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| Titel |
Dimensionless Numbers For Morphological, Thermal And Biogeochemical Controls Of Hyporheic Processes |
| VerfasserIn |
Alberto Bellin, Alessandra Marzadri, Daniele Tonina |
| 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 |
250077525
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| Zusammenfassung |
| Transport of solutes and heat within the hyporheic zone are interface processes that gained
growing attention in the last decade, when several modelling strategies have been
proposed, mainly at the local or reach scale. We propose to upscale local hyporheic
biogeochemical processes to reach and network scales by means of a Lagrangian modelling
framework, which allows to consider the impact of the flow structure on the processes
modelled. This analysis shows that geochemical processes can be parametrized
through two new Damköhler numbers, DaO, and DaT. DaO = Ïup,50-Ïlim is
defined as the ratio between the median hyporheic residence time, Ïup,50 and the
time of consuming dissolved oxygen to a prescribed threshold concentration, Ïlim,
below which reductive reactions are activated. It quantifies the biogeochemical
status of the hyporheic zone and could be a metric for upscaling local hyporheic
biogeochemical processes to reach and river-network scale processes. In addition,
Ïup,50 is the time scale of hyporheic advection; while Ïlim is the representative time
scale of biogeochemical reactions and indicates the distance along the streamline,
measured as the time needed to travel that distance, that a particle of water travels
before the dissolved oxygen concentration declines to [DO]lim, the value at which
denitrification is activated. We show that DaO is representative of the redox status and
indicates whether the hyporheic zone is a source or a sink of nitrate. Values of DaO
larger than 1 indicate prevailing anaerobic conditions, whereas values smaller than
1 prevailing aerobic conditions. Similarly, DaT quantifies the importance of the
temperature daily oscillations of the stream water on the hyporheic environment. It is
defined as the ratio between Ïup,50, and the time limit at which the ratio between
the amplitude of the temperature oscillation within the hyporheic zone (evaluated
along the streamline) and in the stream water is smaller than e-1. We show that
values of DaT > 1 indicate a thermally stable hyporheic zone, where organism
metabolism is not influenced by surface water thermal oscillations and biogeochemical
reaction rates depend on the mean daily stream water temperature. Values smaller
than 1 suggest that organisms need to adapt to the daily thermal variations and
biogeochemical reaction rates will depend on the daily fluctuations induced by stream water. |
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