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Dissolved Organic Phosphorus

jaypeecee

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21 Jan 2015
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Hi Everyone,

I have been sitting on the following scientific paper for a year and I suspect that it may be of interest to others for a variety of reasons. Ever wondered why algae grows in water in which there appears to be no measurable phosphate/phosphorus? Could it just be that the phosphate test kit is only able to detect inorganic phosphate - otherwise known as orthophosphate (PO4---)? Well, stay tuned - the following may be right up your street. Although its primary focus is temperate lakes, I suspect that the paper includes plenty of information that may be of interest to the aquatics hobbyist. Here it is:


JPC
 

_Maq_

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Could it just be that the phosphate test kit is only able to detect inorganic phosphate - otherwise known as orthophosphate (PO4---)?
Yes.
Phosphorus is regularly the limiting nutrient in natural biotopes. That's why microbes (and also plants) have developed ingenious ways to get P. As a result, only small fraction of available P remains in the form of orthophosphate. Precipitation in the sediment is another sink, but it is wrong to consider it lost irreversibly for utilization by microbes & plants.
Measuring orthophosphate in water column is of fairly limited value, then.
 

jaypeecee

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Measuring orthophosphate in water column is of fairly limited value, then.
Hi @_Maq_

Yes, that's the way I see it. If we want to get a full picture of phosphate content in water, we need to consider testing for Total Phosphate. Water Test laboratories are able to conduct such a test. Here's just one example:


I need to stress that I am not promoting this company as I've never used their services!

JPC
 

macek.g

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28 Dec 2008
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Livingston
" but it is wrong to consider it lost irreversibly for utilization by microbes & plants"
Hi
Could you expand on that ...?

Hmmm

  • Soil Mineralogy. The mineral composition of the soil influences the phosphorus adsorption capacity. For example, soils with a high content of Al3+ and Fe3+also tend to have the greatest phosphorus adsorption capacity.
  • Soil pH. Optimum soil pH between 6 and 7 will result in maximum phosphorus availability. At low pH (acidic soils), soils have greater amounts of aluminum and iron, which form very strong bonds with phosphate. At high pH when calcium is the dominant cation, phosphate tends to precipitate with calcium.
  • Other factors. Temperature, moisture, and soil aeration can affect the rate of P mineralization from organic matter decomposition. For example, in warm, humid climates organic matter decomposes faster compared to cool dry climates.

But...
pproximately 30 to 65 percent of total soil phosphorus is in organic forms, which are not plant available, while the remaining 35 to 70 percent is in inorganic forms. Organic forms of phosphorus include dead plant/animal residues and soil micro-organisms. Soil micro-organisms play a key role in processing and transforming these organic forms of phosphorus into plant available forms. The inorganic phosphorus forms can be classified to exist in three different pools:

  • Plant-available (soil solution) phosphorus: This pool is comprised of inorganic phosphorus dissolved in water/soil solution that is readily available for plant uptake.
  • Sorbed phosphorus: This phosphorus pool is comprised of inorganic phosphorus attached to clay surfaces, iron (Fe), aluminum (Al), and calcium (Ca) oxides in soil. The phosphorus in this pool is released slowly for plant uptake.
  • Mineral phosphorus: This phosphorus pool is comprised of primary and secondary phosphate minerals present in soil. Examples of primary phosphorus minerals include apatite, strengite, and variscite. The secondary phosphorus minerals include calcium (Ca), iron (Fe), and aluminum (Al) phosphates. The release of phosphorus from this pool is extremely slow and occurs when the mineral weathers and dissolves in soil water.
 

dw1305

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Hi all,
I need to stress that I am not promoting this company as I've never used their services!
It isn't exactly a company, the page belongs to <"Ohio River Valley Water Sanitation Commission"> and uses the HACH Orthophosphate test kit.
Precipitation in the sediment is another sink, but it is wrong to consider it lost irreversibly for utilization by microbes & plants.
That is the eutrophication issue, in Europe we've already added enough phosphorus to our environment that it would take <"a thousand years to deplete it back to natural levels">, even if we stopped adding it tomorrow.
  • Plant-available (soil solution) phosphorus: This pool is comprised of inorganic phosphorus dissolved in water/soil solution that is readily available for plant uptake.
  • Sorbed phosphorus: This phosphorus pool is comprised of inorganic phosphorus attached to clay surfaces, iron (Fe), aluminum (Al), and calcium (Ca) oxides in soil. The phosphorus in this pool is released slowly for plant uptake.
  • Mineral phosphorus: This phosphorus pool is comprised of primary and secondary phosphate minerals present in soil. Examples of primary phosphorus minerals include apatite, strengite, and variscite. The secondary phosphorus minerals include calcium (Ca), iron (Fe), and aluminum (Al) phosphates. The release of phosphorus from this pool is extremely slow and occurs when the mineral weathers and dissolves in soil water.
That one, unfortunately we are really back to guess work with what is happening in the substrate.

cheers Darrel
 
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