C m
-2 d
ay-1
)
Dissolved organic C export method
• Spatial, depth and temporal sampling of DOC in peat pore water
• Monthly water export calculation via water balance:
Q = P E DS
P = precip.; E = evap.; DS = change in stored water
DS = Y DWT (Y = peat specific yield; WT = water table depth)
• Monthly flux of DOC:
FDOC = Q CDOC (CDOC = monthly mean DOC concentration)
• FDOC uncertainty estimated
• FDOC calculated with and without rainwater DOC input
-70
-20
30
80
130
180
230
Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
mm
Month
Discharge
P
E
Change in storage
DOC export – water balance
Q P E DS
230 180 130 80 30 -20 -70
mm
/mo
nth
DOC export
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan
DO
C
exp
ort
(g C
m-2
mo
nth
-1)
Month
F DO
C (
gC m
-2 m
on
th-1
)
3.5 3.0 2.5 2.0
1.5 1.0 0.5
0.0 -0.5 -1.0
Month (2012-13)
F M A M J J A S O N D J
Annual DOC export 11.7 ± 0.82 (gC m-2 year-1) or, accounting for rain input of DOC: 10.5 ± 1.17 (gC m-2 year-1)
NECB = FCO2-C + FCH4-C + FDOC-C
NECB = 264 – 22 – 11 gC m–2 yr–1
= 231 gC m–2 yr–1
1Roulet et al. (2007) Global Change Biology 13: 397–411
= 10.8 times larger than 6-year mean NECB reported for Mer Bleue bog, and 2.6 times larger than greatest 1
Annual net ecosystem C balance
Summary • Annual NEE for 2012 was 190% greater than the
largest recorded from an analogous Canadian bog.
– length of growing season seems to explain this
– (ecosystem light response and respiration parameters are similar to northern hemisphere analogues)
• NEE sensitive to summertime water table position
– major driver of inter-annual variability?
• Drivers of CH4 fluxes seem to alternate: temperature (winter) and water table (dry summer)
• NECB was very large cf. N. Hem. analogues
– How variable is it inter-annually?
– How does it compare to long-term C accumulation rates?
Acknowledgements • Bev Clarkson, Landcare Research
• Department of Conservation
• Murray and Angela Brewster
• The University of Waikato
• Ngati Hako o Hauraki
Extras
GHG budget for Kopuatai bog
GWP = –970 + (2925) + 40 gCO2-e m–2
= –205 gCO2-e m–2 (GHG sink)
CO2 264 gC m–2
= 970 gCO2 m–2
CH4 22 gC m–2
= 29 gCH4 m–2
DOC (assume converted to CO2)
11 gC m–2
= 40 gCO2 m–2
GWP = global warming potential GWPCO2 = 1 GWPCH4 = 25
Effect of light quality on NEE
Goodrich, J. et al. Changes in photosynthetic capacity and radiation use efficiency lead to increases in net CO2 uptake during overcast conditions at a southern hemisphere peatland. (in prep. for submission to Agric. For. Meteorol.).
2011-12 2012-13
Threshold turbulence for FCH4
CH4_flux_play_1.m
Night-time FCH4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-100
-50
0
50
100
150
200
Friction velocity (m s-1
)
FC
H4 (
nm
ol m
-2s
-1)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-100
-50
0
50
100
150
200
Friction velocity (m s-1
)
FC
H4 (
nm
ol m
-2s
-1)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-100
-50
0
50
100
150
200
Friction velocity (m s-1
)
FC
H4 (
nm
ol m
-2s
-1)
Threshold turbulence for FCH4
CH4_flux_play_1.m
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-100
-50
0
50
100
150
200
Friction velocity (m s-1
)
FC
H4 (
nm
ol m
-2s
-1)
Night-time FCH4 Day-time FCH4
Estimated annual FCH4
Daily mean 59.4 mg C m-2 day-1
Annual total 21.7 g C m-2 year-1
F M A M J J A S O N D0
20
40
60
80
100
120
Date (2012)
FC
H4 (
mg
C m
-2 d
ay-1
)
0 0.05 0.1 0.15 0.2 0.2518
19
20
21
22
23
24
25
Friction velocity (m s-1)
FC
H4 (
g C
m-2
year-1
)(± 1.15 gC m-2 yr-1
(± 5.3%)
Broad research goals
• To describe the annual net ecosystem carbon budget (NECB) at NZ’s largest true raised peat bog
• Determine the sensitivity of NECB components to environmental drivers
• Provide a baseline of “normal” peatland C exchange processes to inform restoration efforts, and to contrast with agricultural peatlands in the region
EC methods
• Open path sensors
– LI-7500 for CO2/H2O
– LI-7700 for CH4
• Flux calculations using EddyPro v4.0
• Fluxes rejected when u* below threshold value
• Gap-filling and CO2 flux partitioning
– Fitting Lloyd & Taylor function to night-time NEE (ER)
– Fitting light response of daytime NEE
– Partitioning via NEE = (GPP ER)
• Preliminary gap-filling FCH4 via daily means of available data
Acknowledgements
• Bev Clarkson, Landcare Research
• Department of Conservation
• Murray and Angela Brewster
• The University of Waikato