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[APD] RE: Determining NO3=>N2 losses from planted tanks

> There is an even easier way, but I'm lacking a key piece of 
> information... do a nitrogen balance. 

Well then acetlyene reduction methods should be used if you want to do this
and take it to that level.
Some overview of potential methods for measuring Denitrification:


I'm using the NO3 disappearance method. I can bug Mete in the lab but it's
a hassle and I just wanted a simple method I can do with a Lamott kit. 
The method I suggested is a dirty method folks can do, but you can do this
if you know some things:
Some regulators of denitrification:

Low O2/Low Eh, redox
Presence of Electron acceptors(NO3, NO2 etc).
*Facultative* anaerobes and population.
Electron donors, Carbon source(adding peat, lignite etc).
Temp(optimum is 30-40C)
NO3 diffusion rate/flux
Plant root density.

The bacteria are Bacillus and Pseudomonas that possess the NO3 reductase
enzyme that allow them to use NO3, NO2 and N2O as the electron acceptor
during oxidation of organic Carbon in anaerobic evnvironments(these are
facultative anaerobes). 
Typical Eh ranges for denitrification of this type: 200-300mv.
It might better to call this NO3 respiration since it involves electron

Lower DOC levels will suppress NO3 respiration although this is a non
linear relations.
So all the peat, lignite etc is helping the NO3 losses very likely.... if
you assume DOC to be limiting the pathway NO3=>N2.
I think many planted tanks are limited in terms of DOC. 
This simple relationship suggest that denitrification rates can be
estimated by DOC extracted from the substrate.
In natural systems, NO3 is very often the limiting factor, but it might be
the opposite in our tanks.   

If you want to see if this occurs in nature, they will often add glucose as
a source of carbon and then measure the Denitrification rates. If they are
higher, then it suggest carbon limitation.

Where is that Roger Miller adding sugar to his tanks? :-)

 Simply save your clippings over 
> a month or two, dry them, weight them on a good analytic balance (I do 
> have access to one, so I could do this for those local to me)...  What 
> I am missing is an estimate of nitrogen in plant tissue on a _dry 
> weight_ basis.

Assume a 9:1 ratio of wet vs dry biomass. Pick only one plant species, say

 It would be important to return the tank to the same 
> state of "pruned" to get a good result.  If lots of us do this, 
> systematic errors involved will be averaged out quite a bit and should 
> give decent agreement.  But lets be realistic here, we're looking for 
> an order of magnitude effect, this should be very apparent if it is 
> occurring...

True. Using several methods will help. 
I can find a few things on this for reasonable estimates and we can compare
our findings.
Hopefully, we can make some sense of it.

> The problem with removing plants to check: At moderate levels of oxygen 
> you have the 2NO3->N2+3O2 reaction occurring, to keep consistent with 
> the marine folks that do deep sand beds call this region the anoxic 
> region. 

The redox level, Eh, is a better gauge of the amount of oxidation that
You need 5 electrons for this one.

There's a difference here between denitification you mention and DNRA, the
microbes are faculatative in Denitrification, they obligate anaerobes with
DNRA that you suggest below. You need a _highly_ reduced environment for
this to occur.DNRA=> Dissimilatroy nitrate reduction to ammonia.

 At even lower oxygen levels, call this area anaerobic, you 
> have the 2NO3- + 11H+ -> 2NH4+ + 3H2O reaction occurring (opposite of 
> biofiltration).  

Naw, look at __all__ those H+'s, that's a lot of reduction energy and a
very low redox value is needed for this to occur, this is not going to
happen easily in a plant tank without high loading into the substrate of
organic matter and with all the O2 production also? 
Soil tanks might have this occur but it's a function of flux in/out and you
cannot have much flux without also adding the O2. 
Removing the plants may drop the overall oxygen 
> concentration in the substrate and favor a reconversion to ammonia  as 
> opposed to nitrogen gas, 

I don't think the redox values even come close in any tanks we commonly

In any event, the removal of plants will only increase the NO3 losses, not
decrease them. So the before and after effects can be compared and even if
they assumed to be equal, we can argue that the loss of NO3 will be less
with plants, than without, do you agree?

so if anything removing the plants might be 
> considered a low limit to denitrification... see latest issue of FAMA 
> Re: Plenums in marine tanks for more discussion about this... Deep sand 
> beds that are too anaerobic turn into nitrate factories.
> Jeff Ludwig
> Elkton, MD

See Soil Science and Wetland soil science research, I have mountains of
references on denitrification and the above link is pretty good.
Check further into those citation references.

Be interested to see what your results are with the budget. 

Tom Barr


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