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| Titel |
²²²Rn behavior in waters from peatlands and eskers of the Amos region, Abitibi-Temiscamingue, Québec, Canada |
| VerfasserIn |
Laureline Berthot, Christine Boucher, Daniele Luigi Pinti, Marie Larocque, Miryane Ferlatte, Sylvain Gagné |
| 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 |
250083040
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| Zusammenfassung |
| 222Rn is a short decay product of U. Being a noble gas not affected by chemical reactions
222Rn can be a suitable tracer in subsurface hydrology, particularly for stream-groundwater
interactions. We recently carried out a Quebec government-funded project for characterizing
the hydrological cycle in peatlands located around fluvioglacial moraines and eskers in the
Abitibi-Temiscamingue region of Québec, eastern Canada. The goal of this project was to
trace water exchanges between the eskers and the surrounding peatlands using stable
isotopes, major chemistry and noble gases (including 222Rn). Samples were taken in
summer 2012 from 46 wells tapping the Saint-Mathieu-de-Berry and Barraute eskers
and the Harricana moraine. Sixteen samples were taken from deeper wells tapping
the Archean fractured bedrock in the clay plain separating these eskers. And 40
samples were collected from piezometers installed at different depths from 0.70m to
4.8Â m in four peatlands located along the flanks of the Saint-Mathieu-de-Berry esker
and the Harricana moraine. 222Rn activity was measured at UQAM using a liquid
scintillation counter (SL-300 from HIDEX®). 222Rn activities in peatland water
range from 0.02 to 16.6 Bq/L. 222Rn activities measured in groundwater flowing
through the esker and moraine aquifers range from 2.8 to 34.9Â Bq/L. These values are
relatively low taking into account that the rock matrix derives from old Archean
granitoids and volcanic rock likely rich in U and Th. However, 234U/238U analyses in
the same waters showed that these hydrologic systems are extremely depleted in
U-derived radionuclides. Interestingly, several peatlands show a good correlation
between the Total Dissolved Salinity (TDS) and the 222Rn activity and with HCO3-,
SO42-, Mg2+ and Ca2+. Salinity in the eskers derives from the deeper fractured
basement aquifer as indicated by a clear correlation between helium isotopes, TDS
and the well depths. A similar relation is observed for the 222Rn. This suggests
that peatlands receives a contribution from deeper waters, either from their flanks
(eskers) or possibly deeper. Using a simple mixing equation between saline and
222Rn-rich deeper waters and less saline and 222Rn-poor peatland water, we can estimate
the maximum contribution of deeper water to be approximately 5% of the total
amount of water found in peatlands. These are minimum values because we do not
take into account the 222Rn losses related to decay and evasion to the atmosphere. |
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