Evaluating Use of Environmental Flows to Aerate Streams by Modelling the Counterfactual Case
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This paper evaluates an experimental environmental flow manipulation by modeling the counterfactual case that no environmental flow was applied. This is an alternate approach to evaluating the effect of an environmental flow intervention when a before-after or control-impact comparison is not possible. In this case, the flow manipulation is a minimum flow designed to prevent hypoxia in a weir on the low-gradient Broken Creek in south-eastern Australia. At low flows, low reaeration rates and high respiration rates associated with elevated organic matter loading in the weir pool can lead to a decline in dissolved oxygen concentrations with adverse consequences both for water chemistry and aquatic biota. Using a one dimensional oxygen balance model fitted to field measurements, this paper demonstrates that increased flow leads to increases in reaeration rates, presumably because of enhanced turbulence and hence mixing in the surface layers. By comparing the observed dissolved oxygen levels with the modeled counterfactual case, we show that the environmental flow was effective in preventing hypoxia.
KeywordsEnvironmental water Hypoxia Reaeration Dissolved oxygen Counterfactual case
This research was supported by the Commonwealth Environmental Water Office, Australia and was undertaken as part of a broader environmental monitoring program led by the Murray Darling Freshwater Research Centre (MDFRC). The project was also supported by the Australian Research Council (Project DP130103619). The project benefited from advice provided by Dr. Gavin Rees (MDFRC) and Geoff Earl (Goulburn Broken Catchment Authority).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no competing interests.
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