Microbiological Comparison of Core and Groundwater Samples Collected from a Fractured Basalt Aquifer with that of Dialysis Chambers Incubated In Situ

Abstract

Microorganisms associated with basalt core were compared to those suspended in groundwater pumped from the same well in the eastern Snake River Plain Aquifer (Idaho, USA). Two wells located at different distances from the source of a mixed-waste plume in the fractured basalt aquifer were examined. In the well more distal from the plume source, an array of dialysis chambers filled with either deionized water or crushed basalt was equilibrated to compare the microorganisms collected in this fashion with those from core and groundwater samples collected in a traditional manner from the same well. The samples were characterized to determine the total amount of biomass, presence of specific populations or physiological groups, and potential community functions. Microorganisms and their activities were nearly undetectable in core and groundwater collected from the well farthest from the plume source and substantially enriched in both core and groundwater from the well closest to the plume source. In both wells, differences (statistically significant for some measures) were found between bacteria associated with the cores and those suspended in the groundwater. Significantly higher populations were found in the basalt- and water-filled dialysis chambers incubated in the open well compared with core and groundwater samples, respectively. For a given parameter, the variation among dialysis chambers incubated at different depths was much less than the high variation observed among core samples. Analyses on selected basalt- and water-filled dialysis chamber samples suggested that these two communities were compositionally similar but exhibited different potential functions. Documented knowledge of cell physiological changes associated with attachment and potential differences between attached and unattached communities in aquifers indicate that careful consideration should be given to the type of sample media (i.e., core, groundwater, substrata incubated in a well) used to represent a subsurface environment.

Keywords:

• aquifer
• attached
• free-living
• groundwater
• microbiology
• subsurface
• TCE

This research was funded by the U.S. Department of Energy, Office of Environmental Management, Environmental Management Science Program, by grant to FSC at the Idaho National Engineering and Environmental Laboratory (INEEL) operated at that time by Lockheed Martin Idaho Technologies Co. under contract DE-AC07-94ID13223 and subsequently operated by Bechtel BWXT, LLC under contract DE-AC07-99ID13727. Assistance in laboratory analyses or field sampling is acknowledged from the following persons: Matt Downing, Mark Delwiche, Brad Blackwelder, Travis McLing, Mark Wilson, Pete Pryfogle, Bob Smith, Shu-mei Li, Jim McKinley, and Teresa Wilson. Jay Anderson and Maribeth Watwood are acknowledged for critical review of the manuscript.

Notes

^a Data are nominal values taken from Bukowski, J. 2000. Fiscal Year 1999 Groundwater Monitoring Annual Report Test Area North, Operable Unit 1-07B, INEEL/EXT-99-01255, U.S. Department of Energy, January 2000.

^a Enumerations are reported per ml of groundwater or per wet g of rock. Iron-reducers are reported as the percent of samples which had positive enrichments (at least one of three triplicate enrichments). Metabolic richness is the number of sole carbon sources oxidized by the whole sample inoculated into Biolog GN microplates. Aerobic and anaerobic mineralization are reported in percent of added ¹⁴C-labeled acetate that was mineralized after 3 days.

^b Data are reported as follows: on the first line, the mean with one standard deviation in parentheses; on the second line, the number of independent samples with a positive assay result over the the total number of independent samples analyzed; on the third line, the range of measured values. Measurements below method detection limits were assumed to be zero for the purpose of mean and standard deviation calculations. nd = no data. bd = below detect with method detection limit following in parenthesis.

^c Most-Probable-Number (MPN) enumerations; for core samples, the MPN matrix contained six dilution levels with five vials per level; for groundwater samples, the MPN matrix contained four dilution levels with three vials per level; for dialysis chamber samples, the MPN matrix contained three dilution levels with three vials per level.

^a Enumerations are reported per ml of groundwater or per wet g of rock. Iron-reducers are reported as the percent of samples which had positive enrichments (at least one of triplicate enrichments). Metabolic richness is the number of sole carbon sources oxidized by the whole sample inoculated into Biolog GN microplates. Mineralization is reported in percent of added 14C-labeled acetate that was mineralized after 3 days. PLFA is reported as total picomoles per g or ml.

^b Data are reported as follows: on the first line, the mean with one standard deviation in parentheses; on the second line, the number of independent samples with a positive assay result over the the total number of independent samples analyzed; on the third line, the range of measured values. Measurements below method detection limits were assumed to be zero for the purpose of mean and standard deviation calculations. nd = no data.

^c Most-Probable-Number (MPN) enumerations; for core samples, the MPN matrix contained six dilution levels with five vials per level; for groundwater samples, the MPN matrix contained four dilution levels with three vials per level.

^d PLFA for groundwater from Kent Sorenson (unpublished data).

^a Presence of band for that sample noted by an “X”; absence of band noted by “(−).”

^b BAND designation corresponds to alphabetical label applied to each band in Figure 6.

^c Sequence identification was obtained by comparison with GenBank database using BLAST. Due to the short sequence amplified from the bands, there were a number of close matches; therefore, group identifications are reported with an example of a high matching sequence.