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Re: NO3 uptake rates

> I´m new here too, and is very interesting your point. Although your
> calculations are rigth, I think you forget the following data to have the
> exact solution:
> 1) The total plant biomass (leaf, roots rizomes etc), not only the harvested
> one.-
> 2) The fact that the plants are feeding the trofic chain, and the N is
> secuestred too  on the biomass of the grazers and predators (micro and macro
> ones) 
> 3) And the most important, the N lost as gas,  by anaerobic bacterias´s
> metabolism
> Toni Trias 

Figuring out how much N2 gas is produced is pretty easy to figure out.
Only anaerobic bacteria will do this and a plant tank is a very highly
aerobic place both in the water column and in the gravel.

You can see how much NO3 is depleted with out plants and algae(keep the tank
dark etc). You won't find much loss. Certainly not much over the course of a
week to even consider at the relative uptake rates of the plants.

Basically it's not worth considering unless you are attempting to be very
precise and scale this up to the ecosystem level.

If you have a batch denitrifier, a coil denitrifer etc, you can remove some
NO3 that way, but if you add O2 to high levels, pump O2 into the
rhizosphere/substrate, use no light(to prevent any interactions with algae)
and no aerobes can convert NO3 to N2, you can see how much N2 is removed
from the system. I really don't think it's enough to fret over.

2# is more plausible. A fair amount is returned via fecal pellets and waste.
But some N is tied up in that but these groups simply don't continue to grow
out of control always increasing do they?
We see an ebb and flow between herbivore densities and algae/plant
densities. If we add 50 shrimp to a 20 gallon tank there will be no algae
and they will likely go after the plants also. If we have 2 shrimp, then
algae may grow some.
Most of the N is returned in waste but some is assimilated into the growth
of the critter. But if the critter dies, the N is returned to the system.

But how much before and after N weights do you think the fish /shrimps get
from eating on the algae in the tanks per week? I'd say not much at all.
The smaller rotifers etc will be recycled since they die and are processed
back again into plant/algae food.

I count this in my own pruning since I most often remove the roots along
with the plant and plant only tops.
Roots are about 1/2 the plant and grow more than the green
leaf/stem/sometimes Rhizome part folks see.
Now when I yank up those roots, many roots hairs, single cells etc get left
behind but these are re mineralized back into NO3/NH4.

I think this a good approach to see how it matched up with the NO3 test and
see if we have good results from both.
How useful is it? Certainly a little and it is interesting. I may try and
add this into the mix to the lab runs. I can do this with stable isotopes in
natural lakes/river/streams but it cost a lot. I'll stick to the lab stuff:)
I have enough to do I think for now:)

Tom Barr