A carbon question

[121]

I've read that dosing a carbon source (like vodka and acetic acid) reduces elevated N & P because closed systems are carbon limited compared to natures Redfield ratio.

Why doesn't bacteria use carbon from carbon dioxide, carbonate and bicarbonate in aquariums?

[cfredallen]

Difference between organic and inorganic carbons I believe. Vodka and Vinegar are organic carbon food sources for the bacteria.

[tmz]

To be useful the carbon needs to be organic( ie bound to H) as it is in carbohydrates( polymers) sugars(monomers) ethanol and acetic acid among other things. The bacteria that perform denitrification are facultative heterotrophs, they can't fix C to H like autotrophic organisms can via photosynthesis.

[disc1]

Because they make their energy by oxidizing those carbon hydrogen bonds and the carbon in CO2 is already as oxidized as it can possibly get.

[Randy Holmes-Farley]

Further, even if we were considering organic carbon, I don't think the redfield ratio and where the water might be in relation to it says anything useful about what is limiting to an organism. It simply details what organisms are made of, not what they are good or not so good at collecting from their environment.

[disc1]

Originally Posted by Randy Holmes-Farley

Further, even if we were considering organic carbon, I don't think the redfield ratio and where the water might be in relation to it says anything useful about what is limiting to an organism. It simply details what organisms are made of, not what they are good or not so good at collecting from their environment.

Amen. Who was it here who recently called the Redfield Ratio the single most abused number in all of biology?

Trying to use it this way also ignores the fact that many organisms uptake phosphate from organic sources or are able to fix their own nitrogen. This would tend to throw any application of the Redfield ratio to the concentration of free nutrients in the water completely out the window.

[tmz]

Well, since no one mentioned it this time . NO3 is reduced not only for food but also in anaerobic respiration, further diabusing the notion of applying the Redfield ratio to the organic carbon dosing process.
Setting aside the extra nitrogen depletion from anaerobic respiration,
even if there was a balanced amount of organic carbon from food or photsynthetic organisms , some would take refractory forms and have limited bio availability , some would be used up by organisms and some exported with organics via skimming and gac. Besides all that organisms vary in the ratio of organic carbon, nitrogen and phosphorous they consume as well as the types of organic carbon The Redfied ratio is an en masse measure useful for an overall perspective but of little value I can see beyond that in the processes under discussion.