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Re: GW:NO3

> Subject: Green water vs nitrate
> 
> I am a bit puzzled about the correlation between the green water problem and
> very low nitrate levels. Green water problems in lakes and rivers due to
> eutrophication seem to contradict this.

Once it gets established, then it hangs on. The NH4+, not the NO3 is the the
main trigger for a bloom. Go see a cattle pond. It has high NH4 and all I've
ever seen had GW.
Adding KNO3 on the other hand is another ball of wax. See below.
Eutrophication has other factors involved and does not say what the NH4:NO3
is in some cases(I test for NH3/NH4+ in estuaries and NO3). A large influx
of NH4 triggers the algae and then they hang on with or without high levels
of NO3. More NO3 helps them once "the snowballs been pushed from the top of
the hill". But say no NH4 was added but NO3 was. Would you still get the
same result? I tried it many many times on my tanks and I always came up
with no. In a natural system? I'll test that one soon enough. A stream might
not be the best test subject but a slow flowing one maybe. A vernal pool
would be real good since they start clean but I have to keep the birds
out:-)  

> But as several people seem to experience this correlation in aquarium, and
> so many other factors are present...

Ferreting these other things out is tricky and the cause of many myths. I've
bought into many and likely still am:)
  
> I have never encountered a green water problem in any of my tanks over a
> period of 10 years and indeed, all my tanks have nitrate levels of a least
> 10 mg NO3 per liter.
> 
> Could these organisms responsible for green water in aquaria be able to
> perform nitrogen fixation?

No, only diazotrophic eubacteria can do this. Eurkaryotes cannot do this
(all algae/plants are). Only a few blue green algae can do this and not that
many. The genera of BGA that infest our tanks cannot do this N2 splitting.
This requires a structure call a heterocyst. The species we have don't have
these. These are easy to spot in a microscope. This N2 reduction is strictly
anaerobic. The enzyme Nitrogenase is heavily dependent on Fe, Mo, and
sometimes V for electron transfers.

> If they are able to grow so fast, they need some
> nitrogen source and lots of it...

No. They only need to be able to concentrate it. They can live in levels
very low and still do quite well. The plants will be stunted if the levels
are this low while the algae are quite able to exist.
You cannot "starve" algae but you can slow them down to some degree by
limiting. But this hurts the plants more so. Plants are much more adapted to
removing things from the soil than the water column unless specific such as
Cabomba, hornwort, water sprite, Riccia etc.

 But GW is an algae that exist in the water column. It's built to withstand
water column depletions and variances in nature which are far more etxreme
than our nice well fed tanks provide. It only has to feed each of it's one
single cells to keep going. A plant has to feed many cells many of which are
not used for photosynthesis etc and also that are not seen like GW. The
small mass of GW in your tank is very visible but it represents only a small
actual mass. What might appear as this huge mass is not that much mass. Just
think about it and consider how much plant trimmings you put in the bucket
and compare that with the worst algae infestation and the mass of only algae
that's in the bucket. You'll find that most of the mass is plant.

> Nitrogen fixation is quite energy consuming, this might explain why these
> organisms are not able to cope with the competition of other algae and
> higher plants in the presence of other N-sources than nitrogen gas.

They are good at fixing N2 but they also very limited by Fe, Mo, and
sometimes V for electron transfers. Got to have those for the reduction to
happen. The competition is not a simple thing where these do exist and same
goes for diatoms, being dependent on Si but needing N at critical stages in
their growth. Timing is important also. Once a trigger is flipped they try
everything to beat out the other and become dominant even if there's not
much to nutrients. Statistically, this works for the algae.
> Then, on
> the other hand, do these organisms disappear when you just add enough
> nitrate?

Nope, you got to kill them first(there will be spores/stages hanging out
waiting till you have a NH4 spike to try it again).
But adding enough NO3 while you kill them (UV/Blackout etc) perhaps raising
up the amount of filtering/biomedia etc helps get the bacterial culture
build up and limits the effects of NH4 spikes. Bacteria, much like
plants/algae, likes the NH4 ion too but they will live well on NO3. Take
care of the bacteria and the plants. When plants and bacteria combine they
make a good place for each other even with competition for nutrients. This
also tells the algae not to try and grow since some one is already there
doing well(algae likes to attempt a takeover when the other is weak-could be
another algae also). Helping the plants and bacteria(feeding NO3 etc) makes
the place pretty stable and keep things under tighter wraps. Algae wait for
unstable environments and shifts to try and get a foot hold.
I think it's an easier method than trying to limit things like PO4 that also
hurts the plants. N seems to be a better **keystone nutrient** IMO for a
plant tank. I could be wrong.

Regards, 
Tom Barr
> 
> Roeland