RECONSTRUCTING PALEOTEMPERATURES OF A SPRING-FED, FRESHWATER RIVER IN FLORIDA USING LIVE, DEAD, AND FOSSIL GASTROPODS

Spring-fed, freshwater fluvial ecosystems across Florida are increasingly threatened by environmental changes and human impacts. The live, dead, and fossil molluscan assemblages within these ecosystems record the environmental conditions of the past and present. This study used specimens of the gastropod Elimia floridensis from fossil (in situ from underwater riverbank sediments), death (loose shell accumulations), and live (living individuals) assemblages from the Wakulla River in northern Florida to reconstruct water paleotemperatures from the Late Pleistocene to today. We analyzed 95 samples from 88 specimens representing eleven sites from the headspring and along the river. Each specimen was processed and analyzed using a mass spectrometer to obtain δ18O and δ13C isotopic values reflecting environmental conditions in the Wakulla River at the time of shell formation. Results show lower δ18O and δ13C isotopic values among the live specimens and higher isotopic values among fossil specimens. Death assemblage specimens show the greatest range of δ18O and δ13C isotopic values, with some specimens isotopically similar to live specimens, some isotopically similar to fossil specimens, and a small number intermediate to both. Temperatures calculated from live specimen isotopic values are comparable to water temperature values measured directly from the modern Wakulla River. Using δ18O isotopic values as a proxy for paleotemperature, results indicate a warming trend in the Wakulla River from the Late Pleistocene (average 16.83 °C) compared to today (average 21.47 °C). Understanding the paleotemperature history of the Wakulla River allows for a more informed analysis of historical trends within the river, such as predation intensity, taphonomic patterns, community biodiversity, and other community restructuring in the context of shifting environmental conditions. This will allow us to better assess future impacts to the ecosystem as water temperatures continue to rise.