Study on Construction of a Wetland Ecosystem and Carbon Transfer
in the Closed Geosphere Experiment Facility
Shizuo SUZUKI, Yasuhiro TAKO, Yuji NAKAMURA
Department of Environmental Simulation
Abstract
The Closed Geosphere Experiment Facility (CGEF) with high airtightness is designed to study carbon
dynamics in terrestrial ecosystems, including the transfer and accumulation of radioactive carbon isotope(14C) released from nuclear facilities to the environment.

A wetland ecosystem dominated by Phragmites

australis, which is widely found in cool-temperate brackish marsh near the spent nuclear fuel reprocessing
plant in Rokkasho, Japan, was introduced into the CGEF where air temperature and CO2 concentration areboth controlled automatically.

A mathematical carbon transfer and accumulation model (CTA model)

which consists of photosynthesis and decomposition sub-models, having the structure of nine reservoir
compartments (three plant, two litter, three soil, and one groundwater compartments), was developed toestimate the carbon dynamics in the wetland ecosystem.

In addition, the gross primary productivity (GPP)model which calculates total photosynthesis of the wetland ecosystem from three environmental variables(light intensity, atmospheric CO2 concentration, air temperature) was developed for the input sub-model for
the CTA model.

The Bayesian probabilistic inversion analysis and a Markov chain Monte Carlo (MCMC)

technique were applied to determine parameters of these two models, using the data obtained from thetwo-year experiment in the CGEF.

The CTA model was applied to a wetland ecosystem around Takahoko

Lake which is located near the spent nuclear fuel reprocessing plant.

The results showed that the modelgave appropriate estimates of carbon reservoirs for the plant growing season.

The seasonal variations in

the amounts of leaf and stem biomass carbon were adequately simulated by the model.

The changes in theamounts of soil carbon in microbial biomass and organic materials were properly estimated within thestandard deviation of the observed data in a real wetland.

Although the amounts of dissolved organiccarbon were partly overestimated, the discrepancy of the estimates was corrected by the re-examination of
the decomposition coefficient of dissolved organic materials in carbon reservoirs.

It was ascertained thatthe currently developed CTA model is applicable for the short-term estimation of carbon transfer andaccumulation in wetland ecosystems.

(c)

-2

Plant biomass carbon (g C m )

250

200

150

1005001-Jun

1-Jul

葉－観測値
L-O

葉－計算値
L-C

稈－観測値
S-O

稈－計算値
S-C

31-Jul30-Aug29-Sep(b)

Dissolved organic carbon (g C m-2)

Soil organic carbon (g C m-2)

10
観測値
O
8

計算値
C

64201-May

1-Jul

31-Aug31-Oct31-Dec

(d)
400
観測値
O
計算値
C
300

200

10001-May

Fig. 1

Soil microbial biomass carbon (g C m-2)(a)1-Jul

31-Aug31-Oct31-Dec0.4
観測値
OO
k9 == 0.387
ｋ9
k9 == 0.581 (1.5倍)
ｋ9

0.3

k9 == 0.774 (2.0倍)
ｋ9

0.2

0.1

0.0
1-Jun

1-Aug

1-Oct

Comparison between model estimates and observation in the real field for four carbon reservoirs.
(a) Plant biomass carbon. L and S indicate leaf and stem biomass carbon, respectively. O and C
represent observed and calculated values, respectively. (b) Soil organic carbon. (c) Soil microbialbiomass carbon. (d) Dissolved organic carbon. k9 means a decomposition coefficient of dissolved
organic materials in carbon reservoirs.

1-Dec