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| Titel |
Impact of sediment heterogeneity on nutrient reactions in rippled streambeds |
| VerfasserIn |
Laura Bardini, Fulvio Boano, Meinhard B. Cardenas, Audrey H. Sawyer, Roberto Revelli, Luca Ridolfi |
| 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 |
250078658
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| Zusammenfassung |
| The interactions between hydraulic and biogeochemical processes in streambeds play a
relevant role for water quality of riverine ecosystems. Streambeds are commonly
characterized by heterogeneous permeabilities as a result of a number of preferential
sedimentation and entrainment of sediments with different size and other diagenetic
processes. Sediment heterogeneity is known to influence water and nutrient exchange with
the stream, but the understanding of its role on nutrient transformation is far from being
complete.
In this work we studied the effect of permeability heterogeneity at bedform scale on the
chemical zonation in a rippled streambed. We considered two heterogeneous permeability
cases derived from field observations, and we numerically simulated patterns of DOC,
dissolved oxygen, and inorganic nitrogen (NO3-, NH4+) within the streambed. We then
compared the simulation results with the concentrations and reaction rates in an equivalent
homogeneous streambed to identify the role of permeability heterogeneity on nutrient
transformations.
Our results show that sediment heterogeneity has a relevant impact on water flow paths
while it does not dramatically alter concentration patterns and nutrient reaction rates. The
reason is that distributions of residence times, that control the reactions, are similar
for the heterogeneous and homogeneous cases. Our findings suggest that water
residence times should be a better indicator and predictor of subsurface reactions than
porewater flow patterns. The variations of permeability have also shown to not alter the
role of the streambed as source/sink of NO3-, observed for different in-stream
concentrations. This result implies that the study of nitrogen fate in shallow stream sediments
does not require a detailed knowledge of bedform-scale permeability variations. |
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