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| Titel |
Identifying flow processes in catchments with porewater isotope profiles |
| VerfasserIn |
Matthias Sprenger, Benjamin Gralher, Markus Weiler |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250072060
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| Zusammenfassung |
| Detecting the movement of water in the vadose and saturated zone in catchments is still a
challenging task in understanding hydrological processes. Little is known about the
interaction between spatial patterns and the subsurface processes to driving forces like
precipitation or radiation. Therefore, our study was aimed to gain new insights into the spatial
patterns of subsurface processes using porewater stable isotopes profiles. First, we drilled
holes to the depth of the soil-bedrock interface at 36 sites and took soil samples of each drill
core in 5 cm intervals. The sample locations are situated in the schistous part of the
Attert catchment in the Grand Duchy of Luxembourg and can be differentiated
according to their topography and vegetation cover into forested hillslopes and
grasslands at plateaus and in the riparian zones. The pore water of these soil samples
was analyzed for the isotopic composition (δ2H and δ18O) with the equilibration
method to derive δD and δ18O values as a function of soil depth. In the next step, we
simulated these isotope profiles with a physically based one-dimensional water flow
model, where rainfall amount, its isotopic composition, evapotranspiration with the
Penman-Monteith equation, and site specific soil physical parameters served as input
parameters. Finally, to test interactions between topographical descriptors and the patterns
in the isotope profiles, a generalized linear mixed model (GLMM) was applied.
The slope, topographic wetness index, elevation, aspect, distance to stream, soil
cover, and land use served as physically based variables. A comparison between the
observed and modeled isotope profiles allowed for detecting anomalies. The differences
between the variation of the measured isotopes on the one hand and the simulated
ones on the other hand could be attributed to the following processes: i) mixing of
water in the vadose zone due to both, temporally rising groundwater table and input
from percolating rainfall water, ii) evaporation processes in the top soil, and iii)
subsurface flow along the soil-bedrock interface. Which one of these processes
dominated at each site depended on the respective physiographic characteristics. The
results of the GLMM supported the hypothesis of an interplay between structural
and functional traits. The results suggests that information about the porewater
stable isotopic composition across the soil profiles seem to be a promising tool to
differentiate between the functional responses and flow pathways in catchments. |
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