Buffering mechanism

Weathering is a major H+ consuming process and pH-buffering mechanism, not only globally and regionally but it also plays a major role in local watersheds in soil processes, in nutrient uptake by plants and in epidiagenetic reactions in sediments. 

The arsenic oxidation state data and the calculated pH at 300°C (see Table H) allow an upper limit on the Eh of the solution in the basalt-water experiment to be estimated from Equation (2). Assuming aH,0 = 1 and As(V) = 15 pg/L, this upper limit Eh value is -400 100 mV. The basalt-fluid redox buffer mechanism of Jacobs and Apted (2) gives an Eh of about -600 mV at 300°C and pH 7.8 (19). This mechanism involves ferrous ironbearing basalt glass + water reacting to magnetite + silica. 

Lyman J. (1957) Buffer mechanism of seawater. Ph.D. dissertation, Univ. California. 

Froelich, P.N. (1988) Kinetic control of dissolved phosphate in natural rivers and estuaries a primer on the phosphate buffer mechanism. Limnol. Oceanogr. 33, 649-668. 

The balance between calcium carbonate production and dissolution is the major pH buffering mechanism of seawater over periods of time at least on the order of thousands of years ( ). The atmospheric carbon dioxide reservoir is less than 2 percent the size of the seawater reservoir ( ) and there is active exchange between these two reservoirs across the air-water interface. Consequently, the carbon dioxide content of the atmosphere and accumulation of calcium carbonate in the deep oceans are closely coupled. 

Sjoberg, E.L. A fundamental equation for calcite dissolution kinetics. Geochim. Cosmochim. Acta 40, 441-447 (1976). Weiss, R.F. Carbon dioxide in water and sea water the solubility of a non-ideal gas. Mar. Chem. 2, 203-215 (1974). Lyman, J. Buffer mechanism of sea water. Ph. D. Thesis,... 

As has already been mentioned, the appearance of carbon dioxide in oxide systems leads to deposition of iron at lower pH. Thus if the hypothetical buffer mechanism existed in the sedimentary basins, maintaining the pH at a constant level, then an increase in the partial pressure of carbon dioxide would have led to deposition of iron in the form of carbonates. The actual picture is more complicated, inasmuch as carbonate and bicarbonate equilibria themselves act as buffers, an increase in COj leading to a decrease in pH and corresponding solution of carbonate and conversely, a drop in icoj causing an increase in pH and deposition of carbonate. 

In this chapter we describe the distribution of CO2, H2CO3, HCOf, and C03 in natural waters, examine the exchange of CO2 between atmosphere and waters, evaluate the buffering mechanisms of fresh waters and seawater, and define their capacities for acid and base neutralization. 

The pH of extracellular fluid is kept within very narrow limits (7.35-7.45) by buffering mechanisms (see also Chapter 1), the lungs, and the kidneys. These three systems do not act independently. For example, in acute blood loss release of ADH and aldosterone restores the blood volume and renal regulation of the pH leads to shifts in K+ and Na+ levels. 

Intracellular Influx of Ca + in Retinal Ischemia Ischemic or energy-deprived cells cannot maintain homeostasis, causing rapid and massive fluxes of Ca, K, Na, and Cl (Hansen, 1985). Under these conditions, the extracellular Ca concentration is rapidly reduced (Nicholson et al., 1977) while intracellular Ca increases (Silver and Erecinska, 1990). Not much is known about how extracellular Ca enters the cells in ischemic conditions. Possible mechanisms include voltage-dependent and receptor-operated Ca " " channels, release of Ca + from internal stores, and Ca" buffering mechanisms (Wang et al., 2002). 

It should be stressed that the exchangeable base cation buffering mechanism does not actually neutralize the acidity but merely stores it in the soil s reserve acidity pool. If the soil is then subjected to leaching, the cost of buffering against acid inputs by this mechanism is depletion of the exchangeable base cations in the soil,... 

Buffering. Heterogeneous dissolution and precipitation reactions are the principal pH buffer mechanisms in natural waters. It has been shown... 

The carotid sinus buffering mechanism is one of the most powerful in the body. When, for example, the buffer nerves are cut, blood pressure rises to markedly hypertensive levels and stays there. If this is so, it might have been confidently anticipated that this mechanism would be called upon as a defense against development of hypertension. Yet clinical observation showed that pressure over the sinus elicited in hypertensive patients as much of a response as in normotensive individuals. In short, it was as active in the hypertensive as in the normotensive. 

This seeming lack of interest of the buffer mechanism to help maintain arterial pressures at normal levels became the subject of study by McCubbin, Green, and myself. The electrical impulses coming from the carotid sinus nerve were measured and it could be shown readily, as others had done, that when pressure within the sinus was raised by intravenous injection of norepinephrine, the impulse traffic to the vasomotor center greatly increased, inhibiting the vasomotor center and reducing the outflow of vasoconstrictor impulses. This led to a decrease in pressure. These observations were in normal dogs. 

Why is it important that blood have several buffering mechanisms to avoid radical pH changes ... 

The buffering mechanism for a mixture of a weak acid and its salt can be explained as follows. The pH is governed by the logarithm of the ratio of the salt and acid ... 

The buffer mechanism in water can also be induced by some heterogeneous systems where exchange reactions between the ions in water and bottom sediments or minerals occur, or dissolution and precipitation of some minerals take place. 

France-Lanord C, Derry LA (1994) 5 C of organic carbon in the Bengal fan Source evolution and transport of C3 and C4 plant carbon to marine sediments. Geochim Cosmochim Acta 58 4809-4814 Froelich PN (1988) Kinetic controls of dissolved phosphate in natural rivers and estuaries A primer on the phosphate buffer mechanism. Littmol Oceanogr 33 649-668 Froelich PN, Bender ML, Heath GR (1977) Phosphoras accumulation rates in metalliferous sediments on the East Pacific Rise. Earth Planet Sci Lett 34 351-359 Froelich PN, Bender ML, Luedtke NA, Heath GR, DeVries T (1982) The marine phosphoras cycle. Am J Sci 282 474-511... 

The massive influx of Na and Ca result in strong cell membrane depolarizations. In many cases, cell depolarization produces the activation of voltage-gated Ca and Na channels (when MTX is tested in excitable cells), providing extra pathways for the further influx of these cations. Eventually, the cell deteriorates and dyes when its [Ca Ji buffering mechanisms are overwhelmed by the dramatic Ca uptake. In all reported studies, prolonged exposure to MTX has deleterious effects on cell viability. 

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