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Modeling Environmental Controls on Net Ecosystem CO2 Exchange of a Tropical Bog

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Modeling Environmental Controls on Net Ecosystem CO2 Exchange of a Tropical Bog Symon Mezbahuddin1, Robert Grant1 and Takashi Hirano2 1Department of Renewable ... – PowerPoint PPT presentation

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Title: Modeling Environmental Controls on Net Ecosystem CO2 Exchange of a Tropical Bog


1
Modeling Environmental Controls on Net Ecosystem
CO2 Exchange of a Tropical Bog
  • Symon Mezbahuddin1, Robert Grant1 and Takashi
    Hirano2

1Department of Renewable Resources, University of
Alberta, Canada 2Research Faculty of Agriculture,
Hokkaido University, Japan
2
Introduction
  • ?Bogs are the peatland ecosystems that get water
    and nutrient inputs only through precipitation
  • ?Drier weather resultant of increased climatic
    events such as El-Niño could alter balance
    between tropical peatland ecosystem
    photosynthesis and respiration and contribute to
    increasing atmospheric CO2
  • ?Eddy covariance (EC) net ecosystem productivity
    (NEP) estimates of natural tropical peatlands
    range from -296 to
  • -594g C m-2y-1 Hirano et al. 2009
  • ? Ecosystem processes X multiple environmental
    factors cause large variations and uncertainties
    in predictions of peatland ecosystem response to
    climate change

3
Objectives
  • ? To examine how wetter vs. drier weather
    conditions cause diurnal, seasonal and
    interannual variations in net ecosystem CO2
    exchange of a tropical bog Sebangau River,
    Palangka Raya, Central Kalimantan, Indonesia
    MAT 26.3?C and MAP 2600 mm by using hourly
    time step process based ecosystem model ecosys
    (Grant et al. 2001) tested against valid eddy
    covariance data.
  • Eddy covariance and micrometeorological data
    (2002-2005) were collected from flux station over
    the site (2?30?42?S 114?2?11?E ) through
    AsiaFlux Network.

4
Objectives contd.
2003 (Total precipitation 2291 mm)
2005 (Total precipitation 2620 mm)
Wet year
Dry year
? (m3m-3)
? (m3m-3)
Figure Hourly measured precipitation and soil
water content at 0-20cm depth during 2003 and
2005 over Palangka Raya peat swamp forest,
Indonesia
5
Conceptual Hypotheses
Hypothesis - I
NEP GPP - RE
Increased atmospheric dryness
Reduced precipitation
Reduced soil water content
Increased vapour pressure deficit
Decreased soil, root and canopy water potentials
Higher potential transpiration
Increased stomatal resistance and consequent
stomatal closure
Less actual transpiration at a cost of CO2
fixation and hence reduced GPP
6
Conceptual Hypotheses contd.
Hypothesis - II
Oxic
NEP GPP - RE
WT
Reduced soil water content
Water table drawdown
WT
Anoxic
Increased peat aeration
Reduced heat capacity of soil
Rapid aerobic peat decomposition
Increased soil temperature
Higher heterotrophic respiration
Faster biogeochemical reaction
Increased ecosystem respiration
7
Hypotheses contd.
Hypothesis - III
However,
Desiccation
Surface peat desiccation
Inhibition of heterotrophic respiration at
surface layers
WT
Partial or complete offset of any increment in
heterotrophic respiration stimulated by deeper
peat aeration
Reduction or elimination of drier and warmer
weather effects on NEP through its impact on RE
8
Study Site
Tower fetches 0.4 km N gt5 km S 0.5 km E 1.5
km W
? Woody peat ? gt10,000 years BP ? Natural swamp
forest ? 4m thick ? Drainage, partial
thinning 8 years before flux tower installation
Figure Map of the study site


