The phosphorus cycle (article) | Ecology | Khan Academy (2024)

Table of Contents

Key points Introduction Natural cycling of phosphorus Eutrophication and dead zones Attribution Works cited References Want to join the conversation? FAQs References

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The slow cycling of phosphorus through the biosphere. How phosphorus-containing fertilizers can cause aquatic dead zones.

Key points

Phosphorus is an essential nutrient found in the macromolecules of humans and other organisms, including $DNA$ ‍.
The phosphorus cycle is slow. Most phosphorus in nature exists in the form of phosphate ion— ${PO}_{4}^{3 -}$ ‍.
Phosphorus is often the limiting nutrient, or nutrient that is most scarce and thus limits growth, in aquatic ecosystems.
When nitrogen and phosphorus from fertilizer are carried in runoff to lakes and oceans, they can cause eutrophication, the overgrowth of algae. The algae may deplete oxygen from the water and create a dead zone.

Introduction

Is phosphorus important? That depends—do you like having $DNA$ ‍, cell membranes, or bones in you body? Hint: The answer is probably yes!

Phosphorus is an essential nutrient for living organisms. It’s a key part of nucleic acids, like $DNA$ ‍ and of the phospholipids that form our cell membranes. As calcium phosphate, it also makes up the supportive components of our bones.

In nature, phosphorus is often the limiting nutrient—in other words, the nutrient that’s in shortest supply and puts a limit on growth—and this is particularly true for aquatic, freshwater ecosystems.

Natural cycling of phosphorus

The phosphorus cycle is slow compared to other biogeochemical cycles such as the water, carbon, and nitrogen cycles. $^{1}$ ‍

In nature, phosphorus is found mostly in the form of phosphate ions— ${PO}_{4}^{3 -}$ ‍. Phosphate compounds are found in sedimentary rocks, and as the rocks weather—wear down over long time periods—the phosphorus they contain slowly leaches into surface water and soils. Volcanic ash, aerosols, and mineral dust can also be significant phosphate sources, though phosphorus has no real gas phase, unlike other elements such as carbon, nitrogen, and sulfur.

Phosphate compounds in the soil can be taken up by plants and, from there, transferred to animals that eat the plants. When plants and animals excrete wastes or die, phosphates may be taken up by detritivores or returned to the soil. Phosphorus-containing compounds may also be carried in surface runoff to rivers, lakes, and oceans, where they are taken up by aquatic organisms.

When phosphorus-containing compounds from the bodies or wastes of marine organisms sink to the floor of the ocean, they form new sedimentary layers. Over long periods of time, phosphorus-containing sedimentary rock may be moved from the ocean to the land by a geological process called uplift. However, this process is very slow, and the average phosphate ion has an oceanic residence time—time in the ocean—of 20,000 to 100,000 years.

Eutrophication and dead zones

Most fertilizers used in agriculture—and on lawns and gardens—contain both nitrogen and phosphorus, which may be carried to aquatic ecosystems in surface runoff. Fertilizer carried in runoff may cause excessive growth of algae or other microbes that were previously limited by nitrogen or phosphorus. This phenomenon is called eutrophication. At least in some cases, phosphorus, not nitrogen, seems to be the main driver of eutrophication. $^{2}$ ‍

Why is eutrophication harmful? Some algae make water taste or smell bad or produce toxic compounds. $^{2}$ ‍ Also, when all of those algae die and are decomposed by microbes, large amounts of oxygen are used up as their bodies are broken down. This spike in oxygen usage can sharply lower dissolved oxygen levels in the water and may lead to death by anoxia —lack of oxygen—for other aquatic organisms, such as shellfish and finfish.

Regions of lakes and oceans that are depleted of oxygen due to a nutrient influx are called dead zones. The number of dead zones has increased for several years, and more than 400 of these zones existed in 2008. One of the worst dead zones is off the coast of the United States in the Gulf of Mexico. Fertilizer runoff from the Mississippi River Basin created a dead zone of over 8,463 square miles. As you can see in the figure below, dead zones are found in areas of high industrialization and population density around the world.

