Phosphorus cycle

The great reservoir of phosphorus is not the atmosphere but the rocks or other deposits which have been formed in past geological ages. These are gradually eroding, releasing phosphates to ecosystems, but much phosphate escapes to the sea, where part of it is deposited in the shallow sediments and part of it lost to the deep sediments. The means of returning phosphorus to the cycle may presently be inadequate to compensate for the loss. Marine birds and fish may play important role in uplifting of sediments thus returning phosphorus to the cycle. This transfer of phosphorus and other materials by birds from the Sea to land is continuing but not at the rate it had occurred in some of the past ages. Man harvest lot of marine fish , , thus accelerating the rate of loss of phosphorus but not enough being cycled as compared to the phosphorus  in parent rocks.

Though, reserves of phosphate Rock are large, situation could become alarming, and we feel concerned with "traffic jam" of dissolved phosphate in the waterways due to increased erosion that may not be compensated for by protoplasm synthesis and sedimentation. One way to overcome this problem is to spray waste water on upland vegetation instead of piping it directly into the water ways.

It may be concluded from above that generally, phosphorus does not move evenly and smoothly from organism to environment and back to organism as it appears from the figure.

There may be achieved a long term equilibrium. Most phosphorus at a time, is tied up either in the organisms (bone) or in solids (organic detritus and inorganic particles making the sediments). In lakes, generally uptake rate is more rapid than the release rate. Concentration of phosphorus at any one time may bear little relation two productivity of the ecosystem. March aur virtually all of the phosphate in the system may be inside living organism at a given time, yet it may be overturning every however with the result that there will be a constant supply of phosphate for organisms able to concentrate it from a very dilute solution. Such systems may remain stable biologically for considerable periods in the the absence of available phosphate.

The concept of turnover is very useful in comparing exchange rates between different components of an ecosystem. Turn over rate is the fraction of the total amount of a substance in in a component which is released any given length of time, whereas turn over time is the reciprocal of this that means the time required to replace quantity of substance equal to the amount in the component. studies with P - 32 labelled fertilizers in land ecosystems have also revealed that much of the phosphorus is locked up and unavailable to plants at any given time.

Impact of human activities on phosphorus cycle

✓ We mine large quantities of        phosphate rocks to make commercial inorganic fertilizers and detergents.

✓ We reduce the available phosphate in soils by cutting down forests.

✓ We disrupt aquatic systems with phosphates from runoff of animal waste and fertilizers and discharge from sewage treatment systems.