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Re: CO2 and it's sources


Amy Ayukawa wrote:

> The recent discussion on CO2 concentrations in water remind me of a
> question 
> I had when I read Diana Walstad's book recently.
> 
> On page 93, she says, "The low productivity of submerged plants is
> not 
> because there is less CO2 in water than in air. (On average, most
> natural 
> waters have about three times more mg/l CO2 than air [8,9]). It is
> because 
> CO2 diffuses so slowly in water (i.e., 10,000 times slower than
> air)."
> 
> I included the last sentence of her quote just to complete her
> thought. What 
> baffles me is the statement that "most natural waters have about
> three times 
> more mg/l CO2 than air". I thought, and the recent APD discussion
> appears to 
> confirm, that the concentration of CO2 in air was about 350 ppm while
> the 
> concentration in sterile water is about 0.5 ppm. Even if the
> concentration 
> in natural water is significantly higher due to decomposition of
> organic 
> wastes, etc., I thought it got no higher than 3-5 ppm. Walstad's
> statement 
> of "three times more mg/l CO2 than air" implies a CO2 concentration
> in 
> natural water of over 1,000 ppm.
> 
> Am I not understanding something or is Walstad wrong?
> 
> Amy

Good question, if I may say so.

I think you are not misunderstanding Walstad or that the CO2 isn't
absorbed from the air to reach those levels in water.  And because
chemistry is an objective science, hopefully all the chemists (I
confess I am not one) will be in agreement that it does not come from
the air but from things in the water  (CO2 geysers and volcanoes are
rare for most freshwater bodies).   Organic compounds and activities
are the only other likely source in nature, which are reasonably
abundant.  In fact, I would guess that it's hard to keep any H2O free
of organics for very long.

Scott H.

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