[Wet Thumb Forum]-NitrAte

[dwalstad]

I was just wondering.
In a natural planted tank, would you have less nitrAte formed than in a tank with the same bioload and plant mass that had filtration going?

1 ion of NH4+ to 1 ion of NO3- is equivalent to 1 molecular weight of NH3+ to 3.44 molecular weight of NO3-

Therefore 1ppm(mg/L) of NH4+ will convert to 3.44ppm(mg/L) of NO3-.

**This conversion is correct. However, when I talked earlier about plants taking up "more", I meant more nitrogen (N). The fact that the nitrate molecule weighs about 3.4 times more than the ammonia molecule is (in my opinion) less relevant to this discussion.

However, let's not forget about soil bacteria. Under anaerobic conditions, they will be converting nitrate to nitrogen gases that will escape from the tank. Also, ammonia gas will escape from the water directly into the air. (That's why fish sealed in plastic shipping bags have such a tough time; much of the ammonia gas stays within the bag keeping water ammonia levels high.)

Therefore, plants and biological filtration only partially control nitrate and ammonia levels. My tanks may have wildly different nitrate readings, varying from 2 to 80 ppm.

[Tyrone Genade]

The conversion of ammonia (NH_3) to nitrate (NO_3-1) via nitrite uses oxygen not water. Water is a byproduct of the process. The exact reactions differ from bacteria to bacteria. See here. This is perhaps a bit more complicated than one may need for explanation however. This may be more "simple".

Because most tanks' pH tend to be below 9 ammonia exists mainly as ammonium (NH_4+) so one would have to add another proton coming loose in the above equations. Because plants maintain a negative electrochemical potential accross their cell walls (i.e. they have a higher concentration of positively charges molecules outside rather than in the cells) the NH_3+ is able to enter the cells without the need for active transport whereas NO_3- has to be pumped accross against the gradient. I am unfortunatly unable to find a nice link to explain this. So we will have to rely on what I can recall from my plant physiology courses.

By the way, the plant maintains this gradient not to import ammonium but to import calcium, magnesium, potassium etc... The latter salts generally occur as insoluble precipitates. The plants pump H+ out of their stems to lower the pH around themselves. The low pH dissolves the salts. This is also why UG filters are not good as they clear the H+ excess away starving the plant of needed minerals.

I think I have now wondered off topic abit...

tt4n

[Maurici]

Is clear that the explanations given by Tyrone to some of the points are very illustrative. You also post:<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> the NH_3+ is able to enter the cells without the need for active transport whereas NO_3- has to be pumped accross against the gradient. <HR></BLOCKQUOTE>I've read that NO3- and NH4+ need a co-transport of protons by the I mechanism (in Epstein terminology)related to differences of intra vs. extracellular pH.
Other information I've found is related to terrestrial plants (like wheat) but can be useful to understand uses of different sources of N in most of our (non natural )tanks (yes, perhaps it would be better to post it on the other plant forum). As an abstract it talk about CO2 inhibition of shoot NO3– assimilation which would contribute to the response of natural ecosystems to rising CO2 levels. Plants vary in their relative dependence upon NH4+ and NO3– as nitrogen sources (Bloom, 1997) and in their balance between shoot and root NO3– assimilation (Andrews, 1986). Their results suggest that rising atmospheric CO2 will favor taxa that prefer NH4+ as a nitrogen source or assimilate NO3– primarily in their roots. I've used its own words (slighty modified) and note that the references refer to bibliography there reported.