International Conference on Environmental Observations, Modeling and Information Systems

ENVIROMIS-200417-25 July 2004,

Akademgorodok, Tomsk, Russia

Modeling of methane emission from natural wetlandsand topography-based surface hydrology

Krylova A.I. and V.N.Krupchatnikoff Institute of Computational Mathematics and Mathematical Geophysics of

Siberian Branch of the Russian Academy of Sciences,pr. Ac.Lavrentieva, 6, Novosibirsk, 630090, Russia,

Ph. (8-3832) 356524, e-mail:vkrup@ommfao1.sscc.ru, alla@climate.sscc.ru

 

Introduction

There are two complementary approaches to determine global and regional wetland source strengths :

1) bottom-up approach: geographical coverage, spatial and temporal flux variations

a) using flux measurements and information on emission period and wetland areas to extrapolate to global and annual scales;

b) using a climate-sensitive model for methane emissions to extrapolate to the global scale;

2) top-down approach: inverse modeling Information on temporal and spatial variation of methane fluxes from soils is

deduced from observational data on CH4 mixing ratio in air, obtained on a global network of NOAA/CMDL field stations.

climate

soil surface

soil depth

water table

rooting depth

soiltemperature

vegetation

CH4 oxidation

NPP

CH4 production

CH4 concentration

pla

nt-

med

iate

d t

ran

spo

rt

ebu

lliti

on

dif

fusi

on

CH4

emission

atmosphere

oxic soil

anoxic soil

Schematic of the one-dimensional methane model

relative pore space

The methane emission model

),(),(),(),(4

ztQztQztFz

ztCt plantebulldiffCH

),(),( ztRztR oxidprod

Model is based on the one-dimensional continuity equation within the entire soil/water column

The diffusive flux Fdiff is calculated using Fick’s first law:

ztCz

zDztF CHCHdiff ,)(),(44

The rate Qebull at which methane in the form of bubbles is removed from depth z is calculated:

)),(()(),(44 threshCHCHebull CztCCfkztQ

The methane production rate Rprod(t,z) at time t and depth z is described as:

10

),(

100 )()()(),(meanTztT

inorgprod QTftfzfRztR

The methane emission model

)1(),()()(),(4 oxCHgrowrootvegplant PztCtfzfTkztQ

The rate Qplant(t,z) at which methane is removed by plants from depth z at time t is calculated from:

The total methane flux to the atmosphere

)()(),()( tFtFuztFtF plantebulldifftot

)(

),()(tw

nsoil

ebullebull dzztQtF dzztQtFns

nroot

plantplant ),()(

Boundary conditions

0),(4

nsoilztCz CH

at the lower boundary nsoil

at the upper boundary u, where u is either the water table w(t) (if w(t) > ns) or the soil surface ns

atmCH CcmuztC )4,(4

l mol M

M Catm

/ 1 1

, 076 . 0

ResultsFigure shows a comparison between simulated and observed methane concentration profiles for the period between 1 June and 30 June 1992. Observational data were taken from Shannon and White [1994].

CHCH44 [ M ] [ M ] CHCH44 [ M ] [ M ]

Coupled model of climate

Atmospheric model (INM/RAS) (Alexeev V., E.Volodin, V.Galin, V. Dymnikov, V. Lykosov, 1998)• Terrain-following vertical coordinate (21 σ-levels)• Semi-implicit formulation of integration in time• Energy conservation finite-difference schemes (2.5°x 2.5°)• Convection (deep, middle, shallow; mass-flux)• Radiation (H2O, CO2, O3, CH4 , N2O, O2; 18 spectral bands for SR and 10

spectral bands for LR) • PBL (5 σ-levels) Land surface model (ICMMG/SB RAS) (V. Krupchatnikov, 1998)

The Land Surface Model considered in this report is an extension of this earlier model development. The model is able to simulate:

terrestrial photosynthesis and respiration of CO2 from land surface, vegetation, methane emissions from natural wetlands, and surface hydrology,surface fluxes of energy and momentum.

Model is implemented globally, many surface type needed to be included.

Atmosphericmodel

Land surfacemodel

soil temperature

NPP

water table

CH4

model

global wetlanddistribution

global data sets:• plant-mediated transport • rooting depth• soil depth• relative pore space

Global methane fluxes Results : Observations and Modeling

Global distribution of peat-rich bogs from 50-600N(from Matthews, E., and I.Fung)

Regional CH4 emission

Tom River basinData

Spatial distribution of statistical moments of topographic index

Upscaling function for obtaining 10’ equivalent of topographic index from its values for 30-arc-second DEM

''' 301062.107.0

• This model is a component of the biosphere model in the coupled model of climate. It has allowed us to evaluate global CH4 fluxes from wetlands, seasonal change of fluxes for the basic areas of concentration peatlands in the northern latitudes.

• The model has been developed for studying the global natural emission of methane from the surface covered with bogs and lakes.

• Simulated results confirm the conclusions obtained on the basis of direct measurements, that Big Vasyugan Bog is the largest source of methane emission to the atmosphere.

• Simulated results allow us to retrieve the character of the distribution and the amount of methane fluxes from the surface earth to the atmosphere.

•The model can be considered as a basis for further research of interactions of the hydrological cycle, climate and emission of methane from the peat-bog ecosystems.

Conclusion