RADIOCARBON DATING LATE HOLOCENE AND HISTORICAL MUSSEL SHELL ASSEMBLAGES IN THE OHIO RIVER VALLEY: A CASE STUDY FROM THE LICKING RIVER, KENTUCKY

Freshwater mussels are one of the most imperiled groups of organisms in North America. Historical mussel assemblages can provide information about baseline conditions in streams, which is essential for understanding the causes of mussel declines and informing conservation targets and actions. Unfortunately, information about historical assemblages is mostly limited to presence/absence reports by 19th- or early 20th-century naturalists. Mussel shells can be preserved within and adjacent to stream channels in several ways, including human or muskrat shell middens as well as within fluvial deposits. These deposits all have their own sources of bias, but they provide information about historical assemblage composition. We determined the age of a fossil muskrat midden discovered at a height of 0.8-0.95 cm within an ~1.3 m inset fluvial terrace on the Licking River, Kentucky. To constrain the age of the assemblage, we radiocarbon dated three plant macrofossils associated with the shells. Plant macrofossils from section heights of 0.65 m, 1.05 m, and 1.35 m yielded percent modern carbon (pMC) values of 98.27, 101.10, and 102.41, indicating the sediments 15 cm above the midden date to the post-bomb era (ca. 1955 to 2020). A historical artifact, a leather shoe, was also found within the sediments at a section height of 0.7 m, just below the shell midden. We modeled the age of the assemblage using the ‘rbacon’ package within RStudio software and derived an age of ca. 1850-1950. The assemblage is noteworthy because its composition is distinctly different from that of the contemporary live mussel assemblage or contemporary muskrat middens. The assemblage contained several federally endangered or threatened species that are extirpated from the river, such as the Northern Riffleshell, Pink Mucket, Clubshell, Rabbitsfoot, and Rayed Bean, and other species that dominated the assemblage are now rare in the river. The age of the assemblage makes it a valuable baseline for conservation because it represents conditions in the river immediately prior to large-scale anthropogenic factors that appear to have altered the fauna. Late Holocene and historical muskrat middens, or other shell deposits, exist on many streams and can help identity the timing and causes of recent mussel declines and inform conservation efforts to address them.