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Re: Phosphorus and algae

Guangyan Wang wrote:
> Hello, I have several questions to ake every about algea. As I have read
> many articles about planted aqurium, I noticed that phosphate in water is
> undesirable. Phosphate can cause algea blooms. However, in all the
> fertilizers for land plants, the phosphate containt is very high. It's
> around 10. Does aquatic plants evolved in a way that it no longer needs
> abandant amount of phospahte to do well?

Nope.  Phosphorus is essential for aquatic plants too.

> Why does high concentration of
> phosphate in water is associated with algea?

In many natural lakes, streams and wetlands the growth of plants and algae
is largely determined by the amount of phosphorus available.  Phosphorus
is the "growth limiting" nutrient.  As a result, any increase in
phosphorus levels often leads directly to an increase in the growth of
both plants and algae.  Conditions in aquaria are often different.

> I understand algea need all the
> nutrients that the plants does. Why is phosphate a major nutrient
> requirement for algea?

Its a major requirement for all living things.  There are no exceptions.
It's part of DNA.

> Doesn't high concentrate of other nutrients also
> cause algea booms?

Yes, if phoshorus is not growth limiting, then some other element or
environmental condition will be.  An change in any condition that is the
primary growth limiting condition translates directly into a change in the
growth rate.  This is a functional definition of the growth limiting

> Does algea utilisize Phosphate better than the plants?

Not to my knowledge, but rooted plants have the option of adsorbing
phosphorus from the substrate, while algae and floating plants must get it
from the water.

> In
> aqautic plants, some nutrients is still absorbed through leaves. Doesn't
> phosphate also incourage the growth og plants?


> Thus, should we also put
> phosphate into our subtrates and water colum to boost the growth of the
> plants?

Most fish foods contain large amounts of phosphorus, so when we add fish
food we add lots of phosphorus.  In fact fish food contains phosphorus way
out of proportion to the plant's need for it.  As a result phosphorus
often builds up in our tank water and substrate.  When that happens,
phosphorus is no longer growth limiting.

If you aren't feeding fish in your aquarium(s) then you will need to add

> If the plants win the competition for the nutrients, wouldn't algea
> have no nutrients to grow?

I'm not sure its that simple.  If plants are satisfying their phosphorus
requirement by taking it from the substrate, then they won't be competing
directly with the algae, which take it from the water column.

> Wouldn't plants grow faster when essential
> nutrients are in the water column.

For rooted plants I don't know if this is true or not.  Certainly it
would be true for floating plants.

> People are deliberate to take out
> phosphate in thier water. Would this action stop the growth of algea? Would
> is slow down the growth of the plants? I have algea again in my tank. I want
> to use phosphate absorbent materials, thus I want your opion.

People report mixed results using phosphate adsorbers.

If phosphorus is growth limiting, then removing it from the water column
will slow down the growth of algae and floating plants.  If the rooted
plants can obtain phosphorus from the substrate, then their growth may be
uneffected.  If phoshorus is not growth limiting, then removing it from
the water will have little or no effect until you bring its concentration
down to levels so low that it becomes growth limiting.

The alternative approach from Sears and Conlin is to increase the
concentrations of dissolved nutrients other than phosphorus to the point
where phosphorus becomes limiting to algae growth.

Roger Miller