ANTHROPOGENIC FLOATING DEBRIS ACCUMULATION IN ESTUARINE SYSTEMS

Floating anthropogenic debris (FAD) accumulation is a growing but under-studied environmental issue within estuarine ecosystems. Assumedly, estuaries do not only act as a major FAD sink, but storm and flooding events might lead to major FAD remobilization, relocation, concentration, and ex-port.

This project aims at gathering insight on the dynamics of FAD distribution in an SC estuary (Little River/Waties Island) as the result of a storm surge event (Hurricane Ian in September 2022). The dynamics of interest include: logged surge level and dynamics; pre-event distribution of FAD, post-event FAD accumulation pattern; duration and conditions necessary to newly ac-cumulate FAD at pre-event locations. We installed a 15-min interval water logger and monitored the FAD dynamics before and after Hurricane Ian at five selected sites considered to represent the full range of location types that acts as FAD sinks (four marsh sites within Dunn Sound; one beach site 1in-side Little River jetties).

While FAD was found in high concentrations together with large amounts of marsh grass debris at the high-water lines at all monitoring sites, the up to 8-ft high hurricane-related surge led to two unexpected effects: a) Major amounts of positively buoyant FAD of any size were lifted up, depleting the loading of the marsh over the whole estuary, and concentrated the material solely within a well-confined surge debris line; b) Larger amounts of cm-sized negatively buoyant FAD appeared within the swash zone of the jetty beach as a kind of bottom boundary layer in rich association with plant litter. The resulting burning questions about the long-term fate of the light FAD dumped at the debris surge line as well as about origin and fate of the bottom FAD are in the focus now.