How can eutrophication be reduced or prevented? Fertilizers, phosphorus-containing detergents, and improperly disposed of sewage can all be sources of nitrogen and phosphorus that drive eutrophication. Using less fertilizer, eliminating phosphorus-containing detergents, and ensuring that sewage does not enter waterways—e.g., from a leaky septic system—are all ways that individuals, companies, and governments can help reduce eutrophication. $^{3, 4}$ ‍

Attribution

This article is a modified derivative of the following articles:

"Biogeochemical cycles" by Robert Bear, David Rintoul, Bruce Snyder, Martha Smith-Caldas, Christopher Herren, and Eva Horne, CC BY 4.0; download the original article for free at http://cnx.org/contents/db89c8f8-a27c-4685-ad2a-19d11a2a7e2e@24.18
"Biogeochemical cycles" by OpenStax College, Concepts of Biology, CC BY 4.0; download the original article for free at http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.10

The modified article is licensed under a CC BY-NC-SA 4.0 license.

Works cited

"Phosphorous Cycle," Lenntech, accessed June 10, 2016, http://www.lenntech.com/phosphorus-cycle.htm.
Stephen R. Carpenter, "Phosphorous Control Is Critical to Mitigating Eutrophication," PNAS 12, no. 105 (2008): 11039-11040. http://dx.doi.org/10.1073/pnas.0806112105.
"How Can Eutrophication Be Slowed?" RMB Environmental Laboratories, Inc., accessed July 10, 2016, http://rmbel.info/how-can-eutrophication-be-slowed/.
"Sources of Eutrophication," World Resources Institute, accessed July 10, 2016, http://www.wri.org/our-work/project/eutrophication-and-hypoxia/sources-eutrophication.

References

"Aquatic Dead Zones." NASA Earth Observatory. Last modified July 17, 2010. http://earthobservatory.nasa.gov/IOTD/view.php?id=44677.

Carpenter, Stephen R. "Phosphorous Control Is Critical to Mitigating Eutrophication." PNAS 12, no. 105 (2008): 11039-11040. http://dx.doi.org/10.1073/pnas.0806112105.

Chislock, Michael F., Enrique Doster, and Alan E. Wilson. "Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems." Nature Education Knowledge 4, no. 4 (2013): 10. http://www.nature.com/scitable/knowledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466.

"Eutrophication." Wikipedia. Last modified June 6, 2016. https://en.wikipedia.org/wiki/Eutrophication.

"How Can Eutrophication Be Slowed?" RMB Environmental Laboratories, Inc. Accessed July 10, 2016. http://rmbel.info/how-can-eutrophication-be-slowed/.

"Limiting Nutrient." Accessed June 10, 2016. https://www.rpi.edu/dept/chem-eng/Biotech-Environ/GrowPresent/limiting.htm.

"Phosphorous Cycle." Lenntech. Accessed June 10, 2016. http://www.lenntech.com/phosphorus-cycle.htm.

"Phosphorous Cycle." The Environmental Literacy Council. Accessed June 10, 2016. http://enviroliteracy.org/air-climate-weather/biogeochemical-cycles/phosphorus-cycle/.

"Phosphorous Cycle." Wikipedia. Last modified May 20, 2016. https://en.wikipedia.org/wiki/Phosphorus_cycle.

Raven, Peter H., George B. Johnson, Kenneth A. Mason, Jonathan B. Losos, and Susan R. Singer. "Biogeochemical Cycles." In Biology, 1209-1214. 10th ed., AP ed. New York: McGraw-Hill, 2014.

"Sources of Eutrophication." World Resources Institute. Accessed June 10, 2016. http://www.wri.org/our-work/project/eutrophication-and-hypoxia/sources-eutrophication.

Wang, Rong, Yves Balkanski, Olivier Boucher, Philippe Ciais, Josep Peñuelas, and Shu Tao. "Significant Contribution of Combustion-Related Emissions to the Atmospheric Phosphorous Budget." Nature Geoscience 8 (2015): 48-54. http://dx.doi.org/10.1038/ngeo2324.

