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Re: where's the NO3 go

> Don't forget the nitrogen content of the detritus that gets washed out of
> filter material.  The N content of detritus can be quite a bit higher than
> the content in undecomposed material, so a small amount of detritus cleaned
> out now and then might contain a disproportionate amount of nitrogen.

Good point, I agree a fair amount can be lost here.

> While O2 or CO2 may be present in substrate bubbles I doubt O2 or CO2 is the
> dominant gas in substrate bubbles -- the exception being bubbles formed by
> algae growing under the gravel line against the well-lit side of an aquarium.
> I doubt that CO2 could ever reach levels necessary to form bubbles.  It is
> just too soluble.  While plants may aerate their rhizosphere (the actual size
> of the area they aerate being disputable) I don't think they do it by pumping
> oxygen out of their roots at levels necessary to form bubbles.

It not the O2 they pump, oit the O2 that the bacteria convert into CO2 which
does build up. Just like O2 forms up on the leaves. But some of the points
may be correct. 
> Nitrogen is normally present in water at about 80% of the concentration
> necessary to maintain bubbles of pure nitrogen, so it doesn't take very much
> of an increase in N2 gas concentrations from denitrification to start bubbles
> forming.

>> 50%? Well the highest levels of denitrification I've found was around 2-3%
>> in Danish Estuaries.
> I didn't have to do more than turn around and grab a volume off my office
> shelf to find out that dentrification losses from fertilized soils easily
> exceed 50% and that dentrification losses in unstratified lakes may consume a
> substantial part (20-30% if I recall correctly) of the influent nitrogen.

Terrestrial soil losses are high, but aquatic substrates are different.
Those are from Oceanography figures and citations of Nitrogen system losses
due exclusively from denitrication.
You need a good deal of organic matter to have this process go.
That's why soil losses are higher.
This is likely true in a rich soil substrate based tank.

> Our aquariums are heavily fertilized and it seems likely to me that some of
> our aquariums lose a substantial amount of nitrogen to denitrification.

Not compared to terrestrial soils.
Consider NO3 levels in soil vs 0-10ppm max that only comes in mainly from
the water column(some from the roots) and the rate of uptake vs the amounts
that denitrifying bacteria which need anaerobic areas.

By the simple virtue of their environment there's low transfer of water/air
etc through this substrate where they exist in enough numbers to cause a
significant NO3 losses.
In an aquatic environment, there needs to be a good amount of organic matter
present and anaerobic conditions for this to happen.

I suppose using a RFUG ands/or comparing a substrate vs and non substrate
tank would give some better clarity.
> Denitrification requires a near absence of oxygen and a readily available
> organic substrate.  Those conditions are easily attained in the substrate and
> in filter media.  Furthermore, the significant denitrification can occur in
> microenvironments -- little anaerobic islands in otherwise aerobic conditions.

That is true.
>> A very simple solution to test this simply requires you to remove the
>> substrate and grow Riccia and/or plants lacking substrate root
>> attachments(Just have all the nutrients in the water column in an empty
>> tank). No substrate, no N2 losses.
> You may easily show that aquariums exist where there is no denitrification.
> That isn't the point.  The point is that anyone who tries to calculate the
> nitrogen balance for an aquarium needs to consider denitrification.  Not
> doing so would be as negligent as ignoring the nitrogen content in fish food.

Fish waste will turn into NH4, extra plant food. I just wonder how much.
What I've read about substrates in water doesn't indicate substantial
losses. But I'll look into it further. The topic does warrant it.

I'll get back on it. Try and remind me later if I forget:) Seriously.

Tom Barr

> Roger Miller