Organic carbon accumulation matter decomposition

Among the carbon reservoirs of the biosphere, a large proportion is stored in soil organic matter and marine sediments (Bolin, 1977). The accumulation of carbon in soils and sediments is a function of the organic carbon balance between net primary production (carbon fixation) and heterotro-phic metabolism (decomposition). The fixation of atmospheric carbon through photosynthesis is the major sonrce of carbon to terrestrial, wetland, and aquatic ecosystem. 

The analysed data on carbon content and also on content of organic N and P in dissolved and particulate state at the end of all the experiments illustrate the stability of OM. The experiments simulate accumulation of resistant insoluble and soluble organic compounds in reservoirs and soils. These compounds appear as the result of decomposition of dead living matter and its living excretions. The processes are not only responsible for transformation of initial OM (oxidation, polymerisation, condensation), but also for synthetic processes, caused by bacterial activity (Kononova, 1963), and this is the water humus of planktonic origin. 

As shown in these reactions, reduction of iron and manganese results in the consumption of H ions, thus resulting in a decrease in H+ ion activity or an increase in pH. For example, in paddy soils of Philippines (Table 4.4) iron comprises 0.63-4.7% of the total soil mass, and manganese content can be as high as 0.1%. The proton to electron ratio is 3 for Fe(OH)3 reduction, as compared to a ratio of 2 for Mn02 reduction. Thus, iron reduction will have a greater effect on the pH increase in acid soils. Reduction of other electron acceptors such as nitrate and sulfate can also have a similar effect on the soil pH. In acid soils, an initial increase in pH can also occur due to rapid decomposition of soil organic matter and accumulation of carbon dioxide. However, acid soils eventually increase in pH due to reduction of oxides of Fe and Mn. 

Globally, extensive areas of peatlands and wetlands have been drained and converted into agricultural lands. Drainage of organic matter-rich soils accelerated the decomposition process and emission of carbon dioxide. Many peatlands that have accumulated organic matter for centuries... 

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