Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany
A dual stable water isotope (<i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and gro...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-09-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/20/3873/2016/hess-20-3873-2016.pdf |
| Summary: | A dual stable water isotope (<i>δ</i><sup>2</sup>H and <i>δ</i><sup>18</sup>O) study was conducted in the developed (managed) landscape of the Schwingbach
catchment (Germany). The 2-year weekly to biweekly measurements of
precipitation, stream, and groundwater isotopes revealed that surface and
groundwater are isotopically disconnected from the annual precipitation cycle
but showed bidirectional interactions between each other. Apparently,
snowmelt played a fundamental role for groundwater recharge explaining the
observed differences to precipitation <i>δ</i> values.
<br><br>
A spatially distributed snapshot sampling of soil water isotopes at two soil
depths at 52 sampling points across different land uses (arable land,
forest, and grassland) revealed that topsoil isotopic signatures were
similar to the precipitation input signal. Preferential water flow paths
occurred under forested soils, explaining the isotopic similarities between
top- and subsoil isotopic signatures. Due to human-impacted agricultural land
use (tilling and compression) of arable and grassland soils, water delivery
to the deeper soil layers was reduced, resulting in significant different
isotopic signatures. However, the land use influence became less pronounced
with depth and soil water approached groundwater <i>δ</i> values.
Seasonally tracing stable water isotopes through soil profiles showed that
the influence of new percolating soil water decreased with depth as no
remarkable seasonality in soil isotopic signatures was obvious at depths
> 0.9 m and constant values were observed through space and time.
Since classic isotope evaluation methods such as transfer-function-based
mean transit time calculations did not provide a good fit between the
observed and calculated data, we established a hydrological model to
estimate spatially distributed groundwater ages and flow directions within
the Vollnkirchener Bach subcatchment. Our model revealed that complex age
dynamics exist within the subcatchment and that much of the runoff must has
been stored for much longer than event water (average water age is 16 years).
Tracing stable water isotopes through the water cycle in combination
with our hydrological model was valuable for determining interactions
between different water cycle components and unravelling age dynamics within
the study area. This knowledge can further improve catchment-specific
process understanding of developed, human-impacted landscapes.</p> |
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| ISSN: | 1027-5606 1607-7938 |