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Re: phosphorus and phosphorus control

On Mon, 22 Nov 1999, Robert H wrote:

> I find this fascinating Roger, I would like to throw in another factor:
> plant mass. What role does the plant mass, the amount of plants in the tank
> play?

Well, I intentionally left plant and algae growth out of the model.  That
lets me assess the potential supply of phosphorus and leaves consumption
by plants and algae as a wild card in the final appraisal.  If I included
it, the plants would compete with sorption and precipitation for their
share of the dissolved inorganic phosphorus supply.

Plant material contains somewhere in the broad range of 0.015 to 0.3
milligrams of phosphorus per gram of fresh plant material, which the plant
obtains from dissolved inorganic phosphorus.  The test cases I assessed
with the model all added 20 milligrams/week of phosphorus, which is enough
to support the growth of 67 grams to 1.3 kilograms of plant mass per week.
And that in a 55 gallon tank!

Typically growth will be lower than the limit imposed by the total
phosphorus influx, and the unused part of the phosphorus supply will
follow the non-biologic routes that I described.

> Is a heavily planted tank more apt to lower levels, or make them
> higher?

Because of plant consumption of phosphorus, the phosphorus levels in a
healthy tank should always be lower than the model describes.

> We all know that whatever goes into a plant must come out from
> decaying leaves and stems. For those of us who tend to plant as thick as a
> jungle, just keeping the tank clear of debris can be a challenge. Does too
> many plants in a tank make the problem worse?

It's hard to thoroughly clean a heavily planted tank, but the more of the
decaying material you can remove, the better.  But if you maintain a
steady or growing plant population in the tank and remove excess material
through pruning and removal then the plants should still reduce the
phosphorus content.

> On the otherhand many people
> also have sparesely planted tanks, or tanks with only very slow growing,
> low light plants. How does that factor into the equation?

The amount of phosphorus removed by the plants depends on the weight of
plant material produced and on the phosphorus content of the plants.
Sparce planting and slow growing, low-light plants produce less plant
material, so have less effect on the phosphorus budget.

Roger Miller