Annual carbon and GHG balance of a raised peat bog in New ... · PDF file–Net cooling...

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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

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

Date (2011-2013)

Seasonal variation in diel CO2 exchange

0 3 6 9 12 15 18 21

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

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

50 100 150 200 250 300 3500

50 100 150 200 250 300 350-300

Day of Year

15-day running means NEE

Water table

Methane flux, FCH4

Little diurnal variation in FCH4

0 3 6 9 12 15 18 210

Time of day

01-Mar-2012 - 30-Apr-2012

0 3 6 9 12 15 18 210

Time of day

01-Feb-2013 - 31-Mar-2013

But…

0 3 6 9 12 15 18 210

Time of day

01-Nov-2012 - 31-Dec-2012

Evidence for plant-mediated CH4 transport?

Controls on FCH4

-300 -200 -100 00

Water table depth (mm)

5 10 15 200

Peat temperature (C)

-300 -200 -100 00

5 10 15 200

-300 -200 -100 00

5 10 15 200

F M A M J J A S O N D J F M A M J J0

F M A M J J A S O N D J F M A M J J-300

F M A M J J A S O N D J F M A M J J5

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

Date (2012)

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

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Discharge

Change in storage

DOC export – water balance

Q P E DS

230 180 130 80 30 -20 -70

DOC export

Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

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

Friction velocity (m s-1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-100

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

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

Date (2012)

0 0.05 0.1 0.15 0.2 0.2518

Friction velocity (m s-1)

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

Annual carbon and GHG balance of a raised peat bog in New ... · PDF file–Net cooling...

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