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| Titel |
Soil water storage, mixing dynamics and resulting travel times through the
critical zone in northern latitudes |
| VerfasserIn |
Matthias Sprenger, Doerthe Tetzlaff, Markus Weiler, Chris Soulsby |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149752
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| Publikation (Nr.) |
 EGU/EGU2017-14134.pdf |
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| Zusammenfassung |
| Water partitioning in the unsaturated zone into groundwater recharge, plant transpiration, and
evaporation is fundamental for estimating storages and travel times. How water is
mixed and routed through the soil is of broad interest to understand plant available
water, contamination transport and weathering rates in the critical zone. Earlier
work has shown how seasonal changes in hydroclimate influence the time variant
character of travel times. A strong seasonality characterizes the northern latitudes
which are particularly sensitive to climate and land use changes. It is crucial to
understand how variation and change in hydroclimate and vegetation phenology
impact time variant storage dynamics and flow path partitioning in the unsaturated
zone.
To better understand the influence of these ecohydrological processes on travel times of
evaporative, transpiration and recharge fluxes in northern latitudes, we characterized soil
physical properties, hydrometric conditions and soil water isotopic composition in the
upper soil profile in two different land scape units in the long term experimental
catchment, Bruntland Burn in the Scottish Highlands. Our two sampling locations
are characterized by podzol soils with high organic matter content but they differ
with regard to their vegetation cover with either Scots Pine (Pinus sylvestris) or
heather (Calluna sp. and Erica Sp). To assess storage and mixing dynamics in the
vadose zone, we parameterized a numerical 1-D flow model using the soil textural
information along with soil moisture and soil water stable isotopes (δ2H and δ18O). The
water flow and transport were simulated based on the Richards and the advection
dispersion equation. Differences between water flows of mobile and tightly bound
soil waters and the mixing between the two pore spaces were considered. Isotopic
fractionation due to evaporation from soil and interception storage was taken into
account, while plant water uptake did not alter the isotopic composition of the soil
water.
The soil physical model was then used for each sampling location to calculate travel times
in a forward mode by introducing a virtual tracer with the precipitation and tracking the fate
of this input signal through the unsaturated zone. This allowed us to derive location-specific
time variant travel times for groundwater recharge, plant transpiration, and soil evaporation
on a daily basis. We especially aimed to assess the influence of plants on the dynamics in the
unsaturated zone. With the analysis ongoing, we expect to find length of vegetation
dormancy and rooting depth relevant for the travel times of the plant water uptake. We
further expect that the rainfall pattern and seasonal evapotranspiration dynamics will
govern the temporal dynamics of the recharge travel times. Our results emphasize
the importance of the vadose zone catchment storage on the non-linear catchment
response resulting from the sensitivity of the soil water dynamics in the upper soil
profile to seasonally variable hydroclimatic forcing and ecohydrological interactions. |
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