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| Titel |
Formation of the chemical composition of water in channel head in postglacial areas (West Pomerania, Poland) |
| VerfasserIn |
Malgorzata Mazurek, Robert Kruszyk, Grażyna Szpikowska |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128686
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| Publikation (Nr.) |
 EGU/EGU2016-8695.pdf |
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| Zusammenfassung |
| The channel head is a zone of hydrological changes determining the hydrochemical features
of water in the final stage of groundwater flow and the start of the surface cycle. The
chemistry of water flowing out of a channel head reflects not only the characteristics of
groundwater feeding the zone, but also changes it undergoes in this area during
the organisation of channel flow. Groundwater interacts with surface water in the
hyporheic zone where water from different environments is mixed and exchanged due to
high hydraulic and chemical gradients. The goal of this study was to assess spatial
differences in the concentrations of nutrients and compounds produced by chemical
weathering in a channel head and to establish the role of the hyporheic zone in the
transformation of the chemical composition of groundwater supplying a 1st-order stream.
The research area was the channel head Żarnowo, located on the southern slope of
the upper Parsęta valley. Three hydrochemical mappings were conducted in the
headwater alcove consisting of three parts developed in a glaciofluvial plain and an
erosional-accumulative alluvial terrace. Water was sampled in places of groundwater outflow
in the footslope zone (9 sites), the hyporheic zone (14 sites), and outflows in the
individual alcove parts and the rivulet they formed (5 sites). Water temperature,
pH, and electrical conductivity were measured in the field. Concentrations of K,
Ca, Mg, Na, Fe, Mn, HCO3, Cl, NO3, PO4, SO4 and SiO2 were determined in
the laboratory. The chemical composition of ground- and surface water shows the
concentration of geogenic components like K, Ca, Mg, Na, HCO3, and SiO2 to be an
effect of chemical weathering and the leaching of its products taking place in a
zero-discharge catchment. Those ions display little spatial variability and a stability of
concentration in individual measurement periods, while the greatest disproportions in their
concentrations among the alcove parts were recorded for Cl, NO3 and PO4, representing an
anthropogenic component. Like iron and manganese, nitrates are components with
the highest horizontal gradients of concentration in the alcove. Nitrate levels drop
considerably in each hyporheic zone. The levels of iron and manganese found in
porewater at the bottom of the alcove can be both high and low, which indicates a
highly local nature of their determinants in the hyporheic zone connected mainly
with changes in its hydrogeochemical conditions. This should be considered an
effect of biogeochemical processes involving a change in the oxidation level of
nitrogen in porewater. The bottom of the channel head is permanently waterlogged, fed
by water with a stable temperature of ca. 8.8∘C, and consequently supporting a
green Cardamino amarae-Beruletum erecti Turmanova 1985 community even in
winter. Plants are a source of organic matter, the decomposition of which brings
about an oxygen deficit necessary for the development of microorganisms deriving
oxygen from oxygen complexes of nitrogen. Those are conditions facilitating a
reduction of nitrates to free nitrogen and the migration of reduced forms of iron and
manganese. |
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