[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: PO4

>> So where does all the PO4 go day after day? How much can the gravel possibly
>> hold? Must all go to the plant at some point.
> Not necessarily....
> If the gravel has laterite (or lateritic soils), it can hold alot.

That was my point. Recall my tanks you saw in CA? None had laterite, the tap
is loaded with PO4 and the plant growth was excellent. PO4 levels dropped
fast during the course of the week after the water change.

> In the
> aerobic portions of acidic iron bearing substrates,  ferric ion will react
> with inorganic phosphate. The resulting phosphate compounds are highly
> insoluble and tend to stay in the aquarium bottom.  When the substrate is
> disturbed, the small particles can become suspended in the water column.
> These suspended iron particles will also react with phosphate. The
> insoluble iron phosphate compound can then accumulate in the substrate.

So my substrate should "grow"?

> This interaction between iron and phosphates is used as a basis for
> advanced waste treatment methods for phosphate removal from domestic
> waste-waters.

And they remove it by removal of the iron PO4 sludge that settles out. We
can get "sludge" from our tanks therefore. A number of these wastewater
processes are pH dependent, dosing dependent etc.
> Boyd has studied pond water using an experimental pond (over 20 years old
> without renovation at Auburn University in Alabama) and reported water
> phosphorus concentrations of 0.04 ppm with a soil bound phosphorus of 1000
> ppm!! He found the concentration was greatest at a depth of 1-2 inches.
> This was an experimental pond  in Alabama.  Just below the surface, the
> phosphorus concentration in the water surrounding the sediment particles
> was one ppm while the adjacent surface water was one tenth that value.
> This is described in more detail in my PAM article.

Stop! Boyd's experiment does not address THE _question_ here.
Plant uptake of PO4. It simply addresses iron binding and PO4 levels in the
substrate of a pond. Nothing more. There is no outflow in this pond(or is
there?) so nutrients will build up. We remove plant mass very often in our
tank, exporting PO4, Iron , NO3 etc. Two very different systems.

An experiment that _would_ address the issue and perhaps answer the question
of plant uptake would be to remove the substrate and grow the plants in a
bare tank. Riccia is a simple common plant. Water sprite would be another.
Both floaters. PO4 could not be removed in a bare bottomed tank. This
experiment would address the PO4 uptake rates of plants at the levels we are
interested in. These other experiments do not answer your question.

Any precipitation of iron phosphate could be seen and removed and analyzed
in such a tank. This could also be done in a substrate based tank but the
chemical analysis would be more difficult and uptake would be more weighted
on the analysis of the substrate.

I have a small tank sitting out back that I could do this simple experiment
on. I guess I have to now:)

Tom Barr