Do biofilm communities respond to the chemical signatures of fracking? A test involving streams in North-central Arkansas

Abstract

BackgroundUnconventional natural gas (UNG) extraction (fracking) is ongoing in 29 North American shale basins (20 states), with ~6000 wells found within the Fayetteville shale (north-central Arkansas). If the chemical signature of fracking is detectable in streams, it can be employed to bookmark potential impacts. We evaluated benthic biofilm community composition as a proxy for stream chemistry so as to segregate anthropogenic signatures in eight Arkansas River catchments. In doing so, we tested the hypothesis that fracking characteristics in study streams are statistically distinguishable from those produced by agriculture or urbanization.ResultsFour tributary catchments had UNG-wells significantly more dense and near to our sampling sites and were grouped as ‘potentially-impacted catchment zones’ (PICZ). Four others were characterized by significantly larger forested area with greater slope and elevation but reduced pasture, and were classified as ‘minimally-impacted’ (MICZ). Overall, 46 bacterial phyla/141 classes were identified, with 24 phyla (52%) and 54 classes (38%) across all samples. PICZ-sites were ecologically more variable than MICZ-sites, with significantly greater nutrient levels (total nitrogen, total phosphorous), and elevated Cyanobacteria as bioindicators that tracked these conditions. PICZ-sites also exhibited elevated conductance (a correlate of increased ion concentration) and depressed salt-intolerant Spartobacteria, suggesting the presence of brine as a fracking effect. Biofilm communities at PICZ-sites were significantly less variable than those at MICZ-sites.ConclusionsStudy streams differed by Group according to morphology, land use, and water chemistry but not in biofilm community structure. Those at PICZ-sites covaried according to anthropogenic impact, and were qualitatively similar to communities found at sites disturbed by fracking. The hypothesis that fracking signatures in study streams are distinguishable from those produced by other anthropogenic effects was statistically rejected. Instead, alterations in biofilm community composition, as induced by fracking, may be less specific than initially predicted, and thus more easily confounded by agriculture and urbanization effects (among others). Study streams must be carefully categorized with regard to the magnitude and extent of anthropogenic impacts. They must also be segregated with statistical confidence (as herein) before fracking impacts are monitored.

Bacterial Biomarkers of Marcellus Shale Activity in Pennsylvania

“…There were no significant differences in alpha diversity (Chao1, Heip’s evenness, observed, and PD whole tree) between UOG+ and UOG- streams assessed in this study, which is consistent with Johnson et al (2017) , in which there was no association between alpha diversity (Chao1, observed, Shannon evenness, and Shannon Entropy) and proximity to hydraulic fracturing activity. Trexler et al (2014) observed a significant reduction in alpha diversity (Chao1, Heip’s evenness, observed, and PD whole tree) and pH in streams near Marcellus shale activity (UOG development).…”

“…Recent work has found streams near hydraulic fracturing experience drastic shifts in certain bacterial assemblages (Acetobacteraceae, Methylocystaceae, and Phenylobacterium ) and had lower observed bacterial diversity ( Trexler et al, 2014 ). However, a study done in the Fayetteville shale formation did not find any significant difference in alpha diversity based on proximity to hydraulic fracturing, but it too noted an increased abundance of specific taxa ( Microcystis and Synechoccophycideae) in streams near hydraulic fracturing operations ( Johnson et al, 2017 ). Furthermore, that study noted little work has been done on evaluating the impact of hydraulic fracturing on streams.…”

Stoichiometric Shifts in Soil C:N:P Promote Bacterial Taxa Dominance, Maintain Biodiversity, and Deconstruct Community Assemblages

“…Additionally, multiple shared taxa between our two networks [i.e., Spartobacteria unclassified (Verrucomicrobia), Micrococcaceae (Actinobacteria), and Chitinophagaceae (Bacteroidetes)] increased in abundance under P additions. The abundance of taxa within these families may track the availability of P in soils and water ( Johnson et al, 2017 ; Wang et al, 2017 ). Even with P additions communities seemed to remain partially reliant on Solirubrobacteriaceae taxa.…”

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

“…For example, halotolerant bacteria associated with hydrocarbon oxidation, fermentation, and sulfur-cycling metabolisms including the genera Halanaerobium , Halomonas , Vibrio , Halolactibacillus , Marinobacter , and autotrophs belonging to Arcobacter comprise >90% of the microbial communities within flowback and produced fluids 39 . Moreover, recent studies have indicated that streams within proximity to fracking activities have undergone shifts in their bacterial community structure 35 . For example, Methylocystacea, Acetobacteraceae, Phenylobacterium , and Acidobacteriaceae and an increase in methanotrophic bacteria abundance were linked to Marcellus shale activity 40 .…”