Fosforikierto

The fosforikierto, also known as the phosphorus cycle, is the biogeochemical cycle by which phosphorus moves through the lithosphere, hydrosphere, and biosphere. Unlike many other nutrient cycles, the phosphorus cycle does not have a significant atmospheric component. Phosphorus is an essential nutrient for all living organisms, playing a vital role in DNA, RNA, and ATP.

The primary reservoir of phosphorus on Earth is rock and soil. Weathering of these rocks releases phosphorus into the soil and water, primarily in the form of phosphate ions. Plants absorb these phosphates from the soil, and they enter the food web when herbivores consume the plants. Carnivores then obtain phosphorus by eating other animals.

When organisms die, decomposers break down their organic matter, returning the phosphorus to the soil and water. However, a significant portion of phosphorus can also be lost to the deep ocean through sedimentation, where it can remain for geological timescales. This process makes the return of phosphorus from the ocean to land very slow.

Human activities, particularly the use of phosphate fertilizers in agriculture and the discharge of sewage, have significantly accelerated the phosphorus cycle. This can lead to eutrophication of water bodies, a process where excessive nutrient enrichment causes algal blooms and oxygen depletion, harming aquatic ecosystems.