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8.11.3. Phosphorus cycle

Phosphorus cycle

The phosphorus is a component of molecules such as nucleic acids (ADP and ATP) and ATP molecule that use living organisms to exchange energy in chemical reactions. In addition, phosphorus is an essential part of skeletons and lakes.

The phosphorus cycle is very slow, compared to other biogeochemical cycles such as carbon or nitrogen.

Phosphorus is found in nature, usually in the form of the phosphate ion PO43-. The main phosphorous reserve is phosphate sedimentary rocks, but they are not within the reach of living beings.

When phosphate rocks weather, the phosphorus passes into the soil and surface waters.

The plants can absorb phosphates from the soil and incorporate them into their structures. Herbivores, by feeding on plants, will cause phosphorus to pass from plants to other levels of the food chain.

When plants and animals die, phosphates are released and can be absorbed by detritivores or incorporated into the soil.

Phosphates can also be carried by runoff water into rivers, lakes and oceans, where they can be absorbed by aquatic organisms.

Phosphate compounds in the bodies or debris of marine beings accumulate at the bottom and generate new sedimentary rocks. These rocks will remain here for many years (20,000 to 100,000) until tectonic movements lift the rock to the mainland and the phosphorus is once again available to plants.

An important reserve of phosphorus is the accumulations of the excrement of seabirds, called "guano", which can be used as fertilizer. As we saw in the case of nitrogen, the excess of these elements can cause eutrophication problems .

Phosphorus is the main limiting factor in aquatic ecosystems. In areas where ocean currents raise phosphorus from the seabed, plankton and the fish that feed on them proliferate.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.