A tracer experiment to study flow paths of water in a forest soil

  • Feyen H
  • Wunderli H
  • Wydler H
 et al. 
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Abstract

This contribution discusses a tracer experiment, which was performed
to study the flow paths of water in a macroporous forest soil. The
experiment was performed in the framework of a study on the cycling
of nitrogen in forested Prealpine catchments, in which losses of
nitrate from virtually pristine areas were observed. Two soil plots
with distinct micro-topography and top-soil were investigated: a
well drained mor humus on a mound and a wet muck humus in a small
depression. To reveal the effect of the soil horizons on the flow
regime, tracers were applied both onto the soil surface and injected
into the sub-soil. Tracers injected directly into the gleyic sub-soil
reached the outlet (at a distance of 3.3 m) about 1000 times faster
than could be expected from the saturated hydraulic conductivity
of the soil matrix. Peak concentrations were observed after 18 (muck
humus, tracer recovery 31%) to 70 min (mor humus, tracer recovery
40%). The peak concentration was 10 times smaller on the drier mor
humus plot as compared to the muck humus. The mobile water content
of the sub-soil varied between 0.5 (muck humus) and 1.3% (mor humus)
of the total available soil water. The discrepancy in residence time,
peak concentration and volume of mobile water between both sub-soils
can be attributed to the differently structured sub-soil (longer
travel distance and mixing volume in the drier mor humus). Tracers
applied onto the soil surface resulted in a much slower breakthrough
(tracer peaks after 400-700 min). Thus, in contrast to the sub-soil,
flow through the matrix was the predominating transport process in
the upper humus layers of both plots.

Author-supplied keywords

  • Forest soil
  • Hydrology
  • Macropore flow
  • Nitrogen cycle
  • Plot scale
  • Tracer experiments

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Authors

  • H Feyen

  • H Wunderli

  • H Wydler

  • A Papritz

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