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Rohan Khapre
8 years agoPosted 8 years ago. Direct link to Rohan Khapre's post “phosphorous cycle is perf...”
phosphorous cycle is perfect or imperfect cycle ?
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(8 votes)
- Lisa Ni
  8 years agoPosted 8 years ago. Direct link to Lisa Ni's post “It is an imperfect cycle....”
  It is an imperfect cycle. This is because not all phosphorous can be retained in the cycle no matter how hard you try. Even without human interference, some phosphorous is going to escape from the cycle.
  Comment on Lisa Ni's post “It is an imperfect cycle....”
  (11 votes)
Zulhiyadi
5 years agoPosted 5 years ago. Direct link to Zulhiyadi's post “is there a way that we bl...”
is there a way that we block the cycle?
example : after using phosphorous for fertilizer, we make irrigation canal for fertilizer residu to transport and we harfest the residu to make fertilizer again?
is that possible?
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(7 votes)
- Ivana - Science trainee
  5 years agoPosted 5 years ago. Direct link to Ivana - Science trainee's post “Do you mean to recycle? S...”
  Do you mean to recycle? Sounds nice to me. Not sure what agriculture engineers can say about it. We should ask them :D
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  (7 votes)
Vela, Camelia
7 years agoPosted 7 years ago. Direct link to Vela, Camelia's post “what happens if there is ...”
what happens if there is too much nitrogen or phosphorus in an environment?
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(5 votes)
- asingh03.sf
  6 years agoPosted 6 years ago. Direct link to asingh03.sf's post “If too much nitrogen or p...”
  If too much nitrogen or phosphorus is present in an environment, plant growth is greatly increased. This is due to the fact that both nitrogen and phosphorus are limiting nutrients. While this abundance of nutrients may be fine in your backyard, it can potentially be very harmful. For example, when too much nitrogen and phosphorus are present in a marine biome, eutrophication takes place. This leads to dead zones.
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  (6 votes)
Isaac D. Cohen
6 years agoPosted 6 years ago. Direct link to Isaac D. Cohen's post “If it takes such a long t...”
If it takes such a long time for Phosphorous to go back to the land from the ocean, and it sounds like surface runoff carries phosphorous to the ocean much quicker, will we eventually run out of Phosphorus?
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(4 votes)
- Sweetrin69
  6 years agoPosted 6 years ago. Direct link to Sweetrin69's post “Well, I do think it is p...”
  Well, I do think it is possible, mostly because most of the industrial phosphorous is obtained from rocks so of course it is necessary for millions of years to pass before new rocks are formed, it is a limited nutrient by all means. But I don't think we are going to be able to see such a thing happening in quite a long time. I think it is by far easier that all our continental water reservoirs become euthrophicated before that.
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  (4 votes)
melinaxiewu
3 years agoPosted 3 years ago. Direct link to melinaxiewu's post “How can phosphorus escape...”
How can phosphorus escape rocks?
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(3 votes)
- FrozenPhoenix45
  3 years agoPosted 3 years ago. Direct link to FrozenPhoenix45's post “Phosphorus can escape roc...”
  Phosphorus can escape rocks when natural processes like wind and weathering chip away phosphorus in a soluble form, where it is then ingested by animals
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  (4 votes)
karen victor
3 years agoPosted 3 years ago. Direct link to karen victor's post “what is the time frame of...”
what is the time frame of the phosphorus cycle?
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(3 votes)
- Hind Saud
  3 years agoPosted 3 years ago. Direct link to Hind Saud's post “20,000 to 100,000 years”
  20,000 to 100,000 years
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  (3 votes)
Nikki
4 years agoPosted 4 years ago. Direct link to Nikki's post “does phosphate return to ...”
does phosphate return to the soil and does phosphorus get decomposed by decomposers first?
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(2 votes)
- Ivana - Science trainee
  4 years agoPosted 4 years ago. Direct link to Ivana - Science trainee's post “Phosphate is not back in ...”
  Phosphate is not back in its chemical free form but via organism since it gets incorporated in living organisms therefore once they decay you have phosphorus in the soil.
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  (2 votes)
Quinn Raffo
4 years agoPosted 4 years ago. Direct link to Quinn Raffo's post “What are the biotic and a...”
What are the biotic and abiotic factors in this cycle?
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- Hind Saud
  3 years agoPosted 3 years ago. Direct link to Hind Saud's post “Biotic factors are the li...”
  Biotic factors are the living things in an ecosystem so they do not recycle. Abiotic factors are the different physical and chemical components available like temperature, air, water, minerals, rocks,and PH
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  (2 votes)
630302278
3 years agoPosted 3 years ago. Direct link to 630302278's post “How can I explain the pho...”
How can I explain the phosphorus cycle really easily
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Felix
4 years agoPosted 4 years ago. Direct link to Felix's post “Where does it stay the sh...”
Where does it stay the shortest amount of time? Explain why.
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(2 votes)

