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| Titel |
Landscape control of uranium and thorium in boreal streams – spatiotemporal variability and the role of wetlands |
| VerfasserIn |
F. Lidman, C. M. Mörth, H. Laudon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 11 ; Nr. 9, no. 11 (2012-11-23), S.4773-4785 |
| Datensatznummer |
250007411
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| Publikation (Nr.) |
 copernicus.org/bg-9-4773-2012.pdf |
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| Zusammenfassung |
| The concentrations of uranium and thorium in ten partly nested streams in
the boreal forest region were monitored over a two-year period. The
investigated catchments ranged from small headwaters (0.1 km2) up to a
fourth-order stream (67 km2). Considerable spatiotemporal variations
were observed, with little or no correlation between streams. The fluxes of
both uranium and thorium varied substantially between the subcatchments,
ranging from 1.7 to 30 g km−2 a−1 for uranium and from 3.2 to
24 g km−2 a−1 for thorium. Airborne gamma spectrometry was
used to measure the concentrations of uranium and thorium in surface soils
throughout the catchment, suggesting that the concentrations of uranium and
thorium in mineral soils are similar throughout the catchment. The fluxes of
uranium and thorium were compared to a wide range of parameters
characterising the investigated catchments and the chemistry of the stream
water, e.g. soil concentrations of these elements, pH, TOC (total organic carbon), Al, Si and
hydrogen carbonate, but it was concluded that the spatial variabilities in the
fluxes of both uranium and thorium mainly were controlled by wetlands. The
results indicate that there is a predictable and systematic accumulation of
both uranium and thorium in boreal wetlands that is large enough to control
the transport of these elements. On the landscape scale approximately
65–80% of uranium and 55–65% of thorium entering a wetland were
estimated to be retained in the peat. Overall, accumulation in mires and
other types of wetlands was estimated to decrease the fluxes of uranium and
thorium from the boreal forest landscape by 30–40%, indicating that
wetlands play an important role for the biogeochemical cycling of uranium
and thorium in the boreal forest landscape. The atmospheric deposition of
uranium and thorium was also quantified, and its contribution to boreal
streams was found to be low compared to weathering. |
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