Particle transport of ^(234)U-^(238)U in the Kalix River and in the Baltic Sea

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Andersson, P. S., Porcelli, D., Wasserburg, G. J., Ingri, J.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 1998
• Subjects: Kalix; Northern Sweden
• Online Access: https://doi.org/10.1016/S0016-7037(97)00342-6

The role of particles for U isotope transport was investigated in the Kalix River watershed, a particle-poor, Fe/Mn-rich river in northern Sweden, and in the Baltic Sea estuary. Particles >0.45μm are strongly enriched in U and contain 20-50% of the total riverine uranium budget and <1% of the total U in brackish waters (3-7 PSU). The particles have high δ^(234)U which is close to that of dissolved U in the associated water, indicating that U on particles is dominantly nondetrital and isotopically exchanges rapidly with the ambient dissolved U. Particles at the river mouth are dominated by nondetrital Fe-Mn oxyhydroxides. Uranium and Fe are strongly correlated, clearly demonstrating that secondary Fe-oxyhydroxide is the major carrier of U in river water. There is no evidence for significant association of U with Mn-oxyhydroxide. Apparent U distribution coefficients (K_d^(Fe)) were calculated for U between the authigenic Fe on particles and the solution. These values appear to be relatively constant throughout the year. This suggests an equilibrium between Fe in solution and authigenic Fe-oxyhydroxides on detrital particles. High values of K_d^(Fe) calculated for one summer as well as high U concentrations in brackish waters can be explained by U scavenging by biogenic phases with low authigenic Fe content. © 1998 Elsevier Science Ltd. Received June 18, 1997; accepted in revised form September 24, 1997. This work was supported by Swedish Natural Science Research Council grants G/GU 06331-311 and G/GU 06331-312 to PSA and DOE grant DE-FG-03-88ER-13851. We thank the Swedish Meteorological and Hydrological Institute for allowing us to participate in the R/V Argos cruise. Magnus Hedberg gave us invaluable support. Reviews by J. Edmond and D. Turner significantly improved the manuscript. This is Div. Contr. No. 5695 (950).