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Re: NO3 and some resolve

>>> Something is using up
>>> the NO3 because the test detected less than 5 mg/l.  So I added another 1/4
>>> tsp KNO3 to get between 5 to 10 mg/l of N03.
>> 
>> This is clear evidence of plant useage.
> 
> Well, almost.   Don't forget about denitrification.  There are cases
> where denitrification can consume a pretty large amount of nitrate.  In
> that case there can be declines in nitrate concentrations without much
> plant use.

Yes, perhaps. Can you tell how much? Difficult. Check out the end of this
rant if your interested in a way though.
 I had a batch denitrifier way back when. I was looking for the holy grail
of never doing water changes. I used Ozone, had a huge sump from hell, I
used algae scrubbers, Coils, 4-5 inches of sand/lava and lastly I used
plants.
Guessy which one did the trick and which boat I've been on since? The tank
was packed with fish and always had high NO3's till the plants came along.
I guess I'm still conservative using KNO3 on my own tanks. Always after fish
food sources hopefully.
Cyclic batch units looked so cool I had to have one. But they gave me an
opportunity to see what was  happening but my test kit then was a cheesy
Tetra kit. No I can't say exactly how much but the plants where the only
thing that dropped the NO3 fast(they were emmersed then, still did not have
a clue how to grow much underwater well). I regret that I did not do a more
through exhaustive test and had better kits before I got into plants so
much. It was much more a presence absence thing. But the plants where the
only thing that lowered the NO3 consistently. The batch unit got sold(but I
got so many oooo's and ahhh's) to a reefer along with a bunch of other junk
I didn't need. Don't ever get one:)

I have not seen one yet nor tested a tank as such that the denitrification
is or was a cause for any concern regarding NO3 usage as far as I could
tell. I could be wrong but I wouldn't bet on it. Terrestrial systems are
quite another thing though. Bacteria do get a huge part of the NH4 we add as
fertilizers in the soil in those systems. Much of it gets lost as N2O and
N2. Not good. 

 Some tanks are anaerobic in large parts but there little flow in and out of
these areas as well. How does one get large removal rates without
sacrificing low flows in/out of the gravel? All the O2 produced or in the
water column is not that great for ananerobes. You need to get your NO3 rich
water in/out of the gravel to do this. Plants can remove the reduced
minerals out of this zone but they are not going to add NO3 down there for
the bacteria.
To put it simply, it takes too long to remove NO3 this way or too much
money(Batch methods). The coils can work but they also have this low flow
rate issue. They also suck at low pH's that most of us have so....
Batch unit sought to get around this idea but it didn't meet my needs one
bit. Plants did. Hard to say how much.

Plants don't have all these issues. They are fast to respond, far less
sensitive, exceed the bacterial removal rates. I don't have enough facts or
enough testing but my general notion is still it's evidence of the plants
removing it, whether it's mainly the plants is another source of infinite
debate that the APD is so good at.
But it does seem that they do have the total advantage here for access,
uptake and placement in a plant tank. They can the nutrients anywhere.
NO3->N2/N2OBacteria cannot. They can also handle large flows in/out. the
Bacteria are limited by their anaerobic needs. Too much flow in from the O2
rich water and they die.
 
> I have problems explaining how denitrification might work at a
> signficant rate in a water column-fertilized planted tank, especially in
> a new tank.  Just the same, I think some of the reported nitrogen use
> rates would required truely huge plant growth rates (or nitrogen
> accumulation rates) unless some of that nitrate is consumed through
> bacterial denitrification.

Growth rates are a multi nutrient/light CO2 thing. There are limits to be
sure, but some aquatic plants will grow at break neck speeds. We call them
noxious weeds:)

But as far as who gets what(as in that elusive N molecule) in a planted tank
or a FW environment, I have a way to track and trace it. As bacteria/plants
and algae are all after this one more than most any other one. My Prof at
school is doing a project with isotopic N14 and N 15 ratios and preferencial
uptakes. You can use the natural isotopes or dope a system too. You can
track the movement of a single(or group of N's) N through a food web. It's
expensive but I'm trying to work on him to do a plant/bacteria/algae run as
my own project:) Being a TA helps:) This gets around all the BS and
complexity and cuts right to the chase. We have some good people for this
molecular marker procedure. I think I'll get it funded as primary producers
are important and competition for this resource has some larger
implications. Bio departments like that(I like it as well). He's the
Chairman also. Some resolve is in sight:) Then maybe/hopefully I'll be able
to say how "clear" the evidence might be or not.
Regards,
Tom Barr