Buffer capacity seawater

In low-mineral freshwaters with low buffer capacity, atmospheric CO2 has a significant influence on pH. The effect of increased atmospheric CO2 composition on the pH of seawater is small due to its large buffering capacity. Seawater pH is ca. 8.2, while low-mineral lakes have often low buffering capacities and can exhibit a pH as low as 3, partly due to anthropogenic... 

The amount of acid or base that a buffer solution can neutralize before dramatic pH changes begins to occur is called its buffering capacity. Blood and seawater both contain several conjugate acid-base pairs to buffer the solution s pH and decrease the impact of acids and bases on living things. 

Morel, F., McDuff, R. E. and Morgan, J. J. Theory of interaction intensities, buffer capacities, and pH stability in aqueous systems, with application to the pH of seawater and a heterogeneous model ocean system. Mar. 

Another potential connection between Si-metaboHsm and photosynthetic competency has been proposed by Milligan and Morel (2002). Those authors demonstrated that biogenic silica provides good buffering capacity in seawater, and could potentially be used as a proton donor. Specifically, MiUigan and Morel suggest that to enhance the activity of RubisCO, which is undersaturated for CO2 at ambient... 

The redox buffering capacities of seawater illustrated by the ranges of pe in which electron acceptors are stable (ordinate) plotted against the concentration of the electron acceptor in seawater. Although O2 and NO3 reduction dominate the redox reactions and the range of pe in seawater and sediments of the ocean, the most abundant electron acceptors are SO4 and CO2 and they occupy a relatively small range of pe. 

The deposition flux of sulphur from the atmosphere on to the oceans and land surfaces has increased by approximately 2 5 and 163%, respectively. Although this input has essentially no impact on the chemistry of seawater, due to its buffer capacity and the large amount of sulphate (SO -) it contains (see... 

This has been attributed to the anaerobic respiration by microorganisms like Desulfovibrio in seep sediments (Aharon, 2000) they use the abundant reduced carbon forms as electron donors and seawater-derived S042 as an electron acceptor. In addition to H2S, this metabolism can also produce carbonate species and ammonia whose concentration and type depend on the nature of the reduced carbon substrates and on the buffering capacity of the environment. Sulphate and H2S often show a linear, inverse relationship in profiles of seep sediment pore fluids, further indicating the link between sulphate reduction and H2S production (Aharon, 2000). 

Seawater has a relatively strong pH buffering capacity that is largely controlled by the concentration of CO2 in water according to the reaction ... 

In high pH seawater nee from Ci, the proton uptake was prevented (Fig 1B A). At the same time there was a pronounced reduction in the total amount of O2 prc uced (from 48 to 18 pmol/g fw). This reduced O2 production in Ci-free high pH seawater, is of a similar magnitude as the integrated transient O2 production rate (photosynthetic buffering capacity) in high pH seawater of normal (c 2 niM) Ci content(Fig 1C). In both cases, the use of the bound CXD2 is probably restricted by protons derived from an internal pool (1). Consequently, when A. nodosum from Fig 1C was returned to darkness, and normal seawater... 

FIGURE 3. Some properties of different brown algae. A, per cent of the outer cell membrane area of the meristc erm covered by mitochondria B, COL compensation level in air C, CO2 uptake from air (o) and HC03 uptake from seawater at pH 9.85 ( scale enlarged 20 times) D, photosynthetic buffering capacities in Ci-fiee seawater at pH 8.0 (o) and at pH9.7( ). 

In low-mineral freshwaters with low buffering capacity, both atmospheric CO2 and biological decomposition has a huge impact on the pH. The effect of atmospheric CO2 on the pH of seawater is much smaller but multiphase equilibria follows from the interaction with dissolved and solid mineral carbonates. 

Seawater pH ranges from 7.8-S.3. This narrow pH range is due to reactions that cause the interchange of carbon dioxide in the air with seawater and photosynthesis. Changes in the pH of seawater are buffered by the carbonate system and the presence of undissociated boric acid [7]. The buffering capacity and the constancy of natural waters such as seawater are discussed in Ref 8. 

Seasalt also may cause errors in the spectrophotometric signal. These salt effects are either a suppression of the analyte absorbance (e.g., in the determination of silicate and phosphate) by the ions of seawater or an effect of the buffer capacity of seawater (e.g., shifts in the reaction pH interfere with the determination of ammonia). 

Chemical procedures which are affected by the buffer capacity of the seawater, e.g., determination of ammonia, either require an adjustment of the matrix for standards or the analytical results must be corrected for a salinity error. 

This implies that the pH is changed if the solution is not buffered, especially in the vicinity of the metal surfaces. Because the buffer capacity of seawater is not suMdent ammonium chloride is added both as a complexant and as a buffer ... 

The indophenol blue produced by the same amount of ammonia is less in seawater than in pure water. This salt effect is caused by (i) magnesium ions, as also stated by Grasshoff and Johannsen (1974) and (u) by buffering capacity of seawater. Increasing amounts of Mg ions and increasmg buffer capacity decrease the final reaction pH. Consequently, the salt effect can be assumed to be caused by the pH. The chloride ion has no influence. 

The equilibria represented by Eqs. (2.18) through (2.23) further indicate that as OH is introduced, then Eqs. (2.19) and (2.20) are displaced to the right, resulting in proton production. This opposes any rise in pH and accounts for the buffering capacity of seawater. Irrespective of this, however, Eqs. (2.18) through (2.23) indicate that this buffering action is accompanied by the formation of calcareous deposits on cathodic surfaces exposed to seawater. 

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