How do humans impact the phosphorus cycle?

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Humans affect the phosphorus cycle mainly by the use of fertilizers and raising livestock, especially hogs. Fertilizers and hog waste are high in phosphorus, which makes its way into the soil (where it is necessary in moderate amounts) and, due to runoff, in water. Another factor is in the use of detergents, many of which contain sodium tripolyphosphate, or STPP. The phosphate in STPP, the use of which has been severely curtailed due to environmental regulations, can lead to algal blooms in water, which can kill fish and other plants. It is by these activities that we alter the phosphorus and, in reality, the nitrogen cycle as well.

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How do humans impact nitrogen, carbon, and phosphorus?

The human body is mostly composed of water (70%).  This means that hydrogen and oxygen are the two most common elements in the human body.  But carbon, nitrogen, and phosphorus are among the other most common elements in the human body (sulfur is also up there).  These three elements are derived from food eaten by a person.  Carbon is the principle element in all major classes of biological molecules (proteins, lipids, sugars/starches, and nucleic acids).  Nitrogen is used in amino acids and nucleic acids.  Phosphorus is used primarily in phosphate groups (nucleic acids and ATP, among others).  So the human body incorporates all of these elements from food into these various components of the body.  When the body dies and decomposes in the ground, these atoms are reincorporated into the natural cycle through the soil, bacteria, plants, and eventually animals (including humans) again.

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How do human impacts the phosphorus cycle?

When excessive plant nutrients enter bodies of water, algae overgrow. Phosphorus is naturally found in soil and and is an ingredient in fertilizers. As weathering, runoff and erosion occurs, increased amounts of phosphates are added to bodies of water resulting in an overgrowth of algae or eutrophication. This can wreak havoc on the aquatic biome. Normally, phosphorus in the form of PO4, is taken up by plants and animals that consume the plants. Rain acts as an agent of weathering and causes phosphates to be removed from rocks and allows its entry into the soil and water. Phosphorus can end up on the ocean floor. This phosphorus is not available to the cycle. Phosphate is even excreted in feces. Phosphorus only gets into the soil by weathering of rocks. Phosphorus in dead plants returns to the soil by decomposition. However, when people farm and ship the crops elsewhere, the land becomes deficient of phosphorus. It must artificially be added by the use of fertilizers.

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How can the impacts that humans have on the phosphorus cycle be prevented?

Human beings have severely impacted the global phosphorus cycle. The application of phosphorus based fertilizers to the soil and increased amount of phosphorus in livestock feed is causing more phosphorus in manure. This leads to an increase in the phosphorus content of the soil. The erosion of this soil, coupled with surface runoff, is causing an increased amount of phosphorus in our water resources. This situation has been worsened by poor land management practices and deforestation. Water resources also receive phosphorous pollutants through phosphorous containing detergents. 

A number of steps can be taken to minimize the human impact on the phosphorus cycle. One step would be to control the amount of phosphorus input to the soil through limited fertilizer application. Similarly, we can control the amount of phosphorus in animal feed. Appropriate soil protection measures, including strategic uses of plants and modern farming techniques will ensure lesser surface runoff. We can also find alternative detergents that do not contain phosphorus. An awareness of phosphorus pollution and sharing of responsibility by all the stakeholders is also needed.

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