SMES - Phosphorus Cycle (Lesson)
Phosphorus Cycle
The phosphorus cycle is probably the easiest of the biogeochemical cycles to describe. Phosphorus does not exist in the atmosphere except in dust particles. It is necessary for living organisms, as it is the backbone of nucleic acids (DNA and RNA) and other important biological molecules. Phosphorus tends to move through a local cycle, whereas the other cycles are global in nature, mostly because of the Earth's weather. Since phosphorus is limited in the atmosphere, it is unlikely to move great distances.
Phosphorus is found in soil, rock, and sediments. It is released from these rock forms through chemical weathering in the form of phosphate (PO4-3). Phosphate is highly soluble in aqueous solutions and can be absorbed from the soil into plants through their roots. Often phosphorus is a limiting factor for plant growth, as little of it is released into the environment.
Phosphorus can enter the water table and ultimately travel to the oceans, where it settles on the ocean floor. Later, through geological processes, ocean mixing, and upwelling, these rocks on the ocean floor may rise and become new land surfaces, with the result that their components can reenter the terrestrial cycles.
Humans affect the phosphorus cycle by mining phosphorus-rich rocks for the purpose of processing them and adding them to commercial inorganic fertilizers. The phosphorus is easily leached into the groundwater and can find its way into aquatic ecosystems; where it can help promote algae and other aquatic plant growth that can lead to overgrowth of these plants and ultimately eutrophication of the pond or lake. Phosphorus also can be added to ecosystems by humans through the release of untreated sewage, agricultural runoff, and detergents.
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