Phosphorus cycle sizes

These ectoenzymes play a significant part in phosphorus cycling in natural waters. In lakes and oceans, phosphorus is partitioned among particulate and dissolved inorganic and organic fractions and is rapidly transformed from one fraction to another. Estimates of the size of the labile dissolved organic phosphorus pool in waters off the coast of Hawaii (0.01-0.2 /rg at P L 1), and its rapid turnover (0.008-0.04 h 1), presumably facilitated by extracellular phosphatases, are comparable with those of PO4- (Smith et al., 1985) and indicate the importance of ectoenzymes in the major nutrient cycles. 

Major differences in size (filterable, particulate) and chemical reactivity (condensed, organic) of phosphorus forms in samples can be used as the basis for speciation, as shown in Table 1. Of these fractions, total phosphorus (TP) and FRP are perhaps the most commonly measured, although it is arguable that the understanding of the aquatic phosphorus cycle is somewhat lopsided because of that bias. For example, wastewater discharge licenses often specify a maximum permissible concentration of TP, and provide an indication of the maximum potentially bioavailable phosphorus discharged. However, FRP, comprising mostly orthophosphate, is a measure of the amount of most readily bioavailable phosphorus. 

Human activity has an enormous influence on the global cycling of nutrients, especially on the movement of nutrients to estuaries and other coastal waters. For phosphorus, global fluxes are dominated by the essentially one way flow of phosphorus carried in eroded materials and wastewater from the land to the oceans, where it is ultimately buried in ocean sediments. The size of this flux is currently estimated at 22 x 106 tons per year. Prior to increased human agricultural and industrial activity,... 

With tetraaryl-substituted P-chiral ligands the major effect on the asymmetric environment is created by the conformation of the chelate cycle, rather than by the relative size of the substituents on phosphorus. TTius, two catalytic precursors 139 and 140 of the same chiral diphosphine can have two opposite arrangements of the phenyl and o-tolyl rings in the solid state, and still (quite imsurprisingly) yield the hydrogenahon product with tile same sense of enantioselection (Figure 1.19). ... 

The properties of the macrocycles are dependant upon ring size. The properties of small (9-11-membered macrocycles) are similar to common heterocycles. The lone pairs (LP s) of the phosphorus atoms are predisposed by the cycle conformation and the configuration of corresponding P-atoms. The larger macrocyclic ligands could wrap around the cental ion giving the stable coordination chelates... 

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