Decay of organic matter and

Rainwater recharges the top of the profile and reacted water drains from the bottom. We take discharge through the soil to be 4 m yr-1 and assume the dispersivity or (see Chapter 20) is 1 cm. The rainwater is dilute and in equilibrium with the CO2 fugacity of the atmosphere, 10-3 5. Within the soil, however, the soil gas is taken to contain additional CO2 as a result of the decay of organic matter, and root respiration. The pore fluid is assumed to maintain equilibrium with the soil gas and CO2 fugacity within the soil is held constant over the simulation, at 10-2. 

Conditions on the inside of a rock may be considerably different from those at the surface. Carbon dioxide can be produced by the decay of organic matter, and an acid-base reaction between CO2 and metal oxides produces metal carbonates. Typical reactions of this type are the following ... 

Carbon. Two sources of carbon are generally recognized as contributing to the carbon load of groundwaters (1) the CO2 present in the soil atmosphere that is derived from plant root respiration and decay of organic matter and... 

The carbon isotopic composition of XCO2 in seawater is mainly controlled by two processes, the biochemical fractionation due to the formation and decay of organic matter, and the physical fractionation during gas exchange at the air-sea boundary (Broecker and Maier-Reimer 1992). Surface water is enriched in C, beeause photosynthesis preferentially removes from the CO2. Deeper water masses have lower 5 C values, since nearly all of the organie matter that is produeed by photosynthesis is subsequently remineralized in the water eolumn. Broeeker and Maier-Reimer (1992) showed that if there were no air-sea gas exchange, the relationship between 5 C and PO4 in the oeean would be... 

Sulfur-containing amino acids and proteins form very strong soluble complexes with mercury 12, 50, 51). Humic acids are formed by partial decay of organic matter and may have sulfur-bearing residual proteins bound to quinoid polymers, thus acting as strong complexers of relatively... 

Our complex modern life style was made possible by the discovery and refining of fossil fuels, fuels that are the result of the decay of organic matter laid down millions of years ago. The natural gas that heats our homes, the gasoline that powers our automobiles, and the coal that provides much of our electrical power are fossil fuels. Vast reserves of petroleum, the source of liquid hydrocarbon fuels such as gasoline and coal, exist in many areas of the world. However, although large, these reserves are limited, and we are using them up at a much faster rate than they can be replaced. 

Evershed RP, Bland HA, van Bergen PF, Carter JF, Horton MC, Rowley-Conwy PA (1997) Volatile compounds in archaeological plant remains and the Mail-lard reaction during decay of organic matter. Science 278 432-433... 

Carbon dioxide in the atmosphere has some influence on the composition of ores. The decay of organic matter can produce carbon dioxide, and it reacts with many metal oxides to produce metal carbonates. For example,... 

Sediment deposition on the seafloor traps interstitial water. After deposition, complex reactions take place in the sediment, most of them fueled by the decay of organic matter, such as sulfate reduction, denitrification,... Because of fast diffusion rates of most cations in seawater, the presence of interstitial water makes exchange between overlying sedimentary layers a much easier process than if sediment deposition was dry. The book by Berner (1980) is entirely dedicated to these processes and only a short example is given here. 

Sources. By-product of many industrial processes around oil wells and in areas where petroleum products are processed, stored, or used decay of organic matter occurs naturally in coal, natural gas, oil, volcanic gases, and sulfur springs. 

Eutrophication A complex series of inter-related changes in the chemical and biological status of a water body most often manifested by a depletion of the oxygen content caused by decay of organic matter resulting from a high level of primary productivity and typically caused by enhanced nutrient input. 

Products resulting from the decay of organic matter—e.g. Indian nitre and South African nitre. The value of saltpetre for the manufacture of gunpowder and in the chemical industries is greatly in excess of its value as a fertilizer and consequently nitre is not usually regarded as a source of potash supply. (6) Blast furnace and cement-kiln dust. (7) The insoluble potash minerals—e.g. felspar, alunite, leucite, etc. 

Figure 24-1 The nitrogen cycle. Conversion of N2 (oxidation state 0) to NH4+ by nitrogen-fixing bacteria, assimilation of NH4+ by other organisms, decay of organic matter, oxidation of NH4+ by the nitrifying bacteria Nitrosomas and Nitro-bacter, reduction of N03 and N02 back to NH4+, and release of nitrogen as N2 by denitrifying bacteria are all part of this complex cycle.1...

This process consumes oxygen and produces C02. As a result, the oxygen content of air in soil may be as low as 15%, and the carbon dioxide content may be several percent. Thus, the decay of organic matter in soil increases the equilibrium level of dissolved C02 in groundwater. This lowers the pH and contributes to weathering of carbonate minerals, particularly calcium carbonate. 

At the macromolecular level, adsorption of clay particles to biological molecules such as proteins reduces their rate of decomposition by protecting them from microbial attack (Jenkinson 1981). On a larger scale, entrapment of organic matter in soil aggregates reduces the rate of decomposition at least while the aggregate persists. On a soil-profile scale, Shields and Paul (1973) showed that the rate of decay of organic matter on the soil surface was... 

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