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| Titel |
Chlorine-36 and chlorine concentrations within several compartments of a deciduous forest ecosystem in Meuse/Haute-Marne (France) |
| VerfasserIn |
Julie Pupier, Lucilla Benedetti, Didier Bourlès, Elisabeth Leclerc, Yves Thiry |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083475
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| Zusammenfassung |
| Chlorine-36 is a cosmogenic nuclide mainly produced in the atmosphere by interactions
between energetic particles originating from the cosmic radiations and 40Ar. Because of its
long half-life (T1-2 = 3.01 105 yr) and its high mobility, chlorine-36 is a critical radionuclide
concerning radioactive waste repository sites. Moreover, it has been shown that inorganic
chlorine could be enriched along the trophic chain due to its high solubility and
bioavailability (Ashworth and Shaw, 2006). Additionally, many studies during the last
decades have established that due to chlorination process, organic chlorine may account for a
large proportion of the total soil chlorine pool (more than 80 % in surface soils of temperate
ecosystems. Redon et al., 2012).
The aim of this study is thus to measure chlorine-36 in all the compartments of the
biogeochemical cycle, to better understand its recycling in the biosphere.
The study site is the experimental beech forest site of the Andra long-term monitoring and
testing system (OPE*). It is located at Montiers-sur-Saulx, North-East of France and is
associated to the future radioactive waste repository site of Bure. Since March 2012,
rainwater above (rainfall collected from a 45 m high tower built on purpose) and
below (throughfall and stemflow) the canopy, has been collected monthly, as well as
soil solutions (gravitational and bound waters) at four depths (0, 10, 30, 60 cm
deep).
Chlorine-36 and chlorine have been measured in the rainfall samples between March and July
2012 and in water solutions collected from all compartments of the biosphere using isotope
dilution mass spectrometry at the french AMS national facility ASTER located at
CEREGE.
The results yielded from the rainfall samples allow to study the temporal fluctuations of
chlorine-36 in the atmosphere, which represents the main inflow of chlorine-36 in its
biogeochemical cycle. The first results indicate a flow increase during the late spring-early
summer. Santos et al., 2004 have also observed a similar pattern in southern Spain. This
increase might be due to a tropopause break, a natural process which occurs in spring
and in fall. This break implies an increase of the air masses exchange between
the tropopause and the stratosphere and therefore could cause high chlorine-36
inflow.
All together, those results allow to draw a profile of the evolution of chlorine-36
concentrations in the various pools of the biogeochemical cycle (from the upper rainfall
through stemflow and throughfall to the lower soil). Both 36Cl and Cl concentrations in
stemflow samples are 25-50% higher than in the rainfall and throughfall samples. In water
solutions collected from the soil, chlorine-36 concentrations vary between 3 to 8 10 3 at/ml,
with an increase in the concentration at 30 cm depth.
To understand the chlorine-36 recycling in soil, the next step will be to isolate and measure
the 36Cl concentrations in the inorganic and organic fractions of chlorine in a soil
profile.
* : OPE : Observatoire Pérenne de l’Environnement (SOERE), French national long-term
monitoring and experimental system for research in environment, www.andra-ope.fr
Ashworth, D. J. and Shaw, G. (2006). A comparison of the soil migration and plant uptake of
radioactive chlorine and iodine from contaminated groundwater. Journal of environmental
radioactivity, 89(1) :61–80.
Redon, P.-O., Jolivet, C., Saby, N. P. a., Abdelouas, A., and Thiry, Y. (2012). Occurrence of
natural organic chlorine in soils for different land uses. Biogeochemistry (In press), doi :
10.1007/s10533- 012-9771-7.
Santos, F., Lopez-Gutierrez, J., Garcia-Leon, M., Schnabel, C., Synal, H., and Suter, M.
(2004). Analysis of 36Cl in atmospheric samples from Seville (Spain) by AMS. Nuclear
Instruments and Methods in Physics Research Section B : Beam Interactions with Materials
and Atoms, 223-224 :501–506. |
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