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[APD] RE: algae

 There seems to be quite a lack of knowledge in scientific
> literature about the role of heterotrophs in aquaria and aquaculture
> systems, though. But it seems logic that having a nice and balanced
> community of heterotrophs that can degrade organic matter down to very low
> concentrations helps higher plants by releasing N, P from their organic
> products. From mass balance studies it is known that one can remove
> substantial amounts of P by removing suspended solids in aquaculture
> systems.

I think there's a lot of knowledge out there about microbial cycling in
But there's far less known about periphyton/epiphytes - microbial role and
how it is affected by healthy growing plants that live in optimum
Periphyton has the ability to remove very very low amounts of PO4 and
organic DOP. Plants do not use this fraction. That we do know. 

Your test kits typicallly ALL measure total PO4, this includes the DOP, a
similar thing can be said for DON. 
Often you will get a small or low residual PO4 measurement with a  good
kit. But that does not mean there's plant available PO4. It does mean 
there's plenty of PO4 for the algae though. Periphyton is not PO4 limited
till it's less than 3 ppb, yes per _billion_ and even that's debateable if
limition occurs. It's impossible to measure down this low without a wide
error range. Measuring to close 10ppb is feasible on a regular basis but
3ppb would be impossible. 
Emergent Plants are limited in the 50ppb range, submersed plants down in
the 20-50ppb rang. Still, roughly a factor of 10X or more than higher

I've discussed this in terms of the Evergaldes and the princple researcher
with the South Florida water management district. They have the lowest PO4
mandate anywhere, 10ppb levels of PO4. The Glades is a periphyton dominate
ecosystem(40-55% production).   

Based off these types of research, adding PO4 will help the plants and we
do see this pattern in the Glades and many Florida lakes that have high
plant densities. 
You can also see it at the plant fest, we go down a hard water river that
starts in a spring that comes out of an old PO4 mining operation. 

Comparing apples and oranges is what is going on here, the
microphytes(algae) and the macrophytes(plants) live in different
> But to come back to the original question: the idea would be, like Roger
> Miller says, to select a window of conditions. Unther those conditions
> plants are better competitors than algae. 

But they are different, not really competitors, both are in different
niches. I don't think you can compare them on equal terms. NH4 means a lot
more to an algal spore than to a an adult plant. Both will prefer one over
the other, but, each autotroph will respond differently to this cation.

'Clean' water, free of dissolved
> organic matter seems to be part of the solution. 

Well, yes and no. At high light is becomes more dominate, at low light, the
rate of reminerilization is slow enough to supply the plants, the light is
low enough not to support much algae growth. But with CO2 enriched system
this can certainly play a large role.

Maybe also that is logic if
> you compare an aquarium with the lakes Tom mentioned: fish density and
> production per m3 will always be higher in an aquarium than in a lake.

Yes, you certainly need consistent export and import of nutrients/plant
matter etc.
That's the balance we all seek.

Tom Barr

>> Roeland

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