University of Wisconsin–Milwaukee

Data from the physics of water

Voracious invasive mussels create enough turbulence in the surrounding water that it actually disrupts Lake’s Michigan’s natural currents near the lake bottom.

Photo by Pete Amland
Qian Liao
Qian Liao, assistant professor of civil engineering and mechanics, modified equipment so that it operates in the lake, quantifying the physics of the air-water transfer process.

That is the initial finding of Qian Liao, assistant professor of civil engineering and mechanics, and Harvey Bootsma, a scientist with the School of Freshwater Sciences, when they applied a unique apparatus to the question of whether quaggas alter how nutrients in the lake are mixed.

Quaggas filter-feed by siphoning water containing phytoplankton and then expelling just the water, creating micro-jets. And they do it at an extraordinary rate, about three liters per mussel per day, according to consumption rates reproduced in a lab setting.
But to determine the rolemussels play in the mixing of nutrients, Liao and Bootsma must quantify that rate in the lake, rather than the lab.

Liao has modified a system called Particle Image Velocimetry (PIV), which captures images of very small particles and charts them as they move through the water. The system uses a vertical laser sheet that penetrates water, illuminating the flow and showing how the interplay between the lake current and the current created by the mussels’ filter-feeding can affect their consumption rate.

So far, the PIV equipment has shown that filtering can boost turbulence near the lake bottom by 40 to 80 percent compared to a portion of the bottom without mussels.

The two scientists also are applying the free-floating PIV equipment to another of Bootsma’s studies – the exchange of greenhouse gases between the lake and the atmosphere. Because his system quantifies the physics of the current air-water transfer models, Liao says he hopes the work will lead to improvements in the models.

“We want to be the first group to quantify how turbulence and other factors, like wind, waves, precipitation, and heat exchange across the air-water interface, affect the exchange of CO2 and other gases between the lake and atmosphere,” says Liao.