PROVENANCE OF HURRICANE-INDUCED SALT MARSH SEDIMENTATION ALONG THE SOUTHEAST US COAST

Salt marshes provide a range of ecosystem services including protecting the mainland from storm erosion and coastal flooding. Storms may help marshes maintain their elevation relative to sea level by contributing inorganic sediment derived from estuarine, terrestrial, and marine environments. Understanding these sediment sources is important for quantifying long-term marsh health and resiliency. This study explores the provenance and relative contributions of sediment from Hurricane Irma to four salt marshes behind Amelia Island (FL), Sapelo Island (GA), and Hilton Head (SC), and within Cape Romain (SC). Two months after the hurricane, surface samples were collected along transects from mainland-adjacent to island-adjacent salt marshes. We revisited the Cape Romain sites following Hurricanes Florence and Michael and sampled both marsh storm deposits and adjacent environments. Samples were analyzed for provenance using inorganic (grain size) and organic (TOC, TN, C/N, δ¹⁵N, and δ¹³C content) proxies. δ¹³C values following the Irma event ranged from from -16.99 ± 0.13 to -25.72 ± 1.67 with an average of -20.50 ± 1.76, matching expected ranges for proximal estuarine creeks and bays and highlighting the importance of proximal sources. We observe more negative δ¹³C further from the barrier islands across all sites, which may reflect preferential riverine influence. At Cape Romain, where we sampled both fluvial and marine end-member reservoirs, we observe a distinctive terrestrial influence, with marsh deposits from our river-proximal transect displaying significantly more negative δ¹³C values (p<0.01). Overall, our results indicate a complex mixture of sediments delivered to the marsh surface during storms, with a predominant contribution from proximal bays.