Briefly, fracking involves drilling first vertically, then horizontally, toward a gas-bearing formation. The mechanics and process of hydraulic fracturing and modern shale gas development has been previously described ( Hubbert and Willis, 1954 Arthur et al., 2008 Ground Water Protection Council and ALL Consulting, 2009). Despite recent increases in prevalence, the impact of unconventional natural gas extraction, referred to as hydraulic fracturing or fracking, on headwater stream ecosystems has yet to be evaluated. Aquatic microbial community structure changes in response to biogeochemical alterations from anthropogenic sources, including agricultural, industrial, and recreational activities ( Wassel and Mills, 1983 Clivot et al., 2013 Sun et al., 2013). The first biotic response to environmental perturbations can be seen at the lowest trophic levels, as microbial communities can readily respond to changes in their surrounding abiotic environments. In particular, aquatic microbial communities are central to energy flow within these ecosystems ( Peterson et al., 2001 Findlay et al., 2002 Gulis and Suberkropp, 2003 Hall and Tank, 2003 Puddu et al., 2003 Wright and Covich, 2005 Hall et al., 2012 Schelker et al., 2012). Low-order stream ecosystems provide habitats for unique and local communities, and impact diversity ( Meyer et al., 2007) and quality of regional freshwater ecosystems ( Peterson et al., 2001 Alexander et al., 2007 Freeman et al., 2007 Wipfli et al., 2007). However, the importance of headwater streams on downstream ecosystem health has only recently received attention. Headwater streams are central to ecosystem functioning, and they are particularly sensitive to anthropogenic disturbances due to the combination of direct pollutant inputs to the watershed and the transmission of impacts from adjacent riparian terrestrial ecosystems ( Sweeney, 1992 Lemke et al., 1997 Pusch et al., 1998 Lemke and Leff, 1999 Maloney and Weller, 2011 Janisch et al., 2012 Webber, 2012 Ding et al., 2013). This study revealed apparent shifts in the autochthonous microbial communities and highlighted potential members that could be responding to changing stream conditions as a result of nascent industrial activity in these aquatic ecosystems. It should be noted that many of the OTUs enriched in MSA+ sites are putative acidophilic and/or methanotrophic populations. Further, several of these OTUs were strongly negatively correlated with pH and positively correlated with the number of wellpads in a watershed. ![]() For example, operational taxonomic units (OTUs) within the Acetobacteracea, Methylocystaceae, Acidobacteriaceae, and Phenylobacterium were greater than three log-fold more abundant in MSA+ sites as compared to MSA− sites. Beta diversity analyses revealed distinct microbial community structure between sites with and without Marcellus shale activity. Microbial community analyses showed significant reductions in species richness as well as evenness in sites with Marcellus shale activity. Approximately 3.2 million 16S rRNA gene sequences were retrieved from a total of 58 samples. Further, we describe the relationship between microbial community structure and environmental parameters measured. High-throughput sequencing of the 16S rRNA gene was performed to characterize the microbial community structure of water, sediment, bryophyte, and biofilm samples from 26 headwater stream sites in northwestern Pennsylvania with different histories of fracking activity within Marcellus shale formations. Hydraulic fracturing and horizontal drilling have increased dramatically in Pennsylvania Marcellus shale formations, however the potential for major environmental impacts are still incompletely understood. 6Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.5Department of Civil and Environmental Engineering, University of Tennessee Knoxville, Knoxville, TN, USA. ![]()
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