Difference between revisions of "Phosphorus model cons"

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== '''Weaknesses of the Phosphorus Model''' ==
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[[Image:pcycle model.jpg|right|thumb|300px|A schematic of the modelled phosphorus cycle.]]
  
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As with any model, simplification has both advantages and disadvantages.  This article describes some of the '''phosphorus model cons'''.
  
In computer modeling there is a continuum between (1) conceptual-type models that aim to simplify a system down to include only its most important elements, in particular those that govern its behaviour, and (2) simulation-type models which are highly detailed and try as much as possible to avoid making assumptions about what is important; instead they try to include as much detail as possible in the expectation that nothing important will be omitted. The phosphorus model is very much a conceptual-type model. As such, it is important to realise that it will not be the most appropriate model to use for many purposes.
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==Model description==
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In computer modelling there is a continuum between two caricature classes of models:
 +
# conceptual-type models that aim to simplify a system down to include only its most important elements, in particular those that govern its behaviour  
 +
# simulation-type models which are highly detailed and try as much as possible to avoid making assumptions about what is important; instead they try to include as much detail as possible in the expectation that nothing important will be omitted
 +
By simplifying to only the most important fluxes and state variables, the phosphorus model is very much a conceptual-type model.
  
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==Disadvantages==
 
Potential weaknesses of a conceptual approach include the likelihood of omitting something important. Every assumption runs the risk of being incorrect in an important way and thereby making model results divorced from reality. It only takes one unreasonable assumption or omission, if it relates to a key part of the system, to invalidate the model's results.
 
Potential weaknesses of a conceptual approach include the likelihood of omitting something important. Every assumption runs the risk of being incorrect in an important way and thereby making model results divorced from reality. It only takes one unreasonable assumption or omission, if it relates to a key part of the system, to invalidate the model's results.
  
 
Some major simplifications made in the phosphorus model are as follows:
 
Some major simplifications made in the phosphorus model are as follows:
  
(a) horizontal variations are completely ignored. The model is unable to simulate differences between different ocean basins, between high and low latitudes, or between deep and shallow water environments.
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# horizontal variations are completely ignored. The model is unable to simulate differences between different ocean basins, between high and low latitudes, or between deep and shallow water environments.
 
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# vertical variations can only be captured in an approximate way due to only two boxes in the vertical.
(b) vertical variations can only be captured in an approximate way due to only two boxes in the vertical.
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# only the major fluxes are included. Fluxes deemed to be of lesser importance, such as the delivery of phosphorus to the surface ocean within dust, are not included.
 
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# the representation of biology is extremely simplified. Limitation of growth rate due to light, temperature and other nutrients (for instance nitrogen, silicate and iron) are not included at all in the model, despite plentiful evidence that they are important at various times and places in the real ocean.  
(c) only the major fluxes are included. Fluxes deemed to be of lesser importance, such as the delivery of phosphorus to the surface ocean within dust, are not included.
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# different types of phytoplankton are not distinguished in the model.
 
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# there is no day-night cycle and no seasonal cycle in the model.
(d) the representation of biology is extremely simplified. Limitation of growth rate due to light, temperature and other nutrients (for instance nitrogen, silicate and iron) are not included at all in the model, despite plentiful evidence that they are important at various times and places in the real ocean.  
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# only inorganic phosphate is modelled. Dissolved organic phosphate (DOP) is not.
 
 
(e) different types of phytoplankton are not distinguished in the model.
 
 
 
(f) there is no day-night cycle and no seasonal cycle in the model.
 
 
 
(g) Only inorganic phosphate is modelled. Dissolved organic phosphate (DOP) is not.
 
  
 
The motivation for all of these omissions is the expectation that their addition does not fundamentally change the behaviour of the model. It is predicted that adding these features would not greatly alter the model’s general long-term response to, for instance, changes in the amount of phosphorus in the ocean, or changes in the input rate of phosphate down rivers.
 
The motivation for all of these omissions is the expectation that their addition does not fundamentally change the behaviour of the model. It is predicted that adding these features would not greatly alter the model’s general long-term response to, for instance, changes in the amount of phosphorus in the ocean, or changes in the input rate of phosphate down rivers.
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* [[Phosphorus model details]]
 
* [[Phosphorus model details]]
 
* [[Phosphorus model pros]]
 
* [[Phosphorus model pros]]
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==References==
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The phosphorus cycle model has not been published separately, though it is a key component of the [[Nitrogen-phosphorus model|nitrogen-phosphorus]] and [[Silicon-phosphorus model|silicon-phosphorus]] models.
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* Tyrrell, T. (1999).  [http://www.nature.com/nature/journal/v400/n6744/abs/400525a0.html The relative influences of nitrogen and phosphorus on oceanic primary production].  ''Nature'' '''400''', 525–531.
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* Yool, A. and Tyrrell, T. (2003).  [http://www.agu.org/pubs/crossref/2003/2002GB002018.shtml Role of diatoms in regulating the ocean's silicon cycle].  ''Global Biogeochemical Cycles'' '''17''', 1103, doi:10.1029/2002GB002018.
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==External links==
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* [http://en.wikipedia.org/wiki/Phosphorus Description of the chemical element phosphorus], [[Wikipedia]]
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* [http://en.wikipedia.org/wiki/Phosphorus_cycle Description of the phosphorus cycle], [[Wikipedia]]
  
 
[[Category:Biogeochemistry]]
 
[[Category:Biogeochemistry]]
 
[[Category:Phosphorus model]]
 
[[Category:Phosphorus model]]

Revision as of 10:36, 27 March 2008

A schematic of the modelled phosphorus cycle.

As with any model, simplification has both advantages and disadvantages. This article describes some of the phosphorus model cons.

Model description

In computer modelling there is a continuum between two caricature classes of models:

  1. conceptual-type models that aim to simplify a system down to include only its most important elements, in particular those that govern its behaviour
  2. simulation-type models which are highly detailed and try as much as possible to avoid making assumptions about what is important; instead they try to include as much detail as possible in the expectation that nothing important will be omitted

By simplifying to only the most important fluxes and state variables, the phosphorus model is very much a conceptual-type model.

Disadvantages

Potential weaknesses of a conceptual approach include the likelihood of omitting something important. Every assumption runs the risk of being incorrect in an important way and thereby making model results divorced from reality. It only takes one unreasonable assumption or omission, if it relates to a key part of the system, to invalidate the model's results.

Some major simplifications made in the phosphorus model are as follows:

  1. horizontal variations are completely ignored. The model is unable to simulate differences between different ocean basins, between high and low latitudes, or between deep and shallow water environments.
  2. vertical variations can only be captured in an approximate way due to only two boxes in the vertical.
  3. only the major fluxes are included. Fluxes deemed to be of lesser importance, such as the delivery of phosphorus to the surface ocean within dust, are not included.
  4. the representation of biology is extremely simplified. Limitation of growth rate due to light, temperature and other nutrients (for instance nitrogen, silicate and iron) are not included at all in the model, despite plentiful evidence that they are important at various times and places in the real ocean.
  5. different types of phytoplankton are not distinguished in the model.
  6. there is no day-night cycle and no seasonal cycle in the model.
  7. only inorganic phosphate is modelled. Dissolved organic phosphate (DOP) is not.

The motivation for all of these omissions is the expectation that their addition does not fundamentally change the behaviour of the model. It is predicted that adding these features would not greatly alter the model’s general long-term response to, for instance, changes in the amount of phosphorus in the ocean, or changes in the input rate of phosphate down rivers.

Further information

References

The phosphorus cycle model has not been published separately, though it is a key component of the nitrogen-phosphorus and silicon-phosphorus models.

External links