Spatial variability of in situ microbial activity: biotracer tests

Area of Science:

• Environmental Science
• Geomicrobiology
• Hydrogeology

Background:

• Biotracer tests offer a method to assess in situ biodegradation potential in field-scale systems.
• Understanding microbial activity spatial variability is crucial for effective environmental remediation.

Purpose of the Study:

• To evaluate the biotracer method's utility in characterizing microbial activity spatial variability.
• To compare biodegradation potential in a Utah surficial aquifer and an Arizona regional aquifer.

Main Methods:

• Field experiments were conducted at two contaminated aquifer sites (Utah and Tucson, Arizona).
• Biotracer mass recovery and biodegradation rate coefficients were determined through tracer tests and model calibration.
• Core samples were analyzed to assess bacterial cell densities.

Main Results:

• Biotracer mass recovery decreased with increasing residence time at the Tucson site.
• Biodegradation rate coefficients showed minimal spatial variability (factor of 2.5) at the Tucson site.
• The Utah site exhibited greater spatial variability in biodegradation rates (order of magnitude) and higher microbial activity near injection wells, correlating with higher bacterial cell densities.

Conclusions:

• Biotracer tests are valuable for in situ characterization of microbial activity and biodegradation potential.
• The study highlights the utility of biotracer tests for evaluating spatial variability in aquifer microbial activity.
• Observed differences in spatial variability are consistent with site-specific hydrogeological and microbiological conditions.