Carbon Source Utilization Profiles for Microbial Communities from Hydrologically Distinct Zones in a Basalt Aquifer |
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Authors: | FS Colwell RM Lehman |
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Institution: | (1) Biotechnologies Department, Idaho National Engineering Laboratory, P.O. Box 1625, Idaho Falls, ID 83415-2203, USA, US |
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Abstract: | Abstract
The Eastern Snake River Plain aquifer has hydrologically distinct zones in basalt flow units and interbedded sediments. The
zones that differ markedly in physical features (e.g., porosity and permeability) have similar groundwater chemistries. The
primary objective of this study was to determine whether intervals within the aquifer that contrast on the basis of permeability
have distinct communities of unattached microorganisms based on functional attributes. Aquifer sampling was conducted using
a submersible pump to obtain whole-well (w) samples, and a straddle-packer pump (SPP) to obtain samples from specific aquifer
intervals that were vertically distributed in the open borehole. The SPP intervals ranged from 4.6 to 6.1 m in length and
were located from 142 to 198 m below land surface. A community-level physiological profile (CLPP) was used to determine functional
characteristics of the microbial community in the groundwater samples based on the community response to 95 sole organic carbon
sources. Surface soil samples at the site were analyzed in a similar manner for comparison. The total bacterial population
in the groundwater samples was determined using acridine orange direct counts. Principal components analysis (PCA) of the
CLPP dataset distinguished between surface soil and aquifer microbial communities. Soils scored low in the respiration of
polymers, esters, and amines and high in bromosuccinate, when compared to aquifer samples. The W samples were distinct from
SPP samples. The 180- to 198-m interval, with the lowest hydraulic conductivity of all intervals, yielded samples that grouped
together by PCA and cluster analysis. Direct counts varied between 104 and 105 cells ml−1, and showed no relationship to the depth of the sample or to the hydraulic conductivity of the sample interval. Differences
between microbial communities based on respired carbon compounds were discerned in separate, hydrologically distinct intervals
within the borehole, although these differences were slight. Differences among aquifer intervals were less apparent than differences
between surface soils and groundwater, and may be related to variations in hydrologic properties over the intervals sampled.
The results suggest that free-living microbial communities in basalt aquifers, as characterized by CLPP are relatively unaffected
by wide ranges in hydraulic conductivity when other abiotic factors are essentially equal.
Received: 14 December 1995; Revised: 12 April 1996 |
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