Phosphorus cycles

Phosphorus is essential to all living systems. Within biological systems the most abundant forms of phosphorus are phosphate diester bonds, which form the links within nucleic molecules. Phosphate is an indispensable portion of the ATP molecule. The hydrolysis of phosphate from ATP to ADP forms the basis of most energy transfer reactions within biological systems. Phospholipids and sugar phosphates are constituents of all living cells. 

However, phosphorus is not abundant in the biosphere and it often limits microbial growth. The availability of this element is restricted by its tendency to precipitate in the presence of several polyvalent metal ions at neutral to alkaline pH. Large, slowly cycled phosphate reservoirs occur in marine and other aquatic sediments, whereas small, actively cycled reservoirs comprise dissolved phosphate in 

The microbial cycling of phosphorus does not alter its oxidation state. Most phosphorus transformations mediated by microorganisms can be viewed as inorganic to organic phosphate transfers or as transfers of phosphate from insoluble, immobilized forms to soluble or mobile compounds. Various microorganisms have evolved transport systems for the regulated acquisition of phosphate from the environment. 

Solubilization of insoluble ferric phosphates may occur when microorganisms reduce ferric ions to ferrous ions under anaerobic conditions. 

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One of the things that environmental scientists do IS to keep track of important elements in the biosphere—in what form do these ele ments normally occur to what are they transformed and how are they returned to their normal state Careful studies have given clear although compli cated pictures of the nitrogen cycle the sulfur cy cle and the phosphorus cycle for example The carbon cycle begins and ends with atmospheric carbon dioxide It can be represented in an abbrevi ated form as... 

As just implied, the land-based phosphorus cycle is connected to the water-based cycle via the rivers and sewers. It has been estimated that, on a global scale, about 2 million... 

Fig. 4-8 The global phosphorus cycle. Values shown are in Tmol and Tmol/yr. (Adapted from Lerman et al. (1975) and modified to include atmospheric transfers. The mass of P in each reservoir and rates of exchange are taken from Jahnke (1992), MacKenzie et al. (1993) and Follmi (1996).)...

Table 4-1 Response of phosphorus cycle to mining output. Phosphorus amounts are given in TgP (1 Tg = 10 g). Initial contents and fluxes as in Fig. 4-7 (system at steady state). In addition, a perturbation is introduced by the flux from reservoir 7 (mineable phosphorus) to reservoir 2 (land phosphorus), which is given by 12 exp(0.07t) in units of Tg P/yr...

Follmi, K. B. (1996). The phosphorus cycle, phospho-genesis and marine phosphate-rich deposits. Earth Sci. Rev. 40, 55-124. 

The following sections summarize only the most prominent interactions between the elemental cycles and the links in the hydrologic cycle. Water also plays a role in many chemical and biological reactions that are beyond the scope of this discussion. The carbon, nitrogen, sulfur, and phosphorus cycles are discussed in detail in Chapters 11, 12, 13, and 14, respectively. 

Unlike other biogeochemical elements, phosphorus does not have a significant atmospheric reservoir. Thus, while some amount of phosphorus is occasionally dissolved in rain, this does not represent an important link in the phosphorus cycle. River runoff is the primary means of transport between the land surface and oceans, and unlike the other elements discussed. 

Fig. 14-7 The global phosphorus cycle. Values shown are Tmol and Tmol/yr for reservoirs and fluxes, respectively. (T = 10 ).

Graham, W. F. (1977). Atmospheric pathways of the phosphorus cycle. Ph.D. Thesis, University of Rhode Island. 

Ecologically, copper is a trace element essential to many plants and animals. However, high levels of copper in soil can be directly toxic to certain soil microorganisms and can disrupt important microbial processes in soil, such as nitrogen and phosphorus cycling. Copper is typically found in the environment as a solid metal in soils and soil sediment in surface water. There is no evidence that biotransformation processes have a significant bearing on the fate and transport of copper in water. 

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