Microbial
Community Changes in Hydraulic Fracturing
Fluids and Produced Water from Shale Gas Extraction
- Publication date
- Publisher
Abstract
Microbial
communities associated with produced water from hydraulic
fracturing are not well understood, and their deleterious activity
can lead to significant increases in production costs and adverse
environmental impacts. In this study, we compared the microbial ecology
in prefracturing fluids (fracturing source water and fracturing fluid)
and produced water at multiple time points from a natural gas well
in southwestern Pennsylvania using 16S rRNA gene-based clone libraries,
pyrosequencing, and quantitative PCR. The majority of the bacterial
community in prefracturing fluids constituted aerobic species affiliated
with the class <i>Alphaproteobacteria</i>. However, their
relative abundance decreased in produced water with an increase in
halotolerant, anaerobic/facultative anaerobic species affiliated with
the classes <i>Clostridia</i>, <i>Bacilli</i>, <i>Gammaproteobacteria</i>, <i>Epsilonproteobacteria</i>, <i>Bacteroidia</i>, and <i>Fusobacteria</i>. Produced water collected at the last time point (day 187) consisted
almost entirely of sequences similar to <i>Clostridia</i> and showed a decrease in bacterial abundance by 3 orders of magnitude
compared to the prefracturing fluids and produced water samplesfrom
earlier time points. Geochemical analysis showed that produced water
contained higher concentrations of salts and total radioactivity compared
to prefracturing fluids. This study provides evidence of long-term
subsurface selection of the microbial community introduced through
hydraulic fracturing, which may include significant implications for
disinfection as well as reuse of produced water in future fracturing
operations