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The importance of colloids and mires for the transport of uranium isotopes through the Kalix River watershed and Baltic Sea

Porcelli, D. and Andersson, P. S. and Wasserburg, G. J. and Ingri, J. and Baskaran, M. (1997) The importance of colloids and mires for the transport of uranium isotopes through the Kalix River watershed and Baltic Sea. Geochimica et Cosmochimica Acta, 61 (19). pp. 4095-4113. ISSN 0016-7037. doi:10.1016/S0016-7037(97)00235-4.

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The importance of colloids and organic deposits for the transport of uranium isotopes from continental source regions and through the estuarine environment was investigated in the mire-rich Kalix River drainage basin in northern Sweden and the Baltic Sea. Ultrafiltration techniques were used to separate uranium and other elements associated with colloids > 10 kD and >3 kD from "solute" uranium and provided consistent results and high recovery rates for uranium as well as for other elements from large volume samples. Uranium concentrations in 0.45 µm-filtered Kalix River water samples increased by a factor of 3 from near the headwaters in the Caledonides to the river mouth while major cation concentrations were relatively constant. ^(234)U/^(238)U ratios were high (δ^(234)U = 770-1500) throughout the basin, without showing any simple pattern, and required a supply of ^(234)U-rich water. Throughout the Kalix River, a large fraction (30-90%) of the uranium is carried by >10 kD colloids, which is compatible with uranium complexation with humic acids. No isotopic differences were found between colloid-associated and solute uranium. Within the Baltic Sea, about half of the uranium is removed at low salinities. The proportion that is lost is equivalent to that of river-derived colloid-bound uranium, suggesting that while solute uranium behaves conservatively during estuarine mixing, colloid-bound uranium is lost due to rapid flocculation of colloidal material. The association of uranium with colloids therefore may be an important parameter in determining uranium estuarine behavior. Mire peats in the Kalix River highly concentrate uranium and are potentially a significant source of recoil ^(234)U to the mirewaters and river waters. However, mirewater data clearly demonstrate that only small ^(234)U/^(238)U shifts are generated relative to inflowing groundwater. A simple box model of uranium accumulation in peat and transport through the mire that is compatible with the mire data demonstrates that with efficient removal of uranium from solution, only small shifts in ^(234)U/^(238)U ratios can be generated in mirewater uranium. The measurements and model calculations show that mirewaters are not the primary source of the uranium in the river. Bedrock groundwaters with high ^(234)U/^(238)U ratios and uranium concentrations must be the dominant source of riverine uranium.

Item Type:Article
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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 1997 Elsevier Science Ltd. Received February 3, 1997; accepted in revised form June 3, 1997. This work was supported by DOE grant DEFG-03-88ER-13851 and by a Swedish Natural Science Research Council (NFR) grant to PSA (G/GU 06331-311, G/GU 06331-312). Conversations with James Chen, Dimitri Papanastassiou, and Allan Rodhe are greatly appreciated. We thank the Swedish Meteorological and Hydrological Institute for allowing us to participate in the R.V. Argos cruise. Magnus Hedberg provided invaluable technical and field support and kindly determined 14C peat ages. Magnus Land generously provided groundwater samples. This is Div. Contr. No. 5690 (945).
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG03-88ER13851
Swedish Natural Science Research Council (NFR)G/GU 06331-311
Swedish Natural Science Research Council (NFR)G/GU 06331-312
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Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5690
Lunatic Asylum Lab945
Issue or Number:19
Record Number:CaltechAUTHORS:20131119-114514566
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Official Citation:D. Porcelli, P.S. Andersson, G.J. Wasserburg, J. Ingri, M. Baskaran, The importance of colloids and mires for the transport of uranium isotopes through the Kalix River watershed and Baltic Sea, Geochimica et Cosmochimica Acta, Volume 61, Issue 19, October 1997, Pages 4095-4113, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42570
Deposited By: Ruth Sustaita
Deposited On:19 Nov 2013 22:40
Last Modified:10 Nov 2021 16:25

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