Bacterial Biomarkers of Marcellus Shale Activity in Pennsylvania

Abstract

Unconventional oil and gas (UOG) extraction, also known as hydraulic fracturing, is becoming more prevalent with the increasing use and demand for natural gas; however, the full extent of its environmental impacts is still unknown. Here we measured physicochemical properties and bacterial community composition of sediment samples taken from twenty-eight streams within the Marcellus shale formation in northeastern Pennsylvania differentially impacted by hydraulic fracturing activities. Fourteen of the streams were classified as UOG+, and thirteen were classified as UOG- based on the presence of UOG extraction in their respective watersheds. One stream was located in a watershed that previously had UOG extraction activities but was recently abandoned. We utilized high-throughput sequencing of the 16S rRNA gene to infer differences in sediment aquatic bacterial community structure between UOG+ and UOG- streams, as well as correlate bacterial community structure to physicochemical water parameters. Although overall alpha and beta diversity differences were not observed, there were a plethora of significantly enriched operational taxonomic units (OTUs) within UOG+ and UOG- samples. Our biomarker analysis revealed many of the bacterial taxa enriched in UOG+ streams can live in saline conditions, such as Rubrobacteraceae. In addition, several bacterial taxa capable of hydrocarbon degradation were also enriched in UOG+ samples, including Oceanospirillaceae. Methanotrophic taxa, such as Methylococcales, were significantly enriched as well. Several taxa that were identified as enriched in these samples were enriched in samples taken from different streams in 2014; moreover, partial least squares discriminant analysis (PLS-DA) revealed clustering between streams from the different studies based on the presence of hydraulic fracturing along the second axis. This study revealed significant differences between bacterial assemblages within stream sediments of UOG+ and UOG- streams and identified several potential biomarkers for evaluating and monitoring the response of autochthonous bacterial communities to potential hydraulic fracturing impacts.

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.…”

“…This finding is consistent with ref. 31, which reports no observed changes in microbial alpha diversity with proximity to OG activity in northeastern Pennsylvania (31). No significant variation in microbial community structure was observed among sDII categories (Fig.…”

“…Releases of produced water into surface water have led to accumulation of metals in freshwater mussel shells (30) and are reported to cause changes in streambed microbial community structure (29,31,32). Benthic macroinvertebrate communities are sensitive to changes in water quality, and changes in benthic macroinvertebrate community structure have occurred in streams in Arkansas within watersheds undergoing extraction of natural gas from the Fayetteville Shale (33).…”

“…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).…”

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

“…For example, a halotolerant Halomonadaceae species was shown to be enriched in HF-exposed anaerobic sediments treated with DBNPA (39). Other halotolerant bacteria have also emerged as bacterial biomarkers of UOG impacts in freshwater streams (40). HF fluids contain high abundances of halophilic and halotolerant bacteria (41), which can be displaced to streams in the event of an HF fluid spill.…”