Phosphorus enters the environment from rocks or deposits laid down on the earth many years ago. Phosphate rock in the commercially available form is called apatite. Other deposits may be from fossilized bone or bird droppings called guano. Weathering and erosion of rocks gradually releases phosphorus as phosphate ions, which are soluble in water. Land plants need phosphate as a fertilizer or nutrient.
Phosphate is incorporated into many molecules essential for life, such as ATP (adenosine triphosphate), which is important in the storage and use of energy. Phosphate is also in the backbone of DNA and RNA, molecules involved in genetic coding.
When plant materials and waste products decay through bacterial action, the phosphate is released and returned to the environment for reuse.
Much of the phosphate eventually is washed into the water from erosion and leaching. Again water plants and algae utilize the phosphate as a nutrient. Studies have shown that phosphate is the limiting agent in the growth of plants and algae. If phosphate is not present in sufficient quantity, the plants exhibit slow growth or will be stunted. If too much phosphate is present, excess growth may occur, particularly in algae.
A large percentage of the phosphate in water is precipitated from the water as iron phosphate, which is insoluble. If the phosphate is in shallow sediments, it may be readily recycled back into the water for further reuse. In deeper sediments in water, it is available for use only as part of a general uplifting of rock formations for the cycle to repeat itself.
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