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Titel |
Surface Water - Groundwater Interactions in Wetlands: Sr Isotope Constraints |
VerfasserIn |
Emmanuelle Pételet-Giraud, Philippe Négrel |
Konferenz |
EGU General Assembly 2011
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 13 (2011) |
Datensatznummer |
250049798
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Zusammenfassung |
This paper focuses on Strontium isotopes as a tool to better constrain hydrosystem
functioning in wetlands context. Waters derive their Sr isotopic signatures (87Sr/86Sr) from
interaction with rock matrix without isotopic fractionation. The isotopic signature of water
draining various igneous rocks, or carbonated rocks from different ages are clearly distinct, in
that way Sr isotopes are a good tracer of the water-rock interactions as and thus a
good tracer of water origin in a watershed. The measured differences in 87Sr/86Sr
ratios are the result of mixing of Sr from different sources with different isotopic
compositions, the signature variations within the hydrosystem can provide information
concerning the sources of Sr and the different mixing processes involved. Complex
relations between surface and groundwater in the specific context of wetlands are
illustrated through the Sr isotopic tool. Examples presented were selected from
various geological and hydrogelogical contexts in order to highlight the Sr isotopes
potentialities.
For instance, the hydrosystem functioning of a small alluvial aquifer along the
Allier River (France) was investigated through couple isotopic and chemical tracing
and constraints to evaluate riverbank aquifer recharge and study hydraulic links
with rivers and chemical transfer between surface and groundwater. The Allier
River drains Eocene to Miocene sedimentary formations, including sequences of
clastic and carbonate sediments. The groundwater in the riverbank alluvial aquifer
drains Quaternary Allier river alluvial deposits encompassing silicate components
of granitic-gneissic and basaltic origin from the Massif Central. These alluvial
deposits overlie sandy-clayey deposits made up mainly of clay, sand and gravel from
crystalline, metamorphic and volcanic rocks from the Massif Central and Oligocene
lacustrine carbonaceous deposits. These deposits were mainly supplied by lake
sedimentation owing to certain marine incursions evidenced by combining fossil and fauna
associations and isotopic tracing. The complex local geological settings favour large
variations of Sr isotopic signatures in both groundwaters and surface water. Sr isotopic
compositions measured in surface and groundwater can be explained by at least three
end-members in a 87Sr/86Sr versus 1/Sr diagram. The three end-members can be
identified according to the drained lithologies, and the water samples, that plot along
mixing lines within this type of diagram can be explained by mixings of water from
different origins. In optimal conditions, especially when all the possible sources of Sr
are well constrained, it is possible to quantify the water proportions of the mixing
and thus to better constrain the hydrosystem functioning for a better management. |
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