Phosphorus cycle

Diagram of the phosphorus cycle

The phosphorus cycle is a biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth.

Overview

Phosphorus is an essential nutrient for plants and animals. It forms part of important life-sustaining molecules such as DNA and RNA, and is a critical component of ATP, the energy currency of cells. The phosphorus cycle is unique among the major biogeochemical cycles in that it does not include a gas phase, and phosphorus is typically found in the form of phosphate ions (PO₄³⁻) in the environment.

Sources of Phosphorus

Phosphorus cycle in nature

Phosphorus is primarily found in rocks and is released through the process of weathering. As rocks break down, phosphate is released into the soil and water. Plants absorb phosphate from the soil, and it moves through the food chain as animals consume plants and other animals.

Movement Through Ecosystems

Phosphorus movement in ecosystems

In ecosystems, phosphorus moves through the food web from producers to consumers and eventually to decomposers. When plants and animals die, decomposers such as bacteria and fungi break down the organic matter, releasing phosphorus back into the soil or water, where it can be reused by plants.

Human Impact

Global phosphorus fertilizer application

Human activities have significantly altered the phosphorus cycle. The use of fertilizers in agriculture has increased the amount of phosphorus in the soil, which can lead to eutrophication of water bodies when excess phosphorus runs off into lakes and rivers. This can cause algal blooms, which deplete oxygen in the water and harm aquatic life.

Phosphorus in Aquatic Systems

Phosphorus cycle in wetlands

In aquatic systems, phosphorus is a limiting nutrient, meaning that its availability can control the rate of growth of algae and aquatic plants. Phosphorus enters aquatic systems through runoff from land, and it can be recycled within the water body as organisms die and decompose.

Global Phosphorus Cycle

Phosphorus in marine environments

The global phosphorus cycle involves the movement of phosphorus from the land to the ocean and back again. Phosphorus is transported to the ocean via rivers and streams, where it can be deposited in marine sediments. Over geological time scales, tectonic activity can uplift these sediments, returning phosphorus to the land.

Related Pages

• Biogeochemical cycle
• Eutrophication
• Nutrient cycle
• Fertilizer