The development of unconventional oil and gas (UOG) resources from the Marcellus and Utica shales underlying much of central and western Pennsylvania has proceeded rapidly in recent years. Our inter-disciplinary team, comprised of researchers across different USGS programs and in collaboration with the Pennsylvania Department of Conservation and Natural Resources-Bureau of Forestry, has been investigating the potential for UOG development to impact watersheds and shallow groundwater quality. The Pennsylvania State Forests are an ideal study area as they contain a wide gradient of disturbance and potential impact from unconventional gas extraction while having minimal other anthropogenic impacts. We hypothesize a relationship between increasing density of UOG development and quantifiable impacts to water quality and stream biota. We utilized the vulnerability assessment published in 2015 by Entrekin et al, which incorporates a wide selection of potential natural and UOG-related stressors to identify 25 headwater streams across a gradient of potential impact from UOG development. These streams were sampled in Spring and Fall over the course of two years to quantify the relationship between shale gas development and water quality. Our sampling effort included the characterization of the organic and inorganic geochemistry of these streams, as well as their microbial and benthic macroinvertebrate communities.
Results/Conclusions
Our data show that the majority of these streams are characterized by low specific conductance (<100 µS/cm), with most trace elements in the low ppb range. We observed significant differences in stream chemistry and microbial community structure between Spring and Fall sampling campaigns. No strong relationships were found between the assessed potential vulnerability and alterations in water quality or first-year benthic macroinvertebrate sample, however, several streams within the study were found to have significantly elevated conductivity (>100 µS/cm), along with elevated concentrations of Sr (60 µg/L) to the study average (40 µg/L). Alterations in microbial community structure were found to have significant relationships to elevated specific conductance, Sr, and U, and increased impervious surface areas related to oil and gas development. These data are providing a comprehensive assessment of geochemical and biological variability in headwater streams in the Marcellus region and will aid in the assessment of any changes in biogeochemical conditions and ecological responses to UOG development.