Areas of oil and gas development (OGD) have experienced decreased population density and water quality. Sampling and analysis of bird feathers are commonly used to indicate environmental pollution because heavy metals and other pollutants become incorporated into the feather structure and are an indication of exposure during the time the feathers were growing. In particular, passerines (songbirds) do not store calcium for egg shell production in their legs but instead need to obtain it in their diet by feeding on calcium-rich items in the days preceding egg laying. Nestlings require calcium for successful development and acquire it during the time in the nest when they are being fed by their parents. These traits potentially make riparian songbirds a good indicator of the environmental health of local aquatic and riparian areas. In particular, exposure to barium, radium, and strontium are important because they follow and often replace calcium in biogeochemical cycles, and are found in very high concentrations in oil and gas wastes. Indeed, Latta et al. (2015) observed higher concentrations of barium and strontium in Louisiana waterthrush (Parkesia motacilla) feathers collected from active areas of oil and gas development (OGD) compared to areas with little/no OGD in two different geographical areas, Pennsylvania (Marcellus) and Arkansas (Fayetteville). These results suggest that releases of oil and gas wastes result in bioaccumulation of barium and strontium in aquatic and riparian species.
Results/Conclusions
The higher strontium and barium concentrations may indicate potential impacts from OGD, but isotopic signatures are often required to distinguish OGD from other possible sources of contamination. Several isotopic ratios have been proposed to trace unconventional OGD including 226Ra/228Ra, 11B/10B, 7Li/6Li, and 87Sr/86Sr. Here we will utilize the high concentration of strontium with a distinct 87Sr/86Sr in Marcellus (PA) and Fayetteville Shale (AR) wastewater to determine if the higher concentrations observed in the Louisiana waterthrush feathers are sourced from OGD. Marcellus and Fayetteville Shales both have a narrow range of 87Sr/86Sr ratios (0.709-0.711) that are distinct from other oil and gas wastewaters (0.716-0.720) and from most background surface water (0.712-0.714) or water impacted by coal mining (0.714-0.715). We analyzed 87Sr/86Sr ratios in microwave-digested feathers by thermal ionization mass spectrometry. Our methodology helps link water quality within a watershed and subsequent bioaccumulation in a riparian bird species. Our results demonstrate the use of 87Sr/86Sr as a new method to identify sources of contamination and track the movement of contaminants through the food chain.