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Creator |
2b59c59b8b188fbe2c6521f3fc64e944 |
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Creator |
ext-09b1de539e7a0a3ffe55234fd3217467 |
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Creator |
ext-46f58aa410f0ae16c686a5adeec1a12f |
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Creator |
ext-8cb1bdc3997a42b075eb0147c85fb2ba |
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Creator |
ext-ae3f505a5b733ce3d6fa2d3fbfb3d42f |
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Creator |
ext-b86e63d3de7d00f2369ba81bd898979d |
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Date |
2008-04 |
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Is Part Of |
repository |
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Is Part Of |
pb454cfd30be8c0952d50d0a9a4de697f |
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abstract |
Boreal regions will be very sensitive to global warming which should induce an important
reduction of the permafrost area, and also probably a significant modification of
the hydrological regime of these high latitude regions. In permafrost areas the hydrological
characteristics of rivers are indeed very specific with the occurrence of three highly
contrasted periods: a very low water period from October to May, a spring flood
in May/June, and a relatively high water period in summer, from June to the end of
September [1]. However, previous geochemical studies interested in boreal systems
do not take these temporal variations into account.
<br></br><br></br>
In this work, we propose to characterize the temporal variability of dissolved chemical
fluxes carried by boreal rivers under permafrost conditions. For this purpose, two
rivers draining the South of the basaltic plateau of Putorana in Central Siberia (Kochechumo
and Nizhnaya Tunguska) were sampled along the year and an extended spatial sampling
of the watershed was carried out during the summer. The dissolved load of these water
samples were analysed for major and trace element concentrations as well as for strontium
and uranium isotopic compositions
<br></br><br></br>
On the basis of element concentration variations, three periods can be marked out,
matching the three hydrological periods. Variations of concentration ratios as well
as
variations of Sr isotope ratios show however that annual concentration pattern cannot
be explained solely by dilution processes but have to involve the contribution of
different sources. Thus, the significant increase of aluminium and iron concentrations
when the spring flood discharge occurs is certainly linked to the presence of colloidal
substances, most likely originating from upper soil horizons during the period of
snow melting.
<br></br><br></br>
Temporal variations of (<sup>234</sup>U/<sup>238</sup>U) activity ratios are also
observed in the dissolved load of the two rivers, with higher values in winter (>2)
than in spring and summer (from 1.2 to 1.5). We propose that in winter, when all surface
waters are frozen, the only contribution to the riverine water flux would come from
deep underground reservoirs having high rock/water ratios and long periods of interaction
thus producing high uranium activity ratios [2]. In summer, the contribution of surface
waters, flowing over
the permafrost in the active layer (suprapermafrost flow), would be predominant and
thus constitute the main chemical flux carried by these rivers.
<br></br><br></br>
Overall, permafrost regions represent very specific hydrogeochemical systems compared
to tropical and temperate systems with two different fluxes over the year : a deep
water flux in winter and a predominant surface water flux in spring and summer.
[1] Pokrovsky O., Schott J., Kudryatvtzev D.I., Dupré B. (2002). Basalt weathering
in Central Siberia under permafrost conditions.Geochim. Cosmochim. Acta 69, 5659-5680.
<br></br><br></br>
[2] Durand S., Chabaux F., Rhis S., Duringer P., Elsass P. (2005). U isotope ratios
as tracers of groundwater inputs into surface waters : Example of the Upper Rhine
hydrosystem. Chem. Geol. 220, 1-19. |
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authorList |
authors |
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presentedAt |
ext-b78d3db0e877ea94a445d304a6d4dc8d |
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status |
nonPeerReviewed |
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volume |
10 |
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type |
AcademicArticle |
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type |
Article |
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label |
Bagard, M. L. ; Chabaux, F.; Pokrovsky, O. S.; Prokushkin, A. S.; Viers, J. and
Dupré, B. (2008). Temporal variations of chemical weathering fluxes in boreal rivers
under permafrost conditions. Example of the Nizhnaya Tunguska watershed (Central Siberia).
In: Geophysical Research Abstracts, 10, article no. EGU2008-A-04760. |
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label |
Bagard, M. L. ; Chabaux, F.; Pokrovsky, O. S.; Prokushkin, A. S.; Viers, J. and Dupré,
B. (2008). Temporal variations of chemical weathering fluxes in boreal rivers under
permafrost conditions. Example of the Nizhnaya Tunguska watershed (Central Siberia).
In: Geophysical Research Abstracts, 10, article no. EGU2008-A-04760. |
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Title |
Temporal variations of chemical weathering fluxes in boreal rivers under permafrost
conditions. Example of the Nizhnaya Tunguska watershed (Central Siberia) |
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in dataset |
oro |