Journal
CANADIAN JOURNAL OF EARTH SCIENCES
Volume 49, Issue 6, Pages 758-771Publisher
CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
DOI: 10.1139/E2012-025
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- Natural Sciences and Engineering Research Council of Canada (NSERC)
- PFSN
- FFCR
- NSERC Northern Research Chair
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This study documents the spatiotemporal variability of riverine uranium contents and fluxes in rivers discharging into the Hudson, James, and Ungava bays (HJUB). Samples retrieved during a monitoring program of the Koksoak, Great Whale, La Grande, and Nelson rivers were analyzed for dissolved uranium concentration [U] and activity ratio (U-234/U-238). Field surveys conducted during baseflow and snowmelt in six other rivers of the HJUB basin provided complementary data. It is estimated that altogether, the studied rivers export 3.4 x 10(5) mol/year of U towards the HJUB, with a discharge weighted average (U-234/U-238) of 1.27. Two main factors appear to control seasonal fluctuations in dissolved U exports from HJUB rivers: snowmelt and anthropogenic flow control. Under natural hydrological regimes, the dilution of U caused by snowmelt does not compensate for the associated increase in discharge, and riverine U fluxes are intensified during springtime. Contrastingly, the timing of riverine U exports is decoupled from hydroclimatic conditions in rivers affected by flow-control structures. Despite the seasonal variations in riverine U contents, the sampling profiles carried along two of the monitored rivers reveal that within the study region, sample locality is at least as important as sampling time for evaluating riverine U fluxes. In addition, a compilation of data from North American rivers reveals that spatial variations in riverine U contents seem to respond to a prominent lithological control, as rivers draining sedimentary rocks (with abundant carbonates) tend to present overall higher U contents and lower (U-234/U-238) variability than the rivers of the Canadian Shield.
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