Sedimentary Cycle

Lesson 10: Bio-geo-chemical cycles

Phosphorous cycle

Mineral elements required by living organisms are obtained from inorganic sources. Available forms occur as salts dissolved in soil water. Mineral cycles consists of two phases :
salt phase and rock phase. Mineral salts come directly from earth’s crust and then enter water cycle. The dissolved phosphorus from the soil is absorbed by plants and converted to organic form. It travels to various trophic levels from plants. When plants and animals die the decomposers attack them and liberate phosphorus to environment. This process proceeds in cyclic way. Phosphorous reaches the oceans and settles down as sediment.

Again, the keystones of getting phosphorus into trophic systems are plants. Plants absorb phosphorous from water and soil into their tissues, tying them to organic molecules. Once taken up by plants, phosphorus is available for animals when they consume the plants.
When plants and animals die, bacteria decompose their bodies, releasing some of the phosphorus back into the soil. Once in the soil, phosphorous can be moved 100s to 1,000s of miles from where they were released by riding through streams and rivers. So the water cycle plays a key role of moving phosphorus from ecosystem to ecosystem.

In some cases, phosphorous will travel to a lake, and settle on the bottom. There, it may turn into sedimentary rocks, limestone, to be released millions of years later. So sedimentary rocks act like a back, conserving much of the phosphorus for future ones.

Last modified: Thursday, 29 December 2011, 8:20 AM