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The Importance of colloids for the behavior of uranium isotopes in the low-salinity zone of a stable estuary

Andersson, Per S. and Porcelli, D. and Gustafsson, Ö. and Ingri, J. and Wasserburg, G. J. (2001) The Importance of colloids for the behavior of uranium isotopes in the low-salinity zone of a stable estuary. Geochimica et Cosmochimica Acta, 65 (1). pp. 13-25. ISSN 0016-7037. doi:10.1016/S0016-7037(00)00514-7.

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Particle-mediated removal processes of U isotopes were investigated during spring flood discharge in the low-salinity zone (LSZ, up to 3 practical salinity units [psu]) of a stable estuary. A shipboard ultrafiltration cross-flow filtration (CFF) technique was used to separate particles (>0.2 μm) and colloids (between 3000 daltons (3 kD) and 0.2 μm) from ultrafiltered water (<3 kD) containing “dissolved” species. Sediment traps were used to collect sinking material. Concentration of Fe and organic C, which are indicators of the major U carrier phases, were used to interpret the behavior of ^(234)U-^(238)U during estuarine mixing. Colloids dominated the river water transport of U, carrying ≈90% of the U. On entering the estuary, colloids accounted for the dominant fraction of U to about a salinity of 1 psu, but only a minor fraction (<5%) at 3 psu. A substantial fraction of the total U is removed at <1 psu by Fe-organic rich colloids that aggregate and sink during initial estuarine mixing in the Kalix River estuary. In contrast, at salinities >1 psu, there is a general correlation between U and salinity in all filtered fractions. The ^(234)U/^(238)U ratios in different filtered fractions and sinking particles were generally indistinguishable at each station and showed enrichment in ^(234)U, compared with secular equilibrium (δ^(234)U = 266–567). This clearly shows that all size fractions are dominated by nondetrital U. Consideration of U isotope systematics across the estuary reveals that substantial U exchange must occur involving larger particles at least to 1 psu and involving colloids at least to ≈1.5 psu. Further exchange at higher salinities may also occur, as the proportion of U on colloids decreases with increasing salinity. This may be due to decreasing colloid concentration and increasing stabilization of uranyl carbonate complexes during mixing in the estuary. The results show that although U is a soluble element that shows generally conservative mixing in estuaries, removal occurs in the very low salinity zone, and this zone represents a significant sink of U. Variation in composition and concentration of colloidal particles between different estuaries might thus be an important factor for determining the varying behavior of U between estuaries.

Item Type:Article
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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:© 2001 Elsevier Science Ltd. Received November 16, 1999; accepted in revised form July 14, 2000. This work was supported by grants from the Swedish Natural Science Research Council (NFR, G/GU 0631-314, 315, and 316) to PSA and the U.S. Dept. of Energy (DOE, DE-FG03-88ER13851 to G.J.W. For assistance during sampling we gratefully acknowledge H. Holmström, A. Widerlund, and M. Zacher. We thank the crew of R/V KBV005 and Umeå Marine Research Center for assistance and collaboration during fieldwork. The reviewer’s comments are much appreciated. This is CIT Div. Contr. No. 8608 (1025).
Funding AgencyGrant Number
Swedish Natural Science Research Council (NFR)G/GU 0631-314
Swedish Natural Science Research Council (NFR)G/GU 0631-315
Swedish Natural Science Research Council (NFR)G/GU 0631-316
Department of Energy (DOE)DE-FG03-88ER13851
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Caltech Division of Geological and Planetary Sciences8608
Lunatic Asylum Lab1025
Issue or Number:1
Record Number:CaltechAUTHORS:20131119-070801709
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Official Citation:Per S Andersson, D Porcelli, Ö Gustafsson, J Ingri, G.J Wasserburg, The importance of colloids for the behavior of uranium isotopes in the low-salinity zone of a stable estuary, Geochimica et Cosmochimica Acta, Volume 65, Issue 1, 1 January 2001, Pages 13-25, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42543
Deposited By: Ruth Sustaita
Deposited On:19 Nov 2013 15:45
Last Modified:10 Nov 2021 16:24

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