The phosphorus cycle refers to the movement of phosphorus within and between the biosphere, hydrosphere and geosphere. The phosphorus cycle matters because phosphorus is an essential nutrient for sustaining life on Earth, where it plays a central role in the transfer of energy within organisms, the structure of the genetic material, and in the composition of cell membranes, bones and teeth. When other resources such as light and water are abundant, ecosystem productivity and biomass is often limited by the amount of available phosphorous. This is the primary reason we mine phosphorus, which serves as an essential component of the fertilizer used to enhance soil quality for agricultural activities .
The phosphorus cycle is an essential part of How the Earth System Works. Click the image on the left to open the Understanding Global Change Infographic . Locate the phosphorus cycle icon and identify other Earth system processes and phenomena that cause changes to, or are affected by, the cycling of phosphorus.
Phosphorus cycles through both the abiotic and biotic parts of the Earth system, especially in the biosphere, hydrosphere, and geosphere. Phosphorus is found in the Earth’s crust, primarily in sedimentary rocks that contain phosphate (PO43-) minerals. As these rocks weather and erode, dissolved phosphates enter the soil and travel via rivers to the ocean. Primary producers (photosynthesizing organisms), both on land and in the ocean, absorb the phosphate needed to produce organic compounds necessary for the survival and growth of all organisms. The phosphate acquired by organisms is returned to the soil or water through animal excretions (poop) and through the decomposition of dead organisms. Humans greatly influence the phosphorus cycle through the release of mined phosphates into ecosystems, especially in the form of fertilizers, but also from detergents and sewage waste. There are no major gaseous forms of phosphorus, so aside from wind distributing small particles of dust containing phosphorus, only very small amounts of phosphorus move through the atmosphere.
Phosphorus levels can vary significantly in aquatic and terrestrial habitats, and can be affected by various human activities and environmental phenomena, including:
The rock cycle, especially by rates of weathering and erosion. Different rock types have considerably different concentrations of phosphorus. Thus, the type of rock that is weathered plays a major role in determining the concentration of phosphorous (and other nutrients) in soils, freshwater environments, and coastal waters. The phosphorous levels, in turn, influence the biodiversity of plants and animals are present.
The Earth system model below includes some of the processes and phenomena related to the phosphorus cycle. These processes operate at various rates and on different spatial and temporal scales. For example, geologic processes, such as uplift and weathering occur over thousands to millions of years, while human influences on the phosphorus cycle happen over months to years. Can you think of additional cause and effect relationships between the parts of the phosphorus cycle and other processes in the Earth system?
Click the icons and bolded terms (e.g. agricultural activities, soil quality, erosion, and nutrient level) on this page to learn more about these process and phenomena. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you.
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