Aquatic ecology and Biodiversity

Unit 6- Biogeochemical cycles

6.4. Phosphorus cycle

Phosphorus is an important and necessary chemical for both plants and animals as it is an essential constituent of DNA, RNA, fats such as phospholipids, bones and teeth of animals. Phosphates are also a critical component of ATP, the cellular energy carrier as they serve as an energy ‘release' for organisms to use in building proteins or contacting muscles. Like calcium, phosphorus is important to vertebrates; in the human body, 80% of phosphorous is found in teeth and bones.
Phosphorus circulates through water, the earth's crust, and living organisms. It is not present in the atmosphere and is most likely to enter food chains following the slow weathering of phosphate rock deposits. Some of the released phosphates become dissolved in soil water which is taken up by plant roots. Phosphates are not very soluble in water and not found in many types of rocks. Phosphorus is therefore the main limiting factor for plant growth in most soils and aquatic ecosystems. Animals obtain phosphorus by eating plants and/or herbivores. Dead organisms and animal wastes return phosphorus to the soil, to streams and eventually to ocean floors as rock deposits. People disrupt the phosphorus cycle by mining large amounts of phosphate rock for fertilizers and detergents and through runoff of such substances plus animal waste and sewage into aquatic ecosystems.