Pore water chemistry

The study of the chemistry of sediment pore water provides important information on chemical reactions occurring in sediments. In many cases, the reactions between pore waters and solids are not obvious from observations of the solids, but because of the large solid to solution ratio in sediments, major changes 

However, there is a strong tendency to higher supersaturations with respect to aragonite in the Bahamian sediments, and lower saturation states in the south Florida sediments. Because aragonite is generally the dominate carbonate phase in these sediments, control of the IAP by the most abundant phase does not generally explain these observations. 

Both field and laboratory observations are consistent with the idea that dissolution can proceed faster than precipitation in carbonate sediments (also see Pytkowicz, 1971 Berner et al., 1978 Moulin et al 1985 Burton and Walter, 1987), and that the pore waters reach steady-state ion activity products close to those of the most unstable phase (dissolution processes will be discussed later in this chapter). Carbonate ion may be pumped down to values at saturation with less soluble phases, as dissolution of the more soluble material eventually causes its removal. However, the persistence of high magnesian calcites in sediments for long periods of time indicates that this process does not involve a large amount of mass transfer under normal marine conditions. 

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Mozley PS, Carothers WW (1992) Elemental and isotopic compositions of siderite in the Kuparuk formation, Alaska effect of microbial activity and water/sediment interaction on early pore-water chemistry. J Sed Pet 62 681-692... 

Electrokinetic remediation is limited by the type of contaminant, heterogeneities or anomalies in the soil, extreme pHs, pore water chemistry, lack of pore water, contaminant and noncontaminant ion concentrations, metals precipitation, and reduction-oxidation changes induced by the process electrode reactions. It may be difficult to estimate the time that will be required to remediate a site using this technology. Laboratory treatability testing may provide a false indication of the applicability of electrokinetic remediation at a specific site. Further research is required to determine the technology s limitations and ramifications. 

Bradbury, M. H. Baeyens, B. 2002. Pore-water Chemistry in Compacted Resaturated MX-Bentonite Physicochemical Characterisation and Geochemical Modelling. Paul Scherrer Institut, Villigen, Switzerland, PSI Berichl Nr. 02-10, 42... 

Fernandez, A. M., Cuevas, J. Rivas, P. 2001. Pore water chemistry of the FEBEX bentonite. Materials Research Society Symposium Proceedings, 663, 573—588. 

Little Rock Lake. Net IAG in LRL takes place primarily in or near the sediment. It can be evaluated by measurements of pore-water chemistry, comparison of hypolimnetic and epilimnetic chemistry, and calculation of ion budgets. An example of each approach follows. 

Numerous measurements of pore-water chemistry have been made in LRL throughout the experiment (4, 17, 59). Typical vertical pore-water profiles (Figure 6) indicate that the sediments are acting as sinks for sulfate... 

McCaffrey, R.3., Myers, A.C., Davey, E., Morrison, G., Bender, M., Luedtke, N., Cullen, D., Froelich, P. and Klinkhammer, G., 1980. The relation between pore water chemistry and benthic fluxes of nutrients and manganese in Narragansett Bay, Rhode Island. Limnol. Oceanogr., 25(1) 31-44. 

Emerson et al., 1982) have demonstrated that this approach will not work for studying the carbonate chemistry of deep sea sediment pore waters. The reason is that the solubility of carbonates changes substantially with temperature and pressure, and they are reactive enough to change the pore water chemistry when the cores are recovered. Consequently, most recent studies have relied on extracting pore waters in situ. The major difficulty with this technique is that it usually is not possible to obtain closely spaced samples or samples very near the sediment-water interface. This interface is, unfortunately, the region where most of the chemical changes associated with the carbonate-C02 system take place. 

Reaves (1986) described another study specifically aimed at relating calcium carbonate preservation to chemical diagenesis in sediments. He compared Mercinaria shells and pore water chemistry in intertidal mud flat and tidal creek... 

Budd D.A. (1988) Aragonite-to-calcite transformation during fresh-water diagenesis of carbonates Insights from pore-water chemistry. Geol. Soc. Amer. Bull. 100, 1260-1270. 

Thortenson D.C. and Mackenzie F.T. (1974) Time variability of pore water chemistry in recent carbonate sediments, Devil s Hole, Harrington Sound. Bermuda. Geochim. Cosmochim. Acta 38, 1-19. 

Gardner, L.R. (1973) The effect of hydrologic factors on the pore water chemistry of intertidal marsh sediments. Southeast. Geol. 15, 17-28. 

The effect of R on metal concentrations in soil pore water is of interest because it can characterize soil pore water at different water content, and also to explain the effect of different values of R in procedures for extracting equilibrium soil pore water. Water extracts are often used to measure pore water chemistry and thus... 

Sheppard, M. I., Thibault, D. H., and Smith, P. A. (1992). Effect of extraction techniques on soil pore-water chemistry. Commun. Soil Sri. Plant Anal. 23(13-14), 1643—1662. 

Groundwater or soil pore-water chemistry generally differs from the chemistry of laboratory solutions due to both inorganic and organic solutes which can act as catalysts or inhibitors to dissolution (e.g., Ganor and Lasaga, 1998). For example, much effort has been expended to... 

Cerhng T. E. (1996) Pore water chemistry of an alkaline lake Lake Turkana. In The Limnology, Climatology, and Paleoclimatology of the East African Lakes (eds. T. C. Johnson and E. O. Odada). Gordon and Breach, Amsterdam, pp. 225-240. 

While all of these reactions are favored thermodynamically, they are almost always enzymatically catalyzed by bacteria. It has been observed from the study of pore waters in deepsea sediments (e.g., Froelich et al., 1979) and anoxic basins (e.g., Reeburgh, 1980) that there is an ordered sequence of redox reactions in which the most energetically favorable reactions occur first and the active electron acceptors do not overlap significantly. Bacteria are energy opportunists. Using estimates of the stoichiometry of the diagenesis reactions (Table 2) one can sketch the order and shape of reactant profiles actually observed in sediment pore-water chemistry... 

There has always been some reluctance to assume that the pH in a porous medium is controlled solely by the carbonate buffer system in the pore waters. There are arguments that H ions on particle surfaces can affect pH measurements (Stumm and Morgan, 1981) and, even more importantly, comprehensive models of pore-water chemistry are beginning to demonstrate that H adsorption on mineral surfaces may play an important role in controlling the pH of pore waters. Conclusions of the pH measurements, however, have been confirmed by millimeter-scale measurements of both Pco and calcium concentration in the pore waters (Hales et al., 1997 Cai et al., 1995 Wenzhofer et ah, 2001.)... 

The influence of seagrass beds on fine-grained sediments near San Salvador Island was investigated by Short et al (1985), and Morse et al (1987) studied their influence on pore-water chemistry in coarser-grained sediments near the Berry Islands. Their influence was less in the coarse-grained sediments, but even in these sediments, elevated alkalinity values in... 

FeS formation can play an important role in regulating pore-water chemistry. Systems with more intense FeS formation have a tendency to become more supersaturated with respect to aragonite. N-poor organic matter appeared to result in more corrosive conditions. 

Hines M. E., Orem W. H., Lyons W. B., and Jones G. E. (1982) Microbial activity and bioturbation-induced oscillations in pore water chemistry of estuarine sediments in spring. Nature 299, 433-435. 

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