Cycle of phosphorus in water

Phosphorus cycle in water - a complex of chemical and biochemical reactions to the circulation of phosphorus compounds in water reservoirs.

Phosphorus sources in water:

Phosphorus, which flows into the water reservoir, circulates between layers of water in a variety of ways, depending on the type of lake and its trophic status. In the water tank there are two phosphate circuits: small and large circuits.

A small phosphorus cycle takes place in a period of stagnation when the stratification of the water is clearly indicated. The whole process takes place in an epilimnion. In the oxygenated and exposed surface of the water are phosphate ions, which are taken up by phytoplankton and incorporated into their body. Circulating circulatory movements in the epilimnion do not allow plankton organisms to fall into the deeper layers of water, so the organic form of phosphorus is decomposed by enzymes again into phosphate ions that can be re-assimilated. This process can be repeated many times.

If organic phosphorus falls into the deeper layers of water through the metallimnion to hypolymnion, it only mineralizes in these deeper layers. Chemical transformation of phosphorus in water leads to precipitation and it is accumulated in bottom sediments. From the upper part of the water, phosphorus to the bottom falls not only in the form of dead organic matter but also in association with calcium, iron, aluminum and mineral suspensions. Where oxygen is present in the zone of contact of bottom sediments with water, Fe iron ions bind persistent phosphate ions to trap them, and in this form are deposited in bottom sediments. If hypolymnion is lacking oxygen, trivalent iron passes to bivalent Fe. As iron phosphate (2+) is better soluble, it releases phosphorus from bottom sediments to water - it is an internal enrichment process.

Extremely reducing sulfates in water are converted to hydrogen sulphide, and then a large proportion of iron Fe forms insoluble sulphides on the surface of bottom sediments and is excluded from phosphorus precipitation, even during the period of circulation. Degraded lakes under extreme reduction conditions in bottom sediments produce methane. Despite the stable thermal stratification, methane bubbles float upward, transporting considerable amounts of phosphorus to the lake's production layer. The methane convection is the main mechanism of internal fertilization, and the formation of hydrogen sulphide in the water is the moment when eutrophication of the lake takes place in avalanche mode. : nitrogen circulation in aquatic environment. Bibliography

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