LEVERAGING BARIUM ISOTOPES TO EVALUATE UTILITY OF FRESHWATER BIVALVE SHELLS AS PALEOENVIRONMENTAL MONITORS OF RIVER GEOCHEMISTRY IN THE LOWER ALLEGHENY RIVER WATERSHED, PENNSYLVANIA

The objective of this study is to evaluate the spatial and temporal distribution of barium (Ba) concentrations and isotope composition in the Allegheny River watershed, and to assess the utility of freshwater bivalve shells as bio-monitors for riverine chemistry. While Ba is widely used to understand biogeochemical cycling in marine systems, the Ba isotope systematics of freshwater environments are less well constrained. The Allegheny River watershed in Pennsylvania is a critical drinking water resource for Pittsburgh, and its history of energy extraction and industrial activity makes it a unique watershed to study Ba geochemistry. The Allegheny is also home to a diverse assemblage of freshwater bivalves, which are potentially useful monitors of biogeochemical systems due to their sessile existence, long lifespan, and continuously precipitated carbonate shells. Because Ba is incorporated into the aragonite lattice of the shell in significant concentrations, the Ba isotopic composition of bivalve shells has the potential to record temporal trends in the watershed and may prove useful as a paleoenvironmental indicator.

Our study area includes the lower Allegheny River, Kiskiminetas River, Buffalo Creek, and Pine Creek. In November 2021 and April 2022 we collected water samples throughout the study area, and individual live specimens of Corbicula fluminea, an invasive clam species, from both Buffalo Creek and Pine Creek. Water samples and whole valves of 3 Corbicula specimens from each site were analyzed for Ba concentration, isotope composition, and trace metals. In general, the Ba concentrations in the shells and the stream water in which they grew were positively correlated. δ¹³⁸Ba values (permil deviation of the ¹³⁸Ba/¹³⁴Ba from NIST standard 3104a) in water samples ranged from 0.16‰ to 0.27‰ (± ≤0.04‰), demonstrating measurable variability in Ba isotope composition across the watershed. δ¹³⁸Ba values in shells ranged from 0.23‰ to 0.35‰. Preliminary results suggest that Ba isotope composition in shells reflects that of the co-located river water, indicating shells could serve as valuable paleoenvironmental monitors of Ba river chemistry. These results are part of an ongoing study that includes monthly water samples and annual to decadal records from the analysis of native mussel species shells.