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Re: CO2 concentrations in water

> From: "Amy Ayukawa" <amyayukawa at hotmail_com>
> Subject: RE: Carbon Dioxide Concentrations in Water
> 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

	By volume,

> while the 
> concentration in sterile water is about 0.5 ppm.

	By weight.  Water is something like 800 times as dense as air.

> 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" 

	i.e., both in weight per unit volume.  _Neither_ of the others was
in those units, though mg/L is about the same as mg/kg for water.

>implies a CO2 concentration in 
> natural water of over 1,000 ppm.
> Am I not understanding something or is Walstad wrong?

	Just watch out for units!

Paul Sears        Ottawa, Canada