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.
28.13 ECOSYSTEM
An ecosystem is a natural unit consisting of all plants, animals and micro-organisms (biotic factors) in an area functioning together with all of the non-living physical (abiotic) factors of the environment. An ecosystem is a completely independent unit of interdependent organisms that share the same habitat. Ecosystems usually form a number of food webs, which show the interdependence of the organisms within the ecosystem. Examples of ecosystems are rain forest, savanna, desert, coral reef and urban ecosystem.
Similar to an ecosystem is a biome, which is a climatically and geographically defined area of ecologically similar climatic conditions such as communities of plants, animals and soil organisms, often referred to as ecosystems. Biomes are defined based on factors such as plant structures (such as trees, shrubs and grasses), leaf types (such as broadleaf and needle-leaf), plant spacing (forest and woodland) and climate. Unlike ecozones, biomes are not defined by genetic, taxonomic or historical similarities. Biomes are often identified with particular patterns of ecological succession and climax vegetation.