poster

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Preliminary assessment of VOC fluxes from a rain
forest performed in the LBA site of Manaus
Paolo Stefani, Riccardo Valentini, Giorgio
Matteucci , Paolo Ciccioli, Enzo Brancaleoni
, Massimiliano Frattoni , Antonio D. Nobre
and Alessandro C. De Araujo Department
of Forest Science (DISAFRI), Università della
Tuscia, Via C. De Lollis, 01100, Viterbo,
ITALY Istituto sullInquinamento Atmosferico
del CNR, Area della Ricerca di Roma, Via Salaria
Km 29.300, 00016, Monterotondo Scalo, ITALY
INPA Manaus, Avenida André Araùjo, 2936,
Petropolis, Manaus, AM, BRASIL
INTRODUCTION To precisely assess the turnover of
carbon from vegetation covered areas, it is
essential to quantify the amount of assimilated
carbon that is released into the atmosphere in
the form of isoprenoid compounds. A suitable
way to do it is to measure fluxes of biogenic
volatile organic compounds (BVOC) by relaxed
eddy accumulation (REA). To gain information on
the carbon balance of primary rain forests of
the Amazon basin within the LBA project, a
measuring site was set up 80 km North of the
city of Manaus. A 40 m meteorological tower
equipped with an eddy correlation system for CO2
and water vapour and a relaxed eddy accumulation
system fort VOC was installed in the parcel of
the forest ZF2, managed by INPA. A pictorial
view of the tower and the apparatuses present in
it is shown in Figure 1. The first objective was
to get preliminary information on the fraction
of assimilated carbon that was emitted by the
plant in the form of isoprene and monoterpenes.
We are also interested to quantify the impact of
short-term (light and temperature) and long-term
effects (seasonality) on BVOC emissions. We
report here the preliminary results obtained in
our site.
More systematic data were collected in December
1999 and January 2000. Fluxes of isoprenoids
are reported in Figure 3 together trends of PAR,
air temperature and CO2 assimilation. Experimental
data were used to derive the basal emission of
BVOC at the canopy level (Eo). Values of Eo were
obtained by fitting the G93 algorithm (Gentler et
al., 1993) for isoprene and monoterpenes with the
actual observations. It was found that values of
Eo of 1100 and 230 ng m-2 s-1 provided
continuous curves quite close to our
observations. The possibility to use the G93
algorithm allowed us to better estimate the
amount of assimilated carbon that was emitted as
BVOC at the starting of the raining season.
EXPERIMENTAL VOC fluxes were measured with an
improved REA system (Figure 1) based on the
original design described by Valentini et al.
(1997). A description of the modifications made
can be found in Ciccioli et al. (1999). Samples
of VOC were collected on traps filled with
graphitic carbons set in series. They were
analysed by GC-MS according to the procedure
previously described (Ciccioli et al., 1999).
Isoprene and monoterpene were identified and
quantified by using selected ions.
Plot of emitted versus assimilated carbon are
shown in Figure 4. The regression analysis showed
that ca 0.70 of assimilated carbon was emitted
as isoprene and monoterpenes by the rain forest
in Manaus. Isoprene accounted for ca. 85 of
reduced carbon emission. More extensive
investigations are planned to confirm our
preliminary observations indicating the light and
temperature dependence of emission of both
isoprene and monoterpene from tropical plants
present in the Amazon basin. In addition we
intend to follow the seasonality of BVOC
emissions to see if corrections need to be made
to the G93 algorithm for the seasonality. All
this activity will be performed within the frame
of the LBA-Carbosink project sponsored by the
European Union.
Fig. 1
RESULTS AND DISCUSSION Before to start
systematic investigations, preliminary flux
measurements were carried out in August 1999.
Results obtained are shown in Figure 2. They
showed that fluxes of isoprene were ca. one order
of magnitude higher than those of monoterpenes.
Emission from these last components was comprised
most of ?-pinene, sabinene, ?-pinene and
limonene. Preliminary data showed also that BVOC
accounted for ca. 0.5 of the assimilated carbon.
Fig. 4
REFERENCES Ciccioli P., Brancaleoni E., Frattoni
M., Di Palo V., Valentini R., Tirone G., Seufert
G., Bertin N., Hansen U., Csiky O., Lenz R.,
Sharma M., (1999) Emission of reactive terpene
compounds from orange orchards and their removal
by within-canopy processes. J. Geophys. Res.,
104, 8077-8094 Guenther, A.B., Zimmerman, P.R.,
Harley P.C., Monson R.K. and R. Fall (1993)
Isoprene and monoterpene emission rate
variability model evaluations and sensitivity
analyses. J. Geophys. Res., 98,
12609-12617 Valentini R., Greco S., Seufert G.,
Bertin N., Ciccioli P., Cecinato A., Brancaleoni
E., Frattoni M. (1997) Fluxes of biogenic VOC
from Mediterranean vegetation by trap enrichement
relaxed eddy accumulation. Atmos. Environ., 31
(SI), 229-238.
Fig. 2
for more information Paolo Stefani p.stefani_at_tisc
alinet.it University of Tuscia Department of
Forest Science and Environment Via De Lellis,
01100 Viterbo- Italy phone [phone] fax
39 0761 357389