『Abstract
The uranium (U) content and 234U/238U activity
ratio were determined for water samples collected from Korea's
Han River in spring, summer, and winter 2006 to provide data that
might constrain the origin of U isotope fractionation in river
water and the link between U isotope systematics in river waters
and the lithological nature of the corresponding bedrock. The
large difference in the major dissolved loads between the two
major branches of the Han River, the North Han River (NHR) and
South Han River (SHR), is reflected in the contrasting U content
and 234U/238U activity ratio between the
tributaries: low U content (0.08-0.75 nM; average, 0.34 nM) and
small 234U/238U activity ratio (1.03-1.22;
average, 1.09) in the NHR; and high U content (0.65-1.98 nM; average,
1.44 nM) and large 234U/238U activity ratio
(1.05-1.45; average, 1.24) in the SHR. The large spatial differences
in U content and 234U/238U activity ratio
are closely related to both lithological differences between the
two tributaries and groundwater input. The low U content and small
234U/238U activity ratio in the NHR arise
mainly from a combination of surface and meteoric weathering of
the dominant silicate rocks in this branch and congruent dissolution
of already weathered (secular equilibrium) materials. In contrast,
the high U content and large 234U/238U activity
ratio in the SHR are ascribed to the dissolution of carbonates
and black shales along with significant inputs of deep groundwater.
Keywords: 234U/238U fractionation; Silicate
weathering; Carbonate dissolution; Black shale; Groundwater input;
Han River』
1. Introduction
2. Study area
2.1. Geography and climate
2.2. Geology
3. Sampling and analytical methods
4. Results
4.1. Major elements and Sr isotopes
4.2. Uranium isotopes
5. Discussion
5.1. Seasonal variation
5.2. Spatial variation
5.3. Role of groundwater input
6. Conclusions
Acknowledgements
References