The demand for natural gas, and the need for efficient extraction, has led to the development of hydraulic fracturing, an unconventional oil and natural gas (UOG) technique. Understanding the effects of UOG development on microbial communities in streams is particularly important because microorganisms are critical to energy flow within these ecosystems. For instance, microorganisms fix gases, break down organic matter, and release nutrients for use by the food web. We used a dual pronged approach to study the effects of UOG development on microbial biodiversity and function via a laboratory microcosm experiment and an observational study of streams with and without UOG development within their watersheds. The laboratory microcosm study simulated stream contamination with produced water, a byproduct of UOG operations, using sediment from three freshwater streams (one reference and two with UOG development). For the observational study, sediment and biofilm samples were collected from 20 streams with UOG development and 7 reference streams. In both studies, microbial activity was assessed by measuring the production of CO2 (aerobic and anaerobic) and CH4 (anaerobic) and prokaryotic community composition was examined via Illumina amplicon sequencing of the 16S rRNA gene.
Results/Conclusions
In the microcosm experiment, produced water from hydraulic fracturing reduced the diversity and evenness of sediment microbial communities. This suggests that this potential pollutant is harmful to many microbial taxa and can alter community composition. Produced water also changed microbial function; it had a negative effect on microbial aerobic and anaerobic CO2 production in the reference stream sediment but a positive effect on this microbial activity in the sediment of streams with UOG development. The difference in response to produced water between the reference stream, and those with UOG development, suggests that microbial communities in streams with UOG development may have had prior exposure to produced water and adapted to benefit from its constituents. Data from the observational study indicated that water chemistry and prokaryotic β-diversity were more variable in the streams with UOG development when compared to the reference streams. Taken together, this may indicate that variation in water chemistry due to UOG development can destabilize microbial community composition and function in freshwater streams. The observed impacts of UOG development on microbial community composition and function could have cascading effects on stream health by altering the availability of oxygen and other nutrients that are used by higher trophic levels.