TOWARDS ESTABLISHING PRE-FRACKING GEOCHEMICAL BASELINE: INTRA-ANNUAL GROWTH OF LAMPSILIS CARDIUM IN CENTRAL OHIO

North American rivers are home to more than 300 species of freshwater mussels— the highest species richness in the world. These animals function as biological chart recorders and thus offer a unique archive of past environmental conditions from terrestrial ecosystems. Furthermore, because they can produce up to several centimeters of shell carbonate in a single year they offer one of the highest temporal resolution environmental proxies available.

The recent expansion of hydraulic fracturing associated with deep-basin shale-gas reservoir development may adversely impact riverine ecosystems. To rigorously document the impacts of fracking however, baseline environmental conditions must be established. Here we present new data on the intra-annual growth of the freshwater mussel Lampsilis cardium from an unimpacted site in central Ohio. These findings are part of a much larger study designed to link high-resolution environmental variability with shell geochemistry.

Specimens of L. cardium from the same cohort were grown for one complete year (2010) in indoor raceway tanks at the Columbus Zoo & Aquarium Freshwater Mussel Conservation & Research Center (O’Shaughnessy Reservoir, Scioto River, 15 km NW of Columbus, OH) and under natural conditions (sediment laden cages suspended from a dock adjacent to the mussel facility). Specimens from each site were collected in April, September and at the end of the year. Water samples for oxygen isotope analysis (δ¹⁸O_W) were collected weekly and temperatures monitored continuously throughout the year.

Predicted shell carbonate oxygen isotope values (δ¹⁸O_S) agree with point-sampled observed δ¹⁸O_S values and are consistent with previous finding that little or no shell growth occurs below 12°C. During the hottest months of the year observed δ¹⁸O_S values are higher than predicted values. Conversely, in the cooler autumn months, observed values are lower than predicted. These observations suggest L. cardium preferentially precipitates its shell during optimal growth temperatures. Higher resolution micromilled samples suggest shell individual samples represent as little as three days of growth. This observation will facilitate calibration of shell carbonate geochemistry with high-resolution environmental variability to establish pre-fracking baseline conditions.