For several decades, high-salinity water brought to the surface during oil and gas (O&G) production has been treated and discharged to waterways under National Pollution Discharge Elimination System (NPDES) permits. Freshwater bivalve shells living in streams receiving these wastewaters may record temporal fluctuations in water chemistry caused by releases of such water. By quantifying partitioning between the shell and the water we may be able to reconstruct these changes through time. This will allow us to understand how water management practices are impacting environmental conditions in the absence of historical water quality data. To test this, mussels were grown in sediment-laden cages in a reservoir, and water chemistry was monitored weekly. Another group of mussels was grown in containers in which known concentrations of O&G produced water was added. A third group of shells was collected from a river upstream and downstream of a centralized waste treatment facility (CWT) accepting, treating, and discharging O&G wastewaters, and from 2 rivers with no history of oil and gas development. Shells were harvested and analyzed for trace metals by LA ICP-MS. Oxygen isotopes were used to assign dates to shell sections. 87Sr/86Sr was measured to fingerprint the source of Sr.
Results/Conclusions
Results from the reservoir-grown shells showed that during periods of appreciable shell growth, Sr/Ca in the shell carefully tracks Sr/Ca in the water with a predictable partitioning coefficient, consistent with other freshwater mollusk literature. Shells collected downstream of the CWT exhibited elevated Sr/Ca during periods of suspected highest discharge of O&G wastewater, and 87Sr/86Sr supported the O&G origin of the strontium. Conversely, the shell collected just upstream of the discharge and both shells collected from rivers with no O&G development exhibited very little change in Sr/Ca or 87Sr/86Sr, suggesting this change was likely due to the discharge of the CWT. These results suggest that mussel shells record high resolution water chemistry data through time, documenting the impacts of water management decisions on surface water quality. The documentation of water quality from such high resolution records could be applied to other sources of pollution.