Geoscience Reference
In-Depth Information
Fig. 3.10
Two-box radionuclide mass-balance model developed by Dominik et al. (
1987
)and
modified by Le Cloarec et al. (
2007
) to assess sediment residence times in soil and river channels.
FA atmospheric fallout flux; SS area of soil; SR area of river; IS radioactive inventory in soil box;
IR radioactive inventory in river box; FR flux/export from river box (catchment);
constant of
radioactive decay; kS rate of output from soil box; kR rate of output from river (modified from
Evrard et al.
2010
)
ʻ
basis of the vertical distribution of
7
Be within the channel bed material. Fitzgerald
et al. (
2001
), for example, used
7
Be depth profiles to examine the amount of sediment
deposition and resuspension along a section of the Fox River in Wisconsin where the
resuspension of contaminated bed sediments is thought to be the primary source of
PCBs to the overlying water column and Green Bay. Fitzgerald et al. (
2001
) argue
that changes in
7
Be activity with depth are indicative of the timing and nature of scour
and fill. For a majority of the cores obtained from the channel bed
7
Be decreased
with depth. This downward decreasing trend in
7
Be activity is likely to result from
the continued deposition of
7
Be tagged sediment that, upon isolation from additional
atmospheric inputs, decays. Thus, the older sediments with the lowest activities are
at the bottom of the profile. In contrast, a peak in
7
Be activity at depth may be
produced by the slow deposition and mixing of
7
Be tagged sediment, followed by
the rapid deposition of diluted
7
Be containing sediment that buries enriched
7
Be
layer. The break in
7
Be activity can therefore be used to identify differences in the
rate of deposition, and potentially, the amount of deposition that occurred during an
individual event.
Search WWH ::
Custom Search