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Re: nitrate reduction

Steve Pushak wrote:

> >Someone else on the APD asked about ammonia appearing after the addition
> >of several Jobe's sticks to the substrate. In the anaerobic environment
> >in the substrate, bacteria act upon nitrate and reduce it to ammonia.

To which George Booth responded:

> This is the second time I've seen reference to this.  It is my understanding
> that nitrate does NOT get reduced to ammonia, but to elemental N2.  I thought
> there was something about the bacteria using the oxygen for energy and being
> lazy about not spending the time to scrounge up enough H to build ammonia.
> Does anyone else have info on this?

I have a little. It's 20 years old, but I don't know that the state of
knowledge has changed all that much.

In the usual process of denitrification nitrate is converted through:

NO3- --> NO2- --> NO --> N2O --> N2

Gaseous nitrogen is the end product and usually the only noticable
product.  Nitrous oxide (N2O) can also be produced in measurable

There were 17 known genera of bacteria capable of reducing nitrate to
gaseous nitrogen and/or nitrous oxide.  Nitrate can also be reduced to
nitrite and in some cases to ammonia by some 45 genera of bacteria.

The relative importance of nitrogen gas production and ammonia production
is variable.  Reduction to ammonia or organic nitrogen might account for
as much as 40% of the total nitrate loss in some aquatic soils, but lower
percentages (2.8 to 5.5 percent) might be more representative.  The
relative importance of nitrogen gas and ammonia production appears to be

My reference doesn't say, but I suspect that these studies include
relatively low-nitrogen soils where a substantial part of the nitrogen
losses are actually from the assimilative uptake of nitrogen by bacteria.
That would account for some of the rather high percentages cited.

I set up a paludarium several years ago explicitly to act as a
denitrifying filter.  I also talked to a number of reefers who were also
using or interested in using denitrifiers.  I never saw measurable ammonia
in the effluent from my denitrifier and never heard of others who did.

I figure that because of denitrification it's probably a waste of time to
put a fertilizer containing nitrate or nitrite into an anoxic substrate.
In the same case, ammonia production is also possible but it may or may
not happen and any ammonia produced may or may not ever get back out of
the substrate in any kind of problem concentration.

If you're interested in reading more, you might try tracking down

National Research Council, 1978.  Nitrates:  an environmental assessment.
	National Academy of Sciences, Washington, DC. 723 pp.  ISBN

Roger Miller

In Albuquerque, where it seems the spring runoff is starting.