Biogeochemical dynamics and microbial community development under sulfate- and iron-reducing conditions based on...

Area of Science:

• Microbial ecology
• Geochemistry
• Environmental science

Background:

• Anoxic sediments host crucial biogeochemical processes like iron and sulfate reduction.
• Microbial communities driving these reactions are vital for subsurface ecosystems.
• Understanding microbial dynamics under changing conditions is challenging due to diverse energy-harnessing mechanisms, including electron shuttles.

Purpose of the Study:

• To investigate the impact of the model electron shuttle 9,10-anthraquinone-2,6-disulfonate (AQDS) on microbial communities and biogeochemical processes in freshwater aquifer sediments.
• To monitor changes in redox conditions and microbial community composition over time in response to amendments.

Main Methods:

• Experimental bioreactors were established using freshwater aquifer sediment.
• Amendments included ferric iron, sulfate, acetate, and the electron shuttle AQDS.
• Redox conditions and microbial community composition were monitored throughout the experiment.

Main Results:

• AQDS addition enhanced the initial rate of FeIII reduction but had minimal impact on overall microbial community structure.
• Initially, Geobacter species dominated, followed by Desulfosporosinus species, irrespective of AQDS presence.
• Significant ferric iron reduction occurred during the phase dominated by sulfate-reducing bacteria.

Conclusions:

• The study questions the sole reliance on dominant microbial processes for classifying subsurface sediments due to interconnected biogeochemical consequences.
• Microbial iron and sulfate reduction are closely linked, with iron reduction occurring even under ostensibly sulfate-reducing conditions.
• Further research is needed to understand these interactions across diverse environmental conditions to improve subsurface process models.