Phosphorus reservoir concentrations

Calcitonin is a polypeptide hormone that (along with PTH and the vitamin D derivative, 1,25-dihydroxycholecalciferol) plays a central role in regulating serum ionized calcium (Ca2+) and inorganic phosphate (Pi) levels. The adult human body contains up to 2 kg of calcium, of which 98 per cent is present in the skeleton (i.e. bone). Up to 85 per cent of the 1 kg of phosphorus present in the body is also found in the skeleton (the so-called mineral fraction of bone is largely composed of Ca3(P04)2, which acts as a body reservoir for both calcium and phosphorus). Calcium concentrations in human serum approximate to 0.1 mg ml-1 and are regulated very tightly (serum phosphate levels are more variable). 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

The first step in solving this problem is to write down a series of equations, one for each reservoir, that expresses the balance between the phosphorus supplied to each reservoir (the source) and the phosphorus removed from each reservoir (the sink). Corresponding to each of the arrows in Figure 3-1 is a flux of phosphorus equal to the water flux multiplied by the concentration of phosphorus in the reservoir from which the water is flowing. Let sat be the concentration of phosphate in the surface Atlantic, sind in the surface Indo-Pacific, dind in the deep Indo-Pacific, ant in the Antarctic, and dat in the deep Atlantic. Express all concentrations in units of 10 3 mole P/m3. 

The phosphate content of each reservoir is the volume of that reservoir multiplied by the concentration of phosphate in that reservoir. Volumes are constant, so the rate of change of the content is the volume multiplied by the rate of change of the concentration. But for each reservoir, the rate of change of the content is the sum of all the fluxes of phosphorus in (the sources) minus the sum of all the fluxes of phosphorus out (the sinks). Thus, the content of the first reservoir, Atlantic surface, changes at the rate... 

Residence times are calculated by dividing the concentration of phosphorus contained in a given reservoir by the sum of fluxes out of the reservoir. Where ranges are reported for reservoir size and flux, maximum and minimum residence timp values are given these ranges reflect the uncertainties inherent in reservoir size and flux estimates. Fluxes used to calculate residence times for each reservoir are as follows R1 (F ), R2... 

The reservoir representing the land (2) is defined as the amount of P contained in the upper 60 cm of the soil. This rather narrow definition of the land reservoir is made because it is through the upper portions of the soil system that the major interactions with the other P reservoirs occur. Specifically, most plants receive their nutritive P needs from the upper soil horizons and the return of P to the soil system by the decomposition of plant matter is also concentrated in this upper soil zone. Similarly, the major interactions with the atmosphere, ground-waters, and rivers occur near the soil surface. And, finally, phosphate in the form of fertilizer is applied directly to the soil surface. Thus, in attempting to represent the land and its interaction with other reservoirs, the surface soil horizon most directly interacts with all components and best represents the d)mamical nature of this reservoir. Phosphorus in soils deeper than 60 cm and in crusted rocks is included in the sediment reservoir (1). This reservoir accounts for all of the particulate P that exchanges with the other reservoirs only on very long time-scales. 

Riley, 1975). The 11 ions, except for iodine, compose more than 99.9% of salinity. Iodine is one of the most abundant micronutrients in seawater, with a total concentration of 5 X 10 to 6 X 10 g-l (0.4-0.5pM). Other micronutrients, such as nitrogen and phosphorus and many trace ions, are also contained therein. The three main oceans (i.e., the Atlantic, Indian, and Pacific oceans), including adjacent seas, occupy 70.8% of the earths surface (total sea area of 360.8 X 10 km ). Of the sea area, the ratio of the continental shelf (less than 200m deep), between 200 and 2000 m deep, and over 2000 m deep is 7.6, 8.5, and the remaining 83.9%, respectively. The total volume of seawater is 1.37 X 10 m (mean depth 3795 m) (Bowden, 1975). The ocean is thus a huge reservoir of iodine. 

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