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Re: [APD] CO2 Experiment #2

Charley Bay wrote:

> This technique is famously used by water beetles
> and the water spider, Argyroneta aquatica:  Go to
> the surface, and a water bubble is "captured" over
> the hairy abdomen.  Then, submerge:  The critter
> consumes O2 from the bubble, and exhausts CO2 into
> the bubble.  However, the CO2 dissolves *very well*
> into the water, so the critter can stay submerged
> a *lot* longer than it should have been able from
> the original bubble -- as more CO2 builds up in
> the bubble, it diffuses into the water, and as
> the relative O2 in the bubble decreases, more O2
> diffuses into the bubble from the surrounding water.
> Even in some oxygen-depleted waters, the critter
> may be able to stay underwater *indefinately*
> (although more typically the bubble shrinks to
> a steady-state, and the critter goes up to replenish
> a more efficient gas mix, because N2 typically
> accumulates in the bubble).
> Take-away message, and much of the bane of our
> instrument's existence:  The bubble will *never*
> fully dissolve.  To force it to "dissolve", you'd
> need to dramatically increase the fluid pressure
> (and most of the time that's constant, or even
> decreasing, as you move to the surface).

> BTW, Paul Krumbholz mentioned this in the past
> on the APD (28-Jul-1995, 
> <http://www.thekrib.com/Plants/CO2/diffuser.html>)

Ah, but you said it so much nicer and far more interesting. :-)

Many thanks.

Stuart Halliday
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