Phosphorus deposition calculation

In freshwater ecosystems, the amounts of phosphorus introduced to sediments are estimated to be of the order of 1 Tg P y while the amounts released from sediments annually are estimated to be less than 1 Tg P (Pierrou, 1976). Emery et al. (1955) calculated that the amount of phosphorus deposited in ocean sediments is 13 Tg P y. The amount of phosphorus released from ocean sediments is unknown but is probably relatively small, as the reducing conditions (lack of oxygen) required occur relatively rarely in the ocean. The uptake of phosphorus by phytoplankton in the ocean has been variously calculated as 1300 Tg P y (Emery et al., 1955) and 990 Tg P y (Stumm, 1973). A similar estimate, about 1000 Tg P y, can be made for the amount of phosphorus deposited in oceanic detritus (Pierrou, 1976). 

The potential for N deposition to contribute to the eutrophication of freshwater lakes is probably quite limited. Eutrophication by atmospheric inputs of N is a concern only in lakes that are chronically N-limited. This condition occurs in some lakes that receive substantial inputs of anthropogenic P and in many lakes where both P and N are found in low concentrations (e.g., Table III). In the former case the primary dysfunction of the lakes is an excess supply of P, and controlling N deposition would be an ineffective method of water-quality improvement. In the latter case the potential for eutrophication by N addition (e.g., from deposition) is limited by low P concentrations additions of N to these systems would soon lead to N-sufficient, and phosphorus-deficient, conditions. The results of the NSWS shown in Table III, for example, can be used to calculate the increase in N concentration that would be required to push N-limited lakes into P limitation (assuming total P concentrations do not change). An increase of only... 

Figure 10. Phosphorus settling rates in 1982, calculated as the sediment-trap-measured depositional flux divided by the total particulate P concentration...

Residence Times. Phosphorus residence times with respect to major depositional processes (see Tables II and IV) are summarized in Table VI. In comparison, the total-P residence time based on external loading is about 4.5 years. Residence times were calculated for a mean water-column depth of 85 m, and steady state was assumed. Although transport of P to the sediment surface by the combination of diatoms, calcite, and terrigenous material is relatively rapid, the low burial efficiency results in a relatively long residence time for total P (about 5 years). In comparison, the residence time for Pb is about 0.6 years (20). Thus, the response time for P changes with respect to loading should be on the order of 5-15 years. 

The average concentration of phosphorus was found to be 3000 ppm. Given the calculated yearly material deposition rate, approximately 11 kg phosphorus would have been contributed each year. Cook and Heizer arrived at an annual deposition rate of 124 kg phosphorus to a site area by a standard population of 100 individuals (28). By utilizing this rate, a population of only nine individuals would have been required to account for the amounts of phosphorus found to be present. Because phosphorus as phosphate is the least mobile of the elements tested, this figure can be considered to represent an absolute minimum permanent population estimate for the site during the period of occupation under consideration. It should be remembered, however, that soil phosphate is also found in occluded forms and in organic combination and that these fractions were not totally measured by the procedure utilized (29). Consequently, the minimum population estimate should be increased, perhaps by as much as 50-60%, to about 15 individuals. 

In the simulations here, there are two components to I atmospheric deposition, taken here as 1.5 mmol m year , and canopy leaching, which is calculated on the basis of the canopy P content assuming a rate of 6 mmol year in 1730 (see Sec. 3.1.3). To estimate kp in our standard cases, we assume that the input of phosphorus through atmospheric deposition was exactly balanced by leaching losses in 1730. This is somewhat at odds with several observations suggesting that much of the atmospherically derived P deposited onto tropical forests is retained rather than being leached out of the system (Sec. 3.1.2). Nevertheless, as was discussed in Sec. 3.1.1 almost all of this atmospherically derived P... 

Figure 19 shows the comparison of measured and calculated propylene conversion on phosphorus-poisoned catalyst." Curve 2 compares theory to the low temperature data by adjusting the reaction rate constant. Curve 3 was obtained by reducing the diffusivity of zone 4 by a factor of 25 from its original value, indicating that zone 4 is severely plugged by deposited poisons. 

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