Quote:
Originally Posted by 34cygni
Note that the equation I gave is identical to the one at the beginning of the article you linked to. It's the standard simplified representation of photosynthesis, which is why I said CH2O represents sugar.
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Yes, I was commenting for others.
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Photosynthesis normally tends to raise alk because it consumes CO2, which when drawn down will cause HCO3- to dissociate into CO2 and hydroxide. That's why the persistently low alk and Ca levels reported by DNA and others demand an explanation -- like I said, this has been at the back of my mind for a while...
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Consuming carbon dioxide does not change the alkalinity. Neither does adding it. Hydroxide has one unit of alkalinity, as does HCO
3-, so it's a net zero.
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I don't see where that link provides evidence that marine primary producers consume alk when they're CO2 limited and running on bicarb...
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You are correct that running on bicarbonate does not consume net alkalinity. That's not what I was trying to say. I was referring to the period between the uptake of bicarbonate and the release of the OH
-, which is going to be fairly small, but might affect the alkalinity. There's also some possible consumption into organics into the cell itself, which is going to be small.
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Subtract the OH- common to each step...
HCO3- + H+ ----> H2CO3 ----> CO2 + H2O ----> CH2O + O2
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This is the equation that shows that photosynthesis doesn't change alkalinity. The HCO
3- is balanced by the H
+.
From:
http://www.advancedaquarist.com/2002/2/chemistry
The definition of total alkalinity:
TA = [HCO3-] + 2[CO3--] + [B(OH)4-] + [OH-] + [Si(OH)3O-] + [MgOH+] + [HPO4--] + 2[PO4---] - [H+]