Bacteria- The major group of microorganisms found in groundwater ecosystem is bacteria. The abundance and distribution of bacteria in a given subsurface zone is actually determined by the nature of geological stratum, mineral type, particle size distribution, texture, hydraulic conductivity etc. The nutrient levels decline, when moving down from A and B soil horizons to C horizon accompanied by a proportional decline in bacterial abundance.
However, the number of bacteria does not continue to diminish with depth. Indeed there is again an increase in the bacterial numbers at the capillary fringe zone and at the water table. This is due to the horizontal saturated flow as well as the vertical seasonal fluctuations of the water table which lead to a dynamic mixing of oxygen and nutrients in these regions.
