Phosphorus reservoir amounts

Table 11.2 Summary of phosphorus reservoir amounts, total fluxes, and residence time.

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...

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. 

The land biota reservoir (3) represents the phosphorus contained within all living terrestrial organisms. The dominant contributors are forest ecosystems with aquatic systems contributing only a minor amount. Phosphorus contained in dead and decaying organic materials is not included in this reservoir. It is important to note that although society most directly influences and interacts with the P in lakes and rivers, these reservoirs contain little P relative to soil and land biota and are not included in this representation of the global cycle. 

The global phosphate system is described in Figure 7.10 (Lasaga, 1980). Table 7.1 gives the amounts held by each reservoir, and Table 7.2 the fluxes between reservoirs. Assuming steady-state, calculate the evolution of the world phosphate system if 10000 x 109 kg of phosphorus from fertilizer (mined from an isolated reservoir) were dumped on land in a short period of time. 

Table 7.1. Amounts of phosphorus (KfkgP) stored in each reservoir at t = 0 and the initial...

There are 5 major reservoirs in the Earth system atmosphere, biosphere (vegetation, animals), soils, hydrosphere (oceans, lakes, rivers, groundwater), and the lithosphere (Earth crust). Elemental cycles of carbon, oxygen, nitrogen, sulfur, phosphorus, and other elements interact with the different reservoirs of the Earth system. The carbon cycle has important aspects in tropical forests due to the large amount of carbon stored in the tropical forests and the high rate of tropical deforestation 0acob 1999)-... 

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. 

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