GIS MODELIZATION OF THE METHANE SINK
IN SOILS OF THE ITALIAN PENINSULA
S. Castaldi(1), M. Costantini(2), P. Cenciarelli(2), R. Valentini(3)
Dipartimento di Scienze Ambientali, Seconda Università, di Napoli
(2) Dipartimento di Informatica, Università di Roma “la Sapienza”
(3)
DISAFRI, Università della Tuscia
(1)
AIM of the STUDY
MODELS used for simulations
CH4 is the 2nd most important greenhouse gas. It is
produced in anaerobic environments and consumed in
aerobic soils, which, hence, represent a sink for this
gas. Although required by the Kyoto Protocol, this sink
at national scale has not yet been quantified. At
present, no upscaling of experimental data is possible
for the Italian region because of the paucity of
available flux data. In the present study the CH4 sink
was modeled in a GIS environment. Data refer to the
year 2000.
1. “Tipping bucket” model of soil water content (Potter et al. 1993)
The MODELING ENVIRONMENT
The GIS modeling environment IDRISI Kilimanjaro was
extended by several extra modules written in the open
source language Python. A module calculates soil water
content (model 1) ; a module estimates the normalized
diffusivity (ND) of CH4 in aggregated media (model 2);
a module computes CH4 fluxes by using ND and
biological response of methanotrophs to temperature
(model 3); a module calculates CH4 fluxes in coarse soils
(model 4).
2. Model of gas diffusivity in aggregated media (Jones et al. 2003)
3. Model of CH4 consumption (Ridgwell et al., 1999):
C0CH 4  DCH 4t 
 CH 4  

DCH 4t    F
  1 
Z d   DCH t  K  Z 
4
d
d 

F = costant (Ridgwell, 1999); C0CH4= CH4 conc. in air; DCH4t = methane diffusivity in aggregated media at
time t; Zd max methane consuming depth; Kd = rt * K0; K0 = 8.7*10-4 s-1 (Ridgwell, 1999); rT = 0 if T<0;
rt= EXP(((0.0693* t)- (8.56*10-7* t4))) if T>0
4. Empirical model based on the relationship between water filled pore
space (WFPS) and CH4 uptake, derived by Castaldi and Fierro (2005).
Applied only to coarse soil deeper than 1 m, in forests and shrublands.
 CH 4  9.37  8.90  (1  e 0.098WFPS )
Agricultural soils
0
30
70
115
(mg CH4 m-2 yr-1)
INPUT DATA (georeferenced, UTM 32N)
The agricultural sink was
calculated by assuming that
CH4
consumption
in
agricultural soils is reduced
by a 60% by agricultural
practices with respect to
undisturbed soils (Castaldi
et
al.
2005).
This
percentage reduction was
applied to flux values
derived from the same
models applied to natural
soils.
MARS Data:
SOIL REGIONS (JRC):
texture, max rooting depth.
Derived parameters:
soil total porosity, field
capacity, values for
scalar RDR (Potter et al.
1993)
Daily Max temperature, daily
min temperature, ,daily rain,
daily evapotranspiration
Simulating GIS
environment - IDRISI
Natural soils
CORINE land cover 2000:
Agricultural, except rice
paddies; forests,
shrublands, transition,
grasslands
0
50
100
150
(mg CH4 m-2 yr-1)
Conclusions
The total CH4 sink calculated for the Italian soils in the year
2000 was 45.01 Gg CH4 yr-1, corresponding to a sink of 2.79 Tg
of CO2 equivalents (IPCC, Climate Change 2001, 20 year horizon).
Wetlands and rice paddies are not expected to change this
number significantly, as they cover a very small portion of the
Italian peninsula. Due to its Mediterranean climate and soil type
distribution, Italy can therefore be considered a significant
sink of CH4 if compared to Northern European regions.
REFERENCES
Potter CS et al. (1993) Terrestrial ecosystems production: a process model based on global satellite and surface data. Global Biogeochemical Cycles 7: 811-841.
Jones SB et al. (2003) Gas diffusion measurements and modeling in coarse-textured porous media. Vadose Zone Journal 2: 602-610.
Castaldi S. and Fierro A. (2005) Soil – atmosphere methane exchange in undisturbed and burned Mediterranean shrubland of Southern Italy. Ecosystems 8(2): 182-190.
Castaldi S. et al. (2005) Fluxes of N2O and CH4 from soils of savannas and seasonally-dry ecosystems. Journal of Biogeography (in press).
Figure
1
Methane
consumption rates (mg CH4
m-2 yr-1) calculated for the
Italian agricultural soils.
Overall, in year 2000, these
soils consumed 15.52 Gg
CH4 yr-1, corresponding to
0.96 Tg of CO2 equivalents
removed
from
the
atmosphere.
Figure
2
Methane
consumption rates (mg CH4
m-2 yr-1) calculated for
Italian natural soils. These
include soils from forests,
woodlands,
shrublands,
transition areas and natural
grassland. Overall natural
soils consumed 29.59 Gg
CH4 yr-1, corresponding to
1.83 Tg of CO2 equivalents
removed
from
the
atmosphere.
As expected on the base of
the applied models, the
highest
rates
where
associated
to
Southern
regions,
which
are
characterized by a drier and
warmer climate, although
also soil texture distribution
strongly
influenced
CH4
uptake, with coarse soils
showing
the
highest
consumption rates.