Abstract:
Bivalve shell geochemistry can serve as a useful indicator of changes in coastal environments. There is increasing interest in developing paleoenvironmental proxies from mollusk shell organic components. Numerous studies have focused on how the δ15N obtained from bivalve tissues and shells can be used to trace present-day wastewater input into estuaries. However, comparatively little attention has been paid to tracing the impact of anthropogenic nitrogen loading into estuaries over time. By measuring historic levels of δ15N in the organic fraction of oyster shells (Crassostrea virginica) from archaeological sites around Charleston Harbor and comparing those levels to the δ15N content of modern shells, it is possible to assess how nitrogen has fluctuated historically in the area. Whole-shell samples from the Woodland Period (~1400-800 BP), 18th, 19th, and 20th centuries, and modern controls were measured for %N and δ15N. δ15N was found to not vary significantly with time. The highest δ15N values came from shells dated to the mid and late 19th century. Mean modern δ15N (8.6‰) were found to be similar to mean Woodland Period δ15N (8.5‰). This is in contrast to studies done by Black (2014), but similar to a study done by Darrow et al. (2016). This information could help understand how large-scale anthropogenic nitrogen loading has affected coastal ecosystems over time and guide future remediation. Furthermore, this project will help refine and improve this novel proxy of past environmental conditions.