FAQs

The phosphorus cycle (article) | Ecology | Khan Academy? ›

Phosphorus moves between living organisms and the environment during the phosphorus cycle

cycle
A biogeochemical cycle, or more generally a cycle of matter, is the movement and transformation of chemical elements and compounds between living organisms, the atmosphere, and the Earth's crust. Major biogeochemical cycles include the carbon cycle, the nitrogen cycle and the water cycle.
https://en.wikipedia.org › wiki › Biogeochemical_cycle
Biogeochemical cycle - Wikipedia

. The largest reservoirs of phosphorus are buried in rock and deep ocean sediments. When rocks and sediments weather, or wear down, phosphate ions ( PO A 4 A 3 − ‍ ) are released.

See Details ›

What is the phosphorus cycle paragraph? ›

Phosphorus moves in a cycle through rocks, water, soil and sediments and organisms. Over time, rain and weathering cause rocks to release phosphate ions and other minerals. This inorganic phosphate is then distributed in soils and water. Plants take up inorganic phosphate from the soil.

What are the 7 steps of the phosphorus cycle? ›

Weathering. Weathering of uplifted rocks contributes phosphates to the land. ...
Fertilizer. Phosphate fertilizer applied to fields can run off directly into streams, become part of a soil pool, or be absorbed by plants.
Excretion and Decomposition. ...
Dissolved Phosphates. ...
Geologic Uplift. ...
Weathering.

Learn More ›

What is the phosphorus cycle for dummies? ›

When the plants and animals die they are decomposed by microorganisms During this process, the organic form of phosphorus is converted into the inorganic form, which is recycled to soil and water. Soil and water will end up in sediments and rocks, which will again release phosphorus by weathering.

Read On ›

What are two ways that phosphorus can be returned to the environment? ›

The phosphate acquired by organisms is returned to the soil or water through animal excretions (poop) and through the decomposition of dead organisms.

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Which best summarizes the phosphorus cycle? ›

The phophorus cycle is best described by the movement of phosphorus between land, ocean and living organisms. Hope this answers the question. With this cycle, the atmosphere is not involved.

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How would you summarize the key components of the phosphorus cycle? ›

Through millions of years, phosphorus has moved slowly through the inorganic cycle, starting with the rocks which slowly weather to form soil, from which the phosphorus is gradually leached from the land into rivers and onward to the sea, where it eventually forms insoluble calcium phosphate and sinks to the seafloor ...

Read On ›

How do humans affect the phosphorus cycle? ›

Human actions—mining phosphorus (P) and transporting it in fertilizers, animal feeds, agricultural crops, and other products—are altering the global P cycle, causing P to accumulate in some of the world's soil. Increasing P levels in the soil elevate the potential P runoff to aquatic ecosystems (Fluck et al.

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What is the conclusion of the phosphorus cycle? ›

In conclusion, the phosphorus cycle, a gradual process spanning the hydrosphere, lithosphere, and atmosphere, involves key steps such as weathering, plant uptake, and decomposition. This cycle sustains life by maintaining phosphorus concentrations, essential for energy production and DNA synthesis.

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What are two ways the phosphorus cycle is important to living things? ›

Phosphorus is an essential nutrient for living organisms. It's a key part of nucleic acids, like ‍ and of the phospholipids that form our cell membranes. As calcium phosphate, it also makes up the supportive components of our bones.

Get More Info Here ›

Is the phosphorus cycle fast or slow? ›

Phosphorus moves slowly from deposits on land and in sediments, to living organisms, and than much more slowly back into the soil and water sediment. The phosphorus cycle is the slowest one of the matter cycles that are described here.