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Distribution and transport of radionuclides in a boreal mire: assessing past, present and future accumulation of uranium, thorium and radium
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Swedish Defence Research Agency (FOI), Umeå, Sweden.
Dept. of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
Dept. of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
2013 (English)In: Journal of Environmental Radioactivity, ISSN 0265-931X, E-ISSN 1879-1700, Vol. 121, 87-97 p.Article in journal (Refereed) Published
Abstract [en]

The spatial distribution of U-238, Ra-226, K-40 and the daughters of Th-232, Ra-228 and Th-228, were measured in a small mire in northern Sweden. High activity concentrations of U-238 and Th-232 (up to 41 Bq U-238 kg(-1)) were observed in parts of the mire with a historical or current inflow of groundwater from the surrounding till soils, but the activities declined rapidly further out in the mire. Near the outlet and in the central parts of the mire the activity concentrations were low, indicating that uranium and thorium are immobilized rapidly upon their entering the peat. The Ra-226 was found to be more mobile with high activity concentrations further out into the mire (up to 24 Bq kg(-1)), although the central parts and the area near the outlet of the mire still had low activity concentrations. Based on the fluxes to and from the mire, it was estimated that approximately 60-70% of the uranium and thorium entering the mire currently is retained within it. The current accumulation rates were found to be consistent with the historical accumulation, but possibly lower. Since much of the accumulation still is concentrated to the edges of the mire and the activities are low compared to other measurements of these radionuclides in peat, there are no indications that the mire will be saturated with respect to radionuclides like uranium, thorium and radium in the foreseen future. On the contrary, normal peat growth rates for the region suggest that the average activity concentrations of the peat currently may be decreasing, since peat growth may be faster than the accumulation of radionuclides. In order to assess the total potential for accumulation of radionuclides more thoroughly it would, however, be necessary to also investigate the behaviour of other organophilic elements like aluminium, which are likely to compete for binding sites on the organic material. Measurements of the redox potential and other redox indicators demonstrate that uranium possibly could be reduced in parts of the mire. The results of the study suggest that this mire currently is, and historically has been, an important sink for radionuclides and that it most likely will continue to be so for a long time to come.

Place, publisher, year, edition, pages
Elsevier, 2013. Vol. 121, 87-97 p.
National Category
Ecology Earth and Related Environmental Sciences
URN: urn:nbn:se:umu:diva-73555DOI: 10.1016/j.jenvrad.2012.06.010ISI: 000318962200009OAI: diva2:632800
International Conference on Radioecology and Environmental Radioactivity (ICRER), JUN 19-24, 2011, Hamilton, CANADA

Special Issue

Available from: 2013-06-25 Created: 2013-06-25 Last updated: 2016-06-27Bibliographically approved
In thesis
1. Radionuclide transport in the boreal landscape: Uranium, thorium and other metals in forests, wetlands and streams
Open this publication in new window or tab >>Radionuclide transport in the boreal landscape: Uranium, thorium and other metals in forests, wetlands and streams
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The boreal landscape is complex mosaic of vast forests, lakes and wetlands. Through the landscape flows a fine network of streams and rivers, carrying dissolved and suspended material from atmospheric deposition and weathering of soils and bedrock to downstream recipients. This thesis investigates the transport of U, Th and other metals in the boreal landscape by comparing a set of catchments with contrasting characteristics, ranging from 0.12-68 km2 in area. Using uranium (234U/238U) and oxygen isotopes (δ18O) it was demonstrated that catchment size has a strong impact on the hydrological pathways and on the mobilisation of uranium. Both tracers also displayed a consistent shift towards more superficial sources and more superficial flow pathways when going from winter baseflow conditions to the spring flood. Large spatiotemporal variability was observed with U fluxes ranging from 1.7 -30 g km-2 a-1. Using a wide set of hydrochemical parameters and landscape characteristics it was demonstrated that wetlands play a decisive role for the biogeochemical cycling of many metals. Comparing normalised fluxes of 13 different elements (Al, Ba, Ca, Cr, Cu, La, Mg, Na, Ni, Si, Sr, U and Y) 73% of the spatial variance could be explained based on the wetland coverage and the affinity for organic matter, the latter of which was quantified using thermodynamic modelling. Hence, it was possible to link the large-scale transport patterns of a wide range of metals to fundamental biogeochemical properties. When restraining the analysis to the smaller streams (<10 km2), the explanatory power increased to 88%. For elements such as Na and Si with low affinity for organic matter the decrease in wetland-dominated catchments corresponded closely to the area of mineral soils that had been replaced by peat, indicating that reduced weathering was the main cause of the decrease. For organophilic metals the decrease in wetland-dominated catchments was even greater, suggesting that there also was an accumulation of these metals in the peat. This was confirmed by investigating the distribution of radionuclides in local mire, which revealed considerable accumulation of uranium and thorium along the edges of the mire. Based on the inventories of uranium and thorium and their distribution in the peat it was concluded that the mire historically had been a sink for these metals and that it most likely will continue to be so for a long time to come. All and all, wetlands were estimated to decrease the fluxes of metals from the boreal forests to downstream lakes and oceans by 20-40%, depending on how strongly they bind to organic matter.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. 36 p.
uranium thorium metal transport radionuclide wetland forest stream peat mire
National Category
Environmental Sciences Geochemistry
Research subject
Physical Geography
urn:nbn:se:umu:diva-80485 (URN)978-91-7459-714-1 (ISBN)
Public defence
2013-10-11, KBC-huset, Lilla hörsalen, Umeå universitet, Umeå, 13:00 (English)
Available from: 2013-09-20 Created: 2013-09-18 Last updated: 2013-09-18Bibliographically approved

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Lidman, Fredrik
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