Plants require inorganic phosphate for their nutrition in typical mineral cycle. This phosphate is transferred to consumers and decomposers as organic phosphate. Subsequently it is made available as inorganic phosphate for recycling via mineralizing decomposition.
Phosphorus occurs in soil and rock as calcium phosphate and as hydroxyl apatite. Since phosphate rock is slightly soluble, quite small amounts of phosphorus are leached into solution, resulting in concentration as low as 1 ppb. Since phosphorus is required for all life processes, its concentration in natural water is further reduced by the biological system. Because of seasonal changes in plants and animals production, and because of increased phosphorus input to natural waters from spring runoff, the concentration of phosphorus will vary remarkably over the year.
The input of phosphorus from human activity can be far greater than from natural sources. Domestic sewage contains phosphorus in feces and from commercial detergents, in which phosphates are used; runoff from agricultural areas which have received `fertilizers (normally containing nitrogen, phosphorus and potassium) can be another important source of phosphorus. Therefore in any polluted waters, soluble phosphorus can reach much higher concentration than the non polluted waters. This readily available phosphorus can often lead to the growth of nuisance organisms such as filamentous algae, which can cause taste and odour problems in water supplies and clog filters in water treatment plants. The general problem of Eutrophication of lakes also takes place due to phosphorus.
For the nutrition of plants requires phosphorus in the phosphate form, generally as orthophosphates (PO4). They assimilate it directly, converting the PO4 to the organic form of their protoplasm. Decay of these organisms dissolves and releases the phosphorus for reuse. However in lakes much of the phosphate is removed from the water by the sediment, which elements it form the seasonal water circulation. Phosphorus shows the seasonal changes
The rapid and continuous turnover of Phosphorus which enables phytoplankton populations to expand rapidly in the spring although the actual scarcity of phosphorus in many waters means that it is a limiting nutrient, addition of which can be rapidly assimilated by algae, which then grow profusely.