Most natural aquifers are oligotrophic in nature, therefore are poor in nutrients and exhibit low microbial densities. These are important reservoirs of drinking water. Understanding the dynamics of intrinsic microbial transformations and the inherent oxygen-consuming processes is of vital importance as it can have a tremendous effect on the water quality, and thus on the drinking water supply to many of the world’s communities. Changing the residence times or the composition of infiltrating water will change the distribution of redox zones within aquifers, which may affect the quality of extracted groundwater.
If we closely observed the oligotrophic aquifer system, we realize that there are two constraints in the system. There is slow and small release of natural organic matter in the system. NOM can be a complex molecular compound and cannot be taken by organism so extracellular hydrolysis is required to produce smaller, monomeric molecules which may take considerable period of time. Moreover, even there is sufficient amount of substrates in the system; there is slow kinetic uptake of these nutrients by the microbes which may be due to inaccessibility. This inaccessibility can rises due to biochemical state, spatial variation, occlusion of organic matter, sorption and complexation reaction etc.
It is believed that these microbial communities can sustain solely by the energy supplied by water-rock chemistry.
