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| Titel |
Insights and questions raised from a multi-tracer plot-scale sprinkler experiment with time-lapse 3D GPR in a structured forested soil. |
| VerfasserIn |
Conrad Jackisch, Matthias Sprenger, Niklas Allroggen, Loes van Schaik, Markus Weiler, Erwin Zehe |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097108
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| Publikation (Nr.) |
 EGU/EGU2014-12656.pdf |
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| Zusammenfassung |
| Stable isotopes appear as ideal tracer commonly applied in preferential flow analyses. At the
same time, central assumptions about signature mixing and propagation are founded on
effective parameters merging advective and diffusive flow domains. However, in structured
soils conditions are often far from well-mixed and some established assumptions may need to
be reconsidered.
We conducted a multi-tracer sprinkler experiment at a forested hillslope in the Attert Basin in
Luxembourg with prevailing geogenic and biogenic preferential flow structures. At plot scale
of 1x1 m2 we sprinkled two plots with 50 mm and one plot with 30 mm Brilliant Blue and
Bromide enriched water for 1 hour. The experiments were accompanied by a high resolution
3D time-lapse GPR (Ground-Penetrating Radar) survey scanning 3x3 m2 before, directly
after sprinkling and before excavation one day after sprinkling. Soil moisture was monitored
with a TDR tube probe. Soil profiles were excavated and recorded for dye flow paths and for
one medium resolution Bromide profile. In addition one core for pore water stable
isotope analysis was taken before the sprinkling as reference and at each plot after
sprinkling.
We present the results with focus on the found evidence of preferential flow and the
signals of the different tracers - especially the stable isotopes. While all other methods clearly
show that only minor proportions of the soil took part in the infiltration process and that the
sprinkler water has largely advectively propagated to the saprolite layer at about 80-100 cm
depth, the stable isotopes signals from the cores indicate more intense interaction between the
soil matrix and macropores, especially in the top 50 cm. This leads to the question
of how the isotope signal could mix well, when most of the pore-water did not
directly interact with the infiltration-water. Further questions arise to the use of
tracers in general, due to the known limitations of excavation itself and rather coarse
sampling with sizes 1-2 orders of magnitude larger than most preferential flow
structures - thus blurring the signal. Moreover, considerable uncertainty arises where
intense staining may be due to slow water movement or large quantities of infiltrated
water. Here time-lapse GPR provides promising insights identifying patterns and
states. Moreover, we will discuss whether the use of multiple tracers instead of
just one leads to additional information and better understanding of subsurface
processes. |
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