Phosphorus does not float. Unlike carbon and nitrogen, it has no gaseous phase. The phosphorus cycle moves this element through soil, water, and living organisms, but it never enters the atmosphere. Phosphorus comes from rocks, which weather slowly and release phosphate into soil. Plants absorb it through their roots. Animals get it by eating plants or other animals. When organisms die, decomposers return phosphorus to the soil. Some of it washes into rivers and oceans, where it settles into sediments and, over millions of years, becomes rock again.

The cycle is slow. Weathering releases phosphorus at a rate that limits plant growth in many ecosystems. That is why phosphorus is often the limiting nutrient in freshwater lakes. Human activity has changed the balance. Mining phosphate rock for fertilizer moves large amounts of phosphorus from geological reserves into farms and waterways. Runoff from fields and sewage carries phosphorus into lakes and coastal waters, triggering algal blooms. When the algae die, decomposition consumes oxygen, creating dead zones. Reducing phosphorus pollution means managing fertilizer use and improving wastewater treatment.

Key features

• No atmospheric phase.
• Comes from rock weathering.
• Often the limiting nutrient in freshwater.
• Excess causes algal blooms and dead zones.

Phosphorus is essential for DNA, cell membranes, and bones. Without it, life as we know it would not exist. Too much of it, in the wrong place, causes serious harm.