Using Freshwater Mussel Assemblages to Inform Modern Conservation Efforts in the Midwestern US

Introduction & Background

Freshwater mussels, a keystone species in many aquatic systems, are one of the most endangered species in North America due to overharvesting in the 19th and 20th centuries. Modern conservation efforts are impeded by the lack of population records prior to exploitation. Conservation paleobiology can provide ecological baselines for endangered species with insufficient historical data. Through radiocarbon dating and species identification, species abundances through time can be reconstructed. However, to determine accurate carbon ages, a correction for the radiocarbon reservoir effect (RRE) must be calculated. RREs are driven by the presence of carbonate bedrock in the watershed, which causes freshwater systems to have a lower concentration of 14C than the atmosphere. A mussel shell assemblage from the riverbed of the Ohio River (OH) is examined to determine the age of the assemblage and the species present. Currently, the RRE of the Ohio River is unknown, so a correction will have to be found to obtain precise ages.

Study Area

The shell assemblage was deposited at 20' depth in a clay substrate along a bed of the Ohio River associated with large, flat boulders.

Research Questions

• What is the RRE of the Ohio River?

• What is the age of the Markland Pool mussel assemblage?

Methods

56 shells from the riverbed of the Markland Pool were collected by John Spaeth at EDGE Consulting over the course of three biological surveys of freshwater mussels in the Ohio River. A Eurynia dilatata (aka Spike) was selected for radiocarbon dating in order to determine the age of the deposit. It was cleaned with deionized water, and a multi-year aliquot was cut from the ventral margin. It was then cleaned in the ultrasonic bath, underwent hydrogen peroxide treatment to remove organics and dilute HCl Treatment to remove secondary CaCO₃. Each sample was crushed and homogenized using a mortar and pestle before being sent off to NOSAMs. Radiocarbon Laboratory at Woods Hole Oceanographic Institute. 

Results

Conclusions

• The age of the Markland Pool assemblage is late-Holocene, but we are unable to determine a more precise age without the RRE.

• ~37% of the valves in the Markland Pool assemblage are from now-extinct species, and ~25% are from species now considered critically imperiled to vulnerable.

Future Work

To further this project, two shells from the Ohio River near Cincinnati will be radiocarbon dated. These shells, in the collection of the Museum of Biological Diversity, were collected before nuclear bomb testing and the age is known. These 14C concentrations will provide the RRE correction for this section of the Ohio River. Based on examining water chemistry, it is expected that the Ohio River will have a lower RRE than smaller streams in the Midwest

After the RRE of the river has been determined, the age of the assemblage will be further constrained by radiocarbon dating a shell of a different species from the Markland Pool assemblage.