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Carbon uptake

A controversy has arisen over the following question:

If the reaction:   Ca++ + 2HCO3-  ->  CO2 + CaCO3 + H2O (1)
could be facilitated, would the reaction be to the benefit or detriment of
aquatic plants trying to take up carbon from the water?

The reason for asking this question is that it appears there is a device on
the market which may do this (CarboPlus).

I attempted to answer this question by consulting Aquatic Photosynthesis by
Falkowski and Raven, a recent tome with a whole chapter devoted to uptake
of carbon by aquatic plants.

The bottom line appears to be this:   Since at the leaf surface carbonic
anyhdrase greatly facilitates the reaction:   CO2 + H20 <-> H2CO3 which is
otherwise a pretty slow reaction and since the bicarbonate ion is dominant
at most aquarium pHs (6.5-9) (with increasing importance of the carbonate
at lower pHs) the binding of carbon into CaCO3 is to the net detriment of
plants, especially aquatics.  This point is discussed in some detail on
page 135.

If you are surprised by this conclusion, I invite you to consult the above
reference and form your own conclusion.  I believe you will agree with
mine, but welcome debate on the subject with appropriate references.   

Dave Gomberg, San Francisco            mailto:gomberg at wcf_com