Ammonium Flux

Gardner, W.S., Seitzinger, S.P., and Malczyk, J.M. (1991) The effects of sea salts on the forms of nitrogen released from estuarine and freshwater sediments does ion pairing affect ammonium flux Estuaries 14, 157-166. 

Ammonium fluxes out of sediments have often been calculated based on measured rates of net ecosystem metabolism (NEM based on dissolved O2 uptake or Die release) (Burdige and Zheng, 1998 Hopkinson et al, 2001). In oxic sediments where NTR is likely to play an important role in transformation of NH4+, total DIN rather than the NH4 flux should be more closely related to the stoichiometry of NEM, whereas in anoxic sediments where DNF is important the estimated DIN flux will not equal that predicted by NEM stoichiometry. Calculation of DNF has often been based upon this missing DIN. 

Exchange of dissolved nitrogen species between the soil and water column support several nitrogen reactions. For example, nitrification in aerobic soil layer is supported by ammonium flux from the anaerobic soil layer. Similarly, denitrification in anaerobic soil layer is supported by nitrate flux from the aerobic soil layer and water column (see Chapter 14 for discussion on transport processes). 

Ammonium flux from anaerobic soil layer is governed by the (1) concentration gradient established as a result of ammonium consumption in the aerobic zone due to nitrification and ammonia volatilization, (2) ammonium regeneration rate in the anaerobic soil layer, (3) adsorption coefficient for ammonium, (4) soil CEC, (5) intensity of soil reduction and accumulation of reduced cations, (6) bioturbation at the soil-floodwater interface, and (7) soil porosity. 

The ammonium flux from the anaerobic zone (where NFI4 is in high concentrations) to aerobic zone (where the concentration is low) is regulated by many factors ammonium concentration gradient, ammonium production rate, CEC, adsorption-desorption, intensity of soil reduction, temperature, bioturbation and mixing, and ammonium consumption rate. 

Ammonium flux is upward from soil to water column as the flux value is positive. 

Simon, N. S. 1988. Nitrogen cycling between sediment and the shallow-water column in the transition zone of the Potomac River and estuary. I. Nitrate and ammonium flux. Estuar. Coast. Shelf Sci. 26 483-497. 

Ammonium Chloride. Most ammonium chloride [12125-02-9], NH Cl, is used as rice paddy fertilizer small amounts are used in dry cells and as fluxing agents (see Ammonium COMPOUNDS). 

Uses. Alkah metal and ammonium fluoroborates are used mainly for the high temperature fluxing action required by the metals processing industries (see Metal surface treatments Welding). The tendency toward BF dissociation at elevated temperatures inhibits oxidation in magnesium casting and aluminum alloy heat treatment. 

Ammonium chloride has a number of iadustrial uses, most importantiy ia the manufacture of dry-ceU batteries, where it serves as an electrolyte. It is also used to make quarryiag explosives, as a hardener for formaldehyde-based adhesives, as a flame suppressant, and ia etching solutions ia the manufacture of ptinted circuit boards. Other appHcations iaclude use as a component of fluxes ia ziac and tin plating, and for electrolytic refining of ziac. 

Ammonium chloride is used as a flux ia the melting furnace because the large surface of the cathodes favors the formation of dross, ie, oxide-coated globules of ziac. The dross is separated by Hquation or air-swept milling iato metal and oxide fractions. In the latter, the oxide fraction is swept out of the mill and can be returned to roasting for the elimination of chloride. Metallic ziac is recycled. Overall melting efficiency is 96—98%. 

Improved plow steel and extra improved plow steel, bright and galvanized. Use a suitable solvent to remove lubricant. The wires then should be dipped in commercial muriatic acid until thoroughly cleaned. The depth of immersion in acid must not be more than the broomed length. The acid should be neutralized by rinsing in a bicarbonate of soda solution. Fresh acid should be prepared when satisfactory cleaning of the wires requires more than one minute. (Prepare new solution—do not merely add new acid to old.) Be sure acid surface is free of oil or scum. The wires should be dried and then dipped in a hot solution of zinc-ammonium chloride flux. Use a concentration of 1 lb (454 g) of zinc-ammonium chloride in 1 gal (3.8 L) of water and maintain the solution at a temperature of 180°F (82°C) to 200°F (93°C). 

Flux blankets may be made from zinc ammonium chloride or from ammonium chloride plus frothing agents such as glycerin, tallow or sawdust. These thicken the blanket and lower the surface temperature thus reducing the volatilisation losses of ammonium chloride and the amount of fume which is generated. 

Ammonium chloride is sometimes used as a flux in soldering because it decomposes on heating ... 

Fig. 12-5 The ammonia-ammonium cycle. Each arrow represents one flux. The magnitude of the flux is given in Tg N/yr Where two numbers are given, the top value is the anthropogenic contribution and the lower is the total flux (natural + anthropogenic).

Figure 3. The general nitrogen model for illustrating the bio geochemical cycling in Forest ecosystems. Explanations for the fluxes 1, ammonia volatilization 2, forest fertilization 3, N2-fixation 4, denitrification 5, nitrate respiration 6, nitrification 7, immobilization 8, mineralization 9, assimilatory and dissimilatory nitrate reduction to ammonium 10, leaching 11, plant uptake 12, deposition N input 13, residue composition, exudation 14, soil erosion 15, ammonium fixation and release by clay minerals 16, biomass combustion 17, forest harvesting 18, litterfall (Bashkin, 2002).

Fig. 11.6. Diagram depicting desorption ionization (MALDI, FAB or SIMS). The operating principles of the three techniques are similar. The initiating event is exposure of the analyte to a beam of photons, atoms or ions. In order to prevent damage to the fragile analyte molecules and enhance the conversion of the involatile molecules into gas-phase ions, a matrix is employed. For MALDI, the matrix compounds are UV absorbing compounds such as hydroxycinnamic acid. The most commonly used FAB matrix was glycerol and ammonium chloride was employed by some investigators in SIMS experiments (although at low ion beam fluxes molecular species could be effectively ionized for many analytes with minimal evidence of damage by the primary ion beam).

If 15N ammonium citrate was administered, and glutamate, aspartate, and glycine isolated from liver and intestinal wall protein, all showed 15N uptake. From the results of labeling studies, Schoenheimer finished his Edward K.Dunham lectures in Harvard in 1941 with the phrase— the structural materials [of the body] are in a steady state of flux. The classical picture must thus be replaced by one which takes account of the dynamic state of body structure —an idea which has become an integral part of biochemistry since that time, and which was almost totally dependent on the introduction of isotopes for its discovery. 

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