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| Titel |
The use of O, H and Sr isotopes and carbamazepine to identify the origin of water bodies supplying a shallow alluvial aquifer |
| VerfasserIn |
Lara Sassine, Corinne Le Gal La Salle, Joël Lancelot, Patrick Verdoux |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096518
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| Publikation (Nr.) |
 EGU/EGU2014-12024.pdf |
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| Zusammenfassung |
| Alluvial aquifers are of great socio-economic importance in France since they supply 82% of
drinking water production, though they reveal to be very vulnerable to pesticides and
emerging organic contaminants. The aim of this work is to identify the origin of water bodies
which contribute to the recharge of an alluvial aquifer for a better understanding of its
hydrochemistry and transfer of contaminants therein. The study is based on an isotopic and
geochemical tracers approach, including major elements, trace elements (Br, Sr),and isotopes
(δ18O, δ2H, 87Sr/86Sr), as well as organic molecules. Indeed, organic molecules such as
pharmaceutical compounds, more precisely carbamazepine and caffeine, have shown their
use as indicators of surface water in groundwater.
The study area is a partially-confined shallow alluvial aquifer, the so-called Vistrenque
aquifer, located at 15 km from the Mediterranean Sea, in the Quaternary alluviums deposited
by an ancient arm of the Rhône River, in Southern France. This aquifer constitutes a
shallow alluvial layer in a NE-SW graben structure. It is situated between a karst
aquifer in lower Cretaceous limestones, on the NW border, and the Costières Plateau,
on the SE border, having a similar geology as the Vistrenque. The alluvial plain
is crossed by a surface water network with the Vistre as the main stream, and a
canal used for irrigation essentially, the BRL canal, which is fed by the Rhône
River.
δ18O and δ2H allowed to differentiate the BRL canal water, depleted in heavy isotopes (δ2H
= -71.5ovs V-SMOW), and the more enriched local rainwater (δ2H = -35.5ovs
V-SMOW). In the Vistre surface water a binary mixing were evidenced with the BRL canal
water and the rainwater, as end members. Then, in the Vistrenque groundwater both the BRL
and the Vistre contributions could be identified, as they still show contrasting signature with
local recharge. This allows to highlight the surface water contribution to a heavily exploited
alluvial aquifer.
These mixing processes are confirmed by comparing O and H isotopes to major elements
composition. Furthermore, organic compound concentrations such as carbamazepine which
show relatively high concentrations in surface waters, was also detected in groundwater
especially in those influenced by the BRL canal water, and hence may be used as a tracer of
surface water contribution.
On the other hand, 87Sr/86Sr allowed highlighting this time a mixing process between
groundwater bodies contributing to the recharge of the alluvial aquifer. The 87Sr/86Sr vs 1/Sr
plot showed a locale influence on the Vistrenque groundwater by the karst limestone aquifer
(87Sr/86Sr -0.7076; [Sr] =1540 μg/L), and the Costières Plateau water (87Sr/86Sr -0.7090;
[Sr] =320 μg/L).
In conclusion, 18O and 2H isotopes allowed to highlight the influence of surface waters on the
quality of a shallow vulnerable alluvial aquifer, by determining the relationship between the
two water bodies. While 87Sr/86Sr were useful to identify mixing processes between
groundwater bodies from aquifers of different geology, the limestone karst and alluvial
sediments. A multi-isotope approach proved useful to understand the origin of water bodies
and contaminants. |
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