Picture courtesy (Hirano et al. 2007)
9
Modeling Experiment
(a)
? A modeled tropical peat swamp ecosystem of 100
years spin up run using repeated hourly weather
cycles (2002-2005) ? The spinning period allowed
the modeled ecosystem to grow, regenerate and
attain dynamic C equilibrium ? Soil and
vegetation characteristics are from site measured
data reported in different studies
(b)
(b)
Figure Modeling experiment layout (a)
horizontal and (b) vertical
10
Preliminary Results
2003 (dry year)
? (m3m-3)
Figure Hourly measured (dots) and simulated
(lines) precipitation, soil water content at
0-20cm depth and daily water table depths during
2003 over Palangka Raya peat swamp forest,
Indonesia
11
Preliminary Results contd.
2005 (wet year)
? (m3m-3)
Figure Hourly measured (dots) and simulated
(lines) precipitation, soil water content at
0-20cm depth and daily water table depths during
2005 over Palangka Raya peat swamp forest,
Indonesia
12
Preliminary Results contd.
2005 (wet year)
2003 (dry year)
Figure Hourly measured vapour pressure deficit
during 2005 and 2003 over Palangka Raya peat
swamp forest, Indonesia
13
Preliminary Results contd.
H/LE0.36 (Rn gt700 Wm-2)
2005 (wet year)
influxes - effluxes
2003 (dry year)
H/LE0.62 (Rn gt700 Wm-2)
Figure Hourly measured (dots) and simulated
(lines) ecosystem net radiation (Rn), latent heat
(LE) and sensible heat (H) fluxes during 2005 and
2003 over Palangka Raya peat swamp forest,
Indonesia
14
Preliminary Results contd.
2005 (wet year)
influxes - effluxes
2003 (dry year)
Figure Hourly measured (closed symbol), gap
filled (open symbol) and simulated (lines)
ecosystem CO2 fluxes during 2005 and 2003 over
Palangka Raya peat swamp forest, Indonesia
15
Preliminary Results contd.
Table Regression results of simulated vs
measured hourly parameters (2003-2005)
Parameters Units n 1a 2b R2 3RMSD 4RMSE
CO2 flux µmolm-2s-1 12187 0.79 0.90 0.85 4.5 4.5
Rn Wm-2 26304 16 0.93 0.99 10 -
LE flux Wm-2 13924 -31 1.07 0.76 70 57
H flux Wm-2 14282 -01 0.94 0.56 44 32
? (0-20cm) m3m-3 26304 0.11 0.70 0.52 0.02 -
Ts (5cm) ?C 26304 2.90 0.80 0.61 0.47 -
Rn Net radiation LE Latent heat flux H
Sensible heat ? Soil water content Ts Soil
temperature
Table Regression results of simulated vs
measured daily water table depths (m) (2004-2005)
n 1a 2b R2 3RMSD
444 -0.12 0.87 0.77 0.10
1intercept and 2slope from regression of
simulated over measured data 3root mean square
for differences from regression of measured over
simulated data 4root mean square of random
measurement errors calculated for the measured
data based on algorithms described in Richardson
et al. (2006)
16
Preliminary Results contd.
2003 (dry year)
? (m3m-3)
NEP C sink - NEP C source
Open symbols have gt50 gap filled data
Figure Hourly measured (dots) and simulated
(lines) soil water content three day moving
averages of measured (dots) and simulated
(lines) evapotranspiration and net ecosystem
productivity during 2003 over Palangka Raya peat
swamp forest, Indonesia
17
Preliminary Results contd.
2005 (wet year)
? (m3m-3)
NEP C sink - NEP C source
Open symbols have gt50 gap filled data
Figure Hourly measured (dots) and simulated
(lines) soil water content three day moving
averages of measured (dots) and simulated
(lines) evapotranspiration and net ecosystem
productivity during 2005 over Palangka Raya peat
swamp forest, Indonesia
18
Preliminary Results contd.
Table Annual ecosystem carbon balance for
Palangka Raya Drained forest, Indonesia during
2003 and 2005
Components of ecosystem carbon budget 2003 (drier year) 2003 (drier year) 2005 (wetter year) 2005 (wetter year) Values from other studies
Components of ecosystem carbon budget Ecosys EC Ecosys EC Values from other studies
-------------------------------------------------g C m-2----------------------------------------------------------------- -------------------------------------------------g C m-2----------------------------------------------------------------- -------------------------------------------------g C m-2----------------------------------------------------------------- -------------------------------------------------g C m-2----------------------------------------------------------------- -------------------------------------------------g C m-2----------------------------------------------------------------- -------------------------------------------------g C m-2-----------------------------------------------------------------
GPP 3398 34611 3578 - 33705
Ra 1570 - 1431 - -
Rroot 795 - 954 - -
Rh 1450 - 1324 - -
Rsoil 2245 - 2278 - 21004 21305
RE 3815 38381 3709 - -
NEP -217 -3781 -131 -4411 -5422 5223
1Hirano et al. 2007 2Henson 2005 3Suzuki et al.
1999 4Melling et al. 2005 5 Kosugi et al. 2008
5Jauhianen et al. 2005
19
Summary
?There was not a complete shift in ecosystem
energy balance due to water stress resultant of
prolonged dry season. ?Still a reduction in
Bowen ratio (H/LE) due to drier weather condition
resulted lower GPP contributing to lower NEP as
evident in both EC-gap filled and simulated CO2
fluxes.
20
Summary contd.
? Ecosys couldnt up to this point fully capture
the large negative NEPs at the onset of the dry
season. So, we remain inconclusive about our
hypothesis of a possible increase in ecosystem
respiration stimulated by water table drawdown in
drier years. We are currently working on
that. ?Peatlands widely vary in their
physicochemical characteristics. Rigorous testing
of process based models based on our current
fundamental understanding across contrasting
peatlands would be interesting to improve our
insights on peat carbon cycling.
21
Acknowledgements
  1. Mary Louise Imrie Travel Grant
  2. AsiaFlux Network
  3. NSERC Discovery Grant
  4. Faculty of Graduate Studies and Research,
    University of Alberta
  5. University of Alberta Computing Facilities
  6. All of my lab group members.

Thank You
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