Docstoc

Modeling Environmental Controls on Net Ecosystem CO2 Exchange

Document Sample
Modeling Environmental Controls on Net Ecosystem CO2 Exchange Powered By Docstoc
					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
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
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.
                                                                                                                                                           Objectives contd.

                             70
                                       2003 (Total precipitation = 2291 mm)                                                70
                                                                                                                                     2005 (Total precipitation = 2620 mm)
      Precipitation (mmh )
     -1




                                                                                                    Precipitation (mmh )
                                                                                                   -1
                             60                         Dry year                                                           60                    Wet year
                             50                                                                                            50
                             40                                                                                            40
                             30                                                                                            30
                             20                                                                                            20
                             10                                                                                            10
                               0                                                                                            0
                             0.5                                                                                           0.5

                             0.4                                                                                           0.4
 (m3m-3)




                                                                                             (m3m-3)
     (m m )
      -3




                                                                                                  (m m )
                                                                                                  -3
    3




                             0.3




                                                                                                  3
                                                                                                                           0.3

                             0.2                                                                                           0.2

                                   0   30   60   90   120 150 180 210 240 270 300 330 360
                                                                                                                                 0   30   60   90 120 150 180 210 240 270 300 330 360
                                                           Day of year                                                                                 Day of year


Figure: Hourly measured precipitation and soil water content at 0-20cm depth during 2003
                and 2005 over Palangka Raya peat swamp forest, Indonesia
Conceptual Hypotheses
                   Hypothesis - I

                    NEP = GPP - RE

Increased atmospheric      Reduced precipitation
dryness
                           Reduced soil water content
Increased vapour
pressure deficit           Decreased soil, root and canopy
                           water potentials

Higher potential           Increased stomatal resistance and
transpiration              consequent stomatal closure
                           Less actual transpiration at a cost
                           of CO2 fixation and hence reduced
                           GPP
                                   Conceptual Hypotheses contd.
                 Hypothesis - II
                                                      Oxic

                 NEP = GPP - RE                        WT


Reduced soil water      Water table drawdown
                                                       WT
content
                                                      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
                                               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
Study Site             Tower fetches: 0.4 km N; >5 km S; 0.5 km E; 1.5 km W


                                                         ⦿ Woody peat


                                                         ⦿ >10,000 years BP


                                                         ⦿ Natural swamp
                                                         forest

                                                         ⦿ ~ 4m thick


                                                         ⦿ Drainage,
                                                         partial thinning
                                                         ~8 years before
Figure: Map of                                           flux tower
the study site                                           installation
 Picture courtesy:
(Hirano et al. 2007)
 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        (b)
                                                                        (b)
from site measured data reported in
different studies                           Figure: Modeling experiment layout
                                               (a) horizontal and (b) vertical
Preliminary Results
                                                                                               2003 (dry year)

               Precip'n (mmh )
             -1
                                  70
                                  60
                                  50
                                  40
                                  30
                                  20
                                  10
                                   0
                                 0.50
                                 0.45
           (m m )
            (m3m-3)
               3 -3




                                 0.40
                                 0.35
                                 0.30
                                 0.25
                                 0.20
              WT depth (m)




                                  0.0
                                 -0.5
                                 -1.0
                                 -1.5
                                 -2.0
                                        0   30   60   90   120   150   180   210   240   270   300   330   360
                                                                  Day of year


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
                                                                               Preliminary Results contd.

                                                                                     2005 (wet year)

          Precip'n(mmh )
        -1
                             70
                             60
                             50
                             40
                             30
                             20
                             10
                              0
                           0.50
                           0.45
         (m3m) )
          (m3m-3 -3




                           0.40
                           0.35
                           0.30
                           0.25
                           0.20
           WT depth (m)




                            0.0
                           -0.5
                           -1.0
                           -1.5
                           -2.0
                                  0   30   60   90   120   150   180   210   240   270   300   330   360
                                                            Day of year



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
                                                                Preliminary Results contd.

