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| Titel |
Impact of vegetation and ecosystems on chlorine(-36) cycling and its modeling: from simplified approaches towards more complex biogeochemical tools |
| VerfasserIn |
Yves Thiry, Paul-Olivier Redon, Malin Gustafsson, Laura Marang, David Bastviken |
| 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 |
250081533
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| Zusammenfassung |
| Chlorine is very soluble at a global scale with chloride (Cl-), the dominating form. Because
of its high mobility, chlorine is usually perceived as a good conservative tracer in
hydrological studies and by analogy as little reactive in biosphere. Since 36Cl can be
considered to have the same behaviour than stable Cl, a good knowledge of chlorine
distribution between compartments of terrestrial ecosystems is sufficient to calibrate a
specific activity model which supposes rapid dilution of 36Cl within the large pool of stable
Cl and isotopic equilibrium between compartments. By assuming 36Cl redistribution similar
to that of stable Cl at steady-state, specific activity models are simplified interesting tools for
regulatory purposes in environmental safety assessment, especially in case of potential
long term chronic contamination of agricultural food chain (IAEA, 2010). In many
other more complex scenarios (accidental acute release, intermediate time frame,
and contrasted natural ecosystems), new information and tools are necessary for
improving (radio-)ecological realism, which entails a non-conservative behavior of
chlorine.
Indeed observed dynamics of chlorine in terrestrial ecosystems is far from a simple
equilibrium notably because of natural processes of organic matter (SOM) chlorination
mainly occurring in surface soils (Öberg, 1998) and mediated by microbial activities on a
large extent (Bastviken et al. 2007). Our recent studies have strengthened the view that an
organic cycle for chlorine should now be recognized, in addition to its inorganic cycle. Major
results showed that:
organochlorine (Clorg) formation occurs in all type of soils and ecosystems
(culture, pasture, forest), leading to an average fraction of the total Cl pool in soil
of about 80 % (Redon et al., 2012),
chlorination in more organic soils over time leads to a larger Clorg pool and
in turn to a possible high internal supply of inorganic chlorine (Clin) upon
dechlorination. (Gustafsson et al., 2012),
average Cl residence time in forest soils calculated for Clin and Clorg together
was 5-fold higher that the residence time estimated for Clin alone (Redon et al.,
2011),
locally, Cl amount taken up by certain vegetation types can be larger than annual
atmospheric deposits, the Cl in excess being recycled mainly by throughfall
(Thiry, 2010),
root uptake and chlorine transformation rates in soils are essential to calibrate
dynamic compartment models since those processes control the persistence of
chlorine in the whole system but data are still deficient for different land uses
(Van den Hoof & Thiry, 2012).
References:
Bastviken, D., Thomsen, F., Svensson, T., Karlsson, S., Sandén, P., Shaw, G.,
Matucha, M., and Öberg, G. (2007). Chloride retention in forest soil by microbial
uptake and by natural chlorination of organic matter. Geochim. Cosmochim. Acta, 71:
3182-3192.
Gustavsson, M., Karlsson, S.,Öberg, G.,Sandén, P.,Svensson, T.,Valinia, S.,Thiry, Y. and
Bastviken, D. (2012). Organic matter chlorination rates in different boreal soils: the
role of soil organic matter content. Environmental Science & Technology, 46 (3):
1504-1510
Thiry, Y., 2010. Contribution à l’étude du cycle biogéochimique du chlore en écosystème
forestier: cas d’un peuplement de pin sylvestre. Rapport Andra nË ENV.NT.ASTR.10.0068.
IAEA (2010). Handbook of parameter values for the prediction of radionuclide transfer to
humans in terrestrial and freshwater environments. Technical Report Series nË 472, Vienna,
Austria.
Öberg, G. (1998). Chloride and organic chlorine in soil. Acta hydrochimica et
hydrobiologica, 26 (3): 137-144.
Redon, P-O., Abdelouas, A., Bastviken, D., Cecchini, S. Nicolas, M. and Thiry,
Y. (2011). Chloride and organic chlorine in forest soils: storage, residence times,
and influence of ecological conditions. Environmental Science & Technology, 45:
7202-7208.
Redon, P-O., Jolivet, C., Saby, N., 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.
Van den Hoof, C. and Thiry, Y. (2012). Modelling of the natural chlorine cycling in a
coniferous stand: implications for chlorine-36 behaviour in a contaminated forest
environment. Journal of Environmental Radioactivity., 107: 56-67. |
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