Organic decay

Since methane is almost always a byproduct of organic decay, it is not surprising that vast potential reserves of methane have been found trapped in ocean floor sediments. Methane forms continually by tiny bacteria breaking down the remains of sea life. In the early 197Qs it was discovered that this methane can dissolve under the enormous pressure and cold temperatures found at the ocean bottom. It becomes locked in a cage of water molecules to form a methane hydrate (methane weakly combined chemically with water). This "stored" methane is a resource often extending hundreds of meters down from the sea floor. 

Crumbling is not an instant s Act A fundamental pause Dilapidation processes Are organized Decays... 

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...

Additionally, when plants and animals die, the dead organisms decay and give off C02. 

The oxygen uptake rate terms are considered in more detail. Here they are represented by four terms, oxygen uptake rate due to heterotrophic growth (r ), oxygen consumption rate by organism decay (r ), oxygen uptake rate due to Nitrosomonas (r ) and Nitrobacter (r4) respectively. The specific carbonaceous oxygen uptake rate (SCOUR) is defined by (6)... 

Taylor and Velbel point out that biomass storage may also decrease—i.e., the biomass does not always cause a net uptake of nutrients. If organic decay returns more nutrients to the soil solution than are taken up by plants, then a balance does not require mineral weathering, and nutrients are being lost to streams. Biomass decay can exceed biomass uptake when there is, e.g., insect defoliation of trees, storm losses of trees, timber cutting, or fire (Taylor and Velbel, 1991). 

Fulvic acid plays a major role in the transport and deposition of Fe, AI, and other metals in soils. The acid is produced by organic decay in the top of the soil s A horizon. Fulvic acid ligands can form soluble complexes with Fe + and AP+ and other metals, which facilitates metal movement downward through the soil. As a rule of thumb, if the molar ratio of metals/fulvic acid is less than 1/1, the metals are water soluble and mobile (Schnitzer 1971). If that ratio exceeds 1/1, the metals become insoluble and immobile. Thus, as fulvic acids are destroyed by aerobic decay or other processes during downward percolation, the metals precipitate, typically in the soil s B horizon. Precipitation of Fe and Al (and also Mn) oxyhydroxides, in turn, leads to coprecipitation and concentration of trace metals such as Cu, Cd, Zn, Co, Ni, and Pb in the soil (cf. Suarez and Langmuir 1975). 

The removal of dissolved or particulate organic contaminants is most effective where they can be aerobically broken down. Aerobic decay is most rapid in well-aerated, unsaturated soils and is most complete in thick, unsaturated soils. Organic decay in water-saturated soils tends to be anaerobic, which is much slower and produces more noxious products than aerobic decay (see Chap. 5). Because the O and A horizons of a soil are usually relatively acid (cf. Figs. 7.2 and 7.3), the alkalinity of soils chiefly resides in the clays and carbonates within B and C horizons. Because of their carbonate content, mollisols and aridisols can neutralize acid wastes more rapidly and completely than can oxisols and spodosols, for example. 

The x-ray amorphous silica in soils includes opaline silica in the form of plant phytoliths. During plant growth, silica precipitates on the walls of plant cells. After death and organic decay of the plant, the silica phytoliths remain in the soil for many year s as accurate representation of the cell wall. Phytoliths are visible under the microscope and can identify the plants in which they formed. 

KS = the specific substrate utilization rate, mass/mass time D = the organism decay coefficient, 1/time. 

Decay spores are almost universally present. Given the presence of wood, suflScient moisture and air, a tolerable temperature, enough time, and the absence of substances toxic to the decay organism, decay will surely begin and proceed to the total destruction of the wood available. Therefore, there are few truly ancient or archaeological wooden artifacts, and the problems involved in gluing them may often be as much academic as real. 

Organisms, unless consumed by other organisms, decay after death. Decay involves chemical alteration of body tissues and the actions of... 

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