Microbial biomass and activity in subsurface sediments from Vejen, Denmark

Area of Science:

• Geomicrobiology
• Quaternary geology
• Environmental microbiology

Background:

• Subsurface microbial communities play crucial roles in biogeochemical cycles.
• Understanding microbial life in geologically young sediments provides insights into early ecosystem development.
• Glacio-fluvial environments harbor unique microbial populations influenced by sediment characteristics.

Purpose of the Study:

• To characterize the microbial populations in Quaternary glacio-fluvial sediments.
• To investigate the relationships between microbial abundance, activity, and abiotic sediment parameters.
• To compare microbial data from young sediments with those from older geological formations.

Main Methods:

• Collection and analysis of subsurface sediment samples (4-31 m depth).
• Measurement of physicochemical properties: pH, electrical conductivity, chloride, organic matter, grain size.
• Quantification of microbial parameters: viable counts, acridine orange direct counts (AODC), [(3)H]-thymidine incorporation, (14)C-labelled compound mineralization.

Main Results:

• Bacterial abundance ranged from 0.5 to 1,203 x 10^3 CFU/gdw (viable) and 1.7 to 147 x 10^7 cells/gdw (AODC).
• Growth rates and mineralization rates varied significantly, with sediment texture influencing microbial numbers and activity.
• Increasing clay/silt content correlated with higher AODC and decreased mineralization; permeability correlated positively with acetate mineralization.

Conclusions:

• Sediment texture is a key factor influencing microbial populations in young glacio-fluvial sediments.
• No single abiotic parameter fully explains the variation in microbial size and activity.
• Geological age and formation type are likely important determinants of microbial community structure and function.