Exposure History Dependence of Microbial Mediated Substrate Transformation in Groundwater

Monday, December 4, 2017
Davidson Ballroom Foyer (Music City Center)
Charles Paradis , University of Tennessee Knoxville, Knoxville, TN
Larry McKay, Ph.D. , University of Tennessee Knoxville, Knoxville, TN
Terry Hazen, Ph.D. , University of Tennessee Knoxville, Knoxville, TN

The capacity of natural microbial communities to transform a substrate in groundwater has been shown to increase after repeated exposures to the substrate; herein referred to as the “memory effect”. The objectives of this study were to determine: (1) how long the memory effect can last and (2) how the memory effect can alter the structure and function of natural microbial communities. Ethanol substrate was injected into a single groundwater test well for six consecutive weeks to establish a memory effect. The groundwater control well, located up-gradient of the test well, was not injected with ethanol during the first six weeks. Ethanol transformation in the test well was not significant the first week whereas ethanol transformation was significant during weeks two through six. The test and control wells were then monitored for eight additional weeks under ambient conditions. During week 14, ethanol was injected into both the test and control wells. Ethanol transformation was significant in the test well whereas ethanol transformation was not significant in the control well. These results demonstrated that the memory effect lasted at least eight weeks in the test well.

Here we present the hydrological, geochemical, and microbiological data and analyses in hand from the study site and the experimental well pair. This includes: (1) the magnitude and variability of hydraulic conductivity, hydraulic gradient, and effective porosity, (2) the potential for diffusive mass transport, (3) the temporal variability of specific discharge, (4) ethanol transformation to acetate and removal of nitrate and sulfate, (5) utilization/limitation of metal nutrients and/or co-factors, (6) microbial community structure (16S rRNA sequencing), and (7) microbial community function (GeoChip). Finally, we discuss the implications of the memory effort in terms of groundwater remediation with emphasis on the immobilization of redox sensitive metals and radionuclides.


Charles Paradis, University of Tennessee Knoxville, Knoxville, TN
Charlie is a Ph.D. candidate at the University of Tennessee Knoxville. His research interests are broadly aligned with the fate and transport of contaminants in groundwater, particularly field-scale microbial-mediated hydrogeologic processes that are critical to society and nature, e.g., decreasing the toxicity and mobility of contaminants in groundwater.

Larry McKay, Ph.D., University of Tennessee Knoxville, Knoxville, TN
Dr. McKay is the Jones Professor of Hydrogeology and Department Head at the University of Tennessee Knoxville, Earth and Planetary Sciences. His principal research interests are fate and transport of contaminants and tracers in hydrologic systems. He has extensive experience in transport in fractured clay-rich residuum and tills.

Terry Hazen, Ph.D., University of Tennessee Knoxville, Knoxville, TN
Dr. Hazen is the Governor's Chair Professor at the University of Tennessee and Oak Ridge National Laboratory. The Hazen Lab's primary research emphasis is basic and applied field microbial ecology, especially as it relates to bioremediation, biofuels, enhanced oil recovery, and water quality.

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