The role of phosphorousin the environment phosphorous cycle sources of phosphorous applications of phosphorous eutrophication

The Phosphorus Cycle

The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movements of phosphorus, because phosphorus and phosphorus-based compounds are usually solids at the typical ranges of temperature and pressure found on Earth. Phosphorus moves slowly from deposits on land and in sediments, to living organisms, and than much more slowly back into the soil and water sediment. The phosphorus cycle is the slowest of the matter cycles.

Naturally Occurring Phosphorus Phosphorus normally occurs in nature as PO 4, which is 3- called orthophosphate. Most phosphates are found as salts in ocean sediments or in rocks. Over time, geologic processes can bring ocean sediments to land, and weathering will carry terrestrial ions to the ocean. Plants absorb phosphates from the soil and they proceed up the food chain. After death, the animal or plant decays, and the phosphates are returned to the soil. Runoff may carry them back to the ocean or they may be reincorporated into rock.

Biological Phosphorus The primary biological importance of phosphates is as a component of nucleotides, which serve as energy storage within cells (ATP) or when linked together, form the nucleic acids DNA and RNA. Phosphorus is also found in bones, whose strength is derived from calcium phosphate, and in phospholipids (found in all biological membranes). Phosphates move quickly through plants and animals; however, the processes that move them through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest biogeochemical cycles.

Fertilizer Human influences on the phosphate cycle come mainly from the introduction and use of commercial synthetic fertilizers. The phosphate is obtained through mining of certain deposits of calcium phosphate called apatite. Huge quantities of sulfuric acid are used in the conversion of the phosphate rock into a fertilizer product called "super phosphate". Plants may not be able to utilize all of the phosphate fertilizer applied, as a consequence, much of it is lost form the land through the water run-off. The phosphate in the water is eventually precipitated as sediments at the bottom of the body of water. In certain lakes and ponds this may be redissolved and recyled as a problem nutrient.

Human Influences on the Phosphate Cycle

treatment works. Phosphorus Run Off Eutrophication Phosphorus is recognized as one of the major nutrients contributing to the increased eutrophication of lakes and other natural waters. This has led to many water quality problems including increased purification costs, interference with the recreational and conservation value of impoundments, loss of livestock and the possible sub-lethal effects of algal toxins on humans using eutrophic water supplies for drinking. The International Conference on the Protection of the North Sea has recommended a 50% reduction in the input of phosphorus-containing compounds, while the EU Urban Wastewater Treatment Directive will require an effluent standard of no more than 1mg/l phosphate for large

Eutrophication Algal blooms can be destructive, but they are not unnatural. In fact, a natural cycle where populations rise and crash, such as in the Baltic Sea, can be a part of a healthy marine ecosystem. In this case regulation is desirable but reversal measures, if excessive, can be counterproductive. Thus, the aim of restoration efforts must then be not to eliminate the blooms, but return them to their original frequency.

Sunlight Plants die. When they decompose the water is depleted of O 2. Reduced submerged aquatic vegetation (SAV) Light penetration is reduced Fish die because of lack of O 2 Phosphorus ferilizes small Floating aquatic plants Biological Effects of Eutrophication

PhosphorousRemoval Phosphate removal is currently achieved largely by chemical precipitation, which is both expensive and increases sludge volumes by up to 40%. An alternative, biotechnological, approach is that of 'Enhanced Biological Phosphate Removal' ('EBPR') which utilises the ability of some microorganisms to accumulate phosphate (as polyphosphate) in excess of their normal metabolic requirements. EBPR systems, although economically-attractive, require anaerobic pre-treatment zones and display inconsistencies in performance requiring either periodic organic matter supplementation and/or chemical 'polishing' to meet compliance limits.