N:P flux

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. 

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. 

The responsivity and g-r noise may be analyzed to obtain background photon flux and temperature dependence of responsivity, noise, and detectivity. Typically, n > p, and both ate determined by shallow impurity levels. The minority carrier density is the sum of thermal and optical contributions. 

A TBma,) explicit functions of the available concentrations of the other nutrients. This approach allows for a pronounced interdependence between the fluxes of the different nutrients but it does not ensure that the Redfield ratios are maintained. In the second approach the contents of the nutrients in the biota reservoir are forced to remain close to the Redfield ratios. This method was used by Mackenzie et al. (1993) in their study of the global cycles of C, N, P, and S and their interactions. They were able to demonstrate how a human perturbation in one of these element cycles could influence the cycles of the other elements. 

Radiocarbon (14C) is produced in the atmosphere by the cosmic ray neutron flux interacting with 14N[14N(n,p)14C], The 14C hot1 atom then equilibrates with atmospheric C02 which participates in the C-0 cycle and passes into the food chain (biosphere). Most of the radiocarbon is taken up by the oceans which constitute the largest reservoir of C02 within the secondary geochemical cycle. 

In the case of rapid capture, several neutrons are added before conversions of type n p bring the neutron to proton ratio back to reasonable proportions. The r process requires impressive neutron fluxes and extreme densities and temperatures that can only be achieved in type II supernovas or the coalescence of two neutron stars. The details are not yet understood. However, we have no other explanation for the existence of gold and heavy isotopes of tin ( Sn and " Sn), for example. There is another process, namely photodisintegration, which is very short-lasting and leads to nuclei poor in neutrons, or rich in protons (referred to as a p process). 

If molecules i undergo collisions with molecules j during the time dt, the population at (r+(p, /mi), p+X dt) will be different see Fig. 12.12. The flux to (r+(p,-/ n ), p+X,-rff) will be decreased by some collisions that deflect molecule i, changing its momentum. Let this loss of population be denoted drdpidt. Similarly other collisions may deflect additional population of molecules into (r+(p,/mi), p+Xidt). The gain of population due to these collisions is denoted drdpjdt. Thus, when collisions are taken into account, Eq. 12.66 becomes... 

One can also use so-called threshold monitor detectors where the activating reaction has an energy threshold, such as the (n,a), (n,p), and (n,2n) reactions. By exposing a set of threshold detectors (involving different reactions with different thresholds) to a neutron flux, one can determine the relative amounts of different energy groups in the neutron spectrum. Further information about the use of activation detectors to measure neutron fluxes can be found in the textbooks by Knoll (2000) and Tsoidfanidis (1995). 

Diffusion with Electric Current The equations (64), (65), (66), (69) and (70) have been experimentally tested by P. Meares and H. H. Ussing (95) for a Zeo-Karb 315 membrane and NaCl solutions. wNa+ was determined from self-diffusion measurements. At an external concentration up to 0.02 N the flux of the anions could be neglected and ANa+ was directly found from the conductivity of the membrane. 

In the case of hydrostatic pressure arising from gravitational forces, this may be removed by simply neglecting the gravitational body force in the N-S Equation (5). For the thermodynamic pressure, it is less obvious what can be done. However it may be noticed that at equilibrium, the N-P Equation (1) is satisfied and the ion fluxes are zero. It can now be seen that the thermodynamic... 

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.

Of the organic carbon entering the ocean, about 35% accumulated in marine sediments as organic carbon with a molar C/N/P ratio of about 250/20/1 (Mackenzie, 1981) the rest was respired and oxidized to CO2 and evaded the ocean. The nitrogen and phosphorus riverine fluxes of 1 and 0.045 x 1012 moles y1, respectively, represented the nutrient fluxes necessary to support the organic matter accumulation of 11.7 x 1012 moles C y1. 

Carbon-14 Dating. The earth is bombarded by an almost constant flux of cosmic rays, which in the stratosphere generate many particles, including neutrons, 0n1 which react with 7N14 nuclei to form radioactive C-14 by the (n, p) reaction, i.e. the emission of a proton ppx. 

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). 

Christensen, P. B., Rysgaard, S., Sloth, N. P., Dalsgaard, T., and Schwaerter, S. (2000). Sediment mineralization, nutrient fluxes, denitrification and dissimilatory nitrate reduction to ammonium in an estuarine ord with sea cage trout farms. Aquat. Microb. Ecol. 21(1), 73—84. 

Risgaard-Petersen, N., Nielsen, L. P., and Blackburn, T. H. (1998). Simultaneous measurement of benthic denitrification, with the isotope pairing technique and the N-2 flux method in a continuous flow-through system. Water Research. 32(11), 3371—3377. 

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