Response of Aquatic Bacterial Communities to Hydraulic Fracturing in Northwestern Pennsylvania: A Five-Year Study

Abstract

Horizontal drilling and hydraulic fracturing extraction procedures have become increasingly present in Pennsylvania where the Marcellus Shale play is largely located. The potential for long-term environmental impacts to nearby headwater stream ecosystems and aquatic bacterial assemblages is still incompletely understood. Here, we perform high-throughput sequencing of the 16 S rRNA gene to characterize the bacterial community structure of water, sediment, and other environmental samples (n = 189) from 31 headwater stream sites exhibiting different histories of fracking activity in northwestern Pennsylvania over five years (2012–2016). Stream pH was identified as a main driver of bacterial changes within the streams and fracking activity acted as an environmental selector for certain members at lower taxonomic levels within stream sediment. Methanotrophic and methanogenic bacteria (i.e. Methylocystaceae, Beijerinckiaceae, and Methanobacterium) were significantly enriched in sites exhibiting Marcellus shale activity (MSA+) compared to MSA− streams. This study highlighted potential sentinel taxa associated with nascent Marcellus shale activity and some of these taxa remained as stable biomarkers across this five-year study. Identifying the presence and functionality of specific microbial consortia within fracking-impacted streams will provide a clearer understanding of the natural microbial community’s response to fracking and inform in situ remediation strategies.

Shale gas development has limited effects on stream biology and geochemistry in a gradient-based, multiparameter study in Pennsylvania

“…The lowest pH value in the study (5.0) was observed in spring 2017 at Sebring Branch of Mill Run (NWIS ID 01548770), a site in the lowest sDII category with no OG or historic mining activity in its watershed and with the lowest observed specific conductance (14.7 μS/cm), suggesting that the low pH is a function of local geology, hydrology, and/or precipitation. This contrasts the findings of Chen See et al (31), Trexler et al (32), and Ulrich et al (48), which suggested that changes in pH resulting from acids used in shale gas well completion were significantly related to shale gas development in a similar geologic setting.…”

“…Forty physical and chemical parameters were measured for this study (SI Appendix, Table S5), and, of these, specific conductance (as a proxy for TDS) and dissolved Cl, Br, Ca, Na, Li, B, Ba, and Sr are known as useful geochemical tracers of produced water (24,25,28,29,76,77). The pH was measured as a potential indicator for acids used in shale gas well completion and for potential effects on microbial and macroinvertebrate communities (32,33,48,78).…”

“…Furthermore, produced water and produced water impoundment ponds have distinct microbial populations (13,(42)(43)(44)(45)(46)(47), suggesting that microbial community profiles may have a potential utility as biological tracers for produced water. A group of studies focusing on northwestern Pennsylvania have demonstrated changes in microbial community structure in watersheds with OG activity when contrasted to similar watersheds without activity, and report that microorganisms capable of using components of produced water and methane are found in higher abundance in surface water and sediments in watersheds with OG activity than in those without (31,32,48).…”

Bacterial Biomarkers of Marcellus Shale Activity in Pennsylvania

“…Samples from the previous study were classified as HF+ or HF-, based on proximity to hydraulic fracturing. Sequence data from sediment samples from Ulrich et al (2018) and this study were merged and quality filtered at an average expected error of 0.5 and truncation length of 150 bp. All downstream steps for filtering, OTU clustering, and normalization were performed as described above.…”

Surface Water Microbial Community Response to the Biocide 2,2-Dibromo-3-Nitrilopropionamide, Used in Unconventional Oil and Gas Extraction

“…For example, the abiotic half-lives of DBNPA at pH 5, 7, and 9 are 67 days, 63 h, and 73 min, respectively (10). Conversely, low pH has been characteristic of HF-impacted streams (11, 12), which thus provide favorable conditions for the stability of DBNPA and its degradation products.…”