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| Titel |
Evaluation of commercial magnetic iron oxides as sediment tracers in water erosion experiments |
| VerfasserIn |
G. Guzman, V. Barron, J. A. Gómez |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025808
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| Zusammenfassung |
| Water erosion is one of the mayor concerns to sustainability of agricultural systems
in Mediterranean countries, e.g. olive farming areas in Southern Spain. Despite
an increase in the number of published studies on erosion rates and conservation
measures, significant uncertainty persists on actual erosion rates in these areas (Gómez
et al., 2008; Fleskens and Stroosnijder, 2007). Due to the limitations and cost of
technologies traditionally used in erosion measurement, there is a growing interest in
the use of innovative erosion tracers that could be applied to the soil and used to
monitor erosion and deposition rates at experiments performed at different scales and
environments. An example of these innovative traces, which could complement
the potential of more traditional tracers like Cs-137, is rare earths oxides. Due to
its size, D50 ranging from 1.23 to 16.38 μm (Zhang et al., 2003), these rare earth
oxides tagged soil aggregates more or less homogeneously and have been used in
tracking sediment movement at laboratory and field scale, e.g. Polyakov and Nearing,
(2004).
One of the shortcomings of the use of rare earth oxides in the cost derived of the need to
use Inductive Coupled Plasma Mass Spectrometry to determine its concentration in the
tagged soil. The use of mineral magnetic measurements provide a less expensive alternative
to complement erosion and sediment delivery in eroding landscapes (Royall, 2001), and is
also an area of active research. However, most of the studies are based on measurements of
magnetic properties inherent to soil materials, and little research has been done about the
possibility of tagging soils with magnetic materials. Ventura et al. (2002) tagged a
loamy soil with a magnetic tracer for use in rainfall simulation experiments. They
concluded that the magnetic tracer used, magnetic beads of 3.2 mm of mean weight
diameter, although useful in determining erosion and deposition areas presented a
tracer to soil ratio that did not remain constant, probably due to the large size of
the tracer, and hence impede their use in quantifying erosion and sedimentation
rates.
This communication presents our current results on the evaluation of the potential
use of magnetic iron oxides (Fe3O4), sold commercially as a pigment, as erosion
tracers. Due to its size, similar to that or rare earth oxides, and little mobility in soils
they have the potential to substitute, or complement, rare earth oxides as a tracer
elements, with the advantage of using non-expensive and quick measurements,
magnetic susceptibility, instead of ICPMS. This communication will present our
preliminary results on the performance of these magnetic tracers that were applied as
a dry mixed on the soil following the methodology of Zhang et al. (2003). Our
results suggest that the tagged soil following this methodology vary moderately
their average aggregate size distribution in most of the cases, Table 1, although not
systematically.
Soil D50 (mm) Significant diferences p 8000 15.66 1.10E-05
> 4000 14.66 1.22E-05
> 2000 11.53 1.22E-05
> 1000 7.12 1.13E-05
> 500 5.59 1.38E-05
> 250 6.29 1.44E-05
> 125 14.41 1.30E-05
> 63 16.30 1.50E-05
> 45 6.17 1.98E-05
> 25 2.21 2.23E-05
> 10 0.05 3.55E-05
Percolation tests suggest that the magnetic oxide used is strongly bond to the soil
aggregates, and it is not significantly leached to deeper soil layer, not tagged, trough
percolated water, Table 3.
Soil Before percolation test (m-3 kg-1) After percolation test (m-3 kg-1)
Average Stdsv Average Stdsv
Alameda 1.40E-05 9.24E-07 1.34E-05 7.43E-07
Benacazón 1.48E-05 3.54E-07 1.36E-05 2.76E-07
Conchuela 1.31E-05 1.67E-06 1.35E-05 7.39E-07
Pedrera 1.28E-05 1.38E-06 1.36E-05 2.91E-07
Table 3: Magnetic susceptibility of tagged soil layer before and after the percolation
test.
Evaluation of the soil loss estimated trough variation of magnetic susceptibility of the
tagged soil layer on soil boxes, 0.7 m2, during rainfall simulation tests provides an indication
of the viability of this technique to estimate soil losses by water erosion without
direct collection of the lost runoff and sediment, Table 4. It is important to indicate
that results in Table 4 were obtained using bulk density values that incorporate the
effect of soil consolidation on the variation of the magnetic susceptibility of the
soil.
Soil Measured soil losses (t/ha) Estimated soil losses (t/ha)
S1 S2 S3 S1 S2 S3
Alameda 11.37 27.98 47.15 17.73 17.60 53.43
Benacazón 1.88 6.87 14.78 - 10.73 19.42
Conchuela 16.80 46.66 86.58 23.30 47.56 89.27
Pedrera 14.03 33.38 52.33 22.72 31.48 46.44
Table 4: Measured and estimated cumulative soil losses (t/ha) of four soils after three
rainfall simulations.
References
Fleskens, L., Stroosnijder, L., 2007. Is soil erosion in olive groves as bad as often
claimed? Geoderma 141, 260–271
Gómez, J.A., Giráldez, J.V., Vanwalleghem, T. 2008. Comments on “Is soil erosion in
olive groves as bad as often claimed?” by L. Fleskens and L. Stroosnijder. Geoderma 147:
93-95.
Polyakov, V.O., Nearing, M.A. 2004. Rare earth element oxides for tracing sediment
movement. Catena 55: 255-276.
Royall, D. 2001 Use of mineral magnetic measurements to investigate soil erosion and
sediment delivery in a small agricultural catchment in limestone terrain. Catena 46:
15-34.
Ventura, E., Nearing. M.A., Amore, E., Norton, L.D. 2002. The study of detachment and
deposition on a hillslope using a magnetic tracer. Catena 48:149-161.
Zhang, X.C., Nearing, M.A., Polyakov, V.O., Friedrich, J.M. 2003. Using rare-eart oxide
tracers for studying soil erosion dynamics. Soil Sci. Soc. of Am. J. 67: 279-288. |
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