Tuesday, April 26, 2011

In the Wake of the Blades

An interesting confluence of science, two reports today on the effects of blades; one the effect of the blades used to propel boats on life in the bay:
A new study by researchers at the Virginia Institute of Marine Science shows that turbulence from boat propellers can and does kill large numbers of copepods—tiny crustaceans that are an important part of marine food webs.

The study—by VIMS graduate student Samantha Bickel, VIMS professor Kam Tang, and Hampton University undergraduate Joseph Malloy Hammond—appears in the March issue of the Journal of Experimental Marine Biology and Ecology.
 I don't doubt that spinning blades can kill zooplankton, but how bad is it in "real life"?
They compared the percentage of live and dead copepods collected from these sites using a dye that is only taken up by living copepods. The results of their comparison showed a much higher fraction of dead copepods in the channel (34%) than in the marina (5.9% dead) or along the shoreline (5.3%).

A field experiment in the York River near the VIMS campus confirmed the results of the Hampton River study. Here, they sampled copepods from within the wakes of passing boats, and again found a link between turbulence and mortality: the percentage of copepod carcasses increased from 7.7% outside the wakes to 14.3% inside the wakes.
So scale this up for me?  Is it a significant source of mortality when averaged over the whole Bay?  How much of the Bay is churned by a boat wake over the course of the lifetime of a copepod?

The second article concerns the effects of the wakes of the blades of wind powered generators:
While wind turbines primarily are a source of renewable energy, they also produce wakes of invisible ripples that can affect the atmosphere and influence wind turbines downstream -- an issue being researched in a newly launched study led by the University of Colorado Boulder's Julie Lundquist, assistant professor in the atmospheric and oceanic sciences department.

The study, called the Turbine Wake and Inflow Characterization Study, or TWICS, also includes researchers from the National Oceanic and Atmospheric Administration, the U.S. Department of Energy's National Renewable Energy Laboratory, or NREL, and the Lawrence Livermore National Laboratory in Livermore, Calif.

Scientists and wind energy developers will use results of the study to better understand power production and increase the productivity of wind farms, according to the researchers.

"Today's massive wind turbines stretch into a complicated part of the atmosphere," said Lundquist, who also is a joint appointee at NREL. "If we can understand how gusts and rapid changes in wind direction affect turbine operations and how turbine wakes behave, we can improve design standards, increase efficiency and reduce the cost of energy."
 As I've noted before, it's tempting to think of wind energy as an unlimited (if some what inconvenient) form of renewable energy.  But the fact is, to take energy out of the wind, you have to slow the wind, and at some point, that starts to have it's own unintended and probably deleterious effects.

Now, a musical interlude, from the Wake of the Flood:

Wake up, discover that you are the eyes of the world...

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