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Titel |
Hydrodynamic controls on oxygen dynamics in a riverine salt wedge estuary, the Yarra River estuary, Australia |
VerfasserIn |
L. C. Bruce, P. L. M. Cook, I. Teakle, M. R. Hipsey |
Medientyp |
Artikel
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Sprache |
Englisch
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ISSN |
1027-5606
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Digitales Dokument |
URL |
Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 4 ; Nr. 18, no. 4 (2014-04-10), S.1397-1411 |
Datensatznummer |
250120331
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Publikation (Nr.) |
copernicus.org/hess-18-1397-2014.pdf |
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Zusammenfassung |
Oxygen depletion in coastal and estuarine waters has been increasing rapidly
around the globe over the past several decades, leading to decline in water
quality and ecological health. In this study we apply a numerical model to
understand how salt wedge dynamics, changes in river flow and temperature
together control oxygen depletion in a micro-tidal riverine estuary, the
Yarra River estuary, Australia. Coupled physical–biogeochemical models have
been previously applied to study how hydrodynamics impact upon seasonal
hypoxia; however, their application to relatively shallow, narrow riverine
estuaries with highly transient patterns of river inputs and sporadic
periods of oxygen depletion has remained challenging, largely due to
difficulty in accurately simulating salt wedge dynamics in morphologically
complex areas. In this study we overcome this issue through application of a
flexible mesh 3-D hydrodynamic–biogeochemical model in order to predict the
extent of salt wedge intrusion and consequent patterns of oxygen depletion.
The extent of the salt wedge responded quickly to the sporadic riverine
flows, with the strength of stratification and vertical density gradients
heavily influenced by morphological features corresponding to shallow points
in regions of tight curvature ("horseshoe" bends). The spatiotemporal
patterns of stratification led to the emergence of two "hot spots" of
anoxia, the first downstream of a shallow region of tight curvature and the
second downstream of a sill. Whilst these areas corresponded to regions of
intense stratification, it was found that antecedent conditions related to
the placement of the salt wedge played a major role in the recovery of
anoxic regions following episodic high flow events. Furthermore, whilst a
threshold salt wedge intrusion was a requirement for oxygen depletion,
analysis of the results allowed us to quantify the effect of temperature in
determining the overall severity and extent of hypoxia and anoxia. Climate
warming scenarios highlighted that oxygen depletion is likely to be
exacerbated through changes in flow regimes and warming temperatures;
however, the increasing risk of hypoxia and anoxia can be mitigated through
management of minimum flow allocations and targeted reductions in organic
matter loading. A simple statistical model (R2 > 0.65) is
suggested to relate riverine flow and temperature to the extent of
estuary-wide anoxia. |
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