VITAL EFFECTS ON STABLE CARBON ISOTOPES IN FRESHWATER MUSSELS SHELLS

Freshwater bivalve shells record geochemical information at the time of precipitation. Most of the C that forms the shell is precipitated from dissolved inorganic carbon (DIC). Therefore shells may record d¹³C_DIC and provide an archive of biogeochemical cycles. However, metabolic C (C_m) that is incorporated into bivalve shells can reduce the precision of the d¹³C_DIC archive. To constrain the fidelity of freshwater shells as d¹³C_DIC recorders, we monitored a plethora of water parameters including d¹³C_DIC and d¹³C_POC every week for one year at the Columbus Zoo and Aquarium Freshwater Mussel Conservation and Research Center and adjacent O’Shaughnessy Reservoir in Ohio. Lampsilis cardium that grew in this water were collected and shells and tissues were analyzed for C isotopes. Based on samples collected from the commissure of the shell, percent C_m on two collection dates was 17.0% and 15.3% in September and December, respectively. We plan to investigate high resolution variations in C_m over the year in several shells. Shells are currently being serial sampled to allow calculation of C_m over the full year with a resolution of ~1 week. Moreover, we conducted an experiment to determine the d¹³C value of respired carbon in this species to assess if the error associated with using soft tissue d¹³C as a proxy of respired carbon d¹³C. These results will allow the use of the d¹³C_shell proxy to be used with more confidence in L. cardium.