FIGURE 2.

(A) Relative abundance of the 16S rRNA gene corresponding to Arcobacter and Marinobacter reconstructed from metagenomes using EMIRGE combined with chloride trends in the same Marcellus Shale natural-gas well (Marcellus-4). (B) CO₂ and NPOC (non-purgeable organic carbon) trends in the Marcellus Shale natural-gas well (Marcellus-4). Temporal trends in nitrogen (C) and sulfur (D) in produced fluids from Utica-Point Pleasant formation and Marcellus Shale natural-gas wells. Plotted values are averages of 4 Utica-Point Pleasant natural-gas wells (Utica-3, Utica-6, Utica-7, Utica-8) and 2 Marcellus natural-gas wells (Marcellus-4 and Marcellus-5); error bars are standard deviations between measurements for Utica wells, range for Marcellus wells. Averages were calculated using the same day after flowback began and converted to days after fracturing. Offset graphs to the left of main graphs indicate measurements in drill muds, injected fluid, or source waters. NH₃/${\text{NH}}_4^{+}$ indicates total ammonia/ammonium which are both measured in this method.