Zoomix

Understanding the mixing generated by zooplankton

Turbulence measurements

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📥  Measurement, Turbulence, Vobster

 

Today I'm going to explain how we measure the turbulence in the lake. But first of all, what is the turbulence?  When I say "turbulence", most of you will think to the motion you experience while flying on an aircraft which is the result of the interaction of the plane with air jet streams in the atmosphere.

But here we are talking about turbulence in water. A swimmer usually can't "feel" the turbulence in a lake, you may in the ocean. We can think the turbulence as random and quick motions of water that move every particles within the lake, such as oxygen, algae and can also change the fluid temperature at very small scales. These movements are very quick and can last few seconds resulting in swirls that you can't actually see in the water (water is transparent!). If you put some dye in the water (see video  at the beginning) you will see that the tracer disperses as little and sometimes tiny eddies until it completely disappears.

Turbulence can be generated in several ways. For example you can stir the water in your tub with your hands or a Daphnia can move its arms (antennas to be precise) in the water like the beast in the video below:

And for my project we want to measure if those zooplankton motions can generate turbulence and how powerful it could be.

To do that we are using a microstructure profiler which measures very quick and tiny temperature variations due to water motions. This variations happen at very small scales (or micro scales that's why microstructure profiler) and are registered by the sensors shown in the image below. And with those tiny shafts, we're able to acquire 100 temperature values every 1 seconds! And the more the turbulence, the more these fluctuations can be.

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From the temperature variations we can estimate how much energy 1 kg of  water generates or dissipates, which is the main parameter we use to describe the turbulence.

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Jake with our microstructure profiler or Mr. SCAMP for friends.

Stay tuned for turbulence results for Daphnia in the next posts!

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