Humans affect the phosphorus cycle primarily through the use of synthetic fertilizer. The general result is the increased amount of runoff phosphorus and the depletion of natural phosphorus deposits.
The Phosphorus cycle refers to the movement of phosphorus through the hydrosphere, biosphere and lithosphere. Because the process of moving phosphate from the soil to the ocean takes so long, it is considered one of the slowest biochemical cycles.
Most of the phosphate used for fertilizer is mined from naturally occurring deposits of apatite (also known as calcium phosphate). Not all of the fertilizer applied to farm lands is consumed by plants. Some of it is swept away by water, which may run off into lakes, leading to an abundance of the nutrient. Some of the phosphate applied on frozen ground is also lost during the spring thaw. All this runoff can lead to an increase in the growth of algae and bacteria, which in turn throws the water ecosystem off balance.
Phosphate serves as one of the key backbones in RNA and DNA. It is also an incorporated element in many of the essential molecules for life such as adenosine triphosphate. Phosphorus can also be found in teeth and bones of mammals, as well as the exoskeleton of insects.