Microbial ecology of the terrestrial subsurface

Area of Science:

• Terrestrial subsurface microbial ecology
• Aquifer microbiology
• Environmental microbiology

Background:

• Microorganisms are the predominant life forms in the terrestrial subsurface.
• Aquifer sediment and groundwater properties critically influence microbial abundance and activity.
• Environmental factors like pH and temperature are generally not limiting in shallow aquifers.

Purpose of the Study:

• To present a current view of microbial ecology in terrestrial subsurface environments, focusing on shallow aquifer sediments.
• To characterize the types, abundance, and metabolic activities of subsurface microorganisms.
• To understand the factors controlling microbial distribution and function in aquifers.

Main Methods:

• Employed aseptic sampling techniques for subsurface material.
• Utilized microbiological and biochemical methods for analysis.
• Conducted vertical profile studies of shallow aquifers and lateral distribution studies.

Main Results:

• Active microbial biomass generally declines with depth in shallow aquifers but can be variable in saturated zones.
• Bacteria are the dominant microorganisms, though eukaryotic microbes are also present.
• Microorganisms exhibit transport and migration within aquifer sediments over significant distances.

Conclusions:

• Aquifer properties such as pore size, nutrient, and electron acceptor availability are key determinants of microbial life.
• Microbial colonization of aquifers can occur during sediment deposition or via transport from surface areas.
• The nutritional ecology of pristine aquifers is typically oligotrophic, relying on organic compounds from overlying soil.