P fluxes

Subsequent operation at pressure drops less than P follows curve B (eq. 1). If pressure is increased above P, flux follows curve C (additional compaction) to P. A new value of is used in equation 1. Operation at pressure drops less than P follows curve D. Flux at P is lowered to J. ... 

Q Flux of absorbed surfactants p Rate of surface renewal by eddies P Power input to impeller P Flux of desorbed surfactants P0 Power input to impeller, no-gas condition... 

Total-P Flux. Two approaches were combined to calculate removal by deposition. During the stratified period deposition was determined from the mass flux, measured by using sediment traps suspended at eight levels in the water column, and the P concentration in the sediment trap material. Positioning of traps at key depths allowed primary and resuspended flux components to be deconvoluted. 

Calcium carbonate precipitation and sedimentation from mid-August through October (ref. 20 see also the following discussion of components) significantly enhanced P fluxes. The impact of calcite precipitation on P removal from the epilimnion is shown in Figure 8. Phosphorus flux into the... 

Phosphorus settling rates were calculated as the ratio of P fluxes to standing-crop concentrations (Figure 10). Observed rates ranged from <0.1... 

Comparison of the depositional fluxes shows that diatoms were the most important particle component transporting P to the sediment surface, accounting for 50-55% of the flux (Table II). Terrigenous material and calcite were also important transport vectors. Deposition varied markedly with season, as shown by the time series plot of the major particle components (Figure 13). The total P flux calculated by using the particle components model agreed with the flux measured by sediment traps (157-227 versus 185 mg/m2). The close agreement indicated that the major particle vectors were represented and associated P concentrations were accurately quantified. 

Transport by Calcite. The annual flux of calcite into the uppermost trap (29 m below the lake surface) was estimated to be 35 g/m2, and the mean measured P content of this phase was estimated at 1.05 mg/g. A comparison of the calculated 29-m P flux, 37 mg/m2, with estimates of deposition to bottom sediment, indicated that 5-16 mg/m2 (13-43% of upper-water-column flux) was returned to the water column. This relatively small regeneration flux was not detected in profiles of meta- and hypolimnetic... 

Assuming a bulk density of 1.05 g/cm3 and a dry weight fraction of 0.1 for the interface sediment, 0.38 mm of sediment would supply the observed 160-m water-column burden of resuspended phases, approximately half the basinwide average annual linear sedimentation. The corresponding amount of sediment was consistent with the mass of allochthonous components in the water column during the March-May spring mixing period (200-300 mg/m3). The quantity of resuspended P was calculated as the product of mass of resuspended sediment (g/m2) and phosphorus concentration in surface sediment (mg of P/g). For a 160-m water column, the amount was 48 mg of P/m2 (25 mg of P/m2 for the mean water-column depth of 85 m). The resuspended P flux (25 mg of P/m2) was also obtained from the product of resuspended Al (mg/m2) and the P Al ratio in bottom sediment. 

The amount of P supplied by resuspension was relatively small compared with water-column standing pools and major flux vectors. Thus, resuspension of bottom sediments may not be a major mode of phosphorus resupply. The pool of resuspendable P is finite. The deposition-resuspension cycle will not increase the amount of P in this pool unless P is added from another source (e.g., by diffusion of P from lower sediment levels). However, the diffusive flux would be relatively small. The resuspendable particulate P can be recycled during spring mixing by repeated deposition and resuspension, but this cycle does not increase the amount of P in the resuspendable pool. Eadie et al. (24) reported a resuspended P flux (sediment-trap-based) of3200 mg of P/m2, 66 times our estimate here. However, this large P flux would require the resuspension of over 2.0 cm of surface sediment and much higher suspended Al levels than were measured in the water column. 

Table V. Summary of Seasonal and Annual P Fluxes in Lake Michigan...

Figure 9.22. Oceanic cycles of organic carbon, nitrogen, and phosphorus. DOC = dissolved organic carbon POC = particulate organic carbon NPP = net primary production DN = dissolved nitrogen PN = particulate nitrogen DP = dissolved phosphorus, PP = particulate phosphorus. C and N fluxes are in units of 1012 moles C and N y1 P fluxes are in units of 1010 moles P y1.

Coelho, J.P., Flindt, M.R., Jensen, H.S., Lillebo, A.I., and Pardal, M.A. (2004) Phosphorus speciation and availability in intertidal sediments of a temperate estuary relation to eutrophication and annual P-fluxes. Estuar. Coastal Shelf Sci. 61, 583-590. 

Smith, S.V. (1991) Stoichiometry of C N P fluxes in shallow-water marine ecosystems. In Comparative Analyses of Ecosystems—Patterns, Mechanisms, and Theories (Cole, J.J., Lovett, G., and Findlay, S.G., eds.), pp. 259-286, Springer-Verlag, Berlin. 

The net flux of P to the ocean (0.8 x 10 mol d i. Fig. 17.3) was calculated by difference (total dissolved and particulate inputs for the entire shelf system minus burial and nearshore export). This flux requires that the dissolved P concentration on the outer shelf be 0.1 pmol L-i, which is in good agreement with observed values (DeMaster and Pope 1996). The marine particulate contribution to the offshore net P flux (0.14 x 10 mol d"i or 26% of the total) was based on the marine particulate N export from the shelf (Daley 1997) and the Redfield N/P ratio of 16. These data indicate that of the total dissolved P reaching the Amazon shelf (0.7-0.8 X 10 mol d l), approximately 100% ultimately is exported in dissolved or particulate form to the open ocean (Table 17.2). 

Howarth, R. W., BiUen, G., Swaney, D., Townsend, A., Jaworski, N., Lajtha, K., Downing, J. A., Elmgren, R., Caraco, N., Jordan, T., Berendse, F., Freney, J., et al. (1996). Regional nitrogen budgets and riverine N P fluxes for the drainages to the North Atlantic Ocean Natural and human influences. Biogeochemistry 35, 75-139. 

Reservoir fluxes (F) represent the P-flux between reservoirs R1—R8 defined in Table 1. The sub-reservoir fluxes (sF) refer to the flux of phosphorus into the marine sediment portion of reservoir 1 via sediment burial,... 

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