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| Titel |
Meta-analysis of the effects of soil properties, site factors and experimental conditions on solute transport |
| VerfasserIn |
J. K. Koestel, J. Moeys, N. J. Jarvis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 16, no. 6 ; Nr. 16, no. 6 (2012-06-13), S.1647-1665 |
| Datensatznummer |
250013326
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| Publikation (Nr.) |
 copernicus.org/hess-16-1647-2012.pdf |
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| Zusammenfassung |
| Preferential flow is a widespread phenomenon that is known to strongly
affect solute transport in soil, but our understanding and knowledge is
still poor of the site factors and soil properties that promote it. To
investigate these relationships, we assembled a database from the
peer-reviewed literature containing information on 733 breakthrough curve
experiments under steady-state flow conditions. Most of the collected
experiments (585 of the 733 datasets) had been conducted on undisturbed soil
columns, although some experiments on repacked soil, clean sands, and glass
beads were also included. In addition to the apparent dispersivity, we
focused our attention on three indicators of preferential solute transport:
namely the 5%-arrival time, the holdback factor, and the ratio of
piston-flow and average transport velocities. Our results suggest that, in
contrast to the 5%-arrival time and the holdback factor, the piston-flow
to transport velocity ratio is not related to preferential macropore
transport but rather to the exclusion or retardation of the applied tracer.
Confirming that the apparent longitudinal dispersivity is positively
correlated with the travel distance of the tracer, our results also
illustrate that this relationship is refined if the normalized 5%-tracer
arrival time is also taken into account. In particular, we found that the
degree of preferential solute transport increases with apparent dispersivity
and decreases with travel distance. A similar but weaker relationship was
observed between apparent dispersivity, 5%-tracer arrival time, and
lateral observation scale, such that the degree of preferential transport
increases with lateral observation scale. However, we also found that the
travel distance and the lateral observation scale in the investigated
dataset are correlated, which makes it difficult to distinguish their
influence on these transport characteristics. We also found that the
strength of preferential transport increased at larger flow rates and water
saturations, which suggests that macropore flow was a more important flow
mechanism than heterogeneous flow in the soil matrix. Nevertheless, our
data show that heterogeneous flow in the soil matrix also occasionally leads to
strong preferential transport. Furthermore, we show that preferential solute
transport under steady-state flow depends on soil texture in a
threshold-like manner: moderate to strong preferential transport was found
to occur only for undisturbed soils that contain more than 8% clay.
Preferential flow characteristics were also absent for columns filled with
glass beads, clean sands, or sieved soil. No clear effect of land use on the
pattern of solute transport could be discerned, probably because the
available dataset was too small and too strongly affected by cross-correlations
with experimental conditions. Our results suggest that, in developing
pedotransfer functions for solute transport properties of soils, it is
critically important to account for travel distance, lateral
observation
scale, and water flow rate and saturation. |
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