Pore water chemistry chemical reactions

A significant amount of seawater is trapped in the open spaces that exist between the particles in marine sediments. This fluid is termed pore water or interstitial water. Marine sediments are the site of many chemical reactions, such as sulfate reduction, as well as mineral precipitation and dissolution. These sedimentary reactions can alter the major ion ratios. As a result, the chemical composition of pore water is usually quite different from that of seawater. The chemistry of marine sediments is the subject of Part 111. 

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... 

The redissolution or burial of organic matter in sediments is a decision that is made jointly by the physics of diffusion, chemistry of organic matter oxidation, and the biology which mediates the chemical reactions. The concentration profile of a solute in sediment pore water is governed by the diffusion equation, which can be written most simply as... 

Many studies of the impact of chemical diagenesis on the carbonate chemistry of anoxic sediments have focused primarily on the fact that sulfate reduction results in the production of alkalinity, which can cause precipitation of carbonate minerals (see previous discussion). However, during the early stages of sulfate reduction (—2-35%), this reaction may not cause precipitation, but dissolution of carbonate minerals, because the impact of a lower pH is greater than that of increased alkalinity (Figure 4). Carbonate ion activity decreases rapidly as it is titrated by CO2 from organic matter decomposition leading to a decrease in pore-water saturation state. This process is evident in data for the Fe-poor, shallow-water carbonate sediments of Morse et al. (1985) from the Bahamas and has been confirmed in studies by Walter and Burton (1990), Walter et al. (1993), and Ku et al. (1999) for Florida Bay, Tribble (1990) in Checker Reef, Oahu, and Wollast and Mackenzie (unpublished data) for Bermuda sediments. 

The role of extra water in such recipes has turned out to be complex and again a question of supramolecular chemistry. It seems to be safe to state that its stmcture and chemical reactivity is far from that of bulk water, as it is tightly bound and activated in the H-bonded system of the IL. Therefore, reactions with water take place quite rapidly. On the other hand, water as a solvating ligand seems to be excluded due to the IL-binding, as for instance deduced from the absence of so-called solvent pores [30]. This is a quite unique situation for colloid chemistry and material synthesis. 

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