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| Titel |
Runoff generation and storage dynamics of a polygonal tundra catchment, Lena River Delta, northern Siberia (Russia) |
| VerfasserIn |
Manuel Helbig, Julia Boike, Moritz Langer, Peter Schreiber, Benjamin R. K. Runkle, Lars Kutzbach |
| 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 |
250072696
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| Zusammenfassung |
| Present understanding of the hydrology of catchments underlain by permafrost is still
insufficient to correctly predict ecological impacts brought about by climate change.
Ice-wedge polygonal tundra is a typical landscape type of the continuous permafrost zone and
is characterised by a pronounced micro- but a flat meso-topography. It consists of polygon
sub-catchments with low-lying centres and surrounding elevated rims that feature a range of
connectedness to other polygons and the inter-rim surface drainage network of troughs above
degraded ice-wedges. This pattern distinguishes the hydrology of polygonal tundra from
other permafrost-affected landscapes. Therefore, this study aims to define the hydrological
functions of characteristic landscape units of polygonal tundra (i.e. polygon rims, centres,
and troughs). We examine runoff generation and water storage dynamics in a small polygonal
tundra catchment in northern Siberia (0.6 km2) by analysing spatially distributed
water balances together with catchment runoff dynamics between May and August
2011.
Despite the evapotranspiration rate (137.9 mm) exceeding precipitation (108.6 mm), and
the low topographic gradient, lateral outflow (60.9 mm – 167.4 mm) considerably influenced
the water storage of the main landscape units within the catchment. Low polygon centres with
intact rims stored snow melt water longer than either polygons with degraded rims or the
troughs. The micro-topography of the rims and the associated soil thaw dynamics determined
the magnitude and the timing of outflow through the blocking function of frozen soils. These
dynamics controlled the redistribution of storage water within the catchment during the
summer.
Hydraulic conductivity in the rims declines by three orders of magnitude within the first
15 cm of the soil. The high conductivities in the shallow soil layers cause a rapid shallow
subsurface drainage of rainwater towards the depressed centres and troughs. Once the rims
are deeply thawed, the re-release of storage water from the centres through deeper and less
conductive layers helps maintain a high water table in the surface drainage network of
troughs throughout the summer.
In turn, catchment runoff was mainly controlled (R2 = 0.99, RMSE = 0.34 L s-1, N =
2165) by the water level (i.e. hydraulic gradient) in this drainage network, and baseflow was
maintained throughout the study period. The interconnected network contracts and
expands in relation to the water level. Together with sharp declines of hydraulic
conductivity within the upper soil layers, this catchment characteristic favours the
observed exponential increase of catchment runoff with ascending water levels in
the network. This relationship promotes enhanced runoff as a response to large,
infrequent inputs of rain or snow melt water whereas vertical water fluxes dominate
during periods of frequent but homogeneously distributed rain events of smaller
magnitude.
This study shows that a nested approach is suitable to identify characteristic
hydrological processes at different scales and to assess how the hydrological functions of the
main landscape units interact on the catchment scale. The results emphasise the need to
account for micro-topography of polygonal tundra and temporal distributions of precipitation
and evapotranspiration when investigating the storage and runoff dynamics, and the
interactions with carbon or energy fluxes. |
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