Discovery Science: Cycle of Matter – Phosphorus Cycle and Water Cycle

Earth Science: Cycle of Matter – Phosphorus Cycle and Water Cycle

Phosphorus plays an important role for all organisms in many processes involving energy transfer and energy maintenance. In addition, water is an indispensable component in all activities of life’s processes.

Phosphorus, which occurs in nature almost exclusively in the form of organic compounds or phosphate, participates in various metabolic reactions. It is also an indispensible component of nucleic acids and enzymes, as well as the building block for bones and teeth. Phosphorus enters the phosphorus cycle exclusively in the form of phosphate
ions (PO4^3-).

These originate principally from the effects of weathering and the breakdown of phosphorus containing rocks, as well as from phosphorus waste. Some of this phosphate is then taken up by plants and is eventually returned to the soil by the so-called phytophagous food chain (through grain cereals and their consumption by animals and humans). At that point it is converted back again to phosphate by bacteria, and it can then reenter the phosphorus cycle.

Another part of the phosphate is washed out through groundwater, streams, and rivers into lakes and the ocean, where most of it is taken up by phytoplankton and then flows back into the food chain. These final phosphorus links are then often returned to the mainland, for instance through fishing activities, so that the cycle is consequently closed once more.

The water cycle

The constant movement of water associated with changes in aggregate conditions, between the oceans, the atmosphere, and the mainland is referred to as the water cycle. The cycle commences with evaporated water (water vapor) rising from water surfaces (especially from the oceans but also from lakes and rivers), from the soil (evaporation), and from the plant cover (transpiration) entering the atmosphere.

The driving force for the formation of water vapor is solar energy. The water vapor drifts away due to air currents, and following condensation and the formation of clouds it is returned to Earth in the form of rain or snow. Approximately 80 percent of this precipitation falls over the oceans. Part of the remaining 20 per-cent evaporates from the mainland and is returned directly back to the atmosphere.

Some of the water also sinks into the ground and so supplies the groundwater. This groundwater later returns to the surface through springs or runs off the land surface into rivers and then back into the ocean. There the water cycle begins again.


If suddenly large amounts of phosphate are added to a lake or a pond, for example, via wastewater, it can destroy the fragile ecological balance Due to rapid algae growth (a sudden increase in food material), animals will quickly reproduce.

This leads to a significant Increase in oxygen consumption, so that in an extreme case a lack of oxygen may make the waters uninhabitable.


GUANO The phosphorus and nitrogen-rich excrement deposits of sea birds are referred to as guano and used to be a popular fertilizer, mainly during the 19th century.