                                 3.5
                                 3.0
                                 2.5
                                                                                  2005
                                                                                (wet year)
 Vapour pressure deifict (KPa)


                                 2.0
                                 1.5
                                 1.0
                                 0.5
                                 0.0
                                    250   251   252       253    254     255
                                 3.5
                                 3.0
                                 2.5
                                 2.0
                                 1.5
                                                                                    2003
                                 1.0                                             (dry year)
                                 0.5
                                 0.0
                                    239   240   241       242    243     244
                                                 Day of year

Figure: Hourly measured vapour pressure deficit during 2005 and 2003 over
                Palangka Raya peat swamp forest, Indonesia
                                                                        Preliminary Results contd.
                                                     Rnobs    LEobs    LEgap     Hobs         Hgap
                                                     Rnsim             LEsim                  Hsim
                                     900
                                     600
                                                                                          H/LE=0.36
                                                                                                  2005
                                     300                                                  (Rn >700 Wm-2)
                                                                                                (wet year)
     Ecosystem energy fluxes (Wm )
     -2




                                       0

                                     -300
                                     -600
                                                                                                     + influxes
                                     -900                                                            - effluxes
                                         250   251     252       253       254          255
                                      900
                                     600

                                     300
                                       0                                                  H/LE=0.62 2003
                                                                                                 (dry year)
                                                                                          (Rn >700 Wm-2)
                                     -300
                                     -600

                                     -900
                                         239   240     241       242       243          244
                                                        Day of year

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
                                                                         Preliminary Results contd.

                                          25
                                          20
                                                                                           2005
      Ecosystem CO2 fluxes (mol m s )
                                          15
      -1



                                          10
                                                                                         (wet year)
      -2




                                           5
                                           0
                                          -5
                                         -10
                                         -15                                             + influxes
                                         -20                                             - effluxes
                                            250   251    252       253    254     255
                                          25
                                          20
                                          15
                                          10
                                           5            0.25 mm                              2003
                                           0
                                          -5
                                                                                          (dry year)
                                         -10
                                         -15
                                         -20
                                            239   240    241       242    243     244
                                                          Day of 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
                                                                       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)
                                                                                  Preliminary Results contd.
                                                                                                 2003
                          0.45                                                                (dry year)
         (mm-3-3)
           (m3 3m )       0.40
                          0.35
                          0.30
                          0.25
                          0.20
                            6
              ET (mmd )
            -1




                            5
                            4
                            3
                            2
                                                                                                            +NEP = C sink
            -2 -1




                             4
              NEP gCm d




                             2                                                                            - NEP = C source
                             0
                            -2                                                                               Open symbols
                            -4                                                                                     have
                            -6                                                                                >50% gap
                                 0   30   60   90   120   150   180   210   240   270   300   330   360        filled data
                                                           Day of year


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
                                                                                  Preliminary Results contd.
                                                                                                2005
                          0.45                                                                (wet year)
        (m3m-3)         0.40
         -3


                          0.35
         3




                          0.30
         (m


                          0.25
                          0.20
                            6
                            5
            ET (mmd )
          -1




                            4
                            3
                            2
                             4                                                                              +NEP = C sink
           -2 -1




                             2                                                                            - NEP = C source
              NEP gCm d




                             0
                            -2                                                                                Open symbols
                            -4                                                                                      have
                            -6                                                                                 >50% gap
                                 0   30   60   90   120   150   180   210   240   270   300   330   360         filled data
                                                           Day of year


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
                                                                           Preliminary Results contd.
Table: Annual ecosystem carbon balance for Palangka Raya Drained forest, Indonesia
during 2003 and 2005
Components                  2003 (drier year)                       2005 (wetter year)                  Values from
of ecosystem                                                                                           other studies
                          Ecosys                EC                Ecosys                  EC
   carbon
   budget

-------------------------------------------------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
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.
                                               Summary contd.


 Ecosys couldn’t 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.
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

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:35
posted:3/19/2012
language:English
pages:21