Many living organisms affect the quality of the ground water. Precipitation and/or solubility of many inorganic compounds depends in some way or other on biological activity of living organisms. The role of bacteria and other organisms in these processes may be either direct or indirect.
The oxygen consumption as a result of the decomposition of organic compounds is one of the most important processes affecting the quality of the ground water. In anoxic environments both iron and manganese are reduced becoming soluble in the ground water.
In weakly buffered ground water the release of the carbon dioxide during decomposition of organic substances decreases the pH of the water promoting the solubility of iron and manganese.
Most of the bacteria living in the ground water are psychrophilic and are attached on soil particles. Only few types of bacteria are free living.
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