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| Titel |
Radiocarbon and geochemical constraints on shallow groundwater recharge in a large arid zone river, Cooper Creek, SW Queensland, Australia |
| VerfasserIn |
Joshua Larsen, Dioni Cendón, Gerald Nanson, Brian Jones |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250044037
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| Zusammenfassung |
| In the arid and semi-arid internally drained Lake Eyre Basin of central Australia, large mud
dominated anabranching river systems transport monsoon derived floodwaters into the centre
of the continent during the summer months, and subsequently spend much of the year under
low to no flow conditions. Cooper Creek has the largest catchment in this basin, and in south
west Queensland has a wide (20-60km) floodplain and multiple channel system. Enlarged
channel segments, known as waterholes or billabongs, can retain water throughout much of
the dry season, and their mud base can often be scoured during floods into the underlying
sandy alluvium where the shallow groundwater table exists ~3-5m below the base of
the waterholes. Little is known of the groundwater recharge mechanisms in this
ecologically important and hydrologically unregulated river system, thus a number of
piezometer transects were construct across the floodplain between two waterholes to
investigate groundwater recharge processes in further detail. Samples recovered from all
piezometers were analysed for major-trace element, water stable isotopes (δ2H and
δ180), 3H and 14C. Water stable isotopes reveal shallow groundwater is recharged by
high magnitude, low frequency monsoonal flood events, with minor evaporative
enrichment probably linked to recent smaller flooding events. 14C dating of dissolved
inorganic carbon reveals recharge is most effective beneath the deepest channel
segments of the waterholes, and that residence time of the shallow groundwater
increases with distance from major waterholes, with the post 1950’s 14C bomb pulse
signature present only in close proximity to the channels. 3H allows further refinement
of the shallow groundwater residence times, with no 3H detected in groundwater
over ~500m from the waterholes, indicating groundwater recharge is slow and
restricted to major flooding events. The increase in groundwater residence time with
distance from waterholes, is also accompanied by an abrupt increase in salinity, and
suggests recent recharge has formed local freshwater lenses above the regional,
more saline groundwater. This increase in salinity with increasing distance from the
waterholes is not accompanied by an increase on the evaporative signal of water stable
isotopes, suggesting evapotranspiration is the dominant mechanism of salinisation
within the shallow groundwater beneath the floodplains and minor channels. This
study demonstrates that detailed chemical analysis of groundwaters from arid and
semi arid areas can provide a useful estimate of recharge where the remote location
makes traditional detailed borehole monitoring difficult or impossible to achieve. |
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