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Re: Aquatic Plants Digest V4 #27

Two misconceptions are being presented here, I'll try to clear them up.
First of all, O2 and CO2 levels in the water are not always completely
independent. Liquid can dissolve only so much gas, and at a given
temperature and pressure this amount - the total for all gasses - is fixed.
At equilibrium the partial pressures of all the dissolved gasses will total
the same as the atmospheric pressure. Adding more CO2 will displae other
gasses from solution. However since most of the dissolved gas in tank water
is nitrogen, and the amount of added CO2 is relatively small, the effects of
adding CO2 on O2 levels will be negligible.

Second, hemoglobin does not bind CO2. The original poster has CO2 mixed up
with CO (carbon monoxide) which does have a high affinity for hemoglobin and
will displace O2 (hence death from breathing car exhaust). A rise in CO2 in
the blood, and a decrease in pH, will both cause a slight decrease in the O2
carrying capacity of hemoglobin but the effects are very small and would not
play a significant role.

Peter G. Aitken