Darling River Fish Death Explainer

Filed under Environment & Pollution, News, Science & Research ~ by Press on  14 Jan 2019

Dead fish litter the banks of a riverAn estimated million fish suffocated in the Murray Darling basin as water oxygen levels plummeted when algae died.

Poor water management was widely blamed. However, mass fish deaths can also be caused by floods, and even raw sewage.

So what’s going on when oxygen gets “sucked out of the water”?

The phenomenon is very well known to water quality engineers – we call it “biochemical oxygen demand” (BOD).

Rivers can replenish their oxygen from contact with the air. However this is a relatively slow process, especially if the water is stagnant (flowing creates turbulence and mixes in more oxygen). So if there is a lot of organic matter present and bacteria are feasting on it, oxygen concentrations in the river can suddenly drop.

In the case of the Darling river, the high BOD load was created by algae, which died when temperatures dropped. This provided a feast for bacteria, lowering oxygen, which in turn killed hundreds of thousands of fish.

Now, unless we clean the river, those rotting fish could become fodder for another round of bacteria, triggering a second de-oxygenation event.

Read the full article at TheConversation

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