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the amount of erosion or deposition that has occurred, respectively. By quantifying
these differences, the magnitude of erosion or deposition since the onset of nuclide
accumulation can be estimated.
Advantages and constraints on the use of this approach have been summarized
by Mabit et al. ( 2008 ), Parsons and Foster ( 2011 ), Mabit et al. ( 2013 ), and, for
7 Be, Walling ( 2013 ). Three of the most commonly cited advantages are that (1) the
method does not involve the use of long-term monitoring equipment, but can quan-
tify erosional or depositional magnitudes using data/samples collected in a single
trip, (2) the estimates of soil loss are based on specific sampling locations that when
combined with data from other sampling locations can provide information on the
spatial variations in erosional and depositional magnitudes across the landscape as
well as for specific landscape elements, and (3) the approach provides retrospective
information on past erosional and depositional processes, something that contempo-
rary monitoring programs are incapable of doing. In addition, the use of more than
one radionuclide, each characterized by a different half-life, allows the magnitude
of erosion or deposition to be determined for a range of timeframes (Table 3.1 ).
Early studies, beginning in the 1960s and 1970s were primarily confined to
the plot scale, but more recent studies have refined the approach and applied it to
larger scales. Gaspar et al. ( 2013 ), for example, combined 137 Cs and 210 Pb ex data to
determine medium to long-term soil redistribution rates at the hillslope scale within
the Pre-Pyrenean Mountains of northeastern Spain. The upper part of the studied,
covered by forest vegetation and characterized by an average slope of 24%, was
found to be relatively stable, exhibiting minor amounts of erosion and deposition
(Fig. 3.6 ). The midslope, characterized by a wide range of land-use/land-cover types
(including patches of forest and terraced fields) was dominated by minor erosion over
the long-term (
100years) as determined by 210 Pb ex ; 137 Cs suggested that over the
medium term, erosion predominated, although local deposition also occurred. The
highest rates of erosion as assessed by 137 Cs were associated with actively culti-
vated areas, whereas abandoned fields exhibited lower rates of erosion. In fact, some
abandoned fields, along with the forested, midslope areas, were generally stable.
Deposition dominated the bottom of the slope characterized by cultivated fields but
a much reduced slope
. Significant erosion was locally noted at a site below a
pathway, suggesting that cultivation has affected soil mobilization along the bottom
of the slope as well. Althoughminor differences exist, there was general agreement in
the predominant processes occurring on the slope over the two timeframes provided
by 137 Cs and 210 Pb; in both cases, the data reflect local land-use and slope charac-
teristics. The detailed magnitudes of erosion and deposition were found, however, to
vary in a complex way across the hillslope through time.
A recent modification to the approach is to establish a sediment budget for a
hillslope or catchment on the basis of the FRN inventories. Sediment budgets are
often required for the development of effective watershed management plans as
they provide important insights into the primary sources of sediment that should
be targeted for remediation, the transfer of sediment between landscape elements
within the catchment, and the amount of sediment exported from the basin mouth
(Dietrich and Dunne 1978 ;Kelseyetal. 1981 ;Reidetal. 1981 ;Trimble 1983 ).
(
15%
)
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