Numerical modelling of methane emissions from thermokarst lakes - - PowerPoint PPT Presentation

Numerical modelling of methane emissions from thermokarst lakes

V.M.Stepanenko1, Е.E.Machulskaya1,2, and M.V.Glagolev3,4

• 1. Moscow State University, Research Computing Center
• 2. Deutscher Wetterdienst
• 3. Moscow State University, Faculty of Soil Science
• 4. University of Yugra, Chanty-Mansiisk

ENVIROMIS-2010, 7 July, Tomsk, Russia

The work is supported by grants: RFBR 09-05-13562-офи_ц, 09-05-00379-а, 10-05-00981-а, П№1394

Atmospheric methane and its sources

IPCC report, 2007 Sources of methane in a climate system ¡

Mtones СН4/yr ¡

Animals (mostly ruminants), without termites ¡

106 ¡ Termites ¡ 23 ¡ Rice paddies ¡ 69 ¡ Natural ¡wetlands, ¡excluding ¡tundra ¡ 113 ¡ Tundra ¡ 19 ¡ Oceans ¡ 14 ¡ Lakes ¡ 5 ¡ Methane hydrates ¡ 4 ¡ Volcanoes ¡ 1 ¡ Other natural sources ¡ 6 ¡ Burials of solid waste products ¡ 33 ¡ Coal industry ¡ 46 ¡ Gas industry ¡ 54 ¡ Biomass burning ¡ 40 ¡ Automobiles ¡ 1 ¡ TOTAL ¡ ~530 ¡

Emission of methane by thermokarst lakes

• 8 - 50% of anthropogenic

emissions in XXI century depending on IPCC scenario (K. Walter et al., 2006, Nature)

Unfreezing “hotspot” – the source of methane during wintertime

• thermokarst lakes

in Northern Siberia

• ccupy

22-48%

• f the area
• satellite images

indicate expanding

• f thermokarst

lakes area

Implication to climate change and climate modeling

• Positive feedback:

Thermokarst development, expansion of lakes

Climate warming

Increase of methane fluxes from thermokarst lakes

We need a modeling tool, a parameterization of thermokarst lakes’ emissions in climate models

Methane emission: bogs and lakes

Mechanism of methane production

• On bogs the substrate for methane production

comes from surface NPP -> modeling approaches are well developed

• In lakes methane is produced (i) from lake bottom

NPP and (ii) from the old organics, that has been sequestered in permafrost and comes to positive temperature region while talik is deepening -> the need for new parameterization Implication to annual cycle

• On bogs cold season emission is very low;
• In lakes methane is produced in talik, that is under

positive temperatures all year round (40-50% of annual emission happen in cold period)

[ ] [ ]

4

4 4 , CH m

CH CH k P E F t z z ∂ ∂ ∂ = + − − ∂ ∂ ∂

Production: Ebullition:

(B. Walter & Heimann, 1996, 2001)

Methane concentration in lake talik

[ ]

( ) [

] [ ] [ ] [ ]

4 4 4 4 4 max

,

e step

E k f CH CH CH CH CH = Δ Δ Δ = −

new

• ld

P P P = +

new

P

• ld

P

( ) ( )

10 ,0 00

exp

T new new new step

P P z f T q = −α

Neglected: vegetation transport F

,0 new

P

• calibrated

parameter

Methane production from

• ld organics decomposition
• happens only under positive temperatures
• is exponentially dependent on temperature
• is proportional to decomposable organics content

Michaelis-Menthen equation for decomposition (1) Analytical law for talik deepening (2)

( )

* 10 ,0 00 T

• ld
• ld
• ld

step

P P C f T q =

,max ,max

, ( , , , )

C

• ld
• ld

C

• ld
• ld

C C

V C C t C C f t t V ∂ = − ∂ α + = α

0 , t t t

z C t h C t = =

( )

( )

2 2 2 2 ,0 2

1 2

• ld

C C C t t

C C C h z

−

⎛ ⎞ = + λ − + λ + γ − ⎜ ⎟ ⎝ ⎠

Combining (1) and (2) yields

* ,0

• ld

P

• calibrated parameter

Methane transfer in the water body

[ ] [ ] [ ] [ ] [ ] [ ]

4 2 2

4 4 2 2 2 2

, 2 , 2

CH

• xid

O

• xid

CO

• xid

CH CH k V t z z O O k V t z z CO CO k V t z z ∂ ∂ ∂ = − ∂ ∂ ∂ ∂ ∂ ∂ = − ∂ ∂ ∂ ∂ ∂ ∂ = + ∂ ∂ ∂

• dissolved gases:
• methane
• oxygen
• carbon dioxide
• processes:
• turbulent diffusion
• methane oxidation

CH4 + O2 = CO2 + 2H2O

(Bastviken et al., 2002)

One-dimensional k-ε model (LAKE)

( )

1 1

A

T p Г

T T S k u n Tdl t z z c z A ρ ∂ ∂ ∂ ∂ ⎛ ⎞ = − + ⋅ ⎜ ⎟ ∂ ∂ ∂ ∂ ⎝ ⎠

∫

r r

2 2 2 2

tg , tg

M x veg M y veg

u u k fv g C u u v t z z v v k fu g C v u v t z z α α ∂ ∂ ∂ = + − ⋅ − + ∂ ∂ ∂ ∂ ∂ ∂ = − − ⋅ − + ∂ ∂ ∂

2

,

M e

E k C = ε

Snow Ice

Water Soil

U H,LE Es Ea S

,

M E

E k E P B t z z ⎛ ⎞ ∂ ∂ ∂ = ν + + + − ε ⎜ ⎟ ∂ ∂ σ ∂ ⎝ ⎠

( )

1 3 2 M

k c P c B c t z z E

ε ε ε ε

⎛ ⎞ ∂ε ∂ ∂ε ε = ν + + + − ε ⎜ ⎟ ∂ ∂ σ ∂ ⎝ ⎠

K-ε turbulence closure Momentum equations Heat equation

Validation: sediments temperature

• Krasnoe Lake,

(near S.-Petersburg)

• 1969 – 1979
• Sortavala station

forcing

Bottom temperature Bottom sediments temperature (3 m depth) Observations: Kusmenko, 1976. Soil heat conductance: Cote and Konrad model (Sen Lu et al., 2007)

Case study: Lake Shuchi

• Time series of atmospheric variables as input to lake model

are extracted from ERA-Interim reanalysis

420 480 540 600 660 720 780 840 900 100 200 300 400 500 600 700 800 900 1000 êî í òðî ëüí û é ¡ýêñï åðèì åí ò ýêñï åðèì åí ò ¡ï ðè ¡ï î ñòî ÿí í î ì ¡

àòì î ñô åðí î ì ¡ä àâëåí èè

Time, days Ebullition methane flux, mg/(m2*day) Control experiment Experiment with constant atmospheric pressure

90% of bubbles during wintertime are intercepted by ice cover and are released when the later thaws

Model calibration: Lake Shuchi

200 210 220 230 240 250 260 270 280 290 300 310 0,58 0,60 0,62 0,64 0,66 0,68 0,70 0,72 0,74 0,76 0,78 0,80 0,82

Pold,0

**10 10, ì î ëü/(êã*ñ)

P new,0*10

10, ¡ì î ëü/(ì 3*ñ)

9,800 11,80 13,80 15,80 17,80 19,80 21,80 23,80 25,80 27,80 29,80 31,80 33,80 35,80 37,80 39,80 41,80 43,80 45,80 47,80 49,80 51,80 53,80 55,20

ΔF

( ) ( )

2 2 2 , , w w s s a a m a a m

F F F F F Δ ≡ − + −

The measure

• f model error
• Calibrated

parameters

• has

single minimum

* ,0 ,0

,

• ld

new

P P

F Δ

2 min

10 / F mg m Δ ≅

Model validation

Annual methane emission, mg/ (m2*yr) ¡ A part of open- water period emission , % ¡ A part of ice- covered period emission, % ¡

Observations ¡ 22658 ¡ 54 ¡ 46 ¡ Model ¡ 22588 ¡ 54 ¡ 46 ¡

Open water period ¡ Ice-covered period ¡

A part of young methane in emissions (observations) , % ¡

47 ¡ 6 ¡

A part of young methane in net generation (model) , % ¡

61 ¡ 32 ¡

Observations: Lake Shuchi (K. Walter et al., 2006) hourly observations of ebullition and diffusion methane fluxes in different lake sections for 2003 – 2004

Remarks on lake methane model

• The values of calibrated parameters

depend on errors (lack of observations!)

• f input parameters: lake depth, water

turbidity, atmospheric forcing, etc.

• The model should be verified on a

significant number of thermokarst lakes

• The model does not consider

thermokarst lake development (deepening, drainage, etc.)

Regional atmospheric model NH3D_MPI

Land surface model of INM:

• 1. Soil (including permafrost)
• 2. Vegetation
• 3. Snow cover
• 4. Walter and Heimann methane

model for bogs

• 5. A set of models for oxic soils

carbon cycling

LAKE model with methane block Atmospheric 3D dynamics in σ-coordinates, methane transport and chemistry

• horizontal spacing 1-10 km
• 30 levels in vertical
• time step 5-10 s
• parallel implementation

using MPI

Research perspectives

• Inverse modeling of atmospheric

methane transport on a regional scale to (i) identify sources (ii) validate and calibrate land surface methane models (bogs and lakes) using measurements

• f atmospheric methane concentration
• Incorporation of lake methane model in

regional and global climate models to assess regional feedback between climate change and thermokarst lakes and